Patent Application
20190345802
Horizontal shale wells have historically required pumping large volumes of water and sand to fracture the rock. The effectiveness of the fracturing may rely on a series of independent stages that are isolated from each other by pressure barriers. The method of isolation can vary from well to well, but the industry has gravitated towards plug and perf operations due to positive correlations between the number of fracture initiation points and well production. To create fracture initiation points, a tubular metal wire line gun may be loaded with explosives, then pumped from the surface to a desired downhole location where the charges may be set off by sending an electrical signal down the wire from surface. The electric signal can selectively set off the detonators (the primary explosive) that may be connected to the charges via a primer cord. A plug may be run in the hole below the perforating guns and set before the first gun of each stage is fired, thereby isolating the previous stage from the next stage to be fractured. Each stage may be defined by a set of individual clusters and a total amount of water and sand that is pumped downhole simultaneously into the clusters. Mechanically, the steps of this process have remained relatively unchanged since wire line pump down operations began.
While the basic steps of the perforating process have not changed, many details of the process have. For example, operators have discovered that increasing the number of fracture initiation points by pumping significantly more sand and water into more clusters can increase the value of the production streams beyond the associated added costs. As a result, the number of clusters per fracture stage, the number of stages, and thus the total number of clusters per well has increased significantly over time.
As the number of stages has increased, it has become increasingly important to reduce the amount of time between stages. When a single well is fractured, the entire hydraulic fracture equipment spread must wait for the wire line operation to finish so that pumping can begin. This could be up to 2.5 hours or more for the deepest stages in a well. When two wells are zipper fractured (one is being fractured while the other undergoes wire line operations), this time can be reduced to 30 to 90 minutes depending on onsite procedures and equipment maintenance. However, in some cases, theoretical time savings from zipper fracturing wells may not be achieved because as the fracturing spread is run more consistently, wear and tear on the fluid ends of the frac pumps increases, which may result in minimal or negative savings from zippering the wells.
Fracturing initiation for the toe stage via toe valves can also present issues. First, toe valves may fail to open, or they may open and then become clogged with debris. In some cases operators may elect to perform a “toe preparation” process that involves mobilizing equipment to site and making sure that the toe valves work so that the more expensive hydraulic fracturing spread will not be forced to wait on malfunctioning toe valves. Toe valves can also restrict the inner diameter of the casing near the toe, necessitating more flexible wiper darts to be run, which can increase the chances of leaving excess cement in the well bore.
As an alternative to toe valves, some operators may perforate the toe of the well by running guns in the well on coiled tubing, a process known as TCP (tubing conveyed perforating). Using TCP, the operator can shoot the total desired number of clusters in the first stage, resulting in one fewer wire line trip to achieve the same total number of clusters in the well. TCP can also give more entry points into the well so that operators are less likely to plug off the openings with debris. Running TCP can also eliminate the need for casing ID restrictions at the toe of the well, increasing the likelihood of a successful cement job. However, TCP is dependent on coiled tubing availability and can be expensive. TCP may also not be able to reach deep enough to reach the toe of some extended lateral wells due to frictional limitations.
The foregoing challenges have led service companies to try alternative fracturing methods to replace the plug and perf process. However, the new techniques have, in general, been cost prohibitive. For example, pressure actuated sliding sleeves allow operators to move very quickly between stages by dropping a ball to seal off the old stage and shift the next stage's sleeve open. However, the higher number of fracture initiation points and lower cost of plug and perf completion designs rendered sliding sleeves unsuitable for many applications. Coil shifted sleeves have also been used, but such operations are very time consuming; adding moving equipment downhole increases the risk of failure. RFID (radio frequency identification) technology has also been applied to casing conveyed perforating, in which charges are run in on the outside of the casing, but these solutions required composite windows in the casing to allow for RF (radio frequency) communication through the casing. Added cost and complexity rendered this solution impractical as well. Thus, plug and perf remains a preferred industry technique for completing wells.
Thus, what is needed in the art are improvements to plug and perf completions that simplify operations so as to allow for reduced cost and reduced time.
A method of fracturing a well can include disposing within the well a plurality of temperature responsive devices each comprising a trigger circuit configured to establish fluid communication through a casing of the well responsive to a downhole temperature and a number of downhole temperature cycles. The method can further include pumping a first frac stage, thereby lowering the downhole temperature for at least a predetermined time period, the lowering of the downhole temperature being detected by each of the trigger circuits. The method can further include stopping pumping of the first frac stage, thereby allowing the downhole temperature to increase, the increased temperature being detected by each of the trigger circuits. Each temperature responsive device, upon detecting a respective predetermined number of temperature cycles and a downhole temperature exceeding a respective predetermined temperature, can trigger establishment of fluid communication through the casing.
