Overall reverse self-displacement synergistic fracturing development method for offshore low-permeability complex fault block oil reservoir

Abstract

The invention discloses an overall reverse self-displacement synergistic fracturing development method for an offshore low-permeability complex fault block oil reservoir. The overall reverse self-displacement synergistic fracturing development method comprises the steps that S1, a low-permeability oil reservoir block is selected; s2, performing synergistic fracturing development feasibility evaluation; s3, developing a synergistic fracturing development geological reservoir scheme design; s4, synergistic fracturing development drilling and completion and fracturing process scheme design are carried out, synergistic fracturing transformation comprises the steps that matrix fracturing transformation is carried out on a reservoir through large-liquid-amount, high-displacement and low-viscosity fracturing fluid, and in the process, a low-sand-ratio silt slug is added, and a pump is stopped for multiple times; fracture forming is conducted through high-viscosity fracturing fluid, and a large-particle-size proppant is added in a high sand ratio to form a high-flow-conductivity main fracture; and S5, designing and implementing according to the scheme. On the basis of the seepage characteristics of the low-permeability reservoir, reverse self-displacement synergistic fracturing transformation and self-injection and self-production are integrally implemented by the oil well, so that the problems of limited well pattern, unbalanced reserve utilization, high development cost, low recovery efficiency and the like in the traditional water injection development mode of the offshore low-permeability reservoir are fundamentally solved, and efficient development of the offshore low-permeability oil field can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of block integral fracturing development in the field of oilfield development, and in particular to an overall reverse self-displacement efficiency-enhancing fracturing development method for offshore low-permeability complex fault block oil reservoirs. Background Art

[0002] The offshore low-permeability sandstone reservoirs are extremely rich in crude oil resources, but a considerable proportion of these low-permeability oil reserves belong to low-permeability complex fault-block reservoirs. Due to the complex reservoir connectivity, it is difficult to deploy an effective water-driven injection-production well network, and there are no economical and efficient development conditions. Therefore, most of them have not been put into effective development and utilization. The main reasons for this situation are: poor reservoir physical properties, poor sand body connectivity and complex relationships, strong heterogeneity, insufficient natural driving energy, low natural production capacity of oil wells, and it is difficult to reach the economic development threshold; if water injection development is adopted, due to the restrictions of the marine environment, offshore oil fields can only concentrate development wells on offshore oil platforms, and the space and drilling trajectory orientation are extremely limited. In addition, the single well control and reserve threshold requirements are high, and only large well spacing and irregular injection-production well networks can be used. In this case, due to the large injection-production well spacing and imperfect injection-production well network, the formation displacement pressure is transmitted slowly, the water injection well is under-injected, and the pressure deficit of the oil production well is unstable, so the water drive efficiency is low and the recovery rate is low.

[0003] On land, the following methods are mainly used to solve the problem of efficient utilization of reserves and improve the recovery rate of such low-permeability oil fields: (1) water injection displacement with small well spacing and regular dense well network; (2) overall fracturing development; (3) pressure-increasing injection or pressure-driven water injection; (4) pressure-driven water injection for medium- and low-permeability reservoirs; (5) horizontal well energy-enhancing fracturing or integrated pressure-driven energy storage for tight reservoirs.

[0004] These methods have certain adaptability in onshore oil fields and have been proven to be effective in field practice, but they are not very adaptable to offshore oil fields. The main reasons are:

[0005] (1) If small well spacing and regular dense well network are used offshore, the investment in oil field construction will increase significantly, and the reserves and production of a single well will not reach the economic threshold, making it difficult to implement. (2) Overall fracturing development requires full consideration of the injection and production well network and the orientation of the fracturing cracks. Fracturing transformation is carried out on oil wells to increase production, and fracturing transformation is carried out on water injection wells to increase injection. This is not only expensive, but practice has shown that this method is more likely to cause water injection and water channeling, which in turn affects the recovery rate. It is also not worth applying offshore. (3) Pressure-raising and injection-increasing or pressure-driven water injection can only solve the problem of increasing injection wells in the short term, but it is easy to cause water channeling, water injection advance, uneven displacement and other problems, and it cannot solve the problems of slow pressure transmission at the oil well end and poor formation fluid supply capacity. (4) Pressure drive for medium and low permeability reservoirs is to increase the recovery rate by injecting oil displacement agent solution into the reservoir with high intensity to achieve energy enhancement, oil washing and displacement. It is divided into two modes: "forward pressure drive" injected from the water injection well end and "reverse pressure drive" injected from the oil production well section. This method is aimed at medium and low permeability reservoirs. Its characteristics are that no sand is added and no cracks are supported. After pressure drive, the cracks gradually close. After the well is shut down, the oil well is opened for production and the water injection well resumes water injection. Since this method does not add sand to support the cracks, if it is used for low permeability reservoirs, the cracks will lose their conductivity after closing. The effective period is short and cannot meet the requirements of high-intensity fluid production and long-term stable production of offshore oil wells. (5) Implementing horizontal well energy-enhancing fracturing or integrated pressure-driven energy storage in tight reservoirs is mainly aimed at tight oil reservoirs. A large amount of pre-fluid containing surfactant is injected into the horizontal well at one time before fracturing to fill the micro-fractures and replenish the formation energy. The pre-fluid has high filtration coefficient and good hydraulic conductivity to expand the filtration channel, and then implement volume fracturing to maximize the connection between micro-fractures, induced fractures and artificial fractures to form a network fracture. Combined with the oil-water infiltration and replacement effect in the well-sealing stage, the purpose of increasing production and recovery is achieved. This method mainly uses a large amount of pre-fluid containing surfactant before fracturing to activate natural micro-fractures and form induced fractures. Such micro-fractures in tight reservoirs do not require artificial support and can remain open for a long time after the construction is completed, thereby increasing the matrix permeability of the reservoir. However, natural fractures are generally not developed in offshore low-permeability reservoirs, and it is difficult to form induced fractures. This method is not targeted at general offshore low-permeability oil fields.

[0006] In view of the above problems, it is of great significance to provide a technical method that meets the requirements of efficient development of offshore low-permeability oil fields. Summary of the invention

[0007] The purpose of the present application is to provide an overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault block reservoirs to solve the problems raised in the above-mentioned background technology.

[0008] To achieve the above objectives, this application provides the following technical solutions:

[0009] The overall reverse self-displacement fracturing development method for offshore low-permeability complex fault block reservoirs includes:

[0010] S1. Select low-permeability oil reservoir blocks as target blocks and collect geological reservoir and engineering data of the target blocks;

[0011] S2. Based on the data collected in step S1, conduct a feasibility assessment of reverse self-displacement enhanced fracturing development in the target block;

[0012] S3. Based on the feasibility assessment of step S2, the target block is optimized for overall reverse self-displacement and enhanced fracturing development well pattern, well type and parameters, and the overall reverse self-displacement and enhanced fracturing development geological reservoir program design is carried out;

[0013] S4. Based on the geological reservoir plan of step S3, the overall reverse self-displacement enhanced fracturing development drilling and completion and fracturing process plan of the target block are designed, wherein the fracturing process includes the reverse self-displacement enhanced fracturing transformation of the oil production well, which includes the first step of fracturing the reservoir matrix with a large liquid volume, high displacement and low viscosity fracturing fluid, during which a low sand ratio silt sand plug is added and the pump is stopped several times; the second step is to fracture and create fractures with a high viscosity fracturing fluid and add a large particle size proppant with a high sand ratio to form a main fracture with high conductivity, so as to connect a large range of reservoir matrix and branch fractures that have been transformed;

[0014] S5. Implement the drilling, completion and fracturing process scheme designed based on step S4.

[0015] Furthermore, in step S1, the conditions that need to be met for selecting low-permeability reservoir blocks are: permeability range 1-100mD, no bottom water influence, certain controlled reserves, meeting the requirements for more than one well development, the reservoir is isolated by faults, the reservoir connectivity is complex, and preliminary evaluation shows that the conditions for water drive development by deploying an injection and production well network are not met.

