Method for precise prevention of proppant and formation sand flowback

Abstract

The present application relates to oil and gas field development technical field, it is a kind of accurate prevention proppant and formation sand return method, comprising: according to the reservoir characteristics, determine sand control measure;Calculate the resistance to external extrusion pressure, the resistance to internal pressure intensity, determine the compression resistance level of casing sliding sleeve;Determine the fracture hole section area of casing sliding sleeve;Determine the type, particle size etc. of proppant;Determine the type of fiber material in the fiber sand suspension fracturing fluid used in fracturing operation;Under high sand ratio condition, inject the consolidation material into the fracture of fracturing, form stable sand consolidation barrier in the fracture;After fracturing, control the drainage flow rate, ensure that drainage flow rate is less than critical sand flow rate, prevent proppant and formation sand return.The present application expands the traditional single point single surface sand control to combined sand control, solves the limitations of single mechanical and chemical sand control, improves sand control effect;By optimizing proppant network laying technology, the oil and gas well productivity is improved, and the later management cost and construction risk are reduced.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and is a method for precisely preventing the return of proppant and formation sand. Background Technology

[0002] In the field of oil and gas exploration and development, proppant return and formation sand return have become major technical challenges, especially for oil and gas resources that are difficult to extract. For example, the Sebei Gas Field in Qinghai Oilfield and the Keshen and Dina Gas Fields in Tarim Oilfield face such problems due to factors such as loose reservoirs, fragile cementation, and high production pressure differentials. Existing mechanical and chemical sand control technologies have their limitations. For example, mechanical sand control is ineffective against fine sand, while chemical sand control is not sustainable. At the same time, for unconventional oil and gas resources, although fracturing has increased production capacity, the increasing intensity of proppant addition and the influence of long-section perforation technology have led to problems such as large proppant return flow in horizontal wells, long return sections, and great difficulty in treatment. It also easily causes casing deformation risks, affecting production efficiency and construction safety. Summary of the Invention

[0003] This invention provides a precise method for preventing proppant and formation sand return, overcoming the shortcomings of the prior art. It can effectively solve the limitations of existing mechanical and chemical sand control technologies, and at the same time, solve the problem of proppant backflow after pressure in unconventional oil and gas reservoirs.

[0004] The technical solution of this invention is achieved through the following measures: a method for precisely preventing the return of proppant and formation sand, comprising:

[0005] Identify the target block and reservoir characteristics, and determine sand control measures based on the reservoir characteristics;

[0006] Based on the external extrusion pressure and internal pressure resistance requirements of the casing sliding sleeve during drilling, completion, and reservoir stimulation, the external extrusion pressure resistance and internal pressure resistance strength are calculated. The pressure resistance level of the casing sliding sleeve is determined by the external extrusion pressure resistance and internal pressure resistance strength. The cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve is calculated to determine the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve.

[0007] Based on formation characteristics and fracturing requirements, the type and particle size of proppant are determined, and the design of multi-stage proppant combination is completed.

[0008] Determine the type of fiber material in the fiber-insulated fracturing fluid used in the fracturing operation. After adding the fiber-insulated fracturing fluid to the proppant and mixing it evenly, inject it into the well.

[0009] Select a consolidation material with rapid consolidation and high strength properties, and inject the consolidation material into the fractured fracture under high sand ratio conditions to form a stable sand-fixing barrier in the fracture, preventing proppant and formation sand from being returned.

[0010] After fracturing, control the drainage flow rate to ensure it is less than the critical sand discharge rate, thus preventing proppant and formation sand from being expelled.

[0011] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0012] The external compressive strength and internal pressure resistance of the above-mentioned sleeve are calculated using the following formula:

[0013] P 外 =ρ 泥浆 ×g×h

[0014] In the formula, P 外 The external compressive force of the sleeve is MPa;

[0015] ρ 泥浆 Density of drilling fluid during cementing, in g / cm³ 3 ;

[0016] g is the acceleration due to gravity, m / s² 2 ;

[0017] h is the vertical well depth, in meters;

[0018] P 内 =1.25P max

[0019] In the formula, P 内 P represents the internal pressure resistance of the sleeve, in MPa. max The pressure exerted on the bushing at maximum displacement is expressed in MPa.

[0020] The cross-sectional area of ​​the fracturing orifice of the above-mentioned casing sliding sleeve is calculated using the following formula:

[0021]

[0022] In the formula, s is the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve, m 2 q represents the flow rate of the oil and gas well, in meters. 3 / min; μ is the flow velocity through the fracturing orifice of the casing sleeve, m / min.

