Polymer oil displacement wall geometric dimension obtaining method based on oil reservoir simulation

Abstract

The invention relates to the technical field of oil exploitation engineering, in particular to a polymer oil displacement wall geometric dimension obtaining method based on oil reservoir simulation. Comprising the following steps: establishing a one-dimensional polymer flooding numerical model (discretized into N grid units) for simulating an actual oil reservoir; based on the one-dimensional polymer flooding numerical model, respectively simulating polymer flooding and water flooding processes under the same parameters; determining the front edge and the rear edge of the oil wall at each moment according to the oil saturation offset of the adjacent grid units at each moment in the polymer flooding process to obtain the width of the oil wall; taking the maximum stable moment of the difference value of the oil saturation of polymer flooding and water flooding as the optimal calculation moment of the height of the oil wall within the appearing time range of the oil wall; and at the optimal calculation moment of the height of the oil wall, calculating the height of the oil wall based on the difference value of the oil saturation of each grid unit in polymer flooding and water flooding in the width range of the oil wall. According to the method, the geometric dimension of the oil wall can be accurately obtained in a simulation mode, and basis and support are provided for optimization of polymer oil displacement.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum production engineering, and in particular to a method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation. Background Art

[0002] Polymer flooding, a highly effective enhanced oil recovery technology, injects a polymer solution into the reservoir to adjust the mobility ratio of the oil and water phases, forming an oil-rich "oil bank" at the displacement front. However, there is still no effective method to characterize the geometry (such as width and height) of this "oil bank" during actual polymer flooding.

[0003] Furthermore, existing technologies primarily characterize the spatial distribution of oil walls using physical simulation experiments and numerical simulation methods. These methods primarily assume that the oil wall's location is a large, concentrated zone of oil saturation. These methods lack parameters describing the wall's geometry and lack criteria for defining its extent. For example, linear interpolation of oil saturation at the interface before and after the wall fails to reflect the nonlinear variations in the wall's morphology. Furthermore, there's a lack of basis for defining the front and back edges of the wall. Due to the complex spatial distribution of oil saturation, traditional methods struggle to accurately quantify the wall's propagation speed and swept volume, resulting in a lack of reliable data support for the formulation and dynamic adjustment of production plans. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the existing technology and provide a method for obtaining the geometric dimensions of the polymer flooding wall based on reservoir simulation. It can accurately obtain the geometric dimensions of the oil wall through simulation, providing a basis and support for the optimization of polymer flooding.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: a method for obtaining the geometric dimensions of a polymer flooding wall based on reservoir simulation, comprising:

[0006] Based on actual reservoir data, a one-dimensional polymer flooding numerical model simulating the actual reservoir is established using reservoir numerical simulation software. The one-dimensional polymer flooding numerical model is discretized into N grid cells along the one-dimensional direction.

[0007] Based on the one-dimensional polymer flooding numerical model, the polymer flooding and water flooding processes under the same parameters are simulated respectively;

[0008] According to the oil saturation offset of adjacent grid cells at each moment in the polymer flooding process, the front and rear edges of the oil wall at each moment are determined, and the distance between the front and rear edges of the oil wall at each moment is taken as the oil wall width at the corresponding moment;

[0009] Within the time range of oil wall appearance, the time when the oil saturation difference between polymer flooding and water flooding is the maximum stable time is taken as the optimal calculation time of oil wall height;

[0010] At the optimal calculation time of the oil wall height, the oil wall height is calculated based on the oil saturation difference of each grid cell within the oil wall width during polymer flooding and water flooding.

[0011] Furthermore, according to the oil saturation offset of adjacent grid cells at each moment in the polymer flooding process, the front and back edges of the oil wall at each moment are determined; specifically, the following steps are performed:

[0012] In the one-dimensional polymer flooding numerical model, the injection well is located at the first grid cell and the production well is located at the Nth grid cell;

[0013] Near the production well, the oil saturation of the xth and x+1th grid cells are respectively denoted as Sp x and Sp x+1 , the oil saturation offset P between the xth and x+1th grid cells f for:

[0014]

[0015] If P f >0, the xth unit grid is the front edge of the oil wall;

[0016] Near the injection well, the oil saturation of the yth and y+1th grid cells are respectively denoted as Sp y and Sp y+1 , the oil saturation offset P between the yth and y+1th grid cells b for:

[0017]

[0018] If P b >0, the yth unit grid is the rear edge of the oil wall.

[0019] Furthermore, when determining the positions of the leading and trailing edges of the oil wall at each moment:

[0020] Near the production well, if 1.0%>P f >0, the xth unit grid is the front edge of the oil wall;

[0021] Near the injection well, if 0 <P b <1.0%, the yth unit grid is the rear edge of the oil wall.

