CN105386753A - Method for constructing pseudo capillary pressure curves by using NMR (nuclear magnetic resonance) logging - Google Patents

Abstract

The invention discloses a method for constructing a pseudo-capillary pressure curve by using nuclear magnetic resonance logging. According to the actually measured nuclear magnetic resonance logging data and limited capillary pressure data, the method sets 7 different relaxation times, divides the nuclear magnetic resonance T2 spectrum into ₈ parts, and calculates the porosity components of the 8 parts percentage content, establish a conversion model between the mercury saturation at different mercury injection pressures and the percentage content of NMR porosity components, and calculate the mercury saturation at different mercury injection pressures according to the obtained conversion model. Based on the mercury saturation and the corresponding mercury injection pressure, the pseudo capillary pressure curve is constructed, and the pore throat radius distribution is obtained according to the pseudo capillary pressure curve, and the evaluation parameters of the reservoir pore structure are calculated to realize the accurate utilization of nuclear magnetic resonance logging data. The purpose of constructing pseudo capillary pressure curve and continuous quantitative evaluation of reservoir pore structure.

Description

A Method of Constructing Pseudo-capillary Pressure Curve Using Nuclear Magnetic Resonance Logging

technical field

The invention belongs to the field of reservoir evaluation, in particular to a method for constructing a pseudo-capillary pressure curve using nuclear magnetic resonance logging.

Background technique

As the country's demand for energy continues to increase, a large number of conventional reservoirs have been developed, and their production is decreasing day by day. Increasing the exploration and development of low-porosity, low-permeability-tight reservoirs has become an important way for the country to solve the shortage of oil and gas supply and ensure energy security. Low-porosity and low-permeability-tight reservoirs often have the characteristics of tight reservoirs, low resistivity contrast, complex pore structure, and strong heterogeneity, which lead to poor application of conventional reservoir evaluation methods and a large number of potential reservoirs. reservoirs are misjudged as water layers or non-reservoirs, and it is difficult to predict reservoir productivity. In order to improve the exploration efficiency of complex reservoirs and reduce development risks, quantitative evaluation of reservoir pore structure is an effective method.

At present, capillary pressure curve is the most effective data to evaluate reservoir pore structure and classify reservoir types. However, limited by the objective conditions of the experiment, the capillary pressure data obtained through the core experiment are very limited, which cannot be used to continuously and quantitatively evaluate the reservoir pore structure. In order to achieve the purpose of continuously and quantitatively evaluating the pore structure of reservoirs, the most commonly used method is to continuously construct pseudo-capillary pressure curves using nuclear magnetic resonance logging data, and use them instead of core capillary pressure curves to continuously and quantitatively evaluate the actual reservoir pore structure. Pore Structure.

There are several methods for constructing pseudo-capillary pressure curves using nuclear magnetic resonance logging data in the published literature:

1. The pseudo-capillary pressure curve construction method based on Swanson parameters. See the article "ANewMethodtoConstructReservoirCapillaryPressureCurvesUsingNMRLoggingDataandItsApplication" written by XiaoLiang et al. in the journal "AppliedGeophysics" in June 2008, which records the method of constructing pseudo-capillary pressure curves based on Swanson parameters. The basic steps of this method include: firstly, according to the capillary pressure curve data measured experimentally, establish a reservoir permeability interpretation model based on Swanson parameters, and use it to calculate the reservoir permeability from nuclear magnetic resonance logging data; then, According to the morphological characteristics of the capillary pressure curve, the correlation between the mercury saturation and NMR porosity and permeability under different mercury injection pressures is established, so as to calculate the mercury saturation by using the rock porosity and permeability parameters, and finally , combined with the calculated mercury injection saturation and mercury injection pressure, to achieve the purpose of reconstructing the pseudo capillary pressure curve.

2. Two-dimensional equal-area scale conversion coefficient method. See the article "Application of Nuclear Magnetic Resonance Logging in Reservoir Pore Structure Evaluation" written by Shao Weizhi et al. in the journal "Logging Technology" in February 2009, which records the use of two-dimensional equal-area scale conversion coefficient method to construct NMR Method of Pseudocapillary Pressure Curves. The basic steps of the method include: firstly, according to the relationship between the pore throat radius and the capillary pressure, the measured capillary pressure curve is transformed into the pore throat radius distribution, and the _T2 spectrum of each sample is determined to correspond to the corresponding pore throat radius distribution by using the differential similarity principle. The horizontal conversion coefficient between the throat radius distributions; then, using the segmented equal _- area scale method, determine the vertical conversion coefficient between the T2 spectrum of each sample and the corresponding pore throat radius distribution; finally, establish the horizontal conversion coefficient and the vertical The relationship between the conversion coefficient and rock porosity and permeability, in order to realize the purpose of constructing pseudo-capillary pressure curve by using nuclear magnetic resonance logging.