[0016] Furthermore, step S2 includes reservoir structural geological conditions, fault types and isolation properties, reservoir physical and lithological characteristics, reservoir oil and gas content, geostress characteristics, fluid properties, sensitivity characteristics and reserve status assessment.

[0017] Furthermore, step S3 includes optimizing the well type in combination with the reservoir sand body distribution, faults and ground stress conditions, optimizing the well pattern and well spacing, and demonstrating the use of sparse well patterns, large well spacing and well location and wellbore trajectory layout schemes that are conducive to the full utilization of inter-well reserves; carrying out the overall reverse self-displacing and efficiency-enhancing fracturing development geological reservoir scheme design, including the purpose of reservoir development, main technical indicators of development, economic indicators, and the content of the scheme implementation and operation plan.

[0018] Furthermore, in step S4, the drilling and completion technology should be designed around the need to implement large-scale reverse self-displacement efficiency-enhancing fracturing transformation on the reservoir, including wellbore size, wellbore structure, mud system, reservoir protection, cementing, logging, completion method, completion casing and tubing selection, completion string and lifting process design, wellhead and Christmas tree selection design; the fracturing process scheme design includes single-well reverse self-displacement efficiency-enhancing fracturing layer and section selection, transformation scale optimization design, fracturing fluid system and special fracturing chemical agent optimization evaluation and parameter design, process string design and pumping program design, and the process implementation requirements are clearly defined.

[0019] Furthermore, step S5 includes: implementing the scheme design, implementing the scheme plan, tracking the implementation effect, and conducting post-evaluation.

[0020] In summary, the technical effects and advantages of the present invention are as follows:

[0021] The present invention adopts a "two-step method" to perform efficient fracturing transformation on the reservoir in view of the characteristics of multi-layer composite development of offshore low-permeability sandstone reservoirs, small layers at multiple permeability levels, poor connectivity, and closure within a certain range. In the first step, the reservoir is first subjected to matrix fracturing transformation with a large liquid volume, high displacement, and low viscosity fracturing fluid to increase the pore pressure and realize reservoir energy enhancement. In this process, a low sand ratio silt sand segment plug is added and the pump is stopped for many times. On the one hand, it plays the role of reducing filtration and assisting in seam creation. At the same time, small particle size proppants can be carried into the deep part of the cracks to achieve effective support for the cracks and prevent the fracturing cracks in the deep part of the reservoir from closing and losing the flow conductivity during the post-pressure production stage. In addition, at this stage, since the oil and gas and other fluids in the storage space in the reservoir voids are compressed, in-situ energy storage is achieved, and the energy can be released during the post-pressure drainage and production stages, realizing the reverse displacement of oil and gas from the deep part of the reservoir along the seepage channel to the cracks and the vicinity of the wellbore. The second step is to use high-viscosity fracturing fluid to create fractures and add large-particle proppants with high sand ratio to form main fractures with high conductivity, connecting a large area of ​​transformed reservoir matrix and branch fractures, thereby greatly improving the range and depth of reservoir utilization.

[0022] This method combines traditional high-viscosity cross-linked gel fracturing with matrix transformation and energy-enhancing displacement to achieve self-injection and self-production, greatly improving the fracturing transformation effect of low-permeability reservoirs, which can increase production by 3-5 times or even more than conventional fracturing, and greatly extend the effective period of single-well fracturing. Based on the above principles, if multiple oil wells in the block are transformed as a whole in this way, the integration of multiple mechanisms of "reservoir transformation + energy enhancement + energy storage" can be achieved for the entire reservoir, without the need to inject water into injection wells for energy replenishment, thereby reducing investment and overall development costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a flow chart of an overall reverse self-displacement enhanced fracturing development method for offshore low-permeability complex fault-block reservoirs in one embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the principle of the "two-step method" construction technology of reverse self-displacing and efficiency-enhancing fracturing of oil wells in one embodiment of the present invention;

[0026] Figure 3 This is a well location map of a certain block B13 well in one embodiment of the present invention;

[0027] Figure 4 This is a production curve diagram of a B13 well fault block in a certain block in one embodiment of the present invention;

