Fracturing method suitable for mixed rock reservoir

Abstract

The invention discloses a fracturing method for a mixed rock reservoir. The fracturing method comprises the steps of pre-pressing construction through guanidine gum gel fracturing fluid, slug construction based on low-viscosity anti-drag water and a small-particle-size proppant, multi-stage acid etching construction, continuous sand adding construction through the guanidine gum gel fracturing fluid and displacement operation. According to slug construction, firstly, low-viscosity anti-drag water and a large-displacement and small-particle-size proppant are adopted for liquid injection; then, guanidine gum gel fracturing fluid is adopted for liquid injection, and the liquid injection step is repeated; natural cracks are filled by utilizing the characteristic of fast diffusion of low-viscosity liquid, so that the opening degree of complex cracks in the layer can be improved as much as possible; the multistage acid etching construction adopts two sets of acid liquid systems of pre-acid and retarded acid and a large-displacement injection mode, so that the etching effect of the wall surface of the crack and the seepage capacity from a matrix to the crack are effectively improved, the oil drainage radius is increased, and the fracturing effect is improved; and a sand fracturing means is further combined, so that multiple functions of increasing matrix pore permeability, oil drainage area, transformation volume and the like can be realized, and the transformation effect of the mixed rock reservoir is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of unconventional oil and gas reservoir exploration and development technology, specifically relating to a fracturing method suitable for mixed sedimentary rock reservoirs. Background Technology

[0002] With the innovation of oil and gas exploration concepts, the exploitation of unconventional oil and gas resources with significant resource potential has attracted increasing attention. Unconventional oil and gas includes tight sandstone oil and gas, shale oil and gas, tight carbonate oil and gas, and tight mixed sedimentary rock oil and gas. Among them, tight mixed sedimentary rock oil and gas is a special category, generally developed in marine-continental transitional environments or at the margins of terrestrial lacustrine basins, with unique sedimentary environments and complex lithologies. In some areas, mixed sedimentary rock reservoirs are formed by the mixing and sedimentation of terrigenous clastic and carbonate components. Mixed sedimentary rock reservoirs consist of endogenic clastic limestone, endogenic clastic sandstone, felsic micritic dolomite, silty mudstone, calcareous mudstone, oolitic limestone, mudstone, and saline-gypsum mudstone, etc., with very complex lithology, and high contents of dolomites, calcareous materials, and siliceous materials. Endogenic clastic limestone and intraclastic sandstone contain well-developed reservoir spaces with large pore sizes and good physical properties, while felsic micritic dolomite has relatively poor physical properties, classifying it as a low-permeability to tight mixed sedimentary reservoir. The basic characteristics of mixed sedimentary reservoirs are: 1) complex lithology and diverse pore throat types; 2) reservoir physical properties are highly correlated with lithology, with intraclastic limestone generally having a porosity greater than 15%, while micritic dolomite has poor physical properties, with a porosity of 10% or less and an average permeability of less than 1.0 × 10⁻⁶. -3 μm 2 3) Densification factors are complex and controlled by a variety of geological factors such as sedimentary facies and later diagenesis.

[0003] Due to their complex lithology and poor physical properties, mixed sedimentary reservoirs require stimulation measures to achieve industrial oil flow. Previously, these reservoirs were considered conventional sandstone and stimulated using conventional hydraulic fracturing, primarily relying on guar gum fracturing fluid to create fracture channels, which were then filled with proppant of varying particle sizes. However, this approach generally yielded poor stimulation results. Therefore, research is needed to develop targeted fracturing techniques to improve stimulation effectiveness. Summary of the Invention

[0004] The main objective of this invention is to address the problems and shortcomings of existing fracturing methods for mixed sedimentary reservoirs, such as low single-well production, rapid production decline, and low efficiency. This invention provides a multi-angle fracturing stimulation method for mixed sedimentary reservoirs. Targeting the characteristics of mixed sedimentary reservoirs, such as high carbonate content and poor physical properties, this method combines chemical dissolution and physical-mechanical techniques to achieve a multi-dimensional stimulation effect encompassing micropores, drainage area, and stimulation volume ("pore, surface, and volume"), thereby increasing post-fracturing production, extending the high-production period, and significantly improving the stimulation effect of mixed sedimentary reservoirs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A fracturing method suitable for mixed sedimentary rock reservoirs includes pre-compression using guar gum gel fracturing fluid, slug construction based on low-viscosity drag-reducing water and small-particle-size proppant, multi-stage acid etching, continuous proppant addition using guar gum gel fracturing fluid, and displacement operation; among which, the key control processes include:

[0007] 1) Slug construction based on low-viscosity drag-reducing water and small-particle-size proppant;

[0008] A first injection was performed using low-viscosity drag-reducing water, high displacement, and small-particle-size proppant (70-140 mesh); a second injection was performed using guar gum gel fracturing fluid while maintaining the same displacement; the above injection steps were repeated.

