A method of plug fracturing and application

Abstract

The application discloses a segment plug type fracturing method and application. The method comprises the following steps: adopting segment plug liquids and isolation liquids with different viscosities, adopting a lower displacement for the isolation liquid injection, adding a finer particle size of the proppant in the isolation liquid, reducing the sand plugging risk, improving the segment fracture complexity, and obviously improving the fracturing construction effect. The application has the advantages of reasonable design, clear method, simple and efficient operation, effective guidance for the segment plug type fracturing construction, reduction of the local blocking effect of the proppant, effective reduction of the sand plugging risk, improvement of the fracture forming efficiency, improvement of the segment fracture complexity, effective support of smaller scale cracks, facilitation of stable production after fracturing, obvious improvement of the fracturing construction effect, and greater economic benefits.

Description

Technical Field

[0001] This invention relates to the field of oil production technology, and more specifically, to a slug fracturing method and its application. Background Technology

[0002] Currently, in fracturing shale oil and gas and tight sandstone oil and gas, the slug injection mode is often used to ensure construction safety. The so-called slug injection mode is to sequentially inject sand-bearing fracturing fluid (hereinafter referred to as slug fluid for simplification) and sand-free fracturing fluid (usually also called isolation fluid, hereinafter referred to as isolation fluid for simplification). Generally, the viscosity ratio and volume ratio of slug fluid to isolation fluid are 1:1, but if the formation is more sensitive to the sand-fluid ratio, the volume ratio of isolation fluid may be appropriately increased.

[0003] While the aforementioned conventional slug fracturing technology has achieved significant results in fracturing practice, it also has many limitations, such as:

[0004] 1) Since the viscosity ratio is generally 1:1, even considering the increased viscosity of the mixed sand fluid after adding proppant, the propulsion within the fracture is essentially piston-like. Once sand plugging occurs after the proppant enters the formation, the spacer fluid struggles to quickly reach the leading edge of the proppant to open the fracture. Even if the spacer fluid can open the fracture to some extent, it does so behind the proppant, having a very limited effect on increasing the fracture width at the proppant front. Therefore, in conventional slug fracturing technology, the spacer fluid has a very small effect on alleviating sand plugging.

[0005] 2) In conventional slug technology, the displacement of the isolation fluid is equal to or nearly equal to that of the slug fluid. Firstly, the proppant in the slug fluid experiences relatively high friction at higher displacement rates. Secondly, if sand plugging occurs at a point in the fracture, the proppant accumulates more rapidly due to the relatively high displacement, making sand plugging more likely. However, for shale oil and gas or tight reservoirs, especially those undergoing fracturing, the overall reservoir filtration coefficient is relatively low, and the risk of sand plugging does not increase with a reduced displacement rate (generally referring to the displacement of the isolation fluid).

[0006] 3) The timing of slug fluid addition may be relatively late. Generally, proppant-containing slug fluid is added after 20% of the total fluid volume of the slug has been injected, with the aim of fully creating fractures. However, numerical simulations of fracture propagation show that the early fracture propagation rate is relatively fast; at 20% fluid volume, the length of the main fracture is generally over 70% of the final fracture length. During the main fracture propagation process, branch fractures and microfractures are formed continuously, not only after the main fracture is created. In other words, if the sand addition is delayed, the fracturing fluid inflow rate into the branch fractures and microfractures may have decreased significantly, or even ceased altogether (branch fractures and microfractures, due to their lateral initiation and extension along the main fracture flanks, experience greater friction during propagation, making them less prone to initiation and extension compared to the main fracture; even if they do initiate and extend, they will stop extending earlier). At this point, even if the proppant in the slug fluid reaches the fracture openings of the branch fractures and microfractures, it is difficult for the proppant to penetrate into these small-scale fractures. Therefore, conventional proppant slugging techniques may result in most of the small-particle-size proppant remaining in the main fracture, leading to a rapid decrease in post-compression production (because seepage channels in the lateral directions of the main fracture are not established).