[0028] Figure 5 This is a well location map of the B4 well in a certain block in one embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0031] This application aims at the problems of low permeability, strong heterogeneity, low natural production capacity, low displacement efficiency of conventional water drive development, and high investment cost of oil field construction and production in offshore low-permeability oil reservoirs. It adapts to the efficient development requirements of offshore oil fields such as large well spacing, sparse well network, high single-well controlled reserves, high single-well production, high oil production rate, and high recovery rate. The oil production wells are deployed as a whole, and all the oil production wells are subjected to reverse self-drive displacement and efficiency-enhancing fracturing transformation. Through the effects of reservoir matrix permeability and energy storage, chemical efficiency enhancement, artificial fracture creation and support, the reservoir liquid production capacity is greatly improved, thereby increasing the single well production, and achieving the purpose of increasing the oil production rate and improving the recovery rate.

[0032] This application provides an overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault block reservoirs, such as Figure 1As shown, including:

[0033] S1. Select low-permeability reservoir blocks as target blocks and collect data on the target blocks, mainly including various geological reservoir and engineering data, drawings, research reports, etc. The conditions that need to be met for selecting low-permeability reservoir blocks are: permeability range 1-100mD, no bottom water influence, certain controlled reserves, meeting the requirements for more than one well development, reservoir isolation by faults, complex reservoir connectivity, and preliminary evaluation shows that there are no conditions for water drive development by deploying injection and production well networks.

[0034] S2. Based on the data collected in step S1, conduct a feasibility assessment of the overall reverse self-displacement and enhanced fracturing development in the target block, including reservoir structural geological conditions, fault types and isolation, reservoir physical and lithological characteristics, reservoir oil and gas content, geostress characteristics, fluid properties, sensitivity characteristics and reserve status assessment. According to the concept of "geology and engineering integration", conduct a comprehensive study and analysis of the geological reservoir characteristics of the target block, determine its sand body deposition characteristics, connectivity, physical properties, heterogeneity, porosity characteristics, fluid characteristics, rock mineralogy and mechanical characteristics, reservoir rock wettability, fault characteristics, edge and bottom water distribution and formation energy driving characteristics, evaluate the reserve status, evaluate the indicators and main risks that can be achieved by implementing the overall reverse self-displacement and enhanced fracturing development in the target block, and study strategies to control risks.

[0035] S3. Based on the feasibility assessment of step S2, the well network, well type and parameter optimization of the overall reverse self-displacement and efficiency-enhancing fracturing development in the target block are carried out, and the overall reverse self-displacement and efficiency-enhancing fracturing development geological reservoir program design is carried out, including the optimization of well types in combination with the distribution of reservoir sand bodies, faults and ground stress conditions, and the optimization of well networks and well spacing, as well as the demonstration of the use of sparse well networks, large well spacing and well locations and wellbore trajectory arrangements that are conducive to the full utilization of inter-well reserves; the overall reverse self-displacement and efficiency-enhancing fracturing development geological reservoir program design is carried out, including the purpose of reservoir development, main technical indicators of development, economic indicators, program implementation and operation plan, etc. Optimize the well network, well type and parameters for development of the target block, design an overall development plan based on step S2, demonstrate the optimization of development indicators, select the best well type based on the distribution of reservoir sand bodies, faults and geostress conditions, optimize the well network and well spacing, and demonstrate the layout of well locations and wellbore trajectories that are sparsely spaced, with large well spacing and conducive to the full utilization of inter-well reserves. Clarify the workload and various development indicators, and formulate relevant risk countermeasures.

[0036] S4. Based on the geological reservoir plan of step S3, the overall reverse self-displacement enhanced fracturing development drilling and completion and fracturing process plan is designed for the target block.

[0037] The drilling and completion technology should be designed around the need to implement large-scale reverse self-displacement and efficiency-enhancing fracturing transformation on the reservoir, including wellbore size, wellbore structure, mud system, reservoir protection, cementing, logging, completion method, completion casing and tubing selection, completion string and lifting process design, wellhead and Christmas tree selection design; the fracturing process scheme design includes single-well reverse self-displacement and efficiency-enhancing fracturing layer and section selection, transformation scale optimization design, fracturing fluid system and special fracturing chemical agent optimization evaluation and parameter design, process string design and pumping program design, and clear process implementation requirements.

