Method for fracturing loose sandstone and application

Abstract

The invention discloses a loose sandstone fracturing method and application. The loose sandstone fracturing method comprises the steps of crack forming construction and bridge plugging sand prevention construction on cracks, the crack forming construction comprises the steps of prepad fluid pump injection and sand fracturing, and the displacement of fracturing fluid used for sand fracturing is larger than that of the fracturing fluid used for prepad fluid pump injection. According to the loose sandstone fracturing process provided by the invention, a process measure for controlling the fracture height and increasing the fracture length and a process measure for bridge plugging and sand prevention of a shot hole and a fracture opening are taken as a main body, the fracture is formed by controlling the displacement, and a floating and sinking blocking agent and a filtrate reducer are added into a fracturing fluid system to form a long fracture, so that the paving length of a consolidation propping agent is increased; the length of a channel for discharging the propping agent and the formation sand is increased, the energy consumption of returning of the propping agent and the formation sand is further increased, meanwhile, bridge plugging of shot holes is achieved through the high-strength stick-shaped propping agent, the mechanical sand prevention effect is achieved, and the problems that an existing fracturing technology is poor in sand prevention or chemical sand prevention effect and short in lasting time are solved.

Description

Technical Field

[0001] This invention relates to the technical field of oil and gas field development engineering, and more specifically, to methods and applications of fracturing loose sandstone. Background Technology

[0002] Existing fracturing techniques for loose sandstone employ high-viscosity fracturing fluid systems (guar gum, polymers, etc.) and filtration reducers to improve fracture creation, based on conventional fracturing designs. They also use tail-fracturing large-particle-size consolidated proppant or biodegradable fibers in conjunction with fracturing filling measures to enhance sand control at the fracturing process level. However, the sand control effect and its duration are still insufficient.

[0003] Specifically, as production progresses, the consolidated proppant and fibers gradually fail, causing a large amount of proppant to return from the borehole, reducing the sand control effect and leading to the discharge of large amounts of formation sand. This often exceeds the capacity for manual sand removal, resulting in production stoppages and significantly impacting high-efficiency production. Furthermore, although screen pipe sand control offers good effectiveness and duration, the screen pipes are prone to clogging and failure after a period of production. In such cases, perforated screen pipe and casing fracturing is often used for secondary fracturing to enhance production. For wells where small-sized screen pipes can be installed, this method can continue to use them for sand control. However, this results in a large skin coefficient, which is detrimental to improving production. Moreover, once the small screen pipes fail again, there are essentially no other production enhancement measures available. For wells where small-sized screen pipes cannot be installed, chemical sand control is the only viable option.

[0004] Judging from the current phenomenon of sand discharge after chemical sand control, the main reason is that the solidification strength of the proppant near the blast hole is insufficient, or the solidification strength of the proppant near the blast hole decreases over time, causing the proppant to return through the joint, thus resulting in sand control failure.

[0005] Therefore, a new sand control technology is needed to address the problems of poor sand control effect and short duration of current fracturing processes or chemical sand control. Summary of the Invention

[0006] To address the problems in existing technologies, this invention proposes a method and application for fracturing loose sandstone. The proposed fracturing process for loose sandstone primarily utilizes controlled fracture length enhancement techniques and bridging and plugging techniques for boreholes and fracture openings to prevent sand formation. By controlling the flow rate to create fractures, and adding buoyancy and settling agents as well as filtration reduction agents to the fracturing fluid system, the length of the consolidated proppant is increased, as are the channels for proppant and formation sand discharge, thereby increasing the energy consumption for their return. Simultaneously, high-strength rod-shaped proppant is used to bridge and plug the boreholes, creating a mechanical sand control effect. This solves the problem of poor or short-lasting sand control effects in current fracturing processes or chemical sand control methods.

[0007] One objective of this invention is to provide a method for fracturing loose sandstone, comprising the steps of fracture creation and bridging and sand-prevention of the fractures. The fracture creation includes the steps of pre-fracturing fluid injection and sand fracturing, wherein the fracturing fluid discharge rate used for sand fracturing is greater than the fracturing fluid discharge rate used for pre-fracturing fluid injection.

[0008] In the method for fracturing loose sandstone according to the present invention, preferably, it includes the following steps:

[0009] (1) Fracturing is carried out by pre-flush pumping and sand fracturing; wherein, the fracturing fluid discharge rate used in sand fracturing is greater than that used in pre-flush pumping.

[0010] (2) Bridge and plug sand prevention construction is carried out on the cracks by pumping consolidation proppant, displacement, pumping rod ceramic proppant, and optionally displacement.

