Patent Application
20050211439
The present invention relates generally to well completion operations, and more particularly methods of stimulation and subsequent isolation of hydrajet stimulated zones from subsequent jetting or stimulation operations, so as to minimize the loss of completion/stimulation fluids during the subsequent well jetting or stimulation operations.
In some wells, it is desirable to individually and selectively create multiple fractures having adequate conductivity, usually a significant distance apart along a wellbore, so that as much of the hydrocarbons in an oil and gas reservoir as possible can be drained/produced into the wellbore. When stimulating a reservoir from a wellbore, especially those that are highly deviated or horizontal, it is difficult to control the creation of multi-zone fractures along the wellbore without cementing a liner to the wellbore and mechanically isolating the zone being fractured from previously fractured zones or zones not yet fractured.
Traditional methods to create fractures at predetermined points along a highly deviated or horizontal wellbore vary depending on the nature of the completion within the lateral (or highly deviated) section of the wellbore. Only a small percentage of the horizontal completions during the past 15 or more years used a cemented liner type completion; most used some type of non-cemented liner or a bare openhole section. Furthermore, many wells with cemented liners in the lateral were also completed with a significant length of openhole section beyond the cemented liner section. The best known way to achieve desired hydraulic fracturing isolation/results is to cement a solid liner in the lateral section of the wellbore, perform a conventional explosive perforating step, and then perform fracturing stages along the wellbore using some technique for mechanically isolating the individual fractures. The second most successful method involves cementing a liner and significantly limiting the number of perforations, often using tightly grouped sets of perforations, with the number of total perforations intended to create a flow restriction giving a back-pressure of about 100 psi or more, due to fluid flow restriction based on the wellbore injection rate during stimulation, with some cases approaching 1000 psi flow resistance. This technology is generally referred to as “limited entry” perforating technology.
In one conventional method, after the first zone is perforated and fractured, a sand plug is installed in the wellbore at some point above the fracture, e.g., toward the heel. The sand plug restricts any meaningful flow to the first zone fracture and thereby limits the loss of fluid into the formation, while a second upper zone is perforated and fracture stimulated. One such sand plug method is described in SPE 50608. More specifically, SPE 50608 describes the use of coiled tubing to deploy explosive perforating guns to perforate the next treatment interval while maintaining well control and sand plug integrity. The coiled tubing and perforating guns were removed from the well and then the next fracturing stage was performed. Each fracturing stage was ended by developing a sand plug across the treatment perforations by increasing the sand concentration and simultaneously reducing pumping rates until a bridge was formed. The paper describes how increased sand plug integrity could be obtained by performing what is commonly known in the cementing services industry as a “hesitation squeeze” technique. A drawback of this technique, however, is that it requires multiple trips to carry out the various stimulation and isolation steps.
More recently, Halliburton Energy Services, Inc. has introduced and proven the technology for using hydrajet perforating, jetting while fracturing, and co-injection down the annulus. In one method, this process is generally referred to by Halliburton as the SURGIFRAC process or stimulation method and is described in U.S. Pat. No. 5,765,642, which is incorporated herein by reference. The SURGIFRAC process has been applied mostly to horizontal or highly deviated wellbores, where casing the hole is difficult and expensive. By using this hydrajetting technique, it is possible to generate one or more independent, single plane hydraulic fractures; and therefore, highly deviated or horizontal wells can be often completed without having to case the wellbore. Furthermore, even when highly deviated or horizontal wells are cased, hydrajetting the perforations and fractures in such wells generally result in a more effective fracturing method than using traditional explosive charge perforation and fracturing techniques. Thus, prior to the SURGIFRAC technique, methods available were usually too costly to be an economic alternative, or generally ineffective in achieving stimulation results, or both.
The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments, which follows.
The present invention is directed to a method of completing a well using a hydrajetting tool and subsequently plugging or partially sealing the fractures in each zone with an isolation fluid. In accordance with the present invention, the hydrajetting tool can perform one or more steps, including but not limited to, the perforating step, the perforating and fracture steps, and the perforating, fracture and isolation steps.
