Compact limestone reservoir atomization acid fracturing sand fracturing composite transformation method

Abstract

The invention belongs to the technical field of oil and gas field development and oil and gas reservoir transformation, and particularly relates to a compact limestone reservoir atomization acid fracturing sand fracturing composite transformation method. The method mainly comprises the following steps: (1) a supercritical atomization acid fracturing web forming stage; (2) a slug temporary plugging prepad fluid fracture forming stage; (3) a multi-particle-size proppant sand adding stage; and (4) a low-viscosity displacing fluid displacing stage. Based on the fracturing thought of'forming a net first and then forming a seam, temporarily plugging a slug and supporting a multi-scale fracture ', the fracturing fluid has the advantages of strong fluidity, strong penetrability and strong breaking lithology of supercritical carbon dioxide, acid solubility of pre-acid, lasting and effective flow conductivity of sand fracturing and the like, and can be widely applied to compact limestone reservoir transformation; and a complex acid etching-supporting composite crack system is formed, and the flow conductivity of the crack is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development and oil and gas reservoir stimulation technology, specifically relating to a composite stimulation method of tight limestone reservoirs using atomized acid fracturing and sand fracturing. Background Technology

[0002] Reservoir stimulation is an essential technique for increasing production in major oil and gas fields both domestically and internationally, and it has been widely applied in carbonate, sandstone, and shale gas reservoirs. Reservoir stimulation mainly includes three categories: hydraulic fracturing, acid fracturing, and acidizing. Hydraulic fracturing is primarily used in sandstone and shale gas reservoirs, acid fracturing in carbonate reservoirs, and acidizing in sandstone and carbonate reservoirs. With the continuous development of exploration and development, oil and gas reservoirs are becoming increasingly complex, and oil and gas prices are falling significantly, placing higher demands on the effectiveness of reservoir stimulation. Acid fracturing is an important means of increasing production in fractured and fracture-vuggy carbonate oil and gas reservoirs. It mainly utilizes acid to corrode the carbonate reservoir matrix, forming an acid-etched fracture system that connects the original fracture spaces and cavern / pore spaces within the carbonate reservoir to access oil and gas resources, and establishes fracture channels for underground oil and gas flow. Compared with conventional carbonate reservoirs, tight carbonate rocks have poorer reservoir properties, higher limestone content, more developed microfractures, and higher clay content. This results in a faster reaction rate between acid and rock, greater acid filtration, shorter distances between acid-etched fractures, blockage of fracture channels by acid-insoluble substances, lower conductivity of acid-etched fractures, and poorer production enhancement effects from acid fracturing.

[0003] Currently, tight limestone reservoirs are gradually becoming a key focus of natural gas exploration. Domestic and international methods for stimulation of tight limestone reservoirs mainly include: ① matrix acidizing; ② acid fracturing / depth acid fracturing, such as pre-fracturing fluid fracturing, multi-stage injection fracturing, solid acid fracturing, closed-loop acidizing, and volumetric acid fracturing; ③ cross-linked acid-carrying proppant fracturing; and ④ proppant fracturing. Due to the denser structure of tight limestone reservoirs, uniform surface etching, lower conductivity of acid-etched fractures, faster acid-rock reaction rates, and shorter effective acid etching distance, increasing single-well production faces greater challenges. While propped fractures created by proppant fracturing have more durable and effective conductivity than acid fracturing, they also suffer from drawbacks such as high reservoir fracturing pressure, greater construction difficulty, and difficulty in connecting non-connected pores and natural fractures. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low fracture conductivity, fast acid-rock reaction rate, and short effective acid etching distance in existing tight limestone reservoir stimulation methods. It combines the advantages of supercritical carbon dioxide's strong fluidity, strong penetration, and strong rock-breaking properties, the acid solubility of pre-concentrated acid, and the sustained and effective conductivity of proppant fracturing. Based on the fracturing concept of "first forming a network, then forming fractures, temporary plugging, and multi-scale fracture support," this invention proposes a composite stimulation method for tight limestone reservoirs using atomized acid fracturing and proppant fracturing. This invention effectively improves fracture conductivity by forming a complex acid-etching-support composite fracture system, aiming to better solve the challenges of tight limestone reservoir stimulation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing includes the following steps: S1: Supercritical atomized acid fracturing is used to form an acid etching fracture network in tight limestone reservoirs; S2: The acid-etched fracture network formed by supercritical atomized acid fracturing is temporarily plugged by medium-viscosity fracturing fluid slugs to form main fractures and branch fracture networks in tight limestone reservoirs; S3: Medium-viscosity fracturing fluid is used to carry proppant and fill the main fracture and branch fracture network to form an acid-etched-propped fracture network; S4: Replace the medium-viscosity fracturing fluid with a displacement fluid to complete the fracturing fluid application; The medium-viscosity fracturing fluid is a polymer fracturing fluid with a viscosity ≥ 60 mPa·s.

