A fracturing method suitable for loose sandstone and capable of comprehensively controlling fracture height

Abstract

The present application relates to a kind of comprehensive control fracture height fracturing method suitable for loose sandstone, comprising the following steps: selecting degradation rate index, particle size value index, sedimentation rate index and not less than two in filtration reduction performance index, to evaluate temporary plugging filtration reducer, obtain the temporary plugging filtration reducer meeting the fracturing requirement of loose sandstone reservoir;Considering geological factors and engineering factors, the construction parameters of the amount of shielding agent and the floating / sinking speed of shielding agent are optimized;Using the temporary plugging filtration reducer after evaluation, the amount of shielding agent and the construction parameters of the floating / sinking speed of shielding agent are used for fracturing construction.The present application can effectively realize the crack initiation of loose sandstone reservoir, effectively control the crack height, and form excellent post-fracturing conductivity.

Description

Technical Field

[0001] This invention relates to the technical field of oil and gas field development engineering - reservoir production enhancement measures, specifically to a fracturing method for comprehensively controlling fracture height applicable to loose sandstone. Background Technology

[0002] The main oilfields in the Bohai Sea are loose sandstone reservoirs. After years of high-speed extraction, complex blockage and damage problems have emerged near the wellbore, making it increasingly difficult to maintain high production capacity. Hydraulic fracturing creates artificial fractures with a certain conductivity, which can penetrate the blockage and damage zone near the wellbore, thereby increasing oil production. The main oilfields in the Bohai Sea are loose sandstone reservoirs with large porosity, high permeability, and weak cementation. These reservoirs experience significant fluid loss during fracturing. Furthermore, the main producing layer is thin and contains a water layer at the bottom, requiring strict control of fracture size to prevent water breach. Therefore, the key to increasing production in the Bohai loose sandstone reservoirs lies in effectively controlling fracture fluid loss and fracture height.

[0003] Measures to reduce acid loss during fracturing operations include increasing fracturing fluid viscosity, reducing fracturing flow rate, and using filtration reducers. Higher fracturing fluid viscosity can reduce acid loss but also cause uncontrolled fracture along the fracture height, making it unsuitable for thin-producing formations and bottom-water reservoirs. Reducing the fracturing flow rate can control fracture height but reduces fracture propagation, leading to less than ideal stimulation results. Chinese invention patent "An oil-soluble filtration reducer that can be rapidly dispersed in water-based guar gum fracturing fluid and its preparation method" (application number: 201210167374.3) discloses an oil-soluble filtration reducer that can be rapidly dispersed in fracturing fluid and its preparation method. This invention provides a product made from petroleum resin, water, and a wetting agent, which is thoroughly stirred to obtain a yellow or brown powder. Chinese invention patent "Filtration reducer composition and filtration reducer method for fractured-vuggy reservoirs" (application number: 201410616883.9) discloses a filtration reducer composition and filtration reducer method for fractured-vuggy reservoirs. This invention relates to a combination of fluid loss reducers and a method for reducing fluid loss in the field of acid fracturing. A temporary plugging fluid loss reducer is a material that can temporarily plug the fracture wall to form a dense filter cake and block the pores and throats of the reservoir matrix surrounding the fracture, thereby reducing the loss of fracturing fluid. However, currently there is no evaluation method for temporary plugging fluid loss reducers used in fracturing to assess their performance.

[0004] Conventional techniques for controlling fracture height involve selecting and utilizing dense clay interlayers above and below the producing layer, adjusting the fracturing fluid displacement, and controlling the fracture height. However, when the producing layer is thin or the interlayer stress is weak, hydraulic fractures can penetrate the producing layer and enter the interlayer, leading to uncontrolled fracture height and potentially breaching the water layer, thus affecting fracturing effectiveness. Low-viscosity fracturing fluids can control fracture height to some extent, but they have extremely high filtration loss for fracturing loose sandstone, making it difficult to form effective hydraulic fractures. In addition, compared to large displacement, small displacement pumping can reduce the net pressure within the fracture to some extent, thereby reducing fracture height. Another method for controlling fracture height is the artificial shielding layer technique. This technique involves applying shielding agents to the upper, lower, or both upper and lower parts of the fracture before proppant fracturing to limit longitudinal fracture extension. However, due to factors such as the rising / sinking rate and dosage of the shielding agent, there is often a risk of insufficient sand plugging and artificial interlayer thickness, failing to form effective stress shielding, leading to uncontrolled fracture height.