[0011] In the method for fracturing loose sandstone described in this invention, preferably, step (1),

[0012] The pre-flush pump injection rate is set at 1.5 to 2.0 times the minimum discharge rate required to achieve fracture pressure in loose sandstone reservoirs; preferably, the pre-flush pump injection rate is 2 to 12 m³ / s. 3 / min (preferably 3-5m) 3 / min); for example, 2, 4, 6, 8, 10, 12m 3 / min; and / or,

[0013] The volume of fracturing fluid used for pre-fracturing fluid injection is 20% to 28% of the total fracturing fluid volume in steps (1) and (2); for example, 20%, 22%, 24%, 26%, 28%; and / or,

[0014] When injecting pre-fracturing fluid, the fracturing fluid used includes fracturing base fluid, floating blocker, and sinking blocker.

[0015] In the technical solution of the present invention, the fracturing pressure of the loose sandstone reservoir is calculated based on reservoir logging data, rock mechanics parameters and geostress parameters. Based on the fracturing pressure, the wellhead construction pressure at different discharge rates is calculated considering the friction of the fracturing fluid system and the friction of the borehole.

[0016] In the method for fracturing loose sandstone described in this invention, preferably,

[0017] Step (1),

[0018] When injecting the pre-fracturing fluid, the viscosity of the fracturing base fluid used is 100–400 mPa·s; for example, 100, 150, 200, 250, 300, 350, or 400 mPa·s; preferably, the fracturing base fluid used is guar gum-based fracturing fluid; and / or,

[0019] The concentration of the fracturing fluid containing the buoyancy blocker used in the pre-fracturing fluid injection is 1wt% to 3wt%; for example, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%; and / or,

[0020] The concentration of the settling inhibitor in the fracturing fluid used for pre-flush injection is 1wt% to 3wt%; for example, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%; and / or,

[0021] The density of the buoyancy-blocking agent is less than or equal to 0.5 g / cm³. 3 The floating velocity in still water is not less than 0.3 m / min, and the particle size is not greater than the particle size corresponding to 140 mesh particles; in the technical solution of the present invention, the floating blocking agent used is a commonly used existing floating blocking agent that meets the above conditions. Preferably, the floating blocking agent is selected from glass microspheres; and / or,

[0022] The density of the sinking blocking agent is not less than 1.5 g / cm³. 3 The settling velocity in still water is not less than 0.45 m / min, and the particle size is not greater than the particle size corresponding to 140 mesh particles. In the technical solution of the present invention, the settling blocking agent used is a commonly used settling blocking agent that meets the above conditions. Preferably, the settling blocking agent is selected from powdered ceramic or powdered sand.

[0023] In the method for fracturing loose sandstone described in this invention, preferably,

[0024] Step (1),

[0025] The flow rate of the fracturing fluid used in the proppant fracturing is the maximum flow rate required to achieve the fracturing pressure of the loose sandstone reservoir; preferably, the flow rate of the fracturing fluid used in the proppant fracturing is 3–12 m³ / s. 3 / min (preferably 6-10m) 3 / min); for example, 2, 3, 4, 6, 8, 10, 12m 3 / min; More preferably, after the pre-flush fluid injection is completed, the fracturing fluid discharge rate is increased to the maximum discharge rate within 5-10 minutes; and / or,

[0026] The volume of fracturing fluid used in proppant fracturing is 60% to 70% of the total volume of fracturing fluid in steps (1) and (2); for example, 60%, 62%, 64%, 66%, 68%, or 70%; and / or,

[0027] Propane fracturing employs a constant proppant-to-fluid ratio; preferably, the proppant-to-fluid ratio is 25%–35%; for example, 25%, 28%, 30%, 32%, or 35%; and / or,

[0028] The sand used for proppant fracturing has a particle size of one or more of the following: 70 / 140 mesh, 40 / 70 mesh, 30 / 50 mesh, and 20 / 40 mesh; and / or,

[0029] The fracturing fluid used in sand fracturing includes fracturing base fluid, sand, and filtration loss reducer.

[0030] In the technical solution of the present invention, the sand used for sand fracturing is selected from commonly used sand, and preferably the sand used for sand fracturing is selected from at least one of ceramsite, coated sand or consolidation proppant.