[0007] Chinese patent CN109267988A discloses a method for adding proppant in shale gas fracturing, including: pre-fracturing reservoir fine evaluation; near-wellbore fracture bending friction evaluation; fracture bending friction elimination; and determination and subdivision of parameters such as volume, proppant-to-fluid ratio, viscosity, and displacement for each proppant and non-proppant slug, with alternating injection of smaller segments. This patent optimizes construction parameters such as initial proppant timing, proppant volume, proppant-to-fluid ratio, fluid viscosity, and displacement, improving proppant efficiency and construction safety, reducing the risk of sand plugging, thereby increasing fracture support efficiency, optimizing the stimulation volume, and enhancing post-fracturing production and economic development benefits of shale gas. However, this patent optimizes conventional slug fracturing proppant technology and cannot fundamentally overcome the limitations of conventional slug fracturing.

[0008] Chinese patent CN108222910A discloses a fixed-displacement slug fracturing process, which includes obtaining formation parameters to determine the fracturing mode of the reservoir rock and analyzing the propagation morphology of hydraulic fractures and natural fractures; conducting slug fracturing operations with one proppant injection stage and one immediately following isolation fluid stage as one slug injection cycle; increasing the proppant ratio in the later stage of proppant injection to test the formation's response to the proppant ratio in the next proppant injection cycle. This solves the problems of ineffective fracturing of hot dry granite reservoirs and the reduction in the fracturing radius over long periods, while also addressing the issues of long injection cycles and large injection volumes in conventional fracturing of hot dry granite reservoirs. However, this patent mainly concerns conventional slug fracturing processes and does not consider the limitations of conventional slug proppant injection methods.

[0009] The literature "Application of Slug-Type Propaning Technology in Shale Gas Fracture Network Fracturing" (Oil & Gas Well Testing, October 2014) describes the use of slug-type proppanting technology to reduce near-wellbore friction, increase fracture complexity to achieve fracture network fracturing, and improve the success rate of fracturing operations. It has been applied in the fracturing operation of a shale gas well in China, achieving good productivity. During the main proppanting process, the slug-type proppanting technology can analyze the formation's sensitivity to a certain proppant ratio in a timely manner and adjust the construction parameters accordingly to avoid proppant blockage. Slug-type fracturing can create new fractures or redirect fractures, playing a role in forming complex fracture networks. This literature describes the application of conventional slug-type fracturing technology in shale gas wells but does not address improvements to overcome the limitations of conventional slug technology.

[0010] In summary, current proppant slug technology has not been improved. Therefore, it is necessary to research and propose a new proppant slug technology to address the limitations mentioned above. Summary of the Invention

[0011] To address the problems existing in the prior art, this invention provides a slug fracturing method and its application. It can effectively reduce the risk of sand plugging, increase the complexity of fractures, improve the fracturing stimulation effect, and facilitate stable production after fracturing. It is applicable to shale oil and gas reservoirs and tight sandstone oil and gas reservoirs.

[0012] One of the objectives of this invention is to provide a slug fracturing method.

[0013] include:

[0014] By using slug and isolation fluids of different viscosities, injecting isolation fluid at a lower flow rate, and adding proppant with finer particle size to the isolation fluid, the risk of sand plugging is reduced, the complexity of the slug fracture is increased, and the fracturing operation effect is significantly improved.

[0015] The method includes the following steps:

[0016] 1) Development of fracturing design and construction plans;

[0017] 2) Determination of the viscosity of slug mortar under different mortar-liquid ratios;

[0018] 3) Determination of the viscosity of the isolation fluid at different stages;

[0019] 4) Determination of the injection displacement of the isolation fluid in different slug segments;

[0020] 5) Determination of the particle size and density of the micro-support in the isolation fluid;

[0021] 6) Acid pretreatment and pre-fluid joint creation construction;

[0022] 7) Segmented application of 70-140 mesh proppant;

[0023] 8) Segmented application of 40-70 mesh proppant;

[0024] 9) Continuous sand addition application with 40-70 mesh proppant;

[0025] 10) Continuous sand addition construction with 30-50 mesh proppant;

[0026] 11) Substitute work.

[0027] In a preferred embodiment of the present invention,

[0028] In step 2), the viscosity of the mixed mortar with two types of proppant, 70-140 mesh and 40-70 mesh, was tested at different sand-liquid ratios.

[0029] In a preferred embodiment of the present invention,

[0030] In step 3), the viscosity ratio of the slug fluid to the separator fluid is greater than or equal to 3:1, preferably greater than or equal to 6:1; determine the corresponding separator fluid viscosity for slugs with different slug fluid ratios.

