A method for acid absorption profile prediction for fractured reservoirs of long well sections

Abstract

The application discloses a method for predicting an acid absorption profile of a fractured reservoir of a long well section, comprising the following steps: establishing a geological model of a to-be-predicted reservoir, obtaining reservoir acid liquid pressure and reservoir parameters of a previous time step, obtaining reservoir acid liquid pressure of a current time step, obtaining wellbore acid liquid pressure of the previous time step, obtaining wellbore acid liquid pressure of the current time step, and then obtaining a first flow rate of acid liquid flowing from the wellbore into the reservoir and a second flow rate of acid liquid in the wellbore; determining a concentration distribution of the acid liquid in the wellbore according to the second flow rate, obtaining an initial reservoir acid absorption profile of the current time step; determining an acid-etched wormhole length of a wellbore wall surface according to the concentration distribution, predicting matrix permeability, obtaining a width of a fracture after corrosion in the reservoir of the current time step, predicting fracture permeability, and then updating reservoir parameters of a next time step and the initial reservoir acid absorption profile by using the predicted permeability.

Description

Technical Field

[0001] The invention belongs to the field of petroleum engineering, and in particular relates to a method for predicting an acid absorption profile of a fractured reservoir in a long well section. Background Art

[0002] Fractured carbonate gas reservoirs are the primary focus of current and future natural gas development in China, and acidizing is one of the primary means of achieving efficient development of these reservoirs. With advances in exploration and development, long horizontal wells have become a key well type for developing these reservoirs. Limited by existing tools and wellbore conditions, running packers in long horizontal well sections is challenging, and the acidizing treatment section lengths are significantly longer than those in vertical wells (≥300 m, with a maximum of 1000 m). To predict the effectiveness of long horizontal well treatment sections, it is necessary to predict the acid absorption profile of the horizontal well during the acidizing process, thereby guiding the design and optimization of long horizontal well acidizing operations.

[0003] Nowadays, the optimization design of construction parameters relies on acidizing models. In the process of realizing the present invention, the inventors found that the existing technology has constructed relatively complete numerical models for the physical and chemical processes of horizontal well acidizing. However, most of these models are numerical models that couple the dual-scale wormhole expansion model. The solution is relatively complex and time-consuming, and it is difficult to consider the acid flow reaction process under the conditions of large natural fractures. However, the development of natural fracture systems is an important feature of fractured carbonate reservoirs. The fracture system is the main channel for acid flow, and its flow mechanism is different from that of acid flow in the matrix. Based on this, there is currently a lack of direct and simple methods to calculate the acid injection parameters for acidizing fractured carbonate rocks in long horizontal wells, making it difficult to provide a basis for the design and construction optimization of long horizontal well acidizing by calculating the acid injection parameters. Summary of the Invention

[0004] To address the above-mentioned problems, the present invention proposes a method for predicting an acid absorption profile of a fractured reservoir in a long well section, comprising: establishing a geological model of the reservoir to be predicted; using the geological model to obtain the reservoir acid pressure and reservoir parameters at the previous time step, and obtaining the reservoir acid pressure at the current time step by analyzing the reservoir acid distribution at the end of the previous time step; and obtaining the wellbore acid pressure at the previous time step, and obtaining the wellbore acid pressure at the current time step by analyzing the wellbore acid distribution at the end of the previous time step, thereby obtaining a first flow rate of acid flowing from the wellbore into the reservoir at the current time step and a second flow rate of acid in the wellbore; determining the concentration distribution of acid in the wellbore based on the second flow rate to obtain an initial reservoir acid absorption profile for the current time step; determining the length of acid-etched wormholes on the wellbore wall based on the concentration distribution to predict matrix permeability; and obtaining the width of fractures in the reservoir after dissolution in the current time step to predict fracture permeability. The predicted permeabilities are then used to update the reservoir parameters for the next time step and the initial reservoir acid absorption profile.

[0005] Preferably, the step of establishing a geological model of the reservoir to be predicted includes: assigning values ​​to the geological model according to actual characteristic parameters of the reservoir to be predicted, and dividing the geological model into a plurality of grids, wherein the characteristic parameters include but are not limited to: reservoir porosity, permeability and formation pressure.

[0006] Preferably, the reservoir acid distribution at the end of the previous time step is calculated using the following expression:

[0007]

[0008] Where ρ represents the density of the acid solution, k x 、k y represents the average permeability in the x and y directions of each grid in the previous time step, P represents the acid pressure in each grid in the previous time step, μ represents the acid viscosity, φ represents the average porosity in each grid, and c l represents the acid fluid compression coefficient, t represents the acid injection time, and x and y represent the horizontal and vertical coordinates of the acid fluid distribution position in the reservoir, respectively.

[0009] Preferably, the step of obtaining the first flow rate of acid fluid flowing from the wellbore into the reservoir includes: utilizing the pressure difference between the reservoir acid fluid pressure and the wellbore acid fluid pressure on both sides of the overlapping edge of each grid and the edge of the wellbore to obtain the flow rate of acid fluid flowing from the wellbore into the reservoir corresponding to the corresponding grid, and obtaining the first flow rate by accumulating the inflow flow rate of each grid.

