Method for evaluating contribution of each component to resistivity of shale oil reservoir at high temperature and high pressure

Abstract

A method for evaluating contribution of each component to shale oil reservoir resistivity at high temperature and high pressure is applied to the field of oil exploration and development. The method comprises the following steps: (1) analyzing the volume percentage of each clay mineral, the pore water content and the mineralization degree of the shale oil reservoir pressure-maintaining closed core; (2) when the fluid pressure is greater than 23MPa, measuring the resistivity of the pressure-maintaining closed rock core at each temperature point; (3) carrying out water balance treatment on pure clay minerals, namely kaolinite, montmorillonite, illite and chlorite, and measuring the resistivity at each temperature point when the fluid pressure is greater than 23MPa; (4) when the fluid pressure is greater than 23MPa, measuring the resistivity of each temperature point of the solution consistent with the mineralization degree of the pore water; and (5) constructing a resistivity evaluation model, and evaluating the contribution of each component to the resistivity of the shale oil reservoir under the condition of high temperature pressure.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of oil exploration and development, and relates to a method for evaluating the contribution of various components to the resistivity of a shale oil reservoir under high temperature and high pressure. BACKGROUND

[0002] Although the shale oil resource potential in China is huge, the effect of shale oil exploitation is not ideal. Since most shale oil resources have problems such as high viscosity and poor mobility, the shale oil horizontal well volume fracturing investment is high, the output is low, and the single well production declines rapidly. Many scholars at home and abroad have proposed in-situ heating modification and in-situ heating conversion technologies for shale oil exploitation. That is, the underground shale oil reservoir is heated in-situ (without collecting the shale oil reservoir to the ground), wherein the in-situ heating modification temperature is relatively low, basically no hydrocarbon is generated from kerogen or crude oil is cracked into natural gas, and the main exploitation method is in-situ heating modification by heating to reduce the viscosity of shale oil and increase the mobility; the in-situ heating conversion temperature is relatively high, and the main exploitation method is in-situ heating conversion by allowing kerogen in immature-low mature source rock to generate hydrocarbon.

[0003] The in-situ heating methods for shale oil exploitation mainly include heat conduction (electric heating rod, steam circulation pipe, dielectric heating, etc.), convection + conduction (injection of steam, hot organic gas and CO2) and radiation + conduction (electric field, electromagnetic wave and microwave, etc.). Since the shale oil reservoir has low permeability, it is difficult and costly to inject hot fluid into the shale oil reservoir. Many scholars at home and abroad have carried out related researches on low-frequency electric field (belonging to dielectric heating), microwave and high-frequency electromagnetic field heating of heavy oil, oil sand, shale oil and shale gas and other unconventional oil and gas reservoirs. In the electric heating method, the electric heating rod and fuel cell rod heating need to specially drill a series of wellbores to place the heating rod into the shale oil reservoir, and there are problems such as uneven heating of the shale oil reservoir, slow overall heating speed and large heat energy loss. The fluid heating method for exploiting shale oil needs to carry out reservoir fracturing modification, or continuously inject hot fluid into the shale oil reservoir at high pressure to form a fracturing channel, or specially drill and install a closed pipeline, which will inevitably increase the cost and operability. The radiation heating method for exploiting shale oil also needs to specially drill a wellbore for placing the radiation equipment, and the microwave heating reservoir depth is difficult to meet the requirements of in-situ shale oil exploitation. In addition, how to greatly improve the power of the microwave instrument and miniaturize the instrument is also a difficult gap to overcome. The combustion heating method has problems of oxidant breakthrough and controllability, and this method has high cost, poor controllability and low recovery rate. Since the shale oil reservoirs in China mostly belong to terrestrial strata, the content of clay minerals is relatively high, and the electrical conductivity is relatively good. Therefore, the low-frequency electric field heating modification technology is used to exploit shale oil without the need for fracturing and injection of conductive medium. The electric current flows through the reservoir area to generate heat by itself through the Joule heating effect, and there is no problem of limited heating depth.

