Deep acid fracturing and sand fracturing composite transformation method for carbonate reservoir

Abstract

The invention belongs to the technical field of oil and gas reservoir transformation, and particularly relates to a deep acid fracturing and sand fracturing composite transformation method for a carbonate reservoir. The method mainly comprises the following steps: (1) a pre-acid pre-fracturing stage; (2) a sand fracturing main fracture forming and secondary sand carrying stage; (3) a multistage combined acid deep acid fracturing and alternative sand conveying stage; (4) a sand fracturing secondary fracture forming and main sand carrying stage; and (5) a displacing liquid displacing stage. The method can be widely applied to carbonate reservoir transformation, the advantages of deep acid fracturing and sand fracturing are integrated, the fracture volume of the carbonate reservoir is increased, a multi-section and multi-stage sand feeding mode is adopted for replacing sand feeding, and the flow conductivity of the acid etching-supporting composite fracture net is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas reservoir stimulation technology, specifically relating to a method for deep acid fracturing and sand fracturing combined stimulation of carbonate reservoirs. Background Technology

[0002] Carbonate reservoirs both domestically and internationally are rich in oil and gas resources. In my country, considerable oil and gas resources have been discovered in carbonate strata in the Ordos Basin, Sichuan Basin, and Tarim Basin. Carbonate reservoirs generally exhibit strong heterogeneity and complex pore-fracture systems, making reservoir stimulation a crucial means to achieve high and stable production in carbonate gas reservoirs.

[0003] Domestic and international methods for stimulating carbonate reservoirs mainly include: ① matrix acidizing, which involves dissolving near-wellbore carbonate rocks with acid to create fractures with conductivity; ② acid fracturing / deep acid fracturing, which involves creating fractures with acid and unevenly etching the fractures to form acid-etched fracture channels, such as pre-fracturing fluid fracturing technology, multi-stage injection fracturing technology, solid acid fracturing technology, closed acidizing technology, and volumetric acid fracturing technology; ③ cross-linked acid-proppant fracturing, which combines acid-etched fractures from acid fracturing with proppant fracturing to form an acid-etched-proppant composite fracture network with higher conductivity; ④ proppant fracturing, which involves creating fractures with non-reactive fluids and filling them with proppant to form conductivity channels.

[0004] Acid fracturing of carbonate reservoirs offers advantages such as better communication of disconnected pores and natural fractures, and a high success rate. However, it also has disadvantages including uniform etching of high-ash carbonate rocks, deterioration of rock properties due to acid-rock reactions, rapid acid-rock reaction rates caused by high reservoir temperatures, and significant acid loss. Propaned fracturing, on the other hand, provides more durable and effective conductivity than acid fracturing, but it also suffers from drawbacks such as high fracturing pressure in carbonate reservoirs, greater construction difficulty, difficulty in communicating disconnected pores and natural fractures, and challenges in residual acid flowback. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of excessively fast reaction rates and severe acid loss caused by acid-rock reaction in existing carbonate reservoir stimulation methods, as well as the high fracturing pressure, high construction difficulty, difficulty in communicating non-connected pores and natural fractures, and difficulty in residual acid backflow caused by sand fracturing. Therefore, this invention combines the advantages of acid fracturing and sand fracturing in carbonate reservoirs to provide a composite stimulation method for deep acid fracturing and sand fracturing in carbonate reservoirs, in order to better solve the problems of carbonate reservoir stimulation.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for deep acid fracturing combined with proppant fracturing in carbonate reservoirs includes the following steps: S1: Pretreatment of carbonate reservoirs using pre-acid; S2: Low-viscosity fracturing fluid is used to create fractures in the pretreated carbonate reservoir, and a multi-stage, multi-segment sand-carrying method is used to obtain a composite fracture network system. S3: Multi-stage combined acid deep fracturing and replacement sand delivery are performed on the composite fracture network system to deeply dissolve the carbonate rock reservoir and obtain the acid-etched composite fracture network system. S4: High-viscosity fracturing fluid is used to create fractures in the acid-etched composite fracture network system, and a multi-stage, multi-segment sand-carrying method is used to obtain the acid-etched-supported composite fracture network system. S5: Replace the high-viscosity fracturing fluid with a displacement fluid to complete the fracturing operation.

[0007] The pre-acid in S1 is a single-phase acid, and the mass fractions of its components are as follows: hydrochloric acid (HCl) 20%–25%, retarder 2.0%–3.0%, drag reducer 0.1%–0.2%, discharge aid 0.3%–0.5%, corrosion inhibitor 1.5%–2.0%, iron ion stabilizer 0.5%–1.0%, and the remainder is water, with a discharge rate of 2.0–4.0 m³. 3 / min.

