Water injection policy optimization method based on dynamic seam recognition

Abstract

The invention discloses a water injection policy optimization method based on dynamic seam identification, and belongs to the technical field of oil and gas field development. Comprising the following steps: establishing a fracture and natural fracture coupling fracture network model; a low-permeability reservoir water injection dynamic fracture model is established, and dynamic fracture parameters are obtained in combination with the low-permeability reservoir water injection dynamic fracture model; production dynamic data and static data of a target block are obtained, dynamic fracture parameters are constrained by means of well spacing and row spacing of the target block, then a water injection dynamic fracture is simulated under the condition of different water injection rates based on a fracture and natural fracture coupling fracture network model, and simulated dynamic fracture parameters are obtained; the simulated dynamic seam parameters are combined with the yield of the corresponding production well group and the water content change of the corresponding production well group to determine simulated reasonable dynamic seam parameters; and determining the reasonable water injection intensity of the mine field based on the water injection rate corresponding to the simulated reasonable dynamic seam parameters, and performing water injection policy adjustment based on the parameters to complete water injection policy optimization.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and in particular relates to a water injection policy optimization method based on dynamic fracture identification. Background Art

[0002] Ultra-low permeability reservoirs have the characteristics of dense reservoirs, poor physical properties, strong heterogeneity, and developed natural fractures. In the early stage of reservoir development, the use of fracturing transformation methods can make the hydraulic fractures and natural fractures in the reservoir communicate with each other to form high-permeability channels for underground oil and gas, thereby effectively improving the formation seepage capacity and expanding the pressure range. In the later stage of development, as the fractures gradually close, the effective permeability of the formation will gradually decrease, and the formation pressure will increase, resulting in a decrease in the amount of fluid in the oil well. By increasing the water injection to increase the formation energy, if the water injection volume is too large, the dynamic fractures of the water injection will extend too fast, which can easily lead to rapid water seepage in the oil wells, the formation of high-permeability channels between oil and water wells, and the weakening of the displacement effect of the residual oil between the wells, making the later management difficult.

[0003] At present, the single reservoir engineering and mine statistical methods have low mine compliance rate and poor availability. They are unable to quantitatively characterize the dynamic fractures in the water injection development process, and cannot achieve reasonable water injection dynamic fracture parameters to guide the optimization of mine injection and production policies, resulting in poor water drive development effects for such fractured reservoirs. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a water injection policy optimization method based on dynamic fracture identification, establish a numerical model of reasonable parameters of water injection dynamic fractures on the basis of fully understanding the fracture characteristics, provide a theoretical basis for the injection and production policy of such oil reservoirs, give full play to the water injection dynamic fractures to increase the water drive range while avoiding water channeling of the injected water along the high permeability channel to cause high water content in the oil well, thereby improving the water drive efficiency, maintaining the formation pressure, and effectively improving the development effect of such oil reservoirs.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a water injection policy optimization method based on dynamic fracture identification, comprising the following steps:

[0007] Using the discrete fracture method, a coupled fracture network model of hydraulic fractures and natural fractures is established based on natural fracture parameters and hydraulic fracture parameters; a dynamic fracture model of water injection in low permeability reservoirs is established based on the water injection dynamic fracture formula, and dynamic fracture parameters are obtained by combining the dynamic fracture model of water injection in low permeability reservoirs;

[0008] Obtain production dynamic data and static data of the target block, use the well spacing and row spacing of the target block to constrain the dynamic fracture parameters, and then simulate the water injection dynamic fractures under different water injection rates based on the fracture network model of hydraulic fractures and natural fractures to obtain the simulated dynamic fracture parameters;

[0009] When the target block is developed to the target stage, the actual dynamic fracture parameters of the mine are obtained by interpreting the pressure measurement data. The dynamic fracture parameters are simulated and combined with the production of the corresponding production well group and the water content change of the corresponding production well group to determine the reasonable dynamic fracture parameters of the simulation;

[0010] The reasonable water injection intensity of the mine is determined based on the water injection volume corresponding to the simulated reasonable dynamic fracture parameters. The water injection policy is adjusted based on the simulated reasonable dynamic fracture parameters, the reasonable water injection intensity of the mine and the actual dynamic fracture parameters of the mine to complete the water injection policy optimization.

