Patent Grant
6957701
This invention relates generally to the field of perforating and treating subterranean formations to increase the production of oil and gas therefrom. More specifically, the invention provides an apparatus and a method for perforating and treating multiple intervals without the necessity of removing equipment from the wellbore between steps or stages.
When a hydrocarbon-bearing, subterranean reservoir formation does not have enough permeability or flow capacity for the hydrocarbons to flow to the surface in economic quantities or at optimum rates, hydraulic fracturing or chemical (usually acid) stimulation is often used to increase the flow capacity. A wellbore penetrating a subterranean formation typically consists of a metal pipe (casing) cemented into the original drill hole. Holes (perforations) are placed to penetrate through the casing and the cement sheath surrounding the casing to allow hydrocarbon flow into the wellbore and, if necessary, to allow treatment fluids to flow from the wellbore into the formation.
Hydraulic fracturing consists of injecting fluids (usually viscous shear thinning, non-Newtonian gels or emulsions) into a formation at such high pressures and rates that the reservoir rock fails and forms a plane, typically vertical, fracture (or fracture network) much like the fracture that extends through a wooden log as a wedge is driven into it. Granular proppant material, such as sand, ceramic beads, or other materials, is generally injected with the later portion of the fracturing fluid to hold the fracture(s) open after the pressure is released. Increased flow capacity from the reservoir results from the easier flow path left between grains of the proppant material within the fracture(s). In chemical stimulation treatments, flow capacity is improved by dissolving materials in the formation or otherwise changing formation properties.
Application of hydraulic fracturing as described above is a routine part of petroleum industry operations as applied to individual target zones of up to about 60 meters (200 feet) of gross, vertical thickness of subterranean formation. When there are multiple or layered reservoirs to be hydraulically fractured, or a very thick hydrocarbon-bearing formation (over about 60 meters), then alternate treatment techniques are required to obtain treatment of the entire target zone. The methods for improving treatment coverage are commonly known as “diversion” methods in petroleum industry terminology.
When multiple hydrocarbon-bearing zones are stimulated by hydraulic fracturing or chemical stimulation treatments, economic and technical gains are realized by injecting multiple treatment stages that can be diverted (or separated) by various means, including mechanical devices such as bridge plugs, packers, downhole valves, sliding sleeves, and baffle/plug combinations; ball scalers; particulates such as sand, ceramic material, proppant, salt, waxes, resins, or other compounds; or by alternative fluid systems such as viscosified fluids, gelled fluids, foams, or other chemically formulated fluids; or using limited entry methods. These and all other methods and devices for temporarily blocking the flow of fluids into or out of a given set of perforations will be referred to herein as “diversion agents.”
In mechanical bridge plug diversion, for example, the deepest interval is first perforated and fracture stimulated, then the interval is typically isolated by a wireline-set bridge plug, and the process is repeated in the next interval up. Assuming ten target perforation intervals, treating 300 meters (1,000 feet) of formation in this manner would typically require ten jobs over a time interval of ten days to two weeks with not only multiple fracture treatments, but also multiple perforating and bridge plug running operations. At the end of the treatment process, a wellbore clean-out operation would be required to remove the bridge plugs and put the well on production. The major advantage of using bridge plugs or other mechanical diversion agents is high confidence that the entire target zone is treated. The major disadvantages are the high cost of treatment resulting from multiple trips into and out of the wellbore and the risk of complications resulting from so many operations in the well. For example, a bridge plug can become stuck in the casing and need to be drilled out at great expense. A further disadvantage is that the required wellbore clean-out operation may damage some of the successfully fractured intervals.
One alternative to using bridge plugs is filling the portion of wellbore associated with the just fractured interval with fracturing sand, commonly referred to as the Pine Island technique. The sand column in the wellbore essentially plugs off the already fractured interval and allows the next interval to be perforated and fractured independently. The primary advantage is elimination of the problems and risks associated with bridge plugs. The disadvantages are that the sand plug does not give a perfect hydraulic seal and it can be difficult to remove from the wellbore at the end of all the fracture stimulations. Unless the well's fluid production is strong enough to carry the sand from the wellbore, the well may still need to be cleaned out with a work-over rig or coiled tubing unit. As before, additional wellbore operations increase costs, mechanical risks, and risks of damage to the fractured intervals.
Another method of diversion involves the use of particulate materials, granular solids that are placed in the treating fluid to aid diversion. As the fluid is pumped, and the particulates enter the perforations, a temporary block forms in the zone accepting the fluid if a sufficiently high concentration of particulates is deployed in the flow stream. The flow restriction then diverts fluid to the other zones. After the treatment, the particulate is removed by produced formation fluids or by injected wash fluid, either by fluid transport or by dissolution. Commonly available particulate diverter materials include benzoic acid, napthalene, rock salt (sodium chloride), resin materials, waxes, and polymers. Alternatively, sand, proppant, and ceramic materials, could be used as particulate diverters. Other specialty particulates can be designed to precipitate and form during the treatment.
Another method for diverting involves using viscosified fluids, viscous gels, or foams as diverting agents. This method involves pumping the diverting fluid across and/or into the perforated interval. These fluid systems are formulated to temporarily obstruct flow to the perforations due to viscosity or formation relative permeability decreases; and are also designed so that at the desired time, the fluid system breaks down, degrades, or dissolves (with or without adding chemicals or other additives to trigger such breakdown or dissolution) such that flow can be restored to or from the perforations. These fluid systems can be used for diversion of matrix chemical stimulation treatments and fracture treatments. Particulate diverters and/or ball sealers are sometimes incorporated into these fluid systems in efforts to enhance diversion.
Another possible process is limited entry diversion in which the entire target zone of the formation to be treated is perforated with a very small number of perforations, generally of small diameter, so that the pressure loss across those perforations during pumping promotes a high, internal wellbore pressure. The internal wellbore pressure is designed to be high enough to cause all of the perforated intervals to fracture simultaneously. If the pressure were too low, only the weakest portions of the formation would fracture. The primary advantage of limited entry diversion is that there are no inside-the-casing obstructions like bridge plugs or sand to cause problems later. The disadvantage is that limited entry fracturing often does not work well for thick intervals because the resulting fracture is frequently too narrow (the proppant cannot all be pumped away into the narrow fracture and remains in the wellbore), and the initial, high wellbore pressure may not last. As the sand material is pumped, the perforation diameters are often quickly eroded to larger sizes that reduce the internal wellbore pressure. The net result can be that not all of the target zone is stimulated. An additional concern is the potential for flow capacity into the wellbore to be limited by the small number of perforations.
