Double-fluid acid fracturing method for carbonate rock open hole horizontal well

Abstract

The invention discloses a double-fluid acid fracturing method for a carbonate rock open hole horizontal well, and relates to the technical field of oil and gas field development. Comprising the steps that a continuous oil pipe connected with a spray gun is tripped into a first acid fracturing point position, after temporary plugging solid acid mixed liquid is injected from an open hole well wall annulus, acidizing liquid is injected from the continuous oil pipe to form double-channel double-liquid injection, acid fracturing is completed, the steps are repeated till acid fracturing of the last but one point position is completed, and the acid fracturing process is completed. The spray gun is aligned to the last point position of acid fracturing, double-channel double-liquid injection is conducted, when one annulus volume of the solution added into the open hole well wall annulus remains, only solid acid is added into the solution, finally, displacement liquid is injected to completely displace the solution in the coiled tubing and the annulus, the well is closed for a period of time, and normal blowout is completed after the acid liquid completes the reaction; according to the method, the effects of deep acid fracturing and acidification are finally achieved, the acid fracturing effect is improved, the economic benefits are improved, the applicability of the acid fracturing technology to different well completion modes is enhanced, and the method is beneficial to application and popularization in open hole wells and super-long horizontal wells.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a double-fluid acid fracturing method for carbonate open-hole horizontal wells. Background Art

[0002] Acid fracturing technology is an efficient means of carbonate reservoir transformation. After construction, the permeability of the reservoir is effectively changed, ultimately achieving increased production and improved mining efficiency. Acid fracturing technology is most commonly used in casing perforation completion, and staged fracturing is performed by inserting a packer. There is also a technology of acid fracturing through hydraulic jet fracturing.

[0003] There are several disadvantages of acid fracturing technology that requires packers: First, acid fracturing after casing perforation completion increases the cost compared with direct acid fracturing of open hole wells; second, when casing cementing and perforating, the residues produced by the explosion of the perforating bullet will form a compaction zone at the front end of the perforation hole, affecting the production effect; third, the acid reacts with the formation quickly. When entering the deep fracture, the fresh acid has become residual acid and cannot effectively acidify the formation to form fractures with high conductivity; fourth, the acid is lost and enters the reservoir, causing pollution, which affects the acid fracturing effect to a certain extent; fifth, the applicability of packers to ultra-long horizontal wells and open hole wells is low, and the number of times the mechanical packer is used to seal and release is limited. It is less suitable for ultra-long horizontal wells that require multiple stages of acid fracturing. At the same time, due to the influence of gravel, organic sediments or irregularities in the open hole, the sealing effect of the packer cannot be guaranteed, and the use of multiple seals in open hole wells is also reduced.

[0004] With the existing hydraulic jet fracturing acidizing technology, the single acid fluid injected through the annulus and tubing reacts quickly with the open hole well wall, easily causing well wall collapse. At the same time, the high reaction rate of the acidizing fluid causes the acid-rock reaction distance to be short, and the transformation effect near the deep cracks cannot be guaranteed. Summary of the invention

[0005] The present invention aims to solve the technical problems that the existing acid fracturing methods have low applicability of using packers, acid loss entering the reservoir to cause damage, and the short action distance of the acid, which cannot ensure the acid fracturing effect. The present invention aims to provide a dual-liquid acid fracturing method for carbonate open-hole horizontal wells, ultimately achieving the effects of deep acid fracturing and acidizing, improving the acid fracturing effect, improving the economic benefits, and enhancing the applicability of the acid fracturing technology to different completion methods, which is beneficial to the promotion and use in open-hole wells and ultra-long horizontal wells.

[0006] The present invention is achieved through the following technical solutions:

[0007] A dual-liquid acid fracturing method for carbonate open hole horizontal wells comprises the following steps:

[0008] S1. Lower the coiled tubing with a spray gun at the bottom to the first point in the open hole horizontal well that needs acid fracturing;

[0009] S2. inject temporary plugging agent liquid A from the annulus of the open hole wall, and then slowly inject temporary plugging solid acid mixed liquid B to squeeze the temporary plugging agent in the temporary plugging agent liquid A into the horizontal open hole section to form a temporary plugging layer;

[0010] S3. After the temporary plugging layer is formed, the temporary plugging solid acid mixture B is continuously injected into the annulus of the open hole wall, and the acidizing liquid C is injected from the coiled tubing to form a dual-channel dual-liquid injection. The acidizing liquid C is sprayed into the reservoir through the spray gun to form holes and cracks. At the same time, the temporary plugging solid acid mixture B is sucked into the cracks by the acidizing liquid C to form liquid replenishment, and finally the acid fracturing at the first point is completed;