[0004] Low frequency electric field heating shale oil reservoirs as conductive medium and heating resistance, and with the adjacent two wells of the purpose of the layer section metal casing connected ground power supply equipment as electrode, using the joule heating effect of low frequency electric field current through the reservoir to heat the shale oil reservoir. Low frequency electric field heating shale oil reservoirs is to add power voltage directly to the reservoir, when the current flows through the shale oil reservoir itself is heated, which belongs to internal heating, high thermal efficiency, low power stability requirements. Using low frequency electric field heating to improve the exploitation of shale oil needs to consume a large amount of electric energy, our country contains oil and gas basin contains a large amount of shale oil resources, but also has rich wind energy and solar energy resources. In addition, the associated natural gas obtained by heating the reservoir to exploit shale oil can be directly used for power generation. These provide important power resources for the use of low frequency electric field heating shale oil reservoirs. Low frequency electric field heating shale oil reservoirs has very low requirements for power stability, and the development of low frequency electric field heating shale oil reservoirs can make full use of unstable wind energy, solar energy and low power grid energy. Wind and solar power generation is used to heat shale oil reservoirs and exploit shale oil, which can efficiently use the wind and solar energy in oil and gas basins, especially the wind and solar energy in western regions, avoid 'abandoning wind and electricity', realize resource optimization and efficient use, increase China's crude oil production, maintain China's energy security and promote national economic development.

[0005] The components that play a conductive role in the high-temperature shale oil reservoir loaded with electric field are mainly clay minerals and pore water, although the metal-containing minerals such as pyrite have good conductivity, but their content is low and dispersedly distributed. One of the core problems of in-situ heating and upgrading to exploit shale oil is to quantitatively evaluate the conductive mechanism of the shale oil reservoir loaded with electric field. By comparing and analyzing the temperature variation characteristics of the resistivity of typical reservoir samples, the quantitative evaluation of the contribution of different types of clay minerals and pore water with different salinities to the resistivity of the shale oil reservoir under different temperature conditions is carried out, the resistivity evaluation model of the shale oil reservoir under different temperature conditions is constructed, and the conductive mechanism of the shale oil reservoir loaded with electric field is analyzed.

[0006] Therefore, the present application provides a method for evaluating the contribution of each component to the resistivity of the shale oil reservoir under high temperature and high pressure. The method can quantitatively evaluate the contribution characteristics of various clay minerals and pore water to the resistivity of the shale oil reservoir under different temperatures, provide important technical parameters for in-situ heating and upgrading to exploit shale oil, and provide support for breaking through the technical bottleneck of shale oil exploitation. SUMMARY

[0007] The present application aims to: a method for evaluating the contribution of each component to the resistivity of shale oil reservoirs under high temperature and high pressure, realizing quantitative evaluation of the contribution characteristics of various clay minerals and pore water to the resistivity of shale oil reservoirs at different temperatures, providing key data for studying the conduction mechanism of shale oil reservoirs, providing important technical parameters for in-situ heating modification and shale oil mining, and providing support for breaking through the technical bottleneck of shale oil mining.

