Characterization method of micro-scale pore nonlinear flow characteristics of shale oil

Abstract

The present application provides a kind of shale oil microscale pore nonlinear flow characteristic characterization method, comprising: step 1, the micro-pore structure distribution of shale core is measured;Step 2, the adsorption capacity of shale core to shale oil fluid is measured;Step 3, the micro-pore flow model considering Darcy flow+non-Darcy flow+boundary layer thickness is used, the flow value of shale oil in different size shale pore changes with driving pressure difference is calculated;Step 4, the nonlinear relationship curve of displacement pressure gradient and flow is drawn using the calculation result;Step 5, the nonlinear characteristic parameter of shale oil flowing in different pores of shale is determined according to the nonlinear relationship curve of displacement pressure gradient and flow.The shale oil microscale pore nonlinear flow characteristic characterization method accurately describes the nonlinear flow characteristics of shale oil when passing through the microscale pore space of shale, and provides a reliable theoretical basis for accurately analyzing the nonlinear seepage mechanism of shale oil.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of percolation theory research in porous media in unconventional oil development, and particularly to a characterization method of nonlinear flow characteristics of shale oil micro-scale pores. BACKGROUND

[0002] In recent years, shale oil and gas resources exploration and development has become a hot issue of research at home and abroad. In the world, with the increasing degree of conventional oil and gas exploration and development, shale oil and gas is gradually becoming an important field and a backup position. The United States is the most successful country in shale oil and gas exploration and development, and the shale oil production in Bakken and Eagle Ford shale areas of the United States reached 194.63 million tons in 2011. According to the prediction of EIA, shale oil will become the main force of future growth of U.S. oil production. In addition to the United States and Canada, Australia, Germany, Sweden and other countries have also begun to research and explore shale oil and gas. China's shale oil has great potential, and the oil and gas center of the Ministry of Land and Resources has preliminarily estimated that the shale oil geological resources in some basins are 15.292 billion tons, of which the Paleogene in Jiyang Depression is estimated to be 984.4 million tons. According to preliminary statistics, there are 330 exploration wells in the Jiyang Depression that have shown oil and gas shows in the Paleogene Shahejie Formation continental shale, showing great potential of shale oil and gas in the Jiyang Depression. The organic matter maturity in the Jiyang Depression is relatively low, and shale oil is mainly used.

[0003] Through the study of the characteristics of fluid nonlinear seepage in low permeability and tight reservoirs, it can be inferred that the flow of shale oil in the ground should also be nonlinear flow characteristics. However, most of the experimental studies on seepage mechanism are based on macroscopic or mesoscopic core experiments, and the experimental results can only reflect the statistical average of fluid flow, which is a macroscopic result reflecting the comprehensive factors of core pore structure, rock mineral composition and surface properties, fluid properties, etc. The results obtained on this basis are inevitably difficult to explain the fundamental reasons for the nonlinear seepage law of low permeability reservoirs.

[0004] In the Chinese patent application with the application number CN201510824025.8, a characterization method of nonlinear seepage characteristics of single-phase fluid through low permeability cores is involved, which includes the following steps: step 1, measuring the conventional physical parameters of the core; step 2, measuring the fluid parameters; step 3, measuring the minimum starting pressure gradient of the single-phase fluid through the low permeability core according to the static method; step 4, experimentally measuring the fluid flow under different displacement pressure gradients, and drawing the relationship curve between the displacement pressure gradient and the flow rate; step 5, fitting the relationship curve between the displacement pressure gradient and the flow rate to obtain the nonlinear seepage parameters.

[0005] In the Chinese patent application with the application number CN201610573709.X, a method for predicting the volume content of dissolution pores in a carbonate reservoir is disclosed, which comprises the following steps: obtaining physical parameters of the carbonate reservoir; calculating the actually measured saturation rock bulk modulus and shear modulus of the carbonate reservoir according to the physical parameters obtained in step one; calculating the bulk modulus, shear modulus of the rock matrix of the carbonate reservoir and the bulk modulus of the pore fluid; establishing a double-porosity medium critical porosity model to calculate the bulk modulus and shear modulus of the rock skeleton of the carbonate reservoir; calculating the bulk modulus and shear modulus of the saturated rock of the carbonate reservoir by using the Gassmann equation; comparing the bulk modulus and shear modulus of the saturated rock of the carbonate reservoir with the actually measured saturation rock bulk modulus and shear modulus of the carbonate reservoir to calculate the error; modifying the volume content of the dissolution pores, sequentially executing steps four to six to calculate the error corresponding to the set dissolution pore condition, and obtaining the optimal dissolution pore volume content.

[0006] In the Chinese patent application with the application number CN201611164619.1, a method for characterizing the micro-pore structure of a tight reservoir is disclosed, which comprises the following steps: step 1, performing mercury injection experiment data processing; step 2, using the processed data to draw a histogram of throat radius and interval mercury saturation frequency; step 3, selecting a main peak radius Rf according to the histogram of throat radius and interval mercury saturation frequency; step 4, performing mercury injection data interception processing; and step 5, calculating the throat and pore configuration coefficient, using the characteristic data of the mercury injection experiment to obtain the sum of the throat radius and the corresponding interval mercury saturation product as the throat and pore configuration coefficient.

