Optimization Method for Injection-Production Well Spacing in Natural Gas Gravity Drainage

Abstract

The present invention relates to an optimization method for the injection-production well spacing in natural gas gravity drive. Well test interpretation is carried out using the test data of exploration wells to obtain the stable production capacity achieved under different injection-production well spacing conditions; considering the gravity segregation effect and the pressure difference displacement effect of the oil-gas density difference, the critical production capacity for achieving stable gravity drive under different well spacing conditions is obtained; an optimization chart for injection-production well spacing considering effective displacement and stable gravity drive is established; according to the relationship chart between injection-production well spacing and oil production, based on the formation dip angle, injection-production well number ratio, and well type of the injection-production well group in the target oilfield, the injection-production well spacing corresponding to the intersection point of the effective displacement curve and the stable gravity drive curve of different well groups is selected as the optimal injection-production well spacing to determine the injection-production well spacing for stable natural gas gravity drive. It can be used to optimize the injection-production well spacing in natural gas gravity drive, and provides a quantitative and operable technical method and implementation steps.

Description

Technical Field

[0001] The present invention relates to the field of natural gas gravity drive, and particularly to an optimization method for the injection-production well spacing in natural gas gravity drive. Background Art

[0002] The technology of injecting natural gas for gravity drive is one of the effective methods to improve the oil recovery rate of oil reservoirs. In the design of the natural gas gravity drive scheme, the reasonable matching of the injection-production well spacing and the injection-production rate is the key to affecting the development effect. At present, the main method for optimizing the injection-production well spacing in natural gas gravity drive is the numerical simulation method, and the injection-production well spacing is optimized by comparing the development effects of different injection-production well spacings. However, the workload of adjusting the well spacing by the numerical simulation method is cumbersome, and it is difficult to adopt differential designs for different injection-production well groups. The larger the injection-production well spacing is, the larger the critical injection-production rate for realizing a stable oil-gas interface is, and at the same time, the lower the production capacity that can be achieved after establishing an effective displacement is. Summary of the Invention

[0003] Aiming at the above problems, the purpose of the present invention is to provide an injection-production well spacing for natural gas gravity drive that takes into account the influences of both establishing an effective displacement and stabilizing the gas-oil interface.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] An optimization method for the injection-production well spacing in natural gas gravity drive, comprising:

[0006] Using the well test data of exploration wells for well test interpretation to obtain the stable production capacity achieved under different injection-production well spacing conditions;

[0007] Considering the gravity segregation effect and the pressure difference displacement effect of the oil-gas density difference to obtain the critical production capacity for realizing stable gravity drive under different well spacing conditions;

[0008] Based on the above stable production capacity and critical production capacity, establish an optimization chart for the injection-production well spacing considering effective displacement and stable gravity drive;

[0009] According to the relationship chart between the injection-production well spacing and the oil production rate, based on the formation dip angle, the injection-production well number ratio, and the well type of the injection-production well group in the target oilfield, select the injection-production well spacing corresponding to the intersection point of the effective displacement curve and the stable gravity drive curve of different well groups as the optimal injection-production well spacing to determine the injection-production well spacing for stable natural gas gravity drive.

[0010] Due to the adoption of the above technical solutions, the present invention has the following advantages:

[0011] It can be used to optimize the injection-production well spacing in natural gas gravity drive, and provides a quantitative and operable technical method and implementation steps. Brief Description of the Drawings

[0012] Upon reading the following detailed description of the preferred embodiments, various other advantages and benefits will become apparent to those of ordinary skill in the art. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to denote the same components. In the drawings:

[0013] Figure 1 is the stable production capacity under different injection-production well spacing conditions;

[0014] Figure 2 is the curve of the injection gas volume coefficient varying with the formation pressure;

[0015] Figure 3 is the critical production rate to achieve stable gravity drive under different well spacing conditions;

[0016] Figure 4 is the schematic diagram of the relationship between injection-production well spacing and oil production rate; and

[0017] Figure 5 is the application diagram of the relationship between injection-production well spacing and oil production rate.

