Method for testing oil and gas reservoir capacity of tight sandstone reservoir

Abstract

The invention relates to the field of petroleum and natural gas engineering, in particular to a method for testing the oil and gas storage capacity of a tight sandstone reservoir in the exploration and development process. A tight sandstone reservoir oil and gas reservoir capacity testing method comprises the following steps: acquiring a pressure-time curve of a tight sandstone target reservoir section and an upper cover rock sample thereof; constructing a pressure drop standard function; respectively fitting the pressure-time curve of the target reservoir section rock sample and the pressure-time curve of the cover rock sample with a pressure drop standard function to obtain a target reservoir section pressure drop function and a cover pressure drop function; and calculating a reservoir physical property similarity coefficient according to the pressure drop function of the target reservoir section, calculating a cap layer physical property deviation coefficient according to the cap layer pressure drop function, taking an arithmetic square root of a product of the reservoir physical property similarity coefficient and the cap layer physical property deviation coefficient as an oil and gas reservoir index, and evaluating the reservoir capacity according to the oil and gas reservoir index. The method has popularization and application values.

Description

Technical Field

[0001] The invention relates to the field of petroleum and natural gas engineering, in particular to a method for testing the oil and gas storage capacity of a tight sandstone reservoir during the exploration and development process. Background Art

[0002] Storage capacity is a key factor in the evaluation of the potential and development effect of unconventional tight oil and gas resources, and directly affects the production of a single well. At present, various oil fields and scientific research units have done a lot of work on the evaluation and characterization of oil and gas storage capacity, which has strongly supported the exploration and development effect of tight oil and gas. It mainly uses a large number of well logging fine interpretations, downhole coring, and low-field nuclear magnetic resonance with high-precision experimental instruments. The overall evaluation of reservoir oil and gas storage capacity is mainly based on single factor analysis, such as the reservoir physical parameters porosity, permeability, microscopic pore structure, oil and gas mobility and other static methods. The invention patent of this application innovatively evaluates the homogeneity of reservoir physical properties and the difference between caprock and reservoir based on the pore pressure response of the reservoir and caprock that affects the storage capacity, and then calculates the storage capacity index to achieve quantitative evaluation and grade classification, which provides new ideas and methods for the quantitative evaluation of the storage capacity of tight sandstone reservoirs. Summary of the invention

[0003] The present invention aims to solve the above problems and proposes a method for testing the oil and gas storage capacity of a tight sandstone reservoir.

[0004] The technical solution of the present invention is: A method for testing the oil and gas storage capacity of a tight sandstone reservoir is as follows: obtaining a pressure-time curve of a target tight sandstone reservoir section and a cap rock sample above it; constructing a pressure drop standard function; fitting the pressure-time curve of the target reservoir section sample and the pressure-time curve of the cap rock sample with the pressure drop standard function respectively to obtain a target reservoir section pressure drop function and a cap pressure drop function; calculating a reservoir property similarity coefficient according to the target reservoir section pressure drop function, calculating a cap property deviation coefficient according to the cap pressure drop function, taking the arithmetic square root of the product of the reservoir property similarity coefficient and the cap property deviation coefficient as an oil and gas storage index, and evaluating the storage capacity with the oil and gas storage index.

[0005] The above-mentioned 0.75<oil and gas reservoir index≤1, the reservoir capacity grade is I; 0.50<oil and gas reservoir index≤0.75, the reservoir capacity grade is II; 0.25<oil and gas reservoir index≤0.5, the reservoir capacity grade is III; 0<oil and gas reservoir index≤0.25, the reservoir capacity grade is IV.

[0006] The specific process of obtaining the target reservoir pressure drop function and the cap rock pressure drop function is as follows: The specific representation form of the pressure drop standard function is: (3) in, r i = r max × i / q (1) (8) x i = π 2 ( r i ×10 -4 ) 2 / (96 μcL 2 ) (2) Where: P j is the pressure drop standard function, dimensionless; i is the number of the pore radius, dimensionless; j It is the number of rock samples, dimensionless, dimensionless; t is time, s; r i is the pore radius, nm; x i for r i Corresponding pressure drop rate, s -1 ; y i is the influence ratio of pressure drop rate, dimensionless; q is the number of different pressure drop rates in the pressure drop standard function, dimensionless; μ is viscosity, cP; c is the gas compressibility factor, psi -1 ; L is the length of the rock sample, cm; r max for r i Maximum value of, nm; The pressure drop standard function is fitted to the pressure-time curve of the target reservoir section rock sample and the pressure-time curve of the cap rock sample, respectively, to obtain the target reservoir section pressure drop function and the cap rock pressure drop function.