Some of the problems resulting from failure to stimulate the entire target zone or using mechanical methods that require multiple wellbore operations and wellbore entries that pose greater risk and cost as described above may be alleviated by using limited, concentrated perforated intervals diverted by ball sealers. The zone to be treated could be divided into sub-zones with perforations at approximately the center of each of those sub-zones, or sub-zones could be selected based on analysis of the formation to target desired fracture locations. The fracture stages would then be pumped with diversion by ball sealers at the end of each stage. Specifically, 300 meters (1,000 feet) of gross formation might be divided into ten sub-zones of about 30 meters (about 100 feet) each. At the center of each 30 meter (100 foot) sub-zone, ten perforations might be shot at a density of three shots per meter (one shot per foot) of casing. A fracture stage would then be pumped with proppant-laden fluid followed by ten or more ball sealers, at least one for each open perforation in a single perforation set or interval. The process would be repeated until all of the perforation sets were fractured. Such a system is described in more detail in U.S. Pat. No. 5,890,536, issued Apr. 6, 1999.
Historically, all zones to be treated in a particular job that uses ball sealers as the diversion agent have been perforated prior to pumping treatment fluids, and ball sealers have been employed to divert treatment fluids from zones already broken down or otherwise taking the greatest flow of fluid to other zones taking less, or no, fluid prior to the release of ball sealers. Treatment and sealing theoretically proceeded zone by zone depending on relative breakdown pressures or permeabilities, but problems were frequently encountered with balls prematurely seating on one or more of the open perforations outside the targeted interval and with two or more zones being treated simultaneously. Furthermore, this technique presumes that each perforation interval or sub-zone would break down and fracture at sufficiently different pressure so that each stage of treatment would enter only one set of perforations.
The primary advantages of ball sealer diversion are low cost and low risk of mechanical problems. Costs are low because the process can typically be completed in one continuous operation, usually during just a few hours of a single day. Only the ball sealers are left in the wellbore to either flow out with produced hydrocarbons or drop to the bottom of the well in an area known as the rat (or junk) hole. The primary disadvantage is the inability to be certain that only one set of perforations will fracture at a time so that the correct number of ball sealers are dropped at the end of each treatment stage. In fact, optimal benefit of the process depends on one fracture stage entering the formation through only one perforation set and all other open perforations remaining substantially unaffected during that stage of treatment. Further disadvantages are lack of certainty that all of the perforated intervals will be treated and of the order in which these intervals are treated while the job is in progress. When the order of zone treatment is not known or controlled, it is not possible to ensure that each individual zone is treated or that an individual stimulation treatment stage has been optimally designed for the targeted zone. In some instances, it may not be possible to control the treatment such that individual zones are treated with single treatment stages.
To overcome some of the disadvantages that may occur during stimulation treatments when multiple zones are perforated prior to pumping treatment fluids, an alternative mechanical diversion method has been developed that involves the use of a coiled tubing stimulation system to sequentially stimulate multiple intervals with separate treatment. As with conventional ball sealer diversion, all intervals to be treated are perforated prior to pumping the stimulation treatment. Then coiled tubing is run into the wellbore with a mechanical “straddle-packer-like” diversion tool attached to the end. This diversion tool, when properly placed and actuated across the perforations, allows hydraulic isolation to be achieved above and below the diversion tool. After the diversion tool is placed and actuated to isolate the deepest set of perforations, stimulation fluid is pumped down the interior of the coiled tubing and exits flow ports placed in the diversion tool between the upper and lower sealing elements. Upon completion of the first stage of treatment, the sealing elements contained on the diversion tool are deactivated or disengaged, and the coiled tubing is pulled upward to place the diversion tool across the second deepest set of perforations and the process is continued until all of the targeted intervals have been stimulated or the process is aborted due to operational upsets.
This type of coiled tubing stimulation apparatus and method have been used to hydraulically fracture multiple zones in wells with depths up to about 8,000 feet. However, various technical obstacles, including friction pressure losses, damage to sealing elements, depth control, running speed, and potential erosion of coiled tubing, currently limit deployment in deeper wells.
Excess friction pressure is generated when pumping stimulation fluids, particularly proppant-laden and/or high viscosity fluids, at high rates through longer lengths of coiled tubing. Depending on the length and diameter of the coiled tubing, the fluid viscosity, and the maximum allowable surface hardware working pressures, pump rates could be limited to just a few barrels per minute; which, depending on the characteristics of a specific subterranean formation, may not allow effective placement of proppant during hydraulic fracture treatments or effective dissolution of formation materials during acid stimulation treatments
Erosion of the coiled tubing could also be a problem as proppant-laden fluid is pumped down the interior of the coiled tubing at high velocity, including the portion of the coiled tubing that remains wound on the surface reel. The erosion concerns are exacerbated as the proppant-laden fluid impinges on the “continuous bend” associated with the portion of the coiled tubing placed on the surface reel.
Most seal elements (e.g., “cup” seal technology) currently used in the coiled tubing stimulation operations described above could experience sealing problems or seal failure in deeper wells as the seals are run past a large number of perforations at the higher well temperatures associated with deeper wells. Since the seals run in contact with or at a minimal clearance from the pipe wall, rough interior pipe surfaces and/or perforation burrs can damage the sealing elements. Seals currently available in straddle-packer-like diversion tools are also constructed from elastomers which may be unable to withstand the higher temperatures often associated with deeper wells.
Running speed of the existing systems with cup seals is generally on the order of 15 to 30 feet-per-minute running downhole to 30 to 60 feet-per-minute coming uphole. For example, at the lower running speed, approximately 13 hours would be required to reach a depth of 12,000 feet before beginning the stimulation. Given safety issues surrounding nighttime operations, this slow running speed could result in multiple days being required to complete a stimulation job. If any problems are encountered during the job, tripping in and out of the hole could be very costly because of the total operation times associated with the slow running speeds.
Depth control of the coiled tubing system and straddle-packer-like diversion tool also becomes more difficult as depth increases, such that placing the tool at the correct depth to successfully execute the stimulation operation may be difficult. This problem is compounded by shooting the perforations before running the coiled tubing system in the hole. The perforating operation uses a different depth measurement device (usually a casing collar locator system) than is generally used in the coiled tubing system.
In addition, the coiled tubing method described above requires that all of the perforations be placed in the wellbore in a separate perforating operation prior to pumping the stimulation job. The presence of multiple perforation sets open above the diversion tool can cause operational difficulties. For example, if the proppant fracture from the current zone were to grow vertically and/or poor quality cement is present behind pipe, the fracture could intersect the perforation sets above the diversion tool such that proppant could “dump” back into the wellbore on top of the diversion tool and prevent further tool movement. Also, it could be difficult to execute circulation operations if multiple perforation sets are open above the diversion tool. For example, if the circulation pressures exceed the breakdown pressures associated with the perforations open above the diversion tool, the circulation may not be maintained with circulation fluid unintentionally lost to the formation.
A similar type of stimulation operation may also be performed using jointed tubing and a workover rig rather than a coiled tubing system. Using a diversion tool deployed on jointed tubing may allow for larger diameter tubing to reduce friction pressure losses and allow for increased pump rates. Also, concerns over erosion and tubing integrity may be reduced when compared to coiled tubing since heavier wall thickness jointed tubing pipe may be used and jointed tubing would not be exposed to plastic deformation when run in the wellbore. However, using this approach would likely increase the time and cost associated with the operations because of slower pipe running speeds than those possible with coiled tubing.
