A storage fracturing method suitable for low-permeability tight oil reservoirs

Abstract

This invention proposes a storage fracturing method suitable for low-permeability tight oil reservoirs. By selecting shale reservoir samples with four different clay mineral contents, an organic swelling inhibitor solution is prepared. Displacement experiments are conducted on the four samples with different clay contents. By measuring the changes in porosity and permeability, sample volume, and sand production before and after displacement with the organic swelling inhibitor solution, the effectiveness of the organic swelling inhibitor under different clay contents is determined. This leads to the determination of the dosage of the organic swelling inhibitor for reservoirs with different clay contents, and a method for evaluating the effect of the swelling inhibitor on the hydration and swelling inhibition of shale reservoirs is derived. This invention's evaluation system is highly effective, employs multiple evaluations, is highly persuasive, and has strong generalizability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field exploration and development, in particular to an energy storage fracturing method suitable for low-permeability tight oil reservoirs. BACKGROUND

[0002] Tight oil and gas has become an important part of China's oil and gas production, and low-permeability tight oil reservoirs are widely distributed and have many types. In China, two main types of reservoirs, tight sandstone and tight limestone, are mainly developed, both of which develop nanoscale micro-pore throat network systems, and the matrix permeability is generally (0.001-1) x 10-3 μm2. Based on the low-permeability characteristics of tight oil reservoirs, fracturing technology must be used for exploration and development. At present, the development mode mainly uses hydraulic fracturing at home and abroad, and the main body of the fracturing fluid system is mainly drag-reducing water + guar gum, and the proppant is mainly quartz sand, ceramic or coated sand, and some blocks also use acidic fracturing fluid, VES fracturing fluid, carboxymethyl fracturing fluid and other systems, all of which aim to improve the fracture reconstruction volume and conductivity. However, the characteristics of China's tight oil reservoirs are quite different from those abroad. Foreign tight oil reservoirs are mainly marine deposits, and the reservoirs are uniformly distributed and natural fractures are developed. In China, they are mainly continental deposits, and the heterogeneity is strong, especially the tight sandstone reservoirs of beach bar sand type, which have poor sand body connectivity, great difficulty in energy supplement, and small sweep range. At present, the main development mode for low-permeability tight oil reservoirs in China is the natural energy depletion type after fracturing reconstruction (see Figure 1 ), which has the problems of rapid reduction of formation energy, rapid production decline, and low final production, and cannot realize the economic benefit development of the reservoir. Moreover, compared with conventional reservoirs, the pore structure of unconventional tight reservoirs is more complex, there is a wide range of "permeability lock" on the relative permeability curve, and the imbibition effect is more obvious. Therefore, for low-permeability tight oil reservoirs, it is the key to effectively develop unconventional tight oil and gas to research a multifunctional fracturing technology that can not only achieve fracturing reconstruction effect, but also supplement formation energy and promote imbibition oil displacement. SUMMARY

[0003] The technical problem to be solved by the present application is to provide an energy storage fracturing method suitable for low-permeability tight oil reservoirs, which can not only achieve fracturing reconstruction effect, but also supplement formation energy and promote imbibition oil displacement.

[0004] The embodiments of the present application are implemented as follows:

[0005] The energy storage fracturing method suitable for low-permeability tight oil reservoirs provided by the embodiments of the present application has the characteristics that it comprises the following steps:

[0006] S1) Evaluation of key reservoir parameters:

[0007] Carrying out the parameter evaluation of the structure, fault and various fissure development, lithology and sensitivity, physical property, rock mechanics parameter and three-directional ground stress parameter, the rock mechanics parameter including the fracture toughness of reservoir horizontal direction and reservoir and upper and lower interlayer vertical direction, and temperature and pressure;

[0008] S2) Optimization of fracturing operation parameters:

[0009] Establishing the geological model, introducing the geological model into the fracturing simulation software, simulating the crack expansion dynamics and fracturing production dynamics prediction under different fracturing operation parameters;

[0010] S3) Optimization of energy supplement scale:

[0011] Optimizing the energy supplement liquid amount by calculation;

[0012] S4) Optimization of energy supplement liquid and guar gum fracturing fluid formula:

[0013] According to the core mineral composition and core CST experimental results, the types and concentrations of clay stabilizers of various liquid systems are optimized; according to the core wettability and oil displacement effect experiment, the types and concentrations of surfactants of the liquid system are optimized; the guar gum fracturing fluid concentration is selected in combination with the process requirements and reservoir characteristics;

[0014] S5) First pre-pressing:

[0015] After injecting the liquid amount of the guar gum fracturing fluid in this stage, half of the optimum dosage of proppant is added, and continuous sanding is adopted;

[0016] S6) First sanding energy supplement operation:

[0017] According to the volume value of the energy supplement liquid, the sanding energy supplement mode is determined, when the volume value of the energy supplement liquid is less than 1000m 3 , the sanding energy supplement mode is adopted first; when it is greater than 1000m 3 , the sanding energy supplement mode is adopted first;

[0018] S7) Second pre-pressing:

[0019] Blocking is carried out by using the guar gum fracturing fluid to carry the temporary plugging ball or temporary plugging agent, and then the process of step S5 is repeated to complete sanding;

[0020] S8) Second sanding energy supplement operation:

[0021] The process of step S7 is repeated, after sanding is completed, the energy supplement liquid is finally injected as the displacement liquid, the liquid amount is the wellbore volume; the pump is stopped to record the instantaneous pressure when the well is closed, the well is closed to diffuse, the pressure drop is measured for a certain time, a pressure gauge with a suitable range is installed at the wellhead, and the well is closed for several hours according to the pump pressure;

[0022] S9) Post-pressing well closure:

[0023] After the fracturing is completed, a pressure gauge with a suitable range is installed at the wellhead according to the pump-off pressure, and a remote wireless pressure transmitter is installed, and if the site conditions are limited, a wellhead storage pressure gauge is installed, and the well is closed for a certain period of time.

[0024] S10) Subsequent normal construction:

[0025] After the well is closed, the return flow, production test and formal production are performed according to the conventional process.

[0026] In some optional embodiments, the fracturing construction parameters in step S2 include displacement, viscosity, liquid volume, support agent volume and the proportion of different particle sizes of support agent, construction sand-liquid ratio, corresponding pumping program, type and amount of temporary plugging agent or temporary plugging ball.

[0027] In some optional embodiments, the specific formula for the calculation in step S3 is as follows:

[0028] V = a p × (C f × V 岩石孔隙 + P i ) × H 垂深 × 100, wherein: V: energy supplement liquid volume; a p : formation pressure increase coefficient after energy supplement; C f : rock compressibility; V 岩石孔隙 : rock pore volume; P i : pre-pressing formation pressure; H 垂深 : vertical depth of the reservoir.

[0029] In some optional embodiments, the displacement of the guar gum fracturing fluid in step S5 is the highest optimized value, the liquid volume is 50-100 m 3 , 20%-30% of the first pre-pressing injection liquid volume, the support agent particle size is 70-140 mesh, and the volume sand-liquid ratio is 7-9%.

[0030] In some optional embodiments, the first energy supplement and then sand adding mode in step S6 includes the following contents:

[0031] The energy supplement liquid is injected at the optimized displacement and liquid volume of step S2, the guar gum fracturing fluid is used to carry support agents with a particle size of 40-70 mesh or 30-50 mesh, the progressive volume sand-liquid ratio is 10%-15%-20%-25% in turn, half of the optimized support agent volume is added, the guar gum fracturing fluid is continued to be used to carry support agents with a particle size of 30-50 mesh or 20-40 mesh, the progressive volume sand-liquid ratio is 30%-35%-40% in turn, and the amount added is half of the optimized support agent volume.

[0032] In some alternative embodiments, the first sanding and then energy supplementing mode in step S6 includes the following: using guar gum fracturing fluid to carry proppant with a particle size of 40-70 mesh or 30-50 mesh, the progressive volume sand liquid ratio is 10%-15%-20%-25% in turn, half of the optimized proppant amount is added, using guar gum fracturing fluid to carry proppant with a particle size of 30-50 mesh or 20-40 mesh, the progressive volume sand liquid ratio is 30%-35%-40% in turn, the amount is half of the optimized proppant amount, the remaining energy supplementing fluid is injected at an optimized displacement under a fracture closure pressure, and the fracture closure pressure optimized displacement is 1 m 3 / min.

[0033] In some alternative embodiments, the guar gum fracturing fluid carrying temporary plugging ball or temporary plugging agent displacement in step S7 is an optimized value, and the fluid amount is 20 m 3 .

[0034] In some alternative embodiments, the pressure drop measuring time in step S8 is 15-20 min, the pump pressure is stopped, and the well is shut in for 2-4 hours.

[0035] In some alternative embodiments, the shut-in time in step S9 is 15-30 days.

