A testing method for the oil and gas storage capacity of a tight sandstone reservoir

Abstract

The present invention relates to the field of oil and gas engineering, in particular to a test method for the oil and gas storage capacity of a tight sandstone reservoir during the exploration and development process. A test method for the oil and gas storage capacity of a tight sandstone reservoir is as follows: obtain the pressure-time curves of the target reservoir section of the tight sandstone and the overlying caprock samples; construct a standard pressure decline function; fit the pressure-time curves of the target reservoir section samples and the caprock samples to the standard pressure decline function respectively to obtain the pressure decline function of the target reservoir section and the pressure decline function of the caprock; calculate the reservoir physical property similarity coefficient according to the pressure decline function of the target reservoir section, calculate the caprock physical property deviation coefficient according to the pressure decline function of the caprock, take the arithmetic square root of the product of the reservoir physical property similarity coefficient and the caprock physical property deviation coefficient as the oil and gas storage index, and evaluate the storage capacity with the oil and gas storage index. The present invention has the value of popularization and application.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas engineering, and 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] The storage capacity is a key factor in the potential evaluation and development effect evaluation of unconventional tight oil and gas resources, directly affecting the single-well production. At present, various oilfields and scientific research institutions have done a lot of work on the evaluation and characterization of the oil and gas storage capacity, which has strongly supported the exploration and development effect of tight oil and gas. Mainly through a large number of fine logging interpretations, downhole coring and relying on high-precision experimental instruments such as low-field nuclear magnetic resonance, etc., the evaluation of the oil and gas storage capacity of the reservoir is mainly analyzed from single factors, such as static methods of physical property parameters of the reservoir such as porosity, permeability, microscopic pore structure, oil and gas mobility, etc. The present application innovatively evaluates the physical property homogeneity of the reservoir and the difference between the caprock and the reservoir according to the pore pressure response of the reservoir and the caprock that affect the storage capacity, and then calculates the storage capacity index to achieve quantitative evaluation and grade division, providing a new idea and method for the quantitative evaluation of the storage capacity of tight sandstone reservoirs. Summary of the Invention

[0003] The present invention aims at 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 as follows:

[0005] A method for testing the oil and gas storage capacity of a tight sandstone reservoir, the method is as follows: obtain the pressure-time curves of the target reservoir section of the tight sandstone and the rock samples of the overlying caprock; construct a pressure drop standard function; respectively fit the pressure-time curves of the target reservoir section rock samples and the caprock rock samples with the pressure drop standard function to obtain the pressure drop function of the target reservoir section and the pressure drop function of the caprock; calculate the reservoir physical property similarity coefficient according to the pressure drop function of the target reservoir section, calculate the caprock physical property deviation coefficient according to the pressure drop function of the caprock, and take the arithmetic square root of the product of the reservoir physical property similarity coefficient and the caprock physical property deviation coefficient as the oil and gas storage index, and evaluate the storage capacity with the oil and gas storage index.

[0006] When 0.75 < oil and gas storage index ≤ 1, the storage capacity grade is grade I; when 0.50 < oil and gas storage index ≤ 0.75, the storage capacity grade is grade II; when 0.25 < oil and gas storage index ≤ 0.5, the storage capacity grade is grade III; when 0 < oil and gas storage index ≤ 0.25, the storage capacity grade is grade IV.

[0007] The specific obtaining process of the pressure drop function of the target reservoir section and the pressure drop function of the caprock is as follows:

[0008] The specific representation form of the pressure drop standard function is:

[0009] (3)

[0010] Wherein,

[0011] r i = r max × i / q (1)

[0012] (8)

[0013] x i = π 2 (r i × 10 -4 ) 2 / (96 μL 2 ) (2)

[0014] In the formula: P j is the pressure drop standard function, dimensionless; i is the number of pore radius, dimensionless; j is the core sample number, dimensionless; t is the time, s; r i is the pore radius, nm; x i is the pressure drop rate corresponding to r i , s -1 ; y i is the proportion of the influence of the pressure drop rate, dimensionless; q is the number of different pressure drop rates in the pressure drop standard function, dimensionless; μ is the viscosity, cP; c is the gas compressibility, psi -1 ; L is the core sample length, cm; r max is the maximum value of r i , nm;

[0015] The pressure drop standard function is respectively fitted with the pressure-time curve of the core samples in the target reservoir section and the pressure-time curve of the caprock samples, and then the pressure drop function of the target reservoir section and the pressure drop function of the caprock are obtained.

