Acid fracturing process method and mining method for ultra-high temperature carbonate reservoir

Abstract

The invention discloses an acid fracturing process method and a mining method for an ultra-high temperature carbonate reservoir. The acid fracturing process method comprises the following steps: forming cracks by using ultra-high temperature resistant gel fracturing fluid, and performing acid etching on the cooled artificial cracks by using a medium-low temperature authigenic acid system; and more ultrahigh-temperature-resistant gel fracturing fluid is used for forming a crack again, and an ultrahigh-temperature-resistant self-generated acid system is used for carrying out acid etching on a subsequently-formed artificial crack. According to the process method, in the early stage, an ultra-high-temperature-resistant gel fracturing fluid is utilized, an acid solution formed by a medium-low-temperature self-generating acid system is used for acid etching of artificial fractures near a wellbore, and an acid solution formed by the ultra-high-temperature-resistant self-generating acid system is used for acid etching of a deep reservoir far away from the wellbore, so that the artificial fractures near the wellbore and far away from the wellbore are both etched by the acid solution; and thus, the artificial fracture has relatively high flow conductivity. The process method can significantly increase the length of the artificial fracture and effectively reform the fracture volume, and provides technical support for high and stable yield of a single well.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high temperature carbonate reservoir ultra-deep acid fracturing technology, and in particular to an ultra-high temperature carbonate reservoir acid fracturing technology method and a mining method. Background Art

[0002] Carbonate reservoirs are rich in existing oil and gas resources and offer significant exploration and development potential, making them a key area for future oil and gas reserve and production increases. Current exploration of carbonate reservoirs reveals that some have a dense matrix and pronounced low porosity and permeability. These carbonate reservoirs primarily rely on natural fractures or fracture-vuggy systems for oil and gas storage. The primary goal of reservoir stimulation is to connect these natural fractures and fracture-vuggy systems through artificial fractures. As target carbonate reservoirs become deeper, the heterogeneity of natural fractures increases, and the accurate prediction of their distribution becomes increasingly challenging, connecting these natural fractures and vuggy systems through stimulation becomes increasingly challenging. Therefore, for deep carbonate reservoir stimulation, connecting more natural fractures and vuggy systems is crucial for the success of the stimulation. Currently, commonly used techniques such as acidizing and fracturing, sand fracturing, and combined stimulation can be used to increase the distance between acid-etched fractures and expand the number of connecting natural fractures and vuggy systems through large-scale stimulation in shallow and intermediate carbonate reservoirs with lower temperatures.

[0003] Ultra-deep, ultra-high-temperature carbonate reservoirs are rich in oil and gas resources, characterized by dense matrices and highly heterogeneous fractures and vugs. Reservoir stimulation is a crucial means of increasing well production and enhancing development effectiveness. Due to the high risk of sanding, acid fracturing is a common technique. Acid is the most crucial component of acid fracturing. Its temperature tolerance determines the length and range of acid-etched fractures. Conventional acid systems and acid fracturing processes struggle to significantly increase the distance of acid-etched fractures. However, in ultra-deep, ultra-high-temperature carbonates, conventional acid systems react rapidly with rock at high temperatures, resulting in short-range acid-etched fractures. While composite acid fracturing techniques, using gel-jet fracturing fluids, can achieve long-range fracture formation, their post-closure conductivity is low, insufficient for high production requirements, and gel-jet sanding is a high-risk process. There is an urgent need for innovative technologies for ultra-deep, ultra-high-temperature carbonate stimulation that can achieve ultra-long-range acid fracturing with low-risk acid fracturing techniques, creating extended acid-etched fractures and improving the ability to connect natural fractures and vugs. Summary of the Invention

[0004] In order to further increase the length of acid-etched cracks in ultra-high temperature carbonate reservoirs and expand the scope of acid fracturing process modification, thereby enriching process routes and increasing selection space, an ultra-high temperature carbonate reservoir acid fracturing process method and mining method are provided in an embodiment of the present invention.

[0005] In a first aspect, an embodiment of the present invention provides an ultra-high temperature carbonate reservoir acid fracturing process, which may include:

[0006] The ultrahigh temperature resistant gel fracturing fluid is used to create fractures, and the artificial fractures after cooling are acid-etched with a medium-low temperature autogenous acid system; more ultrahigh temperature resistant gel fracturing fluid is used to create fractures again, and the subsequently formed artificial fractures are acid-etched with the ultrahigh temperature resistant autogenous acid system.

