Method for controlling extension of multi-scale fractures at different positions of main fracture and fracturing method

Abstract

The invention provides a method for controlling multi-scale fracture extension at different positions of a main fracture and a fracturing method, and belongs to the field of oil and gas exploitation, the method comprises the steps that fracturing fluid is injected to conduct segmented fracture forming construction on the main fracture, and each fracture forming stage expands to generate the main fracture with the preset length; temporarily plugging the end part of the main crack by adopting a temporary plugging agent, and opening the multi-scale crack in the length direction of the main crack through a temporary plugging effect; a propping agent is continuously injected to fill the multi-scale crack; the blocking of the end of the main crack is relieved, the process from the main crack segmented crack forming construction to the multi-scale crack filling is repeated till the crack length of the main crack reaches the maximum value, and a multi-scale crack network is formed in the length direction of the main crack; and a proppant is continuously injected to fill the main crack. According to the fracturing method provided by the invention, the main crack and the branch cracks can be fully extended, and effective support of the main crack and the branch cracks is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploitation, and in particular to a method for controlling the extension of multi-scale cracks at different positions of a main crack and a fracturing method. Background Art

[0002] At present, volume fracturing technology has been applied to tight sandstone, carbonate rock and shale oil and gas reservoirs to varying degrees. Volume fracturing is to form relatively small branch fractures and even smaller micro fractures in addition to conventional large-scale main fractures through certain methods.

[0003] The main technical method currently used is to temporarily plug the main fractures after they have extended a certain distance, so that the fluid enters the microcracks and opens them, so that the microcracks extend and form complex fractures, and proppants are added to form effective support. During fracturing, the initial fluid does not carry proppants, the main fracture is formed and expands along the direction of maximum ground stress, during which some natural fractures are activated, and then fluid carrying proppants is injected to support the fractures. However, since a certain amount of fluid has infiltrated the microcracks in the near-wellbore area at the initial stage of fracturing, the fluid will mainly flow along the direction of the main fracture at this time, and most of the support of the small-particle proppant it carries will be distributed in the branch fractures at the end of the main fracture, and only a small amount of fluid will enter the branch fractures in the near-wellbore area. The existing technical methods cannot fully activate all the natural branch fractures in the main fracture extension area, and the effective support effect of the branch fractures is not ideal.

[0004] Therefore, it is necessary to propose a new volume fracturing method so that both the main fracture and the branch fracture can be fully extended and the effective support of the main fracture and the branch fracture can be guaranteed. Summary of the invention

[0005] In view of the technical problem that the volume fracturing method in the prior art cannot achieve full extension and effective support of both the main fracture and the branch fracture, the present invention provides a method for controlling the extension of multi-scale fractures at different positions of the main fracture. This method can effectively increase the extension range of the main fracture and the branch fracture, and form effective support, thereby providing effective help for improving the fracturing transformation effect.

[0006] To achieve the above-mentioned purpose, the present invention provides, on the one hand, a method for controlling the extension of multi-scale cracks at different positions of the main crack, the method comprising the following steps: injecting fracturing fluid to perform segmented cracking construction on the main crack, and each cracking stage expands to produce a main crack of a predetermined length; after the main crack of the predetermined length is expanded, a temporary plugging agent is used to temporarily plug the end of the main crack, and multi-scale cracks are opened in the length direction of the main crack through the temporary plugging effect; proppant is continuously injected to fill the multi-scale cracks; the plugging of the end of the main crack is released, and the above-mentioned main crack segmented cracking construction is repeated to fill the multi-scale cracks until the crack length of the main crack reaches a maximum value and a multi-scale crack network is formed in the length direction of the main crack; proppant is continuously injected to fill the main crack; wherein the multi-scale cracks include branch cracks and micro cracks.

[0007] In an exemplary embodiment of the present invention, in the first fracture formation stage of the main fracture, before using a temporary plugging agent to temporarily plug the end of the main fracture, a floating agent and a sinking agent may be injected simultaneously to control the fracture height of the main fracture near the wellbore.

[0008] In an exemplary embodiment of the present invention, in each fracture creation stage, the fracturing fluid can be controlled to increase its displacement to the designed maximum displacement within 1 to 2 minutes.

[0009] In an exemplary embodiment of the present invention, in the first fracture formation stage of the main fracture, the volume of the injected fracturing fluid can be controlled to be less than 10% of the total fluid volume of the fracturing construction.

