A fracturing reconstruction method and application for ultra-deep high stress reservoirs

Abstract

The application provides a fracturing reconstruction method and application for ultra-deep high-stress reservoirs, and mainly aims to solve the problems of high fracture pressure, small reconstruction volume and low fracture conductivity of high-stress reservoirs. Specifically, the application analyzes the fracturing problems of the current ultra-deep high-stress reservoirs, points out the limitations of the current technical measures, and proposes a new fracturing reconstruction technology for high-stress reservoirs. The technology takes the pre-composite pressure reduction process, forced fracture expansion process and fracture effective support process as the core, solves the problems of difficult fracturing, difficult fracture expansion and difficult support of high-stress reservoirs, and has good application effect.

Description

Technical Field

[0001] This invention belongs to the field of fracturing, and particularly relates to fracturing stimulation methods, especially to a fracturing stimulation method and application for ultra-deep high-stress reservoirs. Background Technology

[0002] Ultra-deep, high-stress reservoirs often have very high fracture pressures due to their high triaxial stresses, and the difference between the two horizontal principal stresses is also large. This often results in the reservoir not being effectively fractured during fracturing operations, making it impossible to form a large reservoir stimulation spillover space and maintain the conductivity of the fractured fractures.

[0003] The literature "Causes and Technical Countermeasures of High Fracture Pressure in Terrestrial Reservoirs in the Yuanba Area of ​​the Sichuan Basin" explores and tests technical measures and methods to reduce wellhead pressure during fracturing operations, based on an in-depth study of the geological causes of high fracture pressure in reservoirs and the influence of engineering processes on fracture pressure. These measures include: using the direction of the near-maximum horizontal principal stress as the perforation azimuth; employing long well sections, large diameters, high perforation density, and deep penetration perforations (including sandblasting perforations and supplementary perforations) to reduce fracturing pressure; using acid damage (acid soaking, acid washing) technology to remove reservoir contamination and reduce rock strength; and using weighted acid to increase fluid column pressure and large-diameter tubing in conjunction with low-resistivity acid or fracturing fluid systems to reduce operational friction. Field application practice shows that using these technologies alone or in combination can effectively reduce wellhead pressure during fracturing operations, enabling acid fracturing or proppant fracturing of reservoirs.

[0004] The literature "Research on Fracturing Technology of High-Pressure and High-Stress Formations in Jianghan Oilfield" reduces the construction pressure by increasing the amount of pre-flush fluid, using a low sand ratio of 3-5% to grind the near-wellbore, and using repeated pulse pressurization methods, and then carries out fracturing according to conventional methods.

[0005] The literature "Exploration and Application of High-Stress Reservoir Fracturing Technology in Well Chang 2-17" describes a technology that involves pretreatment with soil acid, fracturing with uncrosslinked base fluid, and then injecting a large amount of fracturing fluid at a variable flow rate to reduce formation fracturing pressure and construction pressure, thereby achieving the goal of efficient stimulation.

[0006] The literature "Research and Application of Acid Treatment Technology Before Fracturing in Ultra-High Stress Reservoirs" points out that the characteristics of ultra-high stress reservoirs dictate that fracturing operations generally involve high wellhead pump pressure, high formation fracturing pressure, limited operational parameters, difficulty in increasing pumping rate, difficulty in increasing sand ratio, and failure due to the inability to add sand, which also places high demands on equipment, tubing, and processes for reservoir stimulation. This literature applies acidizing pretreatment technology to reduce wellhead operational pressure, proposes low-damage acid formulation systems for different reservoir characteristics, and sets requirements for the performance evaluation of acidizing corrosion inhibitors. The indoor optimized technology has achieved good results when applied to field operations in oilfields, significantly reducing wellhead pump pressure and solving the technical challenges of fracturing operations in ultra-high stress reservoirs.

[0007] Currently, large-diameter, deep-penetration, and multi-perforation techniques are commonly used for fracturing reservoirs of this type, combined with efficient acid etching systems, weighted acid systems, and conventional pumping methods to improve fracturing effectiveness. However, these techniques are difficult to implement effectively in reservoirs with minimum principal stresses exceeding 140 MPa and stress differences greater than 20 MPa. Furthermore, these measures do not address the issue of maintaining the conductivity of the created fractures. Therefore, more advanced technologies are needed to solve these challenges. Summary of the Invention

[0008] To overcome the problems existing in the prior art, this invention provides a fracturing stimulation method and application for ultra-deep, high-stress reservoirs, mainly to solve the problems of high fracturing pressure, small stimulation volume, and low fracture conductivity in high-stress reservoirs. Specifically, this invention analyzes the current fracturing challenges of ultra-deep, high-stress reservoirs, points out the limitations of current technical measures, and proposes a new high-stress reservoir fracturing stimulation technology. This technology, based on a pre-construction composite depressurization process, a forced fracture enlargement process, and an effective fracture support process, solves the problems of difficulty in fracturing, enlarging, and supporting high-stress reservoirs, and has shown good application results.