[0007] The specific calculation process of the reservoir physical property similarity coefficient is: (5) (4) Where: n is the number of rock samples in the target reservoir section, n= j -1, dimensionless; RI is the reservoir property similarity coefficient, dimensionless; k j It is the total coefficient of core pore connectivity and is dimensionless.

[0008] The specific calculation process of the cap layer physical property deviation coefficient is: (6) Where: G.I. is the caprock physical property deviation coefficient, dimensionless; (a i ) n The influence ratio of the pressure drop rate of the target reservoir section closest to the cap rock in depth is dimensionless; ( a i ) j is the influence ratio of pressure drop rate on cap rock sample, which is dimensionless.

[0009] The specific calculation process of the oil and gas reservoir index is as follows: (7) Where: NI is the oil and gas reservoir index, dimensionless; RI is the reservoir property similarity coefficient, dimensionless; G.I. It is the coefficient of deviation of physical properties of caprock and is dimensionless.

[0010] The pressure-time curve is obtained by conducting a pressure drop test experiment on a rock sample.

[0011] The specific preparation process of the rock sample is as follows: the target reservoir section rock core / cap rock core is made into a standard cylindrical rock core with a height of 5 cm and a diameter of 2.5 cm, and is placed in a constant temperature box at 100°C for drying for 24 hours to make the pores of the standard cylindrical rock core free of moisture, thereby making the target reservoir section rock sample / cap rock sample.

[0012] The pressure drop test experiment is carried out in a tight sandstone reservoir pore connectivity test device; the tight sandstone reservoir pore connectivity test device comprises a constant speed and constant pressure pump, an intermediate container, a vacuum pump and a core holder connected in sequence, the core holder having a target reservoir section rock sample / cap rock sample built in; the intermediate container is also connected to a pressure gauge.

[0013] The specific process of the pressure drop test experiment is as follows: the target reservoir section rock sample / cap rock sample is placed in the core holder; first, the gas is pumped into the intermediate container by a constant speed and constant pressure pump until the pressure gauge displays the designed value and then stops; the core holder is vacuum treated by a vacuum pump, and after the vacuum treatment is completed, the gas in the intermediate container is passed into the core holder, and the data points of pressure and time in the pressure gauge are recorded at the same time, until the pressure of the pressure gauge is stable, and the experiment is ended.

[0014] The technical effects of the present invention are: The present invention proposes a pressure drop standard function, which is fitted to obtain the pressure drop function of the actual rock sample, and the reservoir physical property similarity coefficient and the cap rock physical property deviation coefficient are calculated based on this function. The arithmetic square root of the product of the reservoir physical property similarity coefficient and the cap rock physical property deviation coefficient is used as the oil and gas reservoir index, and the oil and gas reservoir index is used to evaluate the reservoir capacity. The larger the oil and gas reservoir index, the stronger the oil and gas reservoir capacity of the tight sandstone reservoir is. The data of the present invention is derived from actual core experimental tests in the mine, which is accurate and reliable, and the test method is simple and easy to operate. It can be quickly applied to the evaluation of the storage capacity of the mine reservoir, greatly reducing the cost of large-scale coring, logging grade testing and interpretation in the mine. It is also applicable to the evaluation of the storage capacity of similar sandstone reservoirs and has promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Picture 1 This is the fitting diagram of the pressure-time curve of the KL-1 rock sample and the standard function of pressure drop.

[0016] Picture 2 This is the fitting diagram of the pressure-time curve of KL-2 rock sample and the standard function of pressure drop.

[0017] Picture 3 This is the fitting diagram of the pressure-time curve of KL-3 rock sample and the standard function of pressure drop.

[0018] Picture 4 This is the fitting diagram of the pressure-time curve of KL-4 rock sample and the standard function of pressure drop.

[0019] Picture 5 This is the fitting diagram of the pressure-time curve of KL-5 rock sample and the standard function of pressure drop.

[0020] Picture 6 It is the fitting diagram of the pressure-time curve of KL-t rock sample and the standard function of pressure drop.

[0021] Picture 7 It is a schematic structural diagram of a tight sandstone reservoir pore connectivity test device according to the present invention.