[0023] The aforementioned proppant includes small-diameter proppant, medium-diameter proppant, and large-diameter proppant. In the pre-fluidization stage, small-diameter proppant is mixed and injected to achieve efficient placement of microfractures and distal fracture networks. In the proppant-carrying fluid stage, medium-diameter proppant is mixed and injected with a low sand ratio to adjust the flow rate and concentration of the proppant-carrying fluid, ensuring its uniform placement in branch fractures. In the proppant-carrying fluid stage, large-diameter proppant is mixed and injected with a high sand ratio to form fractures with high conductivity in the near-wellbore zone.

[0024] The aforementioned fiber materials include biodegradable and non-biodegradable fibers. A fiber injection device is used to fully mix the fiber materials with fracturing fluid to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is then injected into the proppant at a rate of 0.2% to 0.3% of the proppant mass. The mixture is stirred evenly in a sand mixing truck and pumped into the well.

[0025] The precise proppant and formation sand return prevention method described in this invention expands traditional single-point, single-surface sand control into a combined sand control approach, overcoming the limitations of single mechanical and chemical sand control and improving sand control effectiveness. Simultaneously, in unconventional oil and gas reservoir fracturing and production enhancement, the use of unlimited-level casing sliding sleeves transforms long-section sand control into single-point concentrated sand control, shortening the sand control section and reducing the difficulty of sand control. By optimizing the proppant fracture mesh placement technology, oil and gas well productivity is increased, while reducing subsequent treatment costs and construction risks. Attached Figure Description

[0026] Appendix Figure 1 This is a flowchart of the method for precisely preventing proppant and formation sand return as described in this invention.

[0027] Appendix Figure 2 A schematic diagram of multi-stage proppant combination with sand is provided for the embodiments of this application;

[0028] Appendix Figure 3 This is a schematic diagram of a fiber material encapsulating a support agent, provided for an embodiment of this application.

[0029] Figure 2 In the diagram, 1 represents a small-particle-size proppant; 2 represents a medium-particle-size proppant; and 3 represents a large-particle-size proppant. Detailed Implementation

[0030] The present invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of the present invention.

[0031] Unless otherwise specified, the processes and equipment used in this invention are conventional in the field. For example, during fracturing, the fracturing fluid is divided into pre-fracturing fluid and proppant-carrying fluid; the pre-fracturing fluid is injected first, followed by the proppant-carrying fluid.

[0032] The present invention will be further described below with reference to embodiments:

[0033] Example 1: As Figure 1 As shown, this precise method for preventing proppant and formation sand return includes:

[0034] Step 101: Obtain relevant reservoir parameters (such as porosity, permeability, etc.), determine the target block and reservoir characteristics, and determine sand control measures based on the reservoir characteristics;

[0035] Step 102: Based on the external extrusion pressure and internal pressure resistance requirements of the casing sliding sleeve during drilling, completion, and reservoir stimulation, determine the pressure resistance level of the casing sliding sleeve by measuring the external extrusion pressure and internal pressure resistance strength; calculate the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve to determine the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve.

[0036] Step 103: Based on formation characteristics and fracturing requirements, determine the type and particle size of the proppant, and complete the design of multi-stage proppant combination;

[0037] Step 104: Determine the type of fiber material in the fiber-insulated fracturing fluid used in the fracturing operation, add the fiber-insulated fracturing fluid to the proppant and mix it evenly, then inject it into the well;

[0038] Step 105: Select a consolidation material with rapid consolidation and high strength characteristics, and inject the consolidation material into the fractured fracture under high sand ratio conditions to form a stable sand-fixing barrier in the fracture and prevent proppant and formation sand from returning.

[0039] Step 106: After fracturing, control the drainage flow rate to ensure that it is less than the critical sand discharge rate, and prevent proppant and formation sand from being returned.

[0040] Example 2: This precise method for preventing proppant and formation sand return includes:

[0041] Obtain reservoir-related parameters, determine target blocks and reservoir characteristics, and determine sand control measures based on the reservoir characteristics;

[0042] Based on the external extrusion pressure and internal pressure resistance requirements of the casing sliding sleeve during drilling, completion, and reservoir stimulation, the external extrusion pressure resistance and internal pressure resistance strength are calculated. The pressure resistance level of the casing sliding sleeve is determined by the external extrusion pressure resistance and internal pressure resistance strength, and the optimal pressure resistance level is completed. Based on the critical sand production flow rate evaluation model, the critical sand production velocity is obtained, the fracturing orifice cross-sectional area of ​​the casing sliding sleeve is calculated, and the fracturing orifice cross-sectional area of ​​the casing sliding sleeve is determined.