[0010] In an exemplary embodiment of the present invention, during other fracture formation stages of the main fracture, the volume of the injected fracturing fluid may be controlled to be 20% to 30% of the total fluid volume of the fracturing operation.

[0011] In an exemplary embodiment of the present invention, a proppant with a first particle size may be used to fill multi-scale fractures, and a proppant with a second particle size may be used to fill main fractures, wherein the first particle size is smaller than the second particle size.

[0012] In an exemplary embodiment of the present invention, a fracturing fluid with a first viscosity may be used to carry a proppant with a first particle size, and a fracturing fluid with a second viscosity may be used to carry a proppant with a second particle size, wherein the first viscosity is smaller than the second viscosity.

[0013] In an exemplary embodiment of the present invention, the first viscosity may be 2-3 mPa·s, and the second viscosity may be 30-40 mPa·s.

[0014] In an exemplary embodiment of the present invention, a first construction sand-to-liquid ratio is used to inject proppant to fill multi-scale fractures, and a second construction sand-to-liquid ratio is used to inject proppant to complete sealing of multi-scale fracture openings, wherein the second construction sand-to-liquid ratio is greater than the first construction sand-to-liquid ratio.

[0015] On the other hand, the present invention provides a fracturing method, which comprises: step (1), evaluating key parameters of the target layer and the upper and lower 50m barriers; step (2), evaluating the geological engineering sweet spot and determining the segment cluster perforation position; step (3), optimizing the fracture parameters; step (4), optimizing the fracturing construction parameters; step (5), bridge plug perforation joint operation; step (6), acid pretreatment operation; step (7), using the above method to extend and support the main fracture and branch fracture; step (8), displacement operation; step (9), repeating steps (5) to (8) until the fracturing construction of all segments is completed; step (10), drilling plug after fracturing, backflow, testing and production.

[0016] Through the technical solution provided by the present invention, the present invention has at least the following technical effects:

[0017] (1) The fracturing method of the present invention changes the volume fracturing construction concept of fracturing-temporary plugging-fracturing in the prior art. It uses multiple temporary plugging to fully expand the branch fractures, and cooperates with necessary floating agents, sinking agents, temporary plugging agents and proppants to fully open the natural fractures around the main fractures, so as to effectively increase the extension range of the main fractures and branch fractures.

[0018] (2) The fracturing method of the present invention can ensure that the sand-carrying fluid fully enters the branch fracture, so that the branch fracture is effectively supported and the flow conductivity is guaranteed, thereby effectively improving the hydraulic fracturing transformation effect.

[0019] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0021] Figure 1 A flow chart of a method for controlling the extension of multi-scale fractures at different positions of a main fracture provided by an embodiment of the present invention;

[0022] Figure 2 A technical schematic diagram of a new volume fracturing method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0025] In the present invention, “first”, “second”, etc. are merely used for convenience of description and distinction and cannot be understood as indicating or implying relative importance.

[0026] The common problems in current shale oil and gas volume fracturing operations are that some branch fractures are not fully extended due to the difference in fluid flow distribution in the main fractures and branch fractures, and it is difficult for sand-carrying fluids to enter the branch fractures, making it difficult to form effective support. In order to solve the above problems, the present invention proposes a new volume fracturing technology method. After multi-stage temporary plugging during fracturing construction, a rapidly degradable temporary plugging agent is used to achieve temporary plugging of the main fracture, thereby promoting the opening of the branch fracture. The temporary plugging agent is then dissolved, allowing the main fracture to continue to expand. This cycle promotes the full opening of the main fracture and branch fractures, and allows more proppant to enter the branch fracture, thereby achieving effective long-term diversion.

[0027] It should be noted that the "scale" described in the embodiments of the present invention mainly refers to the crack width; the "multi-scale cracks" described refer to branch cracks and micro cracks. Among them, the crack width of the main crack is greater than the crack width of the branch crack, and the crack width of the branch crack is greater than the crack width of the micro crack.

[0028] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0029] Embodiment 1

[0030] Please refer to Figure 1 A first embodiment of the present invention provides a method for controlling the extension of multi-scale fractures at different positions of a main fracture, the method comprising the following steps:

[0031] Step S101, injecting fracturing fluid to perform the first stage of fracture construction on the main fracture to expand the main fracture to a predetermined length.

[0032] It should be noted that, unlike the method of generating branch cracks and micro cracks after all main cracks are created and simultaneously filling them with proppants, the present embodiment adopts a method of opening the main cracks, branch cracks and micro cracks in multiple stages and then filling them in sections. By dividing the construction of the main cracks into different stages, branch cracks and micro cracks are generated separately in each stage and independently filled with proppants, the effectiveness of filling the branch cracks and micro cracks in different stages can be ensured.