[0009] 2) Multi-stage acid etching process;

[0010] First, inject the first-stage pre-acid at a high flow rate; keep the flow rate constant and inject low-viscosity drag-reducing water as the isolation fluid; then inject the second-stage slow-release acid, and inject low-viscosity drag-reducing water again as the isolation fluid.

[0011] 3) Continuous sand addition for fracturing fluid using guar gum gel;

[0012] Guar gum fracturing fluid carrying small-diameter proppant was used for continuous sand addition operations, and then guar gum fracturing fluid carrying large-diameter proppant was used for continuous sand addition operations.

[0013] In the above scheme, the guar gum gel fracturing fluid can be a conventional guar gum gel fracturing fluid system.

[0014] In the above scheme, the displacement of the guar gum gel fracturing fluid used for pre-compression is 3-8 m³ / h. 3 / min, liquid volume 30-80m 3 .

[0015] In the above scheme, the viscosity of the low-viscosity drag-reducing water is 6-12 mPa·s, and the drag reduction rate of the drag-reducing water is over 70%.

[0016] Furthermore, the slug construction steps based on low-viscosity drag-reducing water and small-particle-size proppant specifically include: injecting low-viscosity drag-reducing water at a displacement of 3–6 m³ / h. 3 / min, liquid volume 50-100m 3 Add proppant with a particle size of 70-140 mesh, maintain a sand-to-liquid ratio of 7-9%, and add 1-3 mg / L of proppant. 3 Keep the displacement constant and inject 20-40m³ 3 The guar gum fracturing fluid was injected; low-viscosity drag-reducing water was continued to be injected at a flow rate of 3-6 m³ / h. 3 / min, liquid volume 50-100m 3 Add proppant with a particle size of 70-140 mesh, maintain a sand-to-liquid ratio of 7-9%, and add 1-3 mg / L of proppant.3 Keep the displacement constant and inject 20-40m³ 3 Guar gum gel fracturing fluid.

[0017] In the above scheme, the components and their mass percentages in the pre-acid include: HCl 8-12%, corrosion inhibitor 1-3%, iron ion stabilizer 1-3%, surfactant 0.5-1%, clay stabilizer 0.5-1.5%; the remainder is water.

[0018] In the above scheme, the components and their mass percentages in the slow-release acid include: HCl 8-12%, formic acid 2-5%, corrosion inhibitor 1-3%, iron ion stabilizer 1-3%, surfactant 0.5-1%, clay stabilizer 0.5-1.5%; the remainder is water.

[0019] Furthermore, iron ion stabilizers can be citric acid, ethylenediaminetetraacetic acid, or isoascorbic acid, etc.; surfactants can be sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or Tween-type anionic nonionic surfactants, etc.; clay stabilizers can be polyethylene quaternary ammonium salt or ammonium chloride.

[0020] In the above scheme, the multi-stage acid etching process specifically includes: injecting the first-stage pre-acid, wherein the flow rate is 3-6m³. 3 / min, liquid volume 40-120m 3 Keep the displacement constant and inject 20-50m³ 3 Low-viscosity, drag-reducing water is used as the isolation fluid; then a second-stage slow-release acid is injected, with a flow rate of 3–6 m³ / h. 3 / min, liquid volume 80~150m³ 3 Maintain the same displacement and continue injecting 50-100m³. 3 Low-viscosity, drag-reducing water is used as the isolation fluid.

