WO2015169676A2

WO2015169676A2 - System, well operation tool and method of well operation

Info

Publication number: WO2015169676A2
Application number: PCT/EP2015/059443
Authority: WO
Inventors: Jarid SHAWD; Kristian Brekke
Original assignee: Interwell As
Priority date: 2014-05-05
Filing date: 2015-04-30
Publication date: 2015-11-12
Also published as: NO20140569A1; NO341120B1; WO2015169676A3

Abstract

The invention relates to system, a well operation tool and a method of fracturing a well. The system (1) comprising an inner sleeve (105) having a first port (109) and an outer sleeve (101) having a second port (108), the first port (109) and the second port (108) in an operational position being adapted to overlap forming a through-going opening extending through the first port (109) and the second port (108) from an inside of the inner sleeve (105) to the outside of the outer sleeve (105), wherein the system in a first position, is adapted to receive a well operation tool (104), in a second position, is adapted for fracturing a well (W) through the through-going opening, in a third position, is adapted to close off the through-going opening, and allowing said well operation tool (104) to be released to a lower position in the well (W).

Description

System, well operation tool and method of well operation

The invention relates to a fracturing system, a well operation tool and method for acquiring oil and gas.

Background of the invention

The demand for natural oil and gas has significantly grown over the years making low productivity oil and gas reservoirs economically feasible, where hydraulic fracturing plays an important part in these energy productions throughout the world. For several decades different technology has been used to enhance methods for producing resources from oil and gas wells. Long horizontal wellbores with multiple fractures is one commonly used process to enhance extraction of oil and gas from wells. This process starts after a well has been drilled and the completion has been installed in the wellbore. Multi stage fracturing is a method that involves pumping large amounts of pressurized water or gel, a proppant and/or other chemicals into the wellbore to create discrete multiple fractures into the reservoir along the wellbore.

One of the technologically advanced methods being used today is simultaneous proppant fracturing of many fractures in one pumping operation. This method involves usage of proppant to prevent fractures from closing. However, this practice can usually cause uneven distribution of proppant between the fractures, which will reduce the efficiency of the fracture system. As a result, this practice can also cause fractures to propagate in areas that are out of the target reservoir. Thus, such method can be inefficient and unsafe. In the description, different wording for fracturing having the same meaning, has been used, such as fracking and frack.

Additionally, proppant fracturing usually involves multiple steps and requires several tools in order to be performed successfully. Such practice that will allow even distribution of proppant between fractures highly depends on setting, plugs between the fracture stages or using frack balls of increasing sizes. In these methods, plugs are either set after each fracture has been perforated and pumped, or frack balls are dropped from the surface to successively open fracturing valves placed along the well. For each stage, balls of different diameters (i.e. starting with the smallest diameter balls) are dropped into the well corresponding to a specific fracturing valve's seat. At a point in the well, the ball will no longer pass through due to a decrease in well diameter. Once the ball is in place, fracking can take place. After fracking, the plugs must be drilled out and the balls must be recovered. With each fracturing stage while setting plugs, much time and energy is expended in tripping out of the hole between the stages and drilling out the plugs. Moreover, land-based rigs are usually rented per day basis, and so any delays can be quite expensive. Also, only about 12-15 different fracture stages is possible with the ball method before a restriction in flow area due to small ball diameter makes fracturing difficult due to large pressure losses.

A fracking system avoiding the use of multiple ball seats of different sizes is disclosed in US 2013/0248189 Al .

Based on the prior art, there is still a need for an improved system and method for fracturing oil and gas wells.

An objective of the present invention is therefore to provide an improved fracturing system, and associated method of use thereof, eliminating the need for ball seats and balls of different sizes.

Another objective of the present invention is to render possible fracturing from the heel of the well to the toe of the well.

Summary of the invention

The invention is set forth in the independent claims, while the dependent claims describe other characteristics of the invention.

