Method for evaluating gas injection capacity of gas storage

Abstract

The invention belongs to the technical field of oil and gas resource development, and particularly relates to a gas storage gas injection capacity evaluation method. The method specifically comprises the following steps: establishing an injection capability binomial theoretical equation according to derivation; a working system is designed, a pressure gauge is delivered to measure the bottom hole pressure, and pressure temperature gradients under different depths of a shaft and measurement data of different working systems of a gas injection well are obtained; obtained data is processed and then substituted into the equation to calculate the coefficient, an injection capacity equation is obtained, and the maximum natural gas injection amount of the corresponding gas injection well under different formation pressure conditions is predicted according to the injection capacity equation. The stable formation pressure data of the test well can be accurately obtained, the gas injection capacity under different formation pressures and gas injection pressures can be predicted, the test process and the analysis method are simple and easy to implement, and a basis is provided for database building and site selection, gas injection well network optimization and injection increasing measure optimization.

Description

Technical Field

[0001] The invention belongs to the technical field of underground natural gas storage, gas injection and production engineering, and oil and gas resource development, and specifically relates to a method for evaluating the gas injection capacity of a gas storage reservoir. Background Art

[0002] Oil and gas reservoir gas storage is built on the basis of gas reservoirs that have been exhausted and abandoned or oil reservoirs that have been exploited to a certain extent, solving the problem of overcapacity of natural gas in summer and insufficient supply in winter. The injection and production capacity of the gas reservoir directly determines the gas storage reservoir's supply guarantee capacity, and accurate evaluation is crucial to the site selection, construction and operation of the gas reservoir.

[0003] At present, the injection capacity evaluation of gas injection wells mainly uses geological analysis of static data in the early stage of oil and gas reservoir exploration and development and dynamic data during the development process. However, with the decrease of formation pressure in the later stage of oil and gas production, the formation pore structure, permeability and fluid distribution have changed significantly. Practice has shown that this method of evaluating injection capacity using original formation parameters will produce large errors.

[0004] For the field test evaluation of injection capacity, since there is no standardized injection capacity evaluation method, the gas well exploration well production capacity evaluation equation is applied for evaluation.

[0005] In order to evaluate the injection capacity of gas wells in gas reservoirs without natural gas sources before the reservoir is built, some people have proposed to use nitrogen instead of natural gas as the injection medium for evaluation. The Chinese invention patent application with application publication number CN111927444A discloses a method for evaluating the injection capacity of gas storage reservoirs in depleted oil and gas reservoirs, which uses the evaluation equation of exploration well production capacity for evaluation. This method solves the problem of evaluating whether gas injection wells can be injected. The disadvantages are that the nitrogen production capacity of the equipment is limited, the nitrogen supply is small, the nitrogen injection time is short, and the bottom hole flow pressure is difficult to achieve stability, which reduces the accuracy of quantitative analysis of reservoir parameters and gas injection capacity.

[0006] When natural gas sources are sufficient, many gas storage facilities directly apply the exploratory well production capacity test and evaluation method for evaluation. This method requires that the formation pressure field is basically stable before the test. The formation pressure is stable before the exploratory well test, while the gas storage injection capacity test is carried out during the strong injection process of the gas reservoir. The well pressure interference is serious and the formation pressure field is unstable. Applying the exploratory well test test method will result in large errors. Summary of the invention

[0007] The purpose of the present invention is to provide a method for evaluating the gas injection capacity of a gas storage reservoir, so as to solve the problem of inaccurate evaluation of the gas injection capacity of a gas injection well caused by directly applying the production capacity test and evaluation method of an exploration well under strong injection and production conditions of a gas storage reservoir.

[0008] In order to solve the above technical problems, the present invention provides a method for evaluating the gas injection capacity of a gas storage reservoir, which collects the bottom hole flow pressure and formation pressure of a test well, and substitutes them into a relationship equation among the bottom hole flow pressure, formation pressure and gas injection volume to obtain the maximum natural gas injection volume corresponding to the test well; the relationship equation is derived based on the Darcy seepage equation, and the production capacity equation coefficient in the relationship equation is derived using multiple groups of test data including bottom hole flow pressure, formation pressure and gas injection volume obtained after testing the test well.