3. Scale method of piecewise nonlinear power function. See the patent "A Method for Continuous and Quantitative Evaluation of Reservoir Pore Structure Using Nuclear Magnetic Resonance Logging Data" invented by Kuang Lichun et al. in January 2010. A method for constructing pseudocapillary pressure curves in . The basic principle is: firstly calculate a parameter reflecting the difference of reservoirs according to rock porosity and permeability And use this parameter to divide the reservoirs into four types. For each type of reservoirs, different subsection power functions are used to construct pseudo-capillary pressure curves. For the first, second and third types of reservoirs, the segmented method is adopted, and different power functions are used in the large pore-throat and small pore-throat sections, while for the fourth type of reservoir, a single The power function of the NMR T ₂ spectrum is transformed into the pore throat radius distribution, and then the pseudo capillary pressure curve is constructed according to the relationship between the pore throat radius and the capillary pressure.

In the process of constructing the pseudo-capillary pressure curve using nuclear magnetic resonance logging data, the existing methods all use two intermediate parameters: porosity and permeability of the rock. However, in actual reservoir evaluation, these two intermediate parameters are difficult to obtain accurately, especially in tight reservoirs and complex lithology gas-bearing reservoirs, the porosity and permeability parameters are more difficult to obtain effectively, giving Using the above method to construct pseudo-capillary pressure curves increases the difficulty. At the same time, the permeability parameters cannot be directly obtained from the NMR T2 spectrum, and special calculation methods are required. _The introduction of these calculation processes will inevitably bring about human errors, and these errors will eventually be transmitted to the structure of the pseudo capillary pressure curve. During the establishment of the model, the error of the pseudo-capillary pressure curve constructed by the existing method is relatively large, which fails to achieve the purpose of accurately and quantitatively evaluating the reservoir pore structure by using the nuclear magnetic resonance logging data.

Contents of the invention

In order to overcome the deficiencies of the existing methods, the present invention provides a method for constructing pseudo-capillary pressure curves using nuclear magnetic resonance logging to realize accurate construction of pseudo-capillary pressure curves based on actually measured nuclear magnetic resonance logging data and limited capillary pressure data Purpose.

In order to solve the above problems, the present invention adopts the following technical solutions:

According to the actual measured nuclear magnetic resonance logging data and limited capillary pressure data, set 7 different relaxation times, divide the nuclear magnetic resonance T2 spectrum into ₈ parts, and calculate the percentage of porosity components in the 8 parts , establish a conversion model between the mercury saturation at different mercury injection pressures and the percentage content of NMR porosity components, and calculate the mercury saturation at different mercury injection pressures according to the obtained conversion model. Saturation and corresponding mercury injection pressure, construct pseudo-capillary pressure curve, and obtain pore-throat radius distribution based on pseudo-capillary pressure curve, calculate reservoir pore structure evaluation parameters, and realize accurate construction of pseudo-capillary by using nuclear magnetic resonance logging data The purpose of pressure curve and continuous quantitative evaluation of reservoir pore structure.

The method of the present invention comprises the following steps:

1) On the basis of analyzing the characteristics of the core mercury injection experiment and the operation process, determine M mercury injection pressures;

₂ ) Using nuclear magnetic resonance logging tools to measure the target reservoir and invert to obtain the actually measured nuclear magnetic resonance logging T2 spectrum;

₃ ) Given 7 different T2 relaxation times, divide the NMR T2 spectrum into ₈ parts, and then calculate the percentage of 8 porosity components;

4) Establish the functional relationship between the mercury saturation at M different mercury injection pressures and the percentage content of the eight porosity components, and use it to calculate the corresponding M mercury injection pressures from the nuclear magnetic resonance logging data M mercury saturation values of ;

5) Draw the constructed pseudo-capillary pressure curve according to the calculated mercury saturation and the given mercury pressure;

6) Using the structural pseudo-capillary pressure curve to obtain the reservoir pore-throat radius distribution, and calculate the average pore-throat radius, maximum pore-throat radius, median radius, median pressure, displacement pressure, average coefficient, sorting coefficient, etc. Reservoir pore structure evaluation parameters.

The M mercury injection pressures involved in step 1) are distributed as follows:

P _c (i)=0.005×2 ^i-1 , i=1,2,...,M

In the formula: P _c (i) is the i-th mercury injection pressure, the unit is MPa.

The seven T ₂ relaxation times given in step 3) are respectively T ₂ (1)=1.0ms, T ₂ (2)=3.0ms, T ₂ (3)=10.0ms, T ₂ (4)= 33.0ms, T ₂ (5) = 100.0ms, T ₂ (6) = 300.0ms, T ₂ (7) = 1000.0ms. For the convenience of description, it is assumed that the minimum T ₂ relaxation time is recorded as T ₂ (0), and the maximum T ₂ relaxation time is recorded as T ₂ (8).