[0005] Existing technologies primarily target fracturing fluid loss reduction techniques, fracture height control methods, and fracture height control processes for oil and gas reservoirs. However, loose sandstone is characterized by large porosity, high permeability, and weak cementation. This necessitates reducing fracturing fluid loss to form effective fractures while simultaneously controlling fracture height to prevent fractures from penetrating water layers. Therefore, the fracturing fluid loss reduction techniques and fracture height control methods and processes disclosed in existing technologies are not suitable for fracturing stimulation of loose sandstone with controlled fracture height.

[0006] Therefore, there is an urgent need for a comprehensive fracturing method for controlling fracture height in loose sandstone. Summary of the Invention

[0007] To address the aforementioned technical issues, a comprehensive fracturing method for controlling fracture height in loose sandstone reservoirs is provided. This method includes an evaluation method for temporary plugging and filtration reduction agents in loose sandstone reservoirs, an optimization method for the dosage of shielding agents and the floating / settling rate of shielding agents, and a construction method for controlling fracture height in loose sandstone reservoirs. This method can effectively control fracture height while initiating fractures in loose sandstone reservoirs, and form excellent post-fracturing conductivity.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A comprehensive fracturing method for controlling fracture height in loose sandstone includes the following steps:

[0010] Select at least two of the following indicators: degradation rate, particle size, settling velocity, and filtration loss reduction performance, to evaluate the temporary plugging filtration loss reducer and obtain a temporary plugging filtration loss reducer that meets the fracturing requirements of loose sandstone reservoirs.

[0011] Taking into account geological and engineering factors, optimize the construction parameters for the amount of masking agent and the rising / sinking speed of the masking agent;

[0012] Using the evaluated construction parameters of temporary plugging and filtration reduction agent dosage, shielding agent dosage, and shielding agent floating / sinking rate, fracturing operations were carried out to control the fracture height of loose sandstone reservoirs and form excellent post-fracturing conductivity.

[0013] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, has a predetermined degradation rate ranging from 95% to 100%.

[0014] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, has a particle size range of 90-150 μm.

[0015] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, includes the following steps for optimizing the construction parameters such as the dosage of high temporary plugging agent and the floating / sinking velocity:

[0016] Based on the formation fracture toughness, construction pressure, and fracture design scale, and according to the linear elastic fracture mechanics theory, the amount of temporary plugging and filtration reduction agent used in construction is optimized.

[0017] Optimize the floating / sinking velocity of the temporary filtration reducer based on its strength, density, diameter, and crack design size.

[0018] In the aforementioned comprehensive fracturing method for controlling fracture height in loose sandstone, preferably, the floating / sinking velocity of the optimized temporary plugging and filtration reduction agent is 0.2 m / min.

[0019] The aforementioned fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, includes the following steps in the fracturing construction method:

[0020] Low-viscosity fracturing fluid carrying a temporary plugging and filtration reduction agent is used as the pre-fracturing fluid to create fractures in the formation and complete the initial fracturing operation.

[0021] After the pre-filled liquid is successfully used to create the crack, the floating and sinking blocking agent is injected using a low-displacement balanced injection method. This maintains a certain opening in the crack while transporting the blocking agent to the upper and lower ends of the crack to form the required artificial barrier layer.

[0022] High-viscosity fracturing fluid is used as the proppant-carrying fluid, along with a combination of proppants of different particle sizes. The proppant-carrying fluid is used to pump the combination of proppants of different particle sizes into the hydraulic fractures of the reservoir, supporting the fractures after fracturing, thereby forming a high-permeability oil and gas channel and completing the fracturing operation.

[0023] The aforementioned fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, further includes the following steps:

[0024] By calculating the minimum horizontal principal stress of the formation, the stress difference between the target layer and the upper and lower interlayers, as well as the distance between the producing layer and the water layer, are determined. Based on the drilling fluid contamination radius and the fracture size designed by the fracturing software, it is determined whether a temporary plugging agent is needed to reduce fluid loss.