[0036] In some alternative embodiments, the energy supplementing fluid in step S4 is composed of 0.2-1.0% clay stabilizer, 0.1-0.5% surfactant, and water.

[0037] The application has the following beneficial effects: the energy storage fracturing method provided by the application is suitable for low-permeability tight oil reservoirs, high-permeability flow channels are formed through fracturing reconstruction, a large amount of energy supplementing fluid is injected at high pressure, pressure is diffused during shut-in, formation energy near the well and at the far end of the fracture is increased, formation pressure is increased, the limit oil drainage radius of the fracture is increased, and the liquid production capacity of the oil reservoir is improved; the effective temporary plugging and turning technology causes multiple fractures to be opened or the fractures to be turned to form branch fractures, promotes the complexity of the fractures, the complex artificial fractures formed after fracturing can communicate a large number of natural fractures in the reservoir, and different particle sizes of proppants are used to support fractures at different levels, so that the number of effective fracture seepage channels through which the reservoir crude oil flows to the well bottom is increased, and the seepage area is expanded. Under this condition, the well is shut in after fracturing, the energy supplementing fluid and the crude oil in the matrix are subjected to imbibition displacement under the action of capillary force, the oil and water in the production layer are redistributed, and thus more crude oil is produced, so that the recovery rate is improved; the method can realize the triple functions of fracturing, energy supplementing, and imbibition oil displacement, simplifies the fracturing process, shortens the fracturing time, and saves economic cost; the pressure effect of the energy supplementing fluid is used to increase the formation pressure; shut-in is beneficial to the penetration of the energy supplementing fluid into the matrix, full contact and displacement with more crude oil, and the improvement of the dynamic degree of the oil reservoir; the problems of low single-well production, rapid production decline, water injection difficulty, and low ultimate recovery rate in the conventional fracturing reconstruction of low-permeability tight oil reservoirs are solved. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of a conventional fracturing process;

[0040] Figure 2 This application contains a flowchart of a storage fracturing process. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0043] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0044] To address the problem of liquid phase damage caused by water-based fracturing fluid entering the reservoir after fracturing in current shale oil and gas reservoirs, leading to pore blockage, reduced pore throat connectivity, decreased reservoir permeability, and consequently reduced oil and gas production, this invention provides a storage-fracturing method suitable for low-permeability tight oil reservoirs. This method includes the following steps (see...) Figure 2 ):

[0045] (1) Evaluation of key reservoir parameters

[0046] Select low-pressure, normal-pressure, low-permeability tight oil reservoirs; conduct assessments including structural, fault and fracture development, lithology and sensitivity, physical properties, rock mechanical parameters (including fracture toughness in the horizontal direction of the reservoir and in the vertical direction between the reservoir and the upper and lower strata), triaxial geostress parameters, temperature and pressure, etc.

[0047] (2) Optimization of fracturing construction parameters

[0048] Based on step (1), a detailed geological model is established using commonly used commercial geological modeling software (such as PETROL). Then, the geological model is imported into commercial fracturing simulation software (such as GOFFER) to simulate fracture propagation dynamics and predict fracturing production dynamics under different fracturing operation parameters. Specific fracturing operation parameters include displacement, viscosity, fluid volume, proppant dosage and the proportion of proppant with different particle sizes, the sand-to-liquid ratio, the corresponding pumping procedure, and the type and dosage of temporary plugging agent or temporary plugging ball, etc.

[0049] (3) Optimization of energy replenishment scale

[0050] Based on steps (1) and (2), the energy replenishment fluid volume is optimized using the following formula:

[0051] V = α p ×(C f ×V 岩石孔隙 +P i )×H 垂深 ×100, where: V: volume of the replenishing liquid; α p : Coefficient of increase in formation pressure after energy replenishment; C f : Rock compressibility coefficient; V 岩石孔隙 : Rock pore volume; P i : Formation pressure before compression; H 垂深 Vertical depth of the reservoir.

[0052] (4) Optimization of the formulation of energy replenishing fluid and guar gum fracturing fluid

[0053] Based on the mineral composition of the core and the results of core CST experiments, the type and concentration of clay stabilizers in various liquid systems were optimized; based on core wettability and oil displacement effect experiments, the type and concentration of surfactants in the liquid system were optimized; combined with process requirements and reservoir characteristics, the concentration of guar gum was optimized, and the performance of guar gum fracturing fluid must meet current industry standards. The replenishing fluid is composed of 0.2–1.0% clay stabilizer, 0.1–0.5% surfactant, and water.