[0011] S4. Repeat step S3 until the acid fracturing of the second to last point of the open hole horizontal section requiring acid fracturing is completed;

[0012] S5. Lift the coiled tubing and drag the spray gun to the last point of the open hole horizontal section that needs acid fracturing. Inject acidizing liquid C from the coiled tubing and temporarily plugging solid acid mixture B from the open hole wellbore annulus at the same time. When the remaining volume of the solution added to the open hole wellbore annulus is equal to the sum of the annular volumes of the vertical well section, the well deviation section, and the remaining annular section from the injection point to the bottom of the horizontal section, no more temporary plugging agent is added to the temporary plugging solid acid mixture B;

[0013] S7. After the last point requiring acid fracturing is completed, the displacement fluid is injected into the annulus of the open hole wall and the coiled tubing to completely displace the acidizing fluid inside the coiled tubing and the temporary plugging agent solution in the annulus of the casing;

[0014] S8. Shut down the well for a period of time, wait for the acid to react with the reservoir and the temporary plugging agent to dissolve, and then release the well normally to complete the double-liquid acid fracturing.

[0015] Furthermore, both the temporary plugging agent liquid A and the temporary plugging solid acid mixed liquid B contain temporary plugging agents, and the temporary plugging agent has a dissolution rate of more than 95% under formation temperature conditions, and a degradation time adjustable from 4 to 360 hours, and releases reservoirs in open hole sections and fractures after degradation.

[0016] Furthermore, the temporary plugging agent liquid A is prepared by dissolving a temporary plugging agent 1 in water, wherein the temporary plugging agent 1 is a composite nano material temporary plugging agent, and the mass concentration of the temporary plugging agent 1 is 1% to 15%, preferably, the mass concentration of the temporary plugging agent 1 is 5% to 10%.

[0017] Furthermore, the injection volume of the temporary plugging agent liquid A is two-thirds of the annulus volume.

[0018] Furthermore, the temporary plugging solid acid mixed solution B is formed by dissolving the temporary plugging agent 2 and the solid acid in water, the mass concentration of the temporary plugging agent 2 is 1% to 15%, preferably 5% to 10%, and the mass concentration of the solid acid is 15% to 30%, preferably 20% to 25%.

[0019] Furthermore, the temporary blocking agent 2 is a temporary blocking ball.

[0020] Furthermore, the solid acid is a mixture of hydroxylamine hydrochloride, betaine hydrochloride, ammonium fluoroborate and ammonium fluoride in a mass ratio of (5-8):(1-3):1:1.

[0021] Furthermore, the solid acid is a mixture of hydroxylamine hydrochloride, betaine hydrochloride, ammonium fluoroborate and ammonium fluoride in a mass ratio of 6:2:1:1.

[0022] Furthermore, the acidifying liquid C is any one or more of gelling acid, thickening acid and emulsifying acid.

[0023] Furthermore, in step S3, the velocity Vt of the acidizing fluid C in the coiled tubing is greater than the velocity Va of the temporarily plugging solid acid mixture B in the annulus of the open hole wall, so as to ensure that when the open hole section is opened by high-pressure perforation of the coiled tubing acid fluid, the temporarily plugging solid acid mixture B can enter the fracture according to the Bernoulli principle.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. Before acid fracturing, the present invention injects a temporary plugging agent into the horizontal open hole section to form a temporary plugging layer so that the acid does not leak, providing a guarantee for continuous liquid supply, and protecting the open hole section from pollution. During acid fracturing, the continuous oil pipe injects acidizing liquid, and the open hole wall annulus injects a temporary plugging solid acid mixed liquid. The acidizing liquid carries the temporary plugging solid acid mixed liquid into the crack according to the Bernoulli principle, and the temporary plugging agent enters the crack to play a supporting role, which can increase the acid fracturing effect. The solid acid has a slow reaction rate, which can effectively prolong the acid-rock reaction time and has a long acting distance in the crack, thereby achieving the effects of deep acid fracturing and acidizing, and enhancing the transformation effect.