[0008] The technical scheme adopted by the present application is: a method for evaluating the contribution of each component to the resistivity of shale oil reservoirs under high temperature and high pressure, characterized by: Step 1: Select a shale oil reservoir pressure-maintaining sealed core sample to be evaluated, analyze the pore water volume percentage and salinity of the reservoir core sample in real-time thawing conditions, then determine the volume percentage of various clay minerals of the reservoir core sample through X-ray diffraction whole rock analysis and X-ray diffraction clay phase content analysis combined with the density of the sample and each component; Step 2: Put the shale oil reservoir pressure-maintaining sealed core parallel sample in liquid nitrogen frozen state into a device that can measure the resistivity of the reservoir sample under high temperature and high pressure conditions, measure the resistivity of the pressure-maintaining sealed core sample at each temperature point under the condition that the fluid pressure is greater than 23 MPa and the temperature range is 25-400℃; Step 3: Perform water balance treatment on pure clay minerals kaolinite, montmorillonite, illite and chlorite respectively, then put them into the resistivity measurement device respectively, fill nitrogen to ensure that the fluid pressure is greater than 23 MPa, and measure the resistivity of these pure clay minerals at each temperature point in step 2 under the condition that the temperature range is 25-400℃; Step 4: Measure the resistivity of the solution consistent with the salinity of the reservoir sample at each temperature point in step 2 under the condition that the fluid pressure is greater than 23 MPa and the temperature range is 25-400℃; Step 5: Based on the resistivity measurement results under the above high temperature and high pressure conditions, construct the objective function f(a,b) of the evaluation model of the resistivity of each component of the shale oil reservoir sample at different temperatures, when the value of the objective function is the smallest, obtain the resistivity of each component of the reservoir and the contact number a, the resistance series number b and the correction coefficient c, and the model calculation obtains the contribution value of each component to the resistivity of the shale oil reservoir at different temperatures ’ i,j The resistivity of the shale oil reservoir sample at different temperatures can be calculated ’ j ,

[0009]

[0010]

[0011] Where a, b, and c are the parallel resistance coefficient, series resistance coefficient, and correction coefficient of each component of the reservoir, respectively, V i This represents the volume percentage of each component in a shale oil reservoir, including various clay minerals and pore water, ρ. i,j The resistivity ρ of component i was experimentally measured at temperature j. j The resistivity ρ of the reservoir sample was experimentally measured at temperature j. ’ i,j The resistivity ρ of component i at temperature j is calculated by the model. ’ j The resistivity of the reservoir sample is calculated by the model at temperature j, where i = 1, 2, ..., m, and j = 1, 2, ..., n are the numbers of various clay minerals and pore water in the shale oil reservoir sample, respectively. The volume percentage is expressed in %, and the resistivity is expressed in Ω∙m.

[0012] The beneficial effects of this invention are as follows: This invention provides a method for evaluating the contribution of various components to the resistivity of shale oil reservoirs under high temperature and high pressure. This method is easy to operate and implement. This method can quantitatively evaluate the contribution characteristics of various clay minerals and pore water to the resistivity of shale oil reservoirs at different temperatures, providing key data for studying the conductivity mechanism of shale oil reservoirs, providing important technical parameters for in-situ heating and upgrading of shale oil, and supporting the breakthrough of technological bottlenecks in shale oil extraction. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the method for evaluating the contribution of each component to the resistivity of shale oil reservoirs under high temperature and high pressure.

[0014] Figure 2 These are the measured values ​​of resistivity of montmorillonite, chlorite, illite, pore water, and core at different temperatures.

[0015] Figure 3 The model obtains calculated values ​​of the contributions of montmorillonite, chlorite, illite, and pore water to the resistivity of shale oil reservoirs at different temperatures, as well as calculated values ​​of the resistivity of reservoir core samples. Detailed Implementation

[0016] Example 1: As Figure 1 The method for evaluating the contribution of each component to the resistivity of shale oil reservoirs under high temperature and high pressure includes the following steps: Step 1: Select pressurized, sealed core samples from the shale oil reservoir to be evaluated. Under real-time thawing conditions, the pore water volume percentage of the reservoir core samples was analyzed to be 1.50%, and the salinity was 10000 mg / L. Then, through X-ray diffraction whole-rock analysis and X-ray diffraction clay relative content analysis, the mass percentages of montmorillonite, chlorite, and illite in the core samples were found to be 16.55%, 10.64%, and 22.14%, respectively. Combined with the core sample, the densities of montmorillonite, chlorite, and illite were 2.55 g / cm³. 3 2.35g / cm 3 3.60g / cm 3 and 2.75g / cm 3 The volume percentages of montmorillonite, chlorite, and illite in the reservoir core samples were determined to be 17.96%, 7.54%, and 20.53%, respectively.