The minimum T ₂ relaxation time T ₂ (0)=0.3ms defined in the step 3); the maximum T ₂ relaxation time T ₂ (8)=3000.0ms.

The 8 porosity component percentages involved in the step 3) are respectively X1, X2, X3, X4, X5, X6, X7 and X8, and the calculation method is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 8</span>}$

where S(t ₎ is the porosity distribution function related to T2 relaxation time.

The functional relationship between the mercury saturation involved in the step 4) and the porosity component percentage is as follows:

$\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>\end{array}\right)\mathrm{<span\; class="notranslate">\; =</span>}\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 18</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 28</span>}}\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 8</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 8</span>}}\end{array}\right)<span\; class="notranslate">\; \&times;</span>\left(\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 3</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 5</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 6</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 7</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 8</span>}\end{array}\right)<span\; class="notranslate">\; +</span>\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\end{array}\right)$

In the formula $\left(\begin{array}{c}{S}_{hg}\left(1\right)\\ S_{hg}\left(2\right)\\ \&Center\; Dot;\\ \&Center\; Dot;\\ S_{hg}\left(i\right)\\ \&Center\; Dot;\\ \&Center\; Dot;\\ S_{hg}\left(m\right)\end{array}\right)$ Indicates the saturation of mercury injection under M different mercury injection pressures, in the form of percentage %;

$\left(\begin{array}{c}x1\\ x2\\ x3\\ x4\\ x5\\ x6\\ x7\\ x8\end{array}\right)$ Indicates the percentage content of 8 porosity components, in the form of percentage %;

$\left(\begin{array}{c}{a}_{11},a_{12},a_{13},...a_{18}\\ a_{\mathrm{twenty\; one}},a_{\mathrm{twenty\; two}},a_{\mathrm{twenty\; three}},...a_{28}\\ \&Center\; Dot;\\ \&Center\; Dot;\\ a_{i1},a_{i2},a_{i3},...a_{i8}\\ \&Center\; Dot;\\ \&Center\; Dot;\\ a_{m,1},a_{m,2},a_{m,3},...a_{m,8}\end{array}\right)$ is the undetermined coefficient matrix, and its value is calibrated by the core experiment data;

$\left(\begin{array}{c}{b}_1\\ b_2\\ \&Center\; Dot;\\ \&Center\; Dot;\\ b_i\\ \&Center\; Dot;\\ \&Center\; Dot;\\ b_m\end{array}\right)$ is an undetermined constant matrix whose value is calibrated by the core experiment data.

In the step 4), when using NMR logging data to calculate the mercury saturation, only calculate the mercury saturation of the mercury injection pressure P _c (i) > 0.08MPa, for the mercury injection pressure P _c (i) The mercury saturation of the part ≤0.08MPa is set equal to 0.

In the step 6), the method of using the pseudo-capillary pressure curve to obtain the reservoir pore throat radius distribution and calculate the reservoir pore structure evaluation parameters is in accordance with the "Tenth Five-Year Plan" planning textbook "Oil Reservoir Physics" for general colleges and universities written by Yang Shenglai and others. The method described on pages 209-233 was carried out.

The beneficial effects of the present invention are: using nuclear magnetic resonance logging data to construct a continuous pseudo-capillary pressure curve, and using the pseudo-capillary pressure curve to obtain reservoir pore-throat radius distribution and calculate reservoir pore structure evaluation parameters, and then realize nuclear magnetic resonance-based The purpose of continuous and quantitative evaluation of reservoir pore structure from well logging data.

Description of drawings

The present invention will be further described below in conjunction with drawings and embodiments.

Fig. 1 is a flowchart of a method for constructing a pseudo-capillary pressure curve using nuclear magnetic resonance logging data provided by the present invention.

Fig. 2 is a schematic diagram of mercury injection capillary pressure curves of four core samples with different pore structures in a reservoir in Southwest China provided by an embodiment of the present invention.

Fig. 3 is a schematic diagram of nuclear magnetic resonance T ₂ spectra of four core samples with different pore structures in a reservoir in Southwest China provided by an embodiment of the present invention.

Fig. 4 is a schematic diagram of the comparison between the mercury intrusion capillary pressure curve and the pseudo-capillary pressure curve of the structure provided by the embodiment of the present invention.

Fig. 5 is a schematic diagram of the comparison between the mercury intrusion capillary pressure curve and the pseudo-capillary pressure curve of the structure provided by the embodiment of the present invention.

Fig. 6 is a schematic diagram of the comparison between the mercury intrusion capillary pressure curve and the structural pseudo-capillary pressure curve of the rock with poor pore structure provided by the embodiment of the present invention.