To overcome some of the limitations associated with completion operations that require multiple trips of hardware into and out of the wellbore to perforate and stimulate subterranean formations, methods have been proposed for “single-trip” deployment of a downhole tool string to allow for fracture stimulation of zones in conjunction with perforating. Specifically, these methods propose operations that may minimize the number of required wellbore operations and time required to complete these operations, thereby reducing the stimulation treatment cost. These proposals include 1) having a sand slurry in the wellbore while perforating with overbalanced pressure, 2) dumping sand from a bailer simultaneously with firing the perforating charges, and 3) including sand in a separate explosively released container. These proposals all allow for only minimal fracture penetration surrounding the wellbore and are not adaptable to the needs of multi-stage hydraulic fracturing as described herein.
Accordingly, there is a need for an improved method and apparatus for individually treating each of multiple intervals of a subterranean formation penetrated by a wellbore while maintaining the economic benefits of multi-stage treatment. There is also a need for a method and apparatus that can economically reduce the risks inherent in the currently available stimulation treatment options for hydrocarbonbearing formations with multiple or layered reservoirs or with thickness exceeding about 60 meters (200 feet) while ensuring that optimal treatment placement is performed with a mechanical diversion agent that positively directs treatment stages to the desired location.
A method of perforating and treating multiple intervals of one or more subterranean formations intersected by a wellbore is disclosed, said method comprising: (a) deploying a bottom-hole assembly (“BHA”) using deployment means within said wellbore, said BHA having a perforating device, a sealing mechanism and at least one pressure equalization means; (b) using said perforating device to perforate an interval of said one or more subterranean formations; (c) actuating said sealing mechanism so as to establish a hydraulic seal in said wellbore; (d) pumping a treating fluid in said wellbore and into the perforations created by said perforating device, without removing said perforating device from said wellbore; (e) establishing pressure communication between the portions of the wellbore above and below said sealing mechanism through said at least one pressure equalization means; (f) releasing said sealing mechanism; and (g) repeating steps (b) through (f) for at least one additional interval of said one or more subterranean formations.
In another embodiment, a stimulation treatment system is disclosed for use in perforating and treating multiple intervals of one or more subterranean formations intersected by a wellbore, said system comprising: (a) a treating fluid; (b) a deployment means deployed within said wellbore; (c) a bottom-hole assembly (BHA) adapted to be deployed in said wellbore with said deployment means, said BHA having at least one perforating device for sequentially perforating said multiple intervals, at least one sealing mechanism, and at least one pressure equalization means, said BHA capable of being positioned within said wellbore, to allow actuation of said perforating device, said sealing mechanism and said pressure equalization means; (d) said sealing mechanism capable of establishing a hydraulic seal in said wellbore, said pressure equalization means capable of establishing pressure communication between portions of said wellbore above and below said sealing mechanism, and said sealing mechanism further capable of releasing said hydraulic seal to allow said BHA to move to a different position within said wellbore, thereby allowing each of said multiple treatment intervals to be treated with said treating fluid separately from said other treatment intervals.
In a further embodiment, an apparatus is disclosed for use in perforating and treating multiple intervals of one or more subterranean formations intersected by a wellbore, said apparatus comprising: (a) a bottom-hole assembly (BHA), adapted to be deployed in said wellbore by a deployment means, said BHA having at least one perforating device for sequentially perforating said multiple intervals, at least one sealing mechanism and at least one pressure equalization means; and (b) said sealing mechanism capable of establishing a hydraulic seal in said wellbore, said pressure equalization means capable of establishing pressure communication between portions of said wellbore above and below said sealing mechanism, and said sealing mechanism further capable of releasing said hydraulic seal to allow said BHA to move to a different position within said wellbore, thereby allowing each of said multiple treatment intervals to be treated separately from said other treatment intervals.
The present invention and its advantages will be better understood by referring to the following detailed description and the attached drawings in which:
The present invention will be described in connection with its preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the invention, this is intended to be illustrative only, and is not to be construed as limiting the scope of the invention. On the contrary, the description is intended to cover all alternatives, modifications, and equivalents that are included within the spirit and scope of the invention, as defined by the appended claims.
The present invention provides a new method, new system, and a new apparatus for perforating and stimulating multiple formation intervals, which allows each single zone to be treated with an individual treatment stage while eliminating or minimizing the problems that are associated with existing coiled tubing or jointed tubing stimulation methods and hence providing significant economic and technical benefit over existing methods.
Specifically, the invention involves suspending a bottomhole assembly in the wellbore to individually and sequentially perforate and treat each of the desired multiple zones while pumping the multiple stages of the stimulation treatment and to deploy a mechanical re-settable sealing mechanism to provide controlled diversion of each individual treatment stage. For the purposes of this application, “wellbore” will be understood to include below ground sealed components of the well and also all sealed equipment above ground level, such as the wellhead, spool pieces, blowout preventers, and lubricator.
The new apparatus consists of a deployment means (e.g., coiled tubing, jointed tubing, electric line, wireline, tractor system, etc.) with a bottomhole assembly comprised of at least a perforating device and a re-settable mechanical sealing mechanism that may be independently actuated from the surface via one or more signaling means (e.g., electronic signals transmitted via wireline; hydraulic signals transmitted via tubing, annulus, umbilicals; tension or compression loads; radio transmission; fiber-optic transmission; etc.) and designed for the anticipated wellbore environment and loading conditions.
In the most general sense, the term “bottomhole assembly” is used to denote a string of components consisting of at least a perforating device and a re-settable sealing mechanism. Additional components including, but not limited to, fishing necks, shear subs, wash tools, circulation port subs, flow port subs, pressure equalization port subs, temperature gauges, pressure gauges, wireline connection subs, re-settable mechanical slips, casing collar locators, centralizer subs and/or connector subs may also be placed on the bottomhole assembly to facilitate other anticipated auxiliary or ancillary operations and measurements that may be desirable during the stimulation treatment.
In the most general sense, the re-settable mechanical sealing mechanism performs the function of providing a “hydraulic seal”, where hydraulic seal is defined as sufficient flow restriction or blockage such that fluid is forced to be directed to a different location than the location it would otherwise be directed to if the flow restriction were not present. Specifically, this broad definition for “hydraulic seal” is meant to include a “perfect hydraulic seal” such that all flow is directed to a location different from the location the flow would be directed to if the flow restriction were not present; and an “imperfect hydraulic seal” such that an appreciable portion of flow is directed to a location different from the location the flow would be directed to if the flow restriction were not present. Although it would generally be preferable to use a re-settable mechanical sealing that provides a perfect hydraulic seal to achieve optimal stimulation; a sealing mechanism that provides an imperfect hydraulic seal could be used and an economic treatment achieved even though the stimulation treatment may not be perfectly diverted.