The claimed system provides a plurality of advantages in addition to the ones stated above, including:

• Unlimited horizontal well length du to that the system is intervention-less,

• Unlimiting number of fracturing stages due to the fact that one fracture per stage is allowed (also known as 'pin point fracturing'). This provides control of individual fracture area and flexibility with respect to fracture spacing and well length. The proposed system and method has no technical limitation to the individual fractures. Since complexity and cost is moved from the fracturing sleeve to the fracturing tool, the cost per fracturing stage is also significantly reduced. This is unlike to the known prior art methods 'Plug and Perforate (P&P)' and 'Multi size ball drop methods',

• Less fracture pinching will be experienced compared to plug and perforate as the fractures are not over displaced from the process of pumping down bridge plugs. Compared to the 'Plug and perforate' method and traditional fracturing sleeve systems, the proposed system's proppant flow back control feature provides undamaged proppant concentration in the fracture close to the wellbore, which reduces risk of fracture pinching,

• Maximum fracturing capacity is obtained by the full bore design compared to multi size ball drop systems that will experience reduced fracture areas being created close to the toe part of the well, • Re-fracturing is possible by the use of coiled tubing or pump down wire line tools to isolate and manually open/close fracturing sleeves,

• Contribution from wellbore between fractures can be important in naturally

fractured reservoirs. This is made possible by specially designed one way annular fracturing packers,

• Intervention less fracturing frees up coiled tubing/ wire line equipment and personnel. However, it is good practice to have a coiled tubing unit standing by for unplanned events,

• Full bore completion, one of the main characteristics of the proposed system provides, if necessary, the possibility of intervention both during and after fracturing,

• One trip installation and operation of the fracturing system frees up the rig for drilling and completion of other wells while the well is being fractured and put on production. Especially in offshore environments with high rig cost, this feature has great cost savings potential,

• Screen out mitigation is included as a redundancy. If the fracture initiation pressure cannot be overcome, or the bottom hole pressure is getting close to the limit, the fracturing tool will end the current fracturing stage and proceed to the next. If screen out still occurs, it will be feasible to wash out the wellbore with coiled tubing and manually progress the fracturing tool to the next sleeve,

• Sand and proppant flow back control is provided from separating the

fracturing and production ports. After a fracturing stage is completed, proppant is trapped behind a closed fracturing port, and the production port is equipped with sand control to contain proppant in the annulus. This feature allows the system to be applied in scenarios such as subsea developments where production of solids cannot be accepted. For less critical on land production, it will reduce the need for resin coated proppant and time needed for cleanup. Currently available fracturing systems use the same ports/perforations for fracturing and production, and can, therefore, not prevent proppant from flowing back into the wellbore during fracturing and production,

• Even clean-up and production can be achieved by using ICD technology made feasible by separation of fracturing and production ports.

The invention relates to system, a well operation tool and a method of fracturing a well. The system for well operation comprises an inner sleeve having a first port and an outer sleeve having a second port, the first port and the second port in an operational position being adapted to overlap forming a through-going opening extending through the first port and the second port from an inside of the inner sleeve to the outside of the outer sleeve, wherein the system

- in a first position, is adapted to receive a well operation tool,

- in a second position, is adapted for fracturing a well through the through-going opening,

- in a third position, is adapted to close off the through-going opening, and allowing said well operation tool to be released to a lower position in the well.

According to an aspect, in the second position of the system, the fracturing may occur from an inside of the well operation tool through the through-going opening.

The well operation tool may be operated by using at least a first and a second ball having the same diameter, and be adapted to open and close the through-going opening by the manipulation from the at least first and second balls and/or different pressures. The well operation tool functions as a 'travelling ball(s) seat(s)', in a way that after completing one stage of fracturing, the same tool is released to another fracturing position in the well, i.e. to perform a next fracturing stage.

The system may further comprise at least one production port, which at least one production port may be different from the through-going opening. The production port may be a standalone modular unit with sand screen/slotted liner attached and may include a one-time, one way valve to prevent back flow into the screen and formation during the fracturing process.