[0038] This application aims at the multi-layer composite development of offshore low-permeability sandstone reservoirs, the characteristics of small layers at multiple permeability levels, poor connectivity, and closedness within a certain range, and adopts a "two-step method" to perform reverse self-displacement fracturing transformation on the reservoir. The reverse self-displacement fracturing transformation of oil wells includes: the first step, such as Figure 2 As shown in the figure on the left, the reservoir is first subjected to matrix fracturing transformation with a large amount of liquid, high displacement and low viscosity fracturing fluid to increase the pore pressure and realize reservoir energy enhancement. In this process, a low sand ratio silt sand plug is added and the pump is stopped several times. On the one hand, it plays a role in reducing filtration and assisting in fracture creation. At the same time, small particle proppants can be carried into the deep part of the fracture to achieve effective support for the fracture and prevent the fractures deep in the reservoir from closing and losing their conductivity during the post-fracturing production stage. In addition, at this stage, since the oil and gas and other fluids in the storage space in the reservoir voids are compressed, in-situ energy storage is achieved, and the energy can be released during the post-fracturing drainage and production stages to achieve reverse displacement of oil and gas from the deep reservoir along the seepage channel to the fractures and near the wellbore. The second step, such as Figure 2 As shown in the figure on the right, high-viscosity fracturing fluid is used to create fractures and large-particle proppants are added at a high sand ratio to form main fractures with high conductivity, connecting a large area of ​​transformed reservoir matrix and branch fractures, thereby greatly improving the range and depth of reservoir utilization.

[0039] This method combines traditional high-viscosity cross-linked gel fracturing with matrix transformation and energy-enhancing displacement to achieve self-injection and self-production, greatly improving the fracturing transformation effect of low-permeability reservoirs, which can increase production by 3-5 times or even more than conventional fracturing, and greatly extend the effective period of single-well fracturing. Based on the above principles, if multiple oil wells in the block are transformed as a whole in this way, the integration of multiple mechanisms of "reservoir transformation + energy enhancement + energy storage" can be achieved for the entire reservoir, without the need to inject water into injection wells for energy replenishment, thereby reducing investment and overall development costs.

[0040] S5. Implement the drilling, completion and fracturing process scheme designed in step S4. Implement according to the scheme design, implement the scheme plan, track the implementation effect, and conduct post-evaluation.

[0041] Example

[0042] The overall reverse self-displacement and enhanced fracturing development of offshore low-permeability complex fault block reservoirs, taking the B13 well block in a certain block as an example, the well location map of the B13 well block in a certain block is as follows Figure 3 shown.

[0043] The oil-bearing stratum in the East Section Ⅰ oil group of a certain offshore block is a braided river delta deposit. Its B13 well area is an independent fault block with an oil layer thickness of 29.7m, an average permeability of 22.8mD, a formation crude oil viscosity of 0.5mPa·s, a geological reserve of 510,000 tons (590,000 cubic meters), poor reservoir properties, and no conditions for water drive development with an injection and production well network. After evaluation and research, a single well was used to control the use of the fault block, and the reverse self-displacement overall efficiency-enhancing fracturing development method provided in this application was used for program design and implementation, and it was predicted that a good development effect could be obtained.

[0044] The specific implementation steps are as follows:

[0045] Step 1: Collect block information, including various geological reservoir and engineering data, maps, research reports, etc.

[0046] Step 2: Conduct a feasibility assessment of the reverse self-displacing and enhanced fracturing development of the B13 well block. Preliminary analysis shows that the oil field block where the B13 well is located is a block structure formed in the late Eocene, cut by multiple faults, rich in reserves, with poor reservoir properties, and relatively independent blocks. It is suitable for overall development using the reverse self-displacing and enhanced fracturing method to achieve the goals of increasing production and improving crude oil recovery.