[0007] In an optional embodiment, the above-mentioned ultrahigh temperature carbonate reservoir acid fracturing process may specifically include:

[0008] Pumping ultra-high temperature resistant gel fracturing fluid in a pressure-limited but unlimited displacement manner to create the first fractures in the reservoir near the wellbore of the target well and form artificial fractures;

[0009] pumping a medium-low temperature autogenous acid system so that the medium-low temperature autogenous acid system generates acid in the artificial fracture and performs acid etching on the artificial fracture;

[0010] After stopping the pump for a first preset time, pumping in ultra-high temperature resistant gel fracturing fluid for secondary fracture creation; wherein the amount of the ultra-high temperature resistant gel fracturing fluid pumped in the secondary fracture creation is not less than twice the amount of the ultra-high temperature resistant gel fracturing fluid pumped in the first fracture creation;

[0011] Pumping an ultrahigh temperature resistant autogenous acid system so that the ultrahigh temperature resistant autogenous acid system generates acid and performs acid etching in the artificial cracks formed by the secondary cracking; wherein the amount of the ultrahigh temperature resistant autogenous acid system is not less than 2.5 times the amount of the ultrahigh temperature resistant gel fracturing fluid pumped for the first cracking.

[0012] Optionally, after pumping the ultra-high temperature resistant autogenous acid system, the following may also be included:

[0013] The pump injects gel-carrying sand fluid to support the artificial fracture near the wellbore, and after shutting in the well for the second preset time, the wellhead is pressure-controlled and released.

[0014] Optionally, the proppant in the pumped gel sand-carrying fluid is ceramsite, and the amount of sand added is 3m 3 / m.

[0015] Optionally, after pumping the ultrahigh temperature resistant autogenous acid system, the method may further include: repeatedly pumping the ultrahigh temperature resistant gel fracturing fluid and the ultrahigh temperature resistant autogenous acid system to allow the acid-etched fractures to reach a preset range of the far wellbore zone of the target well.

[0016] Optionally, after pumping the medium-low temperature autogenous acid system, the fracturing fluid base fluid is pumped to push the medium-low temperature autogenous acid system in the wellbore into the carbonate reservoir.

[0017] Optionally, before pumping the ultra-high temperature resistant gel fracturing fluid, the following steps may also be included:

[0018] Based on the fracturing simulation results of the target well using the fracturing simulation software, the dosage of the ultra-high temperature resistant gel fracturing fluid for the first fracture creation is determined.

[0019] Optionally, the temperature resistance of the ultra-high temperature resistant gel fracturing fluid is not less than 180° C., and the shear rheology test of the ultra-high temperature resistant gel fracturing fluid satisfies the requirement that the viscosity remains at 150 MPa·s±5 MPa·s after 120 minutes.

[0020] Optionally, the medium-low temperature autogenous acidification system has an initial acidification temperature of 90°C and a main acidification temperature range of 120°C±5°C;

[0021] The ultra-high temperature resistant autogenous acid generating system has an acid generating temperature starting at 120°C, and a main acid generating temperature range of 160°C±5°C.

[0022] In a second aspect, an embodiment of the present invention provides a method for exploiting an ultrahigh temperature carbonate reservoir, which may include: transforming the carbonate reservoir according to the ultrahigh temperature carbonate reservoir acid fracturing process method described in the first aspect.

[0023] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0024] The present invention provides an acid fracturing process and mining method for ultrahigh-temperature carbonate reservoirs. This method utilizes ultrahigh-temperature-resistant gel fracturing fluid to create artificial fractures near the wellbore. Acid generated by a medium- and low-temperature autogenous acid system then etches artificial fractures in the deep reservoir away from the wellbore. This acid-etched fractures are then etched in both the near- and far-wellbore zones, resulting in higher conductivity. This process significantly increases the length of artificial fractures and effectively transforms their volume, providing technical support for high and stable production from single wells.

[0025] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 This is a flow chart of the ultra-high temperature carbonate reservoir acid fracturing process provided in an embodiment of the present invention;

[0029] Figure 2A curve diagram of a target well reconstruction construction provided in an embodiment of the present invention;

[0030] Figure 3 Provided in the embodiments of the present invention Figure 2 Morphology diagram of the effective artificial fractures finally formed in the target well. DETAILED DESCRIPTION

[0031] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0032] After analyzing existing data at home and abroad, the inventors found that domestic scholars have conducted extensive research on carbonate rock deep acid fracturing technology. Based on different acid systems and their combined application with fracturing fluids, a series of carbonate rock deep acid fracturing, deep transformation, and volume transformation technologies have been formed. For example, the Shunbei Oilfield of the Northwest Bureau of Sinopec proposed a composite acid fracturing technology of "concentrated transformation of backfill sections + acid damage reduction + shallow tubing + increased fracturing fluid combination to increase displacement + pre-fluid fracture creation + alternating injection of high-conducting fractures + autogenous acid to dredge distal fractures" for ultra-deep and ultra-high temperature fractured carbonate reservoirs ("Key Technologies for Large-Scale Acid Fracturing of Ultra-deep and Ultra-high Temperature Carbonate Fault-Solution Reservoirs in Shunbei Oilfield S Well" by Li Xinyong et al.), and implemented large-scale composite acid fracturing volume transformation. CNPC Southwest Oil and Gas Field, targeting the deep, high-temperature, high-pressure, low-porosity, and medium-to-low-permeability Shuangyushi carbonate reservoir, developed a pre-fluid dosage design based on target temperature and operation rate based on research on acid-etched fracture distances using different acid systems ("Research and Application of Deep Acid Fracturing Technology for Ultra-Deep, High-Temperature Gas Wells in the Qixia Formation" by Zeng Ji et al.). Deep acid fracturing tests using pre-fluid acid fracturing increased the length of acid-etched fractures by 57% compared to gelled acid fracturing. CNPC Bohai Drilling Engineering Co., Ltd., targeting the deep, high-temperature, and complex carbonate reservoirs in the Yangshuiwu buried-hill in North China ("Research on Acid Fracturing Technology for High-Temperature, High-Pressure Wells in Yangshuiwu Buried Hill" by Bai Tianzeng et al.), adopted a method of reducing initial slickwater friction and increasing bottomhole injection pressure to facilitate early activation of natural fractures and create complex fracture networks. The method also enhanced the cross-linking viscosity stability of the fracturing fluid, accelerated high-shear viscoelastic recovery to facilitate the creation of long fractures, and improved the deep communication performance of the acid.