[0054] (5) Primary preloading

[0055] Inject guar gum fracturing fluid at the highest optimized displacement rate, with a flow rate of 50–100 m³. 3 After the liquid volume of the first-stage pre-compression injection is 20% to 30% of the volume, the proppant particle size is 70 to 140 mesh, and the volume sand-liquid ratio is 7 to 9%, half of the optimized proppant dosage is added, and sand is added continuously.

[0056] (6) Primary sand-addition energy replenishment construction

[0057] Based on the volume of the replenishing fluid, the sand replenishment mode is determined. When the volume of the replenishing fluid is less than 1000 m3, the replenishing-first-then-sand-adding-mode is adopted; when it is greater than 1000 m3, the sand-adding-first-then-replenishing-mode is adopted.

[0058] The "energy replenishment followed by sand addition" mode includes the following:

[0059] Inject the replenishing fluid with the optimized displacement and fluid volume from step S2. Use guar gum fracturing fluid to carry proppant with a particle size of 40-70 mesh or 30-50 mesh. The progressive volumetric proppant-to-fluid ratio is 10%-15%-20%-25%. Add half of the optimized proppant dosage. Continue using guar gum fracturing fluid to carry proppant with a particle size of 30-50 mesh or 20-40 mesh. The progressive volumetric proppant-to-fluid ratio is 30%-35%-40%. The amount added is half of the optimized proppant dosage.

[0060] The pre-sand-feed-energy-replenishment mode includes the following: using guar gum fracturing fluid to carry proppant with a particle size of 40-70 mesh or 30-50 mesh, with a progressive volumetric sand-to-fluid ratio of 10%-15%-20%-25%, adding half of the optimized proppant dosage, continuing to use guar gum fracturing fluid to carry proppant with a particle size of 30-50 mesh or 20-40 mesh, with a progressive volumetric sand-to-fluid ratio of 30%-35%-40%, adding half of the optimized proppant dosage, and injecting the remaining energy-replenishing fluid at a flow rate (1 m3 / min) lower than the optimized fracture closure pressure.

[0061] (7) Secondary preloading

[0062] Use guar gum fracturing fluid to carry temporary plugging balls or temporary plugging agents for sealing, and then repeat step S5 to complete the sand addition process;

[0063] (8) Secondary sand reinforcement construction

[0064] Repeat the process of step S7. After sand addition is completed, inject the energy replenishing fluid as the replacement fluid. The fluid volume is equal to the wellbore volume. Record the instantaneous shut-in pressure when the pump is stopped. After shut-in diffusion, measure the pressure drop for a certain period of time. Install a pressure gauge with an appropriate range at the wellhead and shut in the well for several hours according to the pump shutdown pressure.

[0065] (9) Well shut-in after pressure

[0066] After fracturing is completed, a pressure gauge with an appropriate range is installed at the wellhead according to the pump shutdown pressure, and a remote wireless pressure transmitter is also installed. If site conditions are limited, a wellhead storage pressure gauge is installed, and the well is shut in for a certain period of time.

[0067] (10) Subsequent normal construction

[0068] After the well is shut in, the routine procedures of backflow, testing for production, and formal production will be carried out.

[0069] Example 1:

[0070] (1) Evaluation of key reservoir parameters

[0071] Well 1: Interval 2846.0–2852.8 m, formation pressure coefficient 1.011. Reservoir porosity 9.2%, permeability 2.0 × 10⁻³ μm. 2 The oil saturation is 44.5%, indicating a relatively dry oil layer. The lithology consists of fine- to coarse-grained carbonate siltstone with a grain content of 62%–85%. The bottom layer contains a heavier amount of calcite and anhydrite, with an increase in dolomitic content downwards. The cement content is 15%–34%, mainly composed of calcite, dolomite, and anhydrite, with clay minerals accounting for less than 4% of the total content.

[0072] (2) Optimization of fracturing construction parameters

[0073] The construction flow rate was optimized by using simulation software to 2-3m. 3 / min, 500m³ of guar gum fracturing fluid 3 4m of 70 / 140 mesh silt 3 40 / 70 mesh ceramsite 41m 3 30 / 50 mesh ceramsite 9m 3 The dosage of temporary plugging agent is 200 kg, etc.

[0074] (3) Optimization of energy replenishment scale

[0075] The formula used is: V = α p ×(C f ×V 岩石孔隙 +P i )×H 垂深 ×100, the optimized replenishment fluid volume is calculated to be 900m³. 3 .