[0043] The critical sand discharge rate evaluation model can be expressed as follows:

[0044]

[0045] In the formula, v is the critical sand discharge velocity, m / d; h 油 The effective thickness of the oil layer is m; r w Q is the wellbore radius, in cm; c d is the critical volumetric flow rate for sand production obtained from the core sand production simulation test, in mL / min; d is the diameter of the test core, in cm; A is the cross-sectional area of ​​the wellbore, in cm². 2 The casing sleeve can be the conventional unlimited-class casing sleeve used in fracturing operations.

[0046] The infinite-level casing sliding sleeve enables centralized sand control at a single point and optimizes the fracturing hole parameters (equal cross-sectional area of ​​the fracturing hole in the casing sliding sleeve) to ensure a complex fracture network and uniform proppant distribution.

[0047] Based on formation characteristics and fracturing requirements, the type and particle size of proppant are determined, and the design of multi-stage proppant combination is completed.

[0048] Determine the type of fiber material in the fiber-suspended fracturing fluid used in the fracturing operation (to improve the proppant migration distance and proppant profile uniformity), add the fiber-suspended fracturing fluid to the proppant and mix it evenly before injecting it into the well;

[0049] Two consolidation materials with rapid consolidation and high strength properties were selected for use in high sand ratio (sand concentration in the fracturing fracture greater than 10 kg / m³). 2 Under these conditions, the consolidation material is injected into the fractured cracks to form a stable sand-fixing barrier in the cracks, preventing proppant and formation sand from being expelled.

[0050] Consolidation materials with rapid consolidation and high strength characteristics include consolidated sand and graphene-modified cement. On the surface, the two consolidation materials (consolidated sand and graphene-modified cement) are mixed uniformly at a mass ratio of 1:1.2 to 1.5. Through glass plate proppant migration tests and hydraulic fracture simulations, the propagation depth of the largest particle size proppant in the fracture, fracture height, and proppant concentration are determined. The amount of consolidation material required for the consolidated proppant is calculated. The consolidation material is then injected into the fracture at a high sand ratio to form a stable sand-fixing barrier, preventing the return of proppant and formation sand. The selection of the consolidation material should ensure that it has rapid consolidation and high strength characteristics, reaching at least 95% of the optimal consolidation strength before fluid drainage under reservoir temperature and pressure conditions.

[0051] After fracturing, control the drainage flow rate to ensure it is less than the critical sand discharge rate, thus preventing proppant and formation sand from being expelled.

[0052] The flow rate of fluid after fracturing needs to take into account not only the influence of reservoir characteristics and fracturing fluid viscosity on proppant recirculation, but also factors such as fracture closure time, flow pressure differential, and fracture conductivity. During the flowback process, the flow rate is controlled by adjusting the nozzle size to ensure that the flow rate is less than the critical sand production rate, thereby controlling the return of formation sand and proppant in the initial stage of flowback.

[0053] Example 3: As an optimization of the above embodiment, the resistance to external extrusion and internal pressure of the sleeve are calculated using the following formula:

[0054] P 外 =ρ 泥浆 ×g×h

[0055] In the formula, P 外The external compressive force of the sleeve is MPa;

[0056] ρ 泥浆 Density of drilling fluid during cementing, in g / cm³ 3 ;

[0057] g is the acceleration due to gravity, m / s² 2 ;

[0058] h is the vertical well depth, in meters;

[0059] P 内 =1.25P max

[0060] In the formula, P 内 P represents the internal pressure resistance of the sleeve, in MPa. max The pressure exerted on the bushing sleeve at maximum displacement is expressed in MPa.

[0061] Example 4: As an optimization of the above embodiment, the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve is calculated according to the following formula:

[0062]

[0063] In the formula, s is the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve, m 2 q represents the flow rate of the oil and gas well, in meters. 3 / min; μ is the flow velocity through the fracturing orifice of the casing sleeve, m / min.

[0064] Example 5: As an optimization of the above examples, the proppant includes small-diameter proppant, medium-diameter proppant, and large-diameter proppant, forming a multi-stage proppant combination; in the pre-flush stage, small-diameter proppant is mixed and injected to achieve efficient placement of micro-fractures and distal fracture networks; in the proppant-carrying fluid stage, a low sand ratio (sand concentration in the fracturing fracture is less than 10 kg / m³) is used. 2 During the mixing and injection of proppant of medium size, the flow rate and concentration of the proppant-carrying fluid are adjusted to ensure that it is evenly distributed in the branch fractures. During the proppant-carrying fluid stage, large-diameter proppant is mixed with a high sand ratio and injected at high pressure to form fractures with high conductivity in the near-wellbore zone of the fracture opening.

[0065] like Figure 2 As shown, in the pre-liquid stage, small-particle-size proppant 1 is mixed and injected to achieve efficient laying of microcracks and distal crack networks.