[0011] In the specific implementation process, the process of obtaining the natural fracture parameters and the hydraulic fracture parameters is as follows:

[0012] Collect dynamic and static data, combine geological structure and sedimentary background to identify the main controlling factors of fractures, and obtain natural fracture parameters and hydraulic fracture parameters;

[0013] The natural fracture parameters include: the position of the natural fracture, the fracture direction of the natural fracture, the fracture half-length of the natural fracture, the fracture opening of the natural fracture, the fracture height of the natural fracture and the number of fractures of the natural fracture;

[0014] The hydraulic fracture parameters include: the location of the hydraulic fracture, the fracture direction of the hydraulic fracture, the fracture half-length of the hydraulic fracture, the fracture aperture of the hydraulic fracture, the fracture height of the hydraulic fracture and the number of fractures of the hydraulic fracture.

[0015] In the specific implementation process, the process of establishing the low permeability reservoir water injection dynamic fracture model is as follows:

[0016] Based on the parameters of natural fractures and hydraulic fractures, as well as the additional pressure drop between the fracture and the formation contact surface and the additional pressure drop between the fracture and the wellbore, under the set conditions that the model reservoir is homogeneous, of equal thickness and infinite size, the dynamic fractures of water injection are symmetrical along the wellbore, and the closure of dynamic fractures during the shut-in and pressure measurement stage will cause changes in the dynamic fracture length and the dynamic fracture conductivity, the formulas for the dynamic fracture length and the dynamic fracture conductivity are obtained, and the dynamic fracture model for water injection in low permeability reservoirs is established.

[0017] In the specific implementation process, the water injection dynamic fracture formula includes a formula for dynamic fracture length and a formula for dynamic fracture conductivity;

[0018] The formula of dimensionless dynamic crack length in the dynamic crack length is as follows:

[0019]

[0020] The formula of the dimensionless dynamic fracture conductivity in the dynamic fracture conductivity is as follows:

[0021]

[0022] In the above formula, L f is the dimensionless dynamic crack length; L f0 is the initial length of the dimensionless crack; P 0 wD is the dimensionless bottom hole pressure when the fracture is initially closed; P wD is the dimensionless bottom hole pressure when the fracture is closed; θ is the fracture half-length variation factor; k f is the dimensionless dynamic fracture conductivity; k f0 is the initial conductivity of dimensionless fracture; α is the stress sensitivity coefficient of low permeability reservoir; P 0 w is the bottom hole pressure when the fracture is initially closed; P w is the bottom hole pressure when the fracture is closed.

[0023] In the specific implementation process, the production dynamic data and static data of the target block include the number of oil wells, the number of water wells, daily liquid production, daily oil production level, water content, daily water injection volume and effective thickness of the oil layer.

[0024] In the specific implementation process, the process of constraining the dynamic fracture parameters by using the well spacing and row spacing of the target block is as follows:

[0025] In the coupled fracture network model of hydraulic fractures and natural fractures, the well spacing and row spacing are set to be greater than half of the dynamic fracture length in the dynamic fracture parameters to constrain the dynamic fracture length.

[0026] In the specific implementation process, the process of combining the simulated dynamic fracture parameters with the production of the corresponding production well group and the water content change of the corresponding production well group to determine the simulated reasonable dynamic fracture parameters is as follows:

[0027] Based on the dynamic fracture length and dynamic fracture conductivity in the simulated dynamic fracture parameters, the simulated dynamic fracture extension velocity change is obtained; based on the water content change of the corresponding production well group, the water content increase rate of the corresponding production well group is obtained;

[0028] Obtain the curve of change of injection volume and simulated dynamic fracture extension speed, the curve of change of simulated dynamic fracture under different injection volumes, and the curve of change of injection volume and corresponding water content of production wells;

[0029] Reasonable dynamic fracture parameters of the simulation are determined based on the above curves and the daily oil production level in the production of the corresponding production well group under different water injection rates and the water cut increase rate of the corresponding production well group.

[0030] In the specific implementation process, when there is an obvious inflection point in the change curve of the water injection volume and the simulated dynamic crack extension speed, it indicates that the dynamic crack extension speed is too fast, there is a risk of water breakthrough, and the corresponding water injection volume is too large.

[0031] In the specific implementation process, the process of determining the reasonable water injection intensity of the mine is as follows:

[0032]

[0033] In the above formula, Q w is the daily water injection volume, in m 3 / d; h is the effective thickness of the oil layer, in m; q w Reasonable water injection intensity for the mine.