[0033] Among the existing patents for acid fracturing technology for ultra-deep and ultra-high temperature carbonate rocks, Liu Pingli et al.'s "Deep-layer and Ultra-deep High-temperature Carbonate Reservoirs Composite Acid Deep Acid Fracturing Method" (CN115288656A) invented a composite transformation technology for ultra-high temperature carbonate reservoirs above 180°C. The main steps are: injecting agent A and agent B into the transformed reservoir at a pressure below the fracture pressure, where agent A is a low-concentration conventional acid and agent B is a conventional fracturing fluid; shutting down the well for 10-30 minutes; injecting agent B into the transformed reservoir at a pressure above the fracture pressure to create fractures in the formation; simultaneously injecting agent C and agent D into the transformed reservoir, where agent C is a conventional acid and agent D is solid acid particles or powder with a particle size of less than 20 mesh, and the weight ratio of agent C to agent D is 10:1-10:10; injecting agent C into the transformed reservoir at a low displacement; injecting conventional displacement fluid; shutting down the well for 1-5 hours; and opening the well for flowback.

[0034] Fang Yuyan et al., "A self-generated acid composite acid fracturing process for high-temperature deep-well carbonate reservoirs" (CN104975840B) invented a self-generated acid composite acid fracturing process for high-temperature deep-well carbonate reservoirs, including the following steps: 1) injecting slick water into the formation through the oil pipe; 2) injecting non-cross-linked fracturing fluid into the formation through the oil pipe; 3) injecting an autogenous acid system into the formation through the oil pipe; 4) injecting a gelled acid system into the formation at a low rate through the oil pipe; 5) injecting a hydrogel into the formation through the oil pipe. Slippery water is injected into the formation; wherein the volume ratios of the liquids injected in steps 1), 2), 3), 4), and 5) to the total liquid injected into the formation are: 3-10% of the slippery water in step 1), 40-60% of the non-cross-linked fracturing fluid in step 2), 30-50% of the autogenous acid system in step 3), 3-10% of the gelled acid system in step 4), and 3-15% of the slippery water in step 5), wherein the volume units are all m3.

[0035] Jiang Tingxue et al. "A method for acid fracturing carbonate reservoirs" (CN106321054A) A method for acid fracturing carbonate reservoirs, comprising the following steps in sequence: step a: pre-treating the reservoir with slick water; step b: sequentially injecting low-viscosity acid and slick water; step c: sequentially injecting medium / high-viscosity acid, low-viscosity acid and slick water; step d: in the displacement stage, injecting displacement fluid.

[0036] Jiang Tingxue et al.'s "A Method for Improving the Effective Acid Etching Seam Length in Ultra-deep Carbonate Reservoirs and Its Application" (CN113969775A) invented a method for improving the effective acid etching seam length in ultra-deep carbonate reservoirs, characterized in that the method includes: the gelling acid and cross-linking agent of the cross-linked acid system are respectively wrapped by the oil phase and the water phase, so that they are gradually released and react after entering the formation, reducing the amount of acid reaction in the near-wellbore area, and etching the formation only after entering the high-temperature formation for a period of time, thereby improving the acid etching seam length of the acid under high-temperature conditions.

[0037] Lin Tao et al.'s "Large-Scale Composite Acid Fracturing Method for Fracture-Vuggy Carbonate Reservoirs" (CN102022105A) invented a large-scale composite acid fracturing method for fracture-vuggy carbonate reservoirs, comprising the following steps: 1) injecting slick water into the formation through tubing or oil-casing mixed injection, 2) adding powdered pottery into the formation through tubing, 3) injecting acid into the formation through tubing for the first time, 4) injecting acid into the formation through tubing for the second time, and 5) injecting excess displacement fluid into the formation through tubing or oil-casing mixed injection; wherein, the large-scale composite acid fracturing method refers to a process in which the total construction liquid volume is 2000m 3 This invention increases the length of artificial fractures created by acid fracturing to more than 140m, solving the problem that conventional acid fracturing technology in fracture-cavity carbonate reservoirs within 200m of the wellbore cannot reach the reservoir far from the wellbore, and new fracture-cavity reservoirs need to be found through side drilling.