[0031] In the method for fracturing loose sandstone described in this invention, preferably,

[0032] Step (1),

[0033] When using proppant fracturing, the viscosity of the fracturing fluid used is 100–400 mPa·s; for example, 100, 150, 200, 250, 300, 350, or 400 mPa·s; preferably, the fracturing fluid used is guar gum-based fracturing fluid; and / or,

[0034] The concentration of the fluid loss reducer in the fracturing fluid used for proppant fracturing is 1 wt% to 3 wt%; for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%; and / or,

[0035] The filtration loss reducer reduces the fracturing fluid filtration loss by 50% or more, and its natural degradation rate is 90% or more; preferably, the filtration loss reducer is selected from one or more of carboxymethyl cellulose, sulfomethylphenol resin, hydrolyzed polyacrylonitrile, carboxymethyl starch or hydroxyethyl starch.

[0036] In the method for fracturing loose sandstone described in this invention, preferably,

[0037] Step (2),

[0038] Consolidated proppant injection should begin after 80%–90% of the total fracturing fluid volume has been pumped in; for example, after 80%, 82%, 84%, 86%, 88%, or 90% of the total volume; and / or,

[0039] The flow rate of fracturing fluid used for pumping consolidated proppant is 2–12 m³. 3 / min; for example, 2, 4, 6, 8, 10, 12m 3 / min; and / or,

[0040] The volume of consolidated proppant used for pump injection is 2 to 4 times the wellbore volume; for example, 2, 3, or 4 times the wellbore volume; and / or,

[0041] The pumping of consolidated proppant employs a constant sand-to-liquid ratio; preferably, the sand-to-liquid ratio is 1.5 times that used in step (1) for sand fracturing; more preferably, the sand-to-liquid ratio for pumping high-strength consolidated proppant is 37.5%–52.5%; for example, 37.5%, 40%, 45%, 50%, 52.5%; and / or,

[0042] The consolidated strength of the consolidated proppant used is above 6 MPa; and / or,

[0043] The particle size of the consolidated proppant used is one or a combination of 30 / 50 mesh and 20 / 40 mesh; and / or,

[0044] The viscosity of the fracturing fluid used for pumping consolidated proppant is 100–400 mPa·s; for example, 100, 150, 200, 250, 300, 350, and 400 mPa·s.

[0045] In the technical solution of the present invention, the consolidation proppant injected is selected from commonly used consolidation proppants or proppants, preferably with a consolidation strength of 6 MPa or above; preferably, the consolidation proppant used is existing resin-coated sand (such as coated sand).

[0046] In the method for fracturing loose sandstone described in this invention, preferably,

[0047] Step (2),

[0048] The viscosity of the fracturing fluid used in the displacement stage is 100–200 mPa·s; for example, 100, 150, or 200 mPa·s; and / or,

[0049] The volume of fracturing fluid used in the displacement stage is 0.5 to 1.0 times the wellbore volume; for example, 0.5, 0.8, or 1 times the wellbore volume; and / or,

[0050] The displacement rate of the fracturing fluid used in the displacement stage is 2–12 m³ / s. 3 / min; for example, 2, 3, 4, 6, 8, 10, 12m 3 / min.

[0051] In the method for fracturing loose sandstone described in this invention, preferably,

[0052] Step (2),

[0053] The viscosity of the fracturing fluid used for pumping the rod-shaped ceramic proppant is 50% to 80% higher than the viscosity of the fracturing base fluid used in the sand-addition fracturing in step (1); for example, 50%, 55%, 60%, 65%, 70%, 75%, or 80% higher; and / or,

[0054] The volume of fracturing fluid used for pumping the rod-shaped ceramic proppant shall be no less than three times the wellbore volume; and / or,

[0055] The flow rate of fracturing fluid used for pumping rod-shaped ceramic proppant is 2–12 m³ / s. 3 / min; for example, 2, 3, 4, 6, 8, 10, 12m 3 / min; and / or,

[0056] The compressive strength of the rod-shaped ceramic proppant is 69 MPa to 106 MPa; for example, 69, 75, 80, 85, 90, 95, 100, or 106 MPa; and / or,

[0057] The length of the rod-shaped ceramic support is 2 to 4 times the diameter of the perforation aperture; for example, 2, 3, or 4 times; and / or,

[0058] The diameter of the rod-shaped ceramic support is 0.15 to 0.25 times the diameter of the perforation hole; for example, 0.15, 0.2, or 0.25 times.

[0059] In the technical solution of the present invention, the pumped rod-shaped ceramic proppant is selected from commonly used rod-shaped ceramic proppants, which are rod-shaped ceramic proppants made from existing ceramics and clay.