[0026] 2. The present invention adopts a dual-liquid acid fracturing method of injecting simultaneously through two channels, the continuous tubing and the open hole well wall annulus, without the need to insert a mechanical packer, thereby increasing the applicability of acid fracturing to open hole completions and ultra-long horizontal wells. At the same time, the acidizing fluid reacts with the reservoir to reduce the fracturing pressure, thereby reducing operating costs and improving economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0028] Figure 1 It is a schematic diagram of acid fracturing a certain point in the present invention; DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the technical solutions in the embodiments of the present invention are clearly and completely described below in combination with the embodiments and drawings. Obviously, the schematic implementation modes of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0030] The following is a detailed description of an embodiment of a dual-liquid acid fracturing method for carbonate open hole horizontal wells according to the present invention with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions and repeated descriptions of well-known matters are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art.

[0031] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, the terms "include" and "comprising" mentioned in this application may be open-ended or closed-ended. For example, the terms "include" and "comprising" may mean that other substances not listed may also be included or only the listed substances may be included.

[0035] If there is no special explanation, all the steps of the present application can be performed sequentially or randomly, preferably sequentially.

[0036] As one of the methods of reservoir transformation, acid fracturing has been widely used in carbonate reservoir perforation completion or open hole horizontal well packer staged acid fracturing. However, the current acid fracturing technology requires the use of packer stages, which leads to the risk of sand stuck in the pipe string when used in open hole wells. Even if there is no risk of pipe stuck in perforation completion, perforation completion increases the completion cost. At the same time, acid loss enters the reservoir and causes damage, affecting the acid fracturing effect. In addition, the applicability of acid fracturing for ultra-long horizontal wells that require multi-stage acid fracturing is low. Therefore, the applicability and acid fracturing effect of acid fracturing technology for open hole wells and ultra-long horizontal wells need to be improved.

[0037] Based on this, in order to improve the applicability of acid fracturing to open hole wells and ultra-long horizontal wells, reduce the filtration loss of acidizing fluid in the reservoir and extend the acid-rock reaction distance in the fracture to achieve the purpose of improving the acid fracturing effect, the present invention injects a temporary plugging agent into the horizontal open hole section before acid fracturing to form a temporary plugging layer so that the acid does not leak and provide a guarantee for continuous fluid supply, adopts a double-liquid acid fracturing method in which two channels of a continuous tubing and an annulus of the open hole wall are injected simultaneously, and hydrodynamic isolation is realized by using the Bernoulli principle. At the same time, the double-liquid injection is conducive to adding more chemical agents with different functions, and finally the continuous tubing injects the acidizing fluid, and the open hole wall annulus injects the temporary plugging solid acid mixed liquid. The acidizing fluid enters the fracture with the temporary plugging solid acid mixed liquid according to the Bernoulli principle, and the reaction rate of the solid acid is slow, so that the effects of deep acid fracturing and acidification can be achieved, and the transformation effect is enhanced.

[0038] The technical solution of the present invention is further described in detail below in conjunction with embodiments.

[0039] It should be noted that the materials, reagents, methods and equipment used in the examples are conventional materials, reagents, methods and equipment in the art unless otherwise specified.

[0040] Example 1

[0041] A dual-liquid acid fracturing method for carbonate open hole horizontal wells comprises the following steps:

[0042] S1. Lower the coiled tubing with a spray gun at the bottom to the first point in the open hole horizontal well that requires acid fracturing.

[0043] S2. Inject two-thirds of the annular volume of temporary plugging agent liquid A from the open hole wall annulus, and then slowly inject temporary plugging solid acid mixed liquid B to squeeze the temporary plugging agent in the temporary plugging agent liquid A into the horizontal open hole section to form a temporary plugging layer.

[0044] Among them, the temporary plugging agent liquid A is prepared by dissolving a temporary plugging agent 1 in water; the temporary plugging agent 1 adopts a composite nanomaterial temporary plugging agent, and its diameter is determined according to the pore throat distribution of the open hole horizontal section reservoir to ensure that a temporary plugging layer is formed in the open hole horizontal section according to the bridging theory, and the mass concentration of the temporary plugging agent 1 is 8%.

[0045] Among them, the temporary plugging solid acid mixed solution B is formed by mixing and dissolving a temporary plugging agent 2 and a solid acid in water, the mass concentration of the temporary plugging agent 2 is 8%, and the mass concentration of the solid acid is 20%; specifically, the temporary plugging agent 2 is a temporary plugging ball, the diameter of which is larger than the pore throat diameter of the reservoir, ensuring that it can play a supporting role in the reservoir and increase the acidification effect; the solid acid is a mixture of hydroxylamine hydrochloride, betaine hydrochloride, ammonium fluoroborate and ammonium fluoride, and the mass ratio is 6:2:1:1.