[0031] In a preferred embodiment of the present invention,

[0032] In step 4),

[0033] When the slug fluid displacement is less than 16m 3 At a rate of / min, the discharge rate of the isolation fluid is 2-3 m³ lower than that of the slug fluid. 3 / min;

[0034] When the slug fluid displacement is 16m 3 At speeds of 6 / min and above, the discharge rate of the isolation fluid is 3-4 m³ lower than that of the slug fluid. 3 / min.

[0035] In a preferred embodiment of the present invention,

[0036] In step 5),

[0037] The particle size of the microproppant is 140-200 mesh, and the apparent density is 1.05-1.25 g / cm³. 3 .

[0038] In a preferred embodiment of the present invention,

[0039] In step 6),

[0040] For brittle formations, low-viscosity slickwater is used to create the main fracture.

[0041] For formations with strong plasticity, high-viscosity adhesive is used to create the main fracture.

[0042] The volume of the pre-fluid should be 10-15% of the total fluid volume.

[0043] In a preferred embodiment of the present invention,

[0044] In step 7),

[0045] Slug-type construction using slickwater with a viscosity of 10-30 mPa·s carrying 70-140 mesh proppant; liquid volume ≥ 20 m³ 3 Displacement ≥ 4m 3 / min; sand-liquid ratio range 3-20%; the sand-liquid ratio is determined in step 1). The sand-liquid ratio varies for different formations, but is usually in the range of 3-20%.

[0046] The isolation fluid carries a fine proppant, the sand-liquid ratio is 2%-3%-5%, and a continuous sand addition mode is adopted.

[0047] In a preferred embodiment of the present invention,

[0048] In step 8),

[0049] Slug-type construction using slickwater with a viscosity of 20-40 mPa·s carrying 40-70 mesh proppant, with a liquid volume ≥ 20 m³ / s. 3 Displacement ≥ 4m 3 / min; sand-liquid ratio range 3-20%; the sand-liquid ratio is determined in step 1). The sand-liquid ratio varies for different formations, but is usually in the range of 3-20%.

[0050] The isolation fluid carries a fine proppant, the sand-liquid ratio is 2%-3%-5%, and sand is added continuously.

[0051] In a preferred embodiment of the present invention,

[0052] In step 9),

[0053] Slippery water with a viscosity of 20-40 mPa·s is used to carry 40-70 mesh proppant, with continuous sand addition at a sand-to-liquid ratio of 12%-14%-16%-18%-20%; the liquid volume is ≥20 m³ / s. 3 Displacement ≥ 4m 3 / min.

[0054] In a preferred embodiment of the present invention,

[0055] In step 10),

[0056] Slippery water with a viscosity of 30-60 mPa·s is used to carry 30-50 mesh proppant, with continuous sand addition. The sand-to-liquid ratio is 10%-12%-14%-16%-18%, and the liquid volume is ≥20 m³. 3 Displacement ≥ 4m 3 / min.

[0057] In a preferred embodiment of the present invention,

[0058] Step 11): Displacement is performed using slickwater; the displacement fluid volume is 10-20 m³ more than the volume of one wellbore. 3 ;

[0059] The first 10m of displacement fluid volume 3 The slickwater with a viscosity of 30-60 mPa·s was used, and the remaining displacement liquid was slickwater with a viscosity of 1-10 mPa·s.

[0060] The second objective of this invention is to provide an application of the slug fracturing method in oil extraction.

[0061] The overall concept of this invention is:

[0062] 1) Utilizing the principle of viscous fingering, slug fluids and spacers of varying viscosities are employed. Considering that the spacer fluid displaces the slug fluid, the viscosity ratio of the slug fluid to the spacer fluid is designed to be 3:1 or even higher than 6:1 to achieve the viscous fingering effect. The main purpose is twofold: firstly, if sand blockage occurs at a point in the fracture, the viscous fingering effect of the low-viscosity spacer fluid allows it to quickly migrate to the leading edge of the proppant for replenishment, thereby increasing the fracture width and significantly mitigating and effectively eliminating the proppant desanding effect. Secondly, the low-viscosity spacer fluid can further connect and extend the already opened branch fractures and micro-fracture systems.

