Ultra-low permeability reservoir CO 2 Method for determining the limit well spacing of flooding technology

Abstract

The present invention relates to the field of low permeability oil reservoir development engineering, in particular to a CO 2 The method comprises: establishing a method for determining the limit well spacing of ultra-low permeability reservoir CO 2 The invention uses the established numerical simulation component model to calculate the pressure and crude oil viscosity of each grid point between the injection and production wells after n days; calculates the driving pressure gradient of each grid point and draws the driving pressure curve between the injection and production wells; calculates the starting pressure gradient of each grid point and draws the starting pressure gradient curve; determines the relationship between the driving pressure gradient curve and the starting pressure gradient curve until the two curves are tangent, and determines that the injection and production well spacing at this time is the technical limit well spacing. The invention accurately calculates the CO2 injection well spacing of the ultra-low permeability reservoir according to the relationship between the driving pressure gradient curve and the starting pressure gradient curve. 2 The technical limit well spacing of flooding provides a new method and research idea for obtaining the limit well spacing.

Description

Technical Field

[0001] The invention relates to the field of low permeability oil reservoir development engineering, and in particular to a method for determining a limit well spacing of CO2 flooding technology in an ultra-low permeability oil reservoir. Background Art

[0002] Ultra-low permeability reservoirs have poor physical properties, large seepage resistance, and a large starting pressure gradient. Water injection is difficult and has poor results. CO2 injection is conducive to solving the above problems and can effectively improve the recovery rate of crude oil in ultra-low permeability reservoirs. The technical limit well spacing is an important basis for ensuring good displacement effects, determining the location of new wells, and adjusting old wells. If the designed well spacing is too large, the driving pressure gradient between the injection and production wells is lower than the starting pressure gradient, resulting in a non-flowing area between the injection and production wells, and the phenomenon of "no injection and no production" occurs; if the injection and production well spacing is less than the technical limit well spacing, the driving pressure gradient at any point between the injection and production wells is greater than the starting pressure gradient, and effective displacement can be formed. However, if the injection and production well spacing is too small, a large number of wells are required, resulting in poor economic benefits.

[0003] The technical limit well spacing is the injection-production well spacing when the minimum pressure gradient between injection and production wells is equal to the start-up pressure gradient. At present, there are few studies on the technical limit well spacing of CO2 flooding at home and abroad, and the calculation is relatively complicated, involving too many parameters. Summary of the invention

[0004] The purpose of the present invention is to provide a method for determining the technical limit well spacing of CO2 flooding in ultra-low permeability oil reservoirs. The method of the present invention is simple and obtains the technical limit well spacing of CO2 flooding in ultra-low permeability oil reservoirs.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for determining the limit well spacing of CO2 flooding technology in ultra-low permeability oil reservoirs, which comprises the following steps:

[0007] S1. Establish a numerical simulation component model for CO2 flooding in ultra-low permeability reservoirs;

[0008] S2. Setting injection and production wells according to the set well spacing, and using the numerical simulation component model established in step S1 to calculate the pressure and crude oil viscosity values ​​of each grid point between the injection and production wells after n days;

[0009] S3. Calculate the driving pressure gradient of each grid point according to the pressure of each grid point, and draw the driving pressure curve between the injection and production wells;

[0010] S4. Calculate the starting pressure gradient of each grid point according to the crude oil viscosity of each grid point, and draw a starting pressure gradient curve;

[0011] S5. Determine the relationship between the driving pressure gradient curve and the starting pressure gradient curve. If they intersect, it means that the well spacing is large. Reduce the well spacing according to the set value and repeat steps S2-S5. If they separate, it means that the well spacing is small. Increase the well spacing according to the set value and repeat steps S2-S5; until they are tangent, determine that the injection and production well spacing is the technical limit well spacing.

[0012] Preferably, in step 1, a numerical simulation component model of CO2 flooding in ultra-low permeability reservoirs is established using numerical simulation software based on the dissolution, phase change and miscibility of CO2 flooding in crude oil.

[0013] Preferably, in step 2, n is a positive integer ≥90, preferably, n is 90.

[0014] Preferably, in step 3, the formula for calculating the driving pressure gradient of each grid point is:

[0015]

[0016] Where D ri is the driving pressure gradient of the i-th grid point, P(i) is the pressure of the i-th grid point, m is the number of grid points as an optional implementation, and l(i) is the length of the i-th grid point.