[0018] The reference numerals in the drawings are represented as follows:

[0019] 1. The curve of the 1-injection-1-production directional well to achieve stable production capacity;

[0020] 2. The curve of the 1-injection-3-production horizontal well to achieve stable production capacity;

[0021] 3. The curve of the stable gravity drive production capacity at 2.8 degrees;

[0022] 4. The curve of the stable gravity drive production capacity at 5 degrees;

[0023] 5. The curve of the stable gravity drive production capacity at 7 degrees;

[0024] 6. The curve of the stable gravity drive production capacity at 10 degrees;

[0025] I. The quadrant clamped by the downward curve above and the upward curve below, where effective displacement can be established, but stable gravity drive cannot be achieved, resulting in a deterioration of the development effect;

[0026] II. The quadrant above both the downward curve and the upward curve, where neither effective displacement can be established nor stable gravity drive can be achieved. The daily oil production rate continuously decreases to the downward curve and reaches stability, while the development effect deteriorates;

[0027] III. The quadrant clamped by the upward curve above and the downward curve below, where effective displacement cannot be established, but stable gravity drive can be achieved, resulting in the daily oil production rate continuously decreasing to the downward curve and reaching stability;

[0028] IV. In the quadrant below the downward curve and the downward curve, it is the area where an effective displacement can be established and a stable gravity drive can be achieved. Detailed implementation manners

[0029] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be fully conveyed to those skilled in the art.

[0030] According to some embodiments of the present application, an optimization method for the injection-production well spacing of natural gas gravity drive considering effective displacement and stable gas-oil interface is provided. Mainly by establishing a graph of the relationship between injection-production well spacing and oil production, and according to the reservoir dip angle, injection-production well number ratio, and well type of the gas injection well group, the injection-production well spacing of natural gas gravity drive is optimized.

[0031] Step 1. Determine the stable production capacity that can be achieved under different well spacing conditions. Use the test data of exploration wells for well test interpretation and calculate the detection radius of the exploration well test. Calculate the correction coefficient using the exploration well test data. Calculate the stable production capacity that can be achieved under different injection-production well spacing conditions.

[0032] Step 2. Determine the critical production capacity for achieving stable gravity drive under different well spacing conditions. Considering the gravity segregation effect of the oil-gas density difference and the pressure difference displacement effect, calculate the critical production for achieving stable gravity drive under different well spacing conditions.

[0033] Step 3. Establish an optimization graph of injection-production well spacing considering effective displacement and stable gravity drive

[0034] Based on the results obtained in Steps 1 and 2, establish a graph of the relationship between injection-production well spacing and oil production.

[0035] Figure 4 The downward curve in the figure is the maximum daily oil production for establishing effective displacement. The area below this downward curve is the stable daily oil production that can be achieved under the corresponding injection-production well spacing conditions. As the injection-production well spacing increases, the maximum daily oil production for establishing effective displacement gradually decreases.

[0036] Figure 4 The upward curve in the figure is the maximum daily oil production for achieving stable gravity drive. The area below this upward curve is the daily oil production for achieving stable gravity drive that can be achieved under the corresponding injection-production well spacing conditions. As the injection-production well spacing increases, the maximum daily oil production for achieving stable gravity drive gradually increases.

[0037] The two curves divide the entire area into four quadrants. The quadrants in the downward curve and below the downward curve are the ranges where effective displacement can be established and stable gravity drive can be achieved, as shown in Figure 4 The IV region in the figure; the quadrant sandwiched by the downward curve on the top and the upward curve on the bottom can establish effective displacement, but cannot achieve stable gravity drive, resulting in poor development effect, as shown in Figure 4 The first area in the figure; the quadrant where the upward curve is in the upper part and the downward curve is in the lower part cannot establish effective displacement, but stable gravity drive can be achieved, resulting in the daily oil production continuously decreasing to the downward curve and reaching stability, which is shown as Figure 4 The third area in the figure; at the same time, in the quadrant above the downward curve and the upward curve, it is the range where neither effective displacement nor stable gravity drive can be established. The daily oil production continues to decrease to the downward curve and reaches stability. At the same time, the development effect becomes worse, which is shown as Figure 4 Therefore, the intersection of the downward curve and the upward curve is the maximum daily oil production that can establish effective displacement and achieve stable gravity drive, that is, the optimal injection-production well spacing.