[0038] After comprehensive analysis, the inventor believes that the composite acid fracturing process is currently generally used for ultra-deep and ultra-high temperature carbonate reservoirs, with the main purpose of increasing the length of acid-etched cracks. Different types of technical means are used, among which large-volume pumping of low-viscosity slippery water-type pre-fluids to reduce the temperature in the artificial cracks near the wellbore, and then pumping different acid systems are mainly used. After a large amount of pre-fluid enters the formation, the temperature at the bottom of the well and in the cracks near the wellbore can be reduced by 30-50%. Later, high-temperature resistant acid is pumped in. The acid-rock reaction is slower in the low-temperature area of ​​the artificial cracks near the wellbore, which increases the distance of the acid-etched cracks to a certain extent. Some other scholars have studied that by encapsulating the acid (liquid phase or solid phase), the acid system is released at a higher temperature after entering the deep part of the reservoir, and the distance of the acid-etched cracks can be increased.

[0039] At the same time, some scholars have studied the composite reforming process of gelled acid, cross-linked acid, and autogenous acid, using a multi-stage injection method to increase the distance of acid-etched cracks. After analyzing the existing process methods for increasing the distance of acid-etched cracks in ultra-high temperature carbonate reservoirs, the inventors found that the process of large-scale pumping of pre-fluid has limited ability to reduce reservoir temperature. The cooling range is limited to the area adjacent to the wellbore. Deep in the wellbore reservoir, the temperature in the fracture quickly rises to the reservoir temperature, the degree of improvement in the distance of acid-etched cracks is limited, and a large amount of ineffective pre-fluid is wasted. The technology of composite acid fracturing reformation using liquid and solid-phase wrapped acid is complex and costly. In ultra-high temperature and ultra-high stress reservoirs, the wrapped shell is easily damaged, and the acid is released prematurely, making it difficult to penetrate deep into the reservoir. The effect of improving acid fracturing reformation is general and the cost-effectiveness is low. The composite reforming technology of different types of acid systems is difficult to significantly increase the distance of acid-etched cracks because gelled acid, cross-linked acid, and autogenous acid are resistant to temperature differences and the concentration of autogenous acid is low. Comprehensive analysis shows that existing technologies are difficult to meet the goal of ultra-deep, ultra-high temperature, ultra-high stress carbonate reservoir transformation at ultra-deep depths. It is necessary to develop a process technology method that is easy to operate, easy to configure on site, easy to pump, and low-cost, so as to significantly increase the distance between acid-etched fractures in ultra-high temperature carbonate reservoirs and connect ultra-deep reservoirs.

[0040] In view of the above problems, the present invention is proposed to provide an ultra-high temperature carbonate reservoir acid fracturing process and mining method that overcomes the above problems or at least partially solves the above problems.

[0041] An embodiment of the present invention provides an acid fracturing process method for ultra-high temperature carbonate reservoirs, which may include: creating fractures with ultra-high temperature resistant gel fracturing fluid, and acid etching the artificial fractures after cooling with a medium-low temperature autogenous acid system; creating fractures again with more ultra-high temperature resistant gel fracturing fluid, and acid etching the subsequently formed artificial fractures with an ultra-high temperature resistant autogenous acid system.

[0042] The reservoir temperature of the ultra-high temperature carbonate reservoir transformed in the embodiment of the present invention is approximately 185°C. To address the problem of conventional acid fracturing and acid etching fractures being short and limited in scope, making it difficult to achieve the transformation and production increase target, the inventors designed a design using different types of fracturing fluids and acids. In specific implementation, the ultra-high temperature gel-resistant fracturing fluid has a temperature resistance of no less than 180°C, and the shear rheology test of the ultra-high temperature gel-resistant fracturing fluid meets the requirement that the viscosity remains at 150mPa·s±5mPa·s after 120 minutes. The acid generation temperature of the medium-low temperature autogenous acid system starts at 90°C, and its main acid generation temperature range is 120°C±5°C. The acid generation temperature of the ultra-high temperature autogenous acid system starts at 120°C, and its main acid generation temperature range is 160°C±5°C.