[0017] Further preferably, in step 3, m is a positive integer ≥21, preferably, m is 21.

[0018] Preferably, in step 4, the formula for calculating the starting pressure gradient of each grid is:

[0019] G o =A×(K / μ o ) -B

[0020] In the formula, G o is the starting pressure gradient, K is the permeability, μ o is the viscosity of crude oil, and A and B are coefficients to be determined.

[0021] The present invention also provides a system for determining the technical limit well spacing of CO2 flooding in ultra-low permeability reservoirs, the system comprising a component model building module, a calculation module, a driving pressure gradient determination module, a start-up pressure gradient determination module, and a technical limit well spacing determination module;

[0022] The component model building module uses reservoir numerical simulation software to build a reservoir numerical simulation component model based on the effect of CO2 on crude oil viscosity reduction and the impact on the oil phase start-up pressure gradient;

[0023] The calculation module sets injection and production wells according to the set well spacing, and uses the model established by the component model establishment module to calculate the pressure of each grid point between the injection and production wells and the value of crude oil viscosity after the model is calculated n days later;

[0024] The driving pressure gradient determination module calculates the driving pressure gradient of each grid point according to the pressure of each grid point and draws the driving pressure gradient curve; the driving pressure gradient calculation formula of each grid point is:

[0025]

[0026] Where D ri is the driving pressure gradient of the i-th grid point, P(i) is the pressure of the i-th grid point, m is the number of grid points, and l(i) is the length of the i-th grid point;

[0027] The startup pressure gradient determination module calculates the startup pressure gradient of each grid according to the crude oil viscosity and permeability of each grid point, and draws the startup pressure gradient curve; the startup pressure gradient calculation formula of each grid is:

[0028] G o =A×(K / μ o ) -B

[0029] In the formula, G o is the starting pressure gradient, K is the permeability, μ o is the viscosity of crude oil, A and B are coefficients to be determined;

[0030] The technical limit well spacing determination module is used to determine the relationship between the driving pressure gradient curve and the starting pressure gradient curve. If they intersect, it means that the well spacing is too large, and the well spacing is reduced according to the set value, and the module returns to the calculation module; if they are separated, it means that the well spacing is too small, and the well spacing is increased according to the set value, and the module returns to the calculation module; until they are tangent, it is determined that the well spacing at this time is the technical limit well spacing.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] The invention accurately calculates the technical limit well spacing of CO2 flooding in ultra-low permeability reservoirs based on the relationship between the driving pressure gradient curve and the starting pressure gradient curve. The method of the invention is simple, involves fewer related parameters, and provides a new method and research idea for obtaining the limit well spacing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 This is a flow chart of a method for determining the limit well spacing of CO2 flooding technology in ultra-low permeability reservoirs according to a specific embodiment of the present invention;

[0035] Figure 2 This is a driving pressure gradient curve corresponding to a well spacing of 160 m described in a specific embodiment of the present invention;

[0036] Figure 3 This is a startup pressure gradient curve corresponding to a well spacing of 160 m described in a specific embodiment of the present invention;

[0037] Figure 4 A relationship diagram of a driving pressure gradient curve and a start-up pressure gradient curve between injection and production wells corresponding to a well spacing of 160 m in a specific embodiment of the present invention;

[0038] Figure 5 This is a relationship diagram between the driving pressure gradient curve between the injection and production wells and the start-up pressure gradient curve corresponding to the 150m well spacing described in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0039] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0041] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0042] Example 1 A method for determining the limit well spacing of CO2 flooding technology in ultra-low permeability reservoirs

[0043] like Figure 1 As shown, the method for determining the limit well spacing of CO2 flooding technology in ultra-low permeability reservoirs includes the following steps:

[0044] Step S1: According to the dissolution, phase change and miscibility of CO2 flooding in crude oil, a numerical simulation component model of CO2 flooding in ultra-low permeability reservoirs is established using numerical simulation software;

[0045] Step S2: setting injection and production wells according to the set well spacing, and using the numerical simulation component model to calculate the pressure and crude oil viscosity values ​​at each grid point between the injection and production wells after n days; wherein n=90.