[0010] Preferably, the first flow rate is calculated using the following expression:

[0011]

[0012]

[0013] Among them, i represents the sequence number of the grid distributed along the edge of the wellbore, m represents the number of grids distributed along the edge of the wellbore, Q out，i represents the flow rate of acid fluid flowing from the wellbore into the reservoir corresponding to the i-th grid, △x and △y represent the length of the matrix grid in the x and y directions in the grid distributed along the edge of the wellbore, respectively, and P well，i Indicates the wellbore acid pressure corresponding to the i-th grid, P r，i represents the reservoir acid pressure corresponding to the i-th grid, k y，i represents the permeability of the i-th grid along the y direction, Q out Indicates the first flow.

[0014] Preferably, the step of obtaining the second flow rate of the acid liquid in the wellbore includes: dividing the wellbore into two parts along a direction perpendicular to the wellbore axis and passing through the acid inlet, and using one part as the upstream of the acid injection and the other part as the downstream of the acid injection, wherein the acid inlet is located inside the wellbore; using the flow rate of the acid liquid corresponding to the grids distributed along the upstream and downstream directions of the acid injection into the reservoir from the wellbore, the flow rate of the acid liquid in the wellbore upstream and downstream of the acid injection is obtained, and the sum of the flow rate of the acid liquid in the upstream wellbore and the flow rate of the acid liquid in the downstream wellbore is used as the second flow rate.

[0015] Preferably, the step of determining the concentration distribution of the acid liquid in the wellbore includes: using the acid liquid flow rate in the upstream wellbore and the acid liquid flow rate in the downstream wellbore to respectively calculate the first flow velocity and the second flow velocity of the acid liquid in the wellbore, and based on this, obtain the flow velocity of the acid liquid in the wellbore; using the first flow rate to calculate the flow velocity of the acid liquid flowing from the wellbore into the reservoir; and determining the concentration distribution of the acid liquid in the wellbore by analyzing the correlation between the combination of the flow velocity of the acid liquid in the wellbore and the flow velocity of the acid liquid flowing from the wellbore into the reservoir and the concentration distribution of the acid liquid in the wellbore.

[0016] Preferably, the concentration distribution of the acid solution in the wellbore is determined using the following expression:

[0017]

[0018] Where D is the diameter of the wellbore, C is the acid concentration in the wellbore, t is the acid injection time, u x Indicates the flow velocity of the acid in the wellbore, v l represents the flow rate of acid fluid from the wellbore into the reservoir, k c represents the equilibrium constant.

[0019] Preferably, the step of determining the length of the acid-etched wormholes on the wellbore wall according to the concentration distribution includes: obtaining the average filtration rate of the acid in the wellbore at the current time step according to the acid viscosity, and further calculating the expansion rate of the acid-etched wormholes extending from the wellbore wall in combination with the acid concentration distribution, thereby determining the length of the acid-etched wormholes at the next time step.

[0020] Preferably, the matrix permeability includes a first matrix permeability in a non-wormhole tip region in the wormhole region of the reservoir and a second matrix permeability in a region where the wormhole tip is located.

[0021] Preferably, the step of obtaining the width of the fracture after dissolution in the reservoir at the current time step includes: using the acid injection volume to calculate the rock dissolution volume in the reservoir, and then using the correlation between the rock dissolution volume, reservoir thickness and fracture size to obtain the dissolution width of the current fracture, based on which the width of the fracture after dissolution is obtained.

[0022] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0023] The present invention provides a method for predicting acid absorption profiles in fractured reservoirs for long well sections. This method establishes a geological model of the reservoir to be predicted, rapidly simulates the flow process of acid in the wellbore based on the law of conservation of matter, and uses natural fractures as flow channels for the acid during the acidizing process to obtain the reservoir acid pressure and reservoir parameters at the previous time step to obtain the reservoir acid pressure at the current time step. Simultaneously, the wellbore acid pressure at the previous time step is obtained to obtain the wellbore acid pressure at the current time step, thereby obtaining a first flow rate of acid flowing from the wellbore into the reservoir and a second flow rate of acid in the wellbore at the current time step. Subsequently, based on the second flow rate, the concentration distribution of the acid in the wellbore is determined to obtain the initial reservoir acid absorption profile for the current time step. Finally, the initial reservoir acid absorption profile is updated in real time by taking into account the changes in crack width caused by acid on the walls of natural fractures, as well as the growth state of acid-etched wormholes on the wellbore wall and the impact of the growth process on matrix permeability during the acidizing process. The present invention realizes the rapid calculation of the acid absorption profile of the fixed-point diversion acidizing of the fractured reservoir in a long well section, and can directly and simply calculate the acid injection parameters of the fractured carbonate rock acidizing in the long horizontal well.

[0024] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained through the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 This is a step diagram of a method for predicting an acid absorption profile of a fractured reservoir in a long well section according to an embodiment of the present application.

[0027] Figure 2 It is a schematic diagram of a geological model of a method for predicting an acid absorption profile of a fractured reservoir in a long well section according to an embodiment of the present application.

[0028] Figure 3 It is a schematic diagram of reservoir acid pressure distribution in the acid absorption profile prediction method for a fractured reservoir in a long well section according to an embodiment of the present application.

[0029] Figure 4 This is a schematic diagram of the acid fluid flow rate distribution in the wellbore of the acid absorption profile prediction method for a fractured reservoir in a long well section according to an embodiment of the present application.

[0030] Figure 5 This is a schematic diagram of the acid concentration distribution in the wellbore of the acid absorption profile prediction method for a fractured reservoir in a long well section according to an embodiment of the present application.

[0031] Figure 6 It is a schematic diagram of the acid absorption profile distribution of the acid absorption profile prediction method for a fractured reservoir in a long well section according to an embodiment of the present application.

