Reservoir sand fracturing method and application

Abstract

The invention discloses a reservoir sand fracturing method and application. The sand fracturing method for the reservoir comprises the steps of fracture forming through the gel fracturing fluid, fracture expanding through the linear gel fracturing fluid and sand adding construction through the linear gel fracturing fluid. According to the process method for fracturing transformation of the reservoir, the flow conductivity of filled fractures and the effective transformation volume are improved to the maximum extent through the process combination of gel fracture forming, linear gel fracture expanding, medium-displacement linear gel sand adding, constant-propping-agent particle size range and constant-sand-liquid-ratio sand adding and acid liquor and linear gel fracturing fluid composite displacement; therefore, the long-term fracturing stable yield of the shale oil well is improved. Through the implementation of the method, the shale oil reservoir transformation effect can be effectively improved, meanwhile, the construction pump injection procedure is greatly simplified, high displacement needed by conventional slickwater fracturing is not needed, fracturing construction water horsepower and fracturing equipment are reduced, construction is easy and convenient, operation is easy, and safety is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of reservoir transformation, and more specifically, to a method and application of reservoir sand fracturing, and even more specifically, to a method and application of shale oil reservoir sand fracturing. Background Art

[0002] As a hot topic in the field of unconventional oil and gas exploration and development in recent years, shale oil has received extensive attention in China. At present, the shale oil that has been put into development in China is mainly continental deposits. The main process of shale oil fracturing transformation is basically similar to that of shale gas, both of which adopt the fracturing mode of "dense cutting + temporary plugging and diversion + strong sand addition". However, large-scale injection of large amounts of liquid and sand cannot achieve high production effects like shale gas development. Sometimes, the production of two wells in the same block and the same structure is very different under the premise of the same process parameters. The Jurassic continental shale oil reservoir in Sichuan and Chongqing is a representative example. Unlike the marine shale gas reservoir, it has a higher clay mineral content, complex lithology, and contains shell limestone and sandy bands of different thicknesses, resulting in strong mechanical heterogeneity in the vertical direction of the formation. On the one hand, during the hydraulic fracturing process, such shale oil reservoirs usually show increased difficulty in initiating fractures in the formation and limited longitudinal extension of the fractures, resulting in reduced complexity of the fractures, and the actual transformation volume obtained by fracturing is greatly reduced compared to shale gas. On the other hand, under underground temperature and pressure conditions, the viscosity of shale oil differs by hundreds or even thousands of times from that of shale gas, the fluidity of shale oil deteriorates, and the demand for conductivity is higher.

[0003] In order to solve the practical problems of small shale oil reservoir transformation volume and low fracture conductivity, the site further increased the displacement (up to 24m 3 / min), increase the liquid intensity (up to 40m 3 / m or more), increasing the sand addition strength (up to 4t / m or more), using a combination of multi-size proppants (70 / 140 mesh + 40 / 70 mesh + 30 / 50 mesh) and other methods to enhance the fracturing effect, but the results were minimal.

[0004] Therefore, it is necessary to develop a more effective fracturing method for shale oil reservoirs. Summary of the invention

[0005] In order to solve the practical problems of existing reservoirs, especially shale oil reservoirs, such as the difficulty of multi-lithology penetration transformation by fracturing, narrow transformation fracture channels, and reduced conductivity due to the mixing of multi-size supports, the present invention proposes a method and application of reservoir sand fracturing. The process method of reservoir fracturing transformation of the present invention adopts a combination of frozen gel seam creation and linear gel seam expansion, medium displacement linear gel sand addition, constant proppant particle size range and constant sand-liquid ratio sand addition, acid and linear gel fracturing fluid composite displacement process, to maximize the filling fracture conductivity and effective transformation volume, thereby improving the long-term fracturing stable production of oil wells.

[0006] One of the purposes of the present invention is to provide a reservoir sand fracturing method, which comprises the steps of seam creation with gel fracturing fluid, seam expansion with linear gel fracturing fluid, and construction with linear gel fracturing fluid and sand addition.

[0007] The reservoir sand fracturing method of the present invention preferably includes the following steps:

[0008] (1) Evaluation of key reservoir parameters;

[0009] (2) perforating the section to be fractured and then performing acid pretreatment;

[0010] (3) injecting gel fracturing fluid for initial fracture creation;

[0011] (4) injecting linear gel fracturing fluid to expand the fracture;

[0012] (5) Linear glue fracturing fluid and sand construction;

[0013] (6) Composite replacement;

[0014] (7) Optionally repeat the above steps (2) to (6) until the fracturing construction of all fracturing stages of the oil well is completed.

[0015] In the reservoir sand fracturing method of the present invention, preferably:

[0016] Step (1),

[0017] The reservoir is selected from shale oil reservoirs, deep-layer high-stress shale gas reservoirs, complex clastic rocks, and low-permeability matrix-pore carbonate oil and gas reservoirs; preferably shale oil reservoirs; the present invention is particularly suitable for sand fracturing transformation of shale oil reservoirs, and also has good reference significance for sand fracturing of deep-layer, high-stress shale gas reservoirs and complex clastic rocks, and low-permeability matrix-pore carbonate oil and gas reservoirs;

[0018] Based on the evaluation of key reservoir parameters, the fracturing stages are divided and the perforation locations are determined;

[0019] Preferably, the key parameter includes at least one of a geological sweet spot and an engineering sweet spot of the reservoir.