[0021] In the above scheme, the continuous proppant addition step of the guar gum gel fracturing fluid includes: using guar gum gel fracturing fluid to carry small-diameter proppant particles of 40-70 mesh or 30-50 mesh, controlling the volumetric proppant-to-liquid ratio at 10%-15%-20%-25%-30% sequentially, with the volume of each proppant addition stage evenly distributed according to the remaining liquid volume, and the proppant addition amount being 10-100 m³. 3 Continue using guar gum fracturing fluid to carry larger proppant (30-50 mesh or 20-40 mesh) than the proppant used in the previous proppant addition operation. Control the volumetric proppant-to-liquid ratio at 30%-35%-40%, with the volume of each proppant addition stage evenly distributed according to the remaining liquid volume. The amount of proppant added is 5-50 m³. 3 Continuous sand addition is adopted.

[0022] Furthermore, before fracturing operations, based on the parameters of the mixed sedimentary reservoir well, commercially available fracturing simulation software is used to simulate the dynamics of fracture propagation and fracturing production under different fracturing operation parameters to determine whether temporary plugging operations should be carried out.

[0023] Based on the simulation results, if temporary plugging agent or temporary plugging balls are required for temporary plugging operations, then the temporary plugging balls or agents should be carried by guar gum gel fracturing fluid, with a volume of 20-25m³. 3 .

[0024] Furthermore, if a temporary plugging process is required, after the temporary plugging, the above-mentioned slug construction based on low-viscosity drag-reducing water and small-particle-size proppant, multi-stage acid etching construction, and continuous sand addition construction with guar gum gel fracturing fluid are repeated before the replacement operation is carried out.

[0025] In the above scheme, the substitution operation uses activated water, and the components and their amounts in the activated water include: surfactant 0.5-1%, clay stabilizer 0.5-1.5%; the remainder is water.

[0026] Furthermore, the surfactant may be an anionic nonionic surfactant such as dodecylphenol polyoxyethylene ether, sodium stearate, or polyethylene glycol fatty acid ester, and the clay stabilizer may be potassium chloride, ammonium chloride, or polyethylene quaternary ammonium salt.

[0027] In the above scheme, the displacement operation steps include: injecting active water as the displacement fluid, the volume of which is the wellbore volume; stopping the pump and recording the instantaneous pressure at the shut-in point; shutting in the well and allowing it to diffuse; and measuring the pressure drop for 30 to 40 minutes.

[0028] The principle of this invention is as follows:

[0029] This invention addresses the characteristics of mixed sedimentary rock reservoirs, such as high carbonate content and poor physical properties, by combining chemical dissolution and physical-mechanical methods to modify these reservoirs.

[0030] On the one hand, the mixed sedimentary rock reservoir has a high carbonate content. The "two-stage acid etching process" can improve the porosity and permeability of the reservoir matrix, thereby increasing the permeability and improving the matrix flow. Specifically, two acid systems and a high-volume injection method are used. The first stage uses a hydrochloric acid system, which is mainly used to etch the fracture walls and improve the conductivity of the fractures. The second stage uses a slow-speed acid system to reduce the acid-rock reaction rate and increase the acid action distance. The acid is filtered into the reservoir matrix and reacts with the carbonate minerals therein, thereby increasing the porosity and permeability. The high-volume injection method can shorten the acid's near-wellbore action time and achieve deep acid dissolution.

[0031] On the other hand, mixed sedimentary reservoirs generally have poor physical properties, making large-scale stimulation difficult and short-lived using only acidizing or acid fracturing. Furthermore, mixed sedimentary reservoirs contain a large amount of clay and other minerals, making it difficult to effectively maintain the conductivity of fractures after acid etching. This invention employs a "low-viscosity multi-stage alternating, intra-fracture temporary plugging and diversion" process to increase fracture complexity and drainage area, combined with high-strength support from multi-stage fractures to expand the stimulation volume. A pre-placed low-viscosity, drag-reducing water-carrying silt plug utilizes the rapid diffusion of low-viscosity liquids to fill natural fractures, maximizing the opening of complex fractures within the formation. Then, high-viscosity gel fracturing fluid is continuously added to increase fracture conductivity. Finally, a temporary plugging agent is introduced to form a filter cake that temporarily seals the fractures, increasing intra-fracture pressure and forcing one or more new fractures to open in high-stress areas, thereby increasing the stimulation volume.

