Process and apparatus to improve reliability of pinpoint stimulation operations

An anchor tool having a housing, a one-way restrictor device in fluid communication with the housing, and a stabilizer affixed to the housing. The one-way restrictor device is configured to allow restricted flow in a first direction, and to allow flow in a second direction.

BACKGROUND

The present invention relates to subterranean stimulation operations and, more particularly, to processes and apparatus for improving the reliability of pinpoint stimulation operations.

To produce hydrocarbons (e.g., oil, gas, etc.) from a subterranean formation, well bores may be drilled that penetrate hydrocarbon-containing portions of the subterranean formation. The portion of the subterranean formation from which hydrocarbons may be produced is commonly referred to as a “production zone.” In some instances, a subterranean formation penetrated by the well bore may have multiple production zones at various locations along the well bore.

Generally, after a well bore has been drilled to a desired depth, completion operations are performed. Such completion operations may include inserting a liner or casing into the well bore and, at times, cementing a casing or liner into place. Once the well bore is completed as desired (lined, cased, open hole, or any other known completion) a stimulation operation may be performed to enhance hydrocarbon production into the well bore. Where methods of the present invention reference “stimulation,” that term refers to any stimulation technique known in the art for increasing production of desirable fluids from a subterranean formation adjacent to a portion of a well bore. Examples of some common stimulation operations involve hydraulic fracturing, acidizing, fracture acidizing, and hydrajetting. Stimulation operations are intended to increase the flow of hydrocarbons from the subterranean formation surrounding the well bore into the well bore itself so that the hydrocarbons may then be produced up to the wellhead.

Conventional pinpoint stimulation techniques may be susceptible to movements of the hydrajetting tool, which can generally reduce the tool performance. These movements may be caused by a number of factors, including wellbore geometry and tubing movement due to thermal and pressure effects. Further movement may occur around the hydrajetting tool due to the effects of turbulence, vibration, pressure related piston effects and jet thrust. Longer jetting times may compensate for this reduction in tool performance. However, the increase in jetting times may not be desirable.

One suitable hydrajet stimulation method, introduced by Halliburton Energy Services, Inc., is known as the SURGIFRAC and is described in U.S. Pat. No. 5,765,642. The SURGIFRAC process may be particularly well suited for use along highly deviated portions of a well bore, where casing the well bore may be difficult and/or expensive. The SURGIFRAC hydrajetting technique makes possible the generation of one or more independent, single plane hydraulic fractures. 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 perforation and fracturing techniques.

During the SURGIFRAC process, which uses the Bernoulli principle to achieve fluid diversion between fractures, the primary flow goes to the fracture while the secondary, leakoff flow, is supplied by the annulus. In some instances, such as in long horizontal well bores, a large number of fractures may be desired. The formation of each fracture results in some additional leakoff. Consequently, with the increase in the number of fractures, the amount of the secondary, leakoff flow increases and eventually may exceed the amount of the primary flow to the fracture. The increased fluid loss may reduce the efficiency of the operations and increases the cost.

Another suitable hydrajet stimulation method, introduced by Halliburton Energy Services, Inc., is known as the COBRAMAX and is described in U.S. Pat. No. 7,225,869, and is applicable to vertical, deviated, and horizontal wells, which is incorporated herein by reference in its entirety. The COBRAMAX process may be particularly well suited for use along highly deviated portions of a well bore. The COBRAMAX technique makes possible the generation of one or more independent hydraulic fractures without the necessity of zone isolation, can be used to perforate and fracture in a single down hole trip, and may eliminate the need to set mechanical plugs through the use of a sand plug.

The COBRAMAX process involves isolating the hydrajet stimulated zones from subsequent well operations. The primary fluid diversion of the previous regions in the COBRAMAX process is achieved by placing sand plugs in the zones to be isolated. The placement of sand plugs, particularly in horizontal well bores, may require a prescribed flow rate, which may be difficult to achieve when using surface pumping equipment.

Other methods for improving reliability of pinpoint stimulation operations are described in U.S. patent application Ser. No. 12/244,547 filed on Oct. 2, 2008, which is hereby incorporated by reference as if fully reproduced herein.

SUMMARY

The present invention relates to subterranean stimulation operations and, more particularly, to processes and apparatus for improving the reliability of pinpoint stimulation operations.

In some embodiments, an anchor tool comprises a housing, a one-way restrictor device in fluid communication with the housing, and a stabilizer affixed to the housing. The one-way restrictor device may be configured to allow restricted flow in a first direction, and to allow flow in a second direction.

