Method for establishing gas drive theoretical chart of continuous gas drive reservoir

Abstract

The invention discloses a method for establishing a gas drive theoretical chart of a continuous gas drive reservoir, and relates to the technical field of oil-gas field development. Comprising the following steps: establishing a typical gas drive curve based on gas injection reservoir oil-gas two-phase flow; fitting a typical gas drive curve based on gas reservoir historical production data; and on the basis of the fitting relation, a gas drive theoretical plate is obtained by combining a gas drive plate formula. According to the method, the economic recoverable reserves or the technical recoverable reserves can be predicted by utilizing the actual economic limit gas-oil ratio or the technical limit gas-oil ratio, and the corresponding recovery ratio can be calculated, so that the continuous gas drive reservoir development effect is evaluated, the oilfield development strategy is adjusted in time, and the production and operation cost is saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development, in particular to a method for establishing a continuous gas drive reservoir gas drive theory chart. BACKGROUND

[0002] Water injection development reservoirs have perfect water drive theory and different Tong type curve charts to calibrate recoverable reserves and recovery rate, but gas injection reservoirs still lack corresponding gas drive characteristic curves and theory charts to comprehensively evaluate gas drive development effect. Since the 1970s, Tong Xianzhang has obtained water drive characteristic curves by using 25 reservoirs at home and abroad, which are hereinafter referred to as Tong type curve charts, and has obtained a water drive geological reserve calculation formula N=7.5 / B in combination with the water drive characteristic curves of Maximo. Due to defects such as a waterless oil production period and a boundary condition of 98% final water content in the initial conditions of the Tong type curve charts, after that, formula derivation and Tong type curve chart modification about water drive characteristic curves have sprung up, and different literatures have been published by Chen Yuanqian, Yu Qitai, Zhang Jinqing, Gao Wenzhong and Cui Yinghuai, etc. Based on oil-water seepage mechanism, the water drive curves and Tong type curve charts are perfected and modified. However, for continuous gas injection reservoirs for enhancing oil recovery, there is still no perfect gas drive characteristic curve and chart to evaluate development effect. SUMMARY

[0003] To solve at least one of the above problems, the present application provides a method for establishing a continuous gas drive reservoir gas drive theory chart.

[0004] The technical scheme for solving the above problems is as follows: a method for establishing a continuous gas drive reservoir gas drive theory chart, comprising the following steps: S1, based on gas injection reservoir oil and gas two-phase flow, a typical gas drive curve is established: , , , wherein, represents a production oil and gas ratio; represents a reservoir original dissolved gas oil ratio; represents a reservoir cumulative oil production; , represents a to-be-determined coefficient; n , m represents an oil and gas phase permeability to-be-determined coefficient; represents a reservoir crude oil viscosity; represents a crude oil volume coefficient; represents a reservoir natural gas viscosity; represents a natural gas volume coefficient; represents a bound water saturation; represents an original geological reserve of crude oil; S2, a characteristic curve is made based on gas reservoir historical production data and fitted to obtain an oil and gas phase permeability to-be-determined coefficientn and m ; S3, Based on gas reservoir fluid parameters and undetermined coefficient of hydrocarbon phase permeability n and m By combining the gas drive chart formula, the gas drive chart of the target gas reservoir is obtained; the gas drive chart formula is: ,in, , In the formula, f g R represents the gas content; R represents the recovery rate. Indicates the recovery rate under economically extreme conditions; This indicates the economically optimal production ratio of gas to oil. , This represents the coefficients to be determined.

[0005] The beneficial effects of this invention are as follows: by establishing a gas drive theoretical chart, the economically recoverable reserves or technically recoverable reserves can be predicted using the actual economic limit gas-oil ratio or technical limit gas-oil ratio, and the corresponding recovery rate can be calculated, thereby evaluating the development effect of continuous gas drive reservoirs, adjusting oilfield development strategies in a timely manner, and saving production and operation costs. Attached Figure Description

[0006] Figure 1 for and Relationship curve diagram; Figure 2 This is a dynamic production curve of the well group according to an embodiment of the present invention; Figure 3 This is a fitting graph of production data from an embodiment of the present invention to a typical gas-driven curve; Figure 4 This is a gas-driven diagram showing the gas content and recovery rate in an embodiment of the present invention. Detailed Implementation

[0007] The specific embodiments of the present invention will be clearly and completely described below with reference to examples. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments.