[0063] 2) A lower displacement rate can be used when injecting the spacer fluid. Due to the extremely low matrix permeability of shale oil and gas or tight sandstone oil and gas, a lower spacer fluid displacement rate has little impact on fracture formation efficiency. When a lower spacer fluid displacement rate is used, the proppant-containing slug fluid it displaces migrates more slowly in the fracture, resulting in lower fracture entry friction and reducing the likelihood of local proppant blockage and sand plugging formation.

[0064] In addition, a suitable reduction in the discharge rate of the isolation fluid makes it easier for the fluid to migrate into the multi-scale fracture system. If the discharge rate is large, most of the isolation fluid will remain in the main fracture, which is not conducive to the formation of a complex multi-scale fracture network.

[0065] It is worth noting that, considering the relatively small volume of the isolation fluid (generally the volume of one wellbore), reducing the discharge rate can facilitate smooth fluid supply. Otherwise, a relatively high discharge rate might not be possible.

[0066] 3) Adding finer-particle-size proppant to the isolation fluid. Unlike conventional isolation fluids without any proppant, the isolation fluid of this invention is designed to incorporate finer-particle-size proppant. This proppant can freely migrate between the pore particles of proppant of other sizes without affecting the conductivity of other fractures. Furthermore, this fine proppant facilitates entry into fractures of different sizes by the isolation fluid, improving fracture-forming efficiency without affecting the fracture-forming and communication of small-scale fractures. After compression, it can also provide support in even smaller-scale fractures, thus contributing to stable production after compression.

[0067] The specific measures of this invention are as follows:

[0068] 1) Formulation of fracturing design and construction plans

[0069] The fracturing design and construction plan are completed according to conventional methods. This typically includes the selection of fracturing sections, the selection of fracturing methods, the design of fracturing tubing, the optimization of perforation parameters, the determination of displacement, the design of fluid volume, the optimization of proppant concentration, the fracturing pumping procedure, and the prediction of construction pressure.

[0070] 2) Determination of slug mortar viscosity under different mortar-to-liquid ratios

[0071] Using a sand-containing rheometer, the viscosity of mixed slurries with 70-140 mesh and 40-70 mesh proppant particles at different sand-liquid ratios was tested in the laboratory. The sand-liquid ratio was consistent with the sand-liquid ratio designed in step 1). Generally, the sand-liquid ratio for 70-140 mesh proppant was 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, ... 20%; the sand-liquid ratio for 40-70 mesh proppant was 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, ... 20%. Generally, the viscosity of sand-containing slurries is 20% to over 100% higher than that of pure fracturing fluid. The higher the sand-liquid ratio, the higher the viscosity of the sand-containing slurry.

[0072] 3) Determination of the viscosity of the isolation fluid at different stages

[0073] Based on step 2), the viscosity of the isolation fluid is determined for slugs with different sand-to-liquid ratios, according to a slug fluid to isolation fluid viscosity ratio greater than or equal to 3:1, preferably greater than or equal to 6:1.

[0074] To simplify construction, the viscosity ratio of the first slug fluid to the release fluid can be set at 3:1. The viscosity of all release fluids should remain the same as that of the first slug fluid. As construction progresses, the sand-to-liquid ratio of the slug gradually increases, and the viscosity of the mortar also increases. This will result in a larger viscosity ratio between the slug fluid and the release fluid, which will be more conducive to forming a viscous fingering effect.

[0075] 4) Determination of the injection displacement of the isolation fluid in different slug segments

[0076] Based on the requirements of idea 2), each segment of the proppant fluid uses the same displacement rate, which is lower than the corresponding slug fluid displacement rate. For simplicity, the goal can be to maintain the same wellhead drilling pressure (within 1 minute before proppant fluid injection). During the proppant fluid injection phase, due to the appropriately reduced displacement rate and extended injection time, the pressure response characteristics of the proppant after entering the formation can be more easily observed.

[0077] Generally, during conventional fracturing, when the flow rates of the spacer fluid and slug fluid are equal, the pressure rise during spacer fluid operation can reach 2-3 MPa. However, by employing the goal of equal wellhead pressure as described in this invention, the flow rate of the spacer fluid can be reduced by 2-3 MPa. 3 / min, especially when the slug fluid displacement is relatively high, such as 16m 3 For displacement reductions of 600 rpm and above, the reduction can be more significant, such as a reduction of 3-4 m³ / min. 3 / min.