[0034] In the specific implementation process, the process of adjusting the water injection policy based on the simulated reasonable dynamic fracture parameters, the reasonable water injection intensity of the mine and the actual dynamic fracture parameters of the mine is as follows:

[0035] When the actual dynamic fracture parameters of the mine are greater than the reasonable dynamic fracture parameters simulated, small water injection adjustment and profile adjustment and flooding control the fracture extension;

[0036] When the actual dynamic fracture extension speed of the mine is too fast, periodic water injection or normal water injection adjustment;

[0037] When the actual dynamic fracture parameters of the mine are less than the reasonable dynamic fracture parameters simulated, and the water injection energy supplement is not obvious, the water injection is strengthened to gradually extend the dynamic fractures.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention provides a method for optimizing water injection policy based on dynamic fracture identification. The method uses reservoir geological data, well logging data and dynamic monitoring to determine fracture parameters of different reservoirs, considers reservoir characteristics of low permeability reservoirs, establishes a water injection dynamic fracture model, integrates reservoir engineering, numerical simulation and other means, studies the effective fracture half-length and conductivity of water injection dynamic fractures, utilizes natural fractures and hydraulic fractures to communicate, improves the oil and gas seepage capacity, and avoids the formation of high permeability channels between oil and water wells in water injection dynamic fractures. Reasonable water injection dynamic fracture parameters are used to guide the optimization and adjustment of the injection and production mode of the mine, and effectively improves the effect of water drive development of such oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A flow chart of a method for adjusting water injection policy based on dynamic seam identification according to an embodiment of the present invention;

[0041] Figure 2 A geometric representation diagram of a discrete fracture network according to an embodiment of the present invention;

[0042] Figure 3 A curve diagram showing the daily water injection volume and the simulated dynamic fracture extension speed in an embodiment of the present invention;

[0043] Figure 4 This is a simulated dynamic crack change curve diagram of the injection scheme according to an embodiment of the present invention;

[0044] Figure 5 This is a simulated dynamic crack change curve diagram of the embodiment of the present invention using injection scheme 2;

[0045] Figure 6 This is a simulated dynamic crack change curve diagram of the embodiment of the present invention using injection scheme three;

[0046] Figure 7 A curve diagram showing the daily water injection volume and the water content change of the corresponding production wells according to an embodiment of the present invention;

[0047] Figure 8 Graph showing the relationship between the amount of pre-pressure replenishment fluid and formation pressure in the Q well according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0050] The present invention provides a water injection policy optimization method based on dynamic fracture identification, comprising the following steps:

[0051] Collect dynamic and static data, combine geological structure and sedimentary background to identify the main controlling factors of fractures, and obtain natural fracture parameters and hydraulic fracture parameters;

[0052] Using the discrete fracture method, a fracture network model of coupled fractures of hydraulic fractures and natural fractures is established based on the parameters of natural fractures and hydraulic fractures.

[0053] Based on the water injection dynamic fracture formula, a low permeability reservoir water injection dynamic fracture model is established, and the dynamic fracture parameters are obtained by combining the low permeability reservoir water injection dynamic fracture model;

[0054] Obtain production dynamic data and static data of the target block, use the well spacing and row spacing of the target block to constrain the dynamic fracture parameters, and then simulate the water injection dynamic fractures under different water injection rates based on the fracture network model of hydraulic fractures and natural fractures to obtain the simulated dynamic fracture parameters;

[0055] When the target block is developed to the target stage (a certain stage of reservoir development), the actual dynamic fracture parameters of the mine are obtained by interpreting the pressure measurement data, and the dynamic fracture parameters are simulated to determine the reasonable dynamic fracture parameters of the simulation in combination with the production of the corresponding production well group and the water content change of the corresponding production well group;

[0056] The reasonable water injection intensity of the mine is determined based on the water injection volume corresponding to the simulated reasonable dynamic fracture parameters. The water injection policy is adjusted based on the simulated reasonable dynamic fracture parameters, the reasonable water injection intensity of the mine and the actual dynamic fracture parameters of the mine to complete the water injection policy optimization.

[0057] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0058] See also Figure 1 As shown, the present invention provides a water injection policy optimization method based on dynamic fracture identification, which focuses on optimizing the water injection policy based on dynamic fracture parameters, and is mainly carried out in the following steps:

[0059] 1) Collect dynamic and static data, and clarify the main controlling factors of fractures in combination with geological structure and sedimentary background;

[0060] The specific steps are as follows: the static data collected include coring data, imaging logging data, and downhole microseismic data; the dynamic data include well test data, water drive front data, and water absorption indication curve data; at the same time, the geological structure background data of the study area is obtained, mainly including three-dimensional coherent attribute distribution maps, maximum principal stress orientation test data, and tectonic stress background, to clarify the range and orientation of fracture distribution.