In the first preferred embodiment of the invention, coiled tubing is used as the deployment means and the new method involves sequentially perforating and then stimulating the individual zones from bottom to top of the completion interval, with the stimulation fluid pumped down the annular space between the production casing and the coiled tubing. As discussed further below, this embodiment of the new apparatus and method offer substantial improvements over existing coiled tubing and jointed tubing stimulation technology and are applicable over a wide range of wellbore architectures and stimulation treatment designs.
Specifically, the first preferred embodiment of the new method and apparatus involves the deployment system, signaling means, bottomhole assembly, and operations as described in detail below, where the various components, their orientation, and operational steps are chosen, for descriptive purposes only, to correspond to components and operations that could be used to accommodate hydraulic proppant fracture stimulation of multiple intervals.
In the first preferred embodiment for a hydraulic proppant fracture stimulation treatment, the apparatus would consist of the BHA deployed in the wellbore by coiled tubing. The BHA would include a perforating device; re-settable mechanical sealing mechanism; casing-collar-locator; circulation ports; and other ancillary components (as described in more detail below).
Furthermore, in this first preferred embodiment, the perforating device would consist of a select-fire perforating gun system (using shaped-charge perforating charges); and the re-settable mechanical sealing mechanism would consist of an inflatable, re-settable packer; a mechanical re-settable slip device to prevent downward axial movement of the bottomhole assembly when set; and pressure equalization ports located above and below the inflatable re-settable packer.
In addition, in this first preferred embodiment, a wireline would be placed interior to the coiled tubing and used to provide a signaling means for actuation of select-fire perforation charges and for transmission of electric signals associated with the casing-collar-locator used for BHA depth measurement.
Referring now to
With readily-available existing equipment, the height to the top of the coiled tubing injection head 4 could be approximately 90 feet from ground level with the “goose-neck” 12 (where the coil is bent over to go down vertically into the well) approaching approximately 105 feet above the ground. The crane arm 6 and crane base 8 would support the load of the injector head 4, the coiled tubing 106, and any load requirements anticipated for potential fishing operations (jarring and pulling).
In general, the lubricator 2 must be of length greater than the length of the bottomhole assembly to allow the bottomhole assembly to be safely deployed in a wellbore under pressure. Depending on the overall length requirements and as determined prudent based on engineering design calculations for a specific application, to provide for stability of the coiled tubing injection head 4 and lubricator 2, guy-wires 14 could be attached at various locations on the coiled tubing injection head 4 and lubricator 2. The guy wires 14 would be firmly anchored to the ground to prevent undue motion of the coiled tubing injection head 4 and lubricator 2 such that the integrity of the surface components to hold pressure would not be compromised. Depending on the overall length requirements, alternative injection head/lubricator system suspension systems (coiled tubing rigs or fit-for-purpose completion/workover rigs) could also be used.
Also shown in
The side outlet injection valves 22 shown in
The bottomhole assembly storage wellbores 24 shown in
Referring now to
Specifically, a preferred embodiment of the new method involves the following steps, where the stimulation job is chosen, for descriptive purposes, to be a multi-stage, hydraulic, proppant-fracture stimulation.
It will be recognized by those skilled in the art that the preferred suspension method when proppant-laden fluids are involved would be conventional jointed tubing or coiled tubing, preferably with one or more circulation ports so that proppant settling in the wellbore could easily be circulated out of the wellbore. Treatments such as acid fracturing or matrix acidizing may not require such a capability and could readily be performed with a deployment system based on cable such as slickline or wireline, or based on a downhole tractor system.
It will be recognized by those skilled in the art that depending on the objectives of a particular job, various pumping systems could be used and could involve the following arrangements: (a) pumping down the annulus created between the cable or tubing (if the deployment method uses cable or tubing) and the casing wall; (b) pumping down the interior of the coiled tubing or jointed tubing if the suspension method involves the use of coiled tubing or jointed tubing and excess friction and proppant erosion were not of concern for the well depths considered; or (c) simultaneously pumping down the annulus created between the tubing (if the deployment method involves tubing) and the casing wall and the interior of the tubing if excess friction and proppant erosion were not of concern for the well depths considered.
A fifth embodiment of the invention involves deployment of additional tubing strings or cables, hereinafter referred to as “umbilicals”, interior and/or exterior to coiled tubing (or jointed tubing). As shown in FIG. 8A and
The use of an umbilical(s) can provide the ability to hydraulically engage and/or disengage the re-settable mechanical sealing mechanism independent of the hydraulic pressure condition within the coiled tubing. This then allows the method to be extended to use of re-settable mechanical sealing mechanisms requiring independent hydraulic actuation for operation. Perforating devices that require hydraulic pressure for selective-firing can be actuated via an umbilical. This may then allow the wireline, if deployed with the coiled tubing and BHA, to be used for transmission of an additional channel or channels of electrical signals, as may be desirable for acquisition of data from measurement gauges located on the bottomhole assembly; or actuation of other BHA components, for example, an electrical downhole motor-drive that could provide rotation/torque for BHA components. Alternatively, an umbilical could be used to operate a hydraulic motor for actuation of various downhole components (e.g., a hydraulic motor to engage or disengage the re-settable sealing mechanism).
The use of an umbilical(s) can provide the ability to inject or circulate any fluid downhole to multiple locations as desired with precise control. For example, to help mitigate proppant settling on the sealing mechanism during a hydraulic proppant fracture treatment, umbilical(s) could be deployed and used to provide independent continuous or intermittent washing and circulation to keep proppant from accumulating on the sealing mechanism. For example, one umbilical could run to just above the re-settable mechanical sealing mechanism while another is run just below the re-settable mechanical sealing mechanism. Then, as desired, fluid (e.g., nitrogen) could be circulated downhole to either or both locations to wash the proppant from the region surrounding the sealing mechanism and hence mitigate the potential for the BHA sticking due to proppant accumulation. In the case of fluid circulation, it is noted that the umbilical size and fluid would be selected to ensure the desired rate is achieved and is not unduly limited by friction pressure in the umbilical.
In addition to umbilicals comprised of tubing strings that provide hydraulic communication downhole as a signaling means for actuation of BHA components (or possibly as a signal transmission means for surface recording of downhole gauges), in general, one or more wireline or fiber-optic cables could be deployed in the wellbore to provide a electrical or electro-optical communication downhole as a signaling means for actuation of BHA components (or possibly as a signal transmission means for surface recording of downhole gauges).
As alternatives to this sixth embodiment, the tractor system could be self-propelled, controlled by on-board computer systems, and carry on-board signaling systems such that it would not be necessary to attach cable or tubing for positioning, control, and/or actuation of the tractor system. Furthermore, the various BHA components could also be controlled by on-board computer systems, and carry on-board signaling systems such that it is not necessary to attach cable or tubing for control and/or actuation of the components. For example, the tractor system and/or BHA components could carry on-board power sources (e.g., batteries), computer systems, and data transmission/reception systems such that the tractor and BHA components could either be remotely controlled from the surface by remote signaling means, or alternatively, the various on-board computer systems could be pre-programmed at the surface to execute the desired sequence of operations when the deployed in the wellbore.