[0022] Furthermore, after obtaining the oil wall width at each moment, the following steps are also included:

[0023] The relationship between oil wall width and time is characterized using a cubic polynomial.

[0024] Furthermore, within the time range of oil wall appearance, the time when the oil saturation difference between polymer flooding and water flooding is maximized is used as the optimal calculation time for the oil wall height; specifically, the following steps are performed:

[0025] Within the time range of oil wall appearance, at least one moment when the oil saturation difference between polymer flooding and water flooding is stable is recorded as the candidate moment;

[0026] For each candidate time, the average difference in oil saturation between polymer flooding and water flooding in m consecutive grid cells is calculated; where m∈[3,5], the grid cell whose oil saturation after polymer flooding becomes greater than that after water flooding is recorded as the first of the m consecutive grid cells;

[0027] It is determined whether the minimum average difference is less than or equal to a preset threshold. If so, the selected time corresponding to the minimum average difference is used as the optimal calculation time for the oil wall height.

[0028] Furthermore, at the optimal calculation time of the oil wall height, the oil wall height is calculated based on the oil saturation difference of each grid cell within the oil wall width during polymer flooding and water flooding. The specific formula is:

[0029]

[0030] In the formula, x1 and x2 are the positions of the grid cells at the optimal calculation time of the oil wall height and the front and rear edges of the oil wall, respectively; g(x) and f(x) are the oil saturations of the x-th grid cell during polymer flooding and polymer flooding, respectively.

[0031] After adopting the above technical solution, the present invention has the following beneficial effects:

[0032] During polymer flooding, the width and height of the "oil wall" are key parameters that reflect flooding effectiveness and the dynamics of remaining oil. While traditional methods have difficulty accurately measuring these parameters, this new method can precisely quantify the width and height of the oil wall, enabling a deeper and more detailed understanding of its evolution during flooding, providing a solid data foundation for subsequent research and decision-making.

[0033] Based on the oil wall width and height data obtained from the simulation, the polymer flooding scheme can be optimized in a targeted manner, mainly used to guide the adjustment of injection parameters. For example, when the oil wall width is large and the oil wall height is high, the injection rate can be increased and the injection concentration can be reduced; when the oil wall width is small and the oil wall height is low, the injection rate can be reduced and the injection concentration can be increased.

[0034] Before implementing a polymer flooding project, simulations using the method described in this invention can predict flooding effects under different conditions. By varying polymer properties and injection parameters, various flooding scenarios can be simulated to predict the development of oil walls. This helps assess project feasibility early, identify potential problems, and develop appropriate response strategies. This avoids resource waste and inefficiencies caused by inappropriate plans during actual production, saving significant manpower, material resources, and time.

[0035] In summary, the present invention proposes an accurate and efficient method for characterizing the geometric morphology of "oil walls" by combining numerical simulation of oil reservoirs with mathematical modeling. This method solves the shortcomings of traditional technologies in simulation accuracy, mathematical characterization, and practical applications, and provides important theoretical support and practical tools for the optimization of polymer flooding technology. It has broad industry application prospects and socioeconomic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation according to the present invention;

[0037] Figure 2 is a cross-sectional view of a one-dimensional polymer flooding numerical model according to an embodiment of the present invention;

[0038] Figure 3 This is a graph showing the oil saturation at a certain moment during the polymer flooding process according to an embodiment of the present invention;

[0039] Figure 4 This is a range diagram of the front and rear edges of the oil wall at a certain moment in an embodiment of the present invention;

[0040] Figure 5 This is a fitting diagram of the oil wall width according to an embodiment of the present invention;

[0041] Figure 6 This is a fitting diagram of the mathematical expression of the oil wall width according to an embodiment of the present invention;

[0042] Figure 7 The oil saturation curve of polymer flooding minus water flooding in the embodiment of the present invention;

[0043] Figure 8 This is a graph showing the stabilization time of the oil saturation difference between polymer flooding and water flooding according to an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0045] like Figure 1 As shown, a method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation includes:

[0046] Step S1: Based on actual reservoir data, a one-dimensional polymer flooding numerical model simulating the actual reservoir is established using reservoir numerical simulation software. The one-dimensional polymer flooding numerical model is discretized into N grid units along the one-dimensional direction; wherein,

[0047] One-dimensional polymer flooding numerical models can be used to analyze actual wells connected by polymer injection. The well connections are a one-dimensional model. The one-dimensional simulation model created in CMG is configured with geometric parameters such as model length and number of grid cells to reasonably represent the characteristics of the actual reservoir in a specific direction. The specific process of establishing a one-dimensional polymer flooding numerical model may include, but is not limited to:

[0048] Collect relevant data of actual oil reservoirs, including reservoir geometry, permeability, porosity, fluid properties (such as crude oil viscosity and density, water viscosity and density, etc.), initial reservoir pressure and saturation distribution; determine the property parameters of polymers, such as polymer viscosity, adsorption characteristics, etc.