[0060] In the method for fracturing loose sandstone described in this invention, preferably,

[0061] Step (2),

[0062] The fracturing fluid used for pumping the rod-shaped ceramic proppant has a proppant-to-liquid ratio of 50% to 70% of the proppant-to-liquid ratio in step (1) of the proppant fracturing stage; for example, 50%, 55%, 60%, 65%, or 70%; preferably,

[0063] The fracturing fluid used for pumping the rod-shaped ceramic proppant has a sand-to-fluid ratio of 50% for the first wellbore volume pumped during the sand-addition fracturing stage (1), 60% for the second wellbore volume pumped during the sand-addition fracturing stage (1), and 70% for the third wellbore volume and above pumped during the sand-addition fracturing stage (1); and / or,

[0064] After step (2) is completed, a flowback system with the nozzle size gradually increasing is adopted. Once the amount of solid material returned from the wellhead stabilizes, this flowback system and the corresponding production system are maintained.

[0065] In the technical solution of this invention, if the construction pressure increases rapidly during the first and second wellbore volumetric pumping process, subsequent sand fracturing operations should be stopped. After the sand addition is completed in the third wellbore volumetric pumping, the construction should be stopped immediately after the rod-shaped proppant is completely replaced into the formation, and over-displacement operations should not be carried out under the premise of ensuring safe construction.

[0066] In the technical solution of this invention, a return flow system with the nozzle size gradually increasing is adopted to control the liquid discharge speed from the borehole, so as to avoid affecting the consolidation effect of the solidification proppant and production due to excessive speed.

[0067] In the technical solution of this invention, the fracturing fluid and displacement fluid used are commonly used material systems. For example, the existing guar gum-based fracturing fluid is mainly composed of guar gum, KCl, bactericide, clay stabilizer, etc.

[0068] A second objective of this invention is to provide the application of the fracturing method for loose sandstone described in one objective of this invention in oil and gas field development.

[0069] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0070] Compared with the prior art, the present invention has at least the following advantages:

[0071] The present invention proposes a fracturing process for loose sandstone, which mainly consists of controlled fracture length increase process and bridging and plugging of blast holes and fracture openings for sand control. By increasing the fracture length and the length of the consolidation proppant, as well as the mechanical sand control effect of the blast holes formed by the high-strength rod-shaped proppant, the problem of poor sand control effect and short duration of current fracturing processes or chemical sand control is solved. Detailed Implementation

[0072] The present invention will now be described in detail with reference to specific examples and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0073] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0074] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0075] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0076] Example 1

[0077] This technology was tested in a loose sandstone block in the Bohai Sea:

[0078] (1) Seam control and seam length increase technology measures

[0079] The fracturing pressure of loose sandstone reservoirs is calculated based on reservoir logging data, rock mechanics parameters, and geostress parameters. Using this fracturing pressure as a benchmark, the wellhead construction pressure at different discharge rates is calculated, taking into account the friction of the fracturing fluid system and the friction of the blast hole.

[0080] Pre-fluid pump injection: Pre-fluid pump injection should be performed at a flow rate of 1.5 times the minimum flow rate required to reach the rupture pressure. The flow rate of the pre-fluid pump is 4 m³ / s. 3 / min; the proportion of the pre-fracturing fluid injected is 25% of the total fracturing fluid volume of step (1) + step (2);

[0081] When injecting the pre-fracturing fluid, the fracturing fluid used includes fracturing base fluid, a floating blocker (glass microspheres), and a sinking blocker (ceramic powder). The viscosity of the fracturing base fluid is 200 mPa·s, specifically a guar gum-based fracturing fluid, and the density of the floating blocker is 0.45 g / cm³. 3 The floating velocity in still water is 0.5 m / min, and the particle size is 200 mesh; the density of the sinking blocking agent is 1.65 g / cm³. 3 The settling velocity was 0.6 m / min, and the particle size was 200 mesh; the concentration of the buoyancy blocking agent was 2 wt%; the concentration of the settling blocking agent was 2 wt%.

[0082] Sand-filled fracturing operation: After the pre-flush fluid injection is completed, the displacement should be increased to the maximum allowable displacement of 6m³ within 10 minutes. 3 / min, and then sand is added. The fracturing fluid used for sand fracturing includes fracturing base fluid, sand and filtration loss reducer, wherein the viscosity of fracturing base fluid is 150 mPa·s; specifically, it is guar gum-based fracturing fluid, and the filtration loss reducer (carboxymethyl cellulose) meets the requirement of reducing the filtration loss of fracturing fluid by 50% or more, and its natural degradation rate is 90% or more; the concentration of filtration loss reducer added is 2wt%. The proportion of the fluid volume used for sand fracturing is 70% of the total fracturing fluid volume of step (1) + step (2); sand fracturing adopts a constant sand-to-fluid ratio; the sand-to-fluid ratio of sand fracturing is 25%; the sand used for sand fracturing is selected from ceramsite; the particle size of the sand used for sand fracturing is 30 / 50 mesh.

