Permeability determination method based on microelectrode system logging

Abstract

The invention relates to a permeability determination method based on microelectrode system logging. The method mainly solves the problem that permeability parameters of some early-stage oil fields cannot be obtained through an existing method due to little logging information. The method is characterized by comprising the following steps: S1, selecting a plurality of wells, and obtaining different-depth core samples and microelectrode system logging data of a wellbore drilling stratum; s2, measuring the permeability of the core sample in a laboratory; s3, calculating a microelectrode system difference rate of a depth point corresponding to the rock core sample; s4, fitting the core permeability of different depth points with the corresponding microelectrode system difference rate to obtain a relational expression between the core permeability and the microelectrode system difference rate; and S5, obtaining a relational expression between the permeability of different depth points of the whole well and the difference rate of the corresponding microelectrode system. According to the permeability determination method based on the microelectrode system logging, the permeability of the rock is calculated by utilizing the resistivity difference near the well wall caused by invasion of mud to the permeable rock, and evaluation and effective utilization of boundary benefit oil and gas fields before 70 years can be supported.

Description

Technical Field

[0001] The invention relates to the field of well logging evaluation for oil field exploration and development, in particular to a method for determining permeability based on microelectrode system well logging. Background Art

[0002] Permeability is a geological parameter used to describe the ability of a rock to allow fluid to flow through its pores under pressure differential conditions. It is defined as 1 cm of viscosity 1 centipoise when the pressure differential is 1 atmosphere. 3 The fluid passes through a cross-sectional area of ​​1 cm 2 The distance that water flows through in one second is 1 cm, and the permeability of the rock is 1 millidarcy. Porosity is the most important factor affecting permeability, and there is an obvious positive correlation between permeability and porosity. In addition, rock permeability parameters are also affected by other factors, and the influencing factors vary for different rocks. For pure sandstone, the size of rock particles directly affects the size of permeability, and for muddy sandstone, the size of mud content directly affects the size of permeability. In addition, the complexity of the pore structure also directly affects the size of the permeability.

[0003] There are many ways to obtain permeability parameters. The most direct and accurate method is rock physics experiment. That is, rock physics experiments are conducted on core samples obtained by drilling to directly measure the permeability parameters of rocks. The indirect and relatively accurate way is to use geophysical logging methods. Under normal circumstances, geophysical logging can obtain relatively accurate rock porosity parameters through neutron, density, acoustic wave and other porosity logging projects. By using the correlation between permeability and porosity, and considering other influencing factors of different rocks (mud content, median particle size, etc.), permeability parameters can be obtained. With the application and promotion of nuclear magnetic resonance logging technology, the Coates model is used to calculate rock permeability. While considering the size of rock pores, it also considers the influence of pore space type on permeability, with higher accuracy.

[0004] However, there are some oil and gas fields that were discovered before the 1970s, which have not been developed due to in-depth exploration and evaluation or are at marginal benefits, and need further in-depth evaluation. Such oil and gas fields are limited by the logging acquisition technology at that time, and the logging information obtained is only the logging items such as the lateral electrode system, microelectrode, natural potential, well diameter, well deviation, fluid, etc., and even lack porosity logging, and do not have the conditions to use porosity and other parameters to further obtain permeability parameters. Summary of the invention

[0005] In order to overcome the deficiency that some early oil fields cannot obtain permeability parameters by existing methods due to insufficient logging information, the present invention provides a permeability determination method based on microelectrode logging. The permeability determination method based on microelectrode logging calculates the permeability of the rock by utilizing the resistivity difference near the well wall caused by the invasion of mud into permeable rock, which can support the effective utilization of boundary benefit oil and gas fields.

[0006] The technical solution of the present invention is: a method for determining permeability based on microelectrode logging, comprising:

[0007] S1. Select several wells to obtain core samples and microelectrode logging data at different depths of the formation encountered by the wellbore;

[0008] S2. Laboratory measurement of core sample permeability K 0 ;

[0009] S3. Calculate the difference rate of the microelectrode system at the depth point corresponding to the core sample △ R ;

[0010] S4. The core permeability K at different depths 0 The difference rate of the corresponding microelectrode system △ R Perform fitting to obtain the relationship between the two;

[0011] S5. Obtain the permeability K of different depth points in the whole well and the corresponding microelectrode system difference rate △ R The relationship formula.

[0012] Further, the core permeability K in step S4 0 Difference rate with microelectrode system△ R The relationship between

[0013]

[0014] Where: K 0 is the core permeability, in mD; a and b are constants; △ R is the microelectrode system difference rate, dimensionless;

[0015] Furthermore, in step S5, the permeability K and the microelectrode system difference rate Δ R The relationship is

[0016]

[0017] Where: K is the permeability, the unit is mD.

[0018] Furthermore, it also includes:

[0019] S6. Obtain the micropotential resistivity and microgradient resistivity at different depths of the well to be measured, and calculate the permeability at different depths of the well to be measured.

[0020] Furthermore, the logging data in step S1 includes micropotential resistivity R MN With micro-gradient resistivity R MG .

[0021] Furthermore, the microelectrode system difference rate Δ R for

[0022] △ R =(R MN -R MG ) / R MN .

[0023] Furthermore, the well to be tested and the several wells in step S1 are in the same block.