[0020] In the reservoir sand fracturing method of the present invention, preferably:

[0021] Step (2),

[0022] During the perforation, the length of the fracturing section is 50 to 60 m; the spacing between the perforation clusters is 5 to 10 m; and / or,

[0023] During the acid pretreatment,

[0024] The volume of the injected acidic liquid is 10 to 20 m 3 and / or,

[0025] The displacement of acidic liquid is 1.5~2m 3 / min.

[0026] In the reservoir sand fracturing method of the present invention, preferably:

[0027] In step (2), during the acid pretreatment,

[0028] The acidic liquid used includes at least an inorganic acid;

[0029] Preferably, the inorganic acid comprises at least hydrochloric acid and optionally hydrofluoric acid;

[0030] In the acidic liquid, the mass concentration of inorganic acid is 15% to 20%;

[0031] More preferably,

[0032] The inorganic acid is selected from at least one of hydrochloric acid and earth acid;

[0033] More preferably,

[0034] The acidic liquid used also includes a corrosion inhibitor, an iron ion stabilizer and a drainage aid. In the present invention, the acid pretreatment process and the selection of the pretreatment acid solution system used are both conventional operations and formulations on site, and those skilled in the art can make corresponding adjustments according to the geological conditions of the oil well; further preferably,

[0035] The corrosion inhibitor may be a conventional corrosion inhibitor in the prior art, such as at least one selected from imidazolines, quaternary ammonium salts, Mannich bases and the like; commercially available products may be used.

[0036] The iron ion stabilizer can be any conventional iron ion stabilizer in the art, such as at least one selected from acetic acid, citric acid, sodium salt of ethylenediaminetetraacetic acid, etc.; commercially available products can be used.

[0037] The drainage aid can be a conventional drainage aid in the prior art, such as at least one selected from cationic fluorocarbon surfactants, hydrocarbon surfactants, nonionic amphoteric surfactants, composite ion drainage aids, silicone drainage aids and the like; commercially available products can be used.

[0038] More preferably,

[0039] The mass concentration of the corrosion inhibitor is 1% to 3%;

[0040] The mass concentration of the iron ion stabilizer is 1% to 3%;

[0041] The mass concentration of the drainage aid is 1% to 3%.

[0042] In the reservoir sand fracturing method of the present invention, preferably:

[0043] Step (3),

[0044] The viscosity of the gel fracturing fluid is 200-300 mPa·s; and / or,

[0045] The volume of the injected gel fracturing fluid is 2 to 3 times the volume of the wellbore; and / or,

[0046] The displacement of gel fracturing fluid is 6~10m 3 / min.

[0047] In the present invention, the wellbore volume refers to the volume of the entire wellbore. The vertical well type is the volume of the entire vertical well section, and the horizontal well type is the entire wellbore volume of the vertical well section + horizontal well section.

[0048] In the reservoir sand fracturing method of the present invention, preferably:

[0049] Step (4),

[0050] The viscosity of the linear gel fracturing fluid is 30-50 mPa·s; and / or,

[0051] The volume of the injected linear gel fracturing fluid is 2 to 3 times the wellbore volume; and / or,

[0052] The displacement of linear gel fracturing fluid is 8~14m 3 / min, preferably 1 to 3m 3 The displacement increment of / min is increased step by step to the maximum design displacement; the pumping time at each displacement can be selected according to the actual situation on site.

[0053] In the reservoir sand fracturing method of the present invention, it is preferred that the initial displacement of the linear gel fracturing fluid in step (4) is consistent with the displacement of the frozen gel fracturing fluid in step (3).

[0054] In the reservoir sand fracturing method of the present invention, preferably:

[0055] Step (5),

[0056] Linear gel fracturing fluid carries proppant for sand-adding construction with a constant sand-to-liquid ratio;

[0057] Preferably, the proppant particle size range carried is constant.

[0058] In the reservoir sand fracturing method of the present invention, preferably:

[0059] The linear gel fracturing fluid used has a viscosity of 30-50 mPa·s, and the sand adding method is continuous sand adding; the displacement is 8-14 m 3 / min; within the range of 9% to 12% sand-to-liquid ratio, a constant sand-to-liquid ratio is selected for sand addition construction; the volume of the linear gel fracturing fluid can be comprehensively optimized according to the fracture size and transformation volume required for fracturing transformation to achieve the target production, the difficulty of fracture initiation and fracture extension of the formation rock, etc.; preferably, the volume of the injected linear gel fracturing fluid is 900 to 1500m 3 ; preferably 900~1200m 3 ;

[0060] The particle size range of the proppant is 1 / 6 to 1 / 3 of the simulated fracture width; preferably, the particle size range of the proppant is 50 / 80 mesh, 40 / 70 mesh or 30 / 50 mesh.

[0061] In the reservoir sand fracturing method of the present invention, preferably:

[0062] Step (6),

[0063] First use acid to displace, then use linear gel fracturing fluid to continue displacing;

[0064] Preferably, the acid solution used includes an inorganic acid and an acid-based drag reducing agent;

[0065] More preferably,

[0066] When acid displacement occurs, the total amount of liquid injected is 1 / 3 to 1 times the wellbore volume; and / or,

[0067] The displacement of the acid solution is consistent with the displacement during the sand addition construction in step (5); and / or,

[0068] In the acid solution, the mass concentration of the inorganic acid is 15% to 20%; the inorganic acid is selected from hydrochloric acid; further preferably,

[0069] In the present invention, the acid drag reducing agent is selected from the commonly used cationic drag reducing agents, anionic drag reducing agents and nonionic drag reducing agents, and the structure is mainly composed of polyacrylamide derivatives and copolymers thereof; commercially available products are sufficient;

[0070] The mass concentration of the acid resistance reducing agent is the conventional amount, preferably 0.1% to 1%.