In a seventh embodiment of this invention, abrasive (or erosive) fluid jets are used as the means for perforating the wellbore. Abrasive (or erosive) fluid jetting is a common method used in the oil industry to cut and perforate downhole tubing strings and other wellbore and wellhead components. The use of coiled tubing or jointed tubing as the BHA suspension means provides a flow conduit for deployment of abrasive fluid-jet cutting technology. To accommodate this, the BHA is configured with a jetting tool. This jetting tool allows high-pressure high-velocity abrasive (or erosive) fluid systems or slurries to be pumped downhole through the tubing and through jet nozzles. The abrasive (or erosive) fluid cuts through the production casing wall, cement sheath, and penetrates the formation to provide flow path communication to the formation. Arbitrary distributions of holes and slots can be placed using this jetting tool throughout the completion interval during the stimulation job. In general, abrasive (or erosive) fluid cutting and perforating can be readily performed under a wide range of pumping conditions, using a wide-range of fluid systems (water, gels, oils, and combination liquid/gas fluid systems) and with a variety of abrasive solid materials (sand, ceramic materials, etc.), if use of abrasive solid material is required for the wellbore specific perforating application.
The jetting tool replaces the conventional select-fire perforating gun system described in the previous six embodiments, and since this jetting tool can be on the order of one-foot to four-feet in length, the height requirement for the surface lubricator system is greatly reduced (by possible up to 60-feet or greater) when compared to the height required when using conventional select-fire perforating gun assemblies as the perforating device. Reducing the height requirement for the surface lubricator system provides several benefits including cost reductions and operational time reductions.
The jetting tool 310 contains jet flow ports 312 that are used to accelerate and direct the abrasive fluid pumped down jointed tubing 302 to jet with direct impingement on the production casing 82. In this configuration, the mechanical casing collar locator 318 is appropriately designed and connected to the mechanical compression-set, re-settable packer 316 such as to allow for fluid flow upward from below mechanical compression-set, re-settable packer 316 to the circulation/equalization port sub 308. The cross-sectional flow area associated with the flow conduits contained within the circulation/equalization port sub 308 are sized to provide a substantially larger cross-sectional flow area than the flow area associated with the jet flow ports 312 such that the majority of flow within the jointed tubing 302 or BHA preferentially flows through the circulation/equalization port sub 308 rather than the jet flow ports 312 when the circulation/equalization port sub 308 is in the open position. The circulation/equalization port sub 308 is opened and closed by upward and downward axial movement of jointed pipe 302.
In this embodiment, jointed tubing 302 is preferably used with the mechanical compression-set, re-settable packer 316 since the mechanical compression-set, re-settable packer 316 can be readily actuated and de-actuated by vertical movement and/or rotation applied via the jointed tubing 302. Vertical movement and/or rotation is applied via the jointed tubing 302 using a completion rig-assisted snubbing unit with the aid of a power swivel unit as the surface means for connection, installation, and removal of the jointed tubing 302 in to and out of the wellbore. It is noted that the surface hardware, methods, and procedures associated with use of a completion rig-assisted snubbing unit with a power swivel unit are common and well-known to those skilled in the art for connection, installation, and removal of jointed tubing in/from a wellbore under pressure. Alternatively, use of a completion rig with the aid of a power swivel unit, and stripping head in place of the snubbing unit, could accommodate connection, installation, and removal of the jointed tubing in/from a wellbore under pressure; again this is common and well-known to those skilled in the art for connection, installation, and removal of jointed tubing in/from a wellbore under pressure. It is further noted that the surface rig-up and plumbing configuration will include appropriate manifolds, piping, and valves to accommodate flow to, from, and between all appropriate surface components/facilities and the wellbore, including but not limited to, the jointed tubing, annulus between jointed tubing and production casing, pumps, fluid tanks, and flow-back pits.
Since the mechanical compression-set, re-settable packer is actuated via jointed tubing 302 vertical movement and/or rotation, fluid can be pumped down the jointed tubing 302 without the necessity of additional control valves and/or isolation valves that may otherwise be required if an inflatable packer was used as the re-settable sealing device. The interior of the jointed tubing 302 is used in this fashion to provide an independent flow conduit between the surface and the jetting tool 310 such that abrasive fluid can be pumped down the jointed tubing 302 to the jetting tool 310. The jet flow ports 312 located on the jetting tool 310 then create a high velocity abrasive fluid jet that is directed to perforate the production casing 82 and cement sheath 84 to establish hydraulic communication with the formation 86.
It is noted that the jet flow ports 312 may be located within approximately six-inches to one-foot of the mechanical compression-set, re-settable packer 316 such that after pumping the second proppant fracture stage, should proppant accumulation on the top of the mechanical compression-set, re-settable packer 316 be of concern, non-abrasive and non-erosive fluid can be pumped down the jointed tubing 302 and through the jet flow ports 312 and/or the circulation/equalization port sub 308 as necessary to clean proppant from the top of the mechanical compression-set, re-settable packer 316. Furthermore, the jetting tool 310 may be rotated (when the mechanical compression-set, re-settable packer 316 is not actuated) using the jointed tubing 302 which may be rotated with the surface power swivel unit to further help to clean proppant accumulation that may occur above the mechanical compression-set, re-settable packer 316. Since the perforations are created using a fluid jet, perforation burrs will not be created. Since perforation burrs are not present to potentially provide additional wear and tear on the elastomers of the mechanical compression-set re-settable packer 316, the longevity of the mechanical compression-set re-settable packer 316 may be increased when compared to applications where perforation burrs may exist.
It is further noted that the flow control provided by the one-way ball-seat check valve sub 314 and the one-way full-opening flapper-type check valve sub 304 only allows for pressure equalization above and below the mechanical compression-set, re-settable packer 316 when the pressure below the mechanical compression-set, re-settable packer 316 is larger than the pressure above the mechanical compression-set, re-settable packer 316. In circumstances when the pressure above the mechanical compression-set, re-settable packer 316 may be larger than the pressure below the mechanical compression-set, re-settable packer 316, the pressure above the mechanical compression-set, re-settable packer 316 can be readily reduced by performing a controlled flow-back of the just stimulated zone using the annulus between the jointed tubing 302 and the production casing 82; or by circulation of lower density fluid (e.g., nitrogen) down the jointed tubing 302 and up the annulus between the jointed tubing 302 and production casing 82.
The one-way full-opening flapper-type check valve sub 304 is preferred as this type of design accommodates unrestricted pumping of abrasive (or erosive) fluid downhole, and furthermore allows for passage of control balls that, depending on the specific detailed design of individual BHA components, may be dropped from the surface to control fluid flow and hydraulics of individual BHA components or provide for safety release of the BHA. Depending on the specific tool design, many different valving configurations could be deployed to provide the functionality provided by the flow control valves described in this embodiment.