[0046] Step S3: Calculate the driving pressure gradient of each grid point according to the pressure of each grid point, and draw a driving pressure curve between injection and production wells;

[0047] The driving pressure gradient calculation formula for each grid point is:

[0048]

[0049] Where D ri is the driving pressure gradient of the i-th grid point, P(i) is the pressure of the i-th grid point, m is the number of grid points, m = a positive integer of 21, and l(i) is the length of the i-th grid point;

[0050] Step S4: calculating the starting pressure gradient of each grid point according to the crude oil viscosity of each grid point, and drawing a starting pressure gradient curve;

[0051] The calculation formula of the starting pressure gradient of each grid is:

[0052] G o =A×(K / μ o ) -B

[0053] In the formula, G o is the starting pressure gradient, K is the permeability, μ o is the viscosity of crude oil, A and B are unknown coefficients; A is 0.056, and B is 0.893.

[0054] Step S5: According to the relationship between the driving pressure gradient curve and the starting pressure gradient curve, if they intersect, it means that the well spacing is large, and the well spacing is reduced according to the set value, and steps S2-S5 are repeated; if they are separated, it means that the well spacing is small, and the well spacing is increased according to the set value, and steps S2-S5 are repeated; until they are tangent, it is determined that the injection and production well spacing is the technical limit well spacing at this time.

[0055] The technical limit well spacing is calculated based on the parameters of a certain reservoir. The basic parameters of the reservoir are as follows: the reservoir temperature is 126°C, the average porosity is 0.1, and the average permeability is 1×10 -3 μm 2 , the average viscosity of underground crude oil is 2mPa·s, the pressure difference between injection and production wells is 15MPa, and the multiple contact miscible pressure is 28.5MPa. The specific implementation steps are as follows:

[0056] Input the required component data table 1 into the reservoir numerical simulation component model;

[0057] Table 1 Formation crude oil composition data

[0058] Component name <![CDATA[CO2]]> <![CDATA[N2-CH4]]> <![CDATA[C2H-NC5]]> <![CDATA[C6-C7]]> Mole fraction 0.0044 0.2395 0.1470 0.1089 Component name <![CDATA[C8-C11]]> <![CDATA[C 12 -C 15 ]]> <![CDATA[C 16 -C 19 ]]> <![CDATA[C 19 -C 29 ]]> Mole fraction 0.2326 0.1172 0.0827 0.0669

[0059] The spacing between injection and production wells is set to 160m, and the reservoir numerical simulation component model is used to calculate the pressure and crude oil viscosity of each grid point between the injection and production wells at 90 days.

[0060] Usage Calculate the driving pressure gradient of each grid between the injection and production wells, and draw the driving pressure gradient curve between the injection and production wells. Figure 2 shown.

[0061] Use formula G o =0.056×(K / μ o ) -0.893 Calculate the starting pressure gradient of each grid between the injection and production wells, and draw the starting pressure gradient curve between the injection and production wells. Figure 3 shown.

[0062] like Figure 4 As shown in the figure, when the distance between the injection and production wells is 160m, the driving pressure gradient curve between the injection and production wells intersects with the start-up pressure curve, indicating that the injection and production wells cannot be connected and the distance between the wells is too large. Figure 5 As shown, when the well spacing is 150m, the start-up pressure gradient curve is tangent to the driving pressure gradient curve, so the technical limit well spacing is 150m.

[0063] Example 2 A system for determining the critical well spacing of CO2 flooding technology in ultra-low permeability reservoirs

[0064] The system includes a component model building module, a calculation module, a driving pressure gradient determination module, a start-up pressure gradient determination module, and a technical limit well spacing determination module;

[0065] The component model building module uses reservoir numerical simulation software to build a reservoir numerical simulation component model based on the effect of CO2 on crude oil viscosity reduction and the impact on the oil phase start-up pressure gradient;

[0066] The calculation module sets injection and production wells according to the set well spacing, and uses the model established by the component model establishment module to calculate the pressure of each grid point between the injection and production wells and the value of crude oil viscosity after the model is calculated n days later;

[0067] The driving pressure gradient determination module calculates the driving pressure gradient of each grid point according to the pressure of each grid point and draws the driving pressure gradient curve; the driving pressure gradient calculation formula of each grid point is:

[0068]

[0069] Where Dri is the driving pressure gradient of the i-th grid point, P(i) is the pressure of the i-th grid point, m is the number of grid points, and l(i) is the length of the i-th grid point;

[0070] The startup pressure gradient determination module calculates the startup pressure gradient of each grid according to the crude oil viscosity and permeability of each grid point, and draws the startup pressure gradient curve; the startup pressure gradient calculation formula of each grid is:

[0071] G o =A×(K / μ o ) -B

[0072] In the formula, G o is the starting pressure gradient, K is the permeability, μ o is the viscosity of crude oil, A and B are coefficients to be determined;

[0073] The technical limit well spacing determination module is used to determine the relationship between the driving pressure gradient curve and the starting pressure gradient curve. If they intersect, it means that the well spacing is too large, and the well spacing is reduced according to the set value, and the module returns to the calculation module; if they are separated, it means that the well spacing is too small, and the well spacing is increased according to the set value, and the module returns to the calculation module; until they are tangent, it is determined that the well spacing at this time is the technical limit well spacing.