[0007] The above prior art has great differences from the present application and fails to solve the technical problems we want to solve. At the same time, the micro-pore scale of shale is nanoscale, which is much smaller than that of low-permeability oil reservoirs, and has extremely low porosity and permeability characteristics. Therefore, the micro-flow mechanism of shale oil is completely different from that of low-permeability oil reservoirs. The micro-flow mechanism of shale oil at the microscale provides a theoretical basis for the effective utilization of shale oil resources. Therefore, the present application provides a method for characterizing the nonlinear flow characteristics of shale oil microscale pores, thereby solving the above technical problems. SUMMARY

[0008] The purpose of the present application is to provide a method for characterizing the nonlinear flow characteristics of shale oil microscale pores, which is convenient for practical application, simple in parameter acquisition and can accurately characterize.

[0009] The purpose of the present application can be achieved by the following technical measures: a method for characterizing the nonlinear flow characteristics of shale oil microscale pores, which comprises:

[0010] Step 1, measure the micro-pore structure distribution of shale core;

[0011] Step 2, measure the adsorption capacity of shale core to shale oil fluid;

[0012] Step 3, use the micro-pore flow model considering Darcy flow + non-Darcy flow + boundary layer thickness to calculate the flow value of shale oil in different size shale pores with driving pressure difference;

[0013] Step 4, use the calculation results to draw the nonlinear relationship curve of displacement pressure gradient and flow rate;

[0014] Step 5, determine the nonlinear characteristic parameters of shale oil flowing in different pores of shale according to the nonlinear relationship curve of displacement pressure gradient and flow rate.

[0015] The purpose of the application can also be achieved through the following technical measures:

[0016] In step 1, the micro-pore structure distribution of shale core is measured, including the size and number of micro-pores.

[0017] In step 2, the adsorption capacity of shale core to shale oil fluid is measured, which is the adsorption amount of shale to shale oil.

[0018] In step 3, the test results of step 1 and step 2 are used, and the micro-pore flow model considering Darcy flow + non-Darcy flow + boundary layer thickness is applied to calculate the flow value of shale oil in different size shale pores with driving pressure difference.

[0019] In step 3, the micro-pore flow model formula used is:

[0020]

[0021] In the formula: μ—fluid viscosity; Q—micro-pore flow; H—adsorption force influence radius; R—pore radius; δ—boundary layer thickness; f max —maximum adsorption force; ΔP—pressure difference.

[0022] In step 4, the calculation results of step 3 are used to draw the nonlinear relationship curve of displacement pressure gradient and flow rate.

[0023] In step 5, the nonlinear characteristic parameters of shale oil flowing in different pores of shale are determined by using the nonlinear relationship curve of displacement pressure gradient and flow rate drawn in step 4.

[0024] In step 5, the nonlinear characteristic parameters of shale oil flowing in different pores of shale determined include starting pressure gradient, boundary layer thickness, and minimum flow radius.

[0025] The shale oil micro-scale pore nonlinear flow characteristic characterization method in the application actually reflects the influence of three forces, i.e., driving force, internal friction of fluid and flow resistance generated by solid-liquid adsorption force, on the flow process of shale oil in the micro-scale shale pore, accurately describes the nonlinear flow characteristics of shale oil when passing through the shale micro-scale pore space, and calculates the starting pressure gradient and non-flow boundary layer thickness of different pore sizes, thereby providing a reliable theoretical basis for accurately analyzing the shale oil nonlinear seepage mechanism. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The flow chart of a specific embodiment of the shale oil micro-scale pore nonlinear flow characteristic characterization method of the application;

[0027] Figure 2 The micro-pore structure distribution diagram of mudstone in a specific embodiment of the application;

[0028] Figure 3 The flow rate-pressure gradient relationship curve diagram of a micro-pipe with a radius of 2 um in a specific embodiment of the application;

[0029] Figure 4 The flow rate-pressure gradient relationship curve diagram of a micro-pipe with a radius of 1.5 um in a specific embodiment of the application;

[0030] Figure 5 The flow rate-pressure gradient relationship curve diagram of a micro-pipe with a radius of 0.5 um in a specific embodiment of the application. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0032] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit exemplary embodiments according to the application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a presence of the features, steps, operations and / or combinations thereof.

[0033] Example 1:

[0034] In the application of the specific embodiment 1 of the application, the shale oil micro-scale pore nonlinear flow characteristic characterization method of the application includes the following steps:

[0035] In step 1, the micro-pore structure distribution of the shale core is measured, mainly the size and quantity of the micro-pores. Figure 2 It can be seen that the proportion of pores of different diameters accounts for the total number of pores.

[0036] In step 2, the adsorption capacity of the shale core to the shale oil fluid is measured, mainly the adsorption amount of the shale to the shale oil.