[0061] 2) Determine the parameters of natural fractures and hydraulic fractures;

[0062] The specific steps are as follows: carry out a qualitative description of the single well point fracture under the framework background of step 1), and obtain the natural fracture parameters and hydraulic fracture parameters by combining the dynamic and static data;

[0063] The natural fracture parameters include: the position of the natural fracture, the fracture direction of the natural fracture, the fracture half-length of the natural fracture, the fracture opening of the natural fracture, the fracture height of the natural fracture and the number of fractures of the natural fracture;

[0064] The hydraulic fracture parameters include: the location of the hydraulic fracture, the fracture direction of the hydraulic fracture, the fracture half-length of the hydraulic fracture, the fracture aperture of the hydraulic fracture, the fracture height of the hydraulic fracture and the number of fractures of the hydraulic fracture.

[0065] 3) Establish a dynamic fracture model for water injection in low permeability reservoirs based on natural fracture parameters and hydraulic fracture parameters;

[0066] The specific steps are as follows: Based on the natural fracture parameters and the hydraulic fracture parameters, the additional pressure drop between the fracture and the formation contact surface and the additional pressure drop between the fracture and the wellbore are considered. The model assumes that the reservoir is homogeneous, of equal thickness and infinite size, and the dynamic fractures of water injection are symmetrical along the wellbore. The closure of the dynamic fractures during the shut-in and pressure measurement stage will cause changes in the dynamic fracture length and the dynamic fracture conductivity. The water injection dynamic fracture formula, i.e., the formula for the dynamic fracture length and the dynamic fracture conductivity, is obtained to complete the establishment of the dynamic fracture model of water injection in low permeability reservoirs.

[0067] Dynamic crack length L f and fracture conductivity k f It is determined by the following formula:

[0068] The formula of dimensionless dynamic crack length in dynamic crack length is as follows:

[0069]

[0070] The formula of dimensionless dynamic fracture conductivity in dynamic fracture conductivity is as follows:

[0071]

[0072] Among them, L f is the dimensionless dynamic crack length, L f0 is the initial length of the dimensionless crack, P 0 wD is the dimensionless bottom hole pressure when the fracture is initially closed, P wD is the dimensionless bottom hole pressure when the fracture is closed, θ is the fracture half-length variation factor, k f is the dimensionless dynamic fracture conductivity, k f0 is the dimensionless fracture initial conductivity, α is the stress sensitivity coefficient of low permeability reservoir, P 0 w is the bottom hole pressure when the fracture is initially closed, P w is the bottom hole pressure when the fracture is closed.

[0073] 4) Using the discrete fracture method, a fracture network model of hydraulic fractures and natural fractures is established based on the natural fracture parameters and hydraulic fracture parameters;

[0074] The specific steps are as follows: Based on the positions of the natural fractures and hydraulic fractures determined in step 2), the fracture direction f, the fracture half-length x f , crack opening w, crack height x h , the number of fractures N is determined by using a discrete fracture method to establish a coupled fracture network model of hydraulic fractures and natural fractures in the Comsol software, the low permeability reservoir water injection dynamic fracture model in step 3) is embedded in the Comsol hydraulic fracture and natural fracture coupled fracture network model, the dynamic fracture length and fracture conductivity coefficient during water injection development are simulated, the morphology of natural fractures, hydraulic fractures and water injection dynamic fractures is characterized, and the dynamic fracture parameters are obtained.

[0075] 5) Collect dynamic and static production data of the target block, including the number of oil wells, the number of water wells, the daily liquid production q, the daily oil production level qo, the water content fw, the daily water injection volume Qw, the effective thickness of the oil layer h, etc.;

[0076] 6) The dynamic fracture parameters are constrained by using the well spacing and row spacing of the target block, and then the dynamic fractures of water injection are simulated under different water injection rates based on the coupled fracture network model of hydraulic fractures and natural fractures to obtain the simulated dynamic fracture parameters of water injection;

[0077] The specific steps are as follows: in the coupled fracture network model of hydraulic fractures and natural fractures established in step 4), the well spacing L and the row spacing W are set to be greater than half of the dynamic fracture length (dynamic fracture half-length), and the dynamic fracture half-length is constrained to prevent the oil well from being flooded after the dynamic fracture half-length is greater than the well row spacing, and the dynamic fracture parameters are simulated under different water injection conditions based on the coupled fracture network model of hydraulic fractures and natural fractures.

[0078] 7) Simulate dynamic fracture parameters and determine reasonable dynamic fracture parameters by combining the production and water content changes of the corresponding production well group;

[0079] Based on the dynamic fracture length and dynamic fracture conductivity in the simulated dynamic fracture parameters, the simulated dynamic fracture extension velocity change is obtained; based on the water content change of the corresponding production well group, the water content increase rate of the corresponding production well group is obtained;

[0080] Obtain the curve of change of injection volume and simulated dynamic fracture extension speed, the curve of change of simulated dynamic fracture under different injection volumes, and the curve of change of injection volume and corresponding water content of production wells;

[0081] Reasonable dynamic fracture parameters are determined based on the above curves and the daily oil production level in the production of the corresponding production well group under different water injection rates and the water cut increase rate of the corresponding production well group.