[0008] The method for establishing a theoretical chart for continuous gas drive reservoirs includes the following steps: S1. Based on the two-phase flow of oil and gas in gas-injected reservoirs, a typical gas drive curve is established: , , In the formula, Indicates the oil-to-gas ratio in production; Indicates the original dissolved gas-oil ratio of the reservoir; This indicates the cumulative oil production of the reservoir; , Indicates the coefficients to be determined; n ,m Indicates the undetermined coefficient of oil-gas phase permeability; Indicates the viscosity of crude oil in the reservoir; Indicates the crude oil volume coefficient; Indicates the viscosity of the reservoir natural gas; Indicates the natural gas volume factor; Indicates the degree of bound water saturation; Indicates the original geological reserves of crude oil; The above-mentioned typical gas drive curve formula is derived through a series of derivations based on existing technology and the characteristics of gas drive. The specific process is as follows: Kewen Li et al. renormalized the Corey formula and believed it could be applied to the percolation process. The normalized relationship between the relative permeability of the oil and gas phases is as follows: , , In the formula, Indicates the effective relative permeability of the oil phase; Indicates the effective relative permeability in the gas phase; Indicates the effective oil saturation; Indicates the average oil saturation; This indicates the residual oil saturation.

[0009] Based on the actual reservoir conditions, assuming =0.2、 =0.1, and by inversely normalizing the above normalized oil and gas two-phase relative permeability relationship, the formula for the non-standard oil and gas relative permeability curve is obtained: , , In the formula, The value represents the relative permeability of the oil phase at the bound water saturation level; in this embodiment, it is taken as 1. This represents the relative permeability of the gas phase when the residual oil is saturated. Indicates the average gas saturation; Based on the actual reservoir conditions, assuming The value is 0.8, which gives the ratio of relative permeability of oil and gas. With gas saturation Relationship curves, such as Figure 1 As shown.

[0010] according to Figure 1 Fitting and The relationship curve can be used to obtain the gas relative permeability ratio. It can be approximated by the following formula: ; For gas-injected reservoirs, when miscibility is not considered and the injection pressure is maintained at the original formation pressure during development, the original formation reserves and remaining geological reserves of the reservoir can be expressed as follows: , In the formula, Indicates the original geological reserves of crude oil; Indicates the remaining geological reserves of crude oil; A represents the reservoir area; h represents the oil layer thickness; Indicates porosity.

[0011] Subtracting the remaining crude oil geological reserves from the original crude oil geological reserves yields the cumulative oil production at that point in time. .

[0012] The cumulative oil production divided by the original geological reserves of crude oil equals the recovery level. In the formula, R represents the extraction degree.

[0013] Assuming a homogeneous and uniformly thick formation, and neglecting gravity and capillary forces, the formulas for oil production and gas production after gas breakthrough in a gas-injected reservoir under two-phase flow conditions are as follows: , In the formula, Indicates daily oil production; Indicates daily gas production; K represents absolute permeability; Indicates production pressure differential; Indicates the pressure relief radius; Indicates the pressure relief radius.

[0014] The gas-oil ratio is obtained by dividing the daily gas production by the daily oil production. Combined with the ratio of relative permeability of air Based on the approximate formula and extraction level, we can obtain: Taking the common logarithm of the aforementioned formula yields: ,in, , .

[0015] By deriving the formula, a typical gas-driven curve can be obtained.

[0016] Furthermore, based on the typical gas drive curves described above, the dynamic reserve formula for gas-driven reservoirs can also be obtained: .

[0017] S2. Based on historical production data of the gas reservoir, a typical gas drive curve is fitted to obtain the undetermined coefficient of oil-gas phase permeability. n and m ; The historical production data includes the production oil-to-gas ratio, the initial dissolved gas-to-oil ratio, and the cumulative oil production. In this process, the historical production data is substituted into the typical gas drive curve described above and linearly fitted to obtain the slope of the typical gas drive curve. b 2 and intercept a 2. Furthermore, through the slope b 2 and intercept a 2. The undetermined coefficient of oil-gas phase permeation can be obtained. n , m .