[0016] The specific calculation process of the reservoir physical property similarity coefficient is as follows:

[0017] (5)

[0018] (4)

[0019] In the formula: n is the number of core samples in the target reservoir section, n = j - 1, dimensionless; RI is the reservoir physical property similarity coefficient, dimensionless; k j is the total core pore connectivity coefficient, dimensionless.

[0020] The specific calculation process of the caprock physical property deviation coefficient is as follows:

[0021] (6)

[0022] Where: GI is the physical property deviation coefficient of the caprock, dimensionless; (a i ) n is the proportion of the influence of the pressure drop rate of the rock sample in the target reservoir section closest to the caprock in depth, dimensionless; (a i ) j is the proportion of the influence of the pressure drop rate of the caprock rock sample, dimensionless.

[0023] The specific calculation process of the oil and gas accumulation index is as follows:

[0024] (7)

[0025] Where: NI is the oil and gas accumulation index, dimensionless;

[0026] RI is the reservoir physical property similarity coefficient, dimensionless; GI is the physical property deviation coefficient of the caprock, dimensionless.

[0027] The pressure-time curve is obtained by conducting a pressure drop test experiment on the rock sample.

[0028] The specific preparation process of the rock sample is as follows: The core of the target reservoir section / caprock core is made into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, and placed in a constant temperature oven at 100 °C for 24 hours to make the pores of the standard cylindrical core free of moisture, and then the rock sample of the target reservoir section / caprock rock sample is made.

[0029] The pressure drop test experiment is carried out in the experimental test device for the pore connectivity of the tight sandstone reservoir; the experimental test device for the pore connectivity of the tight sandstone reservoir includes a constant speed and constant pressure pump, an intermediate container, a vacuum pump and a core holder connected in sequence, and the core holder contains the rock sample of the target reservoir section / caprock rock sample; the intermediate container is also connected with a pressure gauge.

[0030] The specific process of the pressure drop test experiment is as follows: Place the rock sample of the target reservoir section / caprock rock sample in the core holder; First, use the constant speed and constant pressure pump to inject gas into the intermediate container until the pressure gauge shows the designed value and then stop; Carry out vacuum treatment on the core holder through the vacuum pump. After the vacuum treatment is completed, introduce the gas in the intermediate container into the core holder, and at the same time record the data points of the pressure and time in the pressure gauge until the pressure in the pressure gauge is stable, and the experiment ends.

[0031] The technical effect of the present invention is as follows:

[0032] The present invention proposes a pressure drop standard function, fits the pressure drop function of actual rock samples, calculates the reservoir physical property similarity coefficient and the caprock physical property deviation coefficient based on this, takes the arithmetic square root of the product of the reservoir physical property similarity coefficient and the caprock physical property deviation coefficient as the oil and gas reservoir index, and evaluates the reservoir capacity with the oil and gas reservoir index. The larger the oil and gas reservoir index, the stronger the oil and gas reservoir capacity of the tight sandstone reservoir;

[0033] The data source of the present invention is the actual core experiment test in the oilfield, which is accurate and reliable. Moreover, the test method is simple and easy to operate, can be quickly applied to the evaluation of the reservoir capacity in the oilfield, greatly reduces the costs of a large number of coring, logging level testing and interpretation in the oilfield, is also applicable to the evaluation of the reservoir capacity of similar sandstone reservoirs, and has the value of popularization and application. Brief Description of the Drawings

[0034] Figure 1 It is a fitting diagram of the pressure-time curve of the KL-1 rock sample and the pressure drop standard function.

[0035] Figure 2 It is a fitting diagram of the pressure-time curve of the KL-2 rock sample and the pressure drop standard function.

[0036] Figure 3 It is a fitting diagram of the pressure-time curve of the KL-3 rock sample and the pressure drop standard function.

[0037] Figure 4 It is a fitting diagram of the pressure-time curve of the KL-4 rock sample and the pressure drop standard function.

[0038] Figure 5 It is a fitting diagram of the pressure-time curve of the KL-5 rock sample and the pressure drop standard function.

[0039] Figure 6 It is a fitting diagram of the pressure-time curve of the KL-t rock sample and the pressure drop standard function.

[0040] Figure 7 It is a structural schematic diagram of the experimental test device for the pore connectivity ability of the tight sandstone reservoir of the present invention.