More specifically, the present invention is directed to a method of completing a well in a subterranean formation, comprising the following steps. First, a wellbore is drilled in the subterranean formation. Next, depending upon the nature of the formation, the wellbore is lined with a casing string or slotted liner. Next, a first zone in the subterranean formation is perforated by injecting a pressurized fluid through a hydrajetting tool into the subterranean formation, so as to form one or more perforation tunnels. This fluid may or may not contain solid abrasives. Following the perforation step, the formation is fractured in the first zone by injecting a fracturing fluid into the one or more perforation tunnels, so as to create at least one fracture along each of the one or more perforation tunnels. Next, the one or more fractures in the first zone are plugged or partially sealed by installing an isolation fluid into the wellbore adjacent to the fractures and/or inside the openings of the fractures. In at least one embodiment, the isolation fluid has a greater viscosity than the fracturing fluid. Next, a second zone of the subterranean formation is perforated and fractured. If it is desired to fracture additional zones of the subterranean formation, then the fractures in the second zone are plugged or partially sealed by the same method, namely, installing an isolation fluid into the wellbore adjacent to the fractures and/or inside the openings of the fractures. The perforating, fracturing and sealing steps are then repeated for the additional zones. The isolation fluid can be removed from fractures in the subterranean formation by circulating the fluid out of the fractures, or in the case of higher viscosity fluids, breaking or reducing the fluid chemically or hydrajetting it out of the wellbore. Other exemplary methods in accordance with the present invention are described below.
An advantage of the present invention is that the tubing string can be inside the wellbore during the entire treatment. This reduces the cycle time of the operation. Under certain conditions the tubing string with the hydrajetting tool or the wellbore annulus, whichever is not being used for the fracturing operation, can also be used as a real-time BHP (Bottom Hole Pressure) acquisition tool by functioning as a dead fluid column during the fracturing treatment. Another advantage of the invention is the tubing string provides a means of cleaning the wellbore out at anytime during the treatment, including before, during, after, and in between stages. Tubulars can consist of continuous coiled tubing, jointed tubing, or combinations of coiled and jointed tubing.
A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, which:
FIGS. 10A-C illustrate yet another exemplary method of fracturing multiple zones in a subterranean formation and plugging or partially sealing those zones in accordance with the present invention.
The details of the method according to the present invention will now be described with reference to the accompanying drawings. First, a wellbore 10 is drilled into the subterranean formation of interest 12 using conventional (or future) drilling techniques. Next, depending upon the nature of the formation, the wellbore 10 is either left open hole, as shown in
Once the wellbore 10 is drilled, and if deemed necessary cased, a hydrajetting tool 14, such as that used in the SURGIFRAC process described in U.S. Pat. No. 5,765,642, is placed into the wellbore 10 at a location of interest, e.g., adjacent to a first zone 16 in the subterranean formation 12. In one exemplary embodiment, the hydrajetting tool 14 is attached to a coil tubing 18, which lowers the hydrajetting tool 14 into the wellbore 10 and supplies it with jetting fluid. Annulus 19 is formed between the coil tubing 18 and the wellbore 10. The hydrajetting tool 14 then operates to form perforation tunnels 20 in the first zone 16, as shown in
In the next step of the well completion method according to the present invention, the first zone 16 is fractured. This may be accomplished by any one of a number of ways. In one exemplary embodiment, the hydrajetting tool 14 injects a high pressure fracture fluid into the perforation tunnels 20. As those of ordinary skill in the art will appreciate, the pressure of the fracture fluid exiting the hydrajetting tool 14 is sufficient to fracture the formation in the first zone 16. Using this technique, the jetted fluid forms cracks or fractures 24 along the perforation tunnels 20, as shown in
In another exemplary embodiment, the jetted fluid carries a proppant into the cracks or fractures 24. The injection of additional fluid extends the fractures 24 and the proppant prevents them from closing up at a later time. The present invention contemplates that other fracturing methods may be employed. For example, the perforation tunnels 20 can be fractured by pumping a hydraulic fracture fluid into them from the surface through annulus 19. Next, either and acidizing fluid or a proppant fluid can be injected into the perforation tunnels 20, so as to further extend and widen them. Other fracturing techniques can be used to fracture the first zone 16.
Once the first zone 16 has been fractured, the present invention provides for isolating the first zone 16, so that subsequent well operations, such as the fracturing of additional zones, can be carried out without the loss of significant amounts of fluid. This isolation step can be carried out in a number of ways. In one exemplary embodiment, the isolation step is carried out by injecting into the wellbore 10 an isolation fluid 28, which may have a higher viscosity than the completion fluid already in the fracture or the wellbore.