[0025] The aforementioned fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, further includes the following steps:

[0026] The degree and radius of contamination were determined through well test analysis and oil well production simulation. Fracturing software was used to simulate and determine the scale of construction, discharge rate and pumping procedure.

[0027] The fracturing method for comprehensively controlling fracture height applicable to loose sandstone, preferably, the specific condition for determining whether to use a temporary plugging and filtration reduction agent is: the stress difference between the minimum principal stress of the interlayer and the producing layer is 5 MPa.

[0028] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, uses a low-viscosity fracturing fluid with a viscosity of 10 mPa·s at 80°C.

[0029] The aforementioned fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, includes the following low-viscosity fracturing fluid, specifically comprising, by mass percentage concentration:

[0030]

[0031] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, uses a high-viscosity fracturing fluid with a viscosity of 40 mPa·s at 80°C.

[0032] The aforementioned fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, includes the following high-viscosity fracturing fluid, specifically comprising, by mass percentage concentration:

[0033] Thickener 0.4%;

[0034] 0.2% drag reducer;

[0035] Water remains.

[0036] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, involves a combination of proppants of different particle sizes, which is a mixture of quartz sands of different particle sizes. The particle size of the quartz sands includes a mixture of any particle size from 20 mesh to 40 mesh and any particle size from 40 mesh to 70 mesh, and the particle sizes of the two types of quartz sands mixed are not the same.

[0037] The fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, involves a pumping flow rate of 3m³ during the low-flow-rate balanced injection of the floating and sinking temporary plugging filtration-reducing agent.3 / min.

[0038] The present invention has the following advantages due to the adoption of the above technical solutions:

[0039] In view of the large filtration loss of loose sandstone, providing an evaluation method for temporary filtration loss reducing agents can provide staff with performance evaluation standards for temporary filtration loss reducing agents and optimize the materials of temporary filtration loss reducing agents;

[0040] To address the challenge of controlling fracture height in loose sandstone reservoirs, an optimized method is provided for the dosage of high-level shielding agent and the floating / sinking rate of the agent. This optimization method fully considers geological factors such as formation thickness and geostress distribution, as well as engineering factors such as fracture height, fracture length, and construction pressure. It provides field personnel with a more scientific dosage standard and optimizes the construction parameters of the floating and sinking shielding agent.

[0041] This invention also provides a fracturing construction method for comprehensively controlling fracture height in loose sandstone reservoirs. This method employs a combination of temporary plugging and filtration-reducing low-viscosity pre-fracturing fluid, balanced injection of a shielding agent, and high-viscosity composite proppant-carrying techniques. This effectively achieves fracture initiation in loose sandstone reservoirs while simultaneously controlling fracture height and creating high post-fracturing conductivity. This method eliminates the need for specialized crosslinking agents, significantly reducing construction difficulty and environmental pollution. Furthermore, the temporary plugging and filtration-reducing agent effectively minimizes fracturing fluid loss, preventing water phase intrusion into the oil and gas layer and causing minimal damage to the reservoir, thus maximizing the fracturing stimulation effect. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the evaluation method for the temporary plugging and filtration reduction agent in loose sandstone reservoirs according to the present invention;

[0043] Figure 2 This is a schematic cross-sectional view of the crack with artificial masking agent added according to the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0045] This invention provides a comprehensive fracturing method for controlling fracture height in loose sandstone reservoirs, comprising the following steps: selecting at least two of the following indices: degradation rate, particle size, settling velocity, and filtration loss reduction performance, to evaluate a temporary plugging filtration loss reducer and obtain a temporary plugging filtration loss reducer that meets the fracturing requirements of loose sandstone reservoirs; considering geological and engineering factors, optimizing the dosage of the shielding agent and the floating / sinking velocity of the shielding agent as construction parameters; and using the evaluated temporary plugging filtration loss reducer, the dosage of the shielding agent, and the floating / sinking velocity of the shielding agent as construction parameters to carry out fracturing operations, thereby controlling the fracture height in loose sandstone reservoirs and forming excellent post-fracturing conductivity.