[0049] Determine the boundary conditions of the model, such as the injection rate and injection pressure at the injection end, and the production system at the production end (constant output or constant pressure production).

[0050] When setting the initial reservoir pressure and saturation distribution, it is usually assumed that the initial reservoir is in equilibrium and the oil and water saturations are distributed in a certain manner throughout the reservoir.

[0051] Polymer flooding settings: Define the polymer injection plan, including parameters such as injection concentration, injection time, and injection rate. Consider the migration and action mechanisms of the polymer in the reservoir, such as adsorption, diffusion, and convection, and simulate them by setting corresponding parameters.

[0052] Run the simulation model to calculate the changes in reservoir pressure, saturation, production and other parameters over time during polymer flooding.

[0053] Analyze simulation results and compare them with actual reservoir production data, such as oil production and water content, to assess the accuracy and reliability of the model. Based on the results, adjust model parameters to better fit the actual reservoir conditions.

[0054] Step S2, based on a one-dimensional polymer flooding numerical model, respectively simulating polymer flooding and water flooding processes under the same parameters;

[0055] Step S3, determining the front and rear edges of the oil wall at each moment according to the oil saturation offset of adjacent grid cells at each moment during the polymer flooding process, and taking the distance between the front and rear edges of the oil wall at each moment as the oil wall width at the corresponding moment;

[0056] Step S4, within the time range of the oil wall appearance, the time when the oil saturation difference between polymer flooding and water flooding is maximized is used as the optimal time for calculating the oil wall height;

[0057] Step S5: At the optimal calculation time of the oil wall height, the oil wall height is calculated based on the oil saturation difference of each grid cell within the oil wall width during polymer flooding and water flooding.

[0058] In this embodiment, step S3 determines the front and back edges of the oil wall at each moment according to the oil saturation offset of adjacent grid cells at each moment during the polymer flooding process. Specifically, the step includes:

[0059] In the one-dimensional polymer flooding numerical model, the injection well is located at the first grid cell and the production well is located at the Nth grid cell;

[0060] Near the production well, the oil saturation of the xth and x+1th grid cells are respectively denoted as Sp x and Sp x+1 , the oil saturation offset P between the xth and x+1th grid cells f for:

[0061]

[0062] If P f >0, the xth unit grid is the front edge of the oil wall;

[0063] Near the injection well, the oil saturation of the yth and y+1th grid cells are respectively denoted as Sp y and Sp y+1 , the oil saturation offset P between the yth and y+1th grid cells b for:

[0064]

[0065] If P b >0, the yth unit grid is the rear edge of the oil wall.

[0066] Specifically, in the one-dimensional polymer flooding numerical model, the injection well is in the first grid unit and the production well is in the Nth grid unit. For example, the injection well is located on the left and the production well is located on the right. Close to the production well, the oil saturation of the grid unit generally decreases from right to left. When the data increases, it is temporarily considered as the front edge of the "oil wall", that is, P f>0. According to the results obtained by running the STARS module in the numerical modeling software CMG, the oil saturation of the grid is analyzed using the Results module. The Results module will display a dynamic graph of oil saturation. When a color change occurs at a certain time due to an increase in oil saturation, this time is defined as the time when the "oil wall" first appears. At this time (near the injection well), the grid that first appears to have a darker color is temporarily recorded as the trailing edge of the "oil wall", that is, P b >0, if not satisfied, it can be adjusted forward or backward. Figure 4 This is a range diagram of the front and rear edges of the oil wall at a certain moment.

[0067] In step S3, more specifically, when determining the positions of the leading and trailing edges of the oil wall at each moment:

[0068] Near the production well, if 1.0%>P f >0, the xth unit grid is the front edge of the oil wall;

[0069] Near the injection well, if 0 <P b <1.0%, the yth unit grid is the rear edge of the oil wall.