[0038] Step 4. Determine the injection and production well spacing for natural gas stable gravity drive

[0039] On the basis of steps 1 and 2, the relationship chart between the injection-production well spacing and the oil production is calculated and established. According to the principle of selecting the optimal injection-production well spacing in step 3, based on the formation inclination, injection-production well number ratio, and well type of the injection-production well group of the target oil field, the injection-production well spacing corresponding to the intersection of the effective displacement curve and the stable gravity drive curve of different well groups is selected as the optimal injection-production well spacing.

[0040] According to some embodiments of the present application, the injection-production well spacing of natural gas gravity drive is optimized mainly by using reservoir engineering methods, including the following steps:

[0041] Step 1. Determine the stable production capacity that can be achieved under different well spacing conditions. Use the exploratory well test data, conduct well test interpretation, and calculate the detection radius re of the exploratory well test. Substitute the exploratory well test data into formula (1) to calculate the correction coefficient α.

[0042] The stable production capacity that can be achieved under different injection-production well spacing conditions is calculated using formula (1):

[0043]

[0044] In the formula, α is the correction coefficient;

[0045] Qo——daily oil production, m 3 / d;

[0046] K——permeability, mD;

[0047] h —— Effective thickness, m;

[0048] Δp —— Injection-production pressure difference, MPa;

[0049] μo —— Crude oil viscosity, mPa·s

[0050] Bo —— Crude oil volume factor, m 3 / m 3 ;

[0051] re —— Supply radius, m;

[0052] rw —— Wellbore diameter, m.

[0053] Figure 1 Shows the stable production capacity under different injection-production well spacings of 300m, 500m, 800m, 1000m and 1600m. When the injection-production well spacing increases from 300m to 1600m, the stable production capacity of the production well gradually decreases.

[0054] Step 2. Determine the critical production capacity for achieving stable gravity drive under different well spacing conditions

[0055] Consider the gravity segregation effect and pressure difference displacement effect of the oil-gas density difference as Figure 2 shown. As Figure 2 shown, the boundary between gas and oil is shown as the OCG oil-gas contact surface.

[0056] Calculate the critical production for achieving stable gravity drive under different well spacing conditions using Equation (2):

[0057]

[0058] Where, Qocg —— Critical daily oil production, m 3 / d;

[0059] K —— Permeability, mD;

[0060] h —— Effective thickness, m;

[0061] b —— Perforation thickness, MPa;

[0062] ρ o —— Oil density, kg / m 3 ;

[0063] ρ g —— Gas density, kg / m 3 .

[0064] Step 3. Establish an optimization chart of injection-production well spacing considering effective displacement and stable gravity drive

[0065] Based on Steps 1 and 2, using the results calculated by Equations (1) and (2), establish a relationship chart of injection-production well spacing and oil production, as Figure 4 shown.

[0066] Step 4. Determine the injection-production well spacing for stable gas gravity drive

[0067] Based on Steps 1 and 2, using the relationship chart of injection-production well spacing and oil production established by the results calculated by Equations (1) and (2), according to the principle of selecting the optimal injection-production well spacing in Step 3, based on the formation dip angle, injection-production well number ratio, and well type of the injection-production well groups in the target oilfield, respectively select the injection-production well spacing corresponding to the intersection point of the effective displacement curve and the stable gravity drive curve of different well groups as the optimal injection-production well spacing.

[0068] As Figure 5 shown, Curve 1 indicates that a directional well with 1 injection and 1 production can achieve stable production capacity; Curve 2 indicates that a horizontal well with 1 injection and 3 productions can achieve stable production capacity; Curve 3 indicates the production capacity of 2.8-degree stable gravity drive; Curve 4 indicates the production capacity of 5-degree stable gravity drive; Curve 5 indicates the production capacity of 7-degree stable gravity drive; Curve 6 indicates the production capacity of 10-degree stable gravity drive.