[0033] like Figure 2As shown, in the first fracture formation stage of the main fracture, the main fracture is extended to a certain length, and after the temporary plugging of the fracture end is implemented, the branch fractures in the length direction of the main fracture are opened, and the proppant carried by the fracturing fluid is filled into the branch fractures. After the temporary plugging agent at the end of the main fracture is dissolved, the second fracture formation stage of the main fracture is entered, and the main fracture is extended to a certain length again. After repeating the above temporary plugging operation, the branch fractures in the new length direction of the main fracture are opened, and the proppant carried by the fracturing fluid is filled into the new branch fractures. This cycle is repeated, so that both the main fracture and the branch fracture can be fully extended and effectively supported. This embodiment adopts a low-viscosity fracturing fluid fast-increasing displacement fracture formation strategy to complete the fracture formation construction of the main fracture. Low-viscosity fracturing fluid facilitates the communication and extension of multi-scale fracture systems synchronously or in a very short time; and fast-increasing displacement facilitates the rapid establishment of wellbore pressure.

[0034] Specifically, low-viscosity fracturing fluid can be used to complete the fracturing construction at each fracturing stage, and the fracturing fluid can be controlled to quickly increase the displacement to the designed maximum displacement within 1 to 2 minutes. For example, the viscosity of the low-viscosity fracturing fluid can be 2 to 3 mPa·s.

[0035] Step S102: After the main crack of a predetermined length is expanded, a temporary plugging agent is used to temporarily plug the end of the main crack, and multi-scale cracks are opened in the length direction of the main crack through the temporary plugging effect.

[0036] At this time, the length of the main fracture is relatively short. After temporarily plugging the position near the end, since the main fracture is relatively fixed in the length direction, the increased displacement, in addition to increasing the width of the main fracture, mainly extends in the small and micro-scale branch fractures and micro-cracks near the wellbore. Because there is no flow or the flow velocity is extremely low in the length direction of the main fracture, most of the displacement and liquid volume should act on the small-scale branch fractures and micro-cracks to maximize their length extension.

[0037] Furthermore, before temporarily plugging the end of the main fracture, a floating agent and a sinking agent can be injected simultaneously to control the fracture height of the main fracture near the wellbore. The simultaneous application of the floating agent and the sinking agent can further relatively fix the main fracture in the height direction, ensuring that the net pressure of the main fracture increases rapidly while controlling the fracture height without excessive extension.

[0038] Step S103: continuously inject proppant to fill the multi-scale fractures generated in the first fracture creation stage.

[0039] After continuing to inject low-viscosity fracturing fluid for a certain period of time, small-particle proppant (for example, 70 / 140 mesh) can be injected. At this time, only small-scale branch cracks and micro-cracks should be filled with fluid, and the flow rate of fracturing fluid in the direction of the main cracks is extremely low. Therefore, most of the proppant should be able to enter the small-scale fracture system.

[0040] In the past, when the length of the main fracture was relatively large, there were small-scale branch fractures and micro-fracture systems at different lengths of the main fracture. The added proppant had a relatively large density compared to the fracturing fluid, and its followability with the fracturing fluid was poor. As a result, the fracturing fluid could enter the branch fractures and micro-fractures close to the wellbore, but the proppant was difficult to enter.

[0041] Furthermore, a first construction sand-liquid ratio can be used to inject proppant to fill multi-scale fractures, and a second construction sand-liquid ratio can be used to inject proppant to complete the sealing of the multi-scale fracture openings, wherein the second construction sand-liquid ratio is greater than the first construction sand-liquid ratio. In other words, in the later stage of adding sand in this step, the construction sand-liquid ratio can be appropriately increased to ensure the sealing effect at the branch fractures and micro-cracks, so that it is difficult to enter them again when the fracturing fluid is injected later.

[0042] Step S104, unblocking the end of the main crack and carrying out the second stage of crack-making construction of the main crack to extend the length of the main crack again.

[0043] For example, the dissolution time of the temporary plugging agent can be reasonably designed to ensure that most of the temporary plugging agent at the end of the main crack is dissolved after the above-mentioned construction is completed.

[0044] Step S105, after the main crack expansion in the second crack-making stage is completed, the end of the main crack is temporarily blocked again to open a new multi-scale crack in the length direction of the main crack.