[0037] In step 3, by using the test results of step 1 and step 2, a micro-pore flow model considering Darcy flow + non-Darcy flow + boundary layer thickness is applied to calculate the flow value of the shale oil in the shale pores of different sizes with the driving pressure difference, and the micro-pore flow model formula used is as follows:

[0038]

[0039] In the formula, μ represents the fluid viscosity; Q represents the micro-pore flow; H represents the influence radius of the adsorption force; R represents the pore radius; δ represents the boundary layer thickness; f represents the non-Darcy flow coefficient; F represents the maximum adsorption force; and ΔP represents the pressure difference. max

[0040] In step 4, by using the calculation results of step 3, a nonlinear relationship curve of the displacement pressure gradient and the flow is drawn. Figures 3-5 It can be seen that the trend of the flow with the pressure gradient under different micro-pore radii.

[0041] In step 5, by using the nonlinear relationship curve of the displacement pressure gradient and the flow drawn in step 4, the nonlinear characteristic parameters of the shale oil flowing in the shale pores of different sizes are determined, mainly including the starting pressure gradient, the boundary layer thickness and the minimum flow radius.

[0042] Embodiment 2

[0043] In a specific embodiment 2 of the present application, as shown in Figure 1 , the following steps are included:

[0044] In step 101, the experimental shale core measurement parameters are as follows: the pore diameter size is 20-6000 nm; and the pore quantity proportion is 0.12-21.89%.

[0045] In step 102, the experimental shale adsorption amount parameters are as follows: 10 mg / g.

[0046] In step 103, by using the test results of step 101 and step 102, a micro-pore flow model considering Darcy flow + non-Darcy flow + boundary layer thickness is applied to calculate the flow value of the shale oil in the shale pores of different sizes with the driving pressure difference, and the micro-pore flow model formula used is as follows:

[0047] ​

[0048] In the formula: mu - fluid viscosity; Q - microtubule flow; H - the influence radius of adsorption force; R - pore radius; delta - boundary layer thickness; f max - the maximum adsorption force; Delta P - pressure difference.

[0049] In step 104, the nonlinear relationship curve of displacement pressure gradient and flow is drawn by using the calculation results of step 103.

[0050] In step 105, the nonlinear characteristic parameters of shale oil flowing in different pores of shale are determined by using the nonlinear relationship curve of displacement pressure gradient and flow drawn in step 104, mainly including the starting pressure gradient 0.04 MP / m (pore radius 2um), the minimum flow radius 0.254um when the pressure gradient is 5 MPa.

[0051] Finally, it should be noted that: the above only for the preferred embodiments of the application, and not for the purpose of limiting the application, although the application has been described in detail with reference to the foregoing examples, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

[0052] In addition to the technical features described in the specification, they are known to those skilled in the art.

Claims

1. A method for characterizing the nonlinear flow characteristics of microscale pores in shale oil, characterized in that, The characterization methods for the microscale pore nonlinear flow characteristics of shale oil include: Step 1: Measure the distribution of micropore structure in shale cores; Step 2: Measure the adsorption capacity of shale cores for shale oil fluids; Step 3: Using a microtube flow model that considers Darcy flow, non-Darcy flow, and boundary layer thickness, calculate the flow rate of shale oil in shale pores of different sizes as a function of driving pressure differential. Step 4: Use the calculation results to plot the nonlinear relationship curve between the displacement pressure gradient and the flow rate; Step 5: Determine the nonlinear characteristic parameters of shale oil flow in different pores of mudstone and shale based on the nonlinear relationship curve between displacement pressure gradient and flow rate. In step 1, the distribution of micropore structure in the mudstone and shale core is measured, including the size and number of micropores; In step 3, using the test results from steps 1 and 2, a micropipe flow model considering Darcy flow + non-Darcy flow + boundary layer thickness is applied to calculate the flow rate of shale oil in shale pores of different sizes as a function of driving pressure differential. In step 3, the microtube flow model formula used is: Where: μ—fluid viscosity; Q—microtube flow rate; H—radius of influence of adsorption force; R—pore radius; δ—boundary layer thickness; f max —Maximum adsorption force; ΔP —Pressure difference.

2. The method for characterizing the nonlinear flow characteristics of microscale pores in shale oil according to claim 1, characterized in that, In step 2, the adsorption capacity of shale cores for shale oil fluid and the amount of shale oil adsorbed by the shale are measured.

3. The method for characterizing the nonlinear flow characteristics of microscale pores in shale oil according to claim 1, characterized in that, In step 4, the nonlinear relationship curve between the displacement pressure gradient and the flow rate is plotted using the calculation results from step 3.

4. The method for characterizing the nonlinear flow characteristics of microscale pores in shale oil according to claim 1, characterized in that, In step 5, the nonlinear relationship curve between displacement pressure gradient and flow rate plotted in step 4 is used to determine the nonlinear characteristic parameters of shale oil flow in different pores of mudstone and shale.

5. The method for characterizing the nonlinear flow characteristics of microscale pores in shale oil according to claim 1, characterized in that, In step 5, the nonlinear characteristic parameters of shale oil flow in different pores of mudstone and shale are determined, including the initiation pressure gradient, boundary layer thickness, and minimum flow radius.

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