[0071] In the reservoir sand fracturing method of the present invention, preferably:

[0072] When the linear gel fracturing fluid is used to continue displacement,

[0073] The total amount of linear gel fracturing fluid injected is 0.7 to 1 times the wellbore volume;

[0074] The displacement of the injected liquid is consistent with the displacement during the sand addition construction in step (5).

[0075] The linear gel fracturing fluid and the jelly gel fracturing fluid in the present invention are conventional cross-linkable polymer clean fracturing fluids, wherein the cross-linked one is the jelly gel fracturing fluid; conventional linear gels and jelly gels in the art can be used, and commercially available products with a viscosity that meets the requirements of this application can be used.

[0076] In the reservoir sand fracturing method of the present invention, it is most preferred that:

[0077] (1) Based on the evaluation of key parameters of shale oil reservoirs, geological and engineering sweet spots are selected, and segment cluster division and perforation location optimization are performed. Considering that it is difficult to form a complex fracture network in actual fracturing of continental shale oil, the "short segment and few clusters" method is preferred for segment cluster division, and the spacing between perforation clusters is reduced. The stress interference between fractures and the superposition effect of induced stress are used to promote the diversion of fracture extension as much as possible. The recommended fracturing segment length is 50-60m, and the perforation cluster spacing is 5-10m.

[0078] (2) After the fracturing stage is perforated, inject 10 to 20 m 3 Conventional wellbore acid pretreatment with 15% to 20% HCl can reduce the accumulation of impurities in the blasthole and lower the initial fracture pressure of the rock near the wellbore. The acid injection displacement is 1.5 to 2 m 3 / min, the pretreatment acid is generally hydrochloric acid with a certain concentration of corrosion inhibitor, iron ion stabilizer and drainage aid added; if the shale oil reservoir contains sandy bands, the pretreatment acid can be a soil acid composed of 12% HCl and 3% HF, with a certain concentration of corrosion inhibitor, iron ion stabilizer and drainage aid added.

[0079] (3) Inject gel fracturing fluid with a viscosity of 200-300 mPa·s for initial fracture creation. The displacement of gel fracturing fluid can be determined based on the simulation results of fracturing simulation software such as Gohfer or Stimplan, and the displacement required for vertical penetration is used as the optimal displacement for fracture creation. The recommended displacement is 6-10 m 3 / min, the priority in the gel injection process is to quickly increase the displacement to the design value, the amount of gel liquid used is 2 to 3 times the wellbore volume, and the gel is made of conventional cross-linked polymer products.

[0080] (4) Inject linear glue with a viscosity of 30 to 50 mPa·s to expand the fracture. The linear glue displacement can be confirmed based on the simulation results of fracturing simulation software such as Gohfer or Stimplan, so as to meet the optimal condition of fracture expansion displacement when the net pressure in the fracture is higher than the sum of the horizontal biaxial principal stress difference of the formation and the tensile strength of the rock (σH-σh+St). The recommended displacement is 8 to 14 m 3 / min, the dosage of linear rubber fracturing fluid is 2 to 3 times of the wellbore volume, and conventional polymer products are selected for linear rubber.

[0081] (5) Maintain the displacement of the linear glue, and use the linear glue to carry the proppant with a particle size of 50 / 80 mesh, 40 / 70 mesh or 30 / 50 mesh for continuous sand fracturing. The specific selection of the proppant particle size can be confirmed based on the simulation results of fracturing simulation software such as Gohfer or Stimplan, and the particle size is preferably 1 / 6 to 1 / 3 of the simulated fracture width. The sand-to-liquid ratio of the linear glue carrying the proppant is designed to be a constant value of 9% to 12% until the sand addition is completed.

[0082] (6) Switch to HCl with a concentration of 15% to 20% and mixed with an acid resistance reducing agent for displacement. The displacement of the displacing acid is consistent with the displacement of the aforementioned linear glue, and the amount used is 1 / 3 to 1 times the wellbore volume; then switch to the linear glue to continue displacement until all the sand-carrying fluid in the wellbore in step (5) is replaced into the formation, and the amount used is 0.7 to 1 times the wellbore volume.

[0083] (7) Repeat the above steps (2) to (6) until the fracturing construction of all fracturing stages of the shale oil well is completed.

[0084] A second object of the present invention is to provide an application of the reservoir sand fracturing method as described in any one of the objects of the present invention in oil production.

[0085] Principle of the invention:

[0086] The inventors of the present invention found that although the liquid volume and displacement during fracturing in the prior art increased, the main fracturing fluid was still mainly slippery water or viscous slippery water, and the net pressure generated in the cracks during the fracturing process was not enough to make the cracks penetrate more bedding planes and different lithological interfaces, resulting in the production of crack morphology mainly in the form of a simple "I" or "Feng" shape, and it was almost difficult to produce large-scale shear branch fractures and complex fracture networks, and the overall fracture system had a narrow fracture width; the increase in the amount of sand was actually matched with the increase in the amount of liquid, and the comprehensive sand-to-liquid ratio was still low; the multi-particle size combination was mainly considered to match different fracture widths, but because the actual fracture complexity was relatively low, most of the proppants migrated and settled in the main fracture, and the porosity between the proppant particles was reduced due to the mixed distribution of proppants of different particle sizes in the same channel, which resulted in a reduction in the fracture conductivity. The present invention aims to improve the vertical penetration of fracturing cracks and the effective filling of proppants in cracks, and proposes a new process method for fracturing, sand carrying and proppant laying to improve the flow channel of shale oil and enhance the transformation effect of reservoirs (such as shale oil reservoirs). Specifically:

[0087] (1) Using gel to create cracks and linear glue to expand cracks to promote the full extension of shale oil reservoir fractures in the vertical and horizontal directions

[0088] Before the formal fracturing, after the conventional 15% to 20% concentration of hydrochloric acid is used to pre-treat the wellbore and the near-wellbore formation, a gel fracturing fluid with a viscosity of 200 to 300 mPa·s is injected to quickly increase the displacement to the design value, ensuring that the injection rate is higher than the filtration rate of the formation, so as to quickly establish a higher net pressure in the near-wellbore and near-wellbore formation to achieve initial fracture creation. After the formation is fractured, the high-viscosity gel will adhere to the fracture wall to form a filter cake to reduce filtration; on the other hand, the high-viscosity gel has poor fluidity and is difficult to reach the fracture tip in the first time. Due to the existence of the fracture tip effect, the net pressure generated by the continuous injection of gel diffuses along the longitudinal direction of the reservoir, thereby producing a longitudinal splitting effect. The faster the displacement is increased, the better the longitudinal splitting effect. At this time, since no proppant is added, there is no need to worry about the problem of overpressure pump shutdown. If the equipment overpressure limit is reached due to excessive displacement, the pump can be stopped normally and then restarted. No other operations are required, and the construction safety will be guaranteed.

[0089] Since it is difficult to form complex fractures in shale oil reservoirs, in the present invention, after the gel is used to create fractures, a linear gel with a viscosity of 30 to 50 mPa·s is injected at the same displacement as the gel according to the design amount to further expand the fractures. At this time, because the viscosity of the two fracturing fluids differs by at least 6 times, a "viscous fingering" effect will occur in the fracture at the same displacement, and the linear gel will be closer to the front end of the fracture, thereby achieving fracture expansion. In addition, the net pressure in the fracture depends on the product of the displacement and the viscosity, and is in direct proportion to the product. According to conventional fracturing, the medium-viscosity slippery water with a viscosity of 9 to 12 mPa·s and the 20m 3 / min displacement equivalent, the displacement required for using 30mPa·s linear glue is about 6 to 8m 3 / min can achieve the same net pressure effect, and it also greatly saves water horsepower on site. In addition, because the viscosity of linear glue is higher than that of slippery water, the filtration rate at the same displacement is also much lower than that of slippery water, which is more conducive to seam expansion.

[0090] (2) Use medium displacement linear rubber sand to avoid excessive displacement causing uncontrolled fracture height and uneven proppant distribution

[0091] During the fracturing and sanding stage, a linear adhesive with a viscosity of 30 to 50 mPa·s is used to carry sand, and the displacement is controlled at 8 to 14 m 3 / min. If the displacement is 16~24m 3 / min displacement is consistent, the vertical upper fracture height may be excessively extended or even out of control due to excessive displacement. As a result, with the subsequent proppant sedimentation, the vertical upper propped fracture profile presents a "gourd" shape with narrow upper and wide lower parts, which has a great impact on the fracture conductivity after fracturing. In addition, the turbulence of the sand-carrying fluid is aggravated under high displacement. Due to the existence of the fracture tip effect, the proppant mainly disturbs near the fracture mouth, which is not conducive to the migration of the proppant to the far fracture end, resulting in aggravated non-uniform distribution of the proppant in the fracture. It is often encountered on site that it is difficult to add sand due to high displacement. The above problems can be effectively alleviated by adopting medium displacement to carry sand.

[0092] (3) Use constant proppant particle size and constant sand-to-liquid ratio to avoid the influence of mixed particle sizes on fracture diversion

[0093] Different from the conventional sand-adding fracturing process, the present invention provides a brand-new proppant particle size and sand-liquid ratio design. Entering the fracturing sand-adding stage, the present invention uses a medium-displacement linear glue to carry 50 / 80 mesh, 40 / 70 mesh or 30 / 50 mesh proppant according to a designed constant sand-liquid ratio of 9% to 12% to continuously add sand until the sand-adding is completed. Conventional processes are based on the design of the ideal "main fracture + branch fracture + micro fracture" network fracture morphology formed by fracturing. The proppant is selected in different particle size combinations and the sand-liquid ratio is designed from small to large for sand addition, usually in the form of a slug. However, considering that the fracture morphology actually formed by continental shale oil fracturing is relatively simple, the traditional design may reduce the porosity between the proppant particles due to the mixing of proppants of various particle sizes, thereby affecting the conductivity; the design of the sand-liquid ratio from small to large and the slug-type sand addition will also cause the sand concentration of the proppant in the fracture to be inconsistent at different times, resulting in discontinuity of paving, thereby affecting the conductivity. The above problems can be effectively alleviated by adopting a constant proppant particle size and a constant sand-liquid ratio sand-adding design.