[0032] Compared with the prior art, the beneficial effects of this invention are as follows:

[0033] (1) This invention addresses the high carbonate content characteristic of mixed sedimentary rock reservoirs by employing a multi-stage acid etching process, which can effectively improve the porosity and permeability of the reservoir matrix, enhance the flow capacity from the matrix to the fractures, and improve the etching effect on the fracture walls. The multi-stage acid etching process uses two acid systems: a pre-acid system and a slow-release acid system, along with a high-volume injection method. The pre-acid system uses a hydrochloric acid system, which is mainly used for etching the fracture walls to improve the conductivity of the fractures. The second stage uses a slow-release acid system to reduce the acid-rock reaction rate and increase the acid action distance. The acid is filtered into the reservoir matrix and reacts with the carbonate minerals therein, thereby improving porosity and permeability. The high-volume injection method can shorten the near-wellbore action time of the acid and achieve deep acid dissolution. Through the multi-stage acid etching process, combined with low-viscosity drag-reducing water isolation fluid, the etching effect on the fracture walls and the flow capacity from the matrix to the fractures are improved, the oil drainage radius is increased, and thus the fracturing effect is improved.

[0034] (2) This invention provides a sand fracturing method for promoting complex fractures by using pre-positioned low-viscosity liquid and temporary plugging and diversion. The pre-positioned low-viscosity drag-reducing water carries silt slugs and utilizes the rapid diffusion characteristics of low-viscosity liquid to fill natural fractures, which can maximize the opening degree of complex fractures within the formation. Furthermore, a temporary plugging agent is introduced to form a filter cake to temporarily seal the fractures, increase the pressure within the fractures, and force the high-stress zone within the formation to open one or more new fractures, thereby increasing the stimulation volume. At the same time, the mixed sedimentary rock reservoir contains a large amount of clay and other mineral components, and the conductivity of the fracture walls after acid etching is difficult to maintain effectively. By further combining the sand fracturing method for promoting complex fractures, the conductivity of the fractures and the stimulation volume can be greatly improved, and the production of a single well can be increased.

[0035] (3) The pore surface fracturing method for mixed sedimentary reservoirs described in this invention combines the advantages of acid fracturing and sand fracturing, and can achieve multiple functions such as increasing matrix pore permeability, oil drainage area and stimulation volume, thereby increasing post-fracturing production, extending high-production time, and greatly improving the stimulation effect of mixed sedimentary reservoirs. It effectively solves the problems of low single-well production, rapid production decline and low efficiency of conventional fracturing stimulation of mixed sedimentary reservoirs, and achieves a technological breakthrough for this type of reservoir. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments. 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 are within the scope of protection of the present invention.

[0037] Example 1

[0038] A certain well section, 1672-1677m, has a reservoir porosity of 10-15%, an oil saturation of 59.5%, and is composed of mixed sedimentary rocks with a clay content of 15.5-18.2%, a felsic content of 32.7-37.6%, and a carbonate content of 31.5-36.8%.

[0039] The fracturing method used includes the following steps:

[0040] (1) Preloading: Guar gum fracturing fluid was used with a displacement of 3m³. 3 / min, liquid volume 30m 3 The main components and their mass percentages in the guar gum fracturing fluid are as follows: guar gum 0.35%, NaOH 0.015%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, bactericide (glutaraldehyde) 0.02%, borax 0.045%, and breaker (ammonium persulfate) 0.02%.

[0041] (2) Slug construction based on low-viscosity drag-reducing water and small-particle-size proppant;

[0042] Inject low-viscosity, drag-reducing water and set the discharge rate to 3m³. 3 / min, liquid volume 40m 3 Add 2m of proppant with a particle size of 70-140 mesh. 3 The volumetric sand-to-liquid ratio is 7%; maintaining a constant discharge rate, inject 20m³. 3 Guar gum fracturing fluid (same as step (1)); continue injecting low-viscosity drag-reducing water, setting the flow rate to 3m³ / h. 3 / min, liquid volume 30m 3 Add 2m of proppant with a particle size of 70-140 mesh. 3The volumetric sand-to-liquid ratio is 9%; maintaining a constant discharge rate, inject 40m³. 3 Guar gum fracturing fluid (same as step (1));

[0043] The main components and dosages of the low-viscosity drag-reducing water used include: drag-reducing agent (polyacrylamide) 0.08%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, and clay stabilizer (KCl) 2%; its viscosity is 9 mPa.s, and its drag reduction rate reaches 70%.