[0066] During the sand-carrying fluid stage, a low-sand-ratio proppant 2 is mixed in to adjust the flow rate and concentration of the sand-carrying fluid, so that it is evenly spread in the branch cracks.

[0067] During the proppant-carrying stage, a high-proppant ratio is used to mix large-diameter proppant 3, and the high-pressure injection method creates a fracture with high conductivity in the near-wellbore zone.

[0068] This involves injecting small, medium, and large-sized proppant in stages to improve the proppant's placement effect in cracks.

[0069] Small-size proppant typically refers to quartz sand or ceramsite with a particle size of 210um to 106um (70 mesh to 140 mesh) or even smaller; medium-size proppant typically refers to quartz sand or ceramsite with a particle size of 425um to 210um (40 mesh to 70 mesh); and large-size proppant typically refers to quartz sand or ceramsite with a particle size of 600um to 300um (30 mesh to 50 mesh) and 850um to 425um (20 mesh to 40 mesh).

[0070] Example 6: As an optimization of the above examples, the fiber material includes biodegradable fibers and non-biodegradable fibers. A fiber injection device is used to fully mix the fiber material with fracturing fluid (such as guar gum) to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is injected into the proppant, and the amount of fiber-suspended fracturing fluid added is 0.2% to 0.3% of the mass of the proppant. The mixture is stirred evenly in a sand mixing truck and pumped into the well to increase the proppant migration distance and improve the proppant profile.

[0071] The selection of fiber materials should ensure that they have good flexibility and temperature resistance, and can be fully mixed with proppant and wrapped into clumps. Degradable fibers are used to prevent proppant backflow, while non-degradable fibers are used to prevent formation sand production.

[0072] After the fiber material is injected into the well, it encapsulates the proppant, improving the proppant's transport distance and the uniformity of the proppant profile. For example... Figure 3 As shown, the transport profile of the fiber-encapsulated proppant includes:

[0073] Figure 3 a is a cross-sectional view of the movement of the support without fiber wrapping. Improperly placed support can cause sand to accumulate at the seam.

[0074] Figure 3 b is a cross-sectional view of the transport of the fiber-encapsulated proppant. The proppant is properly laid, which increases the half-length of the support fracture. The proppant at the fracture opening meets the flow conductivity required for oil and gas well production.

[0075] The specific application examples of the precise prevention method for proppant and formation sand return described in this invention are as follows:

[0076] Example 1:

[0077] Taking the Sulige gas field in the Ordos Basin as an example, the reservoirs in this gas field exhibit tight characteristics and contain multiple gas-bearing layers. Large-scale volumetric fracturing technology is essential to achieve the target oil and gas production during extraction. The geological parameters of the Sulige block are particularly unique; its reservoirs are not only tight but also accompanied by complex geological structures. However, after large-scale volumetric fracturing, the gas field faces a severe challenge in controlling sand production. Due to the changes in formation pressure caused by fracturing operations, sand particles in the reservoir are easily loosened and enter the wellbore with the gas flow, leading to wellbore blockage and, in severe cases, even affecting the normal production of the gas well.

[0078] For this scenario, the method for precisely preventing the return of proppant and formation sand described in this invention specifically includes the following steps:

[0079] Step 1: Based on the reservoir characteristics and sand control requirements of the region, precise measures to prevent proppant backflow were formulated. These sand control measures include: Given that one or more high-permeability channels have been artificially established after large-scale fracturing in the region, to ensure the smooth and efficient extraction of gas from tight sandstone, the following work needs to be carried out to prevent proppant backflow: 1) While ensuring high conductivity at the fracture opening, it is necessary to reduce sand-producing points at the fracture opening to prevent long-distance perforation and increase the difficulty of sand control in long well sections; 2) Hydraulic fractures must meet the full fracture network support conditions, and the fracture height should be as uniform as possible to ensure unobstructed flow throughout the fracture channel; 3) Strongly control the flow pressure differential during drainage to prevent incomplete fracture closure leading to a large amount of proppant backflow.

[0080] Step 2: Optimize the infinite-stage casing sliding sleeve fracturing process without perforation. Based on the reservoir stimulation requirements, use conventional fracturing software simulation to select the optimal stimulation displacement and construction scale, and determine the wellbore structure, casing sliding sleeve's resistance to external extrusion and internal pressure, dimensions, etc.

[0081] The resistance to external extrusion and internal pressure of the sleeve are calculated using the following formula:

[0082] P 外 =ρ 泥浆 ×g×h

[0083] In the formula, P 外 The external compressive force of the sleeve is MPa;

[0084] ρ 泥浆 Density of drilling fluid during cementing, in g / cm³ 3 ;

[0085] g is the acceleration due to gravity, m / s² 2 ;

[0086] h is the vertical well depth, in meters;

[0087] P 内 =1.25Pmax

[0088] In the formula, P 内 P represents the internal pressure resistance of the sleeve, in MPa. max The pressure exerted on the bushing at maximum displacement is expressed in MPa.