As alternatives to this seventh embodiment, a sub containing a nipple could be included which could provide the capability of suspending and holding other measurement devices or BHA components. This nipple, for example, could hold a conventional casing-collar-locator and gamma-ray tool that is deployed via wireline and seated in the nipple to provide additional diagnostics of BHA position and location of formation intervals of interest. Additionally, multiple abrasive jetting tools can be deployed as part of the BHA to control perforation cutting characteristics, such as hole/slot size, cutting rate, to accommodate various abrasive materials, and/or to provide system redundancy in the event of premature component failure.
It will be recognized by those skilled in the art that many different components can be deployed as part of the bottomhole assembly. The bottomhole assembly may be configured to contain instrumentation for measurement of reservoir, fluid, and wellbore properties as deemed desirable for a given application. For example, temperature and pressure gauges could be deployed to measure downhole fluid temperature and pressure conditions during the course of the treatment; a densitometer could be used to measure effective downhole fluid density (which would be particularly useful for determining the downhole distribution and location of proppant during the course of a hydraulic proppant fracture treatment); and a radioactive detector system (e.g., gamma-ray or neutron measurement systems) could be used for locating hydrocarbon bearing zones or identifying or locating radioactive material within the wellbore or formation.
Depending on the specific bottomhole assembly components and whether the perforating device creates perforation holes with burrs that may damage the sealing mechanism, the bottomhole assembly could be configured with a “perforation burr removal” tool that would act to scrape and remove perforation burrs from the casing wall.
Depending on the specific bottomhole assembly components and whether excessive wear of bottomhole assembly components may occur if the assembly is run in contact with the casing wall, centralizer subs could be deployed on the bottomhole assembly to provide positive mechanical positioning of the assembly and prevent or minimize the potential for damage due to the assembly running in contact with the casing wall.
Depending on the specific bottomhole assembly components and whether the perforation charges create severe shock waves and induce undue vibrations when fired, the bottomhole assembly may be configured with vibration/shock dampening subs that would eliminate or minimize any adverse effects on system performance due to perforation charge detonation.
Depending on the deployment system used and the objectives of a particular job, perforating devices and any other desired BHA components may be positioned either above or below the re-settable sealing mechanism and in any desired order relative to each other. The deployment system itself, whether it be wireline, electric line, coiled tubing, conventional jointed tubing, or downhole tractor may be used to convey signals to activate the sealing mechanism and/or perforating device. It would also be possible to suspend such signaling means within conventional jointed tubing or coiled tubing used to suspend the sealing and perforating devices themselves. Alternatively, the signaling means, whether it be electric, hydraulic, or other means, could be run in the hole externally to the suspension means or even housed in or comprised of one or more separate strings of coiled tubing or conventional jointed tubing.
With respect to treatments that use high viscosity fluid systems in wells deeper than about 8,000 feet, several major technological and economic benefits are immediately derived from application of this new invention. Reducing the friction pressure limitations allows treatment of deeper wells and reduces the requirement for special fracture fluid formulations. Friction pressure limitations are reduced or eliminated because the high viscosity fluid can be pumped down the annulus between the coiled tubing or other suspension means and production casing. Since friction pressure limitations can be reduced or eliminated from that experienced with pumping high viscosity fluid systems down the interior of coiled tubing, well depths where this technique can be applied are substantially increased. For example, assuming 1-½-inch coiled tubing deployed in a 5-½-inch outer diameter 17-pound-per-foot casing, the effective cross-sectional flow area is approximately equivalent to a 5-inch outer diameter casing string. With this effective cross-sectional flow area, well depths on the order of 20,000 feet or greater could be treated and higher pump rates (e.g., on the order of 10 to 30-barrels-per-minute or more) could be achieved for effective proppant transport and hydraulic fracturing using high viscosity fluids.
Since the annulus typically may have greater equivalent flow area, conventional fracturing fluids can be used, as opposed to special low-viscosity fluids (such as Dowell-Schlumberger's ClearFrac™ fluid) used to reduce friction pressure drop through coiled tubing. The use of conventional fracturing fluid technology would then allow treatment of formations with temperatures greater than 250° F., above which currently available higher-cost specialty fluids may begin to degrade.
The sealing mechanism used could be an inflatable device, a mechanical compression-set re-settable packer, a mechanical compression-set straddle-packer design, cup-seal devices, or any other alternative device that may be deployed via a suspension means and provides a re-settable hydraulic sealing capability or equivalent function. Both inflatable and compression set devices exist that provide radial clearance between seals and casing wall (e.g., on the order of 0.25-inches to 1-inch for inflatable devices or 0.1-0.2 inches for compression-set devices) such that seal wear and tear would be drastically reduced or eliminated altogether. In a preferred embodiment of this invention, there would be sufficient clearance between the sealing mechanism in its deactivated state and the casing wall to allow rapid movement into and out of the wellbore without significant damage to the sealing mechanism or without pressure control issues related to surging/swabbing the well due to tool movement. The increased clearance between the seal surface and the casing wall (when the seal is not actuated) would also allow the coiled tubing/BHA to be tripped in and out of the hole at much faster speeds than are possible with currently available coiled tubing systems. In addition, to minimize potential undesirable seal wear and tear, in a preferred embodiment, the perforating device would accommodate perforating the casing wall such that a perforation hole with a relatively smooth edge would be achieved. Alternatively, the mechanical re-settable sealing mechanism may not need to provide a perfect hydraulic seal and for example, could retain a small gap around the circumference of the device. This small gap could be sized to provide a sealing mechanism (if desired) whereby proppant bridges across the small gap and provides a seal (if desired) that can be removed by fluid circulation. Furthermore depending on the specific application, it is possible that a stimulation job could proceed in an economically viable fashion even if a perfect hydraulic seal was not obtained with the mechanical re-settable sealing mechanism.
Since the perforating device is deployed simultaneously with the re-settable sealing mechanism, all components can be depth controlled at the same time by the same measurement standard. This eliminates depth control problems that existing methods experience when perforation operations and stimulation operations are performed using two different measurement systems at different times and different wellbore trips. Very precise depth control can be achieved by use of a casing-collar-locator, which is the preferred method of depth control.
The gross height of each of the individual perforated target intervals is not limited. This is in contrast to the problem that existing coiled tubing systems possess using a straddle-packer like device that limits application to 15-30 feet of perforated interval height.
Since permanent bridge plugs are not necessarily used, the incremental cost and wellbore risk associated with bridge plug drill-out operations is eliminated.
If coiled tubing is used as the deployment means, it is possible that the coiled tubing string used for the stimulation job could be hung-off in the wellhead and used as the production tubing string, which could result in significant cost savings by eliminating the need for rig mobilization to the well-site for installation of conventional production tubing string comprised of jointed tubing.