[0076] (4) Optimization of the formulation of energy replenishing fluid and guar gum fracturing fluid

[0077] Based on the core mineral composition and CST test results, an organic cationic clay stabilizer with a concentration of 0.5% was selected. Based on core wettability and oil displacement effects tests, an anionic-amphoteric composite surfactant with a concentration of 0.5% was selected. Considering process requirements and reservoir characteristics, guar gum was selected with a concentration of 0.5%. The performance of the guar gum fracturing fluid meets current industry standards. The replenishing fluid is composed of 0.5% organic cationic clay stabilizer, 0.5% anionic-amphoteric composite surfactant, and water.

[0078] (5) Primary preloading: Guar gum fracturing fluid is used with a displacement of 3m³. 3 / min, liquid volume 50m 3 After injecting 20% ​​of the liquid volume for this stage, add 2 μm of proppant with a particle size of 70-140 mesh. 3The volumetric sand-to-liquid ratio is 8%.

[0079] (6) Primary sand replenishment construction: The method of replenishing energy first and then adding sand is adopted.

[0080] ①Use 2m 3 / min displacement, 880m³ of replenishing fluid injected 3 ;

[0081] ② Use guar gum fracturing fluid to carry 20.5m of 40-70 mesh proppant. 3 Progressive volumetric proppant-to-fluid ratio: 10%–15%–20%–25%, continuing to use guar gum fracturing fluid carrying 4.5m of 30–50 mesh proppant. 3 The progressive volumetric sand-liquid ratio is 30%–35%–40%, and continuous sand addition is adopted.

[0082] (7) Secondary preloading:

[0083] ① Use guar gum fracturing fluid carrying 200 kg of temporary plugging agent, with a displacement of 2 m³ / h. 3 / min, liquid volume 20m 3 .

[0084] ② Use guar gum fracturing fluid to carry 2m of proppant with a particle size of 70-140 mesh. 3 The volumetric sand-to-liquid ratio is 8%.

[0085] (8) Secondary sand reinforcement construction:

[0086] ① Use guar gum fracturing fluid to carry 20.5m of 40-70 mesh proppant. 3 Progressive volumetric proppant-to-fluid ratio: 10%–15%–20%–25%, continuing to use guar gum fracturing fluid carrying 4.5m of 30–50 mesh proppant. 3 The progressive volumetric sand-liquid ratio is 30%–35%–40%, and continuous sand addition is adopted.

[0087] ②After sand addition is completed, inject the replenishing fluid as the replacement fluid, with the volume being equal to the wellbore volume; stop the pump and record the instantaneous pressure at shut-in, then measure the pressure drop for 15-20 minutes after shut-in diffusion.

[0088] (9) Well shut-in after fracturing: After fracturing is completed, install a pressure gauge with an appropriate range at the wellhead according to the pump shut-off pressure, and install a remote wireless pressure transmitter. If the site conditions are limited, it is recommended to install a wellhead storage pressure gauge and shut in the well for 20 days (adjust in time according to the changes in wellhead pressure).

[0089] (10) 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.

[0090] Experimental results show that, compared with adjacent wells using conventional fracturing methods (without replenishing fluid and temporary plugging balls), the initial oil production using the energy storage fracturing method described in Example 1 increased by more than 10 times, the stable production period increased by 3 times, and the crude oil recovery rate was significantly improved.

[0091] Example 2:

[0092] (1) Evaluation of key reservoir parameters

[0093] Well 2: The well section is 1217.0–1254.0 m deep, with a formation pressure coefficient of 0.94. The reservoir porosity is 9.3%, permeability is 1.2 × 10⁻³ μm², and oil saturation is 28.8%, classifying it as a poor-oil layer. The lithology is fine- to coarse-grained lithic siltstone containing carbonates, comprising 17% illite, 36% quartz, 20% feldspar, and 16% carbonates. The cementing material contains 25%–35% clay minerals.

[0094] (2) Optimization of fracturing construction parameters

[0095] Optimize construction flow rate using simulation software (5m³) 3 / min, 700m³ of guar gum fracturing fluid 3 10m of 70 / 140 mesh silt 3 60m of 30 / 50 mesh quartz sand 3 , 20 / 40 mesh quartz sand 40m 3 58 temporary plugging balls with a particle size of 15mm, etc.

[0096] (3) Optimization of energy replenishment scale

[0097] The formula used is: V = α p ×(C f ×V 岩石孔隙 +P i )×H 垂深 ×100, the optimized replenishment fluid volume is calculated to be 500m³. 3 .