[0089] Based on the critical sand production rate evaluation model, the critical sand production velocity is obtained, the cross-sectional area of ​​the fracturing orifice is calculated, and the design of the fracturing orifice cross-sectional area is completed. In order to facilitate the formation of a complex fracture network and help the proppant to be evenly distributed in the fracture, the fracturing orifice is preferably an elongated oval hole. The fracture extends perpendicular to the direction of minimum principal stress. Therefore, the number of fracturing orifices should be designed to be evenly distributed in all directions as much as possible while ensuring the compressive strength. The cross-sectional area of ​​the fracturing orifice should be greater than the ratio of the gas well production flow rate to the critical sand production velocity.

[0090] The critical sand discharge flow rate evaluation model is as follows:

[0091]

[0092] In the formula, v is the critical sand discharge velocity, m / d; h 油 The effective thickness of the oil layer is m; r w Q is the wellbore radius, in cm; c d is the critical volumetric flow rate for sand production obtained from the core sand production simulation test, in mL / min; d is the diameter of the test core, in cm; A is the cross-sectional area of ​​the wellbore, in cm². 2 .

[0093] The cross-sectional area of ​​the fracturing orifice of the casing sleeve is calculated using the following formula:

[0094]

[0095] s>q / v

[0096] In the formula, s is the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve, m 2 q represents the gas well production flow rate, in meters. 3 / min; μ is the flow velocity through the fracturing orifice of the casing sleeve, m / min; v is the critical sand discharge velocity, m / d.

[0097] Step 3: Based on formation characteristics and fracturing requirements, select proppant with appropriate particle size and strength. In the pre-fracturing stage, inject small-particle-size proppant to achieve efficient placement of microfractures and distal fracture networks; in the proppant-carrying stage, inject medium-particle-size proppant with a low sand ratio, adjusting the flow rate and concentration of the proppant-carrying fluid to ensure uniform placement in branch fractures; in the proppant-carrying stage, inject large-particle-size proppant with a high sand ratio, using a high-pressure injection method to create highly conductive fractures near the wellbore at the fracture opening.

[0098] Small-size proppant typically refers to quartz sand or ceramsite with a particle size of 210um to 106um (70 mesh to 140 mesh) or even smaller; medium-size proppant typically refers to quartz sand or ceramsite with a particle size of 425um to 210um (40 mesh to 70 mesh); and large-size proppant typically refers to quartz sand or ceramsite with a particle size of 600um to 300um (30 mesh to 50 mesh) and 850um to 425um (20 mesh to 40 mesh).

[0099] Step 4: The fiber material includes biodegradable and non-biodegradable fibers. Using a fiber injection device, the fiber material is thoroughly mixed with fracturing fluid (such as guar gum) to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is injected into the proppant at a rate of 0.2% to 0.3% of the proppant mass. The mixture is stirred evenly in a sand mixing truck and pumped into the well to increase the proppant migration distance and improve the proppant profile.

[0100] The selection of fiber materials should ensure that they have good flexibility and temperature resistance, and can be fully mixed with proppant and wrapped into clumps. Degradable fibers are used to prevent proppant backflow, while non-degradable fibers are used to prevent formation sand production.

[0101] The biodegradable fiber may be the biodegradable fiber mentioned in Chinese patent application document CN105419769A entitled "A biodegradable fiber and a fracturing fluid containing the same and a method for preparing the fracturing fluid", and the non-biodegradable fiber may be the heat-resistant PVA fiber mentioned in Chinese patent application document CN107287668A entitled "A heat-resistant PVA fiber and its use".

[0102] Step 5: Select two consolidation materials with rapid consolidation and high strength properties, and apply them to a high sand ratio (sand concentration in the fracturing fracture greater than 10 kg / m³). 2 Under these conditions, the consolidation material is injected into the fractured cracks to form a stable sand-fixing barrier in the cracks, preventing proppant and formation sand from being expelled.

[0103] The consolidation materials with rapid consolidation and high strength properties include consolidated sand and graphene-modified cement. On the ground, the two consolidation materials (consolidated sand and graphene-modified cement) are mixed uniformly at a mass ratio of 1:1.2 to 1.5. Through glass plate proppant migration tests and hydraulic fracture simulations, the propagation depth of the largest particle size proppant in the fracture, the fracture height, and the proppant concentration are obtained. The amount of consolidation material used in the consolidated proppant is calculated. The consolidation material is then injected into the fracture at a high sand ratio to form a stable sand-fixing barrier within the fracture, preventing the proppant and formation sand from returning.