[0044] (3) Multi-stage acid etching process construction

[0045] Inject the first stage of pre-acid, with a displacement of 3m³. 3 / min, liquid volume 40m 3 Keep the displacement unchanged and inject 30m. 3 Low-viscosity, drag-reducing water-based isolation fluid; injection of secondary slow-release acid at a flow rate of 3m³. 3 / min, liquid volume 80m 3 Keep the displacement unchanged, inject 50m 3 Low-viscosity, drag-reducing water-based barrier fluid;

[0046] The components and their mass percentages in the pre-acid are as follows: HCl 8%, corrosion inhibitor (Mannich base corrosion inhibitor) 2%, iron ion stabilizer (citric acid) 2%, surfactant (SDBS) 0.5%, clay stabilizer (polyethylene quaternary ammonium salt) 0.8%, and the remainder is water.

[0047] The components and their mass percentages in the slow-recovery acid used are as follows: HCl 8%, formic acid 5%, corrosion inhibitor (polyethylene polyamine Mannich base corrosion inhibitor) 2%, iron ion stabilizer (citric acid) 2%, surfactant (SDBS) 0.5%, clay stabilizer (polyethylene quaternary ammonium salt) 0.8%, and the remainder is water;

[0048] (4) Continuous sand addition for fracturing fluid with guar gum gel:

[0049] Guar gum fracturing fluid carrying 30-50 mesh proppant was used, with the volumetric proppant-to-fluid ratio successively set at 10%-15%-20%-25%-30%. The volume of each proppant addition stage was evenly distributed according to the remaining fluid volume, and the proppant addition amount was 20m³. 3 Continue using guar gum fracturing fluid to carry 20-40 mesh proppant, with a volumetric proppant-to-fluid ratio of 30%-35%-40%. The volume of proppant added at each stage is evenly distributed based on the remaining fluid volume, and the proppant addition is 10m³. 3 Continuous sand addition is adopted;

[0050] (5) Substitute work

[0051] After sand addition is completed, active water is injected as the displacement fluid, with the volume being equal to the wellbore volume; the pump is stopped and the instantaneous pressure at shut-in is recorded; the pressure drop is measured for 30 minutes after shut-in diffusion.

[0052] The active water used contains the following components and their mass percentages: surfactant 0.5%, clay stabilizer 0.8%, and the remainder is water.

[0053] (6) After the well is shut in, the backflow, testing and production testing and formal production work will be carried out in accordance with the standard procedures.

[0054] The results show that the production achieved by using the perforated body fracturing method described in Example 1 resulted in an initial daily oil production of over 10 cubic meters. Compared with adjacent wells that used conventional fracturing methods (which did not employ the perforated body fracturing process described in this invention, but only conventional methods), the initial oil production increased by nearly four times, demonstrating the significant effectiveness of the measures.

[0055] Example 2

[0056] A certain well section, 2282–2305 m, has a reservoir porosity of 7–11%, an oil saturation of 55.8%, and is composed of mixed sedimentary rocks with a clay content of 17.1–23.2%, a felsic content of 25.4–33.5%, and a carbonate content of 37.4–56.8%.

[0057] The fracturing method used includes the following steps:

[0058] (1) Preloading: Guar gum fracturing fluid was used with a displacement of 4 m³ / h. 3 / min, liquid volume 80m 3 The main components and their mass percentages in the guar gum gel fracturing fluid are as follows: guar gum 0.35%, NaOH 0.015%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, bactericide (glutaraldehyde) 0.02%, borax 0.045%, and breaker (ammonium persulfate) 0.02%.

[0059] (2) Slug construction based on low-viscosity drag-reducing water and small-particle-size proppant;

[0060] Inject low-viscosity, drag-reducing water and set the discharge rate to 4m³. 3 / min, liquid volume 80m 3 Add 5 μm of proppant with a particle size of 70–140 mesh. 3 The volumetric sand-to-liquid ratio is 7%; maintaining a constant discharge rate, inject 30m³. 3 Guar gum fracturing fluid; continue injecting low-viscosity drag-reducing water, setting the flow rate to 4m³ / h. 3 / min, liquid volume 70m 3 Add 5 μm of proppant with a particle size of 70–140 mesh. 3The volumetric sand-to-liquid ratio is 9%; maintaining a constant discharge rate, inject 30m³. 3 Guar gum gel fracturing fluid;

[0061] The main components and their mass percentages in the low-viscosity drag-reducing water used are as follows: drag-reducing agent (polyacrylamide) 0.08%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%; its viscosity is 9 mPa.s, and its drag reduction rate reaches 70%.