[0082] The specific steps are as follows: draw the curve of water injection volume and simulated dynamic fracture extension speed change, the simulated dynamic fracture change curve under different water injection volumes, and the water injection volume and corresponding production well water content change curve; when the daily oil production level in the corresponding production well group is relatively high and the corresponding production well group water content increase rate is relatively low, obtain the simulated reasonable dynamic fracture parameters, namely, the reasonable dynamic fracture length and the reasonable dynamic fracture conductivity.

[0083] Preferably, in step 7), when there is an obvious inflection point in the curves of the change in water injection volume and the simulated dynamic fracture extension speed, it indicates that the fracture extension speed is too fast, there is a risk of water breakthrough, and the corresponding water injection volume is too large.

[0084] There are differences in the size and change rate of dynamic fracture parameters under different water injection schemes. The water injection volume and the corresponding water content change curve of the production well show that when the water injection volume is small, the water content is low but the daily oil production level is also low. When the water injection volume increases, the daily oil production level continues to increase, and the water content increase rate also increases accordingly. However, when there is an obvious inflection point between the water injection volume and the water content increase rate, the water content increase rate is too large, and there is a risk of water breakthrough. The reasonable water injection volume should be controlled within the water injection volume range corresponding to two adjacent inflection points.

[0085] 8) Determine the reasonable water injection intensity of the mine based on the simulated reasonable dynamic fracture parameters;

[0086] The specific steps are as follows: Based on the water injection volume corresponding to the reasonable dynamic fracture length and the reasonable fracture conductivity in step 7), the reasonable water injection intensity is determined by using the following formula:

[0087]

[0088] In the above formula, Q w is the daily water injection volume, in m 3 / d; h is the effective thickness of the oil layer, in m; q w Reasonable water injection intensity for the mine.

[0089] 9) When the oil reservoir production reaches a certain stage, the actual dynamic fracture parameters of the mine are interpreted using the pressure measurement data, and the water injection policy is adjusted based on the simulated reasonable dynamic fracture parameters and the reasonable water injection intensity of the mine to complete the optimization of the water injection policy.

[0090] When the actual dynamic fracture parameters of the mine are greater than the reasonable dynamic fracture parameters simulated, small water injection adjustment and profile adjustment and flooding control the fracture extension;

[0091] When the actual dynamic fracture extension speed of the mine is too fast, periodic water injection or normal water injection adjustment;

[0092] When the actual dynamic fracture parameters of the mine are less than the reasonable dynamic fracture parameters simulated, and the water injection energy supplement is not obvious, the water injection is strengthened to gradually extend the dynamic fractures.

[0093] The specific steps are as follows: According to the reasonable dynamic crack length L determined in step 7) and step 8), f and fracture conductivity k f And reasonable water injection intensity qw as the standard to optimize the water injection policy:

[0094] ① When the actual dynamic fracture parameters of the mine are too large, small water injection adjustments and profile adjustment and drive adjustment are used to control fracture extension; ② When the actual dynamic fracture extension speed of the mine is too fast, periodic water injection and normal water injection adjustments are performed; ③ When the actual dynamic fracture parameters of the mine are too small and the water injection energy supplement is not obvious, water injection is strengthened to gradually extend the dynamic fractures.

[0095] Example

[0096] This embodiment provides a method for optimizing water injection policy based on dynamic fracture identification, comprising the following steps:

[0097] 1) Collect dynamic and static data, and clarify the main controlling factors of fractures in combination with geological structure and sedimentary background;

[0098] The X reservoir of Baibao Oilfield was selected to collect coring data, imaging logging data, downhole microseismic data, well test data, water drive front data, and water absorption indication curve data. The reservoir belongs to underwater distributary channel deposits. The study area is located in the slope belt of northern Shaanxi, with low tectonic activity and undeveloped faults and folds in the area. Under the action of the paleo-tectonic stress field, there are mainly EW-oriented and SN-oriented fractures formed in the Yanshan period and NE-oriented fractures formed in the Himalayan period in the basin. The maximum horizontal principal stress orientation of the current tectonic stress field is NE-oriented, so that the NE-oriented fractures have a high degree of opening and become efficient diversion fractures because they are parallel to the maximum horizontal principal stress orientation; secondly, the artificial fractures formed by fracturing transformation are distributed according to the maximum horizontal principal stress orientation, that is, NE-oriented, and communicate with the original natural fracture system, making the NE-oriented fractures more active during water injection.