[0009] The beneficial effects are as follows: since directly applying the test and evaluation method for the production capacity of exploratory wells under strong injection and production conditions of a gas storage reservoir will lead to inaccurate evaluation of the gas injection capacity of the gas injection wells, the present invention obtains stable formation pressure through testing, and then conducts tests to obtain multiple groups of bottom hole flow pressure, formation pressure, and injection volume data of the tested wells, and substitutes the multiple groups of data into the derivation equation of the Darcy seepage formula to determine the equation coefficients, thereby obtaining a relationship equation, and the relationship equation is used to calculate the maximum injection volume of natural gas corresponding to the gas injection well under different formation pressure conditions, so as to accurately obtain stable formation pressure data of the test well and predict the gas injection capacity under different formation pressures and gas injection pressures, and the testing process and analysis method are simple and easy to use, providing a basis for selecting a reservoir site, optimizing the gas injection well network, and optimizing injection measures.

[0010] Furthermore, the relation equation is:

[0011] P wf 2 -P R 2 =Aq+Bq 2

[0012] Among them, P R is the formation pressure; P wf is the bottom hole flowing pressure; q is the gas injection volume; A and B are the production capacity equation coefficients in the relationship equation.

[0013] Its beneficial effects are: deriving an evaluation equation for well logging gas injection capacity and finding out relevant parameters affecting well injection volume, which is beneficial to the prediction and analysis of the wells being logged, and providing a basis for selecting a site for building a reservoir, optimizing the gas injection well network and optimizing the injection measures.

[0014] Furthermore, the step of testing the test well includes: conducting a pressure drop test on the test well; and conducting an injection capacity test on the test well according to a set plurality of test work systems, wherein the test work system refers to injecting gas at a set gas injection volume; and obtaining the required test data based on the test results of the two test experiments.

[0015] Its beneficial effects are: calculating multiple groups of test data under different injection rates, so as to solve the production capacity equation coefficient for the injection capacity evaluation equation, which is conducive to calculating the maximum natural gas injection volume of the corresponding gas injection well under different formation pressure conditions, so as to accurately obtain the stable formation pressure data of the test well and predict the gas injection capacity under different formation pressures and gas injection pressures.

[0016] Furthermore, the test time requirement of the test work system is not greater than the maximum test time, and the maximum test time is determined by the numerical well test volume control method.

[0017] Its beneficial effects are: reducing the interference from adjacent wells, making the test results more accurate, and being more conducive to obtaining more accurate stable formation pressure data of the test well and predicting the gas injection capacity under different formation pressures and gas injection pressures.

[0018] Furthermore, the test time requirement of the test work system is slightly greater than the minimum test time. The calculation formula for the minimum test time is:

[0019]

[0020] Among them, t s is the minimum test time; is the porosity; μ is the gas viscosity; C t is the formation compression coefficient; r e is the discharge radius of the flow system; K is the effective permeability.

[0021] The beneficial effects are as follows: since the gas flow time directly affects the accuracy of data analysis, the bottom hole pressure must be stable under each working system. Therefore, the test time of each working system must be slightly longer than the minimum test time to reduce the impact of the test on production, while reducing the test risk and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of a simulation curve of the bottom hole flow pressure and gas injection volume changing with time in the gas injection capacity test of the present invention;

[0023] Figure 2 This is a simulation diagram for determining the overall test time of the present invention (the black circle is a stable pressure field);

[0024] Figure 3 This is a measured diagram of the pressure drop curve of the present invention;

[0025] Figure 4 Inject measured curve graphs for different systems of the present invention;

[0026] Figure 5 It is a static pressure positive gradient analysis curve diagram of the present invention;

[0027] Figure 6 It is a double logarithmic curve fitting analysis diagram of the present invention;

[0028] Figure 7 It is the injection capacity prediction curve diagram of the present invention;

[0029] Figure 8 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0030] The basic concept of the present invention is: based on the derived binomial theoretical equation of injection capacity; designing a working system and sending a pressure gauge to measure the bottom hole pressure, obtaining the pressure and temperature gradient at different depths of the wellbore and the measurement data of different working systems of the gas injection well; performing preliminary processing and well test analysis on the pressure gradient, and substituting the parameters under each working system into the above equation to calculate its coefficient, to obtain the injection capacity equation, and predicting the maximum natural gas injection volume of the corresponding gas injection well under different formation pressure conditions according to the injection capacity equation.

[0031] The present invention will be described in detail below with reference to the accompanying drawings and method embodiments.

[0032] Method Example:

[0033] A method for evaluating the gas injection capacity of a gas storage reservoir according to the present invention is shown in the flow chart as follows: Figure 8 As shown, the specific implementation steps include:

[0034] Step 1: Derive and establish the injection capacity evaluation equation.