[0046] In this step, temporary plugging agent liquid A is injected into the horizontal open hole section before acid fracturing to form a temporary plugging layer to avoid acid loss, thereby ensuring continuous liquid supply and protecting the open hole section from contamination.

[0047] S3. After the temporary plugging layer is formed, the temporary plugging solid acid mixture B is continuously injected into the annulus of the open hole wall, and the acidizing liquid C is injected from the continuous oil pipe to form a dual-channel dual-liquid injection. The acidizing liquid C is sprayed into the reservoir through the spray gun to form holes and then cause the reservoir to crack and form cracks. The temporary plugging solid acid mixture B is sucked in to replenish the cracks with liquid.

[0048] Since the nozzle diameter of the spray gun is smaller than the diameter of the coiled tubing, the flow area of ​​the nozzle is also smaller than the flow area of ​​the tubing. The speed of the acidizing fluid C increases significantly after passing through the nozzle, and the pressure energy is converted into kinetic energy to create holes on the open hole wall. The acidizing fluid C reacts with the reservoir to reduce the reservoir strength and fracturing pressure. The static kinetic energy of the acidizing fluid C in the hole is converted into pressure energy to cause the reservoir to fracture and gradually extend to the deep part of the reservoir.

[0049] Since the pressure of the acidizing fluid C decreases after passing through the nozzle, the pressure at this point in the annulus is also the lowest. The hydrodynamic isolation is formed by acidizing the injection point only without acidizing other positions in the open hole horizontal section.

[0050] Among them, the solid acid is drawn into the crack by the acidizing liquid C. Since the reaction rate of the acidizing liquid is high, the acid-rock reaction distance is short, the concentration of the acidizing liquid is reduced, and the solid acid reacts slowly with the rock, it can be brought into the crack farther away for reaction, effectively extending the seepage capacity of the crack. Therefore, the present invention adopts a method of injecting acidizing liquid into the continuous oil pipe and injecting temporary plugging solid acid mixed liquid into the annulus of the open hole wall at the same time, which can enhance the acid fracturing transformation effect.

[0051] In this step, during the acid fracturing process, the temporary plugging agent will enter the cracks to play a supporting role and increase the acid fracturing effect. The temporary plugging agent 1 in the temporary plugging agent liquid A and the temporary plugging agent 2 in the temporary plugging solid acid mixed liquid B have a dissolution rate of more than 95% under the formation temperature conditions, and the degradation time is adjustable from 4 to 360 hours. After degradation, the reservoir in the open hole section and the cracks is released; therefore, after a period of time, the dissolution of the temporary plugging agent does not affect production.

[0052] S4. Lift the coiled tubing and drag the spray gun to the second point in the open hole horizontal section that needs acid fracturing, then inject a high-displacement acidizing fluid C from the coiled tubing and a solid acid solution B from the open hole wellbore annulus to complete the acid fracturing at the second point.

[0053] S5. Repeat step S4 until the acid fracturing of the second to last point of the open hole horizontal section design is completed.

[0054] S6. Lift up the coiled tubing and drag the spray gun to the last point in the open hole horizontal section that needs acid fracturing. Inject high-displacement acidizing fluid C from the coiled tubing and temporarily plugging solid acid mixture B from the open hole wellbore annulus at the same time. When the remaining volume of the solution added to the open hole wellbore annulus is equal to the sum of the annular volumes of the vertical well section, the well deviation section, and the remaining annular section from the injection point to the bottom of the horizontal section (i.e., one annular volume), no temporary plugging agent is added to the temporary plugging solid acid mixture B to ensure that the last annular volume injected into the fracture is only solid acid solution, so that the vicinity of the last point near the fracture will not be temporarily plugged, and finally complete the acid fracturing of all designed points.

[0055] The acidizing fluid C is selected from any one or more of gelled acid, thickened acid and emulsified acid. The viscosity is maintained above 30 mPa·s during the acid fracturing construction under formation temperature conditions. The acid fluid has no stratification or precipitation. The viscosity drops to 5 mPa·s 3 hours after the acid fracturing is completed.

[0056] S7. After completing the acid fracturing at the last design point, the displacement fluid is injected into the open hole well annulus and the coiled tubing until the acidizing fluid inside the coiled tubing and the temporary plugging agent solution in the casing annulus are completely displaced.

[0057] S8. Shut down the well for a period of time, wait for the acid to react with the reservoir and the temporary plugging agent to dissolve, and then release the well normally to complete the double-liquid acid fracturing.