[0062] The main components and their mass percentages in the guar gum fracturing fluid used are: guar gum 0.35%, NaOH.

[0063] 0.015%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, bactericide (glutaraldehyde) 0.02%, borax 0.045%, and degumming agent (ammonium persulfate) 0.02%;

[0064] (3) Multi-stage acid etching process construction

[0065] Inject the first stage of pre-acid, with a displacement of 4m³. 3 / min, liquid volume 120m 3 Keep the displacement unchanged, inject 40m 3 Low-viscosity, drag-reducing water was used as the isolation fluid; a second-stage slow-release acid was injected at a flow rate of 4m³. 3 / min, liquid volume 150m 3 Keep the displacement unchanged and inject 80m³ 3 Low-viscosity, drag-reducing water is used as the isolation fluid;

[0066] The components and their mass percentages in the pre-acid are as follows: HCl 12%, corrosion inhibitor (Mannich base corrosion inhibitor) 2%, iron ion stabilizer (citric acid) 2%, surfactant (SDBS) 0.5%, clay stabilizer (polyethylene quaternary ammonium salt) 0.8%, and the remainder is water.

[0067] The components and their mass percentages in the slow-recovery acid used are as follows: HCl 12%, formic acid 2%, corrosion inhibitor (Mannich base corrosion inhibitor) 2%, iron ion stabilizer (citric acid) 2%, surfactant (SDBS) 0.5%, clay stabilizer (polyethylene quaternary ammonium salt) 0.8%, and the remainder is water;

[0068] (4) Continuous sand addition for fracturing fluid with guar gum gel:

[0069] Guar gum fracturing fluid carrying 30-50 mesh proppant was used, with the volumetric proppant-to-fluid ratio successively set at 10%-15%-20%-25%-30%. The volume of each proppant addition stage was evenly distributed according to the remaining fluid volume, and the proppant addition amount was 50m³. 3Continue using guar gum fracturing fluid to carry 20-40 mesh proppant, with a volumetric proppant-to-fluid ratio of 30%-35%-40%. The volume of proppant added at each stage is evenly distributed based on the remaining fluid volume, and the proppant addition is 25m³. 3 Continuous sand addition is adopted;

[0070] (5) Add temporary plugging agent or temporary plugging ball:

[0071] The fracturing fluid, consisting of guar gum gel carrying temporary plugging agent, has a displacement of 4 m³. 3 / min, liquid volume 25m 3 The amount of temporary plugging agent used is 300 kg;

[0072] (6) Repeat the construction steps described in (2) to (4);

[0073] (7) Substitution work

[0074] After sand addition is completed, active water is injected as the displacement fluid, with the volume being equal to the wellbore volume; the pump is stopped and the instantaneous pressure at shut-in is recorded; the pressure drop is measured for 40 minutes after shut-in diffusion.

[0075] The active water used contains the following components and their mass percentages: surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, and the remainder is water;

[0076] (8) After the well is shut in, the backflow, testing and production testing and formal production work will be carried out in accordance with the regular procedures.

[0077] Experimental results show that when using the perforated fracturing method described in Example 2, the initial daily oil production is more than 25 cubic meters. Compared with the adjacent wells that used conventional fracturing methods (without perforated fracturing technology), the initial oil production is increased by about 10 times, and the production increase effect is obvious.

[0078] Comparative Example 1

[0079] A certain well section, 1692–1703 m, has a reservoir porosity of 10–12%, an oil saturation of 56.3%, and is composed of mixed sedimentary rocks with a clay content of 16.0–22.5%, a felsic content of 22.3–33.5%, and a carbonate content of 40.8–55.2%.

[0080] The fracturing method used includes the following steps:

[0081] (1) Preloading: Guar gum fracturing fluid was used with a displacement of 4 m³ / h. 3 / min, liquid volume 80m 3The main components and their mass percentages in the guar gum fracturing fluid are as follows: guar gum 0.35%, NaOH 0.015%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, bactericide (glutaraldehyde) 0.02%, borax 0.045%, breaker (ammonium persulfate) 0.02%, and the remainder is water.