The downhole temperature can be at least one of a casing temperature or a wellbore fluid temperature. At least one of the plurality of temperature responsive device can trigger establishment of fluid communication through the casing by detonating an explosive. Detonating the explosive may create pressure to shift a sleeve or port. Detonating the explosive may further allow well pressure to shift an unbalanced piston. In some embodiments, establishment of fluid communication through the casing may include initiating at least one of a thermal, incendiary, or chemical cutting device.
The temperature responsive devices may include at least one temperature responsive perforating sleeve adapted to be installed over a casing joint. The temperature responsive devices may include at least one temperature responsive sub adapted to be threaded between two casing joints. The temperature responsive devices may include at least one temperature responsive perforating device embedded within a casing joint.
The method discussed above may further include disposing within the well at least one temperature responsive isolation mechanism wherein the temperature responsive isolation mechanism is used to form a pressure barrier between frac stages. The isolation mechanism may detonate an explosive, which may, in some embodiments, allow wellbore pressure to act on an unbalanced piston and, in at least some embodiments, create a pressure imbalance to shift a sleeve or port. In some embodiments, the isolation mechanism may create a ball seat.
The method may still further include, prior to pumping the first frac stage, triggering an explosive device of a temperature responsive device located at a toe of the well, the triggering being responsive to a predetermined amount of time above a predetermined temperature threshold detected by the temperature responsive device located at the toe of the well. In such cases, at least one trigger mechanism may be configured to trigger a respective explosive upon detecting a respective predetermined number of temperature cycles, a casing temperature exceeding a respective predetermined temperature, and a respective time delay.
A method of fracturing a well may alternatively or additionally include disposing within the well at least one temperature responsive isolation devices each comprising a trigger circuit configured to establish isolation between at least two well zones responsive to a downhole temperature and a number of downhole temperature cycles. The method may further include pumping a first frac stage, thereby lowering the downhole temperature for at least a predetermined time period, the lowering of the downhole temperature being detected by the at least one trigger circuits. The method may still further include stopping pumping of the first frac stage, thereby allowing the downhole temperature to increase, the increased temperature being detected by the at least one trigger circuits. At least one temperature responsive isolation device, upon detecting a respective predetermined number of temperature cycles and a downhole temperature exceeding a respective predetermined temperature, may triggers the isolation mechanism. Triggering the isolation mechanism may detonate an explosive. Detonation of the explosive may allow wellbore pressure to act on an unbalanced piston and may additionally or alternately create a pressure imbalance to shift a sleeve or port. The isolation mechanism creates a ball seat.
A method of fracturing a well may alternatively or additionally include disposing within the well a temperature responsive toe valve comprising a trigger circuit that opens the valve responsive to a downhole temperature above a predetermined temperature threshold for a predetermined period of time. Subsequent to the predetermined amount of time above a predetermined temperature, one or more frac stages may be pumped. The downhole temperature may be at least one of a casing temperature or a wellbore fluid temperature. The temperature responsive toe valve may open by detonating an explosive, which may create pressure to shift a sleeve or port, which may allow well pressure to shift an unbalanced piston. The temperature responsive toe valve may additionally or alternatively open by initiating at least one of a thermal, incendiary, or chemical cutting device.
A temperature responsive completion device may include an explosive and a trigger circuit configured to trigger the explosive responsive to a downhole temperature and at least one of a number of temperature cycles and a time period above or below a temperature threshold. The temperature responsive device may be a perforating sleeve adapted to be installed over a casing joint. The perforating sleeve is configured to be secured to the casing by welding, slips, and/or mechanical fasteners. The perforating sleeve may be located with respect to the casing by one or more pre-drilled holes in the casing. In other embodiments, the temperature responsive completion device may be a sub adapted to be threaded between two casing joints.
The temperature responsive completion device may also be a remote isolation mechanism. The isolation mechanism may detonate an explosive to create a pressure imbalance to shift a sleeve or port, including, for example by use of an unbalanced piston. In some embodiments, the isolation mechanism may create a ball seat.
The temperature responsive completion device may also be a toe valve. In such embodiments, the trigger circuit may be configured to trigger the explosive responsive to a downhole temperature above a predetermined temperature threshold for a predetermined time period.
In any of the foregoing embodiments, the trigger circuit may include a temperature sensor, a controller, and a plurality of capacitors. The explosive may be a shaped charge, including a unidirectional shaped charge or a bidirectional shaped charge, and the shaped charge may operate in conjunction with a rupture or burst disk.