[0070] Specifically, during the "oil wall" promotion phase, the following two phenomena will occur successively:

[0071] 1. Grid oil saturation Sp near the front edge of the "oil wall" x Meet Sp x >Sp x+1 <Sp x+2

[0072] 2. Grid oil saturation Sp in front of the “oil wall” front (near the production well) x Meet Sp x >Sp x+1 >Sp x+2

[0073] As shown in Table 1, the front and rear edges of the oil wall are determined based on the more accurate range mentioned above, with 1.0%>P f >0 is used as the criterion for judging the oil wall front. The oil saturation gradient meets the above stability criteria. At this time, the shape of the oil wall front is stable. <P b <1.0% is used as the standard for judging the trailing edge of the oil wall, which can accurately define the trailing edge range of the "oil wall" and at the same time show obvious regular changes in the migration of the oil wall.

[0074] Table 1 Threshold verification results

[0075] Threshold "Oil wall" width (number of grids) 0.5％ 7 1.0％ 10 (same as the simulation animation) 1.5％ 14

[0076] In this embodiment, after obtaining the oil wall width at each moment in step S3, the following steps are further included:

[0077] The relationship between oil wall width and time is characterized using a cubic polynomial.

[0078] In this embodiment, in step S4, within the time range of oil wall appearance, the time when the oil saturation difference between polymer flooding and water flooding is maximized is used as the optimal time for calculating the oil wall height; specifically, the step includes:

[0079] Within the time range of oil wall appearance, at least one moment when the oil saturation difference between polymer flooding and water flooding is stable is recorded as the candidate moment;

[0080] For each candidate time, the average difference in oil saturation between polymer flooding and water flooding in m consecutive grid cells is calculated; where m∈[3,5], the grid cell whose oil saturation after polymer flooding becomes greater than that after water flooding is recorded as the first of the m consecutive grid cells;

[0081] It is determined whether the minimum average difference is less than or equal to a preset threshold. If so, the selected time corresponding to the minimum average difference is used as the optimal calculation time for the oil wall height.

[0082] Specifically, through multiple simulations, it is proved that in order to make rational use of resources, when calculating this value, if m is too small, the numerical values of multiple curves will be similar and the calculation accuracy will be poor. If it is too large, it will lead to repeated judgment results and waste of computing power. Therefore, m∈[3,5] is reasonable. When the average difference is less than or equal to 0.1%, the optimal time curve is considered reasonable and its height can be calculated.

[0083] In this embodiment, in step S6, at the optimal calculation time of the oil wall height, the oil wall height is calculated based on the oil saturation difference between each grid cell within the oil wall width during polymer flooding and water flooding. The specific formula is:

[0084]

[0085] In the formula, x1 and x2 are the positions of the grid cells at the optimal calculation time of the oil wall height and the front and rear edges of the oil wall, respectively; g(x) and f(x) are the oil saturations of the x-th grid cell during polymer flooding and polymer flooding, respectively.

[0086] The solutions involved in the above embodiments are described in detail below in conjunction with specific embodiments.

[0087] Taking an oil reservoir in the Dongying Sag of the Bohai Bay Basin as an example, a Figure 2The 1×100 one-dimensional model shown in the figure has a grid of 0.8 m in the i, j, and k directions, permeabilities of 1300, 1300, and 130 mD, a depth of 4700 m at the center of the top surface of each grid block, and a porosity of 0.232. During polymer flooding, water is injected first, followed by polymer injection, and finally water injection. The surface water injection rate is 100 m 3 / d, the maximum bottom hole pressure is 11MPa, the molecular weights of water, polymer, and oil are 0.018, 2400, and 0.2kg / mol, respectively, and the mass densities are 958.4, 1320, and 724kg / m 3 , the model oil saturation is 0.6, polymer type: partially hydrolyzed polyacrylamide (HPAM), concentration is 1375ppm, and polymer injection began on 1991-Qct-28.

[0088] According to the oil saturation offset of adjacent grid cells at each moment in the polymer flooding process, the front and rear edges of the oil wall at each moment are determined, and the distance between the front and rear edges of the oil wall at each moment is taken as the oil wall width at the corresponding moment. Figure 5 As shown. Figure 5 The data in the figure are fitted and analyzed, and the width expression is obtained as follows:

[0089] OW=0.00027×t 3 -0.03398×t 2 +1.09730×t+1.50775

[0090] Within the time range of oil wall appearance, at least one moment when the oil saturation difference between polymer flooding and water flooding is stable is recorded as the candidate moment. Figure 7 The oil saturation curves for polymer flooding minus water flooding at various times are shown. The candidate times were 1991-Nov-27 and 1991-Nov-28, and the two curves were analyzed separately, as shown in Table 2.