[0032] Figure 7 This is a schematic diagram of the correlation between the acid fluid discharge rate and the acid fluid pressure in the wellbore in the acid absorption profile prediction method for a fractured reservoir in a long well section according to an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings and examples, so that the present invention can fully understand how to apply technical means to solve technical problems and achieve technical effects, and thus implement the invention accordingly. It should be noted that, as long as no conflict exists, the various embodiments of the present invention and the various features of the embodiments can be combined with each other, and the resulting technical solutions are all within the scope of protection of the present invention.

[0034] Additionally, the steps shown in the flowcharts of the accompanying drawings may be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowcharts, in some cases the steps shown or described may be performed in an order different from that shown.

[0035] Fractured carbonate gas reservoirs are the primary focus of current and future natural gas development in China, and acidizing is one of the primary means of achieving efficient development of these reservoirs. With advances in exploration and development, long horizontal wells have become a key well type for developing these reservoirs. Limited by existing tools and wellbore conditions, running packers in long horizontal well sections is challenging, and the acidizing treatment section lengths are significantly longer than those in vertical wells (≥300 m, with a maximum of 1000 m). To predict the effectiveness of long horizontal well treatment sections, it is necessary to predict the acid absorption profile of the horizontal well during the acidizing process, thereby guiding the design and optimization of long horizontal well acidizing operations.

[0036] Nowadays, the construction parameter optimization design relies on the acidification model, in the process of implementing the present application, the inventors find that the prior art has constructed a relatively complete numerical model for the physical and chemical process of horizontal well acidification. However, such a model is mostly a numerical model coupled with a double-scale wormhole propagation model, which is relatively complex to solve and time-consuming, and it is difficult to consider the acid liquid flow reaction process under the condition that large natural fractures exist. However, the development of a natural fracture system is an important feature of a fractured carbonate reservoir, and the fracture system is the main channel for acid liquid flow, and its flow mechanism is different from that of acid liquid in the matrix. Accordingly, there is currently a lack of a direct and simple method for calculating the acid injection parameters of a long horizontal well fractured carbonate reservoir, and it is difficult to provide a basis for long horizontal well acidification design and construction optimization through the calculation of acid injection parameters.

[0037] Therefore, in order to solve the above problems, the present application provides a method for predicting the acid absorption profile of a fractured reservoir in a long well section. The method establishes a geological model of the reservoir to be predicted, quickly simulates the flow process of acid liquid in the wellbore based on the conservation of mass, and obtains the reservoir acid liquid pressure and reservoir parameters at the previous time step by taking the natural fractures as the flow channel of the acid liquid in the acidification process, to obtain the reservoir acid liquid pressure at the current time step, and obtains the wellbore acid liquid pressure at the previous time step to obtain the wellbore acid liquid pressure at the current time step, and then obtains the first flow rate of acid liquid flowing from the wellbore into the reservoir and the second flow rate of acid liquid in the wellbore at the current time step. Then, according to the second flow rate, the concentration distribution of the acid liquid in the wellbore is determined to obtain the initial reservoir acid absorption profile at the current time step. Finally, the initial reservoir acid absorption profile is updated in real time by considering the change of the acid liquid in the natural fracture wall to change the fracture width, and considering the influence of the acid erosion wormhole growth state and growth process of the wellbore wall in the acidification process on the matrix permeability. The present application realizes the rapid calculation of the fixed-point diversion acid absorption profile of the fractured reservoir in the long well section, and can directly and simply calculate the acid injection parameters of the long horizontal well fractured carbonate reservoir.

[0038] Figure 1 is a step diagram of the method for predicting the acid absorption profile of a fractured reservoir in a long well section according to the present application. The steps of the method will be described below with reference to Figure 1 .

[0039] As shown in Figure 1 , in step S110, a geological model of the reservoir to be predicted is established. Specifically, the present embodiment obtains the actual reservoir characteristic parameters of the current reservoir to be predicted based on logging interpretation and laboratory experiments. Then, the reservoir geological model in the fixed-point diversion acidification well section as shown in Figure 2 is established using the reservoir characteristic parameters. Figure 2 is a geological model schematic diagram of the method for predicting the acid absorption profile of a fractured reservoir in a long well section according to the present application.

[0040] In the step of establishing a geological model of the reservoir to be predicted, values ​​are assigned to the geological model according to actual characteristic parameters of the reservoir to be predicted, and the geological model is divided into a plurality of grids. The actual reservoir characteristic parameters of the reservoir to be predicted are used to perform non-uniform assignment of values ​​to the geological model according to actual conditions, and the geological model is divided into m groups of grids along the extension direction of the well section. The characteristic parameters include, but are not limited to, reservoir porosity, permeability, and formation pressure.

[0041] In a specific embodiment of the present application, the actual reservoir characteristic parameters of the reservoir to be predicted are shown in Table 1:

[0042] Table 1 Actual reservoir characteristic parameters of the reservoir to be predicted

[0043] parameter Value parameter Value Well diameter 0.16m Acid compressibility <![CDATA[5×10 -5 Pa-1]]> formation pressure 65MPa Natural crack width 300μm Formation fracture pressure 110MPa Type I reservoir permeability 10mD Type II reservoir permeability 5mD Class III reservoir permeability 1mD Class IV reservoir permeability 0.01mD Type I reservoir porosity 10％ Type II reservoir porosity 5％ Type III reservoir porosity 3％ Type IV reservoir porosity 2％ Wellbore diameter 0.15m

[0044] In step S120, the geological model is used to obtain the reservoir acid pressure and reservoir parameters of the previous time step, and the reservoir acid pressure of the current time step is obtained by analyzing the reservoir acid distribution at the end of the previous time step, and the wellbore acid pressure of the previous time step is obtained, and the wellbore acid pressure of the current time step is obtained by analyzing the wellbore acid distribution at the end of the previous time step, thereby obtaining the first flow rate of the acid flowing from the wellbore into the reservoir and the second flow rate of the acid in the wellbore in the current time step.