[0099] 2) Determine the distribution pattern of natural fractures and the parameters of hydraulic fractures;

[0100] According to various data such as imaging logging and core observation, the main trend of natural fractures in this area is between 60°-75° northeast, with a length of about 30-60m, a fracture opening of 0.003mm, and 4 fractures. The main trend of hydraulic fractures is between 60°-75° northeast, with a fracture length of 110m-200m, an average of 160m, a fracture opening of 0.8mm, and 21 fractures.

[0101] 3) Establishment of dynamic fracture model for water injection in low permeability reservoirs

[0102] Considering the additional pressure drop between the fracture and the formation, and the additional pressure drop between the fracture and the wellbore, the model assumes that the reservoir is homogeneous, of equal thickness, and infinite, and the dynamic fractures of water injection are symmetrical along the wellbore. The closure of the dynamic fractures during the shut-in and pressure measurement stage will cause changes in the fracture length and fracture conductivity. The dynamic fracture length L f and dynamic fracture conductivity k f It is determined according to formula (1) and formula (2):

[0103] Among them, L f is the dimensionless dynamic crack length, L f Half of the crack half length is the value to be solved, L f0 is the initial length of the dimensionless crack 2, P 0 wD is the dimensionless bottom hole pressure at the initial closure of the fracture3, P wD is the dimensionless bottom hole pressure when the fracture is closed, θ is the fracture half-length change factor, and k is 6. f is the dimensionless fracture conductivity coefficient of 0.5, k f0 is the initial conductivity of dimensionless fracture 2, α is the stress sensitivity coefficient of low permeability reservoir 0.003, P 0 w is the bottom hole pressure when the fracture is initially closed3, P w is the bottom hole pressure when the fracture is closed.

[0104] 4) Using the discrete fracture method, a coupled fracture network model of hydraulic fractures and natural fractures is established;

[0105] The discrete fracture model is established using the Comsol simulation software. Considering the low permeability of the ultra-low permeability oil reservoir, a nonlinear seepage mathematical model is introduced to describe the seepage law. The modeling process is as follows: according to the established mathematical model, the spatial dimension, material property, physical field, and solution type are selected in turn; the geometric shapes provided by the software are used to establish the discrete model to be studied under the action of Boolean operations to characterize the morphology of natural fractures, hydraulic fractures, and water injection dynamic fractures. The partial differential equations of water injection dynamic fractures as well as boundary conditions and initial conditions are input into the software; grid division and refinement are performed; and reasonable fracture parameters are obtained after solving.

[0106] 5) Collect dynamic and static production data of the target block (number of oil and water wells, daily liquid production of a single well, daily oil production of a single well, water content, daily water injection, effective thickness of oil layer, etc.)

[0107] 233 oil wells, 94 water wells, daily liquid production per well q = 1.95t / d, daily oil production per well qo = 0.67t / d, water content fw = 65.5%, daily water injection Qw = 11.3m 3 / d, effective thickness of oil layer h=9.7m, etc.

[0108] 6) Use the well spacing to constrain the dynamic fracture parameters, and simulate the dynamic fracture parameters under different water injection rates based on the coupling model

[0109] The well spacing in this block is L = 520m, and the row spacing is W = 130m. In the model, the length of the dynamic fracture for water injection is set to be smaller than the well spacing and row spacing. A discrete fracture coupling model is established using basic data, and three water injection schemes are designed respectively. Scheme 1 has a water injection volume of 5m 3 / d, Scheme 2 water injection volume 10m 3 / d, Scheme 3 water injection volume 20m 3 / d, based on the model, the dynamic fracture extension parameters of water injection under different injection schemes are simulated respectively. Figure 2 There is a water injection well in the rectangular oil reservoir. The white lines are the discrete fracture morphology at a certain moment, representing the location, length, and direction of the discrete fractures.