[0045] In the second fracture formation stage of the main fracture, low viscosity fracturing fluid can be continuously injected and combined with the fast displacement strategy to initiate and extend the main fracture again. Since the previous small micro-scale branch fractures and micro-cracks have been completely blocked, the possibility of generating new small micro-scale branch fractures and micro-cracks near the wellbore is relatively small. Only within the newly extended main fracture range can new branch fractures and micro-crack systems be generated again.

[0046] Then repeat the temporary plugging construction near the end of the main crack in the first crack-making stage. At this time, the above-mentioned floating agent and sinking agent can no longer be injected synchronously. This is because the closer to the main crack initiation end, the lower the extension of the crack height. Without the addition of floating agent and sinking agent, the crack height of the main crack near the initiation end is relatively well controlled, and the small micro-scale branch cracks and micro-crack systems near the wellbore do not have the ability to absorb fracturing fluid. Therefore, at this time, most of the liquid volume and displacement injected during fracturing construction will fully play a role in the newly extended main crack, which can promote the moderate extension of the crack height of the far part of the main crack, and have a positive effect on improving the support efficiency in the vertical direction here.

[0047] Step S106: continuously inject proppant to fill the multi-scale fractures generated in the second fracture creation stage.

[0048] This stage of fracturing construction is equivalent to a similar process to the main fracture construction in the first stage. Referring to the operation process and parameters of the previous stage, the proppant can fully fill the small and micro-scale branch fractures and micro-cracks at the main fracture of this stage.

[0049] Step S107, unblocking the end of the main crack, repeating the above-mentioned process of segmented cracking construction of the main crack to fill the multi-scale cracks, until the crack length of the main crack reaches a maximum value and a multi-scale crack network is formed in the length direction of the main crack.

[0050] Repeating the above-mentioned fracturing process can promote the full opening of the main fractures and branch fractures, and allow more proppant to enter the branch fractures, thereby achieving effective long-term diversion.

[0051] Step S108: After the main fracture and the multi-scale fractures are fully extended, proppant is continuously injected to fill the main fracture.

[0052] Furthermore, in this embodiment, in the first fracture formation stage of the main fracture, the volume of the injected fracturing fluid can be controlled to be less than 10% of the total fluid volume of the fracturing operation. In other fracture formation stages of the main fracture, the volume of the injected fracturing fluid can be controlled to be 20% to 30% of the total fluid volume of the fracturing operation.

[0053] Since the main crack expands rapidly during the first fracture creation, a small amount of low-viscosity fracturing fluid should be injected to open the main crack of a predetermined length, so as to avoid excessive pressure that expands the main crack to its maximum length in advance, thereby making it impossible to open the branch cracks and micro-cracks in multiple stages. In other fracture creation stages, the main crack expands slowly, so the volume of injected fracturing fluid should be increased to ensure that the length of the main crack is close or equivalent.

[0054] Furthermore, in this embodiment, a proppant with a first particle size may be used to fill multi-scale fractures, and a proppant with a second particle size may be used to fill main fractures, wherein the first particle size is smaller than the second particle size.

[0055] Furthermore, a fracturing fluid with a first viscosity may be used to carry a proppant with a first particle size, and a fracturing fluid with a second viscosity may be used to carry a proppant with a second particle size, wherein the first viscosity is smaller than the second viscosity.

[0056] Here, there are two reasons for using a higher viscosity fracturing fluid for construction. The first is that a higher viscosity fracturing fluid has a stronger ability to carry large-particle proppants and flow, thus preventing large-particle proppants from being unable to fully support the entire main fracture. The second is that a higher viscosity fracturing fluid also has the function of sweeping away small-particle proppants that were previously retained in the main fracture, so that they are all brought to the end of the main fracture or near the end, thus avoiding the passive impact of improper volume design of small-particle proppants in the early stage.

[0057] Compared with the prior art, the method of this embodiment has at least the following advantages:

[0058] (1) By continuously temporarily plugging, the branch seams are fully extended;

[0059] (2) The sand-carrying fluid fully enters the branch joints, which effectively supports the branch joints and ensures their flow conductivity.

[0060] Embodiment 2

[0061] A second embodiment of the present invention provides a volume fracturing method, the method comprising the following steps:

[0062] Step S201: Evaluate key parameters of the target layer and upper and lower 50m layers.