[0006] The supercritical atomizing acid in S1 is formed by the combination of pre-acid and supercritical carbon dioxide. The pre-acid injection volume is 50-100 mg / L. 3 Supercritical carbon dioxide injection is 50–150 m³. 3 The injection displacement is 2-5m³. 3 / min.

[0007] The pre-acid is a low-viscosity, slow-release acid.

[0008] The specific implementation of S2 is as follows: First, medium-viscosity fracturing fluid carries small-particle-size proppant slugs to temporarily plug the acid-etched fracture network formed by supercritical atomized acid fracturing; second, medium-viscosity fracturing fluid is used to form main fractures and branch fracture networks in tight limestone reservoirs. The small-particle-size proppant is 70-140 mesh ceramsite or quartz sand, and the amount of sand used in the slug is 5-10 mg / L. 3 ; The discharge rate of the medium-viscosity fracturing fluid is 8–12 m³. 3 / min.

[0009] The proppant carried by the medium-viscosity fracturing fluid in S3 consists of medium-sized and large-sized proppant. The medium-sized proppant is 40-70 mesh ceramsite or quartz sand; The large-particle-size proppant is 20-40 mesh ceramsite or quartz sand; The discharge rate of the medium-viscosity fracturing fluid is 8–12 m³. 3 / min.

[0010] The medium-sized proppant presses the small-sized proppant into the branched fracture network, while the large-sized proppant presses the medium-sized proppant into the depth of the fracture, forming an acid-etched-propped fracture network.

[0011] In S4, a displacement fluid is used to replace the medium-viscosity fracturing fluid, and the medium-viscosity fracturing fluid is pushed into the tight limestone reservoir.

[0012] The displacement fluid is low-viscosity slickwater with a viscosity of 5–10 mPa·s, and the displacement rate of the displacement fluid is 8–12 m³ / s. 3 / min.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a composite fracturing method for tight limestone reservoirs using atomized acid fracturing and proppant fracturing, comprising the following steps: (1) Supercritical atomized acid fracturing network formation stage, using supercritical carbon dioxide and pre-powder to form atomized acid, slowing down the acid-rock reaction rate, and forming an acid-etched fracture network in the tight limestone reservoir; (2) Slug plugging pre-powder fracturing stage, using small-particle-size proppant to temporarily plug the acid-etched fracture network, further slowing down the acid-rock reaction rate; (3) Multi-particle-size proppant proppant sand addition stage, adding large-particle-size proppant and medium-particle-size proppant into the fractures, using medium-viscosity fracturing fluid to deepen the fracture depth and width, and improve the fracture conductivity; (4) Low-viscosity displacement fluid displacement stage, injecting fracturing fluid into the tight limestone reservoir, enhancing the support of the fractures. This invention is based on the fracturing concept of "first forming a network and then forming fractures, temporary plugging of segments and multi-scale fracture support". It has many advantages such as the strong fluidity, strong penetration and strong rock breaking ability of supercritical carbon dioxide, the acid solubility of pre-prepared acid and the long-lasting and effective conductivity of sand fracturing. It can be widely used in the stimulation of tight limestone reservoirs to form a complex acid-etched-supported composite fracture system and effectively improve the conductivity of fractures.