[0110] 7) Determine the reasonable dynamic fracture parameters of the simulation based on the production and water content changes of the corresponding production well groups under different water injection rates;

[0111] like Figures 3 to 7 As shown in the figure, the water injection volume and the simulated dynamic fracture extension velocity curve show that the water injection volume is 15m 3 / d, the slope of the crack extension speed becomes larger and an inflection point appears, indicating that there is a risk of water breakthrough at the corresponding water injection volume. 3 / d, 10m 3 / d, 20m 3 / d, there are differences in the dynamic fracture parameters and change rates of water injection. As the water injection volume increases, the extension rate of the fracture half-length increases. Therefore, the water injection volume of Scheme 3 is 20m 3 / d corresponds to the fastest half-length extension of the dynamic fracture, and the water injection volume should be maintained at 20m 3 / d, the water injection volume and the corresponding production well water content change curve show that: water injection volume 8m 3 / d or less, the water content is controlled within 20%, but the daily oil production level is 1.3t. When the water injection volume increases to 8-15m 3 / d, the daily oil production level remained at 2.1t, the water content increased, and the water content remained within 40%. When the water injection volume was 15m 3 / d, the curve has an obvious inflection point, the daily oil production level is maintained at 0.9t, the water cut rise rate is too large, there is a risk of water breakthrough, and the reasonable water injection volume should be controlled at 8-15m 3 / d range, combined with the production and water content change curves of the corresponding production well groups under different water injection schemes, the simulated reasonable water injection dynamic fracture half-length range is 75-90m.

[0112] 8) Determine the reasonable water injection intensity of the mine based on the simulated reasonable dynamic fracture parameters;

[0113] The above steps determine the reasonable water injection volume of 8-15m 3 / d, the effective thickness of the oil layer is 12m, and the reasonable water injection intensity is calculated to be 0.7-1.3m 3 / dm.

[0114] 9) Propose methods to optimize injection-production policies.

[0115] like Figure 8 As shown, based on the reasonable dynamic fracture half-length of 75-90m and the reasonable water injection intensity of 0.7-1.3m 3 / dm, for the uneven water absorption of the early section of the typical well group, the water injection intensity of the lower section is 2.7m 3 / dm, combined with reasonable fracture parameters, implementation of split injection + injection optimization, the lower section water injection intensity of 1.2m 3 / dm, the fracture half-length was controlled to 75.9m, and the monthly rate of the well group decreased by 1.1↓0.52%.

[0116] The present invention provides a method for optimizing water injection policy based on dynamic fracture identification. A numerical model of reasonable parameters of dynamic fractures of water injection is established on the basis of fully understanding fracture characteristics, providing a theoretical basis for injection and production policies of such oil reservoirs. The dynamic fractures of water injection are fully utilized to increase the scope of water drive while avoiding water channeling of injected water along high permeability channels leading to high water content in oil wells, thereby improving water drive efficiency, maintaining formation pressure, and effectively improving the development effect of such oil reservoirs.

[0117] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A water injection policy optimization method based on dynamic fracture identification, characterized in that: The following steps are involved: Using the discrete fracture method, a coupled fracture network model of hydraulic fractures and natural fractures is established based on natural fracture parameters and hydraulic fracture parameters; a dynamic fracture model of water injection in low permeability reservoirs is established based on the water injection dynamic fracture formula, and dynamic fracture parameters are obtained by combining the dynamic fracture model of water injection in low permeability reservoirs; Obtain production dynamic data and static data of the target block, use the well spacing and row spacing of the target block to constrain the dynamic fracture parameters, and then simulate the water injection dynamic fractures under different water injection rates based on the fracture network model of hydraulic fractures and natural fractures to obtain the simulated dynamic fracture parameters; When the target block is developed to the target stage, the actual dynamic fracture parameters of the mine are obtained by interpreting the pressure measurement data. The dynamic fracture parameters are simulated and combined with the production of the corresponding production well group and the water content change of the corresponding production well group to determine the reasonable dynamic fracture parameters of the simulation; The reasonable water injection intensity of the mine is determined based on the water injection volume corresponding to the simulated reasonable dynamic fracture parameters. The water injection policy is adjusted based on the simulated reasonable dynamic fracture parameters, the reasonable water injection intensity of the mine and the actual dynamic fracture parameters of the mine to complete the water injection policy optimization.

2. The water injection policy optimization method based on dynamic seam identification according to claim 1 is characterized in that: The process of obtaining the natural fracture parameters and the hydraulic fracture parameters is as follows: Collect dynamic and static data, combine geological structure and sedimentary background to identify the main controlling factors of fractures, and obtain natural fracture parameters and hydraulic fracture parameters; The natural fracture parameters include: the position of the natural fracture, the fracture direction of the natural fracture, the fracture half-length of the natural fracture, the fracture opening of the natural fracture, the fracture height of the natural fracture and the number of fractures of the natural fracture; The hydraulic fracture parameters include: the location of the hydraulic fracture, the fracture direction of the hydraulic fracture, the fracture half-length of the hydraulic fracture, the fracture aperture of the hydraulic fracture, the fracture height of the hydraulic fracture and the number of fractures of the hydraulic fracture.