[0091] Table 2. Average difference of oil saturation curves at each candidate time

[0092] m 1991-Nov-27 curve 1991-Nov-28 curve 3 0.00159 0.00100 4 0.00204 0.00187 5 0.00245 0.00231

[0093] By comparison, it can be seen from Table 2 that the optimal calculation time for the oil wall height is 1991-Nov-28, m is taken as 3, and then the "oil wall" height is calculated.

[0094] According to the calculation of the width of the "oil wall", its width range is from the 39th grid unit to the 48th grid unit under the current optimal time curve, with a width of 10. Figure 6 Substituting the oil saturation curves of polymer flooding and water flooding into the height calculation formula, it is calculated that the oil wall height is 2.9754% (its physical meaning is the saturation difference).

[0095] The software simulation results were compared with a physical model (an indoor physical simulation model built to a similar scale, using similar injection rates and input volumes to simulate the actual injection-production process between injection and production wells. The oil wall migration process during the test process can be obtained through experimental test data (test pressure, well-ground electrical resistance imaging, and tracer analysis)). The error of the software simulation results for the oil wall geometric dimensions is less than 5%.

[0096] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation, characterized in that: include: Based on actual reservoir data, a one-dimensional polymer flooding numerical model simulating the actual reservoir is established using reservoir numerical simulation software. The one-dimensional polymer flooding numerical model is discretized into N grid cells along the one-dimensional direction. Based on the one-dimensional polymer flooding numerical model, the polymer flooding and water flooding processes under the same parameters are simulated respectively; According to the oil saturation offset of adjacent grid cells at each moment in the polymer flooding process, the front and rear edges of the oil wall at each moment are determined, and the distance between the front and rear edges of the oil wall at each moment is taken as the oil wall width at the corresponding moment; Within the time range of oil wall appearance, the time when the oil saturation difference between polymer flooding and water flooding is the maximum stable time is taken as the optimal calculation time of oil wall height; At the optimal calculation time of the oil wall height, the oil wall height is calculated based on the oil saturation difference of each grid cell within the oil wall width during polymer flooding and water flooding.

2. The method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation according to claim 1, wherein: According to the oil saturation offset of adjacent grid cells at each moment in the polymer flooding process, the front and back edges of the oil wall at each moment are determined. Specifically, In the one-dimensional polymer flooding numerical model, the injection well is located at the first grid cell and the production well is located at the Nth grid cell; Near the production well, the oil saturation of the xth and x+1th grid cells are respectively denoted as Sp x and Sp x+1 , the oil saturation offset P between the xth and x+1th grid cells f for: If P f >0, the xth unit grid is the front edge of the oil wall; Near the injection well, the oil saturation of the yth and y+1th grid cells are respectively denoted as Sp y and Sp y+1 , the oil saturation offset P between the yth and y+1th grid cells b for: If P b >0, the yth unit grid is the rear edge of the oil wall.

3. The method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation according to claim 2, wherein: When determining the positions of the leading and trailing edges of the oil wall at each moment: Near the production well, if 1.0%>P f >0, the xth unit grid is the front edge of the oil wall; Near the injection well, if 0 <P b <1.0%, the yth unit grid is the rear edge of the oil wall.

4. The method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation according to claim 1, wherein: After obtaining the oil wall width at each moment, it also includes: The relationship between oil wall width and time is characterized using a cubic polynomial.

5. The method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation according to claim 1, characterized in that: Within the time range of oil wall appearance, the time when the oil saturation difference between polymer flooding and water flooding is maximized is used as the optimal calculation time for oil wall height; specifically, the following are included: Within the time range of oil wall appearance, at least one moment when the oil saturation difference between polymer flooding and water flooding is stable is recorded as the candidate moment; For each candidate time, the average difference in oil saturation between polymer flooding and water flooding in m consecutive grid cells is calculated; where m∈[3,5], the grid cell whose oil saturation after polymer flooding becomes greater than that after water flooding is recorded as the first of the m consecutive grid cells; It is determined whether the minimum average difference is less than or equal to a preset threshold. If so, the selected time corresponding to the minimum average difference is used as the optimal calculation time for the oil wall height.

6. The method for obtaining geometric dimensions of a polymer flooding wall based on reservoir simulation according to claim 1, characterized in that: At the optimal calculation time of the oil wall height, the oil wall height is calculated based on the oil saturation difference of each grid cell within the oil wall width during polymer flooding and water flooding. The specific formula is: In the formula, x1 and x2 are the positions of the grid cells at the optimal calculation time of the oil wall height and the front and rear edges of the oil wall, respectively; g(x) and f(x) are the oil saturations of the x-th grid cell during polymer flooding and polymer flooding, respectively.

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