[0018] S3, Based on gas reservoir fluid parameters and undetermined coefficient of hydrocarbon phase permeability n and m By combining the gas drive chart formula, the gas drive chart of the target gas reservoir is obtained; the gas drive chart formula is: ,in, , In the formula, f g R represents the gas content; R represents the recovery rate. Indicates the recovery rate under economically extreme conditions; This indicates the economically optimal production ratio of gas to oil. , This represents the coefficients to be determined.

[0019] The gas drive diagram formula mentioned above is derived from the oil and gas flow in the reservoir and the economic limit oil-gas ratio, and is obtained through a series of derivations. The specific derivation process is shown below.

[0020] Once free gas flows in the formation, the formulas for calculating oil and gas production after gas breakthrough in the well are changed: , In the formula, Indicates daily oil production under formation conditions; This indicates the daily gas production under specific geological conditions.

[0021] Introducing the concept of gas cut into gas-driven reservoirs: = In the formula, f g This indicates the gas content.

[0022] Substituting the approximate expression for the relative permeability ratio of the oil and gas phases and the degree of recovery into the above formula, we can obtain: Taking the logarithm of the previous equation yields the preliminary gas drive formula: , , In the formula, This represents the coefficients to be determined.

[0023] In the Tong-style curve chart, a comprehensive water cut of 98% is taken as the economic limit water cut. Therefore, for water-driven reservoirs and gas-driven reservoirs, the comprehensive gas-oil ratio is used. As the economically optimal gas-oil ratio, it is not a fixed value due to various factors such as oil price fluctuations, operating costs, and natural gas prices. The specific value is determined by a comprehensive economic evaluation based on the actual conditions of each gas-injection reservoir. Therefore, when the economically optimal gas-oil ratio is reached, the change in gas cut is as follows: Substituting the previous equation into the preliminary air drive formula yields the air drive limiting formula: .

[0024] By subtracting the preliminary formula from the limit formula of air drive, we obtain the formula for the air drive drawing: ,in, .

[0025] To further illustrate the method of this embodiment of the invention, specific examples are given below.

[0026] A gas injection reservoir in the Tarim Oilfield, at a depth of 5800m and an oil column height of 120m, is a blocky bottom-water anticline reservoir. The original formation pressure was 62.4 MPa, and the formation temperature was 140℃. The average surface density of the crude oil is 0.85 g / cm³. 3 The original gas-oil ratio was 15m. 3 / m 3 The average viscosity of the crude oil in the formation is 2 mPa·s. This reservoir began production in 1990, underwent full-scale water injection development in 1994, and a natural gas injection-assisted gravity drive development test was conducted in 2014. Since the implementation of gas injection development, significant results have been achieved. In the four pilot gas injection well groups, the production of the surrounding first-line wells increased by 2 to 10 times. One of the gas injection well groups has a production section located at the top of the structure. Due to the poor reservoir properties at the high structural position (average porosity 13.2%, average permeability 4.9 mD), water injection was difficult in the early stages, resulting in the enrichment of residual oil. The gas-driven oil production process involves two-phase flow of oil and gas. Gas injection began in this well group in July 2014, and the surrounding first-line wells began to benefit from it in July 2015, with a significant increase in production. The highest daily oil production of the well group reached 160 m³. 3 / d, an increase of 8 times compared to before gas injection. See [see figure for daily oil production and gas-oil ratio after gas injection]. Figure 2 After the gas injection took effect, the gas-oil ratio gradually increased. In 2018, some single wells experienced gas leakage. Currently, the daily oil production is stable at 40 cubic meters per second. 3 / d, the comprehensive gas-oil ratio is nearly 1400m 3 / m 3 . =3000m 3 / m 3 At that time, the economically recoverable reserves of crude oil were 27.39 × 10⁻⁶. 4 m 3 The corresponding recovery rate was 71.3%.

[0027] Its fluid properties are shown in Table 1.

[0028] Table 1 Fluid Properties In this test case, production data after gas injection in July 2014 was used to fit a typical gas drive curve. The fitting results are as follows: Figure 3 As shown in the figure. , Substituting the data into Table 1, we get n = 0.001686; m = 8.83.