[0043] The ultrahigh-temperature carbonate reservoir acid fracturing process provided in the embodiments of the present invention is based on the fracture-forming capabilities and fracture-forming characteristics of different types of fluids. First, ultrahigh-temperature gel-resistant fracturing fluid is used to create fractures, thereby forming artificial fractures near the wellbore. Second, a medium- and low-temperature autogenous acid system is used to generate a certain concentration of acid within the cooled artificial fractures, which is then acid-etched by the artificial fractures formed by the ultrahigh-temperature gel-resistant fracturing fluid. Third, a larger volume of ultrahigh-temperature gel-resistant fracturing fluid is pumped at a high displacement to create fractures again, thereby forming new artificial fractures in the far wellbore. Fourth, an ultrahigh-temperature autogenous acid system is again pumped in to acid-etch the artificial fractures formed by the second ultrahigh-temperature gel-resistant fracturing fluid. During this process, fracturing fluid without a crosslinking agent can be pumped in to displace the autogenous acid and ultrahigh-temperature gel-resistant fracturing fluid previously injected, allowing it to enter the deeper reservoir and acid-etch deeper reservoirs to form artificial fractures with higher conductivity. This process initially utilizes ultra-high-temperature-resistant gel fracturing fluid. Acid generated by a medium- and low-temperature autogenous acid system then etches artificial fractures near the wellbore. The acid generated by the ultra-high-temperature autogenous acid system then etches deeper reservoirs further from the wellbore. This results in acid etching of both artificial fractures near and far from the wellbore, resulting in higher conductivity in the artificial fractures. This process significantly increases the length of artificial fractures and effectively transforms their volume, providing technical support for high and stable production from individual wells.

[0044] In an alternative embodiment, referring to Figure 1 As shown, the above-mentioned ultrahigh temperature carbonate reservoir acid fracturing process may include the following steps:

[0045] Step S10: Based on the fracturing simulation results of the target well by the fracturing simulation software, the amount of the ultra-high temperature resistant gel fracturing fluid for the first fracture creation is determined.

[0046] In this step, the target well is first subjected to a fracturing simulation test using fracturing simulation software. The dosage of fracturing fluid is determined by referring to the simulation calculation results of the fracturing simulation software. For example, if an artificial fracture of about 100m is required, the optimized dosage of ultra-high temperature resistant gel fracturing fluid is 120m 3 .

[0047] Step S11: pumping ultra-high temperature resistant gel fracturing fluid in a pressure-limited but unlimited displacement manner to perform initial fracture creation in the reservoir around the wellbore of the target well and form artificial fractures.

[0048] The first step in the renovation construction design is to pump ultra-high temperature resistant gel fracturing fluid. During the specific implementation, the ultra-high temperature resistant gel fracturing fluid is pumped at the maximum displacement in a pressure-limited but unlimited displacement manner to create high-intensity fractures in the reservoir, thereby forming artificial fractures with maximum capacity.

[0049] Step S12: pumping a medium-low temperature autogenous acid system to generate acid in the artificial cracks and perform acid etching on the artificial cracks.

[0050] After fracturing with the ultra-high-temperature gel-resistant fracturing fluid in step S11, the reservoir temperature near the wellbore decreases to 90-120°C. In step S12, the artificial fractures are acid-etched using a designed medium-low temperature autogenous acid system. The system's initial acid generation temperature in this step is 90°C, with a primary acid generation temperature range of 120°C ± 5°C.

[0051] The medium-low temperature autogenous acid system slowly generates acid in the artificial fractures formed by the ultrahigh temperature resistant gel fracturing fluid in step S11, thereby fully etching the artificial fractures. It should be noted that the amount of medium-low temperature autogenous acid system pumped in this step needs to be greater than the amount of ultrahigh temperature resistant gel fracturing fluid pumped in step S11. This is to account for fluid loss within the fractures and to enhance the acid etching and fracture-forming capabilities. In the specific implementation of this embodiment, the amount of medium-low temperature autogenous acid system used is 150% of the amount of ultrahigh temperature resistant gel fracturing fluid pumped in step S11.

[0052] Step S13: After stopping the pump for a first preset time, pumping in ultrahigh temperature resistant gel fracturing fluid for secondary fracture creation; wherein the amount of ultrahigh temperature resistant gel fracturing fluid pumped in the secondary fracture creation is not less than twice the amount of ultrahigh temperature resistant gel fracturing fluid pumped in the first fracture creation.

[0053] In this step, the pump is stopped for the first preset time to leave enough time for the autogenous acid generation and acid-etched cracks, and then the ultra-high temperature resistant gel fracturing fluid is continued to be pumped. In the specific implementation, the above-mentioned first preset time can be 30 minutes. In this step, the purpose of pumping the ultra-high temperature resistant gel fracturing fluid again is to promote the artificial cracks to continue to extend to the depths of the reservoir along the cracks etched by acid in step S12. When designing this stage in this step, the maximum displacement is used for construction, and the pumping fluid volume is more than 2 times the amount of fracturing fluid pumped for the first time, so as to ensure that the artificial cracks are fully extended to more than 150m. The ultra-high temperature resistant gel fracturing fluid pumped this time is partly used for liquid loss in the cracks, and the other part is used to make new cracks, thereby achieving the purpose of making new cracks and long cracks.

[0054] Step S14: pumping an ultra-high temperature resistant autogenous acid system to generate acid and perform acid etching in the artificial cracks formed by the secondary cracking; wherein the amount of the ultra-high temperature resistant autogenous acid system is not less than 2.5 times the amount of the ultra-high temperature resistant gel fracturing fluid pumped for the first cracking.