The production port can be equipped with proppant/sand control and inflow control, if needed. Further, the production port may have a specialized check valve that prevents leakage during fracturing, but allows "bullheading" after fracturing is completed, i.e. forcibly pumping fluids into a formation.

In an aspect, the well operation tool may comprise a pipe having a first end and a second end, and having multiple through-bores radially spaced along a longitudinal section of the pipe, wherein the first and second end comprises a first and second ball seats adapted for receiving a first and second ball.

In a first position of the system, a first ball may be dropped and register into the first ball seat in the well operation tool.

Pressure increase may cause that the first ball seat releases the first ball through the well operation tool, i.e. the fracturing tool, to the second ball seat. Pressure increases as the first ball seals off all circulation through tubing string. Further, increased pump pressure may cause the inner sleeve to move relative the outer sleeve, e.g. by shearing a first set of shear screws, to the open position (against spring force from spring), i.e. the second position of the system, such that the first port in the inner sleeve overlap with the second port in the outer sleeve forming the through-going opening. In this specific embodiment of the second position of the system, the multiple through-bores in the well operation tool also overlap with the through-going opening. Pressure drops as tubing string is now open to formation through the through-going opening. Signal-2 to operator that the inner and outer sleeves have opened properly and sequence should continue. Fracturing is performed at flow rate and duration as required.

The second ball may be dropped and seats into the first ball seat to stop fracturing and shift the inner sleeve to release the well operation tool. The first ball is still in the second ball seat. Pressure increases as the through-going opening (i.e. the fracture port) has been blocked by relative movement of the inner and outer sleeves. Signal-3 to operator that fracturing has been completed, and sequence should continue. The pump pressure may then be increased above pressure open the second ball seat, and the first ball and well operation tool are released. The inner sleeve may shift back to a third position of the system, where the through-going opening (i.e. fracturing port) is closed automatically by a spring. The first and second positions of the system may be the same, i.e. in order to close the through-going opening, the first port in the inner sleeve is not overlapping with the second port in the outer sleeve. This means that the functionality of the system in the first position and third position may or may not be the same.

In an aspect of the well operation tool, the first and second ball seats comprise pre- tensioned fingers adapted to release the balls when subject to a predetermined pressure force.

The invention relates to a method for fracturing a well by the use of a system as described above, the method comprising the steps of dropping a well operation tool having multiple through-bores radially spaced along a longitudinal direction into the well, and allowing the well operation tool to enter said first position,

- dropping a first ball having a first diameter into the well, allowing the first ball to be received by a first ball seat, in a first end of the well operation tool,

- increasing the pressure in the well, allowing the first ball to slip out of the first ball seat and enter a second ball seat at the opposite axial end of the well operation tool, such that the increased pressure moves the well operation tool to move said inner and outer sleeves such that the first and second port overlap forming the through-going opening, and

- fracturing the well through said through-going opening.

In an aspect of the method, the method further comprising the step of, after fracturing the well, dropping a second ball having the same diameter as the first ball, allowing the second ball to be received by the first ball seat,

- increasing the pressure in the well above a threshold value, such that the well operation tool is moved out of the inner sleeve releasing the first ball and thus the well operation tool to a position lower in the well.

These and other characteristics of the invention will be clear from the following description of a preferential form of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein:

Brief description of the drawings

Figure 1 A shows a typical multi-fractured horizontal well;

Figure IB discloses an overview of main elements of a fracturing assembly in which the present invention may fully constitute or form part of; Figure 1C is an axial cross section along the fracturing assembly of Fig. IB;

Figure ID showing details of the well operation tool;

Figures 2-8 disclose one embodiment of a sequence of operation of the fracturing system according to the invention;

Detailed description of an embodiment of the invention Fig. 1A shows a typical multi-fractured horizontal well W. The individual fractures are denoted F and extends substantially perpendicular to the horizontal well W. The heel H of the well is shown as the curved section on the right hand side in the Figure, while the toe T is in the end of the well on the left hand side in the Figure. The number of individual fractures F may vary, but in the specific figure there is disclosed 32 individual fractures F.