[0083] (2) Sand-blocking technology for blast holes and joints

[0084] Pumping of consolidated proppant: After pumping 85% of the total fracturing fluid (generally in the later stage of sand addition), pumping of consolidated proppant begins. First, pump high-strength consolidated proppant (resin-coated sand) with the same particle size as the fracturing design is pumped. The consolidation strength of the high-strength consolidated proppant used is 7 MPa; the particle size of the high-strength consolidated proppant used is 20 / 40 mesh. A constant sand-to-liquid ratio is used for pumping the consolidated proppant; the sand-to-liquid ratio is 1.5 times that used in step (1) sand addition fracturing; the volume of liquid used for pumping the consolidated proppant is 3 times the wellbore volume; the viscosity of the fracturing fluid used for pumping the high-strength consolidated proppant is 200 mPa·s; the discharge rate of the fracturing fluid used for pumping the high-strength consolidated proppant is 6 m³ / s. 3 / min.

[0085] Displacement operation: After pumping is completed, 0.5 times the wellbore volume is displaced; the fracturing fluid used in the displacement stage is a guar gum-based fracturing fluid with a viscosity of 150 mPa·s; the displacement rate of the fracturing fluid used in the displacement stage is 6 m³ / s. 3 / min.

[0086] High-strength rod-shaped ceramic proppant injection: High-strength rod-shaped ceramic proppant is then pumped in. The proppant's length is three times the perforation diameter (9.5 mm), and its diameter is 0.2 times the perforation diameter. The compressive strength of the pumped rod-shaped ceramic proppant is 86 MPa. During the injection of the rod-shaped ceramic proppant, the fracturing fluid viscosity is increased by 50% compared to the fracturing base fluid viscosity used in proppant fracturing. The fracturing fluid flow rate used for pumping the rod-shaped ceramic proppant is 6 m³ / s. 3 / min; the volume of fracturing fluid used for pumping the rod-shaped ceramic proppant is 3 times the wellbore volume; the sand-to-fluid ratio pumped in the first wellbore volume of the rod-shaped ceramic proppant is 50% of the sand-to-fluid ratio in the sand-addition fracturing stage of step (1), the sand-to-fluid ratio pumped in the second wellbore volume is 60% of the sand-to-fluid ratio in the sand-addition fracturing stage of step (1), and the sand-to-fluid ratio pumped in the third wellbore volume is 70% of the sand-to-fluid ratio in the sand-addition fracturing stage of step (1). After the sand addition is completed in the third wellbore volume, the construction is immediately ended after the rod-shaped proppant is completely replaced to the formation, and over-displacement construction is not carried out under the premise of ensuring safe construction.

[0087] After the fracturing operation is completed, a flowback system is adopted with the nozzle size gradually increasing. Once the amount of solid material returned from the wellhead stabilizes, this flowback system and the corresponding production system are maintained.

[0088] Example 2

[0089] This technology was tested in a loose sandstone block in Northeast China.

[0090] (1) Seam control and seam length increase technology measures

[0091] The fracturing pressure of loose sandstone reservoirs is calculated based on reservoir logging data, rock mechanics parameters, and geostress parameters. Using this fracturing pressure as a benchmark, the wellhead construction pressure at different discharge rates is calculated, taking into account the friction of the fracturing fluid system and the friction of the blast hole.

[0092] Pre-fluid pump injection: Pre-fluid pump injection should be performed at twice the minimum displacement required to reach the rupture pressure, with a displacement of 5 m³ / h. 3 / min; the pre-fracturing fluid volume ratio is 20% of the total fracturing fluid volume of step (1) + step (2);

[0093] When injecting the pre-fracturing fluid, the fracturing fluid used includes fracturing base fluid, a floating blocker (glass microspheres), and a sinking blocker (silt). The viscosity of the fracturing base fluid is 200 mPa·s, specifically a guar gum-based fracturing fluid, and the density of the floating blocker is 0.45 g / cm³. 3 The floating velocity in still water is 0.5 m / min, and the particle size is 200 mesh; the density of the sinking blocking agent is 1.65 g / cm³. 3 The settling velocity was 0.7 m / min, and the particle size was 200 mesh; the concentration of the buoyancy blocking agent was 3 wt%; and the concentration of the settling blocking agent was 1 wt%.