[0045] Specifically, the geological model established in step S110 is used to simulate the dynamic acid injection process of the horizontal well (i.e., simulate the flow of acid in the reservoir to be predicted and the dynamic changes of the reservoir with the flow of acid). The dynamic acid injection process of the horizontal well is timed, and then the duration of the dynamic acid injection process of the horizontal well is divided into several consecutive time steps. Then, based on the simulation results, the reservoir acid pressure and reservoir parameters of the previous time step are obtained to analyze the relationship between the corresponding reservoir acid pressure and reservoir parameters and time, so as to obtain the reservoir acid distribution at the end of the previous time step. Finally, the reservoir acid distribution at the end of the previous time step is used as the initial reservoir acid distribution at the beginning of the current time step to obtain the following: Figure 3 The reservoir acid pressure at the current time step is shown ( Figure 3 Schematic diagram of reservoir acid fluid pressure distribution for an acid absorption profile prediction method for a fractured reservoir with a long well section according to an embodiment of the present application. In the embodiment of the present application, the reservoir acid fluid pressure includes the acid fluid pressure in the reservoir matrix and the acid fluid pressure in the natural fractures within the reservoir.

[0046] Next, while obtaining the reservoir acid distribution at the end of the previous time step based on the simulation results, this embodiment also obtains the wellbore acid pressure at the previous time step. This analysis is used to obtain the corresponding relationship between the wellbore acid pressure and time, thereby obtaining the wellbore acid distribution at the end of the previous time step. The wellbore acid distribution at the end of the previous time step is then used as the wellbore acid distribution at the beginning of the current time step to obtain the wellbore acid pressure at the current time step.

[0047] Finally, based on the principle of conservation of mass, the acid is considered to be slightly compressible. At this point, only when the acid can flow into the reservoir through the wellbore will the acid in the wellbore flow to the corresponding position in the wellbore; conversely, if the acid cannot flow into the reservoir from the wellbore, the acid will be unable to be injected into the wellbore due to pressure buildup. Therefore, in this embodiment of the application, the reservoir acid pressure and the wellbore acid pressure at the current time step are used to calculate the first flow rate of the acid flowing from the wellbore into the reservoir at the current time step, as well as the second flow rate of the acid in the wellbore.

[0048] In the embodiment of the present application, the following expression is used to calculate the reservoir acid distribution at the end of the previous time step:

[0049]

[0050] Where ρ represents the density of the acid solution, k x 、k y represents the average permeability in the x and y directions of each grid in the previous time step, P represents the acid pressure in each grid in the previous time step, μ represents the acid viscosity, φ represents the average porosity in each grid, and c l represents the acid fluid compression coefficient, t represents the acid injection time, and x and y represent the horizontal and vertical coordinates of the acid fluid distribution position in the reservoir, respectively.

[0051] Next, the embodiment of the present application uses the following expression to calculate the permeability of the grid position corresponding to the natural fracture in the reservoir in the reservoir parameters to calculate the corresponding reservoir acid pressure:

[0052]

[0053] Among them, k nf represents the permeability of fractures in the reservoir, w nf Indicates the width of the fracture in the reservoir.

[0054] In the step of obtaining the first flow rate of acid fluid flowing from the wellbore into the reservoir, the pressure difference between the reservoir acid fluid pressure and the wellbore acid fluid pressure on both sides of the overlapping edge of each grid and the wellbore edge is used to obtain the flow rate of acid fluid flowing from the wellbore into the reservoir corresponding to the corresponding grid, and the first flow rate is obtained by accumulating the inflow flow rate of each grid. In an embodiment of the present application, the grids with overlapping edges with the wellbore edge are determined in the geological model. Then, the pressure difference between the reservoir acid fluid pressure and the wellbore acid fluid pressure on both sides of the overlapping edge of each grid and the wellbore edge is calculated for these grids. Then, the pressure difference calculation result is used to further calculate the flow rate of acid fluid flowing from the wellbore into the reservoir corresponding to the corresponding grid. After obtaining the flow rate corresponding to each grid, the inflow flow rate of each grid is accumulated to obtain the first flow rate.

[0055] In the embodiment of the present application, the first flow rate is calculated using the following expression:

[0056]

[0057]

[0058] Among them, i represents the sequence number of the grid distributed along the edge of the wellbore, m represents the number of grids distributed along the edge of the wellbore, Q out，i represents the flow rate of acid fluid flowing from the wellbore into the reservoir corresponding to the i-th grid, △x and △y represent the length of the matrix grid in the x and y directions in the grid distributed along the edge of the wellbore, respectively, and P well，i Indicates the wellbore acid pressure corresponding to the i-th grid, P r，i represents the reservoir acid pressure corresponding to the i-th grid, k y，i represents the permeability of the i-th grid along the y direction, Q out Indicates the first flow.