[0078] 5) Determination of particle size and density of fine proppant in the isolation fluid

[0079] Based on the requirements of idea 3), and considering the free flow from the interparticle gaps of the subsequent proppant, using 70-140 mesh proppant as the standard (if it can flow freely from the interparticle gaps of 70-140 mesh proppant, then it can flow even more freely from the interparticle gaps of 40-70 mesh proppant), the average particle size of 70-140 mesh proppant is 105 mesh, therefore the average diameter of the interparticle gaps in 70-140 mesh proppant is also 105 mesh. Considering unrestricted free flow, a 140-200 mesh micro-particle proppant can be used. The average particle size of this proppant is 170 mesh, approximately 60% smaller than the average interparticle gap diameter of the aforementioned 105 mesh proppant, ensuring its free entry and exit from the cracks laid with the aforementioned 70-140 mesh proppant.

[0080] Regarding the density of the 140-200 mesh proppant, considering the goal of achieving full suspension support in the longitudinal direction, the apparent density should be 1.05-1.25 g / cm³. 3 Left or right is preferable.

[0081] 6) Acid pretreatment and pre-fluid joint creation construction

[0082] Perform the procedure and parameters as per usual. For brittle formations, consider using low-viscosity (2-3 MPa·s) slickwater for fracture creation; for highly malleable formations, use high-viscosity adhesive (50-60 MPa·s) for fracture creation. Other parameters should be determined according to the construction parameters in step 1).

[0083] As per approach 3), considering that the timing of sand addition should be appropriately advanced, the volume of pre-fluid can be reduced from approximately 20% to approximately 10-15%. However, if it is found during on-site construction that the first slug is abnormally sensitive to the sand-fluid ratio, the proportion of pre-fluid should be appropriately increased. Regardless, the proportion of pre-fluid should not exceed 15%.

[0084] 7) Segmented application of 70-140 mesh proppant

[0085] The viscosity and flow rate of the isolation fluid shall be determined according to the parameters specified in steps 3) and 4). The viscosity, volume, flow rate, sand-liquid ratio, and other parameters of other slug fluids shall be determined according to the procedures and parameters specified in the construction plan in step 1).

[0086] The micro-proppant added to the isolation fluid is the 140-200 mesh proppant determined in step 5). Considering the relatively small particle size and density of this micro-proppant, and to ensure that the isolation fluid can smoothly enter small fractures of different sizes, the sand-to-fluid ratio can be designed to be 2%-3%-5%. Considering that the total volume of the isolation fluid is relatively small (approximately one wellbore volume), a continuous sand addition mode can be adopted, with the volume of each sand-to-fluid ratio evenly divided at a 1:1:1 ratio.

[0087] 8) Segmented application of 40-70 mesh proppant

[0088] The viscosity and flow rate of the isolation fluid shall be determined according to the parameters specified in steps 3) and 4). The viscosity, volume, flow rate, sand-liquid ratio, and other parameters of other slug fluids shall be determined according to the procedures and parameters specified in the construction plan in step 1).

[0089] The injection parameters for the isolation fluid shall be performed in accordance with step 7).

[0090] 9) Continuous sand addition construction with 40-70 mesh proppant

[0091] Based on step 8), the construction plan of step 1) shall be implemented.

[0092] Generally, based on the aforementioned slug-type construction, the sand-liquid ratio for continuous sand addition is 12%-14%-16%-18%-20%, and the volume of each sand-liquid ratio is generally half the wellbore volume according to the construction plan determined in step 1).

[0093] 10) Continuous sand addition operation for 30-50 mesh proppant

[0094] Follow the construction plan in step 1).

[0095] 11) Substitute work

[0096] Follow the construction plan in step 1).

[0097] 12) For the construction of other sections, repeat steps 6) to 11) until all sections are completed.

[0098] 13) After pressing, drilling plugging, backflow, testing and production shall be carried out in accordance with the conventional process and parameters.

[0099] The effects of the invention

[0100] This invention is rationally designed, has a clear method, is simple and efficient, and can effectively guide slug fracturing construction, reduce the local resistance effect of proppant, effectively reduce the risk of sand plugging, improve fracture creation efficiency, increase the complexity of slug fractures, effectively support smaller-scale fractures, facilitate stable production after fracturing, and significantly improve the fracturing construction effect, thereby obtaining greater economic benefits. Detailed Implementation

[0101] The present invention will now be described in detail with reference to specific 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.