Fig. IB illustrates an example of the main elements of a fracturing assembly 1 , while Figure 1C is an axial cross section in the longitudinal direction of the fracturing assembly, in which the system 1 according to the present invention may fully constitute or form part of. The arrows S and T in the Figures, show the direction of the system 1 , towards the surface S is to the left in the Figures, while towards the end of the well, i.e. the toe T of the well, is to the right in the Figures. The fracturing assembly, i.e. the system 1 , comprises an outer fracturing sleeve 101 and an inner fracturing sleeve 105, first and second fracturing packers 102A, 102 B, production port 103 and well operation tool 104, also named fracturing tool 104. The outer and inner sleeves 101 , 105 are naturally closed, e.g. by spring force of springs 106, 107 in the first and/or second spring 106, 107, and is opened by the well operation tool 104 (cf. Figure 1C), during fracturing. In Figure IB the second port 108 in the outer sleeve 101 is disclosed. In the natural position, this second port 108 is 'closed', in that it is prevented from being in fluid communication with a first port (not shown in this specific Figure) in the inner sleeve 105. The first and second fracturing packers 102A, 102B are arranged in opposite axial ends of the system 1 and provide the possibility of pin-point fracturing and production from the wellbore, by isolating dedicated zones during both fracturing operations and/ or production operations.

The production port 103 is in this embodiment a standalone modular unit with sand screen/slotted liner attached and may include a one-time, one way valve to prevent back flow into the screen and formation during the fracturing process. The production port 103 can be equipped with proppant/sand control and inflow control, if needed. Further, the production port 103 may have a specialized check valve that prevents leakage during fracturing, but allows "bullheading" after fracturing is completed, i.e. forcibly pumping fluids into a formation. The well operation tool 104 is triggered by ball(s) dropped from the surface into the well and appropriate ball seats, which balls operates the inner and outer sleeves 101 , 105 and isolates the fracture point from the rest of the wellbore.

Figure ID shows details of the well operation tool 104. The well operation tool 104 is a hollow pipe having a first axial end and a second axial end. There is arranged a first ball seat 1 12 in the first end and a second ball seat 1 13 in the second end. The first ball seat 1 12 may be formed as a cup made up of e.g. inclined fingers 1 12', 1 12", 1 12" for easy receptacle of the at least first and second balls 1 10, 1 1 1. This is apparent from the figure. Similarly, the second ball seat 1 13 comprises a plurality of fingers 1 13 ', 1 13 ", 1 13 " ' bending inwardly towards the centre axis of the well operation tool 104. Both ball seats 1 12, 1 13 are adapted to flex when exposed to a pressure from the surface exceeding a predetermined threshold value, such that any ball arranged in said first or second ball seats 1 12, 1 13 can pass through the ball seats 1 12, 1 13.

The well operation tool 104 comprises multiple through bores 1 14 extending from an inside 1 15 of the well operation tool 104, to a radial outside of the well operation tool.

An embodiment of a system 1 , e.g. a fracturing system 1 , according to the invention is shown in fig. 2. The system provides for the opportunity of fracturing from the heel H of the well to the toe T in the well in comparison with the conventional toe- to-heel fracturing systems/methods. The system 1 comprises the following main components; an inner and an outer fracturing sleeve 105, 101 and a well operation tool 104. The inner sleeve 105 comprises a first port 109 and the outer sleeve 101 comprises a second port 108, respectively. During fracturing, the first and second ports 109, 108 form a through-going opening, through which through-going opening fluid, and solids such as proppants etc., may flow. The inner sleeve 105 is arranged on the radial inside of the outer sleeve 101 and may be operated in at least two different positions, including a first position in which the first and second ports 109, 108 are not overlapping, and a second position in which the first and second ports 109, 108 overlap such that fracturing may be performed from the inside of the inner sleeve 105, 101 into the well W formation arranged on the radial outside of the outer sleeve 101. The following sequence illustrates with reference to the Figures 2-8, one fully- functioning embodiment of the operation of the fracturing system according to the invention:

With reference to Fig. 2: 1.) Liner is installed with the first and second ports 109, 108 closed and with open liner ID to facilitate circulation through toe valve during installation into open-hole wellbore.