[0059] In the step of obtaining the second flow rate of the acid solution in the wellbore, first, the wellbore is divided into two parts along a direction perpendicular to the wellbore axis and passing through the acid inlet, and one part is used as the upstream of the acid injection and the other part is used as the downstream of the acid injection, wherein the acid inlet is located inside the wellbore. Figure 2 , with the acid inlet grid position x inAs a benchmark, the wellbore is divided into two parts along the direction perpendicular to the wellbore axis and passing through the acid inlet, and any one part is used as the upstream of the acid injection, and the remaining other part is used as the downstream of the acid injection, and then the flow rate of the acid injected from the acid inlet to the upstream and downstream is calculated respectively. Then, the flow rate of the acid flowing from the wellbore into the reservoir corresponding to the grids distributed along the upstream and downstream directions of the acid injection is used to obtain the flow rate of the acid in the wellbore upstream and downstream of the acid injection, and the sum of the flow rate of the acid in the upstream wellbore and the flow rate of the acid in the downstream wellbore is used as the second flow rate. In an embodiment of the present application, the flow rate of the acid flowing from the wellbore into the reservoir corresponding to the grids having overlapping edges with the edge of the wellbore in the geological model distributed along the upstream and downstream directions of the acid injection is used to calculate the flow rate of the acid in the wellbore upstream and downstream of the acid injection. Finally, the sum of the flow rate of the acid in the upstream wellbore and the flow rate of the acid in the downstream wellbore is used as the second flow rate.

[0060] The acid flow rate in the wellbore upstream of the acid injection is calculated using the following expression:

[0061]

[0062] Among them, Q well1 represents the acid flow rate in the wellbore upstream of the acid injection, x in Indicates the location of the acid inlet grid.

[0063] The acid flow rate in the wellbore downstream of the acid injection is calculated using the following expression:

[0064]

[0065] Among them, Q well2 Indicates the acid flow rate in the wellbore downstream of the acid injection.

[0066] Furthermore, in step S130, the acid concentration distribution within the wellbore is determined based on the second flow rate to obtain an initial reservoir acid absorption profile for the current time step. In this embodiment of the present application, the acid concentration distribution within the wellbore is calculated using the second flow rate in combination with the flow velocity of the acid within the wellbore and the flow velocity of the acid into the reservoir from the wellbore. Subsequently, the acid concentration distribution within the wellbore at the current time step is further combined with the flow velocity of the acid into the reservoir from the wellbore to calculate the initial reservoir acid absorption profile for the current time step.

[0067] In the step of determining the concentration distribution of the acid liquid in the wellbore, first, the acid liquid flow rate in the upstream wellbore and the acid liquid flow rate in the downstream wellbore are used to calculate the first flow velocity and the second flow velocity of the acid liquid in the wellbore, respectively, based on which the flow velocity of the acid liquid in the wellbore is obtained; then, the flow velocity of the acid liquid flowing from the wellbore into the reservoir is calculated using the first flow rate; finally, the concentration distribution of the acid liquid in the wellbore is determined by analyzing the correlation between the combination of the flow velocity of the acid liquid in the wellbore and the flow velocity of the acid liquid flowing from the wellbore into the reservoir and the concentration distribution of the acid liquid in the wellbore.

[0068] Specifically, the first flow velocity of the acid liquid in the wellbore is calculated using the acid liquid flow rate in the upstream wellbore, wherein the first flow velocity is recorded as negative; and the second flow velocity of the acid liquid in the wellbore is calculated using the acid liquid flow rate in the downstream wellbore, wherein the second flow velocity is recorded as positive, and the flow velocity of the acid liquid in the wellbore is the sum of the first flow velocity and the second flow velocity.

[0069] In the embodiment of the present application, the flow velocity of the acid fluid in the wellbore is calculated using the following expression:

[0070]

[0071] Among them, u x Indicates the flow rate of acid in the wellbore, Q well represents the acid flow rate in the wellbore, and D represents the wellbore diameter.

[0072] Next, the flow rate of the acid solution flowing from the wellbore into the reservoir is calculated using the first flow rate. In the embodiment of the present application, the flow rate of the acid solution flowing from the wellbore into the reservoir is calculated using the following expression:

[0073]

[0074] Among them, v l Indicates the flow rate of acid from the wellbore into the reservoir.

[0075] Finally, according to the above-calculated flow velocity of the acid fluid in the wellbore and the flow velocity of the acid fluid flowing from the wellbore into the reservoir, the following equation is obtained: Figure 4 The acid flow rate distribution in the wellbore is shown as follows ( Figure 4 Schematic diagram of the acid flow rate distribution in the wellbore of the method for predicting the acid absorption profile of a fractured reservoir with a long well section according to an embodiment of the present application). Then, the correlation between the combination of the flow rate of the acid in the wellbore and the flow rate of the acid flowing from the wellbore into the reservoir and the concentration distribution of the acid in the wellbore is analyzed, and the following is obtained: Figure 5 The acid concentration distribution in the wellbore is shown in ( Figure 5 Schematic diagram of the acid concentration distribution in the wellbore of the acid absorption profile prediction method for a fractured reservoir with a long well section in an embodiment of the present application), thereby determining the concentration distribution of the acid in the wellbore.

[0076] In the embodiment of the present application, the concentration distribution of the acid solution in the wellbore is determined using the following expression:

[0077]

[0078] Where C represents the acid concentration in the wellbore, k c represents the equilibrium constant.