[0058] Finally, it should be noted that the above specific embodiments are only used to explain in detail the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific implementation method of the present invention and is not used to limit the protection scope of the present invention. Although the present invention is described in detail with reference to the above specific embodiments, ordinary technicians in this field should understand that it is still possible to modify the technical solutions recorded in the above embodiments, or to replace or improve some or all of the technical features therein. These modifications, equivalent replacements and improvements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A dual-liquid acid fracturing method for carbonate open hole horizontal wells, characterized in that: The steps include: S1. Lower the coiled tubing with a spray gun at the bottom to the first point in the open hole horizontal well that needs acid fracturing; S2. inject temporary plugging agent liquid A from the annulus of the open hole wall, and then slowly inject temporary plugging solid acid mixed liquid B to squeeze the temporary plugging agent in the temporary plugging agent liquid A into the horizontal open hole section to form a temporary plugging layer; S3. After the temporary plugging layer is formed, the temporary plugging solid acid mixture B is continuously injected into the annulus of the open hole wall, and the acidizing liquid C is injected from the coiled tubing to form a dual-channel dual-liquid injection. The acidizing liquid C is sprayed into the reservoir through the spray gun to form holes and cracks. At the same time, the temporary plugging solid acid mixture B is sucked into the cracks by the acidizing liquid C to form liquid replenishment, and finally the acid fracturing at the first point is completed; S4. Repeat step S3 until the acid fracturing of the second to last point of the open hole horizontal section requiring acid fracturing is completed; S5. Lift the coiled tubing and drag the spray gun to the last point of the open hole horizontal section that needs acid fracturing. Inject acidizing liquid C from the coiled tubing and temporarily plugging solid acid mixture B from the open hole wellbore annulus at the same time. When the remaining volume of the solution added to the open hole wellbore annulus is equal to the sum of the annular volumes of the vertical well section, the well deviation section, and the remaining annular section from the injection point to the bottom of the horizontal section, no more temporary plugging agent is added to the temporary plugging solid acid mixture B; S7. After the last point requiring acid fracturing is completed, the displacement fluid is injected into the annulus of the open hole wall and the coiled tubing to completely displace the acidizing fluid inside the coiled tubing and the temporary plugging agent solution in the annulus of the casing; S8. Shut down the well for a period of time, wait for the acid to react with the reservoir and the temporary plugging agent to dissolve, and then release the well normally to complete the double-liquid acid fracturing.

2. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 1, characterized in that: The temporary plugging agent liquid A and the temporary plugging solid acid mixed liquid B both contain temporary plugging agents, and the temporary plugging agent has a dissolution rate of more than 95% under formation temperature conditions, and a degradation time adjustable from 4 to 360 hours. After degradation, the reservoir in the open hole section and the fracture is released.

3. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 1, characterized in that: The temporary plugging agent liquid A is prepared by dissolving a temporary plugging agent 1 in water. The temporary plugging agent 1 is a composite nano material temporary plugging agent, and the mass concentration of the temporary plugging agent 1 is 1% to 15%.

4. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 3, characterized in that: The injection volume of the temporary plugging agent liquid A is two-thirds of the annulus volume.

5. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 1, characterized in that: The temporary plugging solid acid mixed solution B is formed by mixing and dissolving a temporary plugging agent 2 and a solid acid in water, wherein the mass concentration of the temporary plugging agent 2 is 1% to 15%, and the mass concentration of the solid acid is 15% to 30%.

6. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 5, characterized in that: The temporary blocking agent 2 is a temporary blocking ball.

7. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 5, characterized in that: The solid acid is a mixture of hydroxylamine hydrochloride, betaine hydrochloride, ammonium fluoroborate and ammonium fluoride, and the mass ratio is (5-8):(1-3):1:

1.

8. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 7, characterized in that: The solid acid is a mixture of hydroxylamine hydrochloride, betaine hydrochloride, ammonium fluoroborate and ammonium fluoride, with a mass ratio of 6:2:1:

1.

9. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 1, characterized in that: The acidifying liquid C may be any one or more of gelling acid, thickening acid and emulsifying acid.

10. A dual-liquid acid fracturing method for carbonate open hole horizontal wells according to claim 1, characterized in that: In step S3, the velocity Vt of the acidizing fluid C in the coiled tubing is greater than the velocity Va of the temporary plugging solid acid mixture B in the annulus of the open hole wall, so as to ensure that the temporary plugging solid acid mixture B can enter the fracture according to the Bernoulli principle when the open hole section is opened by high-pressure perforation of the coiled tubing acid.

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