[0008] The specific implementation method in S2 is as follows: low-viscosity fracturing fluid is injected into carbonate reservoirs at a large volume to form main fractures, branch fractures and micro fractures. A multi-stage and multi-level proppant addition method is adopted. High-viscosity fracturing fluid is used at a large volume to first carry small-diameter proppant and then medium-diameter proppant to partially fill and seal micro fractures and branch fractures, thus obtaining a composite fracture network system. The high-viscosity fracturing fluid is a guar gum fracturing fluid with a viscosity greater than 30 mPa·s, and the low-viscosity fracturing fluid is slickwater with a viscosity of 3 to 5 mPa·s. The range of the high-volume injection is 8-10m. 3 / min; The small-particle-size proppant is 70-140 mesh ceramsite or quartz sand; the medium-particle-size proppant is 40-70 mesh ceramsite or quartz sand. The semi-filling refers to the proppant volume accounting for approximately 30-50% of the total crack volume.

[0009] In the multi-segment, multi-stage sand addition method, "multi-segment" refers to the use of 70-140 mesh quartz sand in the main fracture segment and 40-70 mesh quartz sand in the branch fracture segment. "Multi-stage" refers to the use of 2-4 stages of sand addition in each segment for layered injection.

[0010] The specific implementation of S3 is as follows: a multi-stage injection method of clean self-directing acid and hydrochloric acid is adopted to achieve deep dissolution of carbonate rock reservoirs, form acid etch holes, increase the width and length of dissolution fractures, and obtain an acid etch composite fracture network system.

[0011] The mass fractions of each component of the clean self-turning acid are as follows: 20% hydrochloric acid (HCl), 1.2%–1.5% surfactant thickener, 1.0% iron ion stabilizer, 1.5%–2.0% high-temperature corrosion inhibitor, 2.5% high-temperature corrosion inhibitor, and the remainder is water.

[0012] In S3, the number of injection stages is 4 to 6, and the injection displacement is 4.0 to 6.0 m³. 3 / min, wherein the hydrochloric acid is 20% to 25% hydrochloric acid.

[0013] The specific implementation of S4 is as follows: a high-viscosity fracturing fluid is injected into the acid-etched composite fracture network system in a large volume to send the quartz sand pumped in S2 to the depth of the fracture; a multi-stage sand addition method is adopted to use the high-viscosity fracturing fluid to first carry medium-sized proppant and then carry coarse-sized proppant to completely fill the acid-etched composite fracture network system, thus obtaining the acid-etched-proppant composite fracture network system. The high-viscosity fracturing fluid in S4 is a guar gum fracturing fluid with a viscosity greater than 30 mPa·s; The range of high-volume injection in S4 is 8-10m. 3 / min; The coarse-grained proppant in S4 is 20-40 mesh ceramsite or quartz sand; The medium-sized proppant in S4 is 40-70 mesh ceramsite or quartz sand.

[0014] In the multi-segment, multi-stage sand addition method in S4, the multi-segment refers to the main fracture segment using 40-70 mesh quartz sand, the branch fracture segment using 20-40 mesh quartz sand, and the multi-stage refers to the layered injection of sand in each segment using 2-4 stages of sand addition.

[0015] The displacement fluid in S5 is a low-viscosity slickwater with a viscosity of 3-5 mPa·s.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for deep acid fracturing and proppant fracturing composite stimulation of carbonate reservoirs, specifically including the following steps: (1) Pre-fracturing stage of pre-acid, pre-acid is used to pre-treat the carbonate reservoir, removes near-wellbore contamination, and reduces the fracturing pressure of the carbonate reservoir; (2) Propane fracturing main fracture creation and secondary proppant carrying stage, combining the fracture creation stage and the proppant carrying stage, slowing down the acid-rock reaction rate; (3) Multi-stage combined deep acid fracturing and proppant delivery stage, the large-volume multi-stage injection of acid not only reduces the contact reaction time between the acid and the carbonate reservoir surface, reduces acid filtration loss and acid-rock reaction rate, but also carries the small- and medium-sized proppant filled in the early stage into the deep fracture; (4) Propane fracturing secondary fracture creation and main proppant carrying stage, the high-viscosity fracturing fluid carries the sand and gravel into the fracture, further deepening the fracture depth, accelerating the return of residual acid, and reducing the construction difficulty; (5) Displacement fluid replacement stage. This invention can be widely applied to carbonate reservoir stimulation. It combines the advantages of deep acid fracturing and proppant fracturing, slows down the acid-rock reaction rate, increases the fracture volume of carbonate reservoirs, and adopts a multi-stage proppant delivery mode to effectively improve the conductivity of the acid-etched-supported composite fracture network.