[0063] It mainly includes lithology and whole rock mineral composition, physical properties, rock mechanics and three-dimensional geostress characteristics, natural fractures and horizontal bedding fractures / texture fractures, etc. It mainly uses pilot well cores to conduct test analysis under simulated underground temperature and pressure conditions. If necessary, it is corrected with field test data.

[0064] Step S202: evaluating the geological engineering sweet spot and determining the segment cluster perforation positions.

[0065] The general section length is 60-80m, with 2-4 clusters of perforations in each section, a cluster length of 0.5-1m, a hole density of 16-20 holes / m, and a hole diameter of 9.5-13.5mm. The geological sweet spot and engineering sweet spot are calculated by conventional methods. The geological sweet spot and engineering sweet spot at each perforation section should be nearly equal, or the difference between the minimum and maximum values ​​should be less than 20%.

[0066] Step S203: Optimize crack parameters.

[0067] Using ECLIPSE, a commercial simulation software commonly used in fracturing, hydraulic fractures were set according to the equivalent conductivity method (to reduce the simulation workload, the width of the fracture was enlarged by a certain multiple, and the permeability of the proppant in the fracture was reduced proportionally so that their product, i.e. the conductivity of the fracture, remained unchanged). The orthogonal design method was used to simulate the post-fracturing production dynamics under different fracture parameters (fracture length, conductivity, and fracture spacing). The fracture parameters corresponding to the relative maximum post-fracturing production or the maximum economic net present value were taken as the optimal fracture parameters.

[0068] Step S204: Optimizing fracturing construction parameters.

[0069] Commercial simulation software commonly used in fracturing design, such as MEYER, GOFHER, STIMPLAN, etc., is used to simulate the dynamic changes in fracture parameters under different fracturing construction parameters (displacement, liquid volume, viscosity, proppant dosage and the proportion of proppants with different particle sizes, etc.), and the fracturing construction parameters under the best fracture parameters in step S203 are preferably obtained, that is, the best fracturing construction parameters.

[0070] Step S205: bridge plug and perforation combined operation.

[0071] In the first section, the bridge plug is not lowered, and the coiled tubing is lowered to carry the perforating gun. The other sections are involved in the pumping method to carry the bridge plug and the cluster perforating tool string. After the bridge plug is seated, it is released and the perforating gun is lifted up step by step. After all the cluster perforations are completed, the perforating gun tool is lifted up and the main fracturing process is reversed.

[0072] Step S206: Acid pretreatment operation.

[0073] Conventional hydrochloric acid and conventional formula are generally used. Appropriate adjustments can be made based on the core of step S201, compatibility, acid dissolution rate, etc. The general single-stage acid dosage is 10-20m 3 The acid injection volume is generally 1 to 1.5 m 3 / min, after acid injection, the displacement of acid is 3~6m 3 After the acid reaches the cluster perforation position, the displacement is reduced to the previous acid injection displacement, and then the acid replacement displacement is gradually restored to the previous acid replacement displacement.

[0074] Step S207: Use the method described in the first embodiment to expand, extend and fill the main cracks and branch cracks. The specific implementation sub-steps are as follows.

[0075] Sub-step S2071, low viscosity rapid displacement to create the first stage of main crack construction.

[0076] Refer to the optimization results of step S204 for the main parameters. The general viscosity of the fracturing fluid is 2-3 mPa·s, and the displacement of the fracturing fluid is quickly increased to the designed maximum displacement within 1-2 minutes. When the pre-fluid is used to create fractures, the three-dimensional geometric dimensions of the fracture expand the fastest in the early stage of fracture creation. Generally, when the total fluid volume is 20%-30%, the fracture length has reached more than 70% of the final value.

[0077] In the first stage of seam creation, the liquid volume accounts for a smaller proportion, which can be about 10% of the total liquid volume optimized in step S204, generally 150-250 ml 3 .

[0078] After 40% to 50% of the construction progress in this stage, the floating agent (apparent density 0.7 to 1g / cm 3 ) and sinking agent (apparent density 3.3~3.5g / cm3 The mixing ratio of floating agent and sinking agent is 1:1, and the particle size is 140 / 210 mesh. The volume ratio of the fracturing fluid is 3%-5%-7%. The volume of fracturing fluid at each ratio is 10-15m 3 After that, the remaining fracturing fluid is used to carry the temporary plugging agent in the first stage main crack. The particle size of the temporary plugging agent is 40 / 70 mesh and 30 / 50 mesh, each accounting for 50%. The construction sand-to-liquid ratio is 5%-8%-11%, and the volume of each sand-to-liquid ratio is 5-7m 3 The specific parameters can be adjusted in real time based on the wellhead pressure rising speed. Generally, the wellhead pressure rising speed is required to be around 1MPa / min.