[0079] Next, the initial reservoir acid absorption profile at the current time step is calculated using the following expression: Figure 6 The acid absorption profile distribution shown ( Figure 6 Schematic diagram of acid absorption profile distribution of the acid absorption profile prediction method for a fractured reservoir with a long well section according to an embodiment of the present application):

[0080] R acid =Q out C (10)

[0081] Among them, R acid It represents the initial reservoir acid absorption amount, that is, the initial reservoir acid absorption profile.

[0082] Furthermore, in step S140, the length of acid-etched wormholes on the wellbore wall is determined based on the concentration distribution, thereby predicting the matrix permeability. The width of the fractures in the reservoir after dissolution at the current time step is also obtained to predict the fracture permeability. The predicted permeabilities are then used to update the reservoir parameters for the next time step and the initial reservoir acid absorption profile. Specifically, based on the acid concentration distribution in the wellbore at the current time step and taking into account the dissolution of the wellbore wall by the acid, the length of the corresponding acid-etched wormholes generated on the wellbore wall is predicted. Since acid-etched wormholes form in the matrix within the reservoir, their presence alters the matrix permeability. Therefore, by predicting the length of the acid-etched wormholes, the matrix permeability is predicted. Furthermore, the width of the fractures in the reservoir after dissolution at the current time step is obtained. Since dissolution of fractures affects the permeability of the fractures within the reservoir, the fracture permeability is predicted by taking into account the dissolution of the fractures by the acid within the reservoir. Finally, the currently predicted matrix and fracture permeabilities are used to update the corresponding permeability parameters in the reservoir parameters for the next time step. The updated reservoir parameters are then used to update the corresponding initial reservoir acid absorption profile. Thus, by continuously updating the initial reservoir acid absorption profiles for adjacent time steps, a dynamic reservoir acid absorption profile is obtained. In other words, this embodiment calculates the dynamic acid absorption profile for a fixed-point diversion acid injection during the fixed-point injection acidizing process by updating the reservoir matrix permeability, fracture permeability, and acid pressure within the wellbore. The calculation is terminated until the acid pressure within the wellbore exceeds the formation fracture pressure, and the simulated displacement is redesigned.

[0083] Next, in the step of determining the length of the acid-etched wormholes in the wellbore wall based on the concentration distribution, the average filtration velocity of the acid solution in the wellbore at the current time step is obtained based on the acid solution viscosity. Furthermore, the expansion rate of the acid-etched wormholes extending from the wellbore wall is calculated in combination with the acid solution concentration distribution, thereby determining the length of the acid-etched wormholes in the next time step. This embodiment utilizes the acid solution's inherent viscosity to calculate the average filtration velocity of the acid solution in the wellbore at the current time step. Subsequently, the average filtration velocity is used, combined with the acid solution concentration distribution in the wellbore determined in step S130, to calculate the expansion rate of the acid-etched wormholes extending from the wellbore wall, thereby determining the length of the acid-etched wormholes in the next time step.

[0084] The following expression is used to calculate the expansion rate of acid-etched wormholes extending from the wellbore wall:

[0085]

[0086] Among them, v wh represents the expansion rate of acid-etched wormholes, v i，tip Indicates the acid flow rate at the tip of the wormhole, N AC Indicates the acid corrosion capacity number, V bt，opt represents the optimal wormhole breakthrough volume, v i，opt represents the optimal wormhole tip acid flow rate, h represents the reservoir thickness, r wh Indicates the radius of the acid-etched wormhole.

[0087] Next, the acid flow rate at the wormhole tip is calculated using the following expression:

[0088]

[0089] Where r represents the radius of the acid loss section perpendicular to the wormhole expansion area.

[0090] The acid corrosion capacity number is calculated using the following expression:

[0091]

[0092] Where, β represents the ratio of the mass of dissolved carbonate rock to the mass of total carbonate rock, C represents the mass concentration of acid solution, and ρ acid Indicates the density of acid solution, V co3 represents the ratio of carbonate mineral volume to total rock volume, ρ co3 represents the density of carbonate rock.

[0093] Next, the matrix permeability includes a first matrix permeability of a non-wormhole tip area in the wormhole area of the reservoir and a second matrix permeability in the area where the wormhole tip is located. Specifically, the wormhole area in the embodiment includes the wormhole tip area and the non-wormhole tip area. The first matrix permeability is the matrix permeability of the non-wormhole tip area (the matrix permeability of the non-wormhole tip area in the wormhole area parallel to the growth direction of the acid-etched wormhole), and the second matrix permeability is the matrix permeability of the wormhole tip area.

[0094] The first matrix permeability is calculated using the following expression:

[0095] k wh1 = 10 4 *k my (14)

[0096] wherein k wh1 represents the first matrix permeability, and k my represents the matrix permeability parallel to the growth direction of the acid-etched wormhole.

[0097] The second matrix permeability is calculated using the following expression:

[0098]

[0099] wherein k wh2 represents the second matrix permeability, Δy tip represents the length of the matrix unit where the wormhole tip is located, and L wh,tip represents the length of the wormhole in the matrix unit cell where the wormhole tip is located.

[0100] Further, in the step of obtaining the width of the fracture after dissolution in the reservoir at the current time step, the rock dissolution volume in the reservoir is calculated using the acid injection volume, and then the dissolution width of the current fracture is obtained using the correlation among the rock dissolution volume, the reservoir thickness, and the fracture size, based on which the width of the fracture after dissolution is obtained.