2.) Toe valve drop ball is released to seal tubing string for pressure test and first fracturing packer 102, e.g. an annular isolation packer, is set. 3.) Second fracturing packer 102B, e.g. liner hanger packer, is set.

4. ) Hydro/mechanical packers are set with pressure.

5. Liner pressure integrity test performed.

6. ) Toe valve shear screws fail and initiate circulation for fracturing process.

7. ) The well operation tool 104, i.e elastomer seat fracturing tool, has been previously installed in the inner sleeve 105, i.e. the first fracturing sleeve (closest to the heel H), and is ready for fracturing process to begin. The first ball seat 1 12, i.e. the upper ball seat, is normally closed and second ball seat 1 13, i.e. the lower ball seat, is normally open.

8. ) Start pumping gel/water. 9.) In a first position of the system, a first ball 1 10 (e.g. a fracturing ball) is dropped and registers into the first ball seat 1 12 in the well operation tool 104.

With reference to Fig. 3 :

10.) Pressure increase causes the fingers 1 12', 1 12", 1 12" ' in the first ball seat 1 12 to expand and the first ball 1 10 is released through the well operation tool 104, i.e. the fracturing tool, to the second ball seat 1 13. Pressure increases as the first ball

1 10 seals off all circulation through tubing string (signal- 1 to operator that wellbore is sealed properly at fracturing stage- 1 and sequence should continue).

With reference to Fig. 4: 1 1. ) Increased pump pressure causes a first set of shear screws 1 17 to fail and shift inner sleeve 105 in relation to the outer sleeve 101 to the open position (against spring force from spring 106), i.e. the second position of the system 1 , such that the first port 109 in the inner sleeve 105 overlap with the second port 108 in the outer sleeve 101 forming the through-going opening. In this specific embodiment of the second position of the system 1 , the multiple through-bores 1 14 in the well operation tool 104 also overlap with the through-going opening. Pressure drops as tubing string is now open to formation through the through-going opening. Signal-2 to operator that the inner and outer sleeves 105, 101 have opened properly and sequence should continue.

With reference to Fig. 5 :

12. ) Switch to proppant.

13. ) Fracturing is performed at flow rate and duration as required. 14.) Switch to gel/water for flush of fracture and pad for next stage.

15. ) The second ball 1 1 1 is dropped and seats into the first ball seat 1 12 to stop fracturing and shift the inner sleeve 105 to release the well operation tool 104. The first ball 1 10 is still in the second ball seat 1 13. Pressure increases as the through- going opening (i.e. the fracture port) has been blocked by relative movement of the inner and outer sleeves 101 , 105. Signal-3 to operator that fracturing has been completed, and sequence should continue.

With reference to Fig. 6:

16. ) Pump pressure is increased above pressure to fail second set of shear screws 1 16 in the system 1 which causes fingers 1 13 ', 1 13 ", 1 13 " ' of the second ball seat

1 13 to open, and the first ball 1 10 and well operation tool 104 are released.

With reference to Fig. 7:

17. ) The inner sleeve 105 shifts back to a third position of the system 1 , where the through-going opening (i.e. fracturing port) is closed automatically by a spring 106,

107. In this specific embodiment, the first position and the third position of the system may be the same, i.e. in order to close the through-going opening, the first port 109 in the inner sleeve 105 is not overlapping with the second port 108 in the outer sleeve 101. This means that the functionality of the system 1 in the first position and third position may or may not be the same.

18.) The well operation tool 104 flows to the next fracturing stage, i.e. an identical stage and system 1 as the system 1 according to the present invention, with the second ball seat 1 13 open to facilitate release of the first ball 1 10 to the toe T of the well W. The first ball seat 1 12 remains closed to hold the second ball 1 1 1 in place for pumping down the well operation tool 104 to register into a next stage system 1 , i.e. a second identical fracturing stage. 19.) After the well operation tool 104 has registered into the second fracturing stage-2, stages 9-18 are repeated using new balls but the same well operation tool 104 for the fracturing of all of the stages. This process is repeated until all fracturing stages have been completed.