[0017] Step 2: Place the parallel core samples from the shale oil reservoir in Step 1, which are frozen in liquid nitrogen, into a device capable of measuring the resistivity of reservoir samples under high temperature and high pressure conditions. Under fluid pressure of 25 MPa and temperatures of 25℃, 50℃, 75℃, 100℃, 125℃, 150℃, 175℃, 200℃, 225℃, 250℃, 275℃, and 300℃, the resistivity of the pressurized sealed core samples at these temperature points is measured to be 40.00 Ω∙m, 35.20 Ω∙m, 30.80 Ω∙m, 26.80 Ω∙m, 23.20 Ω∙m, 20.00 Ω∙m, 17.20 Ω∙m, 14.80 Ω∙m, 12.80 Ω∙m, 11.20 Ω∙m, 10.00 Ω∙m, and 9.20 Ω∙m. The resistivity measurement results of the pressurized sealed core samples at these temperature points are shown in the figure. Figure 2 .

[0018] Step 3: The pure clay minerals montmorillonite, chlorite, and illite were subjected to water balance treatment respectively. Then, they were placed separately in a resistivity measuring device, filled with nitrogen to maintain a fluid pressure of 25 MPa, and the resistivity of montmorillonite was measured at temperatures of 25℃, 50℃, 75℃, 100℃, 125℃, 150℃, 175℃, 200℃, 225℃, 250℃, 275℃, and 300℃, respectively: 20.00 Ω∙m, 16.00 Ω∙m, 12.50 Ω∙m, 9.50 Ω∙m, 7.00 Ω∙m, 5.00 Ω∙m, 3.50 Ω∙m, 2.50 Ω∙m, 2.00 Ω∙m, 1.75 Ω∙m, and 1.63 Ω∙m. The resistivity of chlorite was measured to be 1.53 Ω∙m; the resistivity of chlorite was measured to be 30.00 Ω∙m, 24.00 Ω∙m, 18.75 Ω∙m, 14.25 Ω∙m, 10.50 Ω∙m, 7.50 Ω∙m, 5.25 Ω∙m, 3.75 Ω∙m, 3.00 Ω∙m, 2.63 Ω∙m, 2.44 Ω∙m, and 2.29 Ω∙m; the resistivity of illite was measured to be 25.00 Ω∙m, 20.00 Ω∙m, 15.63 Ω∙m, 11.88 Ω∙m, 8.75 Ω∙m, 6.25 Ω∙m, 4.38 Ω∙m, 3.13 Ω∙m, 2.50 Ω∙m, 2.19 Ω∙m, 2.03 Ω∙m, and 1.91 Ω∙m. The resistivity measurement results of pure clay minerals montmorillonite, chlorite, and illite are shown in the figure. Figure 2 .

[0019] Step 4: Under fluid pressure of 25 MPa and temperatures of 25℃, 50℃, 75℃, 100℃, 125℃, 150℃, 175℃, 200℃, 225℃, 250℃, 275℃, and 300℃, the resistivity of solutions with the same pore water salinity as the reservoir samples was measured to be 5.00 Ω∙m, 4.00 Ω∙m, 3.13 Ω∙m, 2.38 Ω∙m, 1.75 Ω∙m, 1.25 Ω∙m, 0.88 Ω∙m, 0.63 Ω∙m, 0.50 Ω∙m, 0.44 Ω∙m, 0.41 Ω∙m, and 0.38 Ω∙m, respectively. The resistivity measurement results of solutions with the same pore water salinity as the reservoir samples are shown in [reference needed]. Figure 2 .

[0020] Step 5: Based on the resistivity measurement results of pressurized sealed cores, various pure minerals, and solutions under the above high temperature and high pressure conditions, construct the objective function f(a,b) of the shale oil reservoir sample resistivity evaluation model for each component at different temperatures. When the value of the objective function is minimized, the resistance parallel coefficient a of each reservoir component is obtained as -31.872, the resistance series coefficient b is 2.121, and the correction coefficient c is 17.256. The model calculates the contribution value ρ of each component to the shale oil reservoir resistivity at different temperatures. ’ i,jAnd the resistivity ρ of shale oil reservoir samples at different temperatures was calculated. ’ j The model yielded calculated values ​​of the contributions of montmorillonite, chlorite, illite, and pore water to the resistivity of shale oil reservoirs at different temperatures, as shown in the table below. Figure 3 The model obtained the calculated resistivity values ​​of reservoir core samples at different temperatures, as shown in the figure. Figure 3 .