[0035] For gas under high pressure conditions, like liquid at room temperature, the compressibility coefficient C can be regarded as a constant. Based on the Darcy flow equation, the binomial theoretical equation of injectivity (i.e., the relationship equation between bottom hole flow pressure, formation pressure and gas injection volume) is derived:

[0036]

[0037]

[0038] P wf 2 -P R 2 =Aq+Bq 2

[0039] in, is the porosity; μ is the gas viscosity; C t is the formation compression coefficient; A and B are the coefficients of the production equation; K is the effective permeability; h is the production layer thickness; P R is the formation pressure; P wf is the bottom hole flowing pressure; q is the gas injection volume; r w is the wellbore radius; S is the skin coefficient.

[0040] Step 2: Perform a pressure drop test and an injection capacity test to obtain formation parameters for calculating the coefficients of the binomial theory equation for injection capacity in step 1.

[0041] 1) Pressure drop test.

[0042] The pressure gauge is lowered into the wellbore, and the pressure and temperature gradient at each depth are measured during the lowering process; the pressure gauge delivery position is determined according to the buried depth of the gas injection layer of the gas injection well and the structure of the pipe string, and the pressure gauge is delivered to a position as close to the middle depth of the reservoir as possible.

[0043] Among them, in order to prevent the test instrument from getting stuck during the lowering process, wireline operation is used for delivery before the test; and the weight of the test tool string is determined according to the current wellhead pressure of the gas storage injection well and the friction resistance of the sealing packing; when the well inclination exceeds 25°, the pressure gauge is delivered to a depth that does not go out of the pipe shoe.

[0044] 2) Injection capability test, test simulation curve such as Figure 1 shown.

[0045] ① Use the numerical well test analysis method to determine the formation pressure distribution around the gas injection well, and determine the test work system based on the size of the stable pressure distribution area.

[0046] Among them, in order to shorten the test time and reduce the pressure impact on the tubing during the injection capacity test, the "back pressure test" test method is selected. In order to reduce the analysis result error caused by the pressure backlash effect, the production increasing sequence is adopted and the production gap between each system is enlarged; 4 test points are selected for the injection capacity test, which are evenly distributed between 20% and 80% of the current maximum gas injection volume; when calculating the injection capacity equation in step three, there are 2 unknown coefficients, A and B. Theoretically, the values ​​of A and B can be calculated for 2 working systems, but the pressure flow data is not stable enough and deviations are easy to occur. Usually, at least 3 working systems are required to be measured. Generally, the stable gas injection volume and injection pressure data under 4 systems are conducive to accurately regressing the values ​​of A and B.

[0047] ② Determine the maximum and minimum test time for each work system.

[0048] Since the gas storage wells are close to each other, in order to reduce the interference of adjacent wells, the numerical well test volume control method is used to determine the maximum test time of each gas injection system to avoid pressure interference from adjacent wells. The simulation diagram is shown in the figure below. Figure 2 shown.

[0049] The length of gas flow time directly affects the accuracy of data analysis. Back pressure well testing requires that the bottom hole pressure must be stable under each working system. Therefore, the test time of each working system must be slightly longer than t sTo reduce the impact of testing on production, while reducing testing risks and costs, the minimum testing time for each gas injection system is:

[0050]

[0051] Among them, t s To stabilize the flow time; is the porosity; μ is the gas viscosity; C t is the formation compression coefficient; r e is the discharge radius of the flow system; K is the effective permeability.

[0052] ③ After the bottom hole pressure reaches stability under each working system, the pressure gauge obtains the pressure data of the gas injection well under different working systems.

[0053] 3) Calculate the coefficients of the binomial theory equation of injection capacity and obtain the injection capacity equation.

[0054] First, the pressure gradient conversion method is used to preliminarily process the pressure gradient test data obtained in the pressure drop test to obtain accurate pressure data at the deep position of the reservoir; then, the pressure data at the deep position of the reservoir obtained after processing is subjected to pressure drop test analysis to obtain formation characteristic parameters such as formation pressure, formation coefficient, permeability, and skin coefficient; the formation pressure and pressure data under each working system and gas injection volume data are substituted into the injection capacity binomial theoretical equation to obtain the gas injection capacity binomial equation coefficients A and B, and the injection capacity equation is obtained.

[0055] Among them, the well test analysis is carried out by double logarithmic curve fitting; the regression A and B values ​​have included the influence of permeability and skin coefficient.

[0056] Step three, calculate the maximum natural gas injection volume of the corresponding gas injection well under different formation pressure conditions according to the injection capacity equation, so as to evaluate the injection capacity of the gas storage reservoir.

