阅读说明：本技术 一种提高核磁共振t2谱表征致密储层孔径分布精度的转换方法 (Improve nuclear magnetic resonance T2Conversion method for spectral characterization of dense reservoir pore size distribution precision ) 是由 黄何鑫 李荣西 于强 周伟 吴小力 覃小丽 赵迪 刘奇 赵帮胜 于 2020-06-08 设计创作，主要内容包括：本发明提供了一种提高核磁共振T<Sub>2</Sub>谱表征致密储层孔径分布精度的转换方法,包括如下步骤：步骤一：对饱和地层水的致密储层样品进行核磁共振测试,获得核磁共振T<Sub>2</Sub>谱；步骤二：对干燥致密储层样品进行恒速压汞实验,获得压汞孔径大小分布数据；步骤三：对压汞孔径大小分布数据进行分段处理；步骤四：使用圆柱形孔隙模型获得T<Sub>2</Sub>与孔径大小之间转换关系；步骤五：将步骤三中的各段数据分别使用步骤四中的转换关系得到各段的T<Sub>2</Sub>与孔径大小之间的转换方法,从而获得完整的T<Sub>2</Sub>谱表征致密储层孔径分布的转换方法。该方法提高了利用核磁共振实验得到孔径分布的准确性。(The invention provides a method for improving nuclear magnetic resonance T 2 The conversion method for the spectral characterization of the precision of the pore size distribution of the tight reservoir comprises the following steps: the method comprises the following steps: performing nuclear magnetic resonance test on a compact reservoir sample of saturated formation water to obtain nuclear magnetic resonance T 2 A spectrum; step two: performing a constant-speed mercury-pressing experiment on the dry and compact reservoir sample to obtain mercury-pressing pore size distribution data; step three: carrying out sectional processing on the mercury intrusion pore size distribution data; step four: obtaining T using a cylindrical pore model 2 The conversion relation with the aperture size; step five: respectively using the conversion relation in the step four to obtain the T of each section 2 Conversion method from aperture size to obtain complete T 2 A conversion method for spectral characterization of tight reservoir pore size distribution. The method improves the accuracy of pore size distribution obtained by nuclear magnetic resonance experiments.)

1. Improve nuclear magnetic resonance T₂The conversion method for the spectral characterization of the precision of the pore size distribution of the tight reservoir is characterized by comprising the following steps of:

the method comprises the following steps: performing nuclear magnetic resonance test on a compact reservoir sample of saturated formation water to obtain nuclear magnetic resonance T₂A spectrum;

step two: carrying out mercury injection experiment on the dry compact reservoir sample to obtain mercury injection pore size distribution data;

step three: carrying out sectional processing on the mercury intrusion pore size distribution data;

step four: obtaining T using a cylindrical pore model₂The conversion relation with the aperture size;

step five: respectively using the conversion relation in the step four to obtain the T of each section₂Conversion method from aperture size to obtain complete T₂A conversion method for spectral characterization of tight reservoir pore size distribution.

2. The method of claim 1 for increasing nuclear magnetic resonance T₂The conversion method for the spectrum characterization of the pore size distribution precision of the tight reservoir is characterized in that the segmented processing method in the step three comprises the following steps: and according to the sequence from the small aperture to the large aperture, performing difference calculation on the aperture size data of different test points, and selecting the aperture size data with the aperture difference within an order of magnitude range as a data segment.

3. The method of claim 1 for increasing nuclear magnetic resonance T₂The conversion method for the spectral characterization of the pore size distribution precision of the tight reservoir is characterized in that the conversion relation obtaining method in the fourth step is as follows:

t expressed using KST model₂Relationship between pore volume and pore fluid volume:

the volume of the lamellar fluid in the cylindrical pore model is:

the surface area of the cylindrical pores is:

Sⁱ＝2πr_t·l (3)

the formula (2) and the formula (3) are brought into the formula (1) to obtain

Order to

Wherein, T₂Representing transverse relaxation time, T_2sDenotes the relaxation, V, of the particle surface_sDenotes the pore fluid volume, V denotes the pore volume, V_s ⁱThe volume of the thin layer fluid in the cylindrical pore model is shown, h represents the thickness of the thin layer fluid, r_tDenotes the pore radius,/. denotes the cylinder height, SⁱExpressed as the surface area of the cylindrical pores, p₂Is the relaxation rate; S/V is the pore specific surface; f_sIs a form factor, dimensionless, to spherical pores, F_s3; for cylindrical pipes, F_s2. Relaxation rate ρ₂Pore shape factor F_sCan be approximately regarded as a constant, so C is a constant value;

by bringing (5), (6) and (7) into (4), T can be obtained₂Conversion relationship with pore radius:

4. the method of claim 3 for increasing nuclear magnetic resonance T₂The conversion method for the spectral characterization of the precision of the pore size distribution of the tight reservoir is characterized in that the C and h values of each section are obtained by the data of each section through the least square principle, so that the T of each section is obtained₂And the conversion method between the pore size and the pore size.

5. The method of claim 1 for increasing nuclear magnetic resonance T₂The conversion method for the spectrum characterization of the pore size distribution precision of the tight reservoir is characterized in that the tight reservoir is one of tight sandstone, shale or mudstone.

6. The method of claim 1 for increasing nuclear magnetic resonance T₂The conversion method for the spectral characterization of the pore size distribution precision of the compact reservoir is characterized in that the nuclear magnetic resonance in the step one is low-field nuclear magnetic resonance, and the mercury intrusion experiment in the step two is constant-speed mercury intrusion.

Technical Field

The invention relates to a reservoir prediction technology, in particular to a nuclear magnetic resonance characterization method of a compact reservoir pore structure, and belongs to the field of petroleum exploration and development.

Background

One of the main features of tight reservoirs compared to conventional reservoirs is the small pore throat space, which makes migration of fluids therein difficult. Therefore, accurate evaluation of the pore structure of the compact reservoir is one of the preconditions for evaluating the potential, the exploitability and the productivity of compact oil and gas resources, nuclear magnetic resonance is a more common test means, and the method needs to test T in a saturated water state₂Converted to a pore radius. The advantages are that (1) the pore size distribution of the fluid can be definitely bound by combining a centrifugal or drying means; (2) by combining the relaxation spectrum of the saturated manganese sample, the pore size distribution occupied by the oil phase can be determined; (3) the control of the throat on the bound fluid or residual oil can be determined by combining a constant-speed mercury pressing experiment.

Usually will T₂Conversion to pore size distribution is an experimental approach incorporating mercury injection. The conventional conversion method is derived by the formula: t is₂＝Cr_tWhere C is the conversion coefficient, r_tPore size obtained for mercury injection. The above methods are described in the prior art of CN104634718A, CN106249306A and the like. However, this method has a problem that T is₂And r_tThe linear relationship of (a) and (b) does not fit well to both. This is more pronounced in tight reservoirs, probably due to the complex pore throat structure and smaller pore size distribution. For this reason, some researchers have obtained empirical formulas based on conventional methods:wherein n is a constant. But the formula is notCan be obtained through mathematical derivation, and simultaneously lacks of physical significance. Moreover, a common conversion method is based on actually measured mercury intrusion pore size distribution data, if the actually measured data are densely distributed in a certain mercury intrusion saturation section, the conversion formula can take more consideration of the weight of the actually measured data, so that the fitting degree of the actually measured data sparse section is poor, and the utilization of T is caused₂The conversion to pore size distribution is less effective.

Thus, the present invention proposes to utilize T₂The new method for converting the pore size distribution also fully considers the cylindrical pore model on the basis of common derivation. On the one hand, the transverse relaxation time T is not well influenced by the linear relation₂And the pore size distribution conversion is carried out, and on the other hand, the proposed model is more in line with the physical significance. In addition, the processing of the mercury intrusion pore size distribution data by the method can be helpful for improving the accuracy of pore size distribution obtained by nuclear magnetic resonance experiments and evaluating the potential of compact oil and gas resources relatively accurately.

Disclosure of Invention

The invention aims to provide a new material which has certain physical significance and is beneficial to improving nuclear magnetic resonance T₂The conversion method for the spectrum characterization of the pore size distribution precision of the compact reservoir relatively accurately evaluates the potential of compact oil and gas resources.