In one embodiment, the isolation fluid 28 is injected into the wellbore 10 by pumping it from the surface down the annulus 19. More specifically, the isolation fluid 28, which is highly viscous, is squeezed out into the annulus 19 and then washed downhole using a lower viscosity fluid. In one implementation of this embodiment, the isolation fluid 28 is not pumped into the wellbore 10 until after the hydrajetting tool 14 has moved up hole, as shown in
In the embodiments shown in
In another exemplary embodiment of the present invention, the isolation fluid 28 is injected into the wellbore 10 adjacent the first zone 16 through the jets 22 of the hydrajetting tool 14, as shown in
In another exemplary embodiment, the isolation fluid 28 is formed of a fluid having a similar chemical makeup as the fluid resident in the wellbore during the fracturing operation. The fluid may have a greater viscosity than such fluid, however. In one exemplary embodiment, the wellbore fluid is mixed with a solid material to form the isolation fluid. The solid material may include natural and man-made proppant agents, such as silica, ceramics, and bauxites, or any such material that has an external coating of any type. Alternatively, the solid (or semi-solid) material may include paraffin, encapsulated acid or other chemical, or resin beads.
In another exemplary embodiment, the isolation fluid 28 is formed of a highly viscous material, such as a gel or cross-linked gel. Examples of gels that can be used as the isolation fluid include, but are not limited to, fluids with high concentration of gels such as Xanthan. Examples of cross-linked gels that can be used as the isolation fluid include, but are not limited to, high concentration gels such as Halliburton's DELTA FRAC fluids or K-MAX fluids. “Heavy crosslinked gels” could also be used by mixing the crosslinked gels with delayed chemical breakers, encapsulated chemical breakers, which will later reduce the viscosity, or with a material such as PLA (poly-lactic acid) beads, which although being a solid material, with time decomposes into acid, which will liquefy the K-MAX fluids or other crosslinked gels.
After the isolation fluid 28 is delivered into the wellbore 10 adjacent the fractures 24, a second zone 30 in the subterranean formation 12 can be fractured. If the hydrajetting tool 14 has not already been moved within the wellbore 10 adjacent to the second zone 30, as in the embodiment of
Once all of the desired zones have been fractured, the isolation fluid 28 can be recovered thereby unplugging the fractures 24 and 34 for subsequent use in the recovery of hydrocarbons from the subterranean formation 12. One method would be to allow the production of fluid from the well to move the isolation fluid, as shown in
The following is an another method of completing a well in a subterranean formation in accordance with the present invention. First, the wellbore 10 is drilled in the subterranean formation 12. Next, the first zone 16 in the subterranean formation 12 is perforated by injecting a pressurized fluid through the hydrajetting tool 14 into the subterranean formation (
Fracturing fluid can be pumped down the annulus 19 as soon as the one or more fractures 24 are initiated, so as to propagate the fractures 24, as shown in
After the fractures 24 have been propagated and the hydrajetting tool 14 has been moved up hole, the isolation fluid 28 in accordance with the present invention can be pumped into the wellbore 10 adjacent to the first zone 16. Over time the isolation fluid 28 plugs the one or more fractures 24 in the first zone 16, as shown, for example, in
After all of the desired fractures have been formed, the isolation fluid 28 can be removed from the subterranean formation 12. There are a number of ways of accomplishing this in addition to flowing the reservoir fluid into the wellbore and to those already mentioned, namely reverse circulation and hydrajetting the fluid out of the wellbore 10. In another method, acid is pumped into the wellbore 10 so as to activate, de-activate, or dissolve the isolation fluid 28 in situ. In yet another method, nitrogen is pumped into the wellbore 10 to flush out the wellbore and thereby remove it of the isolation fluid 28 and other fluids and materials that may be left in the wellbore.
Yet another method in accordance with the present invention will now be described. First, as with the other methods, wellbore 10 is drilled. Next, first zone 16 in subterranean formation 12 is perforated by injecting a pressurized fluid through hydrajetting tool 14 into the subterranean formation, so as to form one or more perforation tunnels 20. The hydrajetting tool 14 can also be rotated or rotated and/or axially moved during this step to cut slots into the subterranean formation 12. Next, one or more fractures 24 are initiated in the first zone 16 of the subterranean formation by injecting a fracturing fluid into the one or more perforation tunnels 20 through the hydrajetting tool 14. Following this step or simultaneous with it, additional fracturing fluid is pumped into the one or more fractures 24 in the first zone 16 through annulus 19 in the wellbore 10 so as to propagate the fractures 24. Any cuttings left in the annulus after the drilling and perforation steps may be pumped into the fracture during this step. Simultaneous with this latter step, the hydrajetting tool 14 is moved up hole. Pumping of the fracture fluid into the formation through annulus 19 is then ceased. All of these steps are then repeated for the second zone 30 and any subsequent zones thereafter. The rate of the fracturing fluid being ejected from the hydrajetting tool 14 is decreased as the tool is moved up hole and even may be halted altogether.