[0055] In this step, the ultrahigh-temperature autogenous acid system is pumped at maximum flow rate, with the pumped volume being at least 2.5 times the amount of ultrahigh-temperature resistant gel fracturing fluid used for fracture formation determined in step S10. The acid from the ultrahigh-temperature autogenous acid system is used to etch the new artificial fractures formed in step S13. This step utilizes the fact that high-temperature autogenous acid does not produce acid in medium- and low-temperature environments. This composite pumping process allows the high-temperature autogenous acid system to penetrate deeper into the reservoir, significantly increasing the distance to the acid-etched fractures and enhancing the acid fracturing effect.

[0056] In another optional embodiment, also referring to Figure 1 As shown, after the ultrahigh temperature resistant autogenous acid system is pumped in step S14, the following steps may also be included:

[0057] Step S15: pumping gel-carrying fluid to support the artificial fracture near the wellbore, shutting in the well for a second preset time, and then controlling the pressure at the wellhead to release the fluid.

[0058] The main purpose of pumping the gel-carrying fluid in this step is to support the artificial fracture near the wellbore. After the well is shut in for the second preset time, the wellhead is pressure-controlled and sprayed to complete the acid fracturing process. In this embodiment, the second preset time can be 4 hours. More specifically, the proppant in the gel-carrying fluid pumped in this step is ceramsite, and the amount of sand added is 3m 3 This step uses high-strength ceramsite to support the near-wellbore, ensuring strong communication between the wellbore and the deep artificial fractures.

[0059] In another optional embodiment, also referring to Figure 1 As shown, after pumping the ultrahigh-temperature-resistant autogenous acid system in step S14, the following steps may be further included: Step S16: Repeatedly pumping the ultrahigh-temperature-resistant gel fracturing fluid and the ultrahigh-temperature-resistant autogenous acid system to extend the acid-etched fracture to a preset range in the far-well zone of the target well. This step is performed before determining whether the preset target range in the far-well zone has been reached. Steps S13 and S14 may be repeated to further extend the fracture and acid-etch it deeper into the reservoir.

[0060] In another optional embodiment, also referring to Figure 1 As shown, after the medium-low temperature autogenous acid system is pumped in step S12, the following steps may be further included: step S17, pumping the fracturing fluid base fluid to push the medium-low temperature autogenous acid system in the wellbore into the interior of the carbonate reservoir.

[0061] This step is to use the fracturing fluid base fluid (fracturing fluid without cross-linking agent). The main purpose is to push all the liquid in the wellbore that has not produced acid into the reservoir to avoid the formation of an acid system in the wellbore.

[0062] In a specific example, the ultra-deep well LT3 in a western oil field is used as an example to illustrate the specific embodiments of the present invention. The well is a vertical well with a stimulation section of 8500m vertical depth and 10m thickness. Pre-pressure assessment shows that the reservoir is dolomitic carbonate rock with a relatively dense matrix, a porosity of less than 5%, and an average permeability of 0.5×10 -3 μm 2 However, the cracks are not developed and the effectiveness of the cracks is poor. Based on the reservoir assessment, it is believed that the well needs to implement large-scale reservoir transformation, expand the transformation volume, and connect the deep reservoir to obtain economically effective production. However, the reservoir temperature of the well reaches 185°C, the conventional acid fracturing and acid etching crack distance is short, and the transformation range is small, making it difficult to achieve the transformation and production increase target. It is necessary to implement the acid fracturing process method provided in the embodiment of the present invention for transformation. Figure 2 The reconstruction construction curve diagram shown and Figure 3 The final effective artificial fracture morphology shown in FIG. 1 is shown. The above-mentioned acid fracturing process in this embodiment includes the following steps:

[0063] Step 10: Use the fracturing simulation software to conduct a fracturing simulation test on the target well. Determine the amount of fracturing fluid based on the simulation results of the fracturing simulation software. According to the simulation calculation of the fracturing software, an artificial fracture of about 100m needs to be formed, and the optimized amount of gel pre-fluid is 120m. 3 At the same time, this step also requires the design of a fracturing fluid. This embodiment uses a high-temperature resistant gel fracturing fluid with a temperature resistance of up to 180°C. After a 120-minute shear rheological test, the viscosity remains at around 150 MPa·s (150 MPa·s±5 MPa·s in this embodiment). This fracturing fluid has a strong high-temperature fracture-forming capability.

[0064] Step 11: This step uses the method of limiting pressure but not limiting displacement to pump the ultra-high temperature resistant gel fracturing fluid. During construction, the displacement is based on the wellhead pressure limit of 120 MPa. The reservoir is transformed and constructed at the maximum displacement. Generally, the displacement should reach 4m 3 / min or more, in specific implementation, 100m 3 / m strength is used as the standard for high-strength seam creation.

