Patent Application
20170145801
The present invention relates to a downhole stimulation system for stimulating production of fluid from a well. The present invention further relates to a downhole stimulation method for stimulating production of fluid from a well by means of the downhole stimulation system according to the present invention.
One of the last steps in completing a well and bringing it into production is to expand expandable sleeves of annular barriers to isolate a production zone, and then the formation in the production zone is fractured in order to increase reservoir contact. The fracturing operation is performed by opening the frac ports and ejecting fluid out through the ports. However, when doing so, there is a risk of the pressure in the production zone increasing more than the pressure within the annular barriers, which may cause the annular barriers to collapse if the pressure difference becomes too large.
It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved downhole stimulation system decreasing the risk of the annular barrier collapsing while stimulating the well.
The above objects, together with numerous other objects, advantages and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a downhole stimulation system for stimulating production of fluid from a well having a top, comprising:
The proppants may be made of a material having a positive buoyancy in the fluid.
Moreover, the displacement means may be an element having an outer element diameter which is substantially equal to the inner diameter of the well tubular structure.
Said displacement means may be a fluid, such as water.
Also, the expandable sleeve may be a metal sleeve.
The downhole stimulation system as described above may further comprise a third annular barrier arranged closer to the top than the first annular barrier and a fourth annular barrier arranged further away from the top than the second annular barrier, the inflatable device being inflated between the second annular barrier and the fourth annular barrier.
Moreover, the tool may comprise several keys arranged at a distance from each other.
In addition, the profile may be a circumferential groove.
Further, the sliding sleeve may be a self-closing sleeve.
Additionally, the sliding sleeve may comprise a spring for closing the sleeve.
Also, a valve may be arranged in the aperture of at least one of the annular barriers.
Said valve may be a one-way valve.
A diameter of the tool body may be smaller than an inner diameter of the well tubular structure, defining a fluid passage between the tool and the well tubular structure.
Moreover, the tool may comprise an inflation pump for inflating the inflatable device.
Furthermore, the tool may comprise a motor for driving the inflation pump.
In addition, the expandable sleeve may have a fracturing device arranged on the outer face of the expandable sleeve for fracturing the formation when the outer face is pressed against the wall of the borehole.
Also, the sliding sleeve and/or the aperture may comprise an identification tag.
Further, the tool may comprise a detection unit for detecting the sliding sleeve and/or the aperture.
Said detection unit may comprise a tag identification means for detecting the sliding sleeve and/or the aperture.
In addition, the sliding sleeve or annular barrier may comprise an identification tag.
Moreover, the detection unit may be adapted to detect the profile of the sliding sleeve and the aperture of the annular barrier in order to detect the first distance between the profile and the aperture.
Furthermore, the tool may comprise an activation means for activating the inflation pump so that the inflatable device is inflated, and for stopping the inflation pump so that the inflatable device is deflated.
The key of the tool may be arranged at a second distance from the inflatable device of the tool, the second distance being equal to or larger than the first distance.
Also, said second distance may be adjustable.
Additionally, the tool body may comprise a telescopic body arranged between the key and the inflatable device, the telescopic body being adapted to adjust the second distance in relation to the detected first distance.
The downhole stimulation system as described above may further comprise an activation sensor adapted to cause the inflatable device to deflate when a condition in the well changes.
Moreover, the tool may further comprise a detection sensor for detecting a condition of the well and/or the sleeve.
Further, the tool may comprise a communication unit for loading information from a reservoir sensor.
Also, the tool may further comprise a self-propelling means, such as a turbine or a propeller.
The well tubular structure may comprise a plurality of sliding sleeves, each sliding sleeve having an identification tag.
Furthermore, at least one of the annular barriers may have at least one intermediate sleeve between the expandable sleeve and the tubular part.
In addition, the expandable sleeve may comprise an opening.
Moreover, the tool may be wireless and may comprise a power supply.