[0094] (4) Using acid composite displacement to avoid closure of near-wellbore fractures

[0095] After the sand addition is completed, HCl and linear glue with a concentration of 15% to 20% and mixed with an acid resistance reducing agent are injected in proportion to complete the displacement of the sand-carrying fluid. On the one hand, the injection of an appropriate amount of HCl is used to displace the sand-carrying fluid, because the acid resistance reducing agent is added to the hydrochloric acid, and the displacement is not affected; on the other hand, after the high-displacement acid enters the formation, the acid reacts with the shale, especially the gray strips in the shale are non-uniformly etched, resulting in the effect of acid-etched fracture conductivity. The acid action distance is also increased due to the higher displacement. The grooves on the fracture wall caused by acid dissolution have a supporting effect on the fracture, which can avoid the closure of the fracture and the "dumpling" phenomenon caused by excessive displacement to a certain extent. If only acid is used for displacement, because the viscosity of the acid is not as good as that of linear glue, the displacement efficiency is low, the required amount is large, and it is not easy to completely replace the proppant settled in the wellbore into the formation; at the same time, only using acid for displacement increases unnecessary costs. Therefore, the acid composite displacement process can effectively improve the connectivity of fractures and especially the conductivity of near-wellbore fractures and save costs.

[0096] In summary, through the implementation of the present invention, the shale oil reservoir transformation effect can be effectively improved, and at the same time the construction pumping procedure is greatly simplified. The high displacement required by conventional slick water fracturing is not required, the water horsepower and fracturing equipment of the fracturing construction are reduced, the construction is simple and easy to operate, the cost is low, and the safety is also guaranteed.

[0097] The endpoints and any values ​​of the scope disclosed in the present invention are not limited to the precise scope or value, and these scopes or values ​​should be understood to include values ​​close to these scopes or values. For numerical ranges, the endpoint values ​​of each scope, the endpoint values ​​of each scope and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article. Hereinafter, in principle, each technical solution can be combined with each other to obtain a new technical solution, which should also be regarded as specifically disclosed in this article.

[0098] Compared with the prior art, the present invention has at least the following advantages:

[0099] The present invention provides a new shale oil fracturing transformation process. In the fracture formation stage, frozen gel is used to form fractures and linear gel is used to expand fractures to promote the full extension of fractures in the vertical and horizontal directions; in the fracturing and sanding stage, medium displacement linear gel is used to carry sand, which can effectively avoid uneven distribution of proppants due to uncontrolled fracture height caused by excessive displacement; constant proppant particle size and sand-liquid ratio design can effectively avoid the mixing of proppants with multiple particle sizes affecting the conductivity of fractures; in the displacement stage, acid and linear gel composite displacement are used to improve the connectivity of fractures from near wells to far wells. Through the implementation of the present invention, the conductivity of shale oil well fracturing fractures and the effective transformation volume can be maximized, thereby improving the long-term stable production of shale oil wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1 A schematic diagram of the design of the sand-adding process displacement and sand-liquid ratio provided in Example 1 of the present invention;

[0101] Description of reference numerals:

[0102] 1-displacement, 2-sand-liquid ratio, 3-acid pretreatment stage, 4-fracturing stage of frozen gel fracturing fluid, 5-fracture expansion stage of linear gel fracturing fluid, 6-sand addition construction stage of linear gel fracturing fluid, 7-acid displacement stage, 8-linear gel fracturing fluid displacement stage. DETAILED DESCRIPTION

[0103] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0104] It should also be noted that the various specific technical features described in the following specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0105] In addition, the various embodiments of the present invention may be arbitrarily combined as long as they do not violate the concept of the present invention. The technical solutions thus formed belong to part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0106] The raw materials used in the examples and comparative examples are all commercially available.

[0107] Example 1

[0108] (1) Well XY is a continental shale oil horizontal well in the eastern Sichuan region. The target layer A of the well has a well depth of 2779m (vertical depth of 2586m), the target layer B has a well depth of 4550m (vertical depth of 2523m), the horizontal section is 1770m long, the formation temperature is 69℃, and the formation pressure before fracturing is less than 1.2. The entire layer section of the well is divided into 8 layers from bottom to top, with a total thickness of 83m. The target layer for fracturing is layer 6~8, with a thickness of 30.2m; layer 6 and layer 8 are gray-black shale interbedded with silty sandy laminae, layer 7 is gray-black shale and siltstone interbedded, with 45cm siltstone developed at the top, 25cm and 75cm thick siltstone developed at the bottom, and gray-black shale interbedded with silty sandy laminae developed in the middle, with occasional 2~4mm thick silty sandy thin layers and 1~3cm thick shell interlayers. The imaging logging of the sublayers ⑥ to ⑧ shows that the fractures are not developed, and the interpreted porosity is 3.8% on average; the clay content is 46.9%, the silica content is 43.8%, and the calcium content is 8.8%; the average Young's modulus is 31.74GPa, and the Poisson's ratio is 0.27; the difference in the horizontal principal stress in two directions is 6.5MPa, and the rock tensile strength is 5MPa. According to this geological feature, the reservoir has a high content of clay minerals, low rock brittleness, and undeveloped natural fractures, which are not conducive to fracturing to form a complex fracture network; in addition, the reservoir contains 0.25 to 0.75m interlayers, and the internal horizontal minimum principal stress difference reaches 2 to 7MPa, which makes it difficult to penetrate the layers and expand the body during the transformation process; it is a normal pressure reservoir, the formation backflow energy is weak, and the shale oil flow channel is required to be high. In order to achieve the full vertical transformation of the sublayers ⑥, ⑦, and ⑧ and to improve the fracture proppant filling conductivity, the process method provided by the present invention is specially adopted, and the specific implementation steps are as follows:

[0109] (2) Through simulation using ABAQUS finite element software, it is found that reducing the cluster spacing and increasing the inter-cluster interference is beneficial to fracture diversion. The optimized cluster spacing is 6.5-10m, 8m on average, and the segment spacing is 15-20m. Through simulation using ECLIPSE reservoir numerical simulation software, the horizontal section length of the well is 1770m. From the perspective of increasing the utilization of the reservoir and improving the horizontal section coverage, the number of perforation clusters is optimized to be 160-180 clusters, and the half-fracture length is 150-180m. Considering the phase distribution characteristics of condensate oil and gas zoning, the conductivity of near-well fractures is optimized to be 8-10D·cm, the conductivity of mid-field fractures is 3-5D·cm, and the conductivity of far-well fractures is 0.5-1D·cm. Finally, combined with geological analysis, the well is divided into 25 segments and 167 clusters. Through simulation using Gohfer fracturing optimization software, the wellbore volume is 50.28m 3 , pretreatment acid 20m 3 , displacing acid 25m 3 The following steps (3) to (5) correspond to a single-stage fracturing fluid volume of 1290m 3 , including 100m 3 , linear glue 1190m 3 ; To achieve longitudinal penetration, the front viscosity is 300mPa·s cross-linked gel, displacement 8m 3 / min, linear viscosity 40mPa·s, displacement 12m 3 / min; single-stage support dosage 100m 3 The proppant is coated sand with a particle size of 40 / 70 mesh, and the constant sand-liquid ratio is optimized to 10%. Figure 1 This is the typical design diagram of the well's displacement and sand-liquid ratio; Figure 1 In the figure, the displacement of the corresponding process section (acid pretreatment stage 3, frozen gel fracturing fluid fracture creation stage 4, linear gel fracturing fluid fracture expansion stage 5, linear gel fracturing fluid sand addition construction stage 6, acid displacement stage 7, linear gel fracturing fluid displacement stage 8) is determined by the line segment corresponding to the displacement 1; the sand-to-liquid ratio of the corresponding process section (linear gel fracturing fluid sand addition construction stage 6) is determined by the line segment corresponding to the sand-to-liquid ratio 2.

[0110] In this embodiment, the acid solution is 15% HCl with 1% mass concentration of quaternary ammonium corrosion inhibitor, 1% mass concentration of cationic fluorocarbon surfactant, and 1% mass concentration of ferric citrate ion stabilizer. During the displacement stage, 0.5% mass concentration of anionic drag reducer is added to the acid solution.

[0111] After the fracturing stage is perforated, inject 20m 3 15% HCl mass concentration for wellbore acid pretreatment, acid injection displacement 2m 3 / min.

[0112] (3) Inject cross-linked gel fracturing fluid with a viscosity of 300 mPa·s for initial fracture creation, and quickly increase the gel injection rate to the designed rate of 8 m within 2 min. 3 / min, gelling liquid dosage 100m 3 .

[0113] (4) Inject linear gel fracturing fluid with a viscosity of 40 mPa·s to expand the fracture. The displacement of the linear gel fracturing fluid is 8 m 3 / minAccording to 2m 3 The displacement increment is increased step by step to the designed displacement value of 12m / min. 3 / min, linear gel fracturing fluid dosage 150m 3 .

[0114] (5) Maintain the linear gel fracturing fluid displacement of 12m 3 / min, add coated sand with a particle size of 40 / 70 mesh at a sand-liquid ratio of 10% for continuous sand fracturing until the sand addition is completed. The viscosity of the linear gel fracturing fluid is 40mPa·s; the amount of linear gel fracturing fluid is 1000m 3 , sand volume 100m 3 .

[0115] (6) Switch to 15% HCl mixed with acid and resistance reducing agent for displacement. The displacement of the displacing acid is consistent with the displacement of the linear glue mentioned above, which is 12m 3 / min, dosage 25m 3 ; Then switch to linear gel fracturing fluid with a viscosity of 40mPa·s to continue displacement, and the displacement of the linear gel remains the same at 12m 3 / min, until all the sand-carrying fluid in the wellbore in step (5) is replaced into the formation, with a dosage of 40m 3 .

[0116] (7) Repeat the above steps (2) to (6) until all 25 stages of fracturing construction of the shale oil well in the example are completed.

[0117] According to the construction parameter design of each fracturing stage in the embodiment, the fracture parameters were inverted using the fracture extension simulation software Gohfer. Compared with the conventional shale oil well fracturing process, the fracture penetration height obtained by the implementation of the present invention increased by 22%, the average support seam width increased by 47%, the fracture conductivity increased by 34%, the effective transformation volume (ESRV) increased by 35%, and the transformation effect was greatly improved. In addition, the frozen gel seam making and linear gel seam expansion provided by the present invention have a displacement reduced by nearly 1 times compared with conventional fracturing, and the corresponding water horsepower is also reduced by 1 times, which greatly saves the cost of the fracturing vehicle group; the constant sand-liquid ratio of a single proppant particle size range is added with sand, and the liquid has a higher sand carrying efficiency. Considering the formation of the main seam advantage channel as the main consideration, the liquid volume does not need to be too large, and the entire fracturing fluid consumption is basically reduced by 1 times compared with conventional slippery water fracturing, and the pumping time is also greatly shortened, and the pumping procedure is simplified and easy to operate.

[0118] Therefore, the present invention specifically proposes a new fracturing process method, which improves the flow channel of shale oil, maximizes the conductivity of filled fractures and the effective transformation volume, enhances the shale oil reservoir transformation effect, and thus improves the long-term fracturing and stable production of shale oil wells.