[0079] The temporary plugging agent in this stage is required to be mostly dissolved during the construction of sub-step S2073.

[0080] Sub-step S2072: In the first stage, low viscosity fracturing fluid is used to extend small micro-scale branch cracks and micro-cracks near the wellbore.

[0081] On the basis of sub-step S2071, continue to inject low-viscosity fracturing fluid with a viscosity of 2 to 3 mPa·s. The main parameters refer to the results in step S204. The general liquid volume is 80 to 100 m 3 , start injecting 70 / 140 mesh proppant when about 50% of the injection is completed. At this time, most of the proppant can only enter the branch fractures and micro fractures near the wellbore.

[0082] Generally, a low sand-to-liquid ratio continuous injection mode is adopted, and the sand-to-liquid ratio is generally 2%-4%-6%. In order to ensure the efficient filling of branch fractures and micro fractures near the wellbore, the liquid volume corresponding to the above sand-to-liquid ratio is generally 15-20-15m 3 At this time, even if the branch cracks and micro cracks have the sand-out effect at their ends, the pressure rise rate will not reach the 1MPa / min of the main cracks, because their pressure rise effect is offset by the buffer of the main cracks connected to them. However, the pressure should still rise to a certain extent. If it does not rise but decreases, the above-mentioned sand-liquid ratio should be appropriately increased.

[0083] Sub-step S2073, second stage main crack construction.

[0084] The construction process and parameters of this stage can refer to sub-step S2071. Considering that even with the top and bottom capping of the cracks and the efficient filling and plugging effect of the branch cracks and microcracks in the first stage, there is still a small amount of fracturing fluid loss when the fracturing fluid flows through the main cracks and microcracks formed in the first stage (but this loss becomes smaller and smaller with time), therefore, the volume of the fracturing fluid in the second stage can be appropriately increased by about 10% compared with the first stage to ensure that the length of the main crack is close or equivalent.

[0085] Sub-step S2074, in the second stage, low viscosity fracturing fluid is used to extend small micro-scale branch cracks and micro-cracks near the wellbore.

[0086] The process and parameters of this stage can refer to sub-step S2072.

[0087] Sub-step S2075, the construction of main cracks in other stages and filling of branch cracks and micro cracks formed in this stage, refer to sub-steps S2071 to S2072.

[0088] Sub-step S2076: uniformly perform proppant injection construction on multiple main fractures.

[0089] In this stage, a relatively high viscosity fracturing fluid with a viscosity of 30-40 mPa·s is used for construction. First, it is convenient to carry large-size proppants. Generally, 60%-70% of 40 / 70 mesh proppants are injected first, and then 30 / 50 mesh proppants are injected. Second, if the 70 / 140 mesh small-size proppants used in the early construction are used too much, the remaining proppants will inevitably remain in the main fractures, which will damage the flow conductivity of the main fractures. For this reason, the relatively high viscosity fracturing fluid also has the function of sweeping the small-size proppants retained in the main fractures in the early stage, so that they are all brought to the end of the main fracture or near the end position, thus avoiding the passive influence of the improper design of the volume of small-size proppants in the early stage.

[0090] Both proppants of different particle sizes are injected continuously. The sand-to-liquid ratio of 40 / 70 mesh proppant is generally 10%-13%-16%-19%, and the fracturing fluid volume of each sand-to-liquid ratio is generally 50-80m 3 ; The sand-to-liquid ratio of 30 / 50 mesh proppant construction is generally 16%-19%-22%, and the volume of each fracturing fluid is generally 10-12m 3 The injection displacement of the two particle size proppants is the maximum displacement optimized in step S204.

[0091] Step S208, replacement operation.

[0092] The displacement volume is determined by 105% to 110% of the sum of the wellbore volume and the surface pipeline volume of the current section. The first 40% to 50% uses a fracturing fluid with a viscosity of 30 to 40 mPa·s to prevent the adverse effect of the sand settling effect of the horizontal wellbore on the construction of the lower bridge plug. After that, a low-viscosity fracturing fluid of 2 to 3 mPa·s is used. Even if it is over-displaced, the viscous fingering effect caused by the viscosity difference can also maintain sufficient conductivity at the seam. The displacement is the highest displacement optimized in step S204.

[0093] Step S209: Fracturing construction of other sections, repeating steps S205 to S208 until the fracturing construction of all sections is completed.