[0046] This invention addresses the high filtration loss characteristic of loose sandstone by providing an evaluation method for temporary plugging and filtration loss reducing agents. This method offers performance evaluation standards for such agents, enabling optimization of their materials. Furthermore, addressing the difficulty in controlling fracture height in loose sandstone reservoirs, this invention provides an optimized method for the dosage and uplift / sinking rates of high-level shielding agents for fracture control. This optimization method fully considers geological factors such as formation thickness and stress distribution, as well as engineering factors such as fracture height, fracture length, and construction pressure. It provides field personnel with a more scientific dosage standard and optimizes the construction parameters for uplift and sinking shielding agents. This invention effectively achieves fracture initiation in loose sandstone reservoirs while simultaneously controlling fracture height and creating excellent post-compression conductivity.

[0047] A comprehensive fracturing method for controlling fracture height in loose sandstone includes the following steps:

[0048] S1: Select at least two of the following indicators: degradation rate, particle size, settling velocity, and filtration loss reduction performance, to evaluate the temporary plugging filtration loss reducer and obtain a temporary plugging filtration loss reducer that meets the fracturing requirements of loose sandstone reservoirs.

[0049] It should be noted that there is no clear order of execution among the steps for evaluating the degradation rate, particle size, settling velocity, and filtration performance of temporary filtration agents. They can be performed in parallel or sequentially, depending on the actual evaluation requirements.

[0050] The evaluation of the degradation rate of the temporary clogging and filter loss reducing agent specifically includes the following steps:

[0051] S111: Place the temporary filtration reduction agent in a 40℃ oven for drying for 12 hours;

[0052] S112: Weigh the temporary clogging and filtration loss reducing agent to obtain the first weight value;

[0053] S113: Add the temporary plugging and filtration reduction agent to the formation water of loose sandstone, and maintain the mass ratio of the temporary plugging and filtration reduction agent to the formation water at 1:50;

[0054] S114: Heat the mixed liquid in a constant temperature water bath for 24 hours;

[0055] S115: Filter the mixture after constant temperature heating using 100-mesh filter paper;

[0056] S116: Place the filtered temporary filtration reducer into an oven and dry it for 12 hours; the staff can select the required temperature according to actual needs, preferably 40℃.

[0057] S117: Weigh the degraded temporary clogging and filtration loss reducing agent to obtain a second weight value;

[0058] S118: The degradation rate of the temporary clogging and filter loss reducing agent is obtained based on the first weight value and the second weight value.

[0059] When the degradation rate is at a predetermined value, the degradation rate performance of the temporary plugging and filtration reduction agent meets the fracturing requirements of loose sandstone, wherein the predetermined value of the degradation rate is in the range of 95-100%.

[0060] In step S118, the degradation rate of the temporary clogging and filter loss reducing agent is calculated using the following formula (1) based on the first weight value and the second weight value:

[0061]

[0062] in,

[0063] R represents the degradation rate of the temporary filtration reduction agent;

[0064] m1 is the first weight value, and its unit is g;

[0065] m2 is the second weight value, and its unit is g.

[0066] The specific steps for evaluating the particle size index of temporary clogging and filtration loss reducing agents include the following:

[0067] S121: Measure the particle size of the filtration loss reducer using a particle size analyzer;

[0068] S122: When the particle size value is within a predetermined particle size range, evaluate the particle size index of the temporary clogging and filtration loss reducing agent. The predetermined particle size range is 90-150 μm.

[0069] The specific steps for evaluating the settling velocity of temporary filtration reducers include the following:

[0070] S131: Measure 500 mL of fracturing fluid for on-site construction using a graduated cylinder, add the target concentration of temporary plugging and filtration reduction agent into the graduated cylinder, and stir evenly with a glass rod;

[0071] S132: After stirring evenly, let stand, use a stopwatch to record the time it takes for the temporary filtration agent to settle to the bottom, and at the same time record the movement distance to calculate the settling velocity.

[0072] The evaluation of the filtration performance of temporary filtration reducers includes the following steps:

[0073] S141: Select core samples based on reservoir properties and process the cores into core sections;

[0074] S142: Measure 500 mL of fracturing fluid for on-site construction using a graduated cylinder, put it into the test tube of the high-temperature and high-pressure filtration instrument, place a core slice, assemble the test tube and put it into the heating jacket;

[0075] S143: Close the outlet valve, apply an initial inlet pressure of 0.05MPa, and heat the high-temperature and high-pressure filter to the experimental temperature within 30 minutes;

[0076] S144: After the high-temperature and high-pressure fluid loss analyzer is heated to the experimental temperature, the inlet pressure is set to 0.5MPa, and fracturing fluid is injected under constant pressure.