Fig. 7 is a comparison between the pseudo capillary pressure curve constructed from the measured nuclear magnetic resonance logging data and the reservoir pore structure evaluation parameters calculated by using the pseudo capillary pressure curve and the core experiment results provided by the method of the present invention. renderings.

detailed description

theoretical analysis

Below, the mercury intrusion capillary pressure curve and NMR T2 spectrum of ₄ representative rock core samples of a certain reservoir in Southwest China are taken as examples to illustrate the basic principles and ideas of the present invention.

Referring to Fig. 2, it shows the mercury injection capillary pressure test results of four samples, wherein, the X-axis is the mercury injection saturation, and the unit is percentage %; the Y-axis is the mercury injection pressure, and the unit is MPa. The shapes of the mercury injection capillary pressure curves of the four samples are completely different, and the pore structures of the rocks they represent are also significantly different. The capillary pressure curve of sample No. 1 is located in the lower left corner of the figure, indicating that the pore structure of the rock is the best; the capillary pressure curve of sample No. 2 is above the capillary pressure curve of sample No. 1, indicating that its pore structure is worse than that of sample No. 1; The capillary pressure curve of sample No. 3 is above the capillary pressure curves of samples No. 1 and No. 2, and below the capillary pressure curve of sample No. 4, which means that its pore structure is worse than that of samples No. 1 and No. 2, but better than that of No. 4 samples. Sample No. 4; the capillary pressure curve of sample No. 4 is at the top of the figure, representing the worst pore structure.

The experimental data of mercury injection capillary pressure corresponding to the four samples are shown in Table 1. It can be seen from Table 1 that during the mercury injection experiment, the mercury injection pressure applied to all samples is the same, that is, the Y-axis coordinates of all the capillary pressure curves in Figure 2 are equal. The method of applying the mercury injection pressure is shown in the following formula:

P _c (i)=0.005×2 ^i-1 , i=1,2,...,13

In the formula: P _c (i) is the i-th mercury injection pressure applied, and the unit is MPa.

Since all the core samples are subjected to the same mercury injection pressure during the mercury injection experiment, the shape of the capillary pressure curve of the core samples is mainly controlled by the saturation of mercury injection. Under the same mercury injection pressure, for rocks with better pore structure, the amount of mercury injected into the rock pore space is more, and the corresponding mercury injection saturation is higher; on the contrary, for rocks with poor pore structure, the pressure The amount of mercury injected into the rock pore space is small, and the corresponding mercury saturation is low.

It can be seen that the capillary pressure curve can be reconstructed only by calculating the mercury saturation at different mercury injection pressures and combining the fixed mercury injection pressure.

Table 1. Capillary pressure experiment data table of mercury injection for four representative core samples

For core samples, when the applied mercury injection pressure is small (less than 0.08MPa), almost no mercury in the non-wetting phase is squeezed into the pore space of the rock, that is, when the mercury injection pressure is less than 0.08MPa, the rock Mercury saturation is small and can be ignored basically, and the shape of capillary pressure curve in this part has little contribution to the evaluation of rock pore structure. Therefore, the present invention proposes only estimating the mercury injection saturation of the part where the mercury injection pressure is greater than 0.08MPa to construct a pseudo-capillary pressure curve, and setting the mercury injection saturation to be equal to 0 for the part where the mercury injection pressure is less than 0.08MPa.

Referring to Fig. 3, it shows the experimental results of the NMR T ₂ spectra of 4 samples, where the X-axis is the T ₂ relaxation time in ms; the Y-axis is the relative amplitude in v/v.

Comparing Figures 2 and 3, it can be found that for rocks with better pore structure, such as sample No. 1 in Figure ₂ , the position of the main peak of the corresponding rock NMR T2 spectrum in Figure ₃ is on the right, and the distribution of the T2 spectrum is relatively large. wide, mainly distributed between 2 and 1600 ms, with large pores as the main distribution, and the large pore components account for a large proportion in the total pores of the rock; for sample No. ₂ with poor pore structure, its NMR T The distribution range of the T 2 spectrum is narrower than that of No. 1 sample, and the distribution of the main peak is relatively to the left, and the proportion of small pore components in the total rock pores increases; for No. 3 sample with worse pore structure, the distribution range of the T ₂ spectrum is relatively Samples No. 1 and No. 2 are narrower, the position of the main peak moves further to the left, and the proportion of small pore components in the total pores of the rock further increases, while the proportion of large pore components decreases relatively; for the pore structure For the worst sample No. ₄ , the position of the main peak of its T2 spectrum is at the far left in Fig. 3. The rock is mainly distributed with small pores, and the proportion of large pores in the total pores of the rock is the lowest.