[0098] (4) Optimization of the formulation of energy replenishing fluid and guar gum fracturing fluid

[0099] Based on the core mineral composition and CST test results, an organic cationic clay stabilizer with a concentration of 1.0% was selected. Based on core wettability and oil displacement effects tests, an anionic-amphoteric composite surfactant with a concentration of 0.5% was selected. Considering process requirements and reservoir characteristics, guar gum with a concentration of 0.3% was selected. The performance of the guar gum fracturing fluid meets current industry standards. The replenishing fluid is composed of 1.0% organic cationic clay stabilizer, 0.5% anionic-amphoteric composite surfactant, and water.

[0100] (5) Primary preloading: Guar gum fracturing fluid is used with a displacement of 5m³.3 / min, liquid volume 100m 3 After injecting 30% of the liquid volume for this stage, add 5 μm of proppant with a particle size of 70–140 mesh. 3 The volumetric sand-to-liquid ratio is 7%.

[0101] (6) Primary sand replenishment construction: The method of replenishing energy first and then adding sand is adopted.

[0102] ①Use 2m 3 / min displacement, 480m³ of replenishing fluid injected 3 ;

[0103] ②Increase displacement to 5m 3 / min, using guar gum fracturing fluid to carry 30m of preferred 30-50 mesh proppant. 3 The volumetric sand-to-liquid ratio is 10-15-20-25%; continue to use guar gum fracturing fluid to carry 20m3 of 20-40 mesh proppant, with a volumetric sand-to-liquid ratio of 30-35-40%, and adopt continuous sand addition.

[0104] (7) Secondary preloading:

[0105] ①Use fracturing fluid containing guar gum to carry temporary plugging balls, with a displacement of 2-5 m³ / h. 3 / min, liquid volume 20m 3 .

[0106] ② Use guar gum fracturing fluid to carry 5m of proppant with a particle size of 70-140 mesh. 3 The volumetric sand-to-liquid ratio is 9%.

[0107] (8) Secondary sand reinforcement construction:

[0108] ①Increase displacement to 5m 3 / min, using guar gum fracturing fluid to carry 30m of preferred 30-50 mesh proppant. 3 The volumetric sand-to-liquid ratio is 10-15-20-25%; continue to use guar gum fracturing fluid to carry 20m3 of 20-40 mesh proppant, with a volumetric sand-to-liquid ratio of 30-35-40%, and adopt continuous sand addition.

[0109] ②After sand addition is completed, inject the replenishing fluid as the replacement fluid, with the volume being equal to the wellbore volume; stop the pump and record the instantaneous pressure at shut-in, then measure the pressure drop for 15-20 minutes after shut-in diffusion.

[0110] (9) Well shut-in after fracturing: After fracturing is completed, install a pressure gauge with an appropriate range at the wellhead according to the pump shut-off pressure, and install a remote wireless pressure transmitter. If the site conditions are limited, it is recommended to install a wellhead storage pressure gauge and shut in the well for 17 days (adjust in time according to the changes in wellhead pressure).

[0111] (10) 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.

[0112] Experimental results show that, compared with adjacent wells using conventional fracturing methods (without replenishing fluid and temporary plugging balls), the initial oil production using the energy storage fracturing method described in Example 2 increased by more than 5 times, the stable production period increased by 5 times, and the crude oil recovery rate was significantly improved.

[0113] Example 3:

[0114] (1) Evaluation of key reservoir parameters

[0115] Well 3: The well section is 2407.2-2409.0 m, with a formation pressure coefficient of 0.639. The reservoir porosity is 6.3%, permeability is 0.5 × 10⁻³ μm², and oil saturation is 40.8%, classifying it as a relatively dry oil-bearing layer. The lithology is fine- to medium-grained feldspathic sandstone, with quartz content ranging from 58% to 64%, feldspar content between 25% and 30%, and rock fragment content around 9% to 15%. The cement content is 15% to 17%, mainly composed of anhydrite, dolomite, and calcite. The absolute content of clay minerals is less than 2%, with illite relative content greater than 90% and chlorite relative content less than 10%.

[0116] (2) Optimization of fracturing construction parameters

[0117] Simulation software was used to optimize the construction flow rate by 2m. 3 / min, 400m³ of guar gum fracturing fluid 3 8m of 70 / 140 mesh silt 3 40 / 70 mesh ceramsite 22m 3 30 / 50 mesh ceramsite 8m 3 The dosage of temporary plugging agent is 200 kg, etc.