[0104] Step 6: After fracturing, control the drainage flow rate to ensure that it is less than the critical sand discharge rate, and prevent proppant and formation sand from being returned.

[0105] The flow rate of fluid discharged after fracturing needs to take into account not only the influence of reservoir characteristics and fracturing fluid viscosity on proppant backflow, but also factors such as fracture closure time, flow pressure differential, and fracture conductivity. During the flowback process, the flow rate is controlled by adjusting the nozzle size to ensure that the flow rate is less than the critical sand production rate, thereby controlling the return of formation sand and proppant in the early stage of flowback and reducing proppant backflow due to incomplete early fracture closure.

[0106] Example 2:

[0107] Taking the Sebei Gas Field in Qinghai Oilfield as an example, the target layer in the gas field is a loose sandstone reservoir. This target layer is characterized by high clay content, high argillaceous content, high mineralization, and undercompactment, resulting in relatively poor diagenesis. The median sandstone grain size is 0.04 mm to 0.07 mm, with significant differences between wells. In the early stages, mechanical sand control tools were mainly used for sand control, but the sand control effect was generally limited due to geological structure and fine sand. Although secondary chemical sand control has achieved some results in recent years, many wells still suffer from issues such as sand control tubing burial, short sand control cycles, and severe casing deformation, which affect the production capacity of gas wells.

[0108] Step 1: Based on the regional reservoir characteristics and sand control requirements, precise measures to prevent formation sand return were formulated. These measures include: given that the regional formation is loose and produces fine siltstone, a stable artificial sand control zone needs to be established. This sand control zone should have the following characteristics: 1) Concentrated sand control openings to prevent long-distance perforations and increase the difficulty of sand control in long well sections; 2) Hydraulic fractures are fully supported, anchoring themselves in the reservoir like nails, improving the stability of the loose formation; 3) Support fractures have good conductivity, providing sufficient channels for gas flow production; 4) The sand control zone is a multi-level strip, effectively preventing formation sand production.

[0109] Step 2: Optimize the infinite-stage casing sliding sleeve fracturing process without perforation. Based on the reservoir stimulation requirements, the optimal stimulation displacement and construction scale are selected through fracturing software simulation. At the same time, the wellbore structure, the external extrusion pressure resistance and internal pressure resistance strength of the casing sliding sleeve, and its dimensions are determined.

[0110] The resistance to external extrusion and internal pressure of the sleeve are calculated using the following formula:

[0111] P 外 =ρ 泥浆 ×g×h

[0112] In the formula, P 外 The external compressive force of the sleeve is MPa;

[0113] ρ 泥浆 Density of drilling fluid during cementing, in g / cm³ 3 ;

[0114] g is the acceleration due to gravity, m / s² 2 ;

[0115] h is the vertical well depth, in meters;

[0116] P 内 =1.25P max

[0117] In the formula, P 内 P represents the internal pressure resistance of the sleeve, in MPa. max The pressure exerted on the bushing sleeve at maximum displacement is expressed in MPa.

[0118] Based on the critical sand production rate evaluation model, the critical sand production velocity is obtained, the cross-sectional area of ​​the fracturing orifice is calculated, and the design of the fracturing orifice cross-sectional area is completed. In order to facilitate the formation of a complex fracture network and help the proppant to be evenly distributed in the fracture, the fracturing orifice is preferably an elongated oval hole. The fracture extends perpendicular to the direction of minimum principal stress. Therefore, the number of fracturing orifices should be designed to be evenly distributed in all directions as much as possible while ensuring the compressive strength. The cross-sectional area of ​​the fracturing orifice should be greater than the ratio of the gas well production flow rate to the critical sand production velocity.

[0119] The critical sand discharge flow rate evaluation model is as follows:

[0120]

[0121] In the formula, v is the critical sand discharge velocity, m / d; h 油 The effective thickness of the oil layer is m; r w Q is the wellbore radius, in cm; c d is the critical volumetric flow rate for sand production obtained from the core sand production simulation test, in mL / min; d is the diameter of the test core, in cm; A is the cross-sectional area of ​​the wellbore, in cm². 2 .

[0122] The cross-sectional area of ​​the fracturing orifice of the casing sleeve is calculated using the following formula:

[0123]

[0124] s>q / v

[0125] In the formula, s is the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve, m 2 q represents the gas well production flow rate, in meters. 3 / min; μ is the flow velocity through the fracturing orifice of the casing sleeve, m / min; v is the critical sand discharge velocity, m / d.