[0077] S145: Open the outlet valve to collect the filtrate into the graduated cylinder and record the volume of the filtrate in real time;

[0078] S146: Record the volume of the filtrate after 30 minutes of experimentation to obtain the first volume value;

[0079] S147: Add the temporary plugging and filtration reduction agent powder to the fracturing fluid in the field to prepare a fracturing fluid containing the temporary plugging and filtration reduction agent at the target concentration;

[0080] S148: Repeat steps S41-S46 with the fracturing fluid containing the temporary plugging and filtrate-reducing agent, and record the volume of the filtrate after 30 minutes of experiment to obtain the second volume value;

[0081] S149: The filtration loss reduction performance of the temporary clogging filtration loss reducing agent is obtained based on the first volume value and the second volume value.

[0082] Step S149 uses the following formula for calculation:

[0083]

[0084] in,

[0085] T represents the filtration loss reduction performance of the temporary filtration loss reducing agent;

[0086] V1 is the first volume value, and its unit is m. 3 ;

[0087] V2 is the second volume value, and its unit is m. 3.

[0088] When the filtration loss reduction performance is within a predetermined value, the filtration loss reduction performance index of the temporary plugging filtration loss reduction agent is evaluated to meet the fracturing requirements of loose sandstone. The predetermined range for the filtration loss reduction performance is 50-100%.

[0089] S2: Considering geological and engineering factors, optimize the construction parameters for the amount of shielding agent and the floating / sinking speed of the shielding agent.

[0090] Optimizing the application parameters for the masking agent dosage and its rising / sinking speed includes the following steps:

[0091] S21: Based on the formation fracture toughness, construction pressure, and fracture design scale, optimize the amount of floating / sinking shielding agent used in construction according to the theory of linear elastic fracture mechanics.

[0092] S22: Optimize the rising / sinking speed of the shielding agent based on its strength, density, diameter, and crack design size.

[0093] Specifically, step S21 includes:

[0094] S211: When the fracture center is inside the producing layer, according to the linear elastic fracture mechanics theory, the stress intensity factors generated by the opening stress on the fracture wall at the upper and lower ends of the fracture are calculated by formulas (3) and (4), respectively:

[0095]

[0096]

[0097] in,

[0098] f is the crack half-height, and its unit is m;

[0099] p(y) is the net pressure inside the crack, and its unit is MPa;

[0100] y is the coordinate along the crack height direction, and its unit is m;

[0101] K u K b These are the stress intensity factors at the top and bottom of the crack, respectively, with units of MPa·m. 0.5 .

[0102] S212: Combining the net pressure distribution of open cracks under artificial diaphragm conditions, and considering the Type I crack propagation criterion, namely:

[0103] K u =K ICu (5)

[0104] Kb =K ICb (6)

[0105] S213: As Figure 1 As shown, a rectangular coordinate system is established with the lower end of the fracture as the origin, the horizontal direction to the right as the positive X-axis, and the vertical direction upward as the positive Y-axis. The bottom hole pressure is p. wf The net pressure p within the crack net The distribution is as follows:

[0106] p net =p wf -(σ b +g b d b ), 0≤y<d b (7)

[0107] p net =p wf -σ b d b ≤y<h b (8)

[0108] p net =p wf -σ r h b ≤y<h b +h (9)

[0109] p ncl =p wf -σ u h b +h≤y<h b +h+h u -d u (10)

[0110] p net =p wf -(σ u +g u d u ), h b +h+h u -d u ≤y<h b +h+h u (11)

[0111] in,

[0112] h represents the thickness of the producing layer, and its unit is m;

[0113] h u This represents the distance the crack travels into the caprock, measured in meters (m).

[0114] h bThis represents the distance the crack penetrates into the bottom layer, measured in meters (m).

[0115] d b The thickness of the settling agent interlayer is expressed in meters (m).

[0116] d u The thickness of the buoyancy agent interlayer is expressed in meters (m).