[0022] Figure numerals: 1. constant speed and constant pressure pump; 2. constant speed and constant pressure pump outlet valve; 3. intermediate container; 4. intermediate container outlet valve; 5. vacuum pump; 6. vacuum pump inlet valve; 8. pressure gauge; 9. core holder. DETAILED DESCRIPTION

[0023] Example 1 A method for testing the oil and gas storage capacity of a tight sandstone reservoir is as follows: obtaining a pressure-time curve of a target tight sandstone reservoir section and a cap rock sample above it; constructing a pressure drop standard function; fitting the pressure-time curve of the target reservoir section sample and the pressure-time curve of the cap rock sample with the pressure drop standard function respectively to obtain a target reservoir section pressure drop function and a cap pressure drop function; calculating a reservoir property similarity coefficient according to the target reservoir section pressure drop function, calculating a cap property deviation coefficient according to the cap pressure drop function, taking the arithmetic square root of the product of the reservoir property similarity coefficient and the cap property deviation coefficient as an oil and gas storage index, and evaluating the storage capacity with the oil and gas storage index.

[0024] Example 2 On the basis of Example 1, it also includes that 0.75<oil and gas reservoir index≤1, the reservoir capacity grade is level I; 0.50<oil and gas reservoir index≤0.75, the reservoir capacity grade is level II; 0.25<oil and gas reservoir index≤0.5, the reservoir capacity grade is level III; 0<oil and gas reservoir index≤0.25, the reservoir capacity grade is level IV.

[0025] Example 3 On the basis of Example 2, it also includes: The specific process of obtaining the target reservoir pressure drop function and the cap rock pressure drop function is as follows: The specific representation form of the pressure drop standard function is: (3) in, r i = r max × i / q (1) (8) x i = π 2 ( r i ×10 -4 ) 2 / (96 μcL 2 ) (2) The pressure drop standard function is fitted to the pressure-time curve of the target reservoir section rock sample and the pressure-time curve of the cap rock sample, respectively, to obtain the target reservoir section pressure drop function and the cap rock pressure drop function.

[0026] Example 4 On the basis of Example 3, it also includes: The specific calculation process of the reservoir physical property similarity coefficient is: (5) (4) The specific calculation process of the cap layer physical property deviation coefficient is: (6) The specific calculation process of the oil and gas reservoir index is as follows: (7).

[0027] Example 5 On the basis of Example 4, it also includes: The pressure-time curve is obtained by conducting a pressure drop test experiment on a rock sample; The specific preparation process of the rock sample is as follows: the target reservoir section rock core / cap rock core is made into a standard cylindrical rock core with a height of 5 cm and a diameter of 2.5 cm, and is placed in a constant temperature box at 100° C. and dried for 24 hours to make the pores of the standard cylindrical rock core free of moisture, thereby making the target reservoir section rock sample / cap rock sample; The pressure drop test experiment is carried out in a tight sandstone reservoir pore connectivity test device; the tight sandstone reservoir pore connectivity test device comprises a constant speed and constant pressure pump 1, an intermediate container 3, a vacuum pump 5 and a core holder 9 connected in sequence, the core holder 9 having a target reservoir section rock sample / cap rock sample built therein; the intermediate container 3 is also connected to a pressure gauge 8; The specific process of the pressure drop test experiment is as follows: the target reservoir section rock sample / caprock rock sample is placed in the core holder 9; first, the gas is pumped into the intermediate container 3 by the constant speed constant pressure pump 1 until the pressure gauge 8 displays the designed value and then stops; the core holder 9 is vacuumed by the vacuum pump 5, and after the vacuum treatment is completed, the gas in the intermediate container 3 is passed into the core holder 9, and the data points of pressure and time in the pressure gauge 8 are recorded at the same time until the pressure of the pressure gauge 8 is stable, and the experiment is ended. The gas is nitrogen.

[0028] Specific experimental cases YY is the main development area of ​​typical tight sandstone reservoirs in my country. It is divided into three sets of main sub-layers YY1~YY3 vertically. KL is a well to be evaluated in this area. In the early stage, downhole coring of the three main sub-layers was carried out, and YY1 was taken as the target reservoir section to develop a test method for the oil and gas storage capacity of tight sandstone reservoirs.