Controlling the sequence of zones to be treated allows the design of individual treatment stages to be optimized based on the characteristics of each individual zone. Furthermore, the potential for sub-optimal stimulation because multiple zones are treated simultaneously is essentially eliminated by having only one open set of perforations exposed to each stage of treatment. For example, in the case of hydraulic fracturing, this invention may minimize the potential for overflush or sub-optimal placement of proppant into the fracture. Also, if a problem occurs such that the treatment must be terminated, the up-hole zones to be stimulated have not been compromised, since they have yet to be perforated. This is in contrast to conventional ball sealer or coiled tubing stimulation methods, where all perforations must be shot prior to the job. Should the conventional coiled tubing job fail, it may be extremely difficult to effectively divert and stimulate over a long completion interval. Additionally, if only one set of perforations is open above the sealing element, fluid can be circulated without the possibility of breaking down the other multiple sets of open perforations above the top sealing element as could occur in the conventional coiled tubing job. This can minimize or eliminate fluid loss and damage to the formation when the bottomhole circulation pressure would otherwise exceed the formation pore pressure.
The entire treatment can be pumped in a single trip, resulting in significant cost savings over other techniques that require multiple wireline or rig work to trip in and out of the hole in between treatment stages.
The invention can be applied to multi-stage treatments in deviated and horizontal wellbores. Typically, other conventional diversion technology in deviated and horizontal wellbores is more challenging because of the nature of the fluid transport of the diverter material over the long intervals typically associated with deviated or horizontal wellbores.
Should a screen-out occur during the fracture treatment, the invention provides a method for sand-laden fluid in the annulus to be immediately circulated out of the hole such that stimulation operations can be recommenced without having to trip the coiled tubing/BHA out of the hole. The presence of the coiled tubing system provides a means to measure bottomhole pressure after perforating or during stimulation operations based on pressure calculations involving the coiled tubing string under shut-in (or low-flow-rate) conditions.
The presence of the coiled tubing or conventional jointed tubing system, if used as the deployment means, provides a means to inject fluid downhole independently from the fluid injected in the annulus. This may be useful, for example, in additional applications such as: (a) keeping the BHA sealing mechanism and flow ports clean of proppant accumulation (that could possibly cause tool sticking) by pumping fluid downhole at a nominal rate to clean off the sealing mechanism and flow ports; (b) downhole mixing applications (as discussed further below); (c) spotting of acid downhole during perforating to aid perforation hole clean-up and communication with the formation; and (d) independently stimulating two zones isolated from each other by the re-settable sealing mechanism. As such, if tubing is used as the deployment means, depending on the specific operations desired and the specific bottomhole assembly components, fluid could be circulated downhole at all times; or only when the sealing element is energized, or only when the sealing element is not energized; or while equalization ports are open or closed. Depending on the specific bottomhole assembly components and the specific design of downhole flow control valves, as may be used for example as integral components of equalization ports subs, circulation port subs or flow port subs, downhole flow control valves may be operated by wireline actuation, hydraulic actuation, flow actuation, “j-latch” actuated, sliding-sleeve actuated, or by many other means known to those skilled in the art of operation and actuation of downhole flow control valves.
The coiled tubing system still allows for controlled flowback of individual treatment stages to aid clean up and assist fracture closure. Flowback can be performed up the annulus between the coiled tubing and the production casing, or alternatively, flowback may even be performed up the coiled tubing string if excessive proppant flowback were not to be considered a problem.
The perforating device may be comprised of commercially-available perforating systems. These gun systems could include what will be referred to herein as a “select-fire” system such that a single perforation gun assembly is comprised of multiple charges or sets of perforation charges. Each individual set of one or more perforation charges can be remotely controlled and fired from the surface using electric, radio, pressure, fiber-optic or other actuation signals. Each set of perforation charges can be designed (number of charges, number of shots per foot, hole size, penetration characteristics) for optimal perforation of the individual zone that is to be treated with an individual stage. With current select-fire gun technology, commercial gun systems exist that could allow on the order of 30 to 40 intervals to be perforated sequentially in a single downhole trip. Guns can be pre-sized and designed to provide for firing of multiple sets of perforations. Guns can be located at any location on the bottomhole assembly, including either above or below the mechanical re-settable sealing mechanism.
Intervals may be grouped for treatment based on reservoir properties, treatment design considerations, or equipment limitations. After each group of intervals (preferably 5 to approximately 20), at the end of a workday (often defined by lighting conditions), or if difficulties with sealing one or more zones are encountered, a bridge plug or other mechanical device would preferably be used to isolate the group of intervals already treated from the next group to be treated. One or more select-fire set bridge plugs or fracture baffles could be run in conjunction with the bottomhole assembly and set as desired during the course of the completion operation to provide positive mechanical isolation between perforated intervals and eliminate the need for a separate wireline run to set mechanical isolation devices or diversion agents between groups of fracture stages.
In general, the inventive method can be readily employed in production casings of 4-½ inch diameter to 7-inch diameter with existing commercially available perforating gun systems and mechanical re-settable sealing mechanisms. The inventive method could be employed in smaller or larger casings with mechanical re-settable sealing mechanisms appropriately designed for the smaller or larger casings.
If select-fire perforating guns are used, each individual gun may be on the order of 2 to 8 feet in length, and contain on the order of 8 to 20 perforating charges placed along the gun tube at shot density ranging between 1 and 6 shots per foot, but preferably 2 to 4 shots per foot. In a preferred embodiment, as many as 15 to 20 individual guns could be stacked one on top of another such that the assembled gun system total length is preferably kept to less than approximately 80 to 100 feet. This total gun length can be run into the wellbore using a readily-available surface crane and lubricator system. Longer gun lengths could also be used, but may require additional or special surface equipment depending on the total number of guns that would make up the complete perforating device. It is noted that in some unique applications, gun lengths, number of charges per gun, and shot density could be greater or less than as specified above as final perforating system design would be impacted by the specific formation characteristics present in the wellbore to stimulated.
In order to minimize the total length of the gun system and BHA, it may be desirable to use multiple (two or more) charge carriers uniformly distributed around and strapped, welded, or otherwise attached to the coiled tubing or connected below the mechanical re-settable sealing mechanism. For example, if it were desired to stimulate 30 zones, where each zone is perforated with a 4-ft gun, a single gun assembly would result in a total length of approximately 150 feet, which may be impractical to handle at the surface. Alternatively, two gun assemblies located opposite one another on the coiled tubing could be deployed, where each assembly could contain 15 guns, and total length could be approximately 75-feet, which could readily be handled at the surface with existing lubricator and crane systems.
An alternative arrangement for the perforating gun or guns would be to locate one or more guns above the re-settable mechanical sealing mechanism. There could be two or more separate gun assemblies attached in such a way that the charges were oriented away from the components on the bottomhole assembly or the coiled tubing. It could also be a single assembly with charges loaded more densely and firing mechanisms designed to simultaneously fire only a subset of the charges within a given interval, perhaps all at a given phase orientation.