20. ) At the very last stage, when all of the fracturing stages are completed, the well operation tool 104 is pumped down to the toe T of the well W, trapping all the balls

1 10, 1 1 1 and sealing off toe valve.

21. ) Start producing well through the production ports 103 and, alternatively additionally through the through-going opening. The invented system 1 gives the opportunity of fracturing one single fracture F

(Figure 1 A) at the time, increasing the possibility of creating even fractures F along the horizontal portion of the well W, by the use of same-sized diameter balls.

The invention has been described in non-limiting embodiments. It is clear that the person skilled in the art may make a number of alterations and modifications to the described embodiments without diverging from the scope of the invention as defined in the attached claims.

Claims

1. System (1) for well operation, comprising an inner sleeve (105) having a first port (109) and an outer sleeve (101) having a second port (108), the first port (109) and the second port (108) in an operational position being adapted to overlap forming a through-going opening extending through the first port (109) and the second port (108) from an inside of the inner sleeve (105) to the outside of the outer sleeve (105), wherein the system

- in a first position, is adapted to receive a well operation tool (104), - in a second position, is adapted for fracturing a well (W) through the through- going opening from an inside of the well operation tool (104) through the through- going opening, the through-going opening being formed by movement of the inner sleeve (105) relative the outer sleeve (101),

- in a third position, is adapted to close off the through-going opening by relative movement of the inner and outer sleeves (105, 101), and allowing said well operation tool (104) to be released to a lower position in the well (W).

2. System according to claim 1 , wherein the well operation tool (104) is operated by using at least a first and a second ball (1 10, 1 1 1) having the same diameter, and is adapted to open and close the through-going opening by the manipulation from the at least first and second balls (1 10, 1 1 1) and/or different pressures.

3. System (1) according to any of the preceding clams, wherein the system (1) further comprises at least one production port (103), which at least one production (103) port is different from the through-going opening.

4. A well operation tool (104) for a system (1) according to any of the preceding claims, the well operation tool (104) comprising a pipe having a first end and a second end, and having multiple through-bores (1 14) radially spaced along a longitudinal section of the pipe, wherein the first and second end comprises a first and second ball seats (1 12, 1 13) adapted for receiving a first and second ball (1 10, 1 1 1).

5. A well operation tool (104) according to claim 4, wherein the first and second ball seats (1 12, 1 13) comprises pre-tensioned fingers (1 12', 1 12", 1 13) adapted to release the balls when subject to a predetermined pressure force.

6. A method for fracturing a well (W) by the use of a system (1) for well operation according to any of the preceding claims 1-3, the method comprising the steps of dropping a well operation tool (104) having multiple through-bores (1 14) radially spaced along a longitudinal direction into the well (W), and allowing the well operation tool (104) to enter said first position,

- dropping a first ball (1 10) having a first diameter into the well (W), allowing the first ball (1 10) to be received by a first ball seat (1 12), in a first end of the well operation tool (104),

- increasing the pressure in the well (W), allowing the first ball (1 10) to slip out of the first ball seat (1 12) and enter a second ball seat (1 13) at the opposite axial end of the well operation tool (104), such that the increased pressure moves the well operation tool (104) to move said inner and outer sleeves (105, 101) such that the first and second port (109, 108) overlap forming the through-going opening, and

- fracturing the well (W) through said through-going opening.

7. Method according to claim 6, further comprising the step of, after fracturing the well (W), dropping a second ball (1 1 1) having the same diameter as the first ball (1 10), allowing the second ball (1 1 1) to be received by the first ball seat (1 12), - increasing the pressure in the well (W) above a threshold value, such that the well operation tool (104) is moved out of the inner sleeve (105) releasing the first ball (1 10) and thus the well operation tool (104) to a position lower in the well (W).