[0117] g b The impedance gradient of the settling agent interlayer is expressed in MPa / m.

[0118] g u The impedance gradient of the buoyant separator is expressed in MPa / m.

[0119] σ r The minimum horizontal principal stress of the producing layer is given in MPa.

[0120] σ u This represents the minimum horizontal principal stress at the top layer, and its unit is MPa.

[0121] σ b This represents the minimum horizontal principal stress at the bottom layer, and its unit is MPa.

[0122] p wf This represents the bottom hole pressure, measured in MPa.

[0123] y is the coordinate along the crack height direction, and its unit is m;

[0124] make

[0125] A=(h b +h+h u ) / 2

[0126] B = (h b +hh u ) / 2

[0127] C=(h u +hh b ) / 2

[0128] Then we can get:

[0129]

[0130]

[0131] After combining the equations, we can obtain information about h. u and h b The numerical solution of the above system of two nonlinear equations can be obtained by applying the quasi-Newton algorithm to solve the nonlinear equation system.

[0132] Depending on the stress distribution and thickness of the reservoir and interlayer, add 100-400 kg each of buoyancy and sinking blocking agents.

[0133] Specifically, step S22 includes:

[0134] When a floating / sinking shielding particle with diameter D moves upward / downward in a fluid, it is subjected to gravity G and frictional resistance F. f and buoyancy F F The combined effect of these three forces yields the buoyancy / sinking rate of the buoyancy / sinking shielding agent, which is calculated using formula (14).

[0135]

[0136] in,

[0137] v represents the floating / sinking rate of the shielding agent, and its unit is m / min;

[0138] ρ ￠ ρ and ρ' represent the densities of the carrying liquid and the buoyancy / sinking blocking agent, respectively, in g / cm³. 3 ;

[0139] D is the diameter of the TBA flotation shielding agent, and its unit is mm;

[0140] g is the acceleration due to gravity, and its unit is m / s². 2 ;

[0141] μ is the viscosity of the carrier liquid, and its unit is mPa·s.

[0142] Based on the designed crack length, construction flow rate, and amount of masking agent, the rising and sinking speed of the masking agent is 0.2 m / min.

[0143] S3: Using the evaluated construction parameters of temporary plugging and filtration reduction agent dosage, shielding agent dosage, and shielding agent floating / sinking rate, fracturing operations are carried out to control the fracture height of loose sandstone reservoirs and form excellent post-fracturing conductivity.

[0144] The aforementioned fracturing method for comprehensively controlling fracture height in loose sandstone, preferably, includes the following steps in the fracturing construction method:

[0145] S31: Low-viscosity fracturing fluid carrying temporary plugging and filtration reduction agent is used as the pre-fracturing fluid to create fractures in the formation and complete the initial fracturing operation.

[0146] S32: After the pre-filled liquid is successfully used to create the crack, the floating and sinking blocking agent is injected using a low-displacement balanced injection method. This maintains a certain opening in the crack while transporting the blocking agent to the upper and lower ends of the crack to form the required artificial barrier layer.

[0147] S33: High-viscosity fracturing fluid is used as the proppant-carrying fluid, along with a combination of proppants of different particle sizes. The proppant-carrying fluid is used to pump the combination of proppants of different particle sizes into the hydraulic fractures of the reservoir, supporting the fractures after fracturing, thereby forming a high-permeability oil and gas channel and completing the fracturing operation.

[0148] The fracturing method further includes the following steps:

[0149] S34: By calculating the minimum horizontal principal stress of the formation, determine the stress difference between the target layer and the upper and lower interlayers, as well as the distance between the production layer and the water layer. Based on the drilling fluid contamination radius and the fracture size designed by the fracturing software, determine whether it is necessary to add a temporary plugging agent to reduce fluid loss.

[0150] S35: Determine the degree and radius of contamination through well test analysis and oil well production simulation, and use fracturing software simulation to determine the scale of construction, discharge rate and pumping procedure.

[0151] In step S34, the forces acting on the producing formation are obtained according to the vertical stress, minimum horizontal principal stress, and maximum horizontal principal stress, mainly through two methods: one is through indoor mechanical performance testing experiments; the other is by calculating the values ​​using well logging parameters.