Additionally, the tool may be connected and powered through a wireline.
The present invention also relates to a downhole stimulation method for stimulating production of fluid from a well by means of the downhole stimulation system according to any of the preceding claims, comprising the steps of:
The downhole stimulation method as described above may further comprise the step of deflating the inflatable device when a predetermined pressure or sequence of pressures is reached.
Moreover, the downhole stimulation method as described above may comprise the following steps:
The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which
All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.
The downhole stimulation system 1 comprises a pump 16 adapted to provide pressurised fluid down the well tubular structure 4 in order to stimulate the well 2, and the pump may also be used for expanding the expandable sleeves 9 of the annular barriers 6, 6A, 6B by letting pressurised fluid in through the aperture 15. The downhole stimulation system 1 further comprises a sliding sleeve 17 having at least one profile 18, and the sliding sleeve 17 is arranged between two annular barriers 6, 6A, 6B and has a closed position and an open position. In the open position, the sliding sleeve 17 allows fluid communication between the inside of the well tubular structure 4 and the production zone 101 through an opening 19 in the well tubular structure 4. The profile 18 of the sliding sleeve 17 is positioned at a first distance Xa from the aperture 15 of the annular space 14.
In addition, the downhole stimulation system 1 comprises a downhole tool 20 for bringing the sliding sleeve 17 from the closed position to the open position. The downhole tool 20 comprises a tool body 21 and an inflatable device 22 adapted to be inflated inside the well tubular structure 4 to divide the inside 5 of the well tubular structure 4 into a first part 5A and a second part 5B. The downhole tool 20 further comprises at least one key 23 engaging the profile 18 in the sliding sleeve 17, so that when the inflatable device 22 has been inflated and the first part of the well tubular structure 4 has been pressurised, the downhole tool is moved downstream and the keys 23 of the downhole tool drag in the profile, forcing the sliding sleeve 17 from the closed position to the open position. The inflatable device 22 is arranged downstream of the aperture 15 of the second annular barrier 6, 6B so that the annular space 14 of the second annular barrier is in fluid communication with the first part 5A of the well tubular structure 4 when the inflatable device 22 is inflated. In this way, the pressurised fluid jetted out through the opening 19 in the well tubular structure 4 is also able to flow from the inside 5 of the well tubular structure in through the aperture 15 of the second annular barrier 6, 6B and into the annular space 14 to equalise the pressure between the production zone 101 and the annular space of the second annular barrier 6, 6B. When fracturing the formation in order to gain more reservoir contact, pressurised fluid is jetted out through such an opening 19 in the well tubular structure 4. However, such an increase in the pressure in the production zone 101 may compromise the isolation properties of the second annular barrier 6, 6B if the inflatable device 22 is not located downstream of the aperture 15 and thus further away from the top of the well 2 than the aperture.
In order to stimulate a well 2, the sliding sleeve 17, through which the fracturing is to occur, is detected, and then the keys 23 of the tool 20 are projected to engage the profile 18 of the sliding sleeve 17. Shortly thereafter or simultaneously, the inflatable device 22 is inflated, and then the inside 5 of the well tubular structure 4 is pressurised, whereby the pressurised fluid in the well tubular structure applies pressure onto the inflatable device 22, moving the downhole tool 20 away from the top of the well 2, sliding the sleeve 17 from a closed position to an open position and letting pressurised fluid from the inside 5 of the well tubular structure 4 in through the aperture 15 of the second annular barrier 6, 6B to equalise the pressure between the production zone 101 and the annular space 14 of the second annular barrier. Subsequently, the inflatable device 22 is deflated when a predetermined pressure or sequence of pressures is/are reached.