Based on the above analysis, it can be found that the proportion of each pore component in the total rock pore has a certain indicating effect on the rock pore structure. Therefore, it should have a strong correlation with the mercury saturation of rocks under different mercury injection pressures. Theoretically, under the same mercury injection pressure, for rocks with better pore structure, the mercury injection saturation is higher, the large pore components account for a larger proportion of the total pores, and the small pore components account for a larger proportion of the total pores. Conversely, for rocks with poor pore structure, the mercury saturation decreases, the proportion of large pore components in the total pores decreases, and the proportion of small pore components in the total pores increases. Big.

On the basis of the above-mentioned experimental analysis, the present invention proposes to use the percentage content of the pore components of each part of the rock in the total pore components of the rock to calculate the mercury saturation under different mercury injection pressures, and then combine the calculated mercury saturation and A method for constructing a pseudo-capillary pressure curve for a given mercury injection pressure value.

In order to visually and quantitatively characterize the proportion of different pore components in the total rock pores, seven different T ₂ relaxation times T ₂ (1), T ₂ (2), T ₂ (3), T ₂ (4 ), T ₂ (5), T ₂ (6) and T ₂ (7), the rock NMR T ₂ spectrum is divided into 8 intervals, and then according to the sum of the rock porosity components and the total porosity in the 8 intervals The percentages of 8 porosity components are calculated from the ratio of porosity. The specific calculation process is as follows:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 8</span>}$

where S(t ₎ is the porosity distribution function related to T2 relaxation time.

After calculating the percentages of the above eight porosity components, the functional relationship between the mercury saturation at different mercury injection pressures and the percentages of the above eight porosity components is established to realize the calculation using NMR logging data. The purpose of constructing the pseudo-capillary pressure curve is to combine the mercury injection saturation with the fixed mercury injection pressure value.

Example 1

Referring to Fig. 1, a method for constructing a pseudo-capillary pressure curve using nuclear magnetic resonance logging, the steps are as follows:

1) According to the characteristics and operation process of the mercury injection experiment, 13 mercury injection pressures were determined;

₂ ) Using nuclear magnetic resonance logging tools to measure the target reservoir and invert to obtain the actually measured nuclear magnetic resonance logging T2 spectrum;

3), given 7 different T ₂ relaxation times T ₂ (1), T ₂ (2), T ₂ (3), T ₂ (4), T ₂ (5), T ₂ (6) and T ₂ (7), the nuclear magnetic resonance T ₂ spectrum is divided into 8 parts, and then the percentage content of 8 porosity components is calculated;

4) Establish the functional relationship between mercury saturation at 13 different mercury injection pressures and the percentage content of 8 porosity components, and use it to calculate 13 mercury saturation values from nuclear magnetic resonance logging data ;

5), take the calculated 13 mercury injection saturation values as the abscissa, and take the given 13 mercury injection pressure values as the ordinate, establish a plane Cartesian coordinate system, and draw the pseudo-capillary pressure curve;

6) According to the relationship between pore-throat radius and capillary pressure, the pore-throat radius distribution of reservoir rocks is obtained, and the average pore-throat radius, maximum pore-throat radius, median radius, median pressure, displacement pressure, and average value are calculated Reservoir pore structure evaluation parameters such as coefficient and sorting coefficient, in order to achieve the purpose of continuous and quantitative evaluation of reservoir pore structure.

The 13 mercury injection pressure values involved in said step 1) are determined by the following formula:

P _c (i)=0.005×2 ^i-1 , i=1,2,...13

In the formula: P _c (i) is the i-th mercury injection pressure applied, and the unit is MPa.

The seven T ₂ relaxation times given in step 3) are respectively T ₂ (1)=1.0ms, T ₂ (2)=3.0ms, T ₂ (3)=10.0ms, T ₂ (4)= 33.0 ms, T ₂ (5) = 100.0 ms, T ₂ (6) = 300.0 ms, and T ₂ (7) = 1000.0 ms.

The minimum T ₂ relaxation time T ₂ (0)=0.3ms defined in the step 3); the maximum T ₂ relaxation time T ₂ (8)=3000.0ms.

The 8 porosity component percentages involved in the step 3) are respectively X1, X2, X3, X4, X5, X6, X7 and X8, and the calculation method is:

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; /</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 8</span>}$

where S(t ₎ is the porosity distribution function related to T2 relaxation time.