[0065] Step 12. The main purpose of this step is to use the acid generated by the medium-low temperature autogenous acid system to acid-etch the artificial cracks formed in step 11. The autogenous acid system selected in this step starts to generate acid after 90°C, and the main acid generation temperature range is about 120°C. The maximum acid generation concentration is about 16% gelled acid concentration. Based on the temperature field simulation of the well transformation process, when the construction displacement reaches 4m3 / min, the bottom hole temperature drops to about 90°C, and the temperature of the reservoir about 75m away from the bottom of the well is about 130°C. Therefore, using the above-mentioned autogenous acid system, the optimized pumping volume is 150m 3During the construction process, acid generation begins after the acid-generating reforming fluid reaches the bottom of the well. When the liquid reaches 75m into the fracture, the acid generation efficiency reaches the best, and the acid concentration can reach 16% in about 30 minutes. At the same time, as the construction continues, the subsequent liquid pushes the generated high-concentration acid system into deeper reservoirs, and the acid etching distance can be increased to more than 100m.

[0066] Step 13: After completing step 12 above, replace a wellbore 55m 3 The main purpose of the fracturing fluid base fluid (fracturing fluid without a crosslinker) is to push all the liquid in the wellbore that has not produced acid into the reservoir, preventing the formation of an acid system in the wellbore. The pump is then stopped for about 30 minutes. The main purpose is to allow the autogenous acid reforming fluid system entering the reservoir to fully produce the acid system and etch the artificial fractures. The artificial fractures formed in steps 11 and 12 (about 120m) are fully etched, forming high-conductivity artificial fractures.

[0067] Step 14: After stopping the pump for 30 minutes, start pumping the same ultra-high temperature resistant gel fracturing fluid as in step 10 at a maximum displacement of 120 MPa. According to the simulation calculation, the total pumping volume is 240 m3. 3 The scale of gel fracturing fluid can extend the artificial fracture to about 180m.

[0068] Step 15. The main purpose of this step is to pump the ultra-high temperature resistant autogenous acid system into the artificial fractures formed in step 14, and generate the main acid system under the condition of near reservoir temperature to etch the artificial fractures formed in step 14. The ultra-high temperature resistant autogenous acid system selected in this step starts to generate acid at a temperature of 120°C. Before 120°C, it is a reformed liquid system without acid etching ability. About 160°C is the main acid generation temperature of the system. The acid concentration can reach 18% gelled acid concentration in 30 minutes, which has a strong etching ability on the artificial fractures of carbonate reservoirs. The optimized autogenous acid dosage in this step is 300m 3 The pumping rate is the maximum operating rate at a pressure limit of 120 MPa. Based on simulations of acid generation efficiency and artificial fracture expansion, this self-generated acid system primarily etches artificial fractures within 120 to 200 meters from the well bottom, resulting in high conductivity for all artificial fractures within 200 meters of the wellbore formed through this modification.

[0069] Step 16: The main purpose of this step is to use gel to carry sand, completely displacing the autogenous acid system in the wellbore into the reservoir, and at the same time using ceramsite to support the artificial fracture within 50m from the bottom of the well. The reservoir thickness of the well transformation section is 10m. According to the design requirements of the embodiment of the present invention, the total sand addition volume is designed to be 30m 3This will ensure that the artificial fractures about 50m near the wellbore are fully supported. Together with the etching of the autogenous acid in the early stage, artificial fractures with higher conductivity are formed, thereby reducing the energy consumption of oil and gas flow near the wellbore and improving the transformation effect. The selected gel-carrying sand fluid is the same as the high-temperature resistant gel fracturing fluid used in step 10. The construction displacement is designed to be the highest displacement under the pressure limit of 120MPa. According to simulation analysis, the sand concentration is 150kg / m 3 , which can effectively support the artificial cracks. The total amount of gel liquid is designed to be 350m 3 After this step, the well is shut in for approximately four hours to allow the autogenous acid system pumped in during the previous step to fully generate acid, allowing sufficient time for the acid-rock reaction to fully etch the artificial fractures. The resulting artificial fractures are primarily supporting fractures near the wellbore and primarily etched fractures in the distal zone. The effective artificial fracture length can reach over 200 meters. Compared to conventional acid fracturing, the effective fracture length is increased by more than three times, significantly increasing the effective stimulation volume.

[0070] The ultra-high temperature carbonate reservoir acid fracturing process provided in the embodiment of the present invention is a composite transformation process method combining ultra-deep and ultra-high temperature carbonate rock acid fracturing, sand fracturing and different temperature-resistant series autogenous acids. The method is based on the temperature field changes at the bottom of the well and in the artificial fractures during the transformation process, and adopts a transformation fluid system adapted to the temperature gradient. The near-wellbore mainly uses ultra-high temperature resistant gel to carry sand to form a high-conductivity artificial support fracture. The range of 50 to 120m mainly uses the medium and low temperature autogenous acid system to generate acid to form etched fractures. The far-well zone range of 120 to 200m mainly uses the ultra-high temperature resistant autogenous acid system to generate high-concentration acid to form etched fractures. Compared with the conventional acid fracturing composite transformation process method, the process method of the invention increases the length of the acid-etched fracture by 2 to 3 times and the transformation volume by more than 5 times, which significantly expands the effective transformation volume and improves the transformation effect. Combined with Figure 3 As shown in the figure, the acid fracturing process can transform the reservoir into a mixed zone of acid erosion and propped fractures (near the wellbore) and an effective acid erosion fracture zone (far from the wellbore). The application well LG3 has a daily oil production of 85m after transformation. 3 , with a daily gas production of 570,000 cubic meters, a 6.5-fold increase in open-flow rate compared to before the transformation. The method of the present invention has been widely applied in the transformation of ultra-deep, ultra-high-temperature (>160°C) carbonate reservoirs at depths of 7,500 meters or more. Through rigorous testing of multiple wells, the process achieved a 100% success rate, increasing the average open-flow rate of the transformed wells by 5.1 times, with the average open-flow rate per well reaching 3.2 million cubic meters of natural gas per day. This technical invention has important reference significance for improving the transformation effect of ultra-deep, ultra-high-temperature carbonate reservoirs.