The profile 18 of the sliding sleeve 17 has circumferential grooves matching the profile of the keys 23, so that the keys are able to get a firm grip on the sliding sleeve. As can be seen in
When the sliding sleeve 17 has been moved to uncover the opening 19 in the well tubular structure 4, pressurised fluid comprising proppants 25 is pumped down the well tubular structure in order to fracture the formation and stimulate the well, as shown in
Furthermore, the proppants 25 are made of a material having a positive buoyancy in the fluid, and the proppants 25 therefore stay at the top of the well so that only the pressurised fluid is ejected through the opening 19 when the formation is fractured, as shown in
As shown in
In
In
A valve 28 may be arranged in the aperture 15 of the annular barrier 6, as shown in
In
In
The downhole tool 20 further comprises a detection unit 37 for detecting the sliding sleeve. The detection unit 37 comprises a tag identification means 38 for detecting the sliding sleeve. The tool 20 further comprises an activation means 39 for activating the inflatable device 22 to both inflate and deflate when e.g. the fracturing operation has ended. The activation means 39 comprises an activation sensor 40 adapted to cause the inflatable device 22 to deflate when a condition in the well changes, such as when a predetermined pressure is reached.
The downhole tool 20 further comprises a detection sensor 27 for detecting a condition of the well and/or the sliding sleeve, so that the operation is terminated if the conditions vary too much from the expected conditions. The tool also comprises a communication unit 47 for loading information from a reservoir sensor if requested.
In order to be able to propel itself up again, the downhole tool 20 comprises a self-propelling means 48, such as a turbine or a propeller. So when descending, a battery in the tool is charged to be ready for use when the tool emerges at the top of the well again. The tool further comprises a fishing neck 49, making the tool easily retrievable from the well.
In
Some of the annular barriers 6 may have at least one intermediate sleeve 55 between the expandable sleeve 9 and the tubular metal part 7, as shown in
In
In
When the stimulation operation through one sliding sleeve has ended, the downhole tool disengages the profile, causing the sliding sleeve to move into the closed position, and the tool moves further away from the top of the well. Then a second sliding sleeve is detected, the keys 23 of the tool are projected to engage the profile of the second sliding sleeve, and the inflatable device is inflated. Then, the inside of the well tubular structure is pressurised, moving the tool away from the top of the well and sliding the second sliding sleeve from a closed position to an open position and letting pressurised fluid from the inside of the well tubular structure in through the aperture of the adjacent annular barrier, e.g. a fourth annular barrier, equalising the pressure between the production zone and the annular space of the fourth annular barrier.
The proppants may comprise glass bubbles, cenospheres, microspheres and/or other similar materials having a structure which is adequate for functioning as a proppant while remaining generally buoyant in a fracturing fluid. The proppant may comprise a composite material, such as a syntactic foam, a porous material, such as an aerogel, a resin-coated aerogel, a resin-coated pumice, a ceramic foam or other type of foamed material, a crystalline material, such as zircon or other similar crystalline materials, or combinations thereof. As used herein, a “porous material” can include particles having cylindrical and/or tubular structures (e.g. having an axial bore) through which fluid can pass. The porous material may be permeable to reservoir fluids, such as a filter material that permits passage of the fluid into and through the proppants, while the structure of the material enables the proppant to keep the fracture from decreasing. The proppants may further comprise, such as in the form of an outermost layer, a friction-reducing additive to facilitate transport of the proppants.
By fluid or well fluid is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is meant any kind of gas composition present in a well, completion, or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements or substances than gas, oil, and/or water, respectively.
By a well tubular structure, a casing or a production casing is meant any kind of pipe, tubing, tubular, liner, string etc. used downhole in relation to oil or natural gas production.
In the event that the tool is not submergible all the way into the casing, a downhole tractor can be used to push the tool all the way into position in the well. The downhole tractor may have projectable arms having wheels, wherein the wheels contact the inner surface of the casing for propelling the tractor and the tool forward in the casing. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor®.
Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14173461.6 | Jun 2014 | EP | regional |
| 15160034.3 | Mar 2015 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/063940 | 6/22/2015 | WO | 00 |