[0041] Reference Signs: 1. Constant speed and constant pressure pump; 2. Outlet valve of the constant speed and constant pressure pump; 3. Intermediate container; 4. Outlet valve of the intermediate container; 5. Vacuum pump; 6. Inlet valve of the vacuum pump; 8. Pressure gauge; 9. Core holder. Detailed Embodiments

[0042] Example 1

[0043] A test method for the oil and gas storage capacity of a tight sandstone reservoir is as follows: obtain the pressure-time curves of the target reservoir section of the tight sandstone and the cap rock sample above it; construct a standard function for pressure decline; fit the pressure-time curves of the target reservoir section rock sample and the cap rock sample to the standard function for pressure decline respectively to obtain the pressure decline function of the target reservoir section and the pressure decline function of the cap rock; calculate the reservoir physical property similarity coefficient according to the pressure decline function of the target reservoir section, calculate the cap rock physical property deviation coefficient according to the pressure decline function of the cap rock, take 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 storage index, and evaluate the storage capacity with the oil and gas storage index.

[0044] Example 2

[0045] On the basis of Example 1, it further includes that when 0.75 < oil and gas storage index ≤ 1, the storage capacity level is Grade I; when 0.50 < oil and gas storage index ≤ 0.75, the storage capacity level is Grade II; when 0.25 < oil and gas storage index ≤ 0.5, the storage capacity level is Grade III; when 0 < oil and gas storage index ≤ 0.25, the storage capacity level is Grade IV.

[0046] Example 3

[0047] On the basis of Example 2, it further includes

[0048] The specific obtaining process of the pressure decline function of the target reservoir section and the pressure decline function of the cap rock is as follows:

[0049] The specific representation form of the standard function for pressure decline is:

[0050] (3)

[0051] Where

[0052] r i =r max ×i / q (1)

[0053] (8)

[0054] x i =π 2 (r i ×10 -4 ) 2 / (96μcL 2 ) (2)

[0055] Fit the standard function for pressure decline to the pressure-time curves of the target reservoir section rock sample and the cap rock sample respectively, and then obtain the pressure decline function of the target reservoir section and the pressure decline function of the cap rock.

[0056] Example 4

[0057] On the basis of Embodiment 3, it further includes

[0058] The specific calculation process of the reservoir physical property similarity coefficient is as follows:

[0059] (5)

[0060] (4)

[0061] The specific calculation process of the caprock physical property deviation coefficient is as follows:

[0062] (6)

[0063] The specific calculation process of the oil and gas accumulation index is as follows:

[0064] (7).

[0065] Embodiment 5

[0066] On the basis of Embodiment 4, it further includes

[0067] The pressure-time curve is obtained by conducting a pressure drop test experiment on a rock sample;

[0068] The specific preparation process of the rock sample is as follows: The core of the target reservoir section / caprock core is made into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, and placed in a constant temperature oven at 100 °C for 24 hours to make the pores of the standard cylindrical core free of moisture, thereby making the rock sample of the target reservoir section / caprock sample;

[0069] The pressure drop test experiment is carried out in an experimental test device for the pore connectivity of a tight sandstone reservoir; the experimental test device for the pore connectivity of a tight sandstone reservoir includes a constant speed and constant pressure pump 1, an intermediate container 3, a vacuum pump 5 and a core holder 9 connected in sequence, and the core holder 9 contains the rock sample of the target reservoir section / caprock sample; the intermediate container 3 is also connected with a pressure gauge 8;

[0070] The specific process of the pressure drop test experiment is as follows: Place the rock sample of the target reservoir section / caprock sample in the core holder 9; First, use the constant speed and constant pressure pump 1 to inject gas into the intermediate container 3 until the pressure gauge 8 shows the designed value and then stop; Carry out vacuum treatment on the core holder 9 through the vacuum pump 5. After the vacuum treatment is completed, the gas in the intermediate container 3 is introduced into the core holder 9, and at the same time, record the data points of the pressure and time in the pressure gauge 8 until the pressure in the pressure gauge 8 is stable, and the experiment ends. Among them, the gas is nitrogen.

[0071] Specific experimental cases

[0072] YY is the main development area of typical tight sandstone reservoirs in China. Vertically, it is divided into three main sub-layers YY1 - YY3. KL is a well to be evaluated in this area. Downhole coring was carried out for the three main sub-layers in the early stage. Taking YY1 as the target reservoir section, a test method for the oil and gas accumulation capacity of tight sandstone reservoirs was carried out.

[0073] Step 1: Prepare rock samples and conduct a pressure drop test experiment to obtain the pressure-time curve of the rock samples in the target reservoir section and the pressure-time curve of the caprock samples.