[0069] The present invention proposes a set of technical methods, and applying this method can be used to optimize the injection-production well spacing of gas gravity drive.

[0070] The present invention provides quantitative and operable technical methods and implementation steps.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optimization method for the injection-production well spacing in natural gas gravity drive, characterized in that, Including: Performing well test interpretation using exploration well test data to obtain the stable production capacity achieved under different injection-production well spacing conditions; Considering the gravity segregation effect and pressure difference displacement effect of the oil-gas density difference to obtain the critical production capacity for achieving stable gravity drive under different well spacing conditions; Based on the above stable production capacity and critical production capacity, establishing an injection-production well spacing optimization chart considering effective displacement and stable gravity drive; According to the relationship chart between injection-production well spacing and oil production, based on the formation dip angle, injection-production well number ratio, and well type of the injection-production well group in the target oilfield, selecting the injection-production well spacing corresponding to the intersection point of the effective displacement curve and the stable gravity drive curve of different well groups as the optimal injection-production well spacing to determine the injection-production well spacing for stable gravity drive of natural gas; The obtaining of the critical production capacity for achieving stable gravity drive under different well spacing conditions includes calculating the critical production for achieving stable gravity drive under different well spacing conditions using Equation (2): (2) Wherein, Q ocg — Critical daily oil production; K — Permeability; h — Effective thickness; b — Perforation thickness; ρ o — Oil density; ρ g — Gas density; μ o — Crude oil viscosity; B o — Crude oil volume factor; r e — Supply radius; r w — Well diameter.

2. The optimization method of the injection-production well spacing for natural gas gravity drive according to claim 1, wherein The performing of well test interpretation using exploration well test data includes: calculating the supply radius of the exploration well test, substituting the exploration well test data into Equation (1) to calculate the correction coefficient, and using Equation (1) to calculate the stable production capacity achieved under different injection-production well spacing conditions: (1) Wherein, Q o — Oil production per day; α — Correction factor; K — Permeability; h — Effective thickness; Δp — Injection-production pressure difference; μ o — Crude oil viscosity; B o — Crude oil volume factor; r e — Supply radius; r w — Well diameter.

3. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 1, wherein, The above-mentioned based on the formation dip angle, injection-production well number ratio, and well type of the injection-production well group in the target oilfield includes: 1-injection-1-production directional well, 1-injection-3-production horizontal well, 2.8-degree formation dip angle, 5-degree formation dip angle, 7-degree formation dip angle, and 10-degree formation dip angle.

4. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 1, wherein The obtaining of the stable production capacity achieved under different injection-production well spacing conditions includes the stable production capacity when the injection-production well spacing is 300m, 500m, 800m, 1000m, and 1600m.

5. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 1, characterized in that Meanwhile, the quadrant below both the effective displacement curve and the stable gravity drive curve is the area for establishing the effective displacement and the range for achieving stable gravity drive.

6. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 5, characterized in that, In the area clamped by the effective displacement curve above and the stable gravity drive curve below, effective displacement can be established, but stable gravity drive cannot be achieved.

7. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 5, wherein In the area clamped by the stable gravity drive curve above and the effective displacement curve below, effective displacement cannot be established, but stable gravity drive can be achieved, resulting in the daily oil production continuously decreasing to the effective displacement curve and reaching stability.

8. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 5, characterized in that In the area above both the effective displacement curve and the stable gravity drive curve, neither effective displacement can be established nor stable gravity drive can be achieved. The daily oil production continuously decreases to the effective displacement curve and reaches stability, and at the same time, the development effect deteriorates.

9. The optimization method for the injection-production well spacing in natural gas gravity drive according to claim 1, characterized in that The intersection point of the effective displacement curve and the stable gravity drive curve is the maximum daily oil production for simultaneously establishing effective displacement and achieving stable gravity drive, which is the optimal injection-production well spacing.

Images