[0118] (3) Optimization of energy replenishment scale

[0119] Based on the small size of the trap where this well is located (oil-bearing area 0.19 km²) 2 Furthermore, no new wells are planned for deployment within the block, and development will rely solely on elastic energy without integrated injection and production systems. Therefore, the replenishment fluid volume will be further increased to maximize the affected area, increase controlled reserves, and pursue high recovery rates for the block. The formula used is: V = α p ×(C f ×V 岩石孔隙 +P i )×H 垂深 ×100, the optimized replenishment fluid volume is calculated to be 4000m³. 3 .

[0120] (4) Optimization of the formulation of energy replenishing fluid and guar gum fracturing fluid

[0121] Based on the core mineral composition and CST test results, an organic cationic clay stabilizer with a concentration of 0.3% was selected. Based on core wettability and oil displacement effects tests, an anionic-amphoteric composite surfactant with a concentration of 0.3% was selected. Considering process requirements and reservoir characteristics, guar gum with a concentration of 0.4% was selected. The performance of the guar gum fracturing fluid meets current industry standards. The replenishing fluid is composed of 0.3% organic cationic clay stabilizer, 0.3% anionic-amphoteric composite surfactant, and water.

[0122] (5) Primary preloading: Guar gum fracturing fluid is used with a displacement of 2m³. 3 / min, liquid volume 80m 3 After injecting 25% of the liquid volume for this stage, add 4 μm of proppant with a particle size of 70–140 mesh. 3 The volumetric sand-to-liquid ratio is 8%.

[0123] (6) Primary sand addition and energy replenishment construction: adopt the sand addition first and then energy replenishment mode.

[0124] ①Use guar gum fracturing fluid to carry 11m of preferred 40-70 mesh ceramsite. 3 The volumetric sand-to-fluid ratio is 10-15-20-25%; continue using guar gum fracturing fluid to carry 4m of 30-50 mesh ceramsite. 3 The volumetric sand-to-liquid ratio is 30-35-40%; continuous sand addition is adopted.

[0125] (7) Secondary preloading:

[0126] ① Use guar gum fracturing fluid carrying 200 kg of temporary plugging agent, with a displacement of 2 m³ / h. 3 / min, liquid volume 20m 3 .

[0127] ② Use guar gum fracturing fluid to carry 70-140 mesh proppant for 4m 3 The volumetric sand-to-liquid ratio is 8%.

[0128] (8) Secondary sand reinforcement construction:

[0129] ①Use guar gum fracturing fluid to carry 11m of preferred 40-70 mesh ceramsite. 3 The volumetric sand-to-fluid ratio is 10-15-20-25%; continue using guar gum fracturing fluid to carry 4m of 30-50 mesh ceramsite. 3 The volumetric sand-to-liquid ratio is 30-35-40%; continuous sand addition is adopted.

[0130] ② After sand addition is completed, inject replenishing fluid as the replacement fluid, with the volume equal to the wellbore volume; record the instantaneous shut-in pressure after pump shutdown, and measure the pressure drop for 15-20 minutes during well shutdown diffusion. Install a pressure gauge with an appropriate range at the wellhead, and shut in the well for 2-4 hours based on the pump shutdown pressure.

[0131] ③ At a discharge rate below the optimized crack closure pressure (0.4–0.8 m³ / h) 3 Inject the remaining energy replenishing fluid at a rate of ( / min).

[0132] (9) Well shut-in after fracturing: After fracturing is completed, install a pressure gauge with an appropriate range at the wellhead according to the pump shut-off pressure, and install a remote wireless pressure transmitter. If the site conditions are limited, it is recommended to install a wellhead storage pressure gauge and shut in the well for 25 days (adjust in time according to the changes in wellhead pressure).

[0133] (10) 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.

[0134] Experimental results show that, compared with adjacent wells using conventional fracturing methods (without replenishing fluid and temporary plugging agent), the initial oil production using the energy storage fracturing method described in Example 3 increased by more than 8 times, the stable production period increased by 6 times, and the oil recovery rate was significantly improved.