The 13 mercury saturation degrees involved in the step 4) are calculated using the following formula:

$\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>\end{array}\right)\mathrm{<span\; class="notranslate">\; =</span>}\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 18</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; one</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 28</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 8</span>}}\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 8</span>}}\end{array}\right)<span\; class="notranslate">\; \&times;</span>\left(\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 3</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 5</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 6</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 7</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 8</span>}\end{array}\right)<span\; class="notranslate">\; +</span>\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 13</span>}}\end{array}\right)$

In the formula, $\left(\begin{array}{c}{a}_{11},a_{12},a_{13},...a_{18}\\ a_{\mathrm{twenty\; one}},a_{\mathrm{twenty\; two}},a_{\mathrm{twenty\; three}},...a_{28}\\ \&Center\; Dot;\\ \&CenterDot;\\ a_{i1},a_{i2},a_{i3},...a_{i8}\\ \&Center\; Dot;\\ \&Center\; Dot;\\ a_{13,1},a_{13,2},a_{13,3},...a_{13,8}\end{array}\right)$ is the undetermined coefficient matrix;

$\left(\begin{array}{c}{b}_1\\ b_2\\ \&Center\; Dot;\\ \&Center\; Dot;\\ b_i\\ \&CenterDot;\\ \&CenterDot;\\ b_{13}\end{array}\right)$ is an undetermined constant matrix

The method for determining the coefficient matrix and the constant matrix is as follows:

Drill a part of representative core samples, carry out NMR and mercury injection experiments at the same time, first, divide the NMR T2 spectrum into ₈ parts according to ₇ given T2 relaxation times, and calculate the 8 rock pores The percent content of the mercury saturation component is used as the independent variable; then, according to the mercury injection capillary pressure experiment data, 13 mercury injection saturation values are determined as the dependent variable; finally, the coefficient matrix and the constant The numeric values of the matrix.

The values in the first to fourth rows of the coefficient matrix and the constant matrix are all set to 0, and the calculated mercury saturation value is also 0.

Example 2

According to the method of constructing pseudo-capillary pressure curve using nuclear magnetic resonance logging described in the present invention, 20 rock core samples drilled from a certain reservoir in Southwest China are processed, and the coefficient matrix and constant matrix in the mercury saturation calculation formula are calibrated Numerically, a model for the capillary pressure curve of the continuous construction was obtained. Using the calibrated model to process the measured NMR logging data, a continuous pseudo-capillary pressure curve is obtained. In order to evaluate the reliability of the capillary pressure curve structure model, the pseudo capillary pressure curves corresponding to the depths of 20 core samples were read and compared with the experimental mercury injection capillary pressure curves.

Referring to Fig. 4 to Fig. 6, the comparison charts of mercury injection capillary pressure curves of three types of representative cores with good pore structure, medium pore structure and poor pore structure and pseudo-capillary pressure curves of structures are listed respectively. It can be seen from the figure that for various types of reservoir rocks, the pseudo capillary pressure curve constructed by the method of the present invention is in good agreement with the mercury injection capillary pressure curve obtained from the core experiment. Table 2 is a statistical table of errors between the evaluation parameters of reservoir pore structure calculated by using the constructed pseudo-capillary pressure curve of 20 core samples and the evaluation parameters of reservoir pore structure obtained from core mercury injection experiments. As can be seen from the statistical results, the error between the evaluation parameters of the reservoir pore structure calculated by the pseudo capillary pressure curve obtained by the method of the present invention and the result obtained by the core mercury injection experiment is small, and the relative errors are all less than 10.0 %, meeting the requirements for quantitative evaluation of actual reservoir pore structure.

Table 220. Statistical table of error statistics of reservoir pore structure evaluation parameters calculated by different methods for 220 core samples