[0152] The horizontal stress difference is a key parameter for determining the amount of shielding agent needed. When the stress difference between the minimum horizontal principal stresses of the interlayer and the producing layer is large, the interlayer provides greater resistance to fracture propagation in the producing layer, and the fracture height can be effectively controlled. When the stress difference between the minimum horizontal principal stresses of the interlayer and the producing layer is small, a shielding agent is needed to control the fracture height because the interlayer provides less resistance to fracture propagation. The stress difference between the minimum principal stresses of the interlayer and the producing layer is 5 MPa.

[0153] In step S35, the main purpose of fracturing loose sandstone is to penetrate the contaminated area caused by drilling fluid loss, forming a high-permeability channel for oil and gas flow, ultimately increasing production. Based on the reservoir's geological model and contamination level, fracturing software is first used to optimize fracture length, fracture height, and conductivity. After determining the fracturing length, the fracturing software is then used to optimize the scale of the operation; this fracturing software is an existing fracturing simulation software in this technical field.

[0154] Displacement refers to the pumping volume of the fracturing truck during fracturing operations, which is related to geological factors and the scale of the operation, such as 5m. 3 / min;

[0155] The pumping procedure refers to the sequence, flow rate, and volume of fluid pumped into the well during hydraulic fracturing.

[0156] In step S31, the pre-fracturing fluid stage uses a low-viscosity fracturing fluid carrying a temporary plugging agent to reduce filtration loss. The purpose of step S31 is to create fractures and cool the formation, preparing for subsequent fracture control and proppant addition. The fluid used to create fractures in the formation at the initial stage of fracturing is the pre-fracturing fluid. Because high-viscosity pre-fracturing fluids have a stronger fracture-creating ability, they are generally used as pre-fracturing fluids in fracturing. However, high-viscosity fracturing fluids are difficult to control fracture height during fracturing operations, and the filtration loss during fracturing of loose sandstone is significant. Therefore, a low-viscosity fracturing fluid carrying a temporary plugging agent to reduce filtration loss is used as the pre-fracturing fluid. Various low-viscosity fracturing fluids disclosed in existing technologies can be used.

[0157] The low-viscosity fracturing fluid described in step S31 has a viscosity of 10 mPa·s at 80°C.

[0158] The low-viscosity fracturing fluid, in terms of mass percentage concentration, specifically includes:

[0159]

[0160] The water used in the preparation can be industrial water, making it well-suited for on-site applications. Both the thickener and drag-reducing agent are existing products in this technical field.

[0161] In step S32, after the pre-filled liquid is successfully used to create a crack, a low-displacement balanced injection of floating and sinking blocking agents is used to maintain a certain opening of the crack while transporting the blocking agents to the upper and lower ends of the crack to form the required artificial barrier layer.

[0162] Low displacement balanced injection: Low displacement is a relative concept, for example, in fracturing software simulation at 4m 3 At a discharge rate of / min, the hydraulic fracture continued to expand, while at a depth of 3m... 3 If, under a displacement injection rate of / min, the crack can remain open without further propagation, then 3m 3 / min displacement is considered low displacement.

[0163] Preferably, the pumping displacement during step S32, when injecting the floating and sinking blocking agent at a low displacement equilibrium, is 3m³. 3 / min.

[0164] In step S33, the high-viscosity fracturing fluid is defined as a high-viscosity liquid compared to the low-viscosity pre-fracturing fluid. For example, if the viscosity of the pre-fracturing fluid is 10 mPa·s and the viscosity of the pre-fracturing fluid is 20 mPa·s, then the viscosity of 20 mPa·s is high-viscosity relative to the viscosity of 10 mPa·s.

[0165] The high-viscosity fracturing fluid used here serves as a carrier for the proppant, and various high-viscosity fracturing fluids disclosed in the prior art can be employed.

[0166] The combination of proppant particles with different sizes involves adding smaller-sized proppant particles in the initial stage and larger-sized proppant particles in the later stage. The smaller-sized proppant particles in the initial stage can enhance the support of microfractures around the main fracture, while the larger-sized proppant particles in the later stage can improve the conductivity of the near-wellbore zone.

[0167] The high-viscosity fracturing fluid described in step S33 has a viscosity of 40 mPa·s at 80°C.