[0017] Furthermore, the small and medium-sized proppant filled in S2 plays a role in S3 as follows: (1) temporarily plugging the microcracks and branch cracks formed in steps S1 and S2, which helps to reduce acid filtration loss; (2) the small and medium-sized proppant filled in step S2 covers the surface of the carbonate reservoir fractures, which helps to slow down the acid-rock reaction and increase the depth of acid stimulation.

[0018] Furthermore, proppant used in semi-filling fracturing can temporarily plug microfractures and complex fracture networks, reducing acid loss. The proppant covers the reservoir fracture surface, slowing down acid-rock reactions and increasing the depth of acid stimulation. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the composite modification method of the present invention.

[0020] Figure 2 This is a schematic diagram of a carbonate reservoir fracture formed using the method described in this invention.

[0021] Figure 3 This is a schematic diagram illustrating the process of filling cracks with sand using the method described in this invention.

[0022] Figure 4 This is a schematic diagram of an acid-etched crack formed using the method described in this invention.

[0023] Figure 5 This is a schematic diagram of an acid-etched-supported composite seam mesh formed using the method described in this invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0025] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0026] The following is a further detailed description with reference to specific embodiments and accompanying drawings.

[0027] A certain basin has a carbonate reservoir buried at a depth of 3450m, with a porosity of 6.4% and a matrix permeability of 0.72%. This invention can be used for hydraulic fracturing operations.

[0028] like Figure 1 As shown, a method for deep acid fracturing combined with proppant fracturing in carbonate reservoirs includes the following steps: S1: In the pre-fracturing stage using pre-acid, the pre-acid discharge rate is 2.0–4.0 m³ / h. 3 Acid fracturing is performed at a rate of / min to pretreat carbonate reservoirs; S2: As Figures 2-3 As shown, the primary and secondary stages of fracturing with proppant include fracture creation and proppant transport. This stage mainly involves fracture creation followed by proppant transport using low-viscosity fracturing fluid, applied over a period of 8–10 meters. 3 A high-volume injection of fracturing fluid per minute into carbonate reservoirs creates main fractures, branch fractures, and micro fractures, connecting reservoirs at the far end of the well. The simulated main fracture length reaches 130–150 m. A multi-stage proppant injection method is adopted, using high-viscosity fracturing fluid at a high volume to first carry 70–140 mesh small-particle proppant, and then carry 40–70 mesh medium-particle proppant to partially fill and seal micro fractures and branch fractures, resulting in a composite fracture network system. S3: As Figure 4As shown, in the multi-stage combined acid deep acid fracturing and successive sand delivery stages, a multi-stage injection method of clean self-directing acid and hydrochloric acid is adopted to achieve deep dissolution of carbonate reservoirs, form acid pores, increase the width and length of dissolution fractures, and obtain an acid-etched composite fracture network system. S4: As Figure 5 As shown, the secondary fracture creation and main proppant carrying stages of sand fracturing are mainly for filling fractures, which will generate fractures during the filling process. High-viscosity fracturing fluid is injected into the acid-etched composite fracture network system at a large flow rate to send the quartz sand pumped in S2 to the depth of the fracture. A multi-stage sand addition method is adopted, using high-viscosity fracturing fluid at a large flow rate to first carry medium-sized proppant and then coarse-sized proppant to completely fill the acid-etched composite fracture network system, thus obtaining the acid-etched-proppant composite fracture network system. S5: Replace the high-viscosity fracturing fluid with a displacement fluid to complete the fracturing operation.

[0029] Preferably, the small and medium-sized proppant filled in step S2 plays a role in step S3 as follows: (1) temporarily plugging the microcracks and branch cracks formed in steps S1 and S2, which helps to reduce acid filtration loss; (2) the small and medium-sized proppant filled in step S2 covers the surface of the carbonate reservoir fractures, which helps to slow down the acid-rock reaction and increase the depth of acid stimulation.

[0030] Example 1: S1: Use single-phase acid 40m 3 Acid pre-fracturing was carried out with a displacement of 3.0 m³ / min to reduce the fracturing pressure of the carbonate reservoir and eliminate near-wellbore contamination.