In other embodiments, a method of diverting flow may comprise pumping fluid through a stimulation tool, passing at least a portion of the fluid from the stimulation tool through an anchor tool, introducing the fluid from the anchor tool at a desired location, and diverting flow at the desired location. Passing the fluid through the anchor tool may comprise passing the fluid through a one-way restrictor device.

In yet other embodiments, a method of improving the performance of a stimulation tool may comprise stabilizing an anchor tool connected to the stimulation tool, introducing a fluid into the stimulation tool, passing a first portion of the fluid out of the stimulation tool and into a formation, and passing a second fluid of the fluid through the stimulation tool to the anchor tool.

In still other embodiments, a hydrajetting bottomhole assembly may comprise a hydrajetting tool, and a hydrajet anchor tool connected to the hydrajetting tool. The hydrajet anchor tool may comprise a housing, a one-way restrictor device in fluid communication with the housing, and a stabilizer affixed to the housing. The one-way restrictor device may be configured to allow restricted flow in a first direction, and to allow flow in a second direction.

Various features and advantages of the present invention will be apparent to those skilled in the art from the description of the preferred embodiments which follows when taken in conjunction with the accompanying drawings. While those skilled in the art may make numerous changes, such changes are within the spirit of the invention.

DETAILED DESCRIPTION

The present invention relates to subterranean stimulation operations and, more particularly, to processes and apparatus for improving the reliability of pinpoint stimulation operations.

Referring toFIG. 1, hydrajet anchor tool100may be connected to workstring102below hydrajetting tool104, such that fluid from hydrajetting tool104may simultaneously pass through jets in hydrajetting tool104into a formation and through hydrajetting tool104into and through hydrajet anchor tool100. Referring now toFIG. 2, hydrajet anchor tool100may have housing106, mandrel108situated within housing106, centralizer112situated generally around housing106, anchor114situated generally around housing106, and a one-way restrictor device. Hydrajet anchor tool100may also have one or more equalizing ports116allowing fluid to flow through housing106, and/or one or more drag blocks118.

Housing106may have a generally tubular construction, configured to allow fluid to pass therethrough and allow hydrajet anchor tool100to cope with hydrajet differential pressures. Housing106may include seals between housing106and mandrel108, and be constructed of any material suitable for downhole use, and may connect to hydrajetting tool104via threads, welding, or other methods. Mandrel108may slide relative to housing106, allowing for equalizing ports116to be selectively opened and closed. Mandrel108may also have a generally tubular construction, be constructed of any material suitable for downhole use, and may have passageway120to allow fluid to pass therethrough.

The one-way restrictor device may be any device for restricting flow in a first direction while allowing unrestricted flow in a second direction. For example, the one-way restrictor device may include moveable body121situated partially, wholly, or otherwise generally within mandrel108. As illustrated inFIGS. 3 and 4, body121may move axially with respect to mandrel108to restrict flow through hydrajet anchor tool100in one direction yet allow flow in the other direction. In some embodiments the flow in one direction may be unrestricted or free flow. Flow in the first direction may be restricted (but not blocked entirely) by jet122(e.g., a port, a regulator, a nozzle, a flow limiting orifice, a simple orifice, a fixed choke, an adjustable choke, and/or any other device allowing pressure to be maintained on one side, while allowing flow therethrough), when body121contacts, joins, or otherwise engages seat124within mandrel108. Jet122may be configured to cope with high velocity sand laden fluid, while allows fluid to maintain pressure within hydrajetting tool104, and simultaneously allowing fluid to be used to set a sand plug105(FIG. 1) in a zone downhole of hydrajetting tool104and hydrajet anchor tool100. In other embodiments, one-way restrictor device may be a port, a regulator, a nozzle, a flow limiting orifice, a simple orifice, a fixed choke, an adjustable choke, and/or any other device. Generally, one-way restrictor device may be in fluid communication with housing106, such that the one-way restrictor device may control passage of fluid through housing106. In some embodiments, the one-way restrictor device may be situated generally within housing106. In other embodiments, the one-way restrictor device may be on either end of housing106, or outside housing106, so long as it restricts flow in a first direction and allows flow in a second direction.