[0135] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. An energy stored fracturing method suitable for use in low permeability tight oil reservoirs, characterized in that, Comprising the following steps: S1) evaluation of key reservoir parameters: Carrying out parameter evaluation of structure, fault and various fissure development, lithology and sensitivity, physical property, rock mechanics parameters and three-directional ground stress parameters, temperature and pressure, said rock mechanics parameters including fracture toughness in horizontal direction of reservoir and vertical direction of reservoir and upper and lower interbeds; S2) optimization of fracturing operation parameters: Establishing a geological model, importing the geological model into fracturing simulation software, simulating crack propagation dynamics and fracturing production dynamic prediction under different fracturing operation parameters; said fracturing operation parameters including discharge capacity, viscosity, liquid volume, proppant volume and proportion of proppants with different particle sizes, operation sand-liquid ratio, corresponding pumping program, type and amount of temporary plugging agent or temporary plugging ball; S3) optimization of energy supplement scale: Optimizing energy supplement liquid volume by calculation; S4) optimization of energy supplement liquid and guar gum fracturing fluid formula: Determining the type and concentration of clay stabilizer of various liquid systems according to core mineral composition and core CST experimental results; determining the type and concentration of surfactant of liquid system according to core wettability and oil displacement effect experiment; selecting the concentration of guar gum fracturing fluid in combination with process requirements and reservoir characteristics; S5) first-stage pre-pressurization: After injecting the liquid volume of the guar gum fracturing fluid in this stage, half of the optimized amount of proppant is added, and continuous sand addition is adopted; S6) first-stage sand addition and energy supplement operation: Based on the volume of the replenishing fluid, the sand-addition replenishing mode is determined. The volume of the replenishing fluid is below 1000 m³. 3 When this is the case, the energy replenishment followed by sand addition mode should be adopted; for depths greater than 1000m 3 At that time, a sand-addition followed by energy replenishment mode is adopted, which includes the following: Energy supplement liquid is injected at the discharge capacity and liquid volume optimized in step S2, and proppants with particle sizes of 40-70 mesh or 30-50 mesh are carried by guar gum fracturing fluid, and the progressive volume sand-liquid ratio is 10%-15%-20%-25% in turn, and half of the optimized amount of proppant is added, and proppants with particle sizes of 30-50 mesh or 20-40 mesh are carried by guar gum fracturing fluid, and the progressive volume sand-liquid ratio is 30%-35%-40% in turn, and the amount added is half of the optimized amount of proppant; S7) second-stage pre-pressurization: Temporary plugging ball or temporary plugging agent is used to block with guar gum fracturing fluid, and then the process of step S5 is repeated to complete sand addition; S8) second-stage sand addition and energy supplement operation: The process of step S7 is repeated, and after sand addition is completed, energy supplement liquid is finally injected as displacement liquid, and the liquid volume is the volume of wellbore; pump stopping pressure is recorded, well closure diffusion is measured, and pressure drop is measured for a certain time, a pressure gauge with a suitable range is installed at the wellhead, and well closure is carried out for a certain time according to pump stopping pressure; S9) post-fracturing well closure: After fracturing is completed, a pressure gauge with a suitable range is installed at the wellhead according to pump stopping pressure, and a remote wireless pressure transducer is installed, and if the site conditions are limited, a storage type pressure gauge is installed at the wellhead, and well closure is carried out for a certain time; S10) subsequent normal operation: After well closure is completed, return flow, production test and formal production are carried out according to the conventional process.

2. The method according to claim 1, wherein, The displacement of the guar gum fracturing fluid in step S5 is the optimized maximum value, and the liquid volume is 50-100 m 3 20%-30% of the first pre-press injection liquid, the proppant particle size is 70-140 mesh, and the volume sand liquid ratio is 7-9%.

3. The method for energy storage fracturing suitable for low permeability tight oil reservoirs according to claim 1 or 2, characterized in that, The first sand adding and then energy supplementing mode in step S6 includes the following contents: using guar gum fracturing fluid to carry proppant with a particle size of 40-70 mesh or 30-50 mesh, the progressive volume sand liquid ratio is 10%-15%-20%-25% in turn, half of the optimized proppant amount is added, using guar gum fracturing fluid to carry proppant with a particle size of 30-50 mesh or 20-40 mesh, the progressive volume sand liquid ratio is 30%-35%-40% in turn, the amount is half of the optimized proppant amount, the remaining energy supplementing fluid is injected at an optimized discharge rate lower than the fracture closure pressure, and the optimized discharge rate is 1 m 3 / min.

4. The method according to claim 3, wherein, The temporary plugging ball or plugging agent carried by the guar gum fracturing fluid in step S7 is discharged at an optimized value, and the liquid volume is 20 m 3 .

5. The method according to claim 1, wherein, The pressure drop time in step S8 is 15-20 min, and well closure is carried out for 2-4 hours after pump stopping pressure.

6. The method according to claim 3, wherein, The energy supplement liquid in step S4 is composed of 0.2-1.0% clay stabilizer, 0.1-0.5% surfactant and water.

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