In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions: improve nuclear magnetic resonance T₂The conversion method for the spectral characterization of the precision of the pore size distribution of the tight reservoir comprises the following steps:

the method comprises the following steps: performing nuclear magnetic resonance test on a compact reservoir sample of saturated formation water to obtain nuclear magnetic resonance T₂A spectrum;

step two: performing a constant-speed mercury-pressing experiment on the dry and compact reservoir sample to obtain mercury-pressing pore size distribution data;

step three: carrying out sectional processing on the mercury intrusion pore size distribution data;

step four: obtaining T using a cylindrical pore model₂The conversion relation with the aperture size;

step five: using the data of step three and step four respectivelyConverting the relation to obtain T of each segment₂Conversion method from aperture size to obtain complete T₂A conversion method for spectral characterization of tight reservoir pore size distribution.

Further, the segmentation processing method in the third step is as follows: and according to the sequence from the small aperture to the large aperture, performing difference calculation on the aperture size data of different test points, and selecting the aperture size data with the aperture difference within an order of magnitude range as a data segment.

Further, the conversion relationship of the step four is as follows:

t expressed using KST model₂Relationship between pore volume and pore fluid volume:

the volume of the lamellar fluid in the cylindrical pore model is:

the surface area of the cylindrical pores is:

S^t＝2πr_t·l (3)

the formula (2) and the formula (3) are brought into the formula (1) to obtain

Order to

Wherein the content of the first and second substances,T₂representing transverse relaxation time, T_2sDenotes the relaxation, V, of the particle surface_sDenotes the pore fluid volume, V denotes the pore volume, V_s ^tThe volume of the thin layer fluid in the cylindrical pore model is shown, h represents the thickness of the thin layer fluid, r_tDenotes the pore radius,/. denotes the cylinder height, S^tExpressed as the surface area of the cylindrical pores, p₂Is the relaxation rate; S/V is the pore specific surface; f_sIs a form factor, dimensionless, to spherical pores, F_s3; for cylindrical pipes, F_s2. Relaxation rate ρ₂Pore shape factor F_sCan be approximately regarded as a constant, so C is a constant value;

by bringing (5), (6) and (7) into (4), T can be obtained₂Conversion relationship with aperture size:

further, the C and h values of each segment can be obtained by the least square principle of each segment of data, so that the T of each segment is obtained₂A method of conversion from pore size;

further, complete T is obtained₂A conversion method for spectral characterization of tight reservoir pore size distribution.

Compared with the prior art, the invention has the following characteristics and advantages:

1. the invention fully considers the pore structure model of the rock, changes the common plane physical model for nuclear magnetic resonance into the cylindrical pore model consistent with mercury intrusion experiment, and improves the nuclear magnetic resonance data T₂And accuracy of the correspondence between pore radii obtained from mercury intrusion data.

2. The method fully considers the characteristics of mercury intrusion data distribution, and reduces fitting errors caused by the data by using piecewise fitting.

Drawings

FIG. 1 is a sectional view of mercury intrusion pore size distribution data

FIG. 2 is a conversion process from a planar physical model to a cylindrical pore model

FIG. 3 shows T obtained by the conversion method of the present invention₂Fitting relation with pore radius

FIG. 4 is a comparison result of the pore size distribution and mercury intrusion pore size distribution calculated by the conversion method of the present invention

FIG. 5 is a graph of T obtained empirically₂Fitting relation with pore radius

FIG. 6 is a comparison of pore size distribution and mercury intrusion pore size distribution calculated by empirical method

FIG. 7 shows T obtained by a conventional method₂Fitting relation with pore radius

FIG. 8 is a comparison of pore size distribution and mercury intrusion pore size distribution calculated by a conventional method

Detailed Description

The details of the present invention can be more clearly understood in conjunction with the accompanying drawings and the description of the embodiments of the present invention. However, the specific embodiments of the present invention described herein are for the purpose of illustration only and are not to be construed as limiting the invention in any way. Any possible variations based on the present invention may be conceived by the skilled person in the light of the teachings of the present invention, and these should be considered to fall within the scope of the present invention.