Centralizer112may allow for both hydrajetting tool104and hydrajet anchor tool100to be substantially centered within wellbore126. Centralizer112may maintain hydrajet anchor tool100in line with a centerline of wellbore126, or centralizer112may otherwise direct hydrajet anchor tool100substantially toward the centerline, such that hydrajet anchor tool100does not rest on one side of wellbore126. In yet other embodiments, centralizer may direct hydrajet anchor tool100slightly toward the centerline. In some embodiments, centralizer112includes one or more packing elements, such as inflatable packers (which in some instances may be inflatable by one or more process fluids), compression packers, swellable packers, and the like. In some embodiments, the packing elements are elastomeric packing elements. In some embodiments, centralizer112may provide a total or partial seal between hydrajet anchor tool100and wellbore126(which may or may not be cased), while allowing diversion of flow through the one-way restrictor device. Centralizer112may be a positive standoff type device, or a variable device. In some embodiments centralizer112provides no seal, but rather allows for a gap while preventing hydrajetting tool104and the hydrajet anchor tool100from resting against wellbore126.

Anchor114may substantially prevent undesirable rotational and axial movement of hydrajetting tool104and of hydrajet anchor tool100, allowing for a more efficient hydrajetting operation. In some embodiments, anchor114allows hydrajetting tool104and hydrajet anchor tool100to be maintained at a fixed position for a desired period. In some instances, this period may cover the duration of hydrajetting operations. For example, anchor114may be configured to reduce or prevent rotational and/or axial movement for a period of approximately ten minutes to an hour, or more, if necessary. Anchor114may include slips, or other elements to grip wellbore126, whether cased or uncased. In some embodiments, anchor114is downhole from centralizer112. Anchor114may be combined with centralizer112, such that one or more single stabilizer elements function to centralize and fix hydrajet anchor tool100in position. The stabilizer(s) may be affixed to housing106, either directly or indirectly. For example, the stabilizer(s) may be generally situated around housing106, above housing106, or below housing106, or the stabilizer(s) may otherwise be situated proximate housing106, so long as the stabilizer(s) either centralize or fix housing106and/or hydrajet anchor tool100in position.

In some embodiments, hydrajet anchor tool100may be used to improve the performance of hydrajetting tool104. Specifically, the tool movements due to pipe extension/shrinkage, temperature and/or pressure can be minimized by engaging anchor114of hydrajet anchor tool100. As would be appreciated by those of ordinary skill in the art, with the benefit of this disclosure, the strength requirements for anchor114are minimal. For instance, in a vertical well, a 10000 ft. tubing, 2⅜″-4.7 lb./ft. would only need 3800 lbs. to stretch a full 1 ft.; or about 319 lb./in. As would be appreciated by those of ordinary skill in the art, with the benefit of this disclosure, in reality, this value will have to be subtracted by some large unknown value, representing friction with wellbore126. Note that, even in “vertical” wells, wells are never truly vertical; some slants occur during the drilling of the well. In horizontal wells, movement can sometimes be large due to the “jerkiness” of the system. However, the pipe friction negates some of this movement. For instance, for a 2000 ft. tubing as in the above example, in a horizontal well, assuming a friction factor of 0.35 between the pipe and the well bore wall, the friction force may be close to 3290 lbs, thus needing an additional help of only 500 lbs to prevent the tool's movement. Similarly, the jet reaction force causes some small side movements of the tool. For instance, a 0.25″ jet at a pressure of 5000 psi may produce a 400 lb. thrust. Consequently, some small additional force will suffice in preventing the movements of hydrajetting tool104during operation. Hydrajet anchor tool100may minimize movements of hydrajetting tool104and improve the efficiency of the hydrajetting process.

Equalizing ports116may allow for equalizing flow through hydrajet anchor tool100, which may be useful in cleaning or reversal of flow through hydrajet anchor tool100, or for equalizing below hydrajet anchor tool100. Equalizing ports116may be sized for erosion reduction, or otherwise maximizing flow area without compromising strength. Equalizing ports116may be in an open or closed position when running the tools, depending on the particular conditions, and may generally include openings in housing106. In some embodiments, equalizing ports116may align with openings in mandrel108to permit selective flow therethrough. As illustrated inFIG. 4, equalizing ports116may be aligned with openings in mandrel108or otherwise “opened,” allowing fluid to enter hydrajet anchor tool, flow up toward body121. Body121may then move upward and away from seat124, allowing fluid to flow around body121and out of hydrajet anchor tool100at an upper end. Various configurations for the size and orientation of equalizing ports116may be used, depending on the particular application. For example, in some embodiments, equalizing ports may be radially set. In some embodiments, equalizing ports may be radially set at approximately 60°, 90°, 120°, or 180° from one another.