[0031] S2: (1) Main crack formation stage: using 5mPa·s slickwater, with a large discharge of 8m³ / min to form the main crack, branch cracks and micro cracks, with a liquid volume of 220m 3 It connects to the reservoir at the far end of the well, and the simulated main fracture length reaches 135m; (2) Secondary proppant-carrying stage: Using guar gum fracturing fluid at 50 mPa·s, a multi-stage proppant-adding method is adopted. First, 70-140 mesh quartz sand is carried into the deep fractures far from the wellbore, and then 40-70 mesh quartz sand is carried into the fractures near the wellbore end, with a displacement of 8.0 m³ / s. 3 / min. The specific operation steps for the multi-segment, multi-stage sand adding mode are as follows: (i) The first stage of adding 70-140 mesh quartz sand ①Liquid volume 26m 3 Displacement 8.0m 3 / min, quartz sand concentration is 6.7%, quartz sand quantity is 1.8m 3 ; ②Liquid volume 33m 3 Displacement 8.0m 3 / min, quartz sand concentration is 9.3%, quartz sand quantity is 3.1m 3 ; ③Liquid volume 43m 3 Displacement 8.0m 3 / min, quartz sand concentration is 11.3%, quartz sand quantity is 4.9m 3 .

[0032] ii) Second stage: 40-70 mesh quartz sand addition stage ①Liquid volume 55m 3 Displacement 8.0m 3 / min, quartz sand concentration is 6.2%, quartz sand quantity is 3.4m 3 ; ②Liquid volume 65m 3 Displacement 8.0m 3 / min, quartz sand concentration is 8.0%, quartz sand quantity is 5.2m 3 .

[0033] The total liquid volume in this stage is 422m. 3 The total sand volume is 18.4m. 3 Among them, 9.8m of 70-140 mesh quartz sand 3 8.6m of 40-70 mesh quartz sand 3 Quartz sand accounts for 30% of the total volume of the crack.

[0034] S3: A three-stage injection method using clean self-directing acid and ordinary acid with large displacement is adopted to achieve deep dissolution of carbonate reservoirs.

[0035] The mass fractions of each component in the self-converting cleaning acid are as follows: 20% hydrochloric acid (HCl), 1.5% surfactant thickener, 1.0% iron ion stabilizer, 1.5% high-temperature corrosion inhibitor, 2.5% high-temperature corrosion inhibitor, and the remainder is water; the ordinary acid is 20% hydrochloric acid (HCl).

[0036] The specific operating steps for multi-stage combined acid fracturing are as follows: ① First-stage combined acid-pressure stage Cleaning self-steering acid volume 24m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 15m 3 5.0m displacement 3 / min.

[0037] ② Second-stage combined acid-pressure stage Cleaning self-steering acid volume 32m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 24m 3 Displacement 6.0m 3 / min.

[0038] ③ Third-level combined acid-pressure stage Cleaning self-steering acid volume 36m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 30m 3 Displacement 6.0m 3 / min.

[0039] The total acid volume in this stage is 161m. 3 The volume of the self-rotating acid solution is 92m³. 3 Ordinary acid volume 69m 3 .

[0040] High-volume, multi-stage acid fracturing injection can not only reduce the contact reaction time between the acid and the reservoir surface, reduce acid filtration loss and acid-rock reaction rate, but also carry the small- and medium-sized proppant particles filled in step S2 into the depths of the fracture.

[0041] S4: (1) Secondary fracture-forming stage: Use guar gum fracturing fluid of 50 mPa·s, with a large flow rate of 8 m³ / min to form more branched fractures, and send the previously pumped quartz sand to deeper parts of the fractures, with a fluid volume of 90 m³ / min. 3 .

[0042] (2) Main sand-carrying stage: Using guar gum fracturing fluid at 50 mPa·s, a multi-stage sand-carrying method is adopted. First, 40-70 mesh quartz sand is carried into the fracture far from the wellbore end, and then 30-40 mesh quartz sand is carried into the fracture near the wellbore end, with a displacement of 8.0 m³ / s. 3 / min. The specific operation steps for the multi-segment, multi-stage sand adding mode are as follows: (i) The first stage of adding 40-70 mesh quartz sand ①Liquid volume 40m 3 Displacement 8.0m 3 / min, quartz sand concentration is 11.2%, quartz sand quantity is 4.2m 3 ; ②Liquid volume 60m 3 Displacement 8.0m 3 / min, quartz sand concentration is 14.6%, quartz sand quantity is 9.0m 3 ; (ii) Second stage: 20-40 mesh quartz sand addition stage ①Liquid volume 43m 3 Displacement 8.0m 3 / min, quartz sand concentration is 12.2%, quartz sand quantity is 5.2m 3 ; ②Liquid volume 58m 3 Displacement 8.0m 3 / min, quartz sand concentration is 16.1%, quartz sand quantity is 8.6m 3 ; ③Liquid volume 33m 3 Displacement 8.0m 3 / min, quartz sand concentration is 8.2%, quartz sand quantity is 2.3m 3 .