Referring to Fig. 7, it is a comparison chart of the pseudo-capillary pressure curve constructed by the method of the present invention, the calculated reservoir pore structure evaluation parameters and the core mercury injection test results. The effect map shown in Fig. 7 is divided into twelve tracks. The first track in the figure includes the natural gamma ray curve (GR) and the caliper curve (CAL), which are mainly used to identify effective sandstone reservoirs; the second track is the depth Trace, unit m; the third trace is deep lateral resistivity curve (RT) and shallow lateral resistivity curve (RXO); the fourth trace includes density logging (DEN) curve, neutron logging (CNL) curve and Acoustic time-difference logging (AC) curves are mainly used to calculate the porosity of the reservoir; the fifth track includes the actually measured nuclear magnetic resonance logging T ₂ spectrum T2_DIST; the sixth track includes the actual The comparison between the measured NMR logging T2 spectral continuous pseudo _- capillary pressure curve and the core mercury injection capillary pressure curve. The black curve in the figure is the pseudo-capillary pressure curve continuously constructed using nuclear magnetic resonance logging data. For the convenience of curve display , in the present invention, the pseudo capillary pressure curve is added to the state of the maximum mercury injection pressure of 20.48MPa, while the discrete curve is the core mercury injection capillary pressure curve; the seventh track shows the pseudo capillary pressure constructed by the method shown in the embodiment of the present invention The comparison chart of the reservoir pore throat radius distribution converted from the pressure curve and the pore throat radius distribution obtained from the mercury injection capillary pressure curve. The discrete curve in the figure is the pore throat radius distribution obtained from the core mercury injection capillary pressure curve. From the results shown in the sixth and seventh tracks, it can be seen that the pseudo capillary pressure curve constructed by the method described in the embodiment of the present invention and the obtained pore throat radius distribution are in good agreement with the results of the core mercury injection experiment. In the eighth track, RM is the average pore-throat radius calculated from the pseudo-capillary pressure curve continuously constructed by the method provided by the embodiment of the present invention, and CRM is the average pore-throat radius obtained from the core mercury injection experiment; The median radius of the pseudo-capillary pressure curve calculated by the method provided by the example, CR50 is the median radius obtained by the core mercury injection experiment; RMAX in the tenth track is the calculation of the pseudo-capillary pressure curve of the continuous structure using the method provided by the embodiment of the present invention CRMAX is the maximum pore throat radius obtained from the core mercury injection experiment. In the eleventh track, PD is the displacement pressure calculated by using the pseudo-capillary pressure curve continuously constructed by the method provided by the embodiment of the present invention, and CPD is the displacement pressure obtained from the core mercury injection experiment; The median pressure calculated from the continuously constructed pseudo-capillary pressure curve provided by the method provided in the example, and CP50 is the median pressure obtained from the core mercury injection experiment. As can be seen from the figure, the reservoir pore structure evaluation parameters calculated by using the pseudo-capillary pressure curve continuously constructed by the method of the present invention are close to the results of the core mercury injection experiment. _The well T2 spectrum is continuously converted into a pseudo-capillary pressure curve to obtain accurate reservoir pore throat radius distribution and reservoir pore structure evaluation parameters.

Finally, it should be noted that: obviously, the above-mentioned embodiments are only examples for clearly illustrating the present invention, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. However, the obvious changes or changes derived therefrom still fall within the scope of protection of the present invention.

Claims (9)