[0021]

[0022]

[0023] Where a, b, and c are the parallel resistance coefficient, series resistance coefficient, and correction coefficient of each component of the reservoir, respectively, V i This represents the volume percentage of each component in a shale oil reservoir, including various clay minerals and pore water, ρ. i,j The resistivity ρ of component i was experimentally measured at temperature j. j The resistivity ρ of the reservoir sample was experimentally measured at temperature j. ’ i,j The resistivity ρ of component i at temperature j is calculated by the model. ’ j The resistivity of the reservoir sample is calculated by the model at temperature j, where i = 1, 2, ..., m, and j = 1, 2, ..., n are the numbers of various clay minerals and pore water in the shale oil reservoir sample, respectively. The volume percentage is expressed in %, and the resistivity is expressed in Ω∙m.

Claims

1. A method for evaluating the contribution of each component to the resistivity of shale oil reservoirs under high temperature and high pressure, characterized in that: Step 1: Select pressurized and sealed core samples from the shale oil reservoir to be evaluated. Analyze the pore water volume percentage and salinity of the reservoir core samples under real-time thawing conditions. Then, determine the volume percentage of various clay minerals in the reservoir core samples by X-ray whole-rock analysis and X-ray clay relative content analysis, combined with the sample and the density of each component. Step 2: Place the parallel sample of the shale oil reservoir pressure-sealed core from Step 1, which is frozen in liquid nitrogen, into a device that can measure the resistivity of reservoir samples under high temperature and high pressure conditions. Under the conditions of fluid pressure greater than 23 MPa and temperature range of 25-400℃, measure the resistivity of the pressure-sealed core sample at each temperature point. Step 3: Perform water balance treatment on pure clay minerals kaolinite, montmorillonite, illite and chlorite respectively, and then put them into resistivity measuring devices. Fill with nitrogen to ensure that the fluid pressure is greater than 23MPa. Under the condition of temperature range of 25-400℃, measure the resistivity of these pure clay minerals at each temperature point in step 2. Step 4: Under conditions where the fluid pressure is greater than 23 MPa and the temperature range is 25-400℃, measure the resistivity of the solution with the same pore water salinity as the reservoir sample at each temperature point in Step 2. Step 5: Based on the resistivity measurement results under the above high temperature and high pressure conditions, construct the objective function f(a,b) of the evaluation model of the resistivity of each component in the shale oil reservoir sample at different temperatures. When the value of the objective function is minimized, obtain the resistance parallel coefficient a, the resistance series coefficient b, and the correction coefficient c of each component in the reservoir. The model calculates the contribution value ρ' of each component to the resistivity of the shale oil reservoir at different temperatures. i,j It is possible to calculate the resistivity ρ' of shale oil reservoir samples at different temperatures. j , ρ' i,j =aV i / ρ i,j +bV i ρ i,j +c Where a, b, and c are the parallel resistance coefficient, series resistance coefficient, and correction coefficient of each component of the reservoir, respectively, V i This represents the volume percentage of each component in a shale oil reservoir, including various clay minerals and pore water, ρ. i,j The resistivity ρ of component i was experimentally measured at temperature j. j The resistivity ρ' of the reservoir sample was experimentally measured at temperature j. i,j The resistivity ρ' of component i at temperature j is calculated by the model. j The resistivity of the reservoir sample is calculated by the model at temperature j, where i = 1, 2, ..., m, and j = 1, 2, ..., n are the numbers of various clay minerals and pore water in the shale oil reservoir sample, respectively. The volume percentage is expressed in %, and the resistivity is expressed in Ω·m.

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