[0043] The total liquid volume in this stage is 324m. 3 The total sand volume is 29.3m. 3 Of which 13.2 m³ is 40-70 mesh quartz sand. 3 , 20~40 mesh quartz sand 16.1m 3 .

[0044] Step S5: A displacement process is performed using slickwater with a viscosity of 5 mPa·s, and the volume of slickwater is 24.8 m³. 3 .

[0045] Example 2: S1: Use single-phase acid 40m 3 A 2.0 m³ / min acid pre-fracturing process was carried out to reduce the fracturing pressure of the carbonate reservoir and eliminate near-wellbore contamination.

[0046] S2: (1) Main crack formation stage: using 5mPa·s slickwater, with a large discharge of 10m³ / min to form the main crack, branch cracks and micro cracks, with a liquid volume of 240m 3 It connects to the reservoir at the far end of the well, and the simulated main fracture length reaches 143m; (2) Secondary proppant-carrying stage: Using guar gum fracturing fluid at 50 mPa·s, a multi-stage proppant-adding method is adopted. First, 70-140 mesh quartz sand is carried into the deep fractures far from the wellbore, and then 40-70 mesh quartz sand is carried into the fractures near the wellbore end, with a displacement of 8.0 m³ / s. 3 / min. The specific operation steps for the multi-segment, multi-stage sand adding mode are as follows: (i) The first stage of adding 70-140 mesh quartz sand ①Liquid volume 28m 3 Displacement 8.0m 3 / min, quartz sand concentration is 6.7%, quartz sand quantity is 2.0m 3 ; ②Liquid volume 35m 3 Displacement 8.0m 3 / min, quartz sand concentration is 9.3%, quartz sand quantity is 3.3m 3 ; ③Liquid volume 45m 3 Displacement 8.0m 3 / min, quartz sand concentration is 11.3%, quartz sand quantity is 5.1m 3 .

[0047] (ii) Second stage: 40-70 mesh quartz sand addition stage ①Liquid volume 60m 3 Displacement 8.0m 3 / min, quartz sand concentration is 6.2%, quartz sand quantity is 3.8m 3 ; ②Liquid volume 70m 3 Displacement 8.0m 3 / min, quartz sand concentration is 8.0%, quartz sand quantity is 5.6m 3 .

[0048] The total liquid volume in this stage is 478m. 3 The total sand volume is 19.8m. 3 Of which 10.4 m³ is 70–140 mesh quartz sand. 3 , 40~70 mesh quartz sand 9.4m 3 Quartz sand accounts for 37% of the total volume of the cracks.

[0049] S3: A four-stage injection method using clean self-directing acid and ordinary acid with large displacement is adopted to achieve deep dissolution of carbonate reservoirs.

[0050] The mass fractions of each component in the self-converting cleaning acid are as follows: 20% hydrochloric acid (HCl), 1.5% surfactant thickener, 1.0% iron ion stabilizer, 1.5% high-temperature corrosion inhibitor, 2.5% high-temperature corrosion inhibitor, and the remainder is water; the ordinary acid is 20% hydrochloric acid (HCl).

[0051] The specific operating steps for multi-stage combined acid fracturing are as follows: ① First-stage combined acid-pressure stage Cleaning self-steering acid volume 24m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 15m 3 5.0m displacement 3 / min.

[0052] ② Second-stage combined acid-pressure stage Cleaning self-steering acid volume 32m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 24m 3 Displacement 6.0m 3 / min.

[0053] ③ Third-level combined acid-pressure stage Cleaning self-steering acid volume 36m 3 Displacement 4.0m3 / min; ordinary acid solution volume 30m 3 Displacement 6.0m 3 / min.

[0054] ④ Fourth-level combined acid-pressure stage Cleaning self-steering acid volume 16m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 10m 3 5.0m displacement 3 / min.

[0055] The total acid volume in this stage is 187m. 3 The volume of the self-rotating acid solution is 108m³. 3 Ordinary acid volume 79m 3 .

[0056] High-volume, multi-stage acid fracturing injection can not only reduce the contact reaction time between the acid and the reservoir surface, reduce acid filtration loss and acid-rock reaction rate, but also carry the small- and medium-sized proppant particles filled in step S2 into the depths of the fracture.

