Method for evaluating oil and gas migration capacity of shale reservoir

Abstract

The present application relates to a kind of shale reservoir oil and gas migration capacity evaluation method, with the arithmetic square root of the pore diameter contribution index of rock to fluid adsorption inhibition index as oil and gas migration capacity index, to evaluate oil and gas migration capacity;0<Oil and gas migration capacity index≤0.35, oil and gas migration capacity is III, oil and gas migration capacity is poor;0.35<Oil and gas migration capacity index≤0.70, oil and gas migration capacity is II, oil and gas migration capacity is moderate;0.75<Oil and gas migration capacity index≤1, oil and gas migration capacity is I, oil and gas migration capacity is good.The present application first combines the pore diameter contribution index of favorable factor influencing fluid migration capacity and the rock to fluid adsorption inhibition index of adverse factor to comprehensively evaluate, calculates oil and gas migration capacity index and establishes division standard, realizes the quantitative evaluation of shale reservoir oil and gas migration capacity.

Description

Technical Field

[0001] The present invention relates to the field of petroleum and natural gas engineering, and in particular to a method for evaluating the oil and gas migration capacity of a shale reservoir during the exploration and development process. Background Art

[0002] Through research and patent comparison, the following representative methods for evaluating the flow capacity of rock pore fluids are found: (1) In the patent application scheme with patent application number ZL2019214625622 and titled "An experimental test device for the dynamic imbibition capacity of rocks", a dynamic imbibition experiment of shale under reservoir temperature and pressure conditions is first carried out, and the injection volume corresponding to different times is recorded by a control computer to obtain the dynamic imbibition capacity during shale fracturing, and then the flow capacity of the fluid in the reservoir pores is evaluated. (2) In the patent application scheme with patent application number CN2021115737576 and titled "A method for characterizing oil and gas phase equilibrium and flow capacity in porous rock media", the oil phase and gas phase flow models are established respectively by fractal dimension and pore size, and the oil phase and gas phase permeabilities are calculated according to the distribution of oil and gas in pores of different sizes, thereby evaluating the pore flow capacity.

[0003] By comparison, it can be seen that the current evaluation of the flow capacity of tight reservoirs is mainly carried out through methods such as indoor small-scale experiments and reservoir numerical simulation. This application is based on another completely new perspective. For the first time, it combines the favorable factor pore contribution index and the unfavorable factor rock fluid adsorption inhibition index that affect the fluid migration capacity to conduct a comprehensive evaluation, calculate the oil and gas migration capacity index and establish a classification standard, thereby realizing the quantitative evaluation of the oil and gas migration capacity of shale reservoirs and providing a basic basis for the evaluation of oilfield resource potential. Summary of the Invention

[0004] The present invention provides a method for evaluating the oil and gas migration capacity of a shale reservoir.

[0005] The technical solution of the present invention is:

[0006] A method for evaluating the oil and gas migration capacity of a shale reservoir uses the arithmetic square root of the rock's fluid adsorption inhibition index and the pore size contribution index as the oil and gas migration capacity index to evaluate the oil and gas migration capacity. When the oil and gas migration capacity index is 0 < 0.35 or less, the oil and gas migration capacity is Class III, indicating poor oil and gas migration capacity; when the oil and gas migration capacity index is 0.35 < 0.70 or less, the oil and gas migration capacity is Class II, indicating moderate oil and gas migration capacity; and when the oil and gas migration capacity index is 0.75 < 1 or less, the oil and gas migration capacity is Class I, indicating good oil and gas migration capacity.