[0014] Furthermore, by adjusting the acidity ratio of low-viscosity, retarded acid, the acid-rock reaction rate can be reduced, and its effective range is much greater than that of conventional acid, enabling more effective communication of fractures in distant well areas. Low-viscosity, retarded acid can improve fracture creation capabilities during fracturing operations, forming wide and deep fractures, which helps increase the channels and area for oil and gas flow. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the composite modification method of the present invention.

[0016] Figure 2 This is a schematic diagram of the supercritical carbon dioxide reaction conditions in this invention.

[0017] Figure 3 This is a schematic diagram of the supercritical atomized acid pressing network formation stage in this invention.

[0018] Figure 4 This is a schematic diagram of the pre-filled fluid slit creation stage of the slit plug temporary plugging method of the present invention.

[0019] Figure 5 This is a schematic diagram of the main fracture and branch fracture network formed by the medium-viscosity fracturing fluid used in this invention.

[0020] Figure 6 This is a schematic diagram of the sand addition stage of the multi-particle-size proppant of the present invention. Detailed Implementation

[0021] 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.

[0022] 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.

[0023] The following is a further detailed description with reference to specific embodiments and accompanying drawings.

[0024] A tight limestone reservoir in a certain basin has a burial depth of 3050m, a porosity of 2.21%, and a matrix permeability of 0.89%. This invention can be used for hydraulic fracturing operations.

[0025] like Figure 1 As shown, a method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and sand fracturing includes the following steps: Step S1: As Figure 3 As shown, in the supercritical atomized acid fracturing network formation stage, supercritical atomized acid fracturing is used to form an acid-etched fracture network in the tight limestone reservoir. like Figure 2 As shown, liquid carbon dioxide is converted into supercritical carbon dioxide under conditions above the critical temperature (31.1℃) and critical pressure (7.38MPa). The precursor acid combines with the supercritical carbon dioxide to form atomized acid. The atomized acid is used to form an acid etching fracture network in the tight limestone reservoir, and the precursor acid and liquid carbon dioxide are mixed and injected into the tight limestone reservoir for fracturing. In this fracturing operation, the precursor acid is a low-viscosity, slow-speed acid with a viscosity of 5-10 mPa·s.

[0026] Step S2: Pre-plugging fluid creation stage for sluice gate sealing; like Figure 4-5 As shown, a network of acid-etched fractures was formed by supercritical atomized acid fracturing using a medium-viscosity proppant-carrying fluid carrying small-particle-size proppant slugs; secondly, a medium-viscosity pre-flush fluid was used to form a main fracture and branch fracture network in a tight limestone reservoir, with the simulated main fracture length reaching 130–150 m.

[0027] Step S3: Multi-size proppant sand addition stage; like Figure 6 As shown, a medium-viscosity fracturing fluid was used to sequentially carry medium- and large-diameter proppant to fill the acid-etched fracture network, resulting in an acid-etched-propped fracture network. The medium-viscosity proppant-carrying fluid used was a polymer fracturing fluid with a viscosity of 60 mPa·s.

[0028] Step S4: Low viscosity displacement fluid displacement stage, medium viscosity fracturing fluid is injected into the tight limestone reservoir.

[0029] This invention is based on the fracturing concept of "first forming a network and then forming fractures, temporary plugging of segments and multi-scale fracture support". It has many advantages such as the strong fluidity, strong penetration and strong rock breaking ability of supercritical carbon dioxide, the acid solubility of pre-prepared acid and the long-lasting and effective conductivity of sand fracturing. It can be widely used in the stimulation of tight limestone reservoirs to form a complex acid-etched-supported composite fracture system and effectively improve the conductivity of fractures.