Jet122may be at a lower end of body121and may be a port, a regulator, a nozzle, a flow limiting orifice, a simple orifice, a fixed choke, an adjustable choke, and/or any other device allowing pressure to be maintained on one side, while allowing restricted flow therethrough. For example, jet122may be a 3/16 jet nozzle. Jet122may have an internal diameter sized to allow a desired rate of sand laden fluid to flow therethrough, and may be configured to be changed with other jets suitable for particular operations, allowing jet122to be optimized for a particular sand plug setting process. Depending on the desired reduction in flow rate, multiple jets may be used in series.

Seat124may be a reduced cross-sectional area suitable for engaging body121. Seat124may be sealed within mandrel108and have an opening to matingly engage body121. Seat124and body121may be configured to seal such that flow through seat124is restricted to flow passing through body121, at least in one direction.

In some embodiments, hydrajet anchor tool100may contain a j-slot (not shown) designed to allow the tool to be operated through reciprocating motion. Thus, anchor114, centralizer112, or both may be set prior to commencing hydrajetting operations. The j-slot may be on mandrel108, which may move with workstring102, and associated lugs may be on a drag spring sleeve (or vice versa).

Hydrajet anchor tool100may be run into wellbore126beneath hydrajetting tool104. During run-in, fluid may be pumped through and around hydrajet anchor tool100or fluid may be bypassed through hydrajet anchor tool100. Once a desired location is reached, hydrajet anchor tool100may be stabilized by setting anchor114and/or centralizer. Setting anchor114may anchor, or otherwise reduce or prevent undesirable rotational and axial movement. Likewise, setting centralizer112may center hydrajet anchor tool100and hydrajetting tool104in wellbore126.

Referring now toFIG. 3, after anchoring and/or centering hydrajet anchor tool100, hydrajetting may commence via introduction of flow through workstring102, into hydrajetting tool104. A first portion of the fluid may flow out of hydrajetting tool104through jets, nozzles, or other orifices107of hydrajetting tool104into the formation to create a cavity in the rock. At the same time, a second portion of the fluid may pass through hydrajetting tool104and into hydrajet anchor tool100connected thereto. As fluid flows through passageway120of hydrajetting tool104, body121may move downward into seat124, such that a restricted amount of fluid may pass through jet122to form a sand plug105(FIG. 1) in a previous zone. Hydrajetting tool104and hydrajet anchor tool100may be moved upward into additional zones, where the process may be repeated. Thus, the various embodiments of the present invention may allow for the performance of an Alpha plug sand setting treatment, while performing hydrajetting operations on the next interval. Likewise, hydrajet anchor tool100may enable pumping into the previous zone to reduce total leakoff while hydrajetting the next interval.

Referring now toFIG. 4, once hydrajetting is complete, mandrel108may be pulled to expose equalizing ports116to passageway120, allowing for reverse circulation. Fluid may be pumped through equalizing ports116and a mule shoe placed at a bottom of hydrajet anchor tool100. Body121may unseat from seat124and move upward, allowing fluid to travel both through and around one-way restrictor device, to ensure sufficient flow rate can be achieved to bring sand to the surface. Thus, reverse circulating may expose a larger flow area and allow for higher flow rates, which may assist in removing any plugged sand at or around jet122. As illustrated, this flow will primarily be around one-way restrictor device, as this path would provide less resistance than through jet122. Thus, the one-way restrictor device may divert flow to jets in hydrajetting tool104when hydrajetting or through larger equalizing ports116when reverse circulating.

The embodiments described herein may be useful to improve the efficiency of various pinpoint stimulation processes. For example, hydrajetting processes may be improved by centralizing and controlling movement, COBRAMAX processes may be improved by applying an Alpha plug technique in vertical, deviated, and horizontal wells, and SURGIFRAC processes may be improved by reducing total leakoff.

In some embodiments, having hydrajetting tool104placed at an optimum distance from the casing/liner/openhole wall for hydrajetting operations is advantageous or even essential. Conventionally, the efficiency of the jetting process may be adversely affected when the optimum standoff is not achieved, leading to greater jetting times and higher differential pressure for compensation. In addition, the designed number of cavities may not be created in the rock, due to increased standoff, and more damage may occur because of increased effect of splash back because of reduced standoff. Hydrajet anchor tool100may thus allow for reduced jetting times, lower differential pressure, and reduced damage.

In some embodiments, hydrajet anchor tool100may help reduce movement of hydrajetting tool104. As described above, movement of hydrajetting tool104caused during hydrajetting operations may generally reduce the performance of the process. Conventionally, longer jetting times may be used to create a cavity in the rock. Movement of hydrajetting tool104during hydrajetting operations may be caused by pipe extension or shrinkage resulting from temperature and/or pressure, or by tremendous turbulence around hydrajetting tool104. The movements caused by temperature and/or pressure may be reduced by adopting effective depth control measures and fluid circulation. However, hydrajet anchor tool100may provide additional reduction in movement of hydrajetting tool104. Thus hydrajet anchor tool100may provide for reduced operating costs and/or otherwise improve the performance of hydrajetting tool104during pinpoint operations.