[0082] (2) Slug construction based on low-viscosity drag-reducing water and small-particle-size proppant;

[0083] Inject low-viscosity, drag-reducing water and set the discharge rate to 4m³. 3 / min, liquid volume 45m 3 Add 2m of proppant with a particle size of 70-140 mesh. 3 The volumetric sand-to-liquid ratio is 7%; maintaining a constant discharge rate, inject 15m... 3 Guar gum fracturing fluid; continue injecting low-viscosity drag-reducing water, setting the flow rate to 4m³ / h. 3 / min, liquid volume 60m 3 Add 4m of proppant with a particle size of 70-140 mesh. 3 The volumetric sand-to-liquid ratio is 9%; maintaining a constant discharge rate, inject 20m³. 3 Guar gum gel fracturing fluid;

[0084] The main components and their mass percentages in the low-viscosity drag-reducing water used are as follows: drag-reducing agent (polyacrylamide) 0.08%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, and the remainder is water; its viscosity is 9 mPa.s, and its drag reduction rate reaches 70%.

[0085] The main components and their mass percentages in the guar gum fracturing fluid used are: guar gum 0.35%, NaOH.

[0086] 0.015%, surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, bactericide (glutaraldehyde) 0.02%, borax 0.045%, degumming agent (ammonium persulfate) 0.02%, the remainder is water;

[0087] (3) Acid etching process construction

[0088] Injecting slow-release acid, with a discharge rate of 4m³ 3 / min, liquid volume 150m 3 Keep the displacement unchanged and inject 80m³ 3 Low-viscosity, drag-reducing water is used as the isolation fluid;

[0089] The components and their mass percentages in the slow-release acid are as follows: HCl 18%, formic acid 2%, corrosion inhibitor (Mannich base corrosion inhibitor) 2%, iron ion stabilizer (citric acid) 2%, surfactant (SDBS) 0.5%, clay stabilizer (polyethylene quaternary ammonium salt) 0.8%, and the remainder is water.

[0090] (4) Add temporary plugging agent or temporary plugging ball:

[0091] The fracturing fluid, consisting of guar gum gel carrying temporary plugging agent, has a displacement of 4 m³. 3 / min, liquid volume 25m 3 The amount of temporary plugging agent used is 300 kg;

[0092] (5) Repeat the construction steps described in (2) to (3);

[0093] (6) Substitute work

[0094] After sand addition is completed, active water is injected as the displacement fluid, with the volume being equal to the wellbore volume; the pump is stopped and the instantaneous pressure at shut-in is recorded; the pressure drop is measured for 40 minutes after shut-in diffusion.

[0095] The active water used contains the following components and their mass percentages: surfactant (dodecylphenol polyoxyethylene ether) 0.5%, clay stabilizer (KCl) 2%, and the remainder is water;

[0096] (7) After the well is shut in, the backflow, testing and production testing and formal production work will be carried out in accordance with the regular procedures.

[0097] Experimental results show that only a single-stage acid etching process was used in the comparative example, and the acid concentration was too high. After acid etching, guar gum fracturing fluid was not continuously added to the fracturing surface. Relying solely on the etching of the fracture wall by high-concentration acid is not suitable for mixed sedimentary reservoirs. When the fracturing method in Comparative Example 1 was used for production, the initial daily oil production was only 2.93 cubic meters. Compared with the adjacent well using the perforated body fracturing method, the initial oil production was poor, and the production increase effect was not obvious.

[0098] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A fracturing method suitable for mixed sedimentary rock reservoirs, characterized in that, This includes pre-compression fracturing using guar gum gel fracturing fluid, slug fracturing based on low-viscosity drag-reducing water and small-particle-size proppant, multi-stage acid etching, continuous proppant addition using guar gum gel fracturing fluid, and displacement operations; among these, key control processes include: 1) Slug construction based on low-viscosity drag-reducing water and small-particle-size proppant; A primary injection is performed using low-viscosity drag-reducing water, high-volume fracturing fluid, and small-particle-size proppant; maintaining the same volume, a secondary injection is performed using guar gum gel fracturing fluid; the above injection steps are repeated. 2) Multi-stage acid etching construction; First, inject the first-stage pre-acid at a high displacement; keep the displacement constant and inject low-viscosity drag-reducing water; then inject the second-stage slow-release acid, and inject low-viscosity drag-reducing water again. 3) Continuous sand addition for fracturing fluid using guar gum gel; Guar gum fracturing fluid carrying small-diameter proppant was used for continuous sand addition operations, and then guar gum fracturing fluid carrying large-diameter proppant was used for continuous sand addition operations.