[0009] One objective of this invention is to provide a fracturing stimulation method for ultra-deep, high-stress reservoirs, comprising:

[0010] (1) Perforation is carried out using equal-diameter perforation technology;

[0011] (2) Acid is used for pretreatment of the wellbore and blast holes;

[0012] (3) Pumping in liquid carbon dioxide;

[0013] (4) Pump low-viscosity slickwater using a pulsed flow rate method;

[0014] (5) Sand addition construction.

[0015] In a preferred embodiment, in step (1), perforation is performed using equal-diameter perforation technology to ensure that the diameter of the downhole perforation hole reaches 16 mm or more.

[0016] In this invention, the large-aperture perforation technology can be found in the published documents "Large-aperture perforation technology and application", "BH56RDX-71-178 type high-density large-aperture perforating bullet" and "Development of series of large-aperture deep-penetrating bullets", etc.

[0017] In a preferred embodiment, in step (2), the acid is selected from at least one of hydrochloric acid, emulsified acid, and oxalic acid.

[0018] In a further preferred embodiment, in step (2), the acid is 5% to 30% hydrochloric acid, for example, 15% hydrochloric acid.

[0019] In a further preferred embodiment, in step (2), the acid injection rate is 0.4 to 0.6 times the wellbore volume, for example, half the wellbore volume; and / or, the acid discharge rate is 1 to 2 m³. 3 / min, preferably 1.2–1.8m 3 / min, for example, 1.5m 3 / min.

[0020] In a preferred embodiment, in step (3), 2% to 15%, preferably 5% to 10% of the designed total liquid volume of liquid CO2 is pumped in, and the discharge rate is increased as much as possible. Preferably, the discharge rate is increased under the condition of not exceeding the design pressure limit. If conditions permit, the discharge rate can be increased to the maximum design discharge rate. The design pressure limit is generally given by the fracturing design.

[0021] In this invention, the total designed liquid volume refers to the total amount of liquid used in the designed pumping procedure, excluding acid and CO2.

[0022] In a preferred embodiment, in step (4), the viscosity of the low-viscosity slickwater is 3 to 6 mPa·s.

[0023] After the liquid CO2 is pumped in, low-viscosity slickwater with high anti-swelling effect (viscosity of 3-6 mPa.s) is pumped in.

[0024] In a further preferred embodiment, in step (4), the total pumping volume of the low-viscosity slickwater is 2% to 15% of the designed total liquid volume, preferably 5% to 10%.

[0025] In a preferred embodiment, in step (4), the pulsed increase in displacement is performed in multiple stages, with each stage having a displacement of [a*x]% of the designed maximum displacement, and each stage pumping 1 to 10 m³. 3 Furthermore, the displacement of adjacent stages is different, where x = 1 to (100 / a) and a = any number from 5 to 20.

[0026] In a further preferred embodiment, in step (4), the pulsed increase in displacement is performed in multiple stages, with each stage having a displacement of [a*x]% of the designed maximum displacement, and each stage pumping 2-8m³. 3 Furthermore, the displacement of adjacent stages is different, where x = 1 to (100 / a) and a = any number from 8 to 15.

[0027] In a further preferred embodiment, in step (4), the pulsed increase in displacement is performed in multiple stages, with each stage having a displacement of [12.5*x]% of the designed maximum displacement, and each stage pumping 6-7m³. 3 Furthermore, the displacement of adjacent stages is different, where x = 1 to 8 (preferably x is an integer);

[0028] For example, in step (4), the pulse increase in displacement is performed as shown in Table 1 below:

[0029] Table 1:

[0030]

[0031] For example, the pulsed flow rate is increased as follows: 5m³ of pump is injected at 25% of the designed maximum flow rate. 3 Pumping 5m³ at 12.5% ​​of the design maximum displacement. 3 Pumping 5m at 37.5% of the design maximum displacement. 3 Pumping 5m at 50% of the maximum designed displacement 3 Pumping 5m at 25% of the maximum design displacement 3 Pumping 5m³ at 62.5% of the design maximum displacement. 3 Pumping 5m at 75% of the maximum designed displacement 3 Pumping 5m at 37.5% of the design maximum displacement. 3 Pumping 5m at the maximum designed displacement 3 The pumping volume at each stage can be adjusted according to the actual situation.