[0057] S4: (1) Secondary fracture-making stage: Use guar gum fracturing fluid of 50 mPa·s at a large flow rate of 10 m³ / min to create more branched fractures, and send the previously pumped quartz sand to deeper parts of the fractures. The fluid volume is 100 m³ / min. 3 .

[0058] (2) Main sand-carrying stage: Using guar gum fracturing fluid at 50 mPa·s, a multi-stage sand-carrying method is adopted. First, 40-70 mesh quartz sand is carried into the fracture far from the wellbore end, and then 30-40 mesh quartz sand is carried into the fracture near the wellbore end, with a displacement of 8.0 m³ / s. 3 / min. The specific operation steps for the multi-segment, multi-stage sand adding mode are as follows: (i) The first stage of adding 40-70 mesh quartz sand ①Liquid volume 42m 3 Displacement 8.0m 3 / min, quartz sand concentration is 11.2%, quartz sand quantity is 4.7m 3 ; ②Liquid volume 65m 3 Displacement 8.0m 3 / min, quartz sand concentration is 14.6%, quartz sand quantity is 9.5m 3 ; (ii) Second stage: 20-40 mesh quartz sand addition stage ①Liquid volume 46m 3 Displacement 8.0m 3 / min, quartz sand concentration is 12.2%, quartz sand quantity is 5.6m3 ; ②Liquid volume 62m 3 Displacement 8.0m 3 / min, quartz sand concentration is 16.1%, quartz sand quantity is 10.0m 3 ; ③Liquid volume 35m 3 Displacement 8.0m 3 / min, quartz sand concentration is 8.2%, quartz sand quantity is 2.9m 3 .

[0059] The total liquid volume in this stage is 350m. 3 The total sand volume is 32.7m. 3 Of which 14.2 m³ is 40-70 mesh quartz sand. 3 18.5m of 20-40 mesh quartz sand 3 .

[0060] Step S5: A displacement process is performed using slickwater with a viscosity of 5 mPa·s, and the volume of slickwater is 26.9 m³. 3 .

[0061] Example 3: S1: Use single-phase acid 40m 3 A 2.0 m³ / min acid pre-fracturing process was carried out to reduce the fracturing pressure of the carbonate reservoir and eliminate near-wellbore contamination.

[0062] S2: (1) Main crack formation stage: using 5mPa·s slickwater, with a large discharge of 10m³ / min to form the main crack, branch cracks and micro cracks, with a liquid volume of 260m³ / min. 3 It connects to the reservoir at the far end of the well, and the simulated main fracture length reaches 156m; (2) Secondary proppant-carrying stage: Using guar gum fracturing fluid at 50 mPa·s, a multi-stage proppant-adding method is adopted. First, 70-140 mesh quartz sand is carried into the deep fractures far from the wellbore, and then 40-70 mesh quartz sand is carried into the fractures near the wellbore end, with a displacement of 10.0 m³ / s. 3 / min. The specific operation steps for the multi-segment, multi-stage sand adding mode are as follows: (i) The first stage of adding 70-140 mesh quartz sand ①Liquid volume 30m 3 Displacement 8.0m 3 / min, quartz sand concentration is 6.7%, quartz sand quantity is 3.0m 3 ; ②Liquid volume 38m 3 Displacement 8.0m 3 / min, quartz sand concentration is 9.3%, quartz sand quantity is 3.8m 3 ; ③Liquid volume 50m 3 Displacement 8.0m 3 / min, quartz sand concentration is 11.3%, quartz sand quantity is 5.8m 3 .

[0063] (ii) Second stage: 40-70 mesh quartz sand addition stage ①Liquid volume 63m 3 Displacement 8.0m 3 / min, quartz sand concentration is 6.2%, quartz sand quantity is 4.3m 3 ; ②Liquid volume 74m 3 Displacement 8.0m 3 / min, quartz sand concentration is 8.0%, quartz sand quantity is 5.8m 3 .

[0064] The total liquid volume in this stage is 515m. 3 The total sand volume is 22.7m. 3 Of which 12.6 m³ is 70–140 mesh quartz sand. 3 , 40~70 mesh quartz sand 10.1m 3 Quartz sand accounts for 45% of the total volume of the crack.

[0065] S3: A four-stage injection method using clean self-directing acid and ordinary acid with large displacement is adopted to achieve deep dissolution of carbonate reservoirs.

[0066] The mass fractions of each component in the self-converting cleaning acid are as follows: 20% hydrochloric acid (HCl), 1.5% surfactant thickener, 1.0% iron ion stabilizer, 1.5% high-temperature corrosion inhibitor, 2.5% high-temperature corrosion inhibitor, and the remainder is water; the ordinary acid is 20% hydrochloric acid (HCl).