[0119] Example 2

[0120] (1) Well XY1C is a horizontal shale gas well in the southeastern Sichuan region. The target point A of the well has an oblique depth of 3940 m (vertical depth of 3674.2 m), the target point B has an oblique depth of 5756 m (vertical depth of 3839.4 m), the horizontal section is 1816 m long, the formation temperature is 112 °C, and the pre-pressure formation pressure is 1.45. The entire target layer of the well is divided into 9 small layers from bottom to top. The high-quality shale in small layers ① to ⑤ is 34.0 m thick. There are mud dolomite interlayers with a cumulative thickness of 64 cm in small layers ① and ③ to ⑤. The stress difference of each interlayer is 5.3 to 6.3 MPa. The clay mineral content of the high-quality shale layer is 30.00% on average, the siliceous mineral content is 52.97% on average, and the carbonate mineral content is 8.83% on average. The Young's modulus of the rock is 31.53 to 44.33 GPa, and the Poisson's ratio is 0.224 to 0.259. The average horizontal stress difference in both directions is about 11.0 MPa, and the difference between the vertical stress and the minimum horizontal principal stress is about 12.6 MPa. The fractures around the well are relatively underdeveloped as a whole, which is basically consistent with the actual drilling FMI results. According to the geological characteristics, the target layer is generally brittle (46.6%) under the confining pressure condition, the horizontal principal stress difference is high, and the formation of complex network fractures is difficult; it is buried deep, and the tensile strength of the penetrated small layer is high (10.67MPa), and it is expected that the crack initiation and extension will be difficult; the horizontal well section mainly penetrates the ①~③ small layers, and the vertical mud dolomite interlayers of the ①, ③~⑤ small layers have a shielding effect and the stress difference within the layer is large, which makes it extremely difficult to penetrate the layer by fracturing. In order to further increase the net pressure and sand addition strength, promote the formation of complex fractures, and improve the transformation effect, the process method provided by the present invention is specially adopted, and the specific implementation steps are as follows:

[0121] (2) Through simulation using ABAQUS finite element software, the reservoir production degree is increased by improving the dense cutting degree, the horizontal section coverage rate is improved, and the average section spacing is optimized to 19.4m and the average cluster spacing to 9.8m;

[0122] According to the simulation of ECLIPSE reservoir numerical simulation software, the horizontal section of the well is 1816m long, the total length of the fracturing section is 1743m, and a total of 30 sections and 131 clusters are divided for perforation and fracturing transformation. According to the simulation of Gohfer fracturing optimization software, the wellbore volume is 60.3m 3 , pretreatment acid 20m 3 , displacing acid 30m 3 The following steps (3) to (5) correspond to a single-stage fracturing fluid volume of 1500m 3 , including 150m 3 , linear glue 1350m 3 ; To achieve longitudinal penetration, the front viscosity is 200mPa·s cross-linked gel, displacement 10m 3 / min, linear viscosity 30mPa·s, displacement 14m 3 / min; single-stage support dosage 138m 3 The proppant is coated sand with a particle size of 40 / 70 mesh, and the constant sand-liquid ratio is optimized to 12%.

[0123] The acid solution is earth acid composed of 12% HCl and 3% HF by mass, with 1% quaternary ammonium salt corrosion inhibitor, 1% cationic fluorocarbon surfactant, and 1% ferric citrate ion stabilizer added. During the displacement stage, 0.6% anionic resistance reducer is added to the acid solution.

[0124] After the fracturing stage is perforated, inject 20m 3 Pretreatment acid is used for wellbore acid pretreatment, and the acid injection displacement is 2m 3 / min.

[0125] (3) Inject cross-linked gel fracturing fluid with a viscosity of 200 mPa·s for initial fracture creation, and quickly increase the gel injection rate to the designed rate of 10 m within 3 min. 3 / min, gelling liquid dosage 150m 3 .

[0126] (4) Inject linear gel fracturing fluid with a viscosity of 30 mPa·s to expand the fracture. The displacement of the linear gel fracturing fluid is increased from 10 m 3 / minAccording to 2m 3 The displacement increment of / min is increased step by step to the designed displacement value of 14m 3 / min, linear gel fracturing fluid dosage 150m3 .

[0127] (5) Maintain the linear gel fracturing fluid displacement of 14m 3 / min, add coated sand with a particle size of 50 / 80 mesh at a sand-liquid ratio of 12% for continuous sand fracturing until the sand addition is completed. The viscosity of the linear gel fracturing fluid is 30mPa·s; the amount of linear gel fracturing fluid is 1150m 3 , sand volume 138m 3 .

[0128] (6) Switch to 15% HCl mixed with acid and resistance reducing agent for displacement. The displacement of the displacing acid is consistent with the displacement of the linear glue mentioned above, which is 14m 3 / min, dosage 30m 3 ; Then switch to linear gel fracturing fluid with a viscosity of 30mPa·s to continue displacement, and the displacement of the linear gel remains the same at 14m 3 / min, until all the sand-carrying fluid in the wellbore in step (5) is replaced into the formation, with a dosage of 50m 3 .

[0129] (7) Repeat the above steps (2) to (6) until all 30 stages of fracturing construction of the shale oil well in the example are completed.