An additional method in accordance with the present invention will now be described. First, as with the other methods, wellbore 10 is drilled. Next, first zone 16 in subterranean formation 12 is perforated by injecting a pressurized fluid through hydrajetting tool 14 into the subterranean formation, so as to form one or more perforation tunnels 20. The hydrajetting tool 14 can be rotated during this step to cut slots into the subterranean formation 12. Alternatively, the hydrajetting tool 14 can be rotated and/or moved axially within the wellbore 10, so as to create a straight or helical cut into the formation 16. Next, one or more fractures 24 are initiated in the first zone 16 of the subterranean formation by injecting a fracturing into the one or more perforation tunnels or cuts 20 through the hydrajetting tool 14. Following this step or simultaneous with it, additional fracturing fluid is pumped into the one or more fractures 24 in the first zone 16 through annulus 19 in the wellbore 10 so as to propagate the fractures 24. Any cuttings left in the annulus after the drilling and perforation steps are pumped into the fracture during this step. Simultaneous with this latter step, the hydrajetting tool 14 is moved up hole and operated to perforate the next zone. The fracturing fluid is then ceased to be pumped down the annulus 19 into the fractures, at which time the hydrajetting tool starts to initiate the fractures in the second zone. The process then repeats.
Yet another method in accordance with the present invention will now be described with reference to FIGS. 10A-C. First, as with the other methods, wellbore 10 is drilled. Next, first zone 16 in subterranean formation 12 is perforated by injecting a pressurized fluid through hydrajetting tool 14 into the subterranean formation, so as to form one or more perforation tunnels 20, as shown in
Next, one or more fractures 24 are initiated in the first zone 16 of the subterranean formation by injecting a fracturing fluid into the one or more perforation tunnels or cuts 20 through the hydrajetting tool 14, as shown in
Next, the hydrajetting tool 14 is moved to the second zone 30, where it perforates that zone thereby forming perforation tunnels or cuts 32. Next, the fractures 34 in the second zone 30 are initiated using the above described technique or a similar technique. Next, the fractures 34 in the second zone are propagated by injecting a second fluid similar to above, i.e., the fluid containing the adhesive and/or consolidation agent into the fractures. Enough of the fracturing fluid is pumped downhole to fill the wellbore and the openings of fractures 24 in the first zone 16. This occurs as follows. The high temperature downhole causes the sand particles in the fracture fluid to bond to one another in clusters or as a loosely packed bed and thereby form an in situ plug. Initially, some of the fluid, which flows into the jetted tunnels and possibly part way into fractures 24 being concentrated as part of the liquid phase, leaks out into the formation in the first zone 16, but as those of ordinary skill in the art will appreciate, it is not long before the openings become plugged or partially sealed. Once the openings of the fractures 24 become filled, enough fracture fluid can be pumped down the wellbore 10 to fill some or all of the wellbore 10 adjacent fractures 24, as shown in
FIGS. 11A-B illustrate the details of the hydrajetting tool 14 for use in carrying out the methods of the present invention. Hydrajetting tool 14 comprises a main body 40, which is cylindrical in shape and formed of a ferrous metal. The main body 40 has a top end 42 and a bottom end 44. The top end 42 connects to coil tubing 18 for operation within the wellbore 10. The main body 40 has a plurality of nozzles 46, which are adapted to direct the high pressure fluid out of the main body 40. The nozzles 46 can be disposed, and in one certain embodiment are disposed, at an angle to the main body 40, so as to eject the pressurized fluid out of the main body 40 at an angle other than 90°.
The hydrajetting tool 14 further comprises means 48 for opening the hydrajetting tool 14 to fluid flow from the wellbore 10. Such fluid opening means 48 includes a fluid-permeable plate 50, which is mounted to the inside surface of the main body 40. The fluid-permeable plate 50 traps a ball 52, which sits in seat 54 when the pressurized fluid is being ejected from the nozzles 46, as shown in
Yet another method in accordance with the present invention will now be described. First, the first zone 16 in the subterranean formation 12 is perforated by injecting a perforating fluid through the hydrajetting tool 14 into the subterranean formation, so as to form perforation tunnels 20, as shown, for example, in
As is well known in the art, a positioning device, such as a gamma ray detector or casing collar locator (not shown), can be included in the bottom hole assembly to improve the positioning accuracy of the perforations.
Therefore, the present invention is well-adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. In particular, as those of skill in the art will appreciate, steps from the different methods disclosed herein can be combined in a different manner and order. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.