[0067] The specific operating steps for multi-stage combined acid fracturing are as follows: ① First-stage combined acid-pressure stage Cleaning self-steering acid volume 26m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 17m 3 5.0m displacement 3 / min.

[0068] ② Second-stage combined acid-pressure stage Cleaning self-steering acid volume 35m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 26m 3 Displacement 6.0m 3 / min.

[0069] ③ Third-level combined acid-pressure stage Cleaning self-steering acid volume 38m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 32m 3 Displacement 6.0m 3 / min.

[0070] ④ Fourth-level combined acid-pressure stage Cleaning self-steering acid volume 19m 3 Displacement 4.0m 3 / min; ordinary acid solution volume 13m 3 5.0m displacement 3 / min.

[0071] The total acid volume in this stage is 206m. 3 The volume of the self-rotating acid solution is 118m³. 3 Ordinary acid volume 88m 3 .

[0072] High-volume, multi-stage acid fracturing injection can not only reduce the contact reaction time between the acid and the reservoir surface, reduce acid filtration loss and acid-rock reaction rate, but also carry the small- and medium-sized proppant particles filled in step S2 into the depths of the fracture.

[0073] S4: (1) Secondary fracture-forming stage: Use guar gum fracturing fluid of 50 mPa·s, with a large flow rate of 10 m³ / min to form more branched fractures, and send the previously pumped quartz sand to deeper parts of the fractures, with a fluid volume of 115 m³ / min. 3 .

[0074] (2) Main sand-carrying stage: Using guar gum fracturing fluid at 50 mPa·s, a multi-stage sand-carrying method is adopted. First, 40-70 mesh quartz sand is carried into the fracture far from the wellbore end, and then 30-40 mesh quartz sand is carried into the fracture near the wellbore end, with a displacement of 9.0 m³ / s. 3 / min. The specific operation steps for the multi-segment, multi-stage sand adding mode are as follows: (i) The first stage of adding 40-70 mesh quartz sand ①Liquid volume 44m 3 Displacement 8.0m 3 / min, quartz sand concentration is 11.2%, quartz sand quantity is 5.1m 3 ; ②Liquid volume 68m 3 Displacement 8.0m 3 / min, quartz sand concentration is 14.6%, quartz sand quantity is 9.6m 3 ; (ii) Second stage: 20-40 mesh quartz sand addition stage ①Liquid volume 48m3 Displacement 8.0m 3 / min, quartz sand concentration is 12.2%, quartz sand quantity is 6.2m 3 ; ②Liquid volume 65m 3 Displacement 8.0m 3 / min, quartz sand concentration is 16.1%, quartz sand quantity is 11.2m 3 ; ③Liquid volume 37m 3 Displacement 8.0m 3 / min, quartz sand concentration is 8.2%, quartz sand quantity is 3.6m 3 .

[0075] The total liquid volume in this stage is 377m. 3 The total sand volume is 35.7m. 3 Of which 14.7 m³ is 40-70 mesh quartz sand. 3 , 20~40 mesh quartz sand 21m 3 .

[0076] Step S5: A slick of viscosity 5 mPa·s is used for the displacement process, with a slick of volume 28.1 m³. 3 .

[0077] Finally, it should be noted that while the foregoing has shown and described the basic principles, main features, and advantages of the present invention, it will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for deep acid fracturing combined with proppant fracturing to stimulate carbonate reservoirs, characterized in that, Includes the following steps: S1: Pretreatment of carbonate reservoirs using pre-acid; S2: Low-viscosity fracturing fluid is used to create fractures in the pretreated carbonate reservoir, and a multi-stage, multi-segment sand-carrying method is used to obtain a composite fracture network system. S3: Multi-stage combined acid deep fracturing and replacement sand delivery are performed on the composite fracture network system to deeply dissolve the carbonate rock reservoir and obtain the acid-etched composite fracture network system. S4: High-viscosity fracturing fluid is used to create fractures in the acid-etched composite fracture network system, and a multi-stage, multi-segment sand-carrying method is used to obtain the acid-etched-supported composite fracture network system. S5: Replace the high-viscosity fracturing fluid with a displacement fluid to complete the fracturing operation; The high-viscosity fracturing fluid is a guar gum fracturing fluid with a viscosity greater than 30 mPa·s, and the low-viscosity fracturing fluid is slickwater with a viscosity of 3 to 5 mPa·s.