Although the perforating device described in this embodiment used remotely fired charges or fluid jetting to perforate the casing and cement sheath, alternative perforating devices including but not limited to chemical dissolution or drilling/milling cutting devices could be used within the scope of this invention for the purpose of creating a flow path between the wellbore and the surrounding formation. For the purposes of this invention, the term “perforating device” will be used broadly to include all of the above, as well as any actuating device suspended in the wellbore for the purpose of actuating charges or other perforating means that may be conveyed by the casing or other means external to the bottomhole assembly or suspension method used to support the bottomhole assembly.
The BHA could contain a downhole motor or other mechanism to provide rotation/torque to accommodate actuation of mechanical sealing mechanisms requiring rotation/torque for actuation. Such a device, in conjunction with an orienting device (e.g., gyroscope or compass) could allow oriented perforating such that perforation holes are placed in a preferred compass direction. Alternatively, if conventional jointed tubing were to be used, it is possible that rotation and torque could be transmitted downhole by direct rotation of the jointed tubing using rotation drive equipment that may be readily available on conventional workover rigs. Downhole instrumentation gauges for measurement of well conditions (casing collar locator, pressure, temperature, pressure, and other measurement gauges) for real-time downhole monitoring of stimulation job parameters, reservoir properties, and/or well performance could also be deployed as part of the BHA.
In addition to the re-settable mechanical diversion device, other diversion material/devices could be pumped downhole during the treatment including but not limited to ball sealers or particulates such as sand, ceramic material, proppant, salt, waxes, resins, or other organic or inorganic compounds or by alternative fluid systems such as viscosified fluids, gelled fluids, foams, or other chemically formulated fluids or other injectable diversion agents. The additional diversion material could be used to help minimize the duration of the stimulation treatment as some time savings could be realized by reducing the number of times the mechanical diversion device is set, while still achieving diversion capabilities over the multiple zones. For example in a 3,000 foot interval where individual zones nominally 100 feet apart are to be treated, it may be desirable to use the re-settable mechanical diversion device working in 500 foot increments uphole, and then divert each of the six stages with a diverting agent carried in the treating fluid. Alternatively, limited entry techniques could be used for multiple intervals as a subset of the gross interval desired to be treated. Either of these variations would decrease the number of mechanical sets of the mechanical diversion device and possibly extend its effective life.
If a tubing string is used as the deployment means, the tubing allows for deployment of downhole mixing devices and ready application of downhole mixing technology. Specifically, the tubing string can be used to pump chemicals downhole and through the flow ports in the bottomhole assembly to subsequently mix with the fluid pumped in the tubing by production casing annulus. For example, during a hydraulic fracturing treatment, it may be desirable to pump nitrogen or carbon dioxide downhole in the tubing and have it mix with the treatment fluid downhole, such that nitrogen-assisted or carbon dioxide-assisted flowback can be accommodated.
This method and apparatus could be used for treatment of vertical, deviated, or horizontal wellbores. For example, the invention provides a method to generate multiple vertical (or somewhat vertical) fractures to intersect horizontal or deviated wellbores. Such a technique could enable economic completion of multiple wells from a single pad location. Treatment of a multi-lateral well could also be performed wherein the deepest lateral is treated first; then a plug is set or sleeve actuated to isolate this lowest lateral; the next up-hole lateral is then treated; another plug is set or sleeve actuated to isolate this lateral; and the process repeated to treat the desired number of laterals within a single wellbore.
If select-fire perforating guns are used, although desirable from the standpoint of maximizing the number of intervals that can be treated, the use of short guns (i.e., 4-ft length or less) could limit well productivity in some instances by inducing increased pressure drop in the near-wellbore reservoir region when compared to use of longer guns. Well productivity could similarly be limited if only a short interval (i.e., 4-ft length or less) is perforated using abrasive jetting. Potential for excessive proppant flowback may also be increased leading to reduced stimulation effectiveness. Flowback would preferably be performed at a controlled low-rate to limit potential proppant flowback. Depending on flowback results, resin-coated proppant or alternative gun configurations could be used to improve the stimulation effectiveness.
In addition, if tubing or cable are used as the deployment means to help mitigate potential undesirable proppant erosion on the tubing or cable from direct impingement of the proppant-laden fluid when pumped into the side-outlet injection ports, an “isolation device” can be rigged up on the wellhead. The isolation device may consists of a flange with a short length of tubing attached that runs down the center of the wellhead to a few feet below the injection ports. The bottomhole assembly and tubing or cable are run interior to the isolation device tubing. Thus the tubing of the isolation device deflects the proppant and isolates the tubing or cable from direct impingement of proppant. Such an isolation device would consist of an appropriate diameter tubing such that it would readily allow the largest outer diameter dimension associated with the tubing or cable and bottomhole assembly to pass through unhindered. The length of the isolation device would be sized such that in the event of damage, the lower master fracture valve could still be closed and the wellhead rigged down as necessary to remove the isolation tool. Depending on the stimulation fluids and the method of injection, an isolation device would not be needed if erosion concerns were not present. Although field tests of isolation devices have shown no erosion problems, depending on the job design, there could be some risk of erosion damage to the isolation tool tubing assembly resulting in difficulty removing it. If an isolation tool is used, preferred practices would be to maintain impingement velocity on the isolation tool substantially below typical erosional limits, preferably below about 180 ft/sec, and more preferably below about 60 ft/sec.
Another concern with this technique is that premature screen-out may occur if fluid displacement during pumping is not adequately measured as it may be difficult to initiate a fracture with proppant-laden fluid across the next zone to be perforated. It may be preferable to use a KCl fluid or some other non-gelled fluid or fluid system for the pad rather than a gelled pad fluid to better initiate fracturing of the next zone. Pumping the job at a higher rate with a non-gelled fluid between stages to achieve turbulent flush/sweep of the casing will minimize the risk of proppant screen-out. Also, contingency guns available on the tool string would allow continuing the job after an appropriate wait time.
Although the embodiments discussed above are primarily related to the beneficial effects of the inventive process when applied to hydraulic fracturing processes, this should not be interpreted to limit the claimed invention which is applicable to any situation in which perforating and performing other wellbore operations in a single trip is beneficial. Those skilled in the art will recognize that many variations not specifically mentioned in the examples will be equivalent in function for the purposes of this invention.
This application is a divisional application Ser. No. 10/085,518 filed Feb. 28, 2002, now U.S. Pat. No. 6,520,255 which is a continuation of application Ser. No. 09/781,597 filed Feb. 12, 2001, now U.S. Pat. No. 6,394,184 which claims the benefit of U.S. Provisional Patent Application Nos. 60/182,687 filed Feb. 15, 2000 and 60/244,258 filed Oct. 30, 2000.
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|---|---|---|---|
| 06182687 | Feb 2000 | US | |
| 06244258 | Oct 2000 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10085518 | Feb 2002 | US |
| Child | 10278519 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09781597 | Feb 2001 | US |
| Child | 10085518 | US |