[0007] The specific solution process of the rock adsorption inhibition index for fluid is as follows:

[0008] (3)

[0009] Where: is the rock adsorption inhibition index for fluids, dimensionless; is the maximum adsorption capacity, unit is m 3 / kg; is the maximum adsorption capacity of other rock samples in the target block, unit: m 3 / kg;

[0010] The maximum adsorption capacity The specific solution process is as follows: take a rock sample from the target block to make the first rock sample, and obtain the pressure through high pressure adsorption experiment. With pressure The mass of the second rock sample at The pressure is converted to The first rock sample quality at Converted into adsorption amount :

[0011] (1)

[0012] Where: is the adsorption capacity, unit is m 3 / kg; For pressure The mass of the first rock sample at the time, in kg; is the initial mass of the first rock sample, in kg; is the density of methane under standard conditions, in kg / m 3 ;

[0013] According to adsorption theory, build pressure and adsorption capacity Relationship:

[0014] (2)

[0015] Where: It is the pressure when the adsorption amount is 0.5 times the maximum adsorption amount, in MPa;

[0016] Fitting the experimental results of the high-pressure adsorption experiment, the pressure at which the adsorption amount is 0.5 times the maximum adsorption amount is obtained P 0.5 and maximum adsorption capacity .

[0017] Among them, the specific solution process of the aperture contribution index is:

[0018] (6)

[0019] in,

[0020] (4)

[0021] (5)

[0022] Where: is the aperture contribution index, dimensionless; is the average pore size distribution value, unit is nm; is the pore size distribution difference, dimensionless; The maximum value of the average pore size distribution value of the target block, in nm; It is the minimum value of the pore size distribution difference of the target block, dimensionless; k i is the average pore size value of each grade of pore size, in nm; It is the percentage of each grade of aperture, unit: % It is the percentage of the pore size grade where the pore size average distribution value is located, unit: %;

[0023] The average pore size distribution value and pore size distribution difference The specific solution process is as follows: take a rock sample from the target block as the second rock sample, obtain the grade pore size distribution ratio of the second rock sample; obtain the average pore size value of each grade pore size k i , the percentage of each grade of aperture And the percentage of the pore size grade where the pore size average distribution value is located ; Then, the average pore size distribution value is calculated according to formula (4) , the pore size distribution difference is calculated according to formula (5) .

[0024] The interval range of the graded pore size distribution of the second rock sample specifically includes [1nm, 3nm), [3nm, 5nm), [5nm, 10nm), [10nm, 50nm), [50nm, 100nm), [100nm, 500nm) and [500nm, 1500nm].

[0025] The specific solution process of the oil and gas migration capacity index is as follows:

[0026] (7)

[0027] Where: is the oil and gas migration capacity index, dimensionless.

[0028] Preferably, a rock sample is taken from the target reservoir, crushed to 80 mesh, dried and dehydrated, and 10 g is taken as the first rock sample; the pressure is The first rock sample quality at Obtained by high-pressure magnetic suspension balance adsorption instrument.

[0029] Preferably, the specific process of obtaining the second rock sample is: taking a rock sample from the target reservoir, processing it into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm as the second rock sample; the grade pore size distribution ratio of the second rock sample is obtained by mercury intrusion testing.

[0030] The technical effects of the present invention are:

[0031] (1) For the first time, the pore size contribution index, a favorable factor affecting fluid migration capacity, and the rock adsorption inhibition index, an unfavorable factor, were combined to comprehensively evaluate the oil and gas migration capacity index, calculate the oil and gas migration capacity index, and establish a classification standard, thus achieving a quantitative evaluation of the oil and gas migration capacity of shale reservoirs;

[0032] (2) Based on the pore size distribution range measured by actual core experiments, the average pore size distribution value and distribution difference are calculated to quantitatively evaluate the role of the overall pore size of the rock in promoting oil and gas migration;

[0033] (3) Based on the curve of pressure and adsorption amount measured in actual core experiments, the rock adsorption inhibition index on fluid is calculated to quantitatively evaluate the inhibitory effect of rock adsorption capacity on oil and gas migration. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the relationship curve between pressure and adsorption amount. DETAILED DESCRIPTION

[0035] Specific experimental cases

[0036] This example provides a method for evaluating the oil and gas migration capacity of shale reservoirs, as follows:

[0037] The target layer of the HL well in the FL block was sampled downhole and marked as HL-1 for this experiment.