2. The method for deep acid fracturing and proppant fracturing combined stimulation of carbonate reservoirs according to claim 1, characterized in that, The pre-acid in S1 is a single-phase acid, and the mass fractions of its components are as follows: hydrochloric acid (HCl) 20%–25%, retarder 2.0%–3.0%, drag reducer 0.1%–0.2%, discharge aid 0.3%–0.5%, corrosion inhibitor 1.5%–2.0%, iron ion stabilizer 0.5%–1.0%, and the remainder is water, with a discharge rate of 2.0–4.0 m³. 3 / min.

3. The method for deep acid fracturing and proppant fracturing combined stimulation of carbonate reservoirs according to claim 1, characterized in that, The specific implementation method in S2 is as follows: low-viscosity fracturing fluid is injected into carbonate reservoirs at a large volume to form main fractures, branch fractures and micro fractures. A multi-stage and multi-level proppant addition method is adopted. High-viscosity fracturing fluid is used at a large volume to first carry small-diameter proppant and then medium-diameter proppant to partially fill and seal micro fractures and branch fractures, thus obtaining a composite fracture network system. The range of the high-volume injection is 8-10m. 3 / min; The small-particle-size proppant is 70-140 mesh ceramsite or quartz sand; the medium-particle-size proppant is 40-70 mesh ceramsite or quartz sand. The semi-filling refers to the proppant volume accounting for approximately 30-50% of the total crack volume.

4. The method for deep acid fracturing and proppant fracturing combined stimulation of carbonate reservoirs according to claim 3, characterized in that, In the multi-stage sand addition method, "multi-stage" refers to adding sand with 70-140 mesh quartz sand to the fractured section far from the wellbore, and adding sand with 40-70 mesh quartz sand to the fractured section close to the wellbore. "Multi-stage" refers to injecting sand in layers using 2-4 stages of sand addition within each stage.

5. The method for deep acid fracturing and proppant fracturing combined stimulation of carbonate reservoirs according to claim 1, characterized in that, The specific implementation of S3 is as follows: a multi-stage injection method of clean self-directing acid and hydrochloric acid is adopted to achieve deep dissolution of carbonate rock reservoirs, form acid etch holes, increase the width and length of dissolution fractures, and obtain an acid etch composite fracture network system.

6. The method for deep acid fracturing and proppant fracturing combined stimulation of carbonate reservoirs according to claim 5, characterized in that, The mass fractions of each component of the clean self-turning acid are as follows: 20% hydrochloric acid (HCl), 1.2%–1.5% surfactant thickener, 1.0% iron ion stabilizer, 1.5%–2.0% high-temperature corrosion inhibitor, 2.5% high-temperature corrosion inhibitor, and the remainder is water.

7. The method for combined deep acid fracturing and proppant fracturing of carbonate reservoirs according to claim 5, characterized in that, In S3, the number of injection stages is 4 to 6, and the injection displacement is 4.0 to 6.0 m³. 3 / min, wherein the hydrochloric acid is 20% to 25% hydrochloric acid.

8. The method for deep acid fracturing and proppant fracturing combined stimulation of carbonate reservoirs according to claim 1, characterized in that, The specific implementation of S4 is as follows: a high-viscosity fracturing fluid is injected into the acid-etched composite fracture network system in a large volume to send the quartz sand pumped in S2 to the depth of the fracture; a multi-stage sand addition method is adopted to use the high-viscosity fracturing fluid to first carry medium-sized proppant and then carry coarse-sized proppant to completely fill the acid-etched composite fracture network system, thus obtaining the acid-etched-proppant composite fracture network system. The high-viscosity fracturing fluid in S4 is a guar gum fracturing fluid with a viscosity greater than 30 mPa·s; The range of high-volume injection in S4 is 8-10m. 3 / min; The coarse-grained proppant in S4 is 20-40 mesh ceramsite or quartz sand; The medium-sized proppant in S4 is 40-70 mesh ceramsite or quartz sand.

9. A method for deep acid fracturing and proppant fracturing combined with proppant fracturing of carbonate reservoirs according to claim 8, characterized in that, In the multi-segment, multi-stage sand addition method in S4, the multi-segment refers to the main fracture segment using 40-70 mesh quartz sand, the branch fracture segment using 20-40 mesh quartz sand, and the multi-stage refers to the layered injection of sand in each segment using 2-4 stages of sand addition.

10. A method for deep acid fracturing and proppant fracturing combined with proppant fracturing of carbonate reservoirs according to claim 1, characterized in that, The displacement fluid in S5 is a low-viscosity slickwater with a viscosity of 3-5 mPa·s.

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