[0029] Step 1: rock sample preparation and pressure drop test experiment to obtain the pressure-time curve of the target reservoir section rock sample and the pressure-time curve of the cap rock sample; Take 5 cores from the target reservoir section YY1 in the depth direction, and take 1 core from the upper cap rock of the target reservoir section, and process them into standard cylindrical cores with a height of 5 cm and a diameter of 2.5 cm; place the above 6 standard cylindrical cores in a constant temperature box at 100°C and dry them for 24 hours to make the pores of the standard cylindrical cores free of moisture, and make the target reservoir section rock samples KL-1 to KL-5 and the cap rock sample KL-t; The target reservoir section rock samples and cap rock samples were placed in the tight sandstone reservoir pore connectivity test device to carry out pressure drop test experiments, and 5 pressure-time curves of the target reservoir section rock samples and 1 pressure-time curve of the cap rock sample were obtained; The specific process of the pressure drop test experiment is as follows: First, close all valves except the outlet valve 2 of the constant speed and constant pressure pump, and use the constant speed and constant pressure pump 1 to pump gas into the intermediate container 3. After the pressure gauge 8 displays the designed value, stop the constant speed and constant pressure pump 1 and close the outlet valve 2 of the constant speed and constant pressure pump; open the inlet valve 6 of the vacuum pump, and use the vacuum pump 5 to evacuate the core holder 9. After the vacuum treatment, close the inlet valve 6 of the vacuum pump, and then open the outlet valve 4 of the intermediate container to pass the gas in the intermediate container 3 into the core holder 9. Open and record the data points of the pressure and the corresponding time in the pressure gauge 8 at the same time until the pressure of the pressure gauge 8 is stable, and end the experiment.

[0030] Step 2: Construct the target reservoir pressure drop function and the cap rock pressure drop function; The two indicators of the pressure drop standard function are the pressure drop rate and the influence ratio of the corresponding pressure drop rate. The specific representation form of the pressure drop standard function is shown in formula (3). Among them, the number of different pressure drop rates in the pressure drop standard function is q =5, pore radius r i Specifically, they are 100nm, 200nm, 300nm, 400nm and 500nm. The pore radius is calculated according to formula (2): r i The corresponding pressure drop rate x i , see Table 1 for details; Table 1 Pressure drop rate ; The pressure drop rate calculated above is x i Fitting with the pressure-time curve, the influence ratio of pressure drop rate is obtained, and the results are shown in Table 2; Table 2 Proportion of influence of pressure drop rate ; According to the data in Table 1 and Table 2 and formula (3), the target reservoir pressure drop function and cap rock pressure drop function are constructed.

[0031] Step 3: Calculate the total core pore connectivity coefficient according to formula (4): k j , and then calculate the reservoir physical property similarity coefficient according to formula (5) RI , the results are shown in Table 3; Table 3 Reservoir physical property similarity coefficient RI .

[0032] Step 4: Calculate the similarity coefficient of caprock properties G.I. ; Using the pressure drop function of the core closest to the cap rock in depth and the pressure drop function of the cap rock core, the reservoir core closest to the cap rock is KL-1. Combining formula (6), the cap rock physical property deviation coefficient can be obtained: G.I. It is 0.545.

[0033] Step 5: Calculate the arithmetic square root of the product of the reservoir physical property similarity coefficient and the cap rock physical property deviation coefficient as the oil and gas reservoir index, and use the oil and gas reservoir index to evaluate the reservoir capacity; Calculate the oil and gas reservoir index according to formula (7): NI is 0.714, and the storage capacity grade is II.

[0034] Traditionally, oil and gas storage capacity is calculated using oil saturation. The average oil saturation of a known reservoir is 55.6%, and the oil saturation range of similar reservoirs is generally 40%-65%. The following formula is used to express it in the same form as the oil and gas reservoir index: NII = (h y - h ymin ) / ( h ymax - h ymin ) Where: NII is the conventional oil and gas storage capacity, dimensionless; h y is the average oil saturation of the reservoir, %; hymax is the maximum oil saturation of similar reservoirs, %; h ymin is the minimum oil saturation of similar reservoirs, %; Calculate the conventional oil and gas storage capacity NII It is 0.624, and the storage capacity grade is also II.

Claims

1. A method for testing the oil and gas storage capacity of a tight sandstone reservoir, characterized in that: The method is as follows: obtaining the pressure-time curves of the target tight sandstone reservoir section and the cap rock samples above it; constructing a pressure drop standard function; fitting the pressure-time curves of the target reservoir section rock samples and the pressure-time curves of the cap rock samples with the pressure drop standard function respectively to obtain the target reservoir section pressure drop function and the cap rock pressure drop function; calculating the reservoir property similarity coefficient according to the target reservoir section pressure drop function, calculating the cap rock property deviation coefficient according to the cap rock pressure drop function, taking the arithmetic square root of the product of the reservoir property similarity coefficient and the cap rock property deviation coefficient as the oil and gas reservoir index, and evaluating the reservoir capacity with the oil and gas reservoir index.

2. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 1, characterized in that: The above-mentioned 0.75<Oil and Gas Reservoir Index≤1, the reservoir capacity grade is I; 0.50<Oil and Gas Reservoir Index≤0.75, the reservoir capacity grade is II; 0.25<Oil and gas reservoir index ≤0.5, the reservoir capacity grade is III; 0<Oil and gas reservoir index ≤0.25, the reservoir capacity grade is IV.

3. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 1, characterized in that: The specific process of obtaining the target reservoir pressure drop function and the cap rock pressure drop function is as follows: The specific representation form of the pressure drop standard function is: （3） in, r i = r max × i / q （1） （8） x i = π 2 ( r i ×10 -4 ) 2 / (96 μcL 2 ) （2） Where: P j is the pressure drop standard function, dimensionless; i is the number of the pore radius, dimensionless; j It is the number of rock samples, dimensionless, dimensionless; t is time, s; r i is the pore radius, nm; x i for r i The corresponding pressure drop rate, s -1 ; y i is the influence ratio of pressure drop rate, dimensionless; q is the number of different pressure drop rates in the pressure drop standard function, dimensionless; μ is viscosity, cP; c is the gas compressibility factor, psi -1 ; L is the length of the rock sample, cm; r max for r i Maximum value of, nm; The pressure drop standard function is fitted to the pressure-time curve of the target reservoir section rock sample and the pressure-time curve of the cap rock sample, respectively, to obtain the target reservoir section pressure drop function and the cap rock pressure drop function.

4. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 3, characterized in that: The specific calculation process of the reservoir physical property similarity coefficient is: （5） （4） Where: n is the number of rock samples in the target reservoir section, n = j -1, dimensionless; RI is the reservoir property similarity coefficient, dimensionless; k j It is the total coefficient of core pore connectivity and is dimensionless.

5. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 4, characterized in that: The specific calculation process of the cap layer physical property deviation coefficient is: （6） Where: GI is the caprock physical property deviation coefficient, dimensionless; (a i ) n The influence ratio of the pressure drop rate of the target reservoir section closest to the cap rock in depth is dimensionless; ( a i ) j is the influence ratio of pressure drop rate on cap rock sample, which is dimensionless.

6. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 1, characterized in that: The specific calculation process of the oil and gas reservoir index is as follows: （7） Where: NI is the oil and gas reservoir index, dimensionless; RI is the reservoir property similarity coefficient, dimensionless; GI It is the coefficient of deviation of physical properties of caprock and is dimensionless.

7. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 1, characterized in that: The pressure-time curve is obtained by conducting a pressure drop test experiment on a rock sample.

8. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 7, characterized in that: The specific preparation process of the rock sample is as follows: the target reservoir section rock core / cap rock core is made into a standard cylindrical rock core with a height of 5 cm and a diameter of 2.5 cm, and is placed in a constant temperature box at 100°C for drying for 24 hours to make the pores of the standard cylindrical rock core free of moisture, thereby making the target reservoir section rock sample / cap rock sample.

9. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 1, characterized in that: The pressure drop test experiment is carried out in a tight sandstone reservoir pore connectivity test device; the tight sandstone reservoir pore connectivity test device comprises a constant speed constant pressure pump (1), an intermediate container (3), a vacuum pump (5) and a core holder (9) which are connected in sequence, and the core holder (9) has a target reservoir section rock sample / cap rock sample built in; the intermediate container (3) is also connected to a pressure gauge (8).

10. The method for testing the oil and gas storage capacity of a tight sandstone reservoir according to claim 9, characterized in that: The specific process of the pressure drop test experiment is as follows: a target reservoir section rock sample / cap rock sample is placed in a core holder (9); first, a constant speed constant pressure pump (1) is used to pump gas into an intermediate container (3) until the pressure gauge (8) displays a designed value and then stops; a vacuum treatment is performed on the core holder (9) by a vacuum pump (5); after the vacuum treatment is completed, the gas in the intermediate container (3) is passed into the core holder (9), and the data points of pressure and time in the pressure gauge (8) are recorded at the same time, until the pressure of the pressure gauge (8) is stable, and then the experiment is ended.

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