In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure's drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose.
Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a given drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.
So-called “plug and perf” fracturing operations may be enhanced by the use of casing conveyed perforating. In casing conveyed perforating, explosives are run into the well with the casing. For example, the explosives may be disposed in/on perforating sleeves like those described herein. These explosives may be triggered at the desired time to perforate the casing, allowing fluid communication between the well bore and the formation, allowing the initiation of fracturing. Initiating the explosives preferably includes communicating data (i.e., a trigger signal) through the steel casing to the various perforating sleeves disposed within the well. Preferably this communication can be performed without excessive power consumption to either send the initiating signal or receive and respond to the initiating signal on the outside of the casing. One way to achieve this goal is to use the temperature cycles that naturally occur as a part of fracturing operations to encode counter signals that can be received and decoded by receiver circuitry disposed in the perforating sleeve. In some embodiments, these same temperature cycles can be used to remotely actuate isolation mechanisms to provide down hole operations without wire line, coiled tubing, or other intervention from surface. The temperature that is monitored as the control input for this process may be a well casing temperature, a wellbore fluid temperature, or any other suitable downhole temperature. For purposes of the following description, operation of the device will be described in terms of casing temperature, but it will be understood that any other suitable downhole temperature may be used.
A well's casing experiences temperature swings resulting from the relatively high temperature of the formation versus the relatively low temperature of the hydraulic fracturing water. This may be understood with reference to
In some embodiments, a minimum time at or below a low temperature threshold may be detected and required as a condition of incrementing the cycle count. This time threshold relates to certain operating practices sometimes implemented in fracturing operations. For example, in some cases, pumping of a frac stage may be interrupted because of some operational issue. If, prior to the interruption, less than a certain amount of pumping had occurred, the operator may desire to re-frac the stage, i.e., to continue pumping into the current stage. Alternatively, if more than a certain amount of pumping had occurred, the operator may consider the frac of that stage to be “good enough” and may want to move on to the next stage. Thus, a minimum time at or below a low temperature threshold can allow the operator to either re-frac a current stage or move to the next stage as appropriate.
The heat transfer model of the casing may be readily understood with respect to the heat transfer coefficients of steel, cement, and shale. Steel has a relatively high heat transfer coefficient of about 43 W/(m-K). Cement has a relatively low heat transfer coefficient of about 0.29 W/(m-K). Shale rock of the formation on the outside of the casing may typically have a heat transfer coefficient higher than the cement but lower than steel. The heat transfer problem may thus be imagined as a pipe (the casing) with water (the fracturing water) flowing through it, wrapped in thermal insulation (cement), surrounded by an infinite heat source (the shale formation). During the pumping stages, because so much water is pumped (sometimes in excess of 5,000 bbls per stage), and because the water is at surface temperature, the steel casing quickly assumes nearly the same temperature as the surface water. The cement is the limiting factor in the heat transfer equation. Because of the insulating properties of the cement, there is never enough heat transferred from the shale formation to warm the casing because of the large amounts of water being pumped during the fracturing job. After a pumping stage is completed, the problem becomes a steady state heat transfer problem. During this non-pumping phase, the shale slowly transfers heat to the casing and the water contained therein, eventually bringing it up to the constant temperature of the shale formation. In the illustration of
Understanding that the downhole temperatures will follow predictable “drop-then-rise” cycles as a result of frac stages being pumped allows a counter signal to be encoded in each cycle. The fracturing sleeves may use this counter signal, with each stage's set of clusters being individually keyed to send a detonation signal based on these well bore cycles. Certain clusters within a stage may be given a time delay to preferentially open a cluster or clusters in a certain order. This may allow time for other operations. For example, acid may be injected into the toe cluster and placed or “spotted” over the remaining clusters to ensure an efficient wellbore cleanup and stimulation.
In addition to having applications for use in multi-stage fracturing operations, a temperature actuated device may function to establish initial wellbore injection in the toe of the well, replacing the pressure actuated toe valves used in many wells today. In some wells, a device may be run in the toe of the well and programmed to open a pathway from the casing to the formation after a time delay and temperature threshold are both exceeded. This time delay may serve at least two functions. First, it may give the rig crew ample time to ensure that the casing is successfully run into position before actuation. Second, it may allow the operator time to pressure test casing integrity before beginning injection or fracture stimulation operations. The temperature threshold may be set so that once a certain temperature (corresponding to the well's bottom hole temperature) is exceeded, actuation and communication between the well and the formation is established to allow for the first toe injection stage to commence.