[0101] Specifically, based on the conservation of mass, it is assumed that all the acid (HCL) participates in the dissolution of the rock on the fracture wall surface in the reservoir, and the rock dissolution volume is calculated using the injected acid volume. In the embodiment, the rock dissolution volume in the reservoir is calculated using the following expression:

[0102]

[0103] wherein Vcaco3represents the rock dissolution volume in the reservoir, wt HCl represents the mass concentration of hydrochloric acid, ρ HCl represents the density of hydrochloric acid, V HCl represents the amount of acid used in construction, represents the molar mass of calcium carbonate in the reservoir, and M HClrepresents the molar mass of hydrochloric acid, Indicates the density of calcium carbonate.

[0104] Next, assuming that the acid dissolves the fractures uniformly in the reservoir, the correlation between the rock dissolution volume, reservoir thickness, and fracture size is used to calculate the dissolution width of a single fracture in the current time step. The following expression is used to calculate the dissolution width of a single fracture:

[0105]

[0106] Among them, w r The dissolution width of a single crack, L nf Represents the length of the fracture in the reservoir.

[0107] Based on this, the width of a single crack after acid etching in the current time step is expressed using the following expression:

[0108]

[0109] in, represents the width of the fracture in the reservoir in the n+1th time step, represents the width of the fracture in the reservoir at the nth time step, where n represents the time step count.

[0110] Furthermore, before obtaining the wellbore acid pressure of the current time step by analyzing the wellbore acid distribution at the end of the previous time step, the wellbore acid pressure in the initial time step is taken as the formation pressure. Based on the wellbore volume of the reformed section in the reservoir to be predicted, the initial wellbore acid pressure, and the amount of injected acid, the wellbore acid pressure distribution in the next time step is calculated. And, the following is obtained: Figure 7 The correlation between the acid fluid discharge rate and the acid fluid pressure in the wellbore is shown in ( Figure 7 This is a schematic diagram of the correlation between the acid fluid discharge rate and the acid fluid pressure in the wellbore for the acid absorption profile prediction method for a fractured reservoir in a long well section of an embodiment of the present application), so as to intuitively obtain the simulation state and stop the simulation process when the acid fluid pressure in the wellbore is greater than the formation fracture pressure.

[0111] In the embodiment of the present application, the following expression is used to calculate the acid fluid pressure distribution in the wellbore:

[0112]

[0113]

[0114] ΔV acid =Q in -Q out (twenty one)

[0115] Where ΔP nrepresents the change in the acid pressure in the wellbore caused by the compressibility of the acid in the wellbore after the acid is injected in the nth time step, k' represents the acid viscosity coefficient, n' represents the acid flow index, ΔV acid Indicates the increase of acid in the wellbore per unit time, V well represents the wellbore volume, Q in Indicates the acid fluid and injection volume in the wellbore, Q out Indicates the amount of acid flowing out of the wellbore.

[0116] The present invention provides a method for predicting acid absorption profiles in fractured reservoirs for long well sections. This method establishes a geological model of the reservoir to be predicted, rapidly simulates the flow of acid in the wellbore based on the law of conservation of matter, and uses natural fractures as flow channels for the acid during the acidizing process to obtain the reservoir acid pressure and reservoir parameters at the previous time step to obtain the reservoir acid pressure at the current time step. Simultaneously, the wellbore acid pressure at the previous time step is obtained to obtain the wellbore acid pressure at the current time step, thereby obtaining a first flow rate of acid flowing from the wellbore into the reservoir and a second flow rate of acid in the wellbore at the current time step. Subsequently, based on the second flow rate, the concentration distribution of the acid in the wellbore is determined to obtain the initial reservoir acid absorption profile for the current time step. Finally, the initial reservoir acid absorption profile is updated in real time by taking into account the changes in fracture width caused by acid on the walls of natural fractures, as well as the growth state of acid-etched wormholes on the wellbore wall and the impact of the growth process on matrix permeability during the acidizing process. The present invention is based on the law of conservation of mass, takes into account the coupled flow of acid in the wellbore and reservoir, and simultaneously dynamically considers the dynamic changes in permeability and natural fracture width caused by the dissolution of the matrix and fracture walls in the reservoir by the acid. It realizes the rapid calculation of the acid absorption profile of the fixed-point diversion acidizing in the fractured reservoir of the long well section, and can directly and simply calculate the acid injection parameters of the fractured carbonate rock acidizing in the long horizontal well.

[0117] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by anyone skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

[0118] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims of the present invention.

[0119] Those skilled in the art will appreciate that the modules or steps of the present invention described above can be implemented using a general-purpose computing device. They can be centralized on a single computing device or distributed across a network of multiple computing devices. Alternatively, they can be implemented using program code executable by a computing device, which can then be stored in a storage device and executed by the computing device. Alternatively, they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0120] Although the embodiments disclosed herein are as described above, the contents described herein are merely embodiments for facilitating understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art may make any modifications and variations in the form and details of the embodiments without departing from the spirit and scope of the present invention. However, the scope of patent protection of the present invention shall remain subject to the scope defined by the appended claims.