[0130] According to the construction parameter design of each fracturing stage in the embodiment, the fracture parameters were inverted using the fracture extension simulation software Gohfer. The half-length of the fracturing fracture was 110-184 m, with an average of 143.1 m, and the fracture height was 30.2-37.6 m, with an average of 33.6 m. The single-stage transformation volume was 100.7-136.2×10 4 m3, with an average of 111.0×10 4 m3, total transformation volume 3329×10 4 Through the implementation of the process of the present invention, the purpose of effectively opening up the ①~⑤ sub-layers by running the horizontal wellbore through the ①~③ sub-layers (the running of the ① and ② sub-layers accounts for 92%) and effectively utilizing the high-quality 34.0m thick gas-bearing shale layer is basically achieved.

[0131] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0132] 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 conventionally understood by those skilled in the art. In the event of a conflict, the definition in this specification shall prevail.

[0133] When this specification uses the prefix "well-known to those skilled in the art", "prior art" or similar terms to introduce materials, substances, methods, steps, devices or components, etc., the objects introduced by the prefix cover those commonly used in the art when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as being suitable for similar purposes.

[0134] In the context of the present specification, any matters or items not mentioned are directly applicable to those known in the art without any changes except those explicitly stated.

Claims

1. A method for reservoir sand fracturing, characterized in that: The method comprises the steps of using frozen gel fracturing fluid to create fractures, using linear gel fracturing fluid to expand fractures, and using linear gel fracturing fluid to add sand for construction.

2. The reservoir sand fracturing method according to claim 1, characterized in that: The following steps are involved: (1) Evaluation of key reservoir parameters; (2) perforating the section to be fractured and then performing acid pretreatment; (3) injecting gel fracturing fluid for initial fracture creation; (4) injecting linear gel fracturing fluid to expand the fracture; (5) Linear glue fracturing fluid and sand construction; (6) Composite replacement; (7) Optionally repeat the above steps (2) to (6) until the fracturing construction of all fracturing stages of the oil well is completed.

3. The reservoir sand fracturing method according to claim 2, characterized in that: Step (1), The reservoir is selected from shale oil reservoirs, deep-layer high-stress shale gas reservoirs, complex clastic rocks, and low-permeability matrix-porous carbonate oil and gas reservoirs; Based on the evaluation of key reservoir parameters, the fracturing stages are divided and the perforation locations are determined; Preferably, the key parameter includes at least one of a geological sweet spot and an engineering sweet spot of the reservoir.

4. The method for reservoir sand fracturing according to claim 2, characterized in that: Step (2), During the perforation, the length of the fracturing section is 50 to 60 m; the spacing between the perforation clusters is 5 to 10 m; and / or, During the acid pretreatment, The volume of the injected acidic liquid is 10 to 20 m 3 and / or, The displacement of acidic liquid is 1.5~2m 3 / min.

5. The method for reservoir sand fracturing according to claim 2, characterized in that: In step (2), during the acid pretreatment, The acidic liquid used includes at least an inorganic acid; Preferably, the inorganic acid comprises at least hydrochloric acid and optionally hydrofluoric acid; The mass concentration of the inorganic acid in the acidic liquid is 15% to 20%.

6. The reservoir sand fracturing method according to claim 2, characterized in that: Step (3), The viscosity of the gel fracturing fluid is 200-300 mPa·s; The volume of the injected gel fracturing fluid is 2 to 3 times the volume of the wellbore; and / or, The displacement of gel fracturing fluid is 6 to 10 m 3 / min.

7. The reservoir sand fracturing method according to claim 2, characterized in that: Step (4), The viscosity of the linear gel fracturing fluid is 30 to 50 mPa·s; The volume of the injected linear gel fracturing fluid is 2 to 3 times the wellbore volume; and / or, The displacement of linear gel fracturing fluid is 8~14m 3 / min, preferably 1 to 3m 3 The displacement increment of / min is increased step by step to the maximum design displacement.

8. The reservoir sand fracturing method according to claim 2, characterized in that: Step (5), Linear gel fracturing fluid carries proppant for sand-adding construction with a constant sand-to-liquid ratio; Preferably, the proppant particle size range carried is constant.

9. The reservoir sand fracturing method according to claim 8, characterized in that: The linear gel fracturing fluid used has a viscosity of 30-50 mPa·s, and the sand adding method is continuous sand adding; the displacement is 8-14 m 3 / min; within the range of 9% to 12% sand-liquid ratio, a constant sand-liquid ratio is selected for sand addition construction; the volume of the linear gel fracturing fluid injected is preferably 900 to 1500m 3 and / or, The particle size range of the proppant is 1 / 6 to 1 / 3 of the simulated fracture width; preferably, the particle size range of the proppant is 50 / 80 mesh, 40 / 70 mesh or 30 / 50 mesh.

10. The reservoir sand fracturing method according to claim 2, characterized in that: Step (6), First use acid to displace, then use linear gel fracturing fluid to continue displacing; Preferably, the acid solution used includes an inorganic acid and an acid-based drag reducing agent; More preferably, When acid displacement occurs, the total amount of liquid injected is 1 / 3 to 1 times the wellbore volume; The displacement of the acid solution is consistent with the displacement during the sand addition construction in step (5); In the acid solution, the mass concentration of the inorganic acid is 15% to 20%; the inorganic acid is selected from hydrochloric acid.

11. The reservoir sand fracturing method according to claim 10, characterized in that: When the linear gel fracturing fluid is used to continue displacement, The viscosity of the injected linear gel fracturing fluid is 30-50 mPa·s; The total amount of linear gel fracturing fluid injected is 0.7 to 1 times the wellbore volume; The displacement of the injected liquid is consistent with the displacement during the sand addition construction in step (5).

12. Use of the reservoir sand fracturing method according to any one of claims 1 to 11 in oil production.

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