[0094] Step S210, post-pressure drilling plug, flowback, testing and production, etc., are performed with reference to conventional processes and parameters and are not repeated here.

[0095] Embodiment 3

[0096] Taking a horizontal well as an example, the third embodiment of the present invention provides a volume fracturing method. The horizontal well is 1000 m long, the reservoir depth is 3500 m, and the well is completed with casing. The specific implementation steps of the volume fracturing method are as follows.

[0097] Step S301, determining the perforation positions of the segment cluster and optimizing the fracture parameters.

[0098] Based on geomechanics, reservoir physical properties and engineering parameters, combined with gas reservoir numerical simulation technology, the total number of perforation clusters required and the location of each perforation cluster are determined.

[0099] Based on the commercial simulation software MEYER, which is commonly used for fracture extension simulation, it was determined to be divided into 9 sections, with 2 to 4 clusters of perforations in each section, a cluster length of 1 m, 18 spiral perforations in each cluster, an angle of 60°, a hole diameter of 9.5 mm, and a perforation interval of 1 m.

[0100] Step S302: Optimizing fracturing construction parameters.

[0101] During each stage of construction, the fracturing displacement is controlled at 8-12m 3 / min. Each stage of fracturing uses low-viscosity slippery water (2-3mPa·s) with a scale of 1030m 3 , high viscosity slippery water (30~40mPa·s) scale is 260m 3 , acid 15m 3 (concentration 20%), 70 / 140 mesh proppant scale 8m 3 , 40 / 70 mesh proppant scale is 29m 3 , 30 / 50 mesh proppant scale is 5.7m 3 Temporary plugging agent (40 / 70 mesh and 30 / 50 mesh, ratio 1:1) scale is 6.4m 3 , floating agent (particle size 140 mesh, apparent density 0.8g / cm 3 ) Scale is 3m 3 , sinking agent (particle size 140 mesh, apparent density 3.3g / cm 3 ) Scale is 3m 3 .

[0102] Step S303: bridge plug and perforation combined operation. Except for the first section, the bridge plug is not put in, and the coiled tubing with perforating gun is directly put in. The remaining sections are perforated according to the design.

[0103] Step S304: acid liquid pretreatment.

[0104] After perforation, acid pretreatment is carried out, with an acid injection volume of 1m 3 / min, after acid injection, the displacement of acid is 3~6m 3 / min. After the acid reaches the perforation position, the displacement is reduced to the previous acid injection displacement, and then the acid replacement displacement is gradually restored to the previous acid replacement displacement.

[0105] Step S305, low viscosity rapid displacement to create the first stage of main crack construction.

[0106] A total of 250m3 of low-viscosity slick water was injected during this phase. 3 , when injecting to 80m 3 When the floating agent and sinking agent are injected, the ratio of floating agent to sinking agent is 1:1, with three sections in total, and the construction sand-liquid ratio is 3%-5%-7%. 10m 3 , a total of 30m 3 Next 20m 3 Low-viscosity slippery water carries temporary plugging agent, and the construction sand-liquid ratio is 5%-8%-11%.

[0107] Step S306, in the first stage, low viscosity fracturing fluid is used to extend small micro-scale branch fractures and micro-fractures near the wellbore.

[0108] After step S305 is completed, continue to inject the remaining low-viscosity slick water, a total of 120m 3 . After injecting 50m 3 When adding 70 / 140 mesh proppant, use low sand-liquid ratio continuous injection mode, the sand-liquid ratio is 2%-4%-6%, and the corresponding liquid volume is 15-20-15m 3 The remaining low-viscosity slippery water is then injected.

[0109] Step S307, second stage main crack construction.

[0110] This stage is similar to step S305, and a total of 250m of low-viscosity slick water is injected. 3 , when injecting to 100m 3 When the floating agent and sinking agent are injected, the ratio of floating agent to sinking agent is 1:1, with three sections in total, and the construction sand-liquid ratio is 3%-5%-7%. 10m 3 , a total of 30m 3 Next 20m 3 Low-viscosity slippery water carries temporary plugging agent, and the construction sand-liquid ratio is 5%-8%-11%.

[0111] Step S308, in the second stage, low viscosity fracturing fluid is used to extend small micro-scale branch cracks and micro-cracks near the wellbore.