[0102] Example 1

[0103] A shale gas well (Well A) in China has a vertical depth of 2270m and a horizontal section length of 1436m. The first fracturing operation consisted of 21 stages.

[0104] Step 1: Complete the fracturing design and construction plan according to conventional methods. Taking the first stage as an example, two types of proppant with particle sizes of 70-140 mesh and 40-70 mesh are used. In the slug-type proppant addition, the proppant-to-liquid ratio of 70-140 mesh proppant is 3%-5%-7%-9%-11%-13%-15%, and the proppant-to-liquid ratio of 40-70 mesh proppant is 7%-9%-11%-13%-15%-17%. The main construction displacement is 16m³. 3 / min.

[0105] Step 2: Test the viscosity of mortar mixed with two types of proppants, 70-140 mesh and 40-70 mesh, at different sand-liquid ratios;

[0106] Step 3: Based on the viscosity test results of the mortar, and according to the viscosity ratio of the first slug fluid to the release fluid (3:1), determine the viscosity of the release fluid.

[0107] Step 4: Based on the main construction discharge volume determined in Step 1, the discharge volume of the isolation fluid is 13m³. 3 / min.

[0108] Step 5: The particle size of the fine proppant in the isolation fluid is determined to be 140-200 mesh, and the apparent density of the proppant is 1.2 g / cm³. 3 .

[0109] Step 6: Pretreatment with 20 cubic meters of acid. Due to the relatively high plasticity of the target formation, high-viscosity adhesive is used for joint creation. The amount of pretreatment liquid before adding sand is 15% of the total liquid volume.

[0110] Step 7, 70-140 mesh proppant segmental application;

[0111] Slug-type construction using slickwater with a viscosity of 10 mPa·s carrying 70-140 mesh proppant; liquid volume 40 m³. 3 16m displacement 3 / min; sand-liquid ratio is 3%-5%-7%-9%-11%-13%-15%;

[0112] The isolation fluid carries a fine proppant, the sand-liquid ratio is 2%-3%-5%, and a continuous sand addition mode is adopted.

[0113] Step 8: Apply 40-70 mesh proppant in a segmented plugging manner;

[0114] Slug-like liquid with a viscosity of 20 mPa·s was used to carry 40-70 mesh proppant in a slug-like manner, with a flow rate of 40 m³. 3 16m displacement 3 / min; sand-to-liquid ratio is 7%-9%-11%-13%-15%-17%.

[0115] The isolation fluid carries a fine proppant, the sand-liquid ratio is 2%-3%-5%, and sand is added continuously.

[0116] Step 9: Continuous application of 40-70 mesh proppant with added sand;

[0117] Slickwater with a viscosity of 20 mPa·s was used to carry 40-70 mesh proppant, with continuous sand addition at a sand-to-liquid ratio of 12-14-16-18-20%; the liquid volume was 300 m³. 3 16m displacement 3 / min.

[0118] Step 10: Continuous application of 30-50 mesh proppant with added sand;

[0119] Slickwater with a viscosity of 40 mPa·s was used to carry 30-50 mesh proppant, with continuous sand addition at a sand-to-liquid ratio of 10-12-14-16-18% and a flow rate of 300 m³. 3 16m displacement 3 / min.

[0120] Step 11, Substitute Work

[0121] Slippery water was used for displacement; the displacement volume was 65m³. 3 ;

[0122] The first 10m of displacement fluid volume 3 The slickwater with a viscosity of 50 mPa·s was used, and the remaining displacement liquid was slickwater with a viscosity of 3 mPa·s.

[0123] Step 12: For the construction of other sections, repeat steps 6-11 until all sections are completed.

[0124] Step 13, including post-pressurization drilling plug, backflow, testing, and production, shall be performed according to standard procedures and parameters.

[0125] Well A underwent 21 stages of fracturing, with a total injection volume of 42,893 m³ into the formation. 3 A total of 2975m³ of sand was added. 3 Numerical simulation showed that the unobstructed flow rate after compression reached 13 × 10⁻⁶. 4 m 3 / d, which increased production by 30% compared to neighboring wells, resulting in significant economic benefits.