[0038] 1. Grind HL-1 into 80 mesh, dry and remove water, take 10g as the first rock sample FL-1-1, and record the initial mass of the first rock sample ; Use high-pressure magnetic suspension balance adsorption instrument to obtain pressure With pressure The first rock sample quality at The relationship between and pressure is expressed as The first rock sample quality at Converted into adsorption amount , get pressure and adsorption capacity The curve graph between Figure 1 As shown;

[0039] Build pressure and adsorption capacity The functional relationship between is shown in formula (2), and Figure 1 The maximum adsorption capacity was obtained by fitting 2.55m 3 / kg, The maximum adsorption capacity of other rock samples in the target block is 8.21MPa. 5.13m 3 / kg; The rock adsorption inhibition index of fluid is calculated by formula (3): It is 0.50, indicating that the adsorption capacity of rocks inhibits the migration capacity of oil and gas.

[0040] 2. HL-1 was processed into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm as the second rock sample HL-1-2. The second rock sample HL-1-2 was tested using a mercury intrusion porosimeter, and the range of the graded pore size distribution of the second rock sample HL-1-2 was found to be [1 nm, 3 nm), [3 nm, 5 nm), [5 nm, 10 nm), [10 nm, 50 nm), [50 nm, 100 nm), [100 nm, 500 nm), and [500 nm, 1500 nm]. The graded pore size distribution percentages of the second rock sample HL-1-2 are shown in Table 1.

[0041] Table 1 The pore size distribution of the second rock sample HL-1-2

[0042] .

[0043] The average pore size distribution value is calculated using formula (4): It is 40.12nm, which belongs to the range of 10nm-50nm. Therefore, the percentage of the pore size level where the pore size average distribution value is located is is 24.92%, and the pore size distribution difference is calculated by formula (5) The maximum value of the average distribution value of the aperture of the target block is 0.67. The minimum value of the pore size distribution difference of the target block is 70.33nm. is 0.42, and the aperture contribution index is calculated by formula (6): It is 0.46.

[0044] 3. Calculate the oil and gas migration capacity index through (7) It is 0.48, so the oil and gas migration capacity is Class II, and the oil and gas migration capacity is medium.

[0045] Traditional methods generally evaluate the oil and gas migration capacity of a reservoir by its permeability. The higher the reservoir permeability, the more numerous, larger, and denser the oil and gas migration pathways. The average permeability of the small layer corresponding to the HL well is known to be 0.027 mD, and the permeability of this type of reservoir ranges from 0.009 mD to 0.049 mD. The following formula is used to evaluate the oil and gas migration capacity:

[0046] ;

[0047] Where: is the traditional oil and gas migration capacity index, dimensionless; is the reservoir permeability, mD; is the maximum permeability of the same type of reservoir, mD; is the minimum permeability of similar reservoirs, mD.

[0048] The value is 0.45, which is also a Class II reservoir according to the classification rules in this application.

[0049] The present invention has been specifically described above through examples. It is necessary to point out that the present embodiments are merely preferred embodiments of the present invention and do not limit the present invention in any way. They are not limited to the forms disclosed herein and should not be construed as excluding other embodiments. Modifications and simple variations made by those skilled in the art that do not depart from the technical concept and scope of the present invention are all within the scope of protection of the technical solution of the present invention.