[0032] In a preferred embodiment, in step (5), a fracturing fluid system capable of physically or chemically reacting with the reservoir is used, the system viscosity meets the requirements of the fracturing stimulation scheme, and the pumping discharge rate is as high as possible to achieve the maximum achievable discharge rate.

[0033] In a further preferred embodiment, in step (5), the fracturing fluid system uses at least one of acidic slickwater and self-growing fracturing fluid; and / or, the viscosity of the fracturing fluid used is 1 to 50 mPa·s; and / or, the pumping discharge rate is the maximum achievable discharge rate.

[0034] Among them, because the discharge rate may not reach the maximum designed discharge rate due to reservoir conditions and wellhead pressure limitations, the maximum discharge rate that can be achieved in actual construction can only be used.

[0035] In a preferred embodiment, in step (5), a density of 1.0-1.1 g / cm³ is used. 3 (Ultra-high strength) proppant.

[0036] In a further preferred embodiment, the proppant has a mesh size of 400-50 mesh (e.g., 140-70 mesh) and a breakage rate of less than 10% under effective reservoir closure stress conditions.

[0037] In a preferred embodiment, in step (5), a low sand ratio of 1-3% is used for sand addition or the sand ratio is designed according to the maximum sand-eating capacity of the reservoir, provided that sand blockage is prevented.

[0038] The second objective of this invention is to provide an application of the method described in the first objective of this invention in the fracturing operation of ultra-deep high-stress reservoirs.

[0039] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0040] Compared with the prior art, the present invention has the following beneficial effects: the present invention can effectively solve the problems of high stress reservoirs being difficult to open, difficult to enlarge fractures, and low post-indentation fracture conductivity and difficulty in expanding the stimulation volume. Attached Figure Description

[0041] Figure 1 A flowchart illustrating the method described in this invention is shown. Detailed Implementation

[0042] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0043] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0044] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0045] Unless otherwise specified, the raw materials used in the embodiments are all publicly available in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0046] The low-viscosity corrosion-inhibiting slickwater system used in Example 1 is an acidic slickwater with a formulation of 5% hydrochloric acid + 0.15% drag reducer + 0.2-0.3% corrosion inhibitor + 0.5% chelating agent. It has the characteristics of low viscosity, high drag reduction and corrosion inhibition, and a viscosity of 3 mPa·s.

[0047]

Example 1

[0048] This invention has been applied in an ultra-deep-sea gas well in the Sichuan Basin. The minimum principal stress of this well is 151 MPa, the stress difference is 25 MPa, and the predicted fracturing pressure during conventional fracturing is 170 MPa, making it difficult to achieve the desired reservoir stimulation effect.

[0049] This invention was employed to achieve constant-diameter perforation, with a perforation diameter reaching 16.1 mm. During fracturing, 40 cubic meters of 15% HCl (displacement of 1.5 m³) was used. 3 Pre-treatment of the wellbore and boreholes was performed at a rate of 4 cubic meters per minute ( / min). Then, 100 cubic meters of liquid carbon dioxide were injected at a rate of 4 cubic meters per minute, with the injection rate increased within the design pressure limit, up to the maximum design rate if conditions permit. Next, 100 cubic meters of low-viscosity slickwater with a viscosity of 4 mPa·s was injected using a pulsed injection method (Table 1). A low-viscosity, corrosion-inhibiting slickwater system was used for pumping during fracturing, carrying 2% sand-to-powder ratio 70 / 140 mesh low-density, high-strength proppant (proppant density 1.08 g / cm³). 3 Under effective reservoir closure stress conditions, the fracturing rate is less than 10%, and the sand ratio is increased to 3% in the later stage.

[0050] In the embodiment, 70 / 140 mesh refers to 70-140 mesh.

[0051] Table 1:

[0052]

[0053] The gas production of this well increased by 40% using this technology, and the application effect was good.

[0054]

Example 2

[0055] This invention has been applied in deep oil wells in Northwest China. The minimum principal stress in this well is 140 MPa, and the stress difference is 22 MPa. Adjacent wells were fractured using conventional methods, but the post-fracturing results were unsatisfactory.