[0126] Step 3: Based on formation characteristics and fracturing requirements, select proppant with appropriate particle size and strength. In the pre-fracturing stage, inject small-particle-size proppant to achieve efficient placement of microfractures and distal fracture networks; in the proppant-carrying stage, inject medium-particle-size proppant with a low sand ratio, adjusting the flow rate and concentration of the proppant-carrying fluid to ensure uniform placement in branch fractures; in the proppant-carrying stage, inject large-particle-size proppant with a high sand ratio, using a high-pressure injection method to create highly conductive fractures near the wellbore at the fracture opening.

[0127] Small-size proppant typically refers to quartz sand or ceramsite with a particle size of 210um to 106um (70 mesh to 140 mesh) or even smaller; medium-size proppant typically refers to quartz sand or ceramsite with a particle size of 425um to 210um (40 mesh to 70 mesh); and large-size proppant typically refers to quartz sand or ceramsite with a particle size of 600um to 300um (30 mesh to 50 mesh) and 850um to 425um (20 mesh to 40 mesh).

[0128] Step 4: The fiber material includes biodegradable and non-biodegradable fibers. Using a fiber injection device, the fiber material is thoroughly mixed with fracturing fluid (such as guar gum) to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is injected into the proppant at a rate of 0.2% to 0.3% of the proppant mass. The mixture is stirred evenly in a sand mixing truck and pumped into the well to increase the proppant migration distance and improve the proppant profile.

[0129] The selection of fiber materials should ensure that they have good flexibility and temperature resistance, and can be fully mixed with proppant and wrapped into clumps. Degradable fibers are used to prevent proppant backflow, while non-degradable fibers are used to prevent formation sand production.

[0130] The biodegradable fiber may be a commercially available biodegradable fiber (such as polylactic acid (PLA)), and the non-biodegradable fiber may be the heat-resistant PVA fiber mentioned in Chinese patent application document CN107287668A entitled "A heat-resistant PVA fiber and its use".

[0131] Step 5: Select two consolidation materials with rapid consolidation and high strength properties, and apply them to a high sand ratio (sand concentration in the fracturing fracture greater than 10 kg / m³). 2 Under these conditions, the consolidation material is injected into the fractured cracks to form a stable sand-fixing barrier in the cracks, preventing proppant and formation sand from being expelled.

[0132] The consolidation materials with rapid consolidation and high strength properties include consolidated sand and graphene-modified cement. On the ground, the two consolidation materials (consolidated sand and graphene-modified cement) are mixed uniformly at a mass ratio of 1:1.2 to 1.5. Through glass plate proppant migration tests and hydraulic fracture simulations, the propagation depth of the largest particle size proppant in the fracture, the fracture height, and the proppant concentration are obtained. The amount of consolidation material used in the consolidated proppant is calculated. The consolidation material is then injected into the fracture at a high sand ratio to form a stable sand-fixing barrier within the fracture, preventing the proppant and formation sand from returning.

[0133] Step 6: After fracturing, control the drainage flow rate to ensure that it is less than the critical sand discharge rate, and prevent proppant and formation sand from being returned.

[0134] The flow rate of fluid discharged after fracturing needs to take into account not only the influence of reservoir characteristics and fracturing fluid viscosity on proppant backflow, but also factors such as fracture closure time, flow pressure differential, and fracture conductivity. During the flowback process, the flow rate is controlled by adjusting the nozzle size to ensure that the flow rate is less than the critical sand production rate, thereby controlling the return of formation sand and proppant in the early stage of flowback and reducing proppant backflow due to incomplete early fracture closure.

[0135] In summary, the method described in this invention utilizes the following key technologies to prevent the return of proppant and formation sand.

[0136] 1) Determine sand control measures based on reservoir characteristics;

[0137] 2) Optimize the fracturing hole parameters of the casing sliding sleeve to ensure a complex fracture network and uniform proppant distribution;

[0138] 3) Multi-stage proppant combined with sand technology: Small, medium and large particle size proppants are injected in stages to improve the proppant placement effect in cracks;

[0139] 4) Encapsulating the proppant with self-polymerized fibers: improves the proppant transport distance and the uniformity of the proppant profile.

[0140] 5) Sealing technology using consolidation materials (such as consolidated sand): forming a stable sand-fixing barrier in the fracture to prevent proppant and formation sand from returning.

[0141] 6) Control of fluid flow rate after fracturing: By adjusting the fluid flow rate, ensure that the flow rate is less than the critical sand discharge rate to prevent proppant and formation sand from being returned.