[0126] Example 2

[0127] A shale gas well (Well B) in China has a vertical depth of 3360m and a horizontal section length of 1521m. The first fracturing operation consisted of 26 segments. Step 1 involved completing the fracturing design and construction plan according to conventional methods. Taking the first segment as an example, two types of proppant with particle sizes of 70-140 mesh and 40-70 mesh were used. In the slug-type proppant addition, the proppant-to-liquid ratio for 70-140 mesh proppant was 3%-5%-7%-9%-11%-13%, and for 40-70 mesh proppant, it was 7%-9%-11%-13%-15%. The main construction displacement was 17m³ / h. 3 / min.

[0128] Step 2: Test the viscosity of mortar mixed with two types of proppants, 70-140 mesh and 40-70 mesh, at different sand-liquid ratios;

[0129] Step 3: Based on the viscosity test results of the mortar, and according to the viscosity ratio of the first slug fluid to the release fluid (3:1), determine the viscosity of the release fluid.

[0130] Step 4: Based on the main construction discharge volume determined in Step 1, the discharge volume of the isolation fluid is 14m³. 3 / min.

[0131] Step 5: The particle size of the fine proppant in the isolation fluid is determined to be 140-200 mesh, and the apparent density of the proppant is 1.21 g / cm³. 3 .

[0132] Step 6: Pretreatment with 15 cubic meters of acid. Due to the relatively high plasticity of the target formation, high-viscosity adhesive is used for joint creation. The amount of pretreatment liquid before adding sand is 15% of the total liquid volume.

[0133] Step 7, 70-140 mesh proppant segmental application;

[0134] Slug-loaded proppant with a viscosity of 15 mPa·s and 70-140 mesh was applied using a slug-loaded liquid with a volume of 50 m³. 3 17m displacement 3 / min; sand-to-liquid ratio is 3%-5%-7%-9%-11%-13%.

[0135] The isolation fluid carries a fine proppant, the sand-liquid ratio is 2%-3%-5%, and a continuous sand addition mode is adopted.

[0136] Step 8: Apply 40-70 mesh proppant in a segmented plugging manner;

[0137] Slug-like liquid with a viscosity of 25 mPa·s was used to carry 40-70 mesh proppant in a slug-like manner, with a flow rate of 50 m³. 3 17m displacement 3 / min; sand-to-liquid ratio is 7%-9%-11%-13%-15%.

[0138] The isolation fluid carries a fine proppant, the sand-liquid ratio is 2%-3%-5%, and sand is added continuously.

[0139] Step 9: Continuous application of 40-70 mesh proppant with added sand;

[0140] Slickwater with a viscosity of 25 mPa·s was used to carry 40-70 mesh proppant, with continuous sand addition at a sand-to-liquid ratio of 10-12-14-16-18%; the liquid volume was 250 m³. 3 17m displacement 3 / min.

[0141] Step 10: Continuous application of 30-50 mesh proppant with added sand;

[0142] Slickwater with a viscosity of 45 mPa·s was used to carry 30-50 mesh proppant, with continuous sand addition at a sand-to-liquid ratio of 8-10-12-14-16% and a liquid volume of 250 m³. 3 17m displacement 3 / min.

[0143] Step 11, Substitute Work

[0144] Slippery water was used for displacement; the displacement volume was 70m³. 3 ;

[0145] The first 10m of displacement fluid volume 3 The slickwater with a viscosity of 55 mPa·s was used, and the remaining displacement liquid was slickwater with a viscosity of 5 mPa·s.

[0146] Step 12: For the construction of other sections, repeat steps 6-11 until all sections are completed.

[0147] Step 13, including post-pressurization drilling plug, backflow, testing, and production, shall be performed in accordance with the standard procedures and parameters.

[0148] Well B underwent a total of 26 stages of fracturing, with a total injection volume of 47,527 m³ into the formation. 3 A total of 2981m³ of sand was added. 3 Numerical simulation showed that the unobstructed flow rate after compression reached 16.5 × 10⁻⁶. 4 m 3 / d, which increased production by 40% compared to neighboring wells, resulting in significant economic benefits.