[0057] The following is a specific example of evaluating the injection capacity of a gas reservoir type gas storage:

[0058] The relative density of natural gas is 0.6; the depth of the gas reservoir is 2802.6-3054.3m; the ball seat of the completion string is located at 2883.33m; and three months of continuous test injection were carried out before the test. The "back pressure test" test method was selected, and the well was shut down first to measure the pressure drop, and then the injection capacity test of four working systems was carried out.

[0059] During normal well opening, the wireline operation is carried out to 2860m to ensure that the wellbore is unobstructed; the wireline is suspended and the pressure gauge is lowered to 2850m, and the flow pressure and temperature gradient are measured in the middle.

[0060] The numerical well test pressure distribution simulation results, using the volume control method to determine the shut-in time and the test time of the four working systems, the shut-in test is 140 hours, and the injection capacity test is 8 hours for each system. The measured pressure curve is as follows Figure 3 Among them, combined with the maximum gas injection production of the gas injection well in the early stage, the injection capacity test system is designed to be 15×10 4 m 3 / d, 25×10 4 m 3 / d, 35×10 4 m 3 / d and 45×10 4 m 3 / d, obtain the pressure data of the gas injection well under the above four working systems, such as Figure 4 shown.

[0061] The static pressure positive gradient test data was preliminarily processed to obtain the wellbore pressure and temperature gradient. The deep static pressure and static temperature data of the formation were converted as shown in Table 1. The fitting curve is as follows: Figure 5 shown.

[0062] Table 1

[0063]

[0064] Then, the pressure data at the deep position of the reservoir obtained after processing is subjected to well test analysis, and the "homogeneous + impermeable boundary" model is selected for double logarithmic curve fitting, such as Figure 6 The formation parameters obtained by fitting are shown in Table 2 below:

[0065] Table 2

[0066] parameter Numeric dimension Formation pressure 33.082 MPa Formation coefficient 926.705 mD·m Effective penetration 6.725 mD Total skin factor -1.02 Fault distance 37.4 m Detection radius 283.0 m Well storage coefficient 1.627 <![CDATA[m 3 / MPa]]>

[0067] Substituting the parameters under the four working systems into the binomial theoretical equation of injection capacity, the binomial equation coefficients of the gas injection well are obtained, and the injection capacity equation is obtained as follows:

[0068] P wf 2 -P R 2 =0.86047q+0.01526q 2

[0069] The injection capacity equation is used to predict the maximum injection volume of natural gas corresponding to the gas injection well under different formation pressure conditions, such as Figure 7 shown.

[0070] The present invention can accurately obtain stable bottom hole pressure data of the test well when there is large interference between wells during the strong injection process of the gas injection wells of the gas storage reservoir, and predict the gas injection capacity under different gas injection pressures through the gas injection capacity evaluation equation; the test process and analysis method are simple and easy to implement, providing technical support for efficient gas injection in the gas storage reservoir.

Claims

1. A method for evaluating the gas injection capacity of a gas storage facility, characterized in that: The bottom hole flow pressure and formation pressure of the test well are collected and substituted into the relationship equation among the bottom hole flow pressure, formation pressure and gas injection volume to obtain the maximum natural gas injection volume corresponding to the test well; the relationship equation is derived based on the Darcy flow equation, and the production capacity equation coefficient in the relationship equation is derived using multiple groups of test data including the bottom hole flow pressure, formation pressure and gas injection volume obtained after testing the test well.

2. The method for evaluating the gas injection capacity of a gas storage facility according to claim 1, characterized in that: The relationship equation is: P wf 2 -P R 2 =Aq+Bq 2 Among them, P R is the formation pressure; P wf is the bottom hole flowing pressure; q is the gas injection volume; A and B are the production capacity equation coefficients in the relationship equation.

3. The method for evaluating the gas injection capacity of a gas storage facility according to claim 1, characterized in that: The steps of testing the test well include: conducting a pressure drop test on the test well; and conducting an injection capacity test on the test well according to a plurality of set test work systems, wherein the test work system refers to injecting gas at a set gas injection volume; and obtaining the required test data based on the test results of the two test experiments.

4. The method for evaluating the gas injection capacity of a gas storage facility according to claim 3, characterized in that: The test time requirement of the test work system shall not be greater than the maximum test time, and the maximum test time shall be determined by the numerical well test volume control method.

5. The method for evaluating the gas injection capacity of a gas storage facility according to claim 3, characterized in that: The test time requirement of the test work system is slightly greater than the minimum test time. The calculation formula for the minimum test time is: Among them, t s is the minimum test time; is the porosity; μ is the gas viscosity; C t is the formation compression coefficient; r e is the discharge radius of the flow system; K is the effective permeability.

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