Claims

1. A method for predicting acid absorption profiles of fractured reservoirs in long well sections, characterized in that: include: Establishing a geological model of the reservoir to be predicted, and dividing the geological model into a plurality of grids; Using the geological model, the reservoir acid pressure and reservoir parameters of the previous time step are obtained, and the reservoir acid pressure of the current time step is obtained by analyzing the reservoir acid distribution at the end of the previous time step, and the wellbore acid pressure of the previous time step is obtained, and the wellbore acid pressure of the current time step is obtained by analyzing the wellbore acid distribution at the end of the previous time step, thereby obtaining the first flow rate of the acid flowing from the wellbore into the reservoir and the second flow rate of the acid in the wellbore in the current time step, wherein the pressure difference between the reservoir acid pressure and the wellbore acid pressure on both sides of the overlapping edge of each grid and the wellbore edge is used to obtain The flow rate of the acid solution corresponding to the corresponding grid flowing from the wellbore into the reservoir is obtained by accumulating the inflow flow rate of each grid to obtain the first flow rate, and dividing the wellbore into two parts along a direction perpendicular to the wellbore axis and passing through the acid inlet, and using one part as the upstream of the acid injection and the other part as the downstream of the acid injection, wherein the acid inlet is located inside the wellbore, and then using the flow rate of the acid solution corresponding to the grids distributed along the upstream and downstream directions of the acid injection to flow into the reservoir from the wellbore to obtain the acid flow rate in the wellbore upstream and downstream of the acid injection, and taking the sum of the acid flow rate in the upstream wellbore and the acid flow rate in the downstream wellbore as the second flow rate; determining, based on the second flow rate, a concentration distribution of the acid liquid in the wellbore to obtain an initial reservoir acid absorption profile for the current time step, wherein a first flow velocity and a second flow velocity of the acid liquid in the wellbore are calculated using the acid liquid flow rate in the upstream wellbore and the acid liquid flow rate in the downstream wellbore, respectively, based on which a flow velocity of the acid liquid in the wellbore is obtained, and then a flow velocity of the acid liquid flowing from the wellbore into the reservoir is calculated using the first flow rate, and further determining the concentration distribution of the acid liquid in the wellbore by analyzing a correlation between a combination of the flow velocity of the acid liquid in the wellbore and the flow velocity of the acid liquid flowing from the wellbore into the reservoir and the concentration distribution of the acid liquid in the wellbore; Based on the concentration distribution, the length of the acid-etched wormholes on the wellbore wall is determined to predict the matrix permeability. The width of the fractures in the reservoir after dissolution in the current time step is obtained to predict the fracture permeability. The predicted permeabilities are then used to update the reservoir parameters for the next time step and the initial reservoir acid absorption profile.

2. The acid absorption profile prediction method according to claim 1, characterized in that: The steps of establishing a geological model of the reservoir to be predicted include: The geological model is assigned values ​​according to actual characteristic parameters of the reservoir to be predicted, and the geological model is divided into a plurality of grids, wherein the characteristic parameters include but are not limited to reservoir porosity, permeability and formation pressure.

3. The acid absorption profile prediction method according to claim 2, characterized in that: The reservoir acid distribution at the end of the previous time step is calculated using the following expression: in, ρ Indicates the density of acid liquid, k x 、 k y Indicates each grid in the previous time step x 、 y The average permeability in the direction, P represents the acid pressure in each grid at the previous time step, μ Indicates the viscosity of the acid, ϕ represents the average porosity within each grid, c l represents the acid compressibility coefficient, t Indicates the acid injection time, x 、 y They represent the horizontal and vertical coordinates of the acid distribution position in the reservoir respectively.

4. The acid absorption profile prediction method according to claim 3, wherein: The first flow rate is calculated using the following expression: in, i Indicates the sequence number of the grid distributed along the edge of the wellbore, m represents the number of grids distributed along the edge of the wellbore, Q out，i Indicates the i The flow rate of acid fluid flowing from the wellbore into the reservoir corresponds to the grid, △ x ,△ y They represent the matrix grids in the grids distributed along the edge of the wellbore. x 、 y The length of the direction, P well，i Indicates the i The wellbore acid pressure corresponding to each grid is P r，i Indicates the i The acid pressure of the reservoir corresponding to each grid is k y，i Indicates the i Grid edge y Directional permeability, Q out Indicates the first flow.

5. The acid absorption profile prediction method according to claim 4, characterized in that: The concentration distribution of acid in the wellbore is determined using the following expression: in, D represents the wellbore diameter, C Indicates the acid concentration in the wellbore. t Indicates the acid injection time, u x Indicates the flow rate of acid in the wellbore. v l Indicates the flow rate of acid from the wellbore into the reservoir, k c represents the equilibrium constant.

6. The method for predicting an acid absorption profile according to any one of claims 1 to 5, wherein: The step of determining the length of the acid-etched wormholes on the wellbore wall according to the concentration distribution includes: Based on the acid viscosity, the average filtration rate of the acid in the wellbore at the current time step is obtained. Combined with the acid concentration distribution, the expansion rate of the acid-etched wormhole extending from the wellbore wall is calculated to determine the length of the acid-etched wormhole at the next time step.

7. The acid absorption profile prediction method according to claim 6, characterized in that: The matrix permeability includes a first matrix permeability in a non-wormhole tip region in the wormhole region of the reservoir and a second matrix permeability in a region where the wormhole tip is located.

8. The acid absorption profile prediction method according to claim 7, characterized in that: The step of obtaining the width of the fracture after dissolution in the reservoir at the current time step includes: The acid injection volume is used to calculate the rock dissolution volume in the reservoir, and then the correlation between the rock dissolution volume, reservoir thickness and fracture size is used to obtain the current fracture dissolution width. Based on this, the width of the fracture after dissolution is obtained.

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