In other embodiments, hydrajet anchor tool100may be advantageous for horizontal wellbores. Conventionally, primary fluid diversion of previous regions in the COBRAMAX technology may be accomplished by placing sand plugs. While this action may be convenient for vertical wellbores, it may not be as straightforward in horizontal wellbores. Placing these plugs in horizontal wellbores may require a very low flow rate, which may be hard to control using surface pumping equipment. Thus, it is desirable to have a system that can produce low flow rates, yet does not plug the orifice. As indicated above, when using high jetting pressures, orifices may be very small to create a low flow rate, which may make the orifices very susceptible to plugging. Jet122may be used to reduce the flow rate, for example to one barrel per minute (bpm) or lower, without using extra small chokes that would tend to plug when exposed to sand. Depending on the desired reduction in flow rate, multiple jets may be used in series to prevent plugging. Therefore, hydrajet anchor tool100may allow for the placement of competent sand plugs at desired locations. Jet122in accordance with an exemplary embodiment of the present invention may be designed to accept 8 Mesh or even larger particles. Thus, use of hydrajet anchor tool100may allow for a reduced time to set sand plugs and/or otherwise improve the capability for creating sand plugs in COBRAMAX operations, especially for horizontal well applications.

In other exemplary embodiments, the present invention may be used in conjunction with SURGIFRAC operations. As indicated above, SURGIFRAC uses the Bernoulli principle to achieve fluid diversion between fractures. Specifically, once a first fracture is created during the SURGIFRAC operations, hydrajetting tool104is moved to a second location to create a second fracture. The primary flow goes to the fracture while leakoff flow is supplied by the annulus, and this is generally considered a “secondary” flow. However, some of the fluids that are being pumped into the annulus will leakoff into the already existing fracture. In long horizontals, many fractures may be desirable. However, each fracture causes additional leakoff and the annulus flow quickly becomes the “primary” flow. Centralizer112of hydrajet anchor tool100may reduce the amount of leak off fluid flow through the annulus from hydrajetting tool104to the existing fractures. Specifically, centralizer112may restrict the path of the leak of fluid flow, thereby reducing the amount of fluids leaked off. Consequently, hydrajet anchor tool100may reduce the annulus flow requirement while maintaining pore-pressure and limited flow influx to let the fracture slowly close without producing sands back into wellbore126after fluid injection has stopped. Hydrajet anchor tool100may also reduce or eliminate the need to pump harder and harder for each subsequent stage, thus reducing fluid losses and saving expense on fluids and/or otherwise improve SURGIFRAC performance in long horizontals. Finally, hydrajet anchor tool100may be designed to mitigate the effects of internal erosion.

As would be appreciated by those of ordinary skill in the art, with the benefit of this disclosure, the term “pinpoint stimulation” is not limited to a particular dimension. For instance, depending on the zones to be isolated, the area subject to the “pinpoint stimulation” may be a few inches or in the order of tens of feet in size. Moreover, although the present invention is disclosed in the context of “stimulation” processes, as would be appreciated by those of ordinary skill in the art, the apparatuses and methods disclosed herein may be used in conjunction with other operations. For instance, the apparatuses and methods disclosed herein may be used for non-stimulation processes such as cementing; in particular squeeze cementing or other squeeze applications of chemicals, fluids, or foams.

As would be appreciated by those of ordinary skill in the art, although the present invention is described in conjunction with hydrajetting tool104, it may be utilized with any stimulation or other jetting tool where it would be desirable to minimize tool movement and/or fluid leak off (e.g., a port, a valve, a window, and the like). Moreover, as would be appreciated by those of ordinary skill in the art, with the benefit of this disclosure, any references to the term “sand” may include not only quartz sand, but also other proppant agents and granular solids, such as beads, slivers, clays, chemical particulates, gels, and other materials. Further, while a sand plug is disclosed, other barriers may be used to isolate the formation and/or divert flow, including any of a number of isolation fluids and/or materials. Additionally, as would be appreciated by those of ordinary skill in the art, with the benefit of this disclosure, although the present invention is described as using one hydrajet anchor tool, two or more hydrajet anchor tools may be used simultaneously or sequentially in the same application to obtain desired results, without departing from the scope of the present invention.

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 and described 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. 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. The terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.