Turning back to
Thus, the clusters may all be programmed at the same or similar temperature set point (e.g., temperature 210 in
The perforating sleeves may be designed so as to be conveyed to the target zone of the wellbore along with (i.e., as part of) the well's casing. In some embodiments, the perforating sleeve may be a substantially cylindrical body either comprising a subassembly with box and pin threads so as to be connected between casing joints. In other embodiments, the perforating sleeve may be designed to be slipped over a casing joint and secured in place.
In each embodiment, batteries 704 provide power to a controller 709 that monitors and records the temperature of casing 710 via a temperature sensor 705. Controller 709 may be formed from various combinations of integrated or discrete circuitry such as microcontrollers, microprocessors, digital signal processors and the like. When controller 709 detects the predetermined sequence of temperature changes for a given perforating sleeve, a trigger signal may be provided to detonate a primary explosive 706 (e.g., a detonator connected to detonation cord) that may in turn set off the secondary explosive, i.e., shaped charge 701/702/703/704. Additional circuitry may be provided as required. For example, capacitors may be provided that are charged by the trigger signal to initiate the explosion. Furthermore, in some embodiments, a single explosive, rather than a primary and secondary explosive may be used. The shaped charges may be mounted within the temperature responsive perforating sleeve's main chamber. Additionally, the charges may be embedded into the exterior of the casing and placed at an angle to decrease the overall profile of the perforating sleeve. In some embodiments, a 90 degree configuration and/or a non-cylindrical shaped charge may be used to achieve the desired exterior size and/or profile.
The secondary explosive (e.g., shaped charge) may be arranged such that on detonation it opens a hole through the casing, thereby providing fluid communication from the interior of the casing to the formation.
Additionally, although embodiments showing shaped charges have been described herein, the devices described herein may alternatively or additionally use incendiary materials, “chemical cutters,” or a combination of both to create a pathway for fracture fluid to flow from the casing to the formation. An incendiary based device may use a fuel or propellant to generate heat and pressure, creating holes in the casing for fracturing fluid flow. Incendiary materials may deflagrate as opposed to detonating. A chemical cutter based device may use an explosive charge and/or high pressure jets containing corrosive material to perforate the casing, which may be heated in the process. Bromine Trifluoride is commonly used as a reactive ingredient of a chemical cutter.
An alternative perforating sleeve design is illustrated in
Also contained within housing 905 is explosive 909. Explosive 909 may be connected to a controller 910, which may be powered by battery 911. Controller 910 may be a controller as described above, i.e., discrete components or an integrated microcontroller, microprocessor, or the like. Controller 910 may trigger explosive 909 in response to temperature changes as described above. Once explosive 909 is triggered, pressure can force piston 907 into the open position, in which piston port 908 aligns with casing port 904, allowing fluid communication between the casing interior and the wellbore. Excess pressure resulting from the explosion may be discharged through port 912. Port 912 may initially be blocked by piston 907 (indicated in
Still another alternative sleeve design is illustrated in
Explosive 1009 may be triggered by a controller 1010, which is powered by battery 1011. The controller may operate in response to temperature as described above. When explosive 1009 is triggered, it may open a hole in housing 1005 allowing wellbore fluid 1012 to enter the recess. This exposure to wellbore pressure may displace piston 1007 (to the left as illustrated) aligning piston port 1008 with casing port 1004, thereby opening the sleeve. It will be appreciated that piston face 1013 must have a greater area than piston face 1014 to ensure that the piston is unbalanced and that unequal forces are acting to move the position to the open position.
Remote Isolation Mechanism
As described above, it may be desirable to provide an isolation mechanism between stages during fracturing operations. Conventionally this has been done with various mechanisms, including progressively sized balls landing on correspondingly sized ball seats deployed within the well. Such conventional arrangements may be used with the perforating sleeve designs described above. Alternatively, fracturing operations efficiency may be improved by providing a remote isolation mechanism that includes a temperature responsive ball seat as described below with reference to
Controller 1410 may be configured to trigger an explosive 1409, which may be configured to open a port 1413 (
As will be appreciated, once the wellbore assembly is run into the well, it will come to thermal equilibrium at a temperature substantially corresponding to the wellbore temperature. The pumping of the first frac stage will cause a first temperature cycle as described above with respect to
Once object 1506 seats (
Described above are various features and embodiments relating to temperature responsive devices for use in a fracturing a wellbore. Such temperature responsive devices may be used in a variety of applications, but may be particular advantageous when used in conjunction with fracturing operations, particularly simultaneous fracturing operations of multiple wells.
Additionally, although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined in any of the various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims.
| Number | Date | Country | |
|---|---|---|---|
| 62668859 | May 2018 | US |