[0071] Based on the same inventive concept, embodiments of the present invention also provide a method for exploiting ultrahigh-temperature carbonate reservoirs. This method may include: transforming the carbonate reservoir using the aforementioned ultrahigh-temperature carbonate reservoir acid fracturing process. This method may combine fracturing with production and drainage processes to maximize oil and gas recovery.

[0072] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for acid fracturing an ultra-high temperature carbonate reservoir, characterized in that: include: Use ultra-high temperature resistant gel fracturing fluid to create fractures, and use medium-low temperature autogenous acid system to acid etch the artificial fractures after cooling; More ultra-high temperature resistant gel fracturing fluid is used to create fractures again, and the subsequently formed artificial fractures are acid-etched with an ultra-high temperature resistant autogenous acid system.

2. The method according to claim 1, characterized in that Specifically include: Pumping ultra-high temperature resistant gel fracturing fluid in a pressure-limited but unlimited displacement manner to create the first fractures in the reservoir near the wellbore of the target well and form artificial fractures; pumping a medium-low temperature autogenous acid system so that the medium-low temperature autogenous acid system generates acid in the artificial fracture and performs acid etching on the artificial fracture; After stopping the pump for a first preset time, pumping in ultra-high temperature resistant gel fracturing fluid for secondary fracture creation; wherein the amount of the ultra-high temperature resistant gel fracturing fluid pumped in the secondary fracture creation is not less than twice the amount of the ultra-high temperature resistant gel fracturing fluid pumped in the first fracture creation; Pumping an ultrahigh temperature resistant autogenous acid system so that the ultrahigh temperature resistant autogenous acid system generates acid and performs acid etching in the artificial cracks formed by the secondary cracking; wherein the amount of the ultrahigh temperature resistant autogenous acid system is not less than 2.5 times the amount of the ultrahigh temperature resistant gel fracturing fluid pumped for the first cracking.

3. The method according to claim 2, characterized in that After pumping the ultra-high temperature resistant autogenous acid system, it also includes: The pump injects gel-carrying sand fluid to support the artificial fracture near the wellbore, and after shutting in the well for the second preset time, the wellhead is pressure-controlled and released.

4. The method according to claim 3, characterized in that The proppant in the pumped gel sand-carrying fluid is ceramsite, and the amount of sand added is 3m 3 / m.

5. The method according to claim 2, characterized in that After pumping the ultrahigh temperature resistant autogenous acid system, the method further includes: repeatedly pumping the ultrahigh temperature resistant gel fracturing fluid and the ultrahigh temperature resistant autogenous acid system to allow the acid-etched fractures to reach a preset range of the far well zone of the target well.

6. The method according to claim 2, characterized in that After the medium-low temperature autogenous acid system is pumped in, the fracturing fluid base fluid is pumped in to push the medium-low temperature autogenous acid system in the wellbore into the interior of the carbonate reservoir.

7. The method according to any one of claims 2 to 6, characterized in that Before pumping the ultra-high temperature resistant gel fracturing fluid, the following steps are also required: Based on the fracturing simulation results of the target well using the fracturing simulation software, the dosage of the ultra-high temperature resistant gel fracturing fluid for the first fracture creation is determined.

8. The method according to any one of claims 1 to 6, characterized in that The temperature resistance of the ultra-high temperature resistant gel fracturing fluid is not less than 180° C., and the shear rheology test of the ultra-high temperature resistant gel fracturing fluid satisfies the requirement that the viscosity remains at 150 MPa·s±5 MPa·s after 120 minutes.

9. The method according to any one of claims 1 to 6, characterized in that The medium-low temperature autogenous acidification system starts acidification at 90°C, and its main acidification temperature range is 120°C ± 5°C; The ultra-high temperature resistant autogenous acid generating system has an acid generating temperature starting at 120°C, and a main acid generating temperature range of 160°C±5°C.

10. A method for mining ultrahigh temperature carbonate reservoirs, characterized in that: include: The ultrahigh temperature carbonate reservoir acid fracturing process according to any one of claims 1 to 9 is used to transform the carbonate reservoir.

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