[0047] Step 3, optimize the well network, well type and parameters of the target block development, and carry out the overall reverse self-drive replacement and enhanced fracturing development geological reservoir plan design. According to research, the fault block is small in area, with a reserve of nearly 600,000 cubic meters, which only meets the requirements of one directional well development and drilling. Therefore, a well is designed for use, and each development index is optimized and demonstrated. According to demonstration, the basic plan elastic drive natural exploitation has a cumulative oil production of 4,200 cubic meters, and the predicted well-controlled reserve recovery rate is 0.7%; the reverse self-drive replacement and enhanced fracturing development plan can produce a cumulative oil production of 50,700 cubic meters, with a predicted recovery rate of 8.6%, which is 7.9% higher than the basic plan elastic drive natural exploitation. According to the demonstration, the geological reservoir plan requires two-stage transformation, with a total liquid volume of not less than 14,000 cubic meters, a half-length of the support fracture of 90 meters, and a main fracture conductivity requirement of 50D cm.

[0048] Step 4: Design drilling, completion and fracturing process schemes for the overall reverse self-displacement fracturing development of the block. The drilling and completion related parameters were designed based on the requirements for large-scale reverse self-displacement fracturing transformation of the reservoir. The fracturing process scheme design carried out layer selection and segment selection, and designed two-stage transformation for the reservoir with an effective thickness of about 30m. In combination with the geological reservoir scheme, the fracturing fluid system and special fracturing chemical agent were optimized and evaluated, parameter design was carried out, fracturing process string design and pumping program design were designed, and the process implementation requirements were clarified. The design separately carried out "two-step" fracturing transformation for two layers. The first layer was 16m thick. The first step of the transformation used 6000 cubic meters of low-viscosity oil displacement fracturing fluid and added 5 cubic meters of 40 / 70 mesh small-size ceramsite. The second step used 600 cubic meters of high-viscosity fracturing fluid and added 70 cubic meters of 20 / 40 mesh ceramsite. The second layer was 10.6m thick. The design used 8000 cubic meters of low-viscosity oil displacement fracturing fluid and added 6 cubic meters of 40 / 70 mesh small-size ceramsite in the first step. The second step used 415 cubic meters of high-viscosity fracturing fluid and added 55 cubic meters of 20 / 40 mesh ceramsite. After simulation, the fracturing fracture parameters can meet the needs of the reservoir.

[0049] Step 5: Implement the plan according to the design. After the well is drilled and completed, it is put into production and trial production after perforation. Figure 4 As shown, the initial natural production capacity is about 30 cubic meters per day, excluding water; after five months, the production drops to 6 cubic meters per day, which is lower than the normal well opening requirement. It is decided to implement the fracturing transformation plan of this embodiment. It will be implemented in December 2023, and the cumulative injection volume of the two layers is 15114m 3 , of which the volume of low viscosity fracturing fluid is 13910m 3 , high viscosity fracturing fluid volume 1204m 3 ; Add sand 137.1m 3 , in which the first step is to add 13.1m of sand 3 (The two floors are 6.1m 3 、7.0m 3 ), the second step is to add sand 124m 3 (The two floors are 71.0m 3 、53.0m 3 ). Construction displacement 5-7m 3 / min, the maximum construction pressure is 49MPa, and the construction process is smooth.

[0050] After the well was completed, it entered the well shut-in stage for 95 hours. At the end of the well shut-in period, the wellhead pressure was stable at 5.9MPa. The converted bottom hole pressure was 6.7MPa higher than the original formation pressure, and the energy storage effect was obvious. After the blowout, the electric pump was put into production. After the liquid was discharged, the initial liquid volume reached 100-120m 3 / d, the initial oil production reached 60m 3 / d, and then the oil production stabilized at more than 50m3 / d, and the production flow pressure remained stable. According to the actual measures, the final recovery rate will reach more than 10%, and the implementation effect of the plan is higher than expected. The production curve of the well is shown in Figure 4 .