[0074] Take 5 cores from the YY1 target reservoir section in the depth direction and 1 core from the caprock above 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 an incubator at 100 °C and dry them for 24 hours to make the pores of the standard cylindrical cores free of moisture, and make the rock samples KL-1 to KL-5 in the target reservoir section and the caprock sample KL-t.

[0075] Place the rock samples in the target reservoir section and the caprock samples respectively in the experimental test device for the pore connectivity of tight sandstone reservoirs to conduct a pressure drop test experiment, and obtain 5 pressure-time curves of the rock samples in the target reservoir section and 1 pressure-time curve of the caprock sample.

[0076] The specific process of the pressure drop test experiment is as follows:

[0077] First, close all valves except the outlet valve 2 of the constant speed and constant pressure pump. Use the constant speed and constant pressure pump 1 to inject gas into the intermediate container 3 until the pressure gauge 8 shows the designed value, then 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 conduct vacuum treatment on the core holder 9 through the vacuum pump 5. After the vacuum treatment, close the inlet valve 6 of the vacuum pump, then open the outlet valve 4 of the intermediate container, and let the gas in the intermediate container 3 flow into the core holder 9. Record the data points of the pressure and the corresponding time in the pressure gauge 8 while opening, until the pressure in the pressure gauge 8 is stable, and end the experiment.

[0078] Step 2: Construct the pressure drop function of the target reservoir section and the pressure drop function of the caprock.

[0079] The two indicators of the pressure drop standard function are the pressure drop rate and the influence ratio corresponding to the pressure drop rate; the specific representation form of the pressure drop standard function is shown in formula (3); among them, the number q of different pressure drop rates in the pressure drop standard function is 5, and the pore radius r i Specifically, it is 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm; according to formula (2), calculate the pressure drop rate x corresponding to each pore radius r i i , as shown in Table 1 for details;

[0080] Table 1 Pressure drop rate

[0081] ;

[0082] Fit the pressure drop rate x obtained from the above calculation i with the pressure-time curve to obtain the proportion of the influence of the pressure drop rate. The results are shown in Table 2;

[0083] Table 2 Proportion of the influence of the pressure drop rate

[0084] ;

[0085] Construct the pressure drop function of the target reservoir section and the pressure drop function of the caprock according to the data in Table 1 and Table 2 and formula (3).

[0086] Step 3: Calculate the total core pore connectivity coefficient k according to formula (4) j , and then calculate the reservoir physical property similarity coefficient RI according to formula (5). The results are shown in Table 3;

[0087] Table 3 Reservoir physical property similarity coefficient RI

[0088] .

[0089] Step 4: Calculate the caprock physical property deviation coefficient GI;

[0090] It is obtained by using the pressure drop function of the core closest to the caprock in depth and the pressure drop function of the caprock core. The reservoir core closest to the caprock is KL-1. Combining with formula (6), the caprock physical property deviation coefficient GI is 0.545.

[0091] Step 5: Calculate the oil and gas reservoir index by taking the arithmetic square root of the product of the reservoir physical property similarity coefficient and the caprock physical property deviation coefficient, and evaluate the reservoir capacity with the oil and gas reservoir index; According to formula (7), the oil and gas reservoir index NI is calculated to be 0.714, and the reservoir capacity level is obtained as level II.

[0092] The traditional oil and gas reservoir capacity is calculated using the oil saturation. Given that the average oil saturation of the reservoir is 55.6%, and the oil saturation range in similar reservoirs is generally 40%-65%. It is expressed in the same form as the oil and gas reservoir index using the following formula:

[0093] NII=(h y - h ymin ) / (h ymax - h ymin )

[0094] Where: NII is the traditional oil and gas reservoir capacity, dimensionless; h yis the average oil saturation of the reservoir, %; h ymax is the maximum oil saturation of the same type of reservoir, %; h ymin is the minimum oil saturation of the same type of reservoir, %;

[0095] The calculated traditional oil and gas storage capacity NII is 0.624, and the storage capacity level is also level II.