Claims

1. A method for evaluating the oil and gas migration capacity of a shale reservoir, characterized in that: The arithmetic square root of the rock's fluid adsorption inhibition index and the pore size contribution index is used as the oil and gas migration capacity index to evaluate oil and gas migration capacity. When the oil and gas migration capacity index is 0 < ≤ 0.35, the oil and gas migration capacity is Class III, indicating poor oil and gas migration capacity; when the oil and gas migration capacity index is 0.35 < ≤ 0.70, the oil and gas migration capacity is Class II, indicating medium oil and gas migration capacity; when the oil and gas migration capacity index is 0.75 < ≤ 1, the oil and gas migration capacity is Class I, indicating good oil and gas migration capacity. The specific solution process of the rock adsorption inhibition index for fluid is as follows: (3) Where: is the rock adsorption inhibition index for fluids, dimensionless; is the maximum adsorption capacity, unit is m 3 / kg; is the maximum adsorption capacity of other rock samples in the target block, unit: m 3 / kg; The maximum adsorption capacity The specific solution process is as follows: take a rock sample from the target block to make the first rock sample, and obtain the pressure through high pressure adsorption experiment. With pressure The first rock sample quality at The pressure is converted to The first rock sample quality at Converted into adsorption amount : (1) Where: is the adsorption capacity, unit is m 3 / kg; For pressure The mass of the first rock sample at the time, in kg; is the initial mass of the first rock sample, in kg; is the density of methane under standard conditions, in kg / m 3 ; According to adsorption theory, build pressure and adsorption capacity Relationship: (2) Where: It is the pressure when the adsorption amount is 0.5 times the maximum adsorption amount, in MPa; Fitting the experimental results of the high-pressure adsorption experiment, the pressure at which the adsorption amount is 0.5 times the maximum adsorption amount is obtained and maximum adsorption capacity ; The specific solution process of the aperture contribution index is as follows: (6) in, (4) (5) Where: is the aperture contribution index, dimensionless; is the average pore size distribution value, unit is nm; is the pore size distribution difference, dimensionless; The maximum value of the average pore size distribution value of the target block, in nm; It is the minimum value of the pore size distribution difference of the target block, dimensionless; is the average pore size value of each grade of pore size, in nm; It is the percentage of each grade of aperture, unit: % It is the percentage of the pore size grade where the pore size average distribution value is located, in %.

2. The method for evaluating the oil and gas migration capacity of a shale reservoir according to claim 1, characterized in that: The average pore size distribution value and pore size distribution difference The specific solution process is as follows: take a rock sample from the target block as the second rock sample, obtain the grade pore size distribution ratio of the second rock sample; obtain the average pore size value of each grade pore size , the percentage of each grade of aperture And the percentage of the pore size grade where the pore size average distribution value is located ; Then, the average pore size distribution value is calculated according to formula (4) , the pore size distribution difference is calculated according to formula (5) .

3. The method for evaluating the oil and gas migration capacity of a shale reservoir according to claim 2, characterized in that: The interval range of the graded pore size distribution of the second rock sample specifically includes [1nm, 3nm), [3nm, 5nm), [5nm, 10nm), [10nm, 50nm), [50nm, 100nm), [100nm, 500nm) and [500nm, 1500nm].

4. The method for evaluating the oil and gas migration capacity of a shale reservoir according to claim 1, characterized in that: The specific solution process of the oil and gas migration capacity index is as follows: (7) Where: is the oil and gas migration capacity index, dimensionless.

5. The method for evaluating the oil and gas migration capacity of a shale reservoir according to claim 1, characterized in that: The specific process of obtaining the first rock sample is as follows: a rock sample is taken from the target reservoir, crushed to 80 mesh, dried and dehydrated, and 10 g is taken as the first rock sample.

6. The method for evaluating the oil and gas migration capacity of a shale reservoir according to claim 1, characterized in that: The pressure is The first rock sample quality at Obtained by high-pressure magnetic suspension balance adsorption instrument.

7. The method for evaluating the oil and gas migration capacity of a shale reservoir according to claim 2, characterized in that: The specific process of obtaining the second rock sample is as follows: a rock sample is taken from the target reservoir, and it is processed into a standard cylindrical core with a height of 5 cm and a diameter of 2.5 cm as the second rock sample; the grade pore size distribution ratio of the second rock sample is obtained by mercury intrusion testing.

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