[0074] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for determining the limit well spacing of CO2 flooding technology in ultra-low permeability reservoirs, characterized in that: It includes the following steps: S1. Establish a numerical simulation component model for CO2 flooding in ultra-low permeability reservoirs; S2. Setting injection and production wells according to the set well spacing, and using the numerical simulation component model established in step S1 to calculate the pressure and crude oil viscosity values ​​of each grid point between the injection and production wells after n days; S3. Calculate the driving pressure gradient of each grid point according to the pressure of each grid point, and draw the driving pressure curve between the injection and production wells; S4. Calculate the starting pressure gradient of each grid point according to the crude oil viscosity of each grid point, and draw a starting pressure gradient curve; S5. Determine the relationship between the driving pressure gradient curve and the starting pressure gradient curve. If they intersect, it means that the well spacing is large, and the well spacing is reduced according to the set value, and steps S2-S5 are repeated; if they are separated, it means that the well spacing is small, and the well spacing is increased according to the set value, and steps S2-S5 are repeated; until they are tangent, it is determined that the injection and production well spacing at this time is the technical limit well spacing; The formula for calculating the driving pressure gradient at each grid point is: Where D ri is the driving pressure gradient of the i-th grid point, P(i) is the pressure of the i-th grid point, m is the number of grid points, and l(i) is the length of the i-th grid point; The formula for calculating the starting pressure gradient of each grid is: G o =A×(K / μ o ) -B In the formula, G o is the starting pressure gradient, K is the permeability, μ o is the viscosity of crude oil, and A and B are coefficients to be determined.

2. The method according to claim 1, characterized in that: According to the dissolution, phase change and miscibility of CO2 flooding in crude oil, a numerical simulation component model of CO2 flooding in ultra-low permeability reservoirs was established using numerical simulation software.

3. The method according to claim 1, characterized in that: n is a positive integer ≥90.

4. The method according to claim 1, characterized in that: m is a positive integer ≥21.

5. A system for determining the critical well spacing of CO2 flooding technology in ultra-low permeability reservoirs, characterized in that: The system includes a component model building module, a calculation module, a driving pressure gradient determination module, a start-up pressure gradient determination module, and a technical limit well spacing determination module; The component model building module uses reservoir numerical simulation software to build a reservoir numerical simulation component model based on the effect of CO2 on crude oil viscosity reduction and the impact on the oil phase start-up pressure gradient; The calculation module sets injection and production wells according to the set well spacing, and uses the model established by the component model establishment module to calculate the pressure of each grid point between the injection and production wells and the value of crude oil viscosity after the model is calculated n days later; The driving pressure gradient determination module calculates the driving pressure gradient of each grid point according to the pressure of each grid point and draws the driving pressure gradient curve; the driving pressure gradient calculation formula of each grid point is: Where D ri is the driving pressure gradient of the i-th grid point, P(i) is the pressure of the i-th grid point, m is the number of grid points, and l(i) is the length of the i-th grid point; The startup pressure gradient determination module calculates the startup pressure gradient of each grid according to the crude oil viscosity and permeability of each grid point, and draws the startup pressure gradient curve; the calculation formula of the startup pressure gradient of each grid is: G o =A×(K / μ o ) -B In the formula, G o is the starting pressure gradient, K is the permeability, μ o is the viscosity of crude oil, A and B are coefficients to be determined; The technical limit well spacing determination module is used to determine the relationship between the driving pressure gradient curve and the starting pressure gradient curve. If they intersect, it means that the well spacing is too large, and the well spacing is reduced according to the set value, and the module returns to the calculation module; if they are separated, it means that the well spacing is too small, and the well spacing is increased according to the set value, and the module returns to the calculation module; until they are tangent, it is determined that the well spacing at this time is the technical limit well spacing.

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