Claims

1. A slug fracturing method, characterized in that... The method includes: Different viscosities of slug fluid and isolation fluid are used; the isolation fluid injection adopts a lower displacement and adds proppant with a finer particle size to the isolation fluid to reduce the risk of sand plugging, increase the complexity of slug fractures, and significantly improve the fracturing construction effect; 1) Development of fracturing design and construction plans; 2) Determination of the viscosity of slug mortar under different mortar-to-liquid ratios; 3) Determination of the viscosity of the isolation fluid at different stages; Determine the corresponding viscosity of the release fluid for slugs with different slug-to-release fluid ratios, based on a slug fluid to release fluid viscosity ratio greater than or equal to 3:

1. 4) Determining the injection displacement of the isolation fluid for different slug segments; 5) Determination of the particle size and density of the micro-support in the isolation fluid; The microproppant has a particle size of 140-200 mesh and an apparent density of 1.05-1.25 g / cm³. 3 6) Acid pretreatment and pre-fluid joint creation construction; The volume of the pre-fluid should be 10-15% of the total fluid volume; 7) Segmented application of 70-140 mesh proppant; Slug-type construction using slickwater with a viscosity of 10-30 mPa·s carrying 70-140 mesh proppant; liquid volume ≥ 20 m³ 3 Displacement ≥ 4m 3 / min, sand-liquid ratio range 3%-20%; The isolation fluid carries fine proppant, the sand-to-liquid ratio is 2%-3%-5%, and a continuous sand addition mode is adopted; 8) Segmented application of 40-70 mesh proppant; Slug-type construction using slickwater with a viscosity of 20-40 mPa·s carrying 40-70 mesh proppant, with a liquid volume ≥ 20 m³ / s. 3 Displacement ≥ 4m 3 / min; sand-to-liquid ratio range 3%-20%; The isolation fluid carries a fine proppant, the sand-to-liquid ratio is 2%-3%-5%, and sand is added continuously. 9) Continuous sand addition for application of 40-70 mesh proppant; 10) Continuous application of 30-50 mesh proppant with added sand; 11) Substitute work.

2. The fracturing method as described in claim 1, characterized in that: In step 2), the viscosity of the mixed mortar with two types of proppants, 70-140 mesh and 40-70 mesh, was tested at different sand-liquid ratios.

3. The fracturing method as described in claim 1, characterized in that: In step 3), the viscosity ratio of slug fluid to separator fluid is greater than or equal to 6:1; determine the corresponding separator fluid viscosity for slugs with different slug fluid ratios.

4. The fracturing method as described in claim 1, characterized in that: In step 4), When the slug fluid displacement is less than 16m 3 At a rate of / min, the discharge rate of the isolation fluid is 2-3 m³ lower than that of the slug fluid. 3 / min; When the slug fluid displacement is 16m 3 At speeds of 6 / min and above, the discharge rate of the isolation fluid is 3-4 m³ lower than that of the slug fluid. 3 / min.

5. The fracturing method as described in claim 1, characterized in that: In step 6), For brittle formations, low-viscosity slickwater is used to create the main fracture. For highly plastic strata, high-viscosity adhesive is used to create the main fracture.

6. The fracturing method as described in claim 1, characterized in that: In step 9), Slickwater with a viscosity of 20-40 mPa·s is used to carry 40-70 mesh proppant, with continuous sand addition at a sand-to-liquid ratio of 12%-14%-16%-18%-20%; the liquid volume is ≥20 m³ / s. 3 Displacement ≥ 4m 3 / min.

7. The fracturing method as described in claim 1, characterized in that: In step 10), Slippery water with a viscosity of 30-60 mPa·s is used to carry 30-50 mesh proppant, with continuous sand addition. The sand-to-liquid ratio is 10%-12%-14%-16%-18%, and the liquid volume is ≥20 m³. 3 Displacement ≥ 4m 3 / min.

8. The fracturing method as described in claim 1, characterized in that: Step 11), use slickwater for displacement; the displacement fluid volume is 10-20 m³ more than the volume of one wellbore. 3 ; The first 10m of displacement fluid volume 3 The slickwater with a viscosity of 30-60 mPa·s was used, and the remaining displacement liquid was slickwater with a viscosity of 1-10 mPa·s.

9. The application of the method as described in any one of claims 1 to 8 in oil extraction.