1. A method for constructing pseudo-capillary pressure curves utilizing nuclear magnetic resonance logging, characterized in that: the method sets 7 different relaxation times according to actually measured nuclear magnetic resonance logging data and limited mercury injection capillary pressure data , divide the NMR T2 spectrum into ₈ parts, calculate the percentage content of porosity components in the 8 parts, and establish the relationship between the saturation of mercury injection and the percentage content of NMR porosity components under different mercury injection pressures. Conversion model, according to the obtained conversion model, calculate the mercury saturation at different mercury injection pressures, construct the pseudo capillary pressure curve according to the calculated mercury saturation and the corresponding mercury injection pressure, and obtain Pore-throat radius distribution, calculation of reservoir pore structure evaluation parameters, and accurate construction of pseudo-capillary pressure curves and continuous quantitative evaluation of reservoir pore structure using nuclear magnetic resonance logging data. 2. A kind of pseudo-capillary pressure curve method utilizing nuclear magnetic resonance logging structure as claimed in claim 1, is characterized in that, described method comprises the following steps: 1) On the basis of analyzing the characteristics of the core mercury injection experiment and the operation process, determine M mercury injection pressures; ₂ ) Using nuclear magnetic resonance logging tools to measure the target reservoir and invert to obtain the actually measured nuclear magnetic resonance logging T2 spectrum; ₃ ) Given 7 different T2 relaxation times, divide the NMR T2 spectrum into ₈ parts, and then calculate the percentage of 8 porosity components; 4) Establish the functional relationship between the mercury saturation at M different mercury injection pressures and the percentage content of the eight porosity components, and use it to calculate the corresponding M mercury injection pressures from the nuclear magnetic resonance logging data M mercury saturation values of ; 5) Draw the constructed pseudo-capillary pressure curve according to the calculated mercury saturation and the given mercury pressure; 6) Obtain the reservoir pore throat radius distribution by using the pseudo-capillary pressure curve of the structure, and calculate the average pore throat radius, maximum pore throat radius, median radius, median pressure, displacement pressure, average coefficient, sorting coefficient, etc. Parameters for evaluation of stratified pore structure. 3. A kind of pseudo-capillary pressure curve method utilizing nuclear magnetic resonance logging structure as claimed in claim 1 or 2, is characterized in that: described step 1) involves M mercury injection pressure points as follows: P _c (i)=0.005×2 ^i-1 , i=1,2,...,M In the formula: P _c (i) is the i-th mercury injection pressure, the unit is MPa. 4. A kind of pseudo capillary pressure curve method utilizing nuclear magnetic resonance logging structure as claimed in claim 1 or 2, is characterized in that: described step 3) given 7 T ₂ relaxation times are T ₂ (1 )=1.0ms, T ₂ (2)=3.0ms, T ₂ (3)=10.0ms, T ₂ (4)=33.0ms, T ₂ (5)=100.0ms, T ₂ (6)=300.0ms, T ₂ (7) = 1000.0 ms, for the convenience of description, set: the minimum T ₂ relaxation time is recorded as T ₂ (0), and the maximum T ₂ relaxation time is recorded as T ₂ (8). 5. A method for constructing a pseudo-capillary pressure curve utilizing nuclear magnetic resonance logging as claimed in claim 1 or 2, characterized in that: the minimum T relaxation time T ₂ (0)=0.3ms defined in the step ₃ ) ; Maximum T ₂ relaxation time T ₂ (8) = 3000.0 ms. 6. A method for constructing a pseudo-capillary pressure curve utilizing nuclear magnetic resonance logging as claimed in claim 1 or 2, wherein the 8 porosity component percentages involved in step 3) are respectively X1 and X2 , X3, X4, X5, X6, X7 and X8, the calculation method is: ${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; =</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; /</span>}{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 8</span>}$ where S(t ₎ is the porosity distribution function related to T2 relaxation time. 7. A kind of method utilizing nuclear magnetic resonance logging to construct pseudo-capillary pressure curves as claimed in claim 1 or 2, is characterized in that: the difference between the mercury saturation and the porosity component percentage content involved in said step 4) The functional relationship is as follows: $\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>\end{array}\right)\mathrm{<span\; class="notranslate">\; =</span>}\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; 8</span>}}\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; two</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; twenty\; three</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 28</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; i8</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ {\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; M,2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; M,3</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; M,8</span>}}\end{array}\right)<span\; class="notranslate">\; \&times;</span>\left(\begin{array}{c}\mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 3</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 5</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 6</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 7</span>}\\ \mathrm{<span\; class="notranslate">\; x</span>}\mathrm{<span\; class="notranslate">\; 8</span>}\end{array}\right)<span\; class="notranslate">\; +</span>\left(\begin{array}{c}{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\\ <span\; class="notranslate">\; \&Center\; Dot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ <span\; class="notranslate">\; \&CenterDot;</span>\\ {\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\end{array}\right)$ In the formula $\left(\begin{array}{c}{S}_{hg}\left(1\right)\\ S_{hg}\left(2\right)\\ \&Center\; Dot;\\ \&Center\; Dot;\\ S_{hg}\left(i\right)\\ \&Center\; Dot;\\ \&CenterDot;\\ S_{hg}\left(m\right)\end{array}\right)$ Indicates the saturation of mercury injection under M different mercury injection pressures, in the form of percentage %; $\left(\begin{array}{c}x1\\ x2\\ x3\\ x4\\ x5\\ x6\\ x7\\ x8\end{array}\right)$ Indicates the percentage content of 8 porosity components, in the form of percentage %; $\left(\begin{array}{c}{a}_{11},a_{12},a_{13},...a_{18}\\ a_{21},a_{\mathrm{twenty\; two}},a_{\mathrm{twenty\; three}},...a_{\mathrm{28}}\\ \&Center\; Dot;\\ \&Center\; Dot;\\ a_{i1},a_{\mathrm{i2}},a_{\mathrm{i3}},...a_{\mathrm{i8}}\\ \&Center\; Dot;\\ \&Center\; Dot;\\ a_{m,1},a_{\mathrm{M,2}},a_{\mathrm{M,3}},...a_{\mathrm{M,8}}\end{array}\right)$ is the undetermined coefficient matrix, and its value is calibrated by the core experiment data; $\left(\begin{array}{c}{b}_1\\ b_2\\ \&Center\; Dot;\\ \&Center\; Dot;\\ b_i\\ \&Center\; Dot;\\ \&CenterDot;\\ b_m\end{array}\right)$ is an undetermined constant matrix whose value is calibrated by the core experiment data. 8. A kind of pseudo-capillary pressure curve method utilizing nuclear magnetic resonance logging structure as claimed in claim 1 or 2, is characterized in that: in described step 4) when utilizing nuclear magnetic resonance logging data to calculate mercury saturation, only Calculate the mercury injection saturation for the part where the mercury injection pressure P _c (i) > 0.08MPa, and set the mercury injection saturation for the part where the mercury injection pressure P _c (i) ≤ 0.08MPa is equal to 0. 9. A method for constructing a pseudo-capillary pressure curve using nuclear magnetic resonance logging as claimed in claim 1 or 2, characterized in that: in the step 6), the pseudo-capillary pressure curve is used to obtain reservoir pore-throat radius distribution and calculate The method for evaluating parameters of reservoir pore structure is carried out in accordance with the method described on pages 209-233 in the "Tenth Five-Year Plan" textbook "Reservoir Physics" written by Yang Shenglai and others.