[0142] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for precisely preventing the return of proppant and formation sand, characterized in that, include: Identify the target block and reservoir characteristics, and determine sand control measures based on the reservoir characteristics; Based on the external extrusion pressure and internal pressure resistance requirements of the casing sliding sleeve during drilling, completion, and reservoir stimulation, the external extrusion pressure resistance and internal pressure resistance strength are calculated. The pressure resistance level of the casing sliding sleeve is determined by the external extrusion pressure resistance and internal pressure resistance strength. The cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve is calculated to determine the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve. Based on formation characteristics and fracturing requirements, the type and particle size of proppant are determined, and the design of multi-stage proppant combination is completed. Determine the type of fiber material in the fiber-insulated fracturing fluid used in the fracturing operation, add the fiber-insulated fracturing fluid to the proppant and mix it evenly before injecting it into the well; Select a consolidation material with rapid consolidation and high strength properties, and inject the consolidation material into the fractured fracture under high sand ratio conditions to form a stable sand-fixing barrier in the fracture, preventing proppant and formation sand from being returned. After fracturing, control the drainage flow rate to ensure it is less than the critical sand discharge rate, thus preventing proppant and formation sand from being expelled.

2. The method for precisely preventing proppant and formation sand return according to claim 1, characterized in that, The resistance to external extrusion and internal pressure of the sleeve are calculated using the following formula: P 外 =ρ 泥浆 ×g×h In the formula, P 外 The external compressive force resisted by the sleeve is expressed in MPa. ρ 泥浆 Density of drilling fluid during cementing, in g / cm³ 3 ; g is the acceleration due to gravity, m / s² 2 ; h is the vertical well depth, in meters; P 内 1.25P max In the formula, P 内 P represents the internal pressure resistance of the sleeve, in MPa. max The pressure exerted on the bushing at maximum displacement is expressed in MPa.

3. The method for precisely preventing proppant and formation sand return according to claim 1 or 2, characterized in that... The cross-sectional area of ​​the fracturing orifice of the casing sleeve is calculated using the following formula: In the formula, s is the cross-sectional area of ​​the fracturing orifice of the casing sliding sleeve, m 2 q represents the flow rate of the oil and gas well, in meters. 3 / min; μ is the flow velocity through the fracturing orifice of the casing sleeve, m / min.

4. The method for precisely preventing proppant and formation sand return according to claim 1 or 2, characterized in that, The proppant includes small-diameter proppant, medium-diameter proppant, and large-diameter proppant. In the pre-liquid stage, small-diameter proppant is mixed and injected to achieve efficient laying of microcracks and distal crack networks. In the sand-carrying liquid stage, medium-diameter proppant is mixed and injected with a low sand ratio to adjust the flow rate and concentration of the sand-carrying liquid so that it is evenly laid in the branch cracks. During the proppant-carrying stage, a high proppant ratio is used to mix large-diameter proppant particles, which forms highly conductive fractures in the near-wellbore zone at the fracture opening.

5. The method for precisely preventing proppant and formation sand return according to claim 3, characterized in that, The proppant includes small-diameter proppant, medium-diameter proppant, and large-diameter proppant. In the pre-liquid stage, small-diameter proppant is mixed and injected to achieve efficient laying of microcracks and distal crack networks. In the sand-carrying liquid stage, medium-diameter proppant is mixed and injected with a low sand ratio to adjust the flow rate and concentration of the sand-carrying liquid so that it is evenly laid in the branch cracks. During the proppant-carrying stage, a high proppant ratio is used to mix large-diameter proppant particles, which forms highly conductive fractures in the near-wellbore zone at the fracture opening.

6. The method for precisely preventing proppant and formation sand return according to claim 1, 2, or 5, characterized in that, The fiber material includes biodegradable and non-biodegradable fibers. A fiber injection device is used to fully mix the fiber material with the fracturing fluid to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is then injected into the proppant at a rate of 0.2% to 0.3% of the proppant mass. The mixture is stirred evenly in a sand mixing truck and pumped into the well.

7. The method for precisely preventing proppant and formation sand return according to claim 3, characterized in that, The fiber material includes biodegradable and non-biodegradable fibers. A fiber injection device is used to fully mix the fiber material with the fracturing fluid to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is then injected into the proppant at a rate of 0.2% to 0.3% of the proppant mass. The mixture is stirred evenly in a sand mixing truck and pumped into the well.

8. The method for precisely preventing proppant and formation sand return according to claim 4, characterized in that, The fiber material includes biodegradable and non-biodegradable fibers. A fiber injection device is used to fully mix the fiber material with the fracturing fluid to form a fiber-suspended fracturing fluid. The fiber-suspended fracturing fluid is then injected into the proppant at a rate of 0.2% to 0.3% of the proppant mass. The mixture is stirred evenly in a sand mixing truck and pumped into the well.

9. The method for precisely preventing proppant and formation sand return according to claim 1, 2, 5, 7, or 8, characterized in that, The bushing slide is an unlimited-level bushing slide.

10. The method for precisely preventing proppant and formation sand return according to claim 6, characterized in that, The bushing slide is an unlimited-level bushing slide.

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