[0094] Sand-filled fracturing operation: After the pre-flush fluid injection is completed, the displacement should be increased to the maximum allowable displacement of 8m³ within 5 minutes. 3 / min, and then sand is added. The fracturing fluid used for sand fracturing includes fracturing base fluid, sand and filtration loss reducer, wherein the viscosity of fracturing base fluid is 100mPa·s; specifically, it is guar gum-based fracturing fluid, and the filtration loss reducer (carboxymethyl cellulose) meets the requirement of reducing the filtration loss of fracturing fluid by 50% or more, and its natural degradation rate is 90% or more; the concentration of filtration loss reducer added is 1wt%; the proportion of the fluid volume used for sand fracturing is 70% of the total fracturing fluid volume of step (1) + step (2); sand fracturing adopts a constant sand-to-fluid ratio; the sand-to-fluid ratio of sand fracturing is 30%; the sand used for sand fracturing is selected from ceramsite; the particle size of the sand used for sand fracturing is 30 / 50 mesh.

[0095] (2) Sand-blocking technology for blast holes and joints

[0096] Pumping of consolidated proppant: After pumping 88% of the total fracturing fluid (generally in the later stage of sand addition), pumping of consolidated proppant (resin-coated sand) begins. The consolidation strength of the high-strength consolidated proppant used is 8 MPa; the particle size of the high-strength consolidated proppant used is 30 / 50 mesh; a constant sand-to-liquid ratio is used for pumping the consolidated proppant; the sand-to-liquid ratio is 1.5 times that used in step (1) sand addition fracturing; the volume of liquid used for pumping the consolidated proppant is 3 times the wellbore volume; the viscosity of the fracturing fluid used for pumping the high-strength consolidated proppant is 150 mPa·s; the discharge rate of the fracturing fluid used for pumping the high-strength consolidated proppant is 8 m³ / s. 3 / min.

[0097] Displacement operation: After pumping is completed, 0.5 times the wellbore volume is displaced; the fracturing fluid used in the displacement stage is a guar gum-based fracturing fluid with a viscosity of 100 mPa·s; the displacement rate of the fracturing fluid used in the displacement stage is 7 m³ / s. 3 / min.

[0098] High-strength rod-shaped ceramic proppant injection: High-strength rod-shaped ceramic proppant is then pumped in. The proppant's length is 4 times the perforation diameter (9.5 mm), and its diameter is 0.25 times the perforation diameter. The compressive strength of the pumped rod-shaped ceramic proppant is 86 MPa. During the injection of the rod-shaped ceramic proppant, the fracturing fluid viscosity is increased by 50% compared to the fracturing base fluid viscosity used in proppant fracturing. The fracturing fluid flow rate used for pumping the rod-shaped ceramic proppant is 8 m³ / s. 3 / min; the volume of fracturing fluid used for pumping the rod-shaped ceramic proppant is 3 times the wellbore volume; the sand-to-fluid ratio pumped in the first wellbore volume of the rod-shaped ceramic proppant is 50% of the sand-to-fluid ratio in the sand-addition fracturing stage of step (1), the sand-to-fluid ratio pumped in the second wellbore volume is 60% of the sand-to-fluid ratio in the sand-addition fracturing stage of step (1), and the sand-to-fluid ratio pumped in the third wellbore volume is 70% of the sand-to-fluid ratio in the sand-addition fracturing stage of step (1). After the sand addition is completed in the third wellbore volume, the construction is immediately ended after the rod-shaped proppant is completely replaced to the formation, and over-displacement construction is not carried out under the premise of ensuring safe construction.

[0099] After the fracturing operation is completed, a flowback system is adopted with the nozzle size gradually increasing. Once the amount of solid material returned from the wellhead stabilizes, this flowback system and the corresponding production system are maintained.

[0100] Comparative Example 1

[0101] It adopts basically the same construction method as Example 1, the only difference being that the fracturing fluid displacement used for sand fracturing is less than that used for pre-fracturing fluid injection, specifically, the displacement of fracturing fluid used for pre-fracturing fluid injection is 6m³. 3 / min; the discharge rate of fracturing fluid used in proppant fracturing is 4m³ / min. 3 / min.

[0102] Comparative Example 2

[0103] It adopts the same construction method as Comparative Example 1, the only difference being that the fracturing fluid used for pre-flush pump injection does not contain buoyancy blockers and sinking blockers; and the fracturing fluid used for sand fracturing does not contain filtration loss reducers.