[0168] The high-viscosity fracturing fluid, in terms of mass percentage concentration, specifically includes:

[0169] Thickener 0.4%;

[0170] 0.2% drag reducer;

[0171] Water remains.

[0172] In step 33, the different particle size proppant combination includes 20-40 mesh quartz sand and 40-70 mesh quartz sand, and the two different particle sizes of quartz sand are mixed to form the different particle size proppant combination.

[0173] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A comprehensive fracturing method for controlling fracture height in loose sandstone, characterized in that, Includes the following steps: Evaluation of temporary plugging and filtration reduction agents was conducted by selecting degradation rate, particle size, settling velocity, and filtration reduction performance indicators to obtain temporary plugging and filtration reduction agents that meet the fracturing requirements of loose sandstone reservoirs. Taking into account geological and engineering factors, the construction parameters for optimizing the dosage of the shielding agent and its rising / sinking speed are determined. The optimization of these parameters specifically includes the following steps: S21: Based on the formation fracture toughness, construction pressure and fracture design scale, optimize the amount of floating / sinking shielding agent used in construction according to the linear elastic fracture mechanics theory. S22: Optimize the rising / sinking speed of the floating / sinking shielding agent based on the strength, density, diameter, and crack design scale of the shielding agent; Using the evaluated construction parameters of temporary plugging and filtration reduction agent dosage, shielding agent dosage, and shielding agent floating / sinking rate, fracturing operations were carried out to control the fracture height of loose sandstone reservoirs and form good post-fracturing conductivity. The fracturing method specifically includes the following steps: Low-viscosity fracturing fluid carrying a temporary plugging and filtration reduction agent is used as the pre-fracturing fluid to create fractures in the formation and complete the initial fracturing operation. After the pre-filled liquid is successfully used to create the crack, the floating and sinking blocking agent is injected using a low-displacement balanced injection method. This maintains a certain opening in the crack while transporting the blocking agent to the upper and lower ends of the crack to form the required artificial barrier layer. High-viscosity fracturing fluid is used as the proppant-carrying fluid, along with a combination of proppants of different particle sizes. The proppant-carrying fluid is used to pump the combination of proppants of different particle sizes into the hydraulic fractures of the reservoir, supporting the fractures after fracturing, thereby forming a high-permeability oil and gas channel and completing the fracturing operation. The fracturing method further includes the following steps: By calculating the minimum horizontal principal stress of the formation, the stress difference between the target layer and the upper and lower strata, as well as the distance between the production layer and the water layer, are determined. Based on the drilling fluid contamination radius and the fracture size designed by the fracturing software, it is determined whether a temporary plugging agent is needed to reduce fluid loss. The fracturing method further includes the following steps: The degree and radius of contamination were determined through well test analysis and oil well production simulation. Fracturing software was used to simulate and determine the scale of construction, discharge rate and pumping procedure.

2. The fracturing method for comprehensively controlling fracture height in loose sandstone according to claim 1, characterized in that, The low-viscosity fracturing fluid has a viscosity of 10 mPa·s at 80°C.

3. The fracturing method for comprehensively controlling fracture height in loose sandstone according to claim 2, characterized in that, The low-viscosity fracturing fluid, in terms of mass percentage concentration, specifically includes: Thickener 0.15%; 0.2% drag reducer; Temporarily clogging and filtration reduction agent 1%; Water remains.

4. The fracturing method for comprehensively controlling fracture height in loose sandstone according to claim 3, characterized in that, The high-viscosity fracturing fluid has a viscosity of 40 mPa·s at 80°C.

5. The fracturing method for comprehensively controlling fracture height in loose sandstone according to claim 4, characterized in that, The high-viscosity fracturing fluid, in terms of mass percentage concentration, specifically includes: Thickener 0.4%; 0.2% drag reducer; Water remains.

6. The fracturing method for comprehensively controlling fracture height in loose sandstone according to claim 5, characterized in that, The different particle size proppant combinations are mixtures of quartz sand with different particle sizes, wherein the particle size of the quartz sand includes any particle size from 20 mesh to 40 mesh and any particle size from 40 mesh to 70 mesh, and the particle sizes of the two types of quartz sand mixed are not the same.

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