[0112] This stage is similar to step S306. After step S307, continue to inject the remaining low-viscosity slick water for a total of 100m3 . After injecting 30m 3 When adding 70 / 140 mesh proppant, use low sand-liquid ratio continuous injection mode, the sand-liquid ratio is 2%-4%-6%, and the corresponding liquid volume is 15-20-15m 3 The remaining low-viscosity slippery water is then injected.

[0113] Step S309: The remaining stages are the construction of main joints and branch joints.

[0114] Referring to step S307 and step S308, the third and fourth stages of the current fracturing are completed.

[0115] Step S310: Propping agents are uniformly injected into multiple main fractures.

[0116] Injection of highly viscous and slippery water, a total of 230m 3 , carrying proppant. First inject 40 / 70 mesh proppant, the stage sand-liquid ratio is 10%-13%-16%-19%, and the volume of each section is 50m 3 ; The sand-liquid ratio of 30 / 50 mesh proppant construction is 16%-19%-22%, and the volume of each section is 10m 3 This stage adopts the maximum design displacement, 12m 3 / min.

[0117] Step S311, replacement operation.

[0118] The displacement volume is 60m 3 . First 30m 3 High viscosity slippery water is used, and the last 30m 3 Low viscosity slippery water is used. The maximum design displacement is used in this stage, 12m 3 / min.

[0119] Step S312: Construction of other sections.

[0120] Repeat steps S305 to S311 until all segments are constructed.

[0121] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0122] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0123] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for controlling the extension of multi-scale cracks at different positions of a main crack, characterized in that: The method comprises: Inject fracturing fluid to perform segmented fracturing on the main fracture, and expand each fracturing stage to produce a main fracture of a predetermined length; After the main crack of the predetermined length is expanded, a temporary plugging agent is used to temporarily plug the end of the main crack, and multi-scale cracks are opened in the length direction of the main crack through the temporary plugging effect; Continuously inject proppant to fill multi-scale fractures; The plugging of the end of the main crack is released, and the above-mentioned process of segmented cracking of the main crack is repeated until the crack length of the main crack reaches a maximum value and a multi-scale crack network is formed in the length direction of the main crack; Continuously inject proppant to fill the main fracture; Wherein, the multi-scale cracks include branch cracks and micro cracks.

2. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 1, characterized in that: In the first fracture formation stage of the main fracture, before the temporary plugging agent is used to temporarily plug the end of the main fracture, the floating agent and the sinking agent are injected simultaneously to control the fracture height of the main fracture near the wellbore.

3. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 1, characterized in that: In each fracture creation stage, the fracturing fluid is controlled to increase its displacement to the designed maximum displacement within 1 to 2 minutes.

4. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 1, characterized in that: In the first fracture formation stage of the main fracture, the volume of the injected fracturing fluid is controlled to be less than 10% of the total fluid volume of the fracturing operation.

5. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 1, characterized in that: During the other fracture formation stages of the main fracture, the volume of the injected fracturing fluid is controlled to be 20% to 30% of the total fluid volume of the fracturing operation.

6. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 1, characterized in that: A proppant with a first particle size is used to fill the multi-scale fractures, and a proppant with a second particle size is used to fill the main fractures, wherein the first particle size is smaller than the second particle size.

7. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 6, characterized in that: A fracturing fluid with a first viscosity is used to carry a proppant with a first particle size, and a fracturing fluid with a second viscosity is used to carry a proppant with a second particle size, wherein the first viscosity is smaller than the second viscosity.

8. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 7, characterized in that: The first viscosity is 2-3 mPa·s, and the second viscosity is 30-40 mPa·s.

9. The method for controlling the extension of multi-scale cracks at different positions of the main crack according to claim 1, characterized in that: A first construction sand-to-liquid ratio is used to inject proppant to fill multi-scale fractures, and a second construction sand-to-liquid ratio is used to inject proppant to seal the multi-scale fracture openings, wherein the second construction sand-to-liquid ratio is greater than the first construction sand-to-liquid ratio.

10. A fracturing method, characterized in that: The fracturing method comprises: Evaluation of key parameters of target layer and upper and lower 50m layers; Evaluation of geological engineering sweet spots and determination of cluster perforation locations; Fracture parameter optimization; Optimization of fracturing operation parameters; Bridge plug and perforation joint operation; Acid pretreatment operations; The method according to any one of claims 1 to 9 is used to extend and fill the main cracks and branch cracks; Replacement work; Repeat the above-mentioned bridge plug and perforation joint operation to the expansion and extension of the main fracture and the branch fracture and the filling and supporting steps until the fracturing construction of all sections is completed; Drill plug, flowback, testing and production after compression.

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