2. The fracturing method according to claim 1, characterized in that, The displacement of the guar gum gel fracturing fluid used in the pre-compression operation is 3-8 m³ / h. 3 / min, liquid volume 30-80m 3 .

3. The fracturing method according to claim 1, characterized in that, The viscosity of the low-viscosity drag-reducing water is 6-12 mPa·s, and the drag reduction rate of the drag-reducing water is over 70%.

4. The fracturing method according to claim 1, characterized in that, The slug construction steps based on low-viscosity drag-reducing water and small-particle-size proppant specifically include: injecting low-viscosity drag-reducing water at a displacement of 3-6 m³ / h. 3 / min, liquid volume 50-100m 3 Add proppant with a particle size of 70-140 mesh, maintain a sand-to-liquid ratio of 7-9%, and add 1-3 mg / L of proppant. 3 Keep the displacement constant and inject 20-40m³ 3 The guar gum fracturing fluid was injected; low-viscosity drag-reducing water was continued to be injected at a flow rate of 3-6 m³ / h. 3 / min, liquid volume 50-100m 3 Add proppant with a particle size of 70-140 mesh, maintain a sand-to-liquid ratio of 7-9%, and add 1-3 mg / L of proppant. 3 Keep the displacement constant and inject 20-40m³ 3 Guar gum gel fracturing fluid.

5. The fracturing method according to claim 1, characterized in that, The pre-acid contains the following components and their mass percentages: HCl 8-12%, corrosion inhibitor 1-3%, iron ion stabilizer 1-3%, surfactant 0.5-1%, clay stabilizer 0.5-1.5%, and the remainder is water.

6. The fracturing method according to claim 1, characterized in that, The slow-release acid comprises the following components and their mass percentages: HCl 8-12%, formic acid 2-5%, corrosion inhibitor 1-3%, iron ion stabilizer 1-3%, surfactant 0.5-1%, clay stabilizer 0.5-1.5%, with the remainder being water.

7. The fracturing method according to claim 1, characterized in that, The multi-stage acid etching process specifically includes: injecting the first-stage pre-acid, wherein the flow rate is 3-6m³. 3 / min, liquid volume 40-120m 3 Keep the displacement constant and inject 20-50m³ 3 Low-viscosity, drag-reducing water is then injected; followed by the injection of a second-stage slow-release acid, with a flow rate of 3–6 m³ / h. 3 / min, liquid volume 80~150m³ 3 Maintain the same displacement and continue injecting 50-100m³. 3 Low viscosity and drag-reducing water.

8. The fracturing method according to claim 1, characterized in that, The continuous proppant addition procedure using guar gum fracturing fluid includes: using guar gum fracturing fluid to carry small-diameter proppant particles of 40-70 mesh or 30-50 mesh, controlling the volumetric proppant-to-liquid ratio at 10%-15%-20%-25%-30% sequentially, with the volume of each proppant addition stage evenly distributed according to the remaining fluid volume, and the proppant addition amount being 10-100 mg / L. 3 Continue using guar gum fracturing fluid to carry larger proppants than those used in the previous proppant addition operation, controlling the volumetric proppant-to-liquid ratio at 30%-35%-40%, with the volume evenly distributed according to the remaining liquid volume in each proppant addition stage. The amount of proppant added is 5-50 m³. 3 Continuous sand addition is adopted.

9. The fracturing method according to claim 1, characterized in that, Before the replacement operation, a temporary plugging operation is carried out. Then, the above-mentioned slug construction based on low-viscosity drag-reducing water and small-particle-size proppant, multi-stage acid etching construction, and continuous sand addition construction of guar gum gel fracturing fluid are repeated. Finally, the replacement operation is carried out.

10. The fracturing method according to claim 1, characterized in that, The replacement operation uses activated water, the components of which and their amounts include: surfactant 0.5-1%, clay stabilizer 0.5-1.5%; the remainder is water.