[0029] When the limiting gas-oil ratio is determined =3000m 3 / m 3 Then, a gas drive chart showing the gas content (fg) versus recovery rate (R) can be drawn (see...). Figure 4 The actual production data of the well group is projected onto the chart. In the chart, each curve represents the GOR (Gas-Oil Ratio) at the economic limit. lim =3000m 3 / m 3 The relationship between recovery rate and gas content under different economic limits, with well groups representing actual production conditions. From Figure 4 It can be seen that when the recovery rate under the economic limit condition is 0.7, which is 70%, it is in good agreement with the actual production situation. Therefore, the predicted final recovery rate is about 70%. The data points are highly correlated with the theoretical curve, which meets the needs of engineering calculations.

[0030] Based on previous research, this invention starts from a simple empirical formula for the relative permeability of oil and gas phases, and plots the relative permeability ratio of oil and gas phases (…). ) and gas saturation ( The relationship curve was analyzed, and it was found that in the two-phase co-permeability zone, most data points satisfy an exponential relationship. Based on this, the gas-oil ratio and cumulative oil production characteristic curves of continuous gas-drive reservoirs were derived. Simultaneously, to facilitate the dynamic analysis of production in continuous gas-injection reservoirs, the concept of gas cut under formation conditions was introduced, and a curve chart showing the relationship between gas cut and recovery rate was derived. Verification using actual production data from a pilot test well group in a gas-injection reservoir in the Tarim Oilfield showed that the derived gas-drive characteristic curves and charts meet engineering application requirements. This method can effectively predict economically recoverable or technically recoverable reserves, providing a reference method for other continuous gas-drive enhanced oil recovery reservoirs.

[0031] The present invention has been disclosed above with preferred embodiments. However, those skilled in the art should understand that these embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Further improvements can be made without departing from the principles of the invention, and these improvements should also be considered as protections of the present invention.

Claims

1. A method for establishing theoretical charts for continuous gas drive reservoirs, characterized in that, Includes the following steps: S1. Based on the two-phase flow of oil and gas in gas-injected reservoirs, a typical gas drive curve is established: , , In the formula, Indicates the oil-to-gas ratio in production; Indicates the original dissolved gas-oil ratio of the reservoir; This indicates the cumulative oil production of the reservoir; , Indicates the coefficients to be determined; n , m Indicates the undetermined coefficient of oil-gas phase permeability; Indicates the viscosity of crude oil in the reservoir; Indicates the crude oil volume coefficient; Indicates the viscosity of the reservoir natural gas; Indicates the natural gas volume factor; Indicates the degree of bound water saturation; Indicates the original geological reserves of crude oil; S2. Based on historical production data of the gas reservoir, a typical gas drive curve is fitted to obtain the undetermined coefficient of oil-gas phase permeability. n and m ; S3, Based on gas reservoir fluid parameters and undetermined coefficient of hydrocarbon phase permeability n and m By combining the gas drive chart formula, the gas drive chart of the target gas reservoir is obtained; The formula for the air-driven drawing plate is: ,in, , In the formula, f g R represents the gas content; R represents the recovery rate. Indicates the recovery rate under economically extreme conditions; This indicates the economically optimal production ratio of gas to oil. , This represents the coefficients to be determined.

2. The method for establishing a theoretical chart for continuous gas drive reservoirs according to claim 1, characterized in that, S2 includes the following steps: Acquire reservoir oil and gas fluid parameters and historical production data; The gas drive characteristic curve is obtained by fitting historical production data, and the slope of the gas drive characteristic curve is used as the undetermined coefficient. The intercept of the gas-driven characteristic curve is used as the coefficient to be determined. ; Based on S1 and reservoir oil and gas fluid parameters, the undetermined coefficient of oil and gas phase permeability is calculated. n and m .

3. The method for establishing a theoretical chart for continuous gas drive reservoirs according to claim 2, characterized in that, In S2, the historical production data includes the production oil-gas ratio, the original dissolved gas-oil ratio, and the cumulative oil production; the reservoir oil-gas fluid parameters include crude oil viscosity, crude oil volume coefficient, natural gas viscosity, natural gas volume coefficient, the original dissolved gas-oil ratio of the reservoir, and the bound water saturation.

4. The method for establishing a theoretical chart for continuous gas drive reservoirs according to claim 3, characterized in that, In S3 , , , In the formula, This represents the coefficients to be determined.

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