[0024] The present invention has the following beneficial effects: by adopting the above scheme, the resistivity difference near the well wall caused by the invasion of mud into permeable rock is used to calculate the permeability of the rock, which can support the evaluation and effective use of the borderline benefit oil and gas fields before the 1970s. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the present invention;

[0026] Figure 2 is a graph showing the relationship between permeability and microelectrode system difference rate in the embodiment;

[0027] Figure 3 3 is a comparison chart of the permeability calculated by the method of the present invention in the embodiment and the core permeability. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings:

[0029] Depend on Figures 1 to 3As shown in FIG. 1 , a method for determining permeability based on microelectrode logging is to calculate permeability parameters using microelectrode logging data. Microelectrode logging mainly includes micropotential logging and microgradient logging. The electrode spacing design of the two is different, so that the detection depths of each are also different. Experiments have shown that the detection depth of microgradient is about 40 mm, and the detection depth of micropotential is about 100 mm. For rocks with good permeability, there is mud invasion, and the mud particles in the mud are left on the well wall to form a mud cake. The resistivity of the mud cake is generally 1-3 times that of the mud, and the resistivity of the flushing zone is more than 5 times higher than that of the mud cake. Therefore, for permeable formations, micropotential logging information mainly reflects the resistivity of the flushing zone near the well wall, and microgradient logging information is greatly affected by the mud cake. There is an obvious amplitude difference between the two. The better the permeability, the greater the difference. Microelectrode logging is a resistivity logging, and its resistivity value is also affected by lithology. When there is calcareous cementation in the sandstone reservoir, the resistivity value will increase and the amplitude difference will decrease.

[0030] Therefore, the present invention establishes a correlation between the microelectrode system difference rate and the permeability parameter to obtain a permeability calculation model.

[0031] Specifically include:

[0032] S1. Select one or more wells in the same block to obtain core samples and microelectrode logging data at different depths of the wellbore formation. The logging data includes micropotential resistivity R MN With micro-gradient resistivity R MG .

[0033] S2. Laboratory measurement of core sample permeability K 0 ;

[0034] S3, according to the micro-potential resistivity R in step S1 MN With micro-gradient resistivity R MG Calculate the microelectrode system difference rate△ R ,

[0035] △ R =(R MN -R MG ) / R MN (1).

[0036] S4, the core permeability K in step S2 0 The difference rate of the microelectrode system in step S3 R Fitting is performed to obtain the core permeability K 0 Difference rate with microelectrode system△ R The relationship between

[0037]

[0038] Where: K0 is the core permeability, in mD; a and b are constants; △ R is the microelectrode system difference rate, dimensionless.

[0039] S5, and then get the permeability K of different depth points in the whole well and the corresponding microelectrode system difference rate △ R The relationship is

[0040]

[0041] Where: K is the permeability, the unit is mD.

[0042] S6. Obtain the micropotential resistivity and microgradient resistivity of the well to be tested at different depths, and calculate the permeability of the well to be tested at different depths according to the formula in step S4. The well to be tested and the wells in step S1 should be in the same block.

[0043] Example:

[0044] S1. Select 4 wells in a certain block and collect micro-electrode logging data to collect micro-potential resistivity R MN With micro-gradient resistivity R MG ;

[0045] S2. Drill cores at different depths and measure the core permeability K 0 , the results are shown in Table 1;

[0046] S3. Calculate the microelectrode system difference rate △ according to formula (1) R The results are shown in Table 1.

[0047] Table 1

[0048]

[0049]

[0050] S4, the core permeability K 0 Difference rate with microelectrode system△ R Fitting, such as Figure 2 , and the core permeability K is obtained 0 Difference rate with microelectrode system△ R The relationship between

[0051]

[0052] S5. Further obtain the permeability K and microelectrode system difference rate △ at any depth R The relationship is:

[0053]

[0054] S6. Obtain the micropotential resistivity and microgradient resistivity at different depths of the well to be tested, and calculate the permeability at different depths of the well to be tested according to formula (3). The calculated permeability is compared with the core permeability. See Table 2 for the comparison. Figure 3 , indicating that both are within one order of magnitude.

[0055] Table 2

[0056]

Claims

1. A method for determining permeability based on microelectrode logging, characterized in that include: S1. Select several wells to obtain core samples and microelectrode logging data at different depths of the formation encountered by the wellbore; S2, laboratory measurement of core sample permeability K0; S3. Calculate the difference rate of the microelectrode system at the depth point corresponding to the core sample △ R ; S4. The core permeability K0 at different depths is compared with the corresponding microelectrode system difference rate △ R Perform fitting to obtain the relationship between the two; S5. Obtain the permeability K of different depth points in the whole well and the corresponding microelectrode system difference rate △ R The relationship formula.

2. The method for determining permeability based on microelectrode logging according to claim 1, characterized in that: In step S4, the core permeability K0 and the microelectrode system difference rate Δ R The relationship between Where: K0 is the core permeability, in mD; a and b are constants; △ R is the microelectrode system difference rate, dimensionless.

3. The method for determining permeability based on microelectrode logging according to claim 2, characterized in that: In step S5, the permeability K and the microelectrode system difference rate Δ R The relationship is Where: K is the permeability, the unit is mD.

4. The method for determining permeability based on microelectrode logging according to claim 3, characterized in that: Also includes: S6. Obtain the micropotential resistivity and microgradient resistivity at different depths of the well to be measured, and calculate the permeability at different depths of the well to be measured.

5. The method for determining permeability based on microelectrode logging according to claim 4, characterized in that: The logging data in step S1 includes micropotential resistivity R MN With micro-gradient resistivity R MG .

6. The method for determining permeability based on microelectrode logging according to claim 5, characterized in that: The microelectrode system difference rate Δ in step S2 R for △ R =(R MN -R MG ) / R MN 。 7. The method for determining permeability based on microelectrode logging according to claim 6, characterized in that: The well to be tested and the several wells in step S1 are in the same block.

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