[0056] This invention was employed to achieve constant-diameter perforation, with a perforation diameter reaching 16.0 mm. During fracturing, 40 cubic meters of 15% HCl (displacement of 1.5 m³) was used. 3Pre-treatment of the wellbore and boreholes was performed at a rate of 4 cubic meters per minute ( / min). Then, 200 cubic meters of liquid carbon dioxide were injected at a rate of 4 cubic meters per minute, with the injection rate increased within the design pressure limit, up to the maximum design rate if conditions permit. Next, 200 cubic meters of low-viscosity slickwater with a viscosity of 10 mPa·s was injected using a pulsed injection method (Table 1). Low-viscosity, corrosion-inhibiting emulsified acid was used for initial acidizing during fracturing, followed by proppant fracturing using acidic slickwater. A low-density, high-strength proppant with a 70 / 140 mesh sand ratio of 1–2% (proppant density 1.06 g / cm³) was used. 3 (Under the effective closure stress conditions of the reservoir, the fracture rate is less than 12%).

[0057] The gas production of this well increased by 30% using this technology, and the application effect was good.

[0058] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A fracturing stimulation method for ultra-deep, high-stress reservoirs, comprising: (1) Use equal-diameter perforation technology to ensure that the diameter of the downhole perforation hole reaches 16 mm or more; (2) Acid is used for pretreatment of the wellbore and blast holes; (3) Pumping liquid carbon dioxide; (4) Pumping low-viscosity slickwater in a pulsed flow rate manner, wherein the viscosity of the low-viscosity slickwater is 3~6 mPa·s; in step (4), the pulsed flow rate manner is carried out in multiple stages, and the flow rate of each stage is [a*x]% of the designed maximum flow rate. Each stage pumps 1~10 m³, and the flow rates of adjacent stages are different, wherein x=1~(100 / a), and a=5~20 any number; (5) Sand addition construction.

2. The fracturing stimulation method according to claim 1, characterized in that, In step (2), the acid is selected from at least one of hydrochloric acid, emulsified acid, and terpineic acid.

3. The fracturing stimulation method according to claim 1, characterized in that, In step (2), the acid is 5% to 30% hydrochloric acid.

4. The fracturing stimulation method according to claim 1, characterized in that, In step (2), the acid injection rate is 0.4 to 0.6 wellbore volumes, and / or the acid discharge rate is 1 to 2 m³ / min.

5. The fracturing stimulation method according to claim 1, characterized in that, In step (2), the acid discharge rate is 1.2~1.8 m³ / min.

6. The fracturing stimulation method according to claim 1, characterized in that, In step (3), 2% to 15% of the designed total liquid volume of liquid CO2 is pumped in.

7. The fracturing stimulation method according to claim 1, characterized in that, In step (3), 5%-10% of the designed total liquid volume of liquid CO2 is pumped in.

8. The fracturing stimulation method according to claim 1, characterized in that, In step (4), the total pumping volume of the low-viscosity slickwater is 2% to 15% of the designed total liquid volume.

9. The fracturing stimulation method according to claim 1, characterized in that, In step (4), the total pumping volume of the low-viscosity slickwater is 5%-10% of the designed total liquid volume.

10. The fracturing stimulation method according to claim 1, characterized in that, In step (4), the pulse increase in displacement is carried out in multiple stages. The displacement of each stage is [a*x]% of the designed maximum displacement. Each stage pumps 2~8 m³, and the displacement of adjacent stages is different. Among them, x=1~(100 / a) and a=8~15 any number.

11. The fracturing stimulation method according to claim 1, characterized in that, In step (4), the pulse increase in displacement is carried out in multiple stages. The displacement of each stage is [12.5*x]% of the designed maximum displacement. Each stage pumps 6~7m³, and the displacement of adjacent stages is different, where x=1~8.

12. The fracturing stimulation method according to claim 1, characterized in that, In step (5), a fracturing fluid system that can physically or chemically react with the reservoir is used, the system viscosity meets the requirements of the fracturing stimulation scheme, and the pumping discharge rate reaches the maximum discharge rate.

13. The fracturing stimulation method according to claim 12, characterized in that, In step (5), the fracturing fluid system uses at least one of acidic slickwater and self-growing fracturing fluid; and / or, the viscosity of the fracturing fluid used is 1~50 mPa·s; and / or, the pumping discharge rate is the maximum discharge rate.

14. The fracturing stimulation method according to claim 12, characterized in that, In step (5), a density of 1.0-1.1 g / cm³ is used. 3 The proppant.

15. The fracturing stimulation method according to claim 14, characterized in that, In step (5), the mesh size of the proppant is 400-50 mesh.

16. The application of the fracturing stimulation method according to any one of claims 1 to 15 in the fracturing construction of ultra-deep high-stress reservoirs.

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