[0030] Example 1: A method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing includes the following steps: S1: Pre-acid injection volume is 50m 3 Liquid carbon dioxide injection is 80m 3 The injection displacement is 2m³. 3 / min, reducing reservoir fracture pressure and forming an acid-etched fracture network; S2: Use a medium-viscosity sand-carrying fluid with a viscosity of 60 mPa·s and a flow rate of 50 m³. 3 8m displacement3 / min, 70-140 mesh quartz sand concentration of 10%, quartz sand amount of 5m 3 The cracks were filled to temporarily seal the acid-etched crack network; A medium-viscosity pre-flush fluid of 60 mPa·s was used, with a high discharge rate of 8 m³ / min to form the main and branch fractures, and a fluid volume of 200 m³ / min. 3 It connects to the distant reservoir and simulates a main fracture length of 128 meters; S3: Uses medium-viscosity sand-carrying liquid with a flow rate of 150m³ 3 8m displacement 3 / min, 40-70 mesh quartz sand concentration is 15%, quartz sand amount is 18.5m 3 The main fracture at the far end of the well is filled, and the small-diameter proppant injected into S2 is injected into the branch fracture network. 200m³ of medium-viscosity sand-carrying liquid 3 8m displacement 3 / min, 20-40 mesh quartz sand concentration is 10%, quartz sand amount is 16m 3 The sand and gravel are pressed into the wellbore to fill the main fracture near the wellhead, and the proppant injected earlier is pushed into the depth of the fracture to enhance the compactness of the fracture and form a tight support structure. S4: A low-viscosity displacement fluid, i.e., slickwater with a viscosity of 5 mPa·s, is used for the displacement process. The sand-carrying fluid is pushed into the tight limestone reservoir, and the volume of slickwater is 20.2 m³. 3 The fracturing operation was completed.

[0031] 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.

[0032] 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 combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing, characterized in that, Includes the following steps: S1: Supercritical atomized acid fracturing is used to form an acid etching fracture network in tight limestone reservoirs; S2: Medium-viscosity fracturing fluid slugs are used to temporarily plug the acid-etched fracture network, forming main fractures and branch fracture networks in tight limestone reservoirs; S3: Medium-viscosity fracturing fluid is used to carry proppant and fill the main fracture and branch fractures to form an acid-etched-propped fracture network; S4: Replace the medium-viscosity fracturing fluid with a displacement fluid to complete the fracturing fluid application; The medium-viscosity fracturing fluid is a polymer fracturing fluid with a viscosity ≥ 60 mPa·s.

2. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 1, characterized in that, The supercritical atomizing acid in S1 is formed by the combination of pre-acid and supercritical carbon dioxide.

3. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 2, characterized in that, The pre-acid injection volume is 50-100 mg / L. 3 Carbon dioxide injection is 50-150m 3 The injection displacement is 2-5m³. 3 / min.

4. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 2, characterized in that, The pre-acid is a low-viscosity, slow-release acid.

5. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 1, characterized in that, The specific implementation of S2 is as follows: First, medium-viscosity fracturing fluid carries small-particle-size proppant slugs to temporarily plug the acid-etched fracture network formed by supercritical atomized acid fracturing; second, medium-viscosity fracturing fluid is used to form main fractures and branch fracture networks in tight limestone reservoirs. The small-particle-size proppant is 70-140 mesh ceramsite or quartz sand, and the amount of sand used in the slug is 5-10 mg / L. 3 ; The discharge rate of the medium-viscosity fracturing fluid is 8–12 m³. 3 / min.

6. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 1, characterized in that, The proppant carried by the medium-viscosity fracturing fluid in S3 consists of medium-sized and large-sized proppant. The medium-sized proppant is 40-70 mesh ceramsite or quartz sand; The large-particle-size proppant is 20-40 mesh ceramsite or quartz sand; The discharge rate of the medium-viscosity fracturing fluid is 8–12 m³. 3 / min.

7. A method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and sand fracturing according to claim 5 or 6, characterized in that, The medium-sized proppant presses the small-sized proppant into the branched fracture network, while the large-sized proppant presses the medium-sized proppant into the depths of the fracture, forming a dense acid-etched-propped fracture network.

8. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 1, characterized in that, In S4, a displacement fluid is used to replace the medium-viscosity fracturing fluid, and the medium-viscosity fracturing fluid is pushed into the tight limestone reservoir.

9. The method for combined stimulation of tight limestone reservoirs using atomized acid fracturing and proppant fracturing according to claim 8, characterized in that, The displacement fluid is low-viscosity slickwater with a viscosity of 5–10 mPa·s, and the displacement rate of the displacement fluid is 8–12 m³ / s. 3 / min.

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