3. The water injection policy optimization method based on dynamic seam identification according to claim 1 is characterized in that: The process of establishing a low permeability reservoir water injection dynamic fracture model is as follows: Based on the parameters of natural fractures and hydraulic fractures, as well as the additional pressure drop at the contact surface between the fracture and the formation and the additional pressure drop between the fracture and the wellbore, the water injection dynamic fracture formula is obtained under the set conditions that the model reservoir is homogeneous, of equal thickness and infinite size, the water injection dynamic fracture is symmetrical along the wellbore, and the closure of the dynamic fracture during the shut-in and pressure measurement stage will cause changes in the dynamic fracture length and the dynamic fracture conductivity, and the water injection dynamic fracture model of low permeability oil reservoirs is established.

4. The water injection policy optimization method based on dynamic seam identification according to claim 3 is characterized in that: The water injection dynamic fracture formula includes a formula for dynamic fracture length and a formula for dynamic fracture conductivity; The formula of dimensionless dynamic crack length in the dynamic crack length is as follows: The formula of the dimensionless dynamic fracture conductivity in the dynamic fracture conductivity is as follows: In the above formula, L f is the dimensionless dynamic crack length; L f0 is the initial length of the dimensionless crack; P 0 wD is the dimensionless bottom hole pressure when the fracture is initially closed; P wD is the dimensionless bottom hole pressure when the fracture is closed; θ is the fracture half-length variation factor; k f is the dimensionless dynamic fracture conductivity; k f0 is the initial conductivity of dimensionless fracture; α is the stress sensitivity coefficient of low permeability reservoir; P 0 w is the bottom hole pressure when the fracture is initially closed; P w is the bottom hole pressure when the fracture is closed.

5. The water injection policy optimization method based on dynamic seam identification according to claim 1 is characterized in that: The production dynamic data and static data of the target block include the number of oil wells, the number of water wells, daily liquid production, daily oil production level, water content, daily water injection volume and effective thickness of the oil layer.

6. The water injection policy optimization method based on dynamic seam identification according to claim 1 is characterized in that: The process of constraining the dynamic fracture parameters by using the well spacing of the target block is as follows: In the coupled fracture network model of hydraulic fractures and natural fractures, the well spacing and row spacing are set to be greater than half of the dynamic fracture length in the dynamic fracture parameters to constrain the dynamic fracture length.

7. The water injection policy optimization method based on dynamic seam identification according to claim 1 is characterized in that: The process of determining the simulated reasonable dynamic fracture parameters by combining the simulated dynamic fracture parameters with the production of the corresponding production well group and the water content change of the corresponding production well group is as follows: Based on the dynamic fracture length and dynamic fracture conductivity in the simulated dynamic fracture parameters, the simulated dynamic fracture extension velocity change is obtained; based on the water content change of the corresponding production well group, the water content increase rate of the corresponding production well group is obtained; Obtain the curve of change of injection volume and simulated dynamic fracture extension speed, the curve of change of simulated dynamic fracture under different injection volumes, and the curve of change of injection volume and corresponding water content of production wells; Reasonable dynamic fracture parameters of the simulation are determined based on the above curves and the daily oil production level in the production of the corresponding production well group under different water injection rates and the water cut increase rate of the corresponding production well group.

8. The water injection policy optimization method based on dynamic seam identification according to claim 7 is characterized in that: When there is an obvious inflection point in the curve of the change of the water injection volume and the simulated dynamic fracture extension speed, it indicates that the dynamic fracture extension speed is too fast, there is a risk of water breakthrough, and the corresponding water injection volume is too large.

9. The method for optimizing water injection policy based on dynamic seam identification according to claim 1, characterized in that: The process of determining the appropriate water injection intensity for a mine is as follows: In the above formula, Q w is the daily water injection volume, in m 3 / d; h is the effective thickness of the oil layer, in m; q w Reasonable water injection intensity for the mine.

10. The water injection policy optimization method based on dynamic seam identification according to claim 8, characterized in that: The process of adjusting the water injection policy based on the simulated reasonable dynamic fracture parameters, the reasonable water injection intensity of the mine and the actual dynamic fracture parameters of the mine is as follows: When the actual dynamic fracture parameters of the mine are greater than the reasonable dynamic fracture parameters simulated, small water injection adjustment and profile adjustment and flooding control the fracture extension; When the actual dynamic fracture extension speed of the mine is too fast, periodic water injection or normal water injection adjustment; When the actual dynamic fracture parameters of the mine are less than the reasonable dynamic fracture parameters simulated, and the water injection energy supplement is not obvious, the water injection is strengthened to gradually extend the dynamic fractures.

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