[0104] Comparative Example 3

[0105] In Example 1, the "fracturing and filling" fracturing method commonly used in the prior art was performed on the well site.

[0106] Comparative Example 4

[0107] In Example 1, the existing technology commonly uses the fracturing method of "fracturing and filling + chemical sand control" to carry out fracturing in the well site.

[0108] The sand control effectiveness of the above embodiments and comparative examples of the present invention is shown in Table 1.

[0109] Table 1

[0110] Example Number of wells implemented Average sand control effectiveness period / day Example 1 5 370 Example 2 10 350 Comparative Example 1 5 300 Comparative Example 2 4 280 Comparative Example 3 7 160 Comparative Example 4 6 251

[0111] The results of Example 1, Comparative Examples 1 and 2 show that the present invention achieves long fractures by controlling the discharge rate and adding floating and sinking blocking agents and filtration loss reducing agents to the fracturing fluid system. This increases the laying length of the consolidated proppant, the channel length for proppant and formation sand discharge, and thus increases the energy consumption of both. At the same time, the use of high-strength rod-shaped proppant achieves bridging of the borehole, forming a mechanical sand control effect, which solves the problem that the current fracturing process or chemical sand control is ineffective and has a short duration.

[0112] The results of Example 1 and Comparative Examples 3 and 4 show that the sand control effectiveness period of the present invention is significantly improved compared with Comparative Examples 3 and 4, especially compared with Comparative Example 3, which is improved by 50% or more, and the overall effect is significant.

[0113] In summary, the fracturing process for loose sandstone proposed in this invention mainly consists of controlled fracture length enhancement technology and bridging and plugging technology for blast holes and fracture openings to prevent sand formation. By controlling the discharge rate to create fractures, adding floating and sinking blocking agents and filtration reduction agents to the fracturing fluid system to create longer fractures, the length of the consolidated proppant is increased, as are the channels for proppant and formation sand discharge, thereby increasing the energy consumption of both. At the same time, the use of high-strength rod-shaped proppant to achieve bridging and plugging of blast holes forms a mechanical sand control effect, solving the problem of poor sand control effect and short duration of current fracturing processes or chemical sand control.

[0114] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0115] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0116] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0117] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A method for fracturing loose sandstone, characterized in that, The process includes the steps of creating a fracture and bridging and plugging the fracture to prevent sand buildup. The fracture creation process includes the steps of pre-flush injection and sand fracturing. The fracturing fluid discharge rate used in sand fracturing is greater than that used in pre-flush injection.

2. The method for fracturing loose sandstone according to claim 1, characterized in that, Specifically, the following steps are included: (1) Fracturing is carried out by pre-flush pumping and sand fracturing; wherein, the fracturing fluid discharge rate used in sand fracturing is greater than that used in pre-flush pumping. (2) Bridge and plug sand prevention construction is carried out on the cracks by pumping consolidation proppant, displacement, pumping rod ceramic proppant, and optionally displacement.

3. The method for fracturing loose sandstone according to claim 2, characterized in that: Step (1), The pre-flush pump injection rate is set at 1.5 to 2.0 times the minimum discharge rate required to achieve fracture pressure in loose sandstone reservoirs; preferably, the pre-flush pump injection rate is 2 to 12 m³ / s. 3 / min; and / or, The volume of fracturing fluid used for pre-fracturing fluid injection is 20% to 28% of the total fracturing fluid volume in steps (1) and (2); and / or, When injecting pre-fracturing fluid, the fracturing fluid used includes fracturing base fluid, floating blocker, and sinking blocker.

4. The method for fracturing loose sandstone according to claim 3, characterized in that: Step (1), When injecting the pre-fracturing fluid, the viscosity of the fracturing base fluid used should be 100–400 mPa·s; preferably, the fracturing base fluid used should be guar gum-based fracturing fluid; and / or, The concentration of the fracturing fluid containing the buoyancy blocker used in the pre-fracturing fluid injection is 1 wt% to 3 wt%; and / or, The concentration of the settling inhibitor in the fracturing fluid used for pre-flush injection is 1 wt% to 3 wt%; and / or, The density of the buoyancy-blocking agent is less than or equal to 0.5 g / cm³. 3 In still water, the floating velocity is not less than 0.3 m / min, and the particle size is not greater than the particle size corresponding to 140 mesh particles; and / or, The density of the sinking blocking agent is not less than 1.5 g / cm³. 3 The sinking velocity in still water is not less than 0.45 m / min, and the particle size is not greater than the particle size corresponding to 140 mesh.