[0051] In addition to this embodiment, it has been implemented in three sea areas. Another typical example is a B4 well fault block in a low permeability block. The well location map is as follows: Figure 5 As shown, the well controlled reserves are 218,000 cubic meters. The method of this application is adopted. The initial elastic drive natural production has a cumulative oil production of 25,600 cubic meters (recovery rate of 11.7%), and then the reverse self-drive fracturing transformation of this application is implemented. The initial production after fracturing reaches 100m 3 / d, the cumulative oil production reached 13,000 cubic meters in 8 months, and the production was stable at 80m 3 / d or more, it is predicted that the production can be increased by 26,300 cubic meters within three years, and the recovery rate can reach 23.8%, an increase of 12.1 percentage points, which has achieved good results.

[0052] Although the preferred implementation cases of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms of specific changes without departing from the scope of protection of the invention spirit and claims, which all fall within the scope of protection of the present invention.

Claims

1. An overall reverse self-displacement fracturing development method for offshore low-permeability complex fault block reservoirs, characterized in that: include: S1. Select low-permeability oil reservoir blocks as target blocks and collect geological reservoir and engineering data of the target blocks; S2. Based on the data collected in step S1, conduct a feasibility assessment of reverse self-displacement enhanced fracturing development in the target block; S3. Based on the feasibility assessment of step S2, the target block is optimized for overall reverse self-displacement and enhanced fracturing development well pattern, well type and parameters, and the overall reverse self-displacement and enhanced fracturing development geological reservoir program design is carried out; S4. Based on the geological reservoir plan of step S3, the overall reverse self-displacement enhanced fracturing development drilling and completion and fracturing process plan of the target block are designed, wherein the fracturing process includes the reverse self-displacement enhanced fracturing transformation of the oil production well, which includes the first step of fracturing the reservoir matrix with a large liquid volume, high displacement and low viscosity fracturing fluid, during which a low sand ratio silt sand plug is added and the pump is stopped several times; the second step is to fracture and create fractures with a high viscosity fracturing fluid and add a large particle size proppant with a high sand ratio to form a main fracture with high conductivity, so as to connect a large range of reservoir matrix and branch fractures that have been transformed; S5. Implement the drilling, completion and fracturing process scheme designed based on step S4.

2. The overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault-block reservoirs according to claim 1 is characterized in that: In step S1, the conditions that need to be met for selecting low-permeability reservoir blocks are: permeability range 1-100mD, no bottom water influence, certain controlled reserves, meeting the requirements for more than one well development, the reservoir is isolated by faults, the reservoir connectivity is complex, and preliminary evaluation shows that it does not meet the conditions for water drive development by deploying an injection and production well network.

3. The overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault-block reservoirs according to claim 1 is characterized in that: Step S2 includes reservoir structural geological conditions, fault types and isolation properties, reservoir physical and lithological characteristics, reservoir oil and gas content, geostress characteristics, fluid properties, sensitivity characteristics and reserve status assessment.

4. The overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault-block reservoirs according to claim 1 is characterized in that: Step S3 includes selecting the best well type based on the distribution of reservoir sand bodies, faults and geostress conditions, optimizing the well pattern and well spacing, and demonstrating the use of sparse well patterns, large well spacing and well location and wellbore trajectory layout schemes that are conducive to the full utilization of inter-well reserves; carrying out the overall reverse self-displacing and enhanced fracturing development geological reservoir scheme design, including the purpose of reservoir development, main technical indicators of development, economic indicators, and the content of the scheme implementation and operation plan.

5. The overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault-block reservoirs according to claim 1 is characterized in that: In step S4, the drilling and completion process should be designed around the need to implement large-scale reverse self-displacement efficiency-enhancing fracturing transformation on the reservoir, including wellbore size, wellbore structure, mud system, reservoir protection, cementing, logging, completion method, completion casing and tubing selection, completion string and lifting process design, wellhead and Christmas tree selection design; fracturing process scheme design includes single well reverse self-displacement efficiency-enhancing fracturing layer and section selection, transformation scale optimization design, fracturing fluid system and special fracturing chemical agent optimization evaluation and parameter design, process string design and pumping program design, and clear process implementation requirements.

6. The overall reverse self-displacement and enhanced fracturing development method for offshore low-permeability complex fault-block reservoirs according to claim 1 is characterized in that: Step S5 includes: implementing the plan according to the design, implementing the plan, tracking the implementation effect, and conducting post-evaluation.

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