Claims

1. A testing method for the oil and gas storage capacity of a tight sandstone reservoir, characterized in that The method is as follows: obtain the pressure-time curves of the tight sandstone target reservoir section and the overlying caprock samples; construct a standard pressure decline function; fit the pressure-time curves of the target reservoir section samples and the caprock samples to the standard pressure decline function respectively to obtain the pressure decline function of the target reservoir section and the pressure decline function of the caprock; calculate the reservoir physical property similarity coefficient according to the pressure decline function of the target reservoir section, calculate the caprock physical property deviation coefficient according to the pressure decline function of the caprock, take the arithmetic square root of the product of the reservoir physical property similarity coefficient and the caprock physical property deviation coefficient as the oil and gas accumulation index, and evaluate the accumulation ability with the oil and gas accumulation index; Among them, the specific process of obtaining the pressure decline function of the target reservoir section and the pressure decline function of the caprock is: The specific representation form of the standard pressure decline function is: （3） Among them, r i = r max × i / q (1) （8） x i =π 2 (r i ×10 -4 ) 2 / (96 μL 2 ) (2) Where: P j is the pressure drop standard function, dimensionless; i is the number of pore radius, dimensionless; j is the number of rock sample, dimensionless; t is time, s; r i is the pore radius, nm; x i is the pressure drop rate corresponding to r i , s -1 ; y i is the proportion of the influence of the pressure drop rate, dimensionless; q is the number of different pressure drop rates in the pressure drop standard function, dimensionless; μ is the viscosity, cP; c is the gas compressibility, psi -1 ; L is the length of the rock sample, cm; r max is the maximum value of r i , nm; Fit the standard pressure decline function to the pressure-time curves of the target reservoir section samples and the caprock samples respectively, and then obtain the pressure decline function of the target reservoir section and the pressure decline function of the caprock.

2. The testing method for the oil and gas storage capacity of the tight sandstone reservoir according to claim 1, wherein 0.75 < oil and gas accumulation index ≤ 1, the accumulation ability level is Grade I; 0.50 < oil and gas accumulation index ≤ 0.75, the accumulation ability level is Grade II; 0.25 < oil and gas accumulation index ≤ 0.5, the accumulation ability level is Grade III; 0 < oil and gas accumulation index ≤ 0.25, the accumulation ability level is Grade IV.

3. The testing method for the oil and gas storage capacity of the tight sandstone reservoir according to claim 1, wherein 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 physical property similarity coefficient, dimensionless; k j is the total core pore connectivity coefficient, dimensionless.

4. The testing method for the oil and gas storage capacity of a tight sandstone reservoir according to claim 3, characterized in that, The specific calculation process of the caprock physical property deviation coefficient is: （6） Where: GI is the physical property deviation coefficient of the caprock, dimensionless; is the proportion of the influence of the pressure drop rate of the rock sample in the target reservoir section closest to the caprock in depth, dimensionless; is the proportion of the influence of the pressure drop rate of the caprock rock sample, dimensionless.

5. The testing method for the oil and gas storage capacity of the tight sandstone reservoir according to claim 1, wherein The specific calculation process of the oil and gas accumulation index is: （7） In the formula: NI is the oil and gas accumulation index, dimensionless; RI is the reservoir physical property similarity coefficient, dimensionless; GI is the caprock physical property deviation coefficient, dimensionless.

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

7. The testing method for the oil and gas storage capacity of the tight sandstone reservoir according to claim 6, characterized in that The specific preparation process of the rock sample is: make the target reservoir section core / caprock core into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm, place it in a constant temperature oven at 100 °C and dry it for 24 hours to make the pores of the standard cylindrical core free of moisture, and then make the target reservoir section rock sample / caprock sample.

8. The test method for the oil and gas storage capacity of the tight sandstone reservoir according to claim 6, characterized in that, The pressure decline test experiment is carried out in a tight sandstone reservoir pore connectivity experimental test device; the tight sandstone reservoir pore connectivity experimental test device includes a constant speed and constant pressure pump (1), an intermediate container (3), a vacuum pump (5) and a core holder (9) connected in sequence, and the core holder (9) contains the target reservoir section rock sample / caprock sample; the intermediate container (3) is also connected with a pressure gauge (8).

9. The testing method for the oil and gas storage capacity of the tight sandstone reservoir according to claim 8, characterized in that, The specific process of the pressure decline test experiment is: place the target reservoir section rock sample / caprock sample in the core holder (9); first, use the constant speed and constant pressure pump (1) to inject gas into the intermediate container (3) until the pressure gauge (8) shows the designed value and then stop; conduct vacuum treatment on the core holder (9) through the vacuum pump (5), after the vacuum treatment is completed, introduce the gas in the intermediate container (3) into the core holder (9), and record the data points of the pressure and time in the pressure gauge (8) at the same time until the pressure in the pressure gauge (8) is stable, and end the experiment.

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