5. The method for fracturing loose sandstone according to claim 2, characterized in that: Step (1), The flow rate of the fracturing fluid used in the proppant fracturing is the maximum flow rate required to achieve the fracturing pressure of the loose sandstone reservoir; preferably, the flow rate of the fracturing fluid used in the proppant fracturing is 3–12 m³ / s. 3 / min; More preferably, after the pre-flush fluid injection is completed, the fracturing fluid discharge rate is increased to the maximum discharge rate within 5-10 minutes; and / or, The volume of fracturing fluid used in proppant fracturing is 60% to 70% of the total volume of fracturing fluid in steps (1) and (2); and / or, Sand fracturing employs a constant sand-to-fluid ratio; preferably, the sand-to-fluid ratio in sand fracturing is 25%–35%; and / or, The sand used for proppant fracturing has a particle size of one or more of the following: 70 / 140 mesh, 40 / 70 mesh, 30 / 50 mesh, and 20 / 40 mesh; and / or, The fracturing fluid used in sand fracturing includes fracturing base fluid, sand, and filtration loss reducer.

6. The method for fracturing loose sandstone according to claim 5, characterized in that: Step (1), When using proppant fracturing, the viscosity of the fracturing fluid used should be 100–400 mPa·s; preferably, the fracturing fluid used should be guar gum-based; and / or, The concentration of the fluid loss reducer in the fracturing fluid used for proppant fracturing is 1 wt% to 3 wt%; and / or, The filtration loss reducer reduces the fracturing fluid filtration loss by 50% or more, and its natural degradation rate is 90% or more; preferably, the filtration loss reducer is selected from one or more of carboxymethyl cellulose, sulfomethylphenol resin, hydrolyzed polyacrylonitrile, carboxymethyl starch or hydroxyethyl starch.

7. The method for fracturing loose sandstone according to claim 2, characterized in that: Step (2), After pumping 80%–90% of the total fracturing fluid volume, begin pumping consolidated proppant; and / or, The flow rate of fracturing fluid used for pumping consolidated proppant is 2–12 m³. 3 / min; and / or, The volume of consolidated proppant used for pump injection is 2 to 4 times the wellbore volume; and / or, The pump-injected consolidated proppant uses a constant sand-to-liquid ratio; preferably, the sand-to-liquid ratio is 1.5 times that used in the sand fracturing in step (1); more preferably, the sand-to-liquid ratio of the pump-injected consolidated proppant is 37.5% to 52.5%; and / or, The consolidated strength of the consolidated proppant used is above 6 MPa; and / or, The particle size of the consolidated proppant used is one or a combination of 30 / 50 mesh and 20 / 40 mesh; and / or, The viscosity of the fracturing fluid used for pumping consolidated proppant is 100–400 mPa·s.

8. The method for fracturing loose sandstone according to claim 2, characterized in that: Step (2), The viscosity of the fracturing fluid used in the displacement stage is 100–200 mPa·s; and / or, The volume of fracturing fluid used in the displacement stage is 0.5 to 1.0 times the wellbore volume; and / or, The displacement rate of the fracturing fluid used in the displacement stage is 2–12 m³ / s. 3 / min.

9. The method for fracturing loose sandstone according to claim 1, characterized in that: Step (2), The viscosity of the fracturing fluid used for pumping the rod-shaped ceramic proppant is 50% to 80% higher than the viscosity of the fracturing base fluid used in step (1) for proppant fracturing; and / or, The volume of fracturing fluid used for pumping the rod-shaped ceramic proppant shall be no less than three times the wellbore volume; and / or, The flow rate of fracturing fluid used for pumping rod-shaped ceramic proppant is 2–12 m³ / s. 3 / min; and / or, The compressive strength of the rod-shaped ceramic proppant is 69 MPa to 106 MPa; and / or, The length of the rod-shaped ceramic support is 2 to 4 times the diameter of the perforation aperture; and / or, The diameter of the rod-shaped ceramic support is 0.15 to 0.25 times the diameter of the perforation hole.

10. The method for fracturing loose sandstone according to claim 2, characterized in that: Step (2), The fracturing fluid used for pumping the rod-shaped ceramic proppant has a proppant-to-fluid ratio of 50% to 70% of the proppant-to-fluid ratio in step (1) of the proppant fracturing stage; and / or, After step (2) is completed, a flowback system with the nozzle size gradually increasing is adopted. Once the amount of solid material returned from the wellhead stabilizes, this flowback system and the corresponding production system are maintained.

11. The application of the fracturing method for loose sandstone according to any one of claims 1-10 in oil and gas field development.