A method for evaluating the content of adsorbed oil and free oil of a tight reservoir at various temperatures

Abstract

The application relates to a method for evaluating the content of adsorbed oil and free oil of a compact reservoir at various temperatures, and is applied to the field of oil exploration and development. The method steps are as follows: ① X-diffraction whole rock analysis and clay phase relative quantity analysis are carried out on the reservoir sample to determine the content of each mineral; ② a low-temperature nitrogen adsorption experiment is carried out on the reservoir sample to obtain the contribution of each pore size range of the reservoir sample to the specific surface area, and the contribution of each mineral to the specific surface area in different pore size ranges is determined according to the content of each mineral; ③ pure mineral powder samples with different particle diameters are soaked in n-dodecane, then dried at different temperatures, and nuclear magnetic resonance T2 spectrum measurement is carried out to determine the thickness of the oil film adsorbed on the surface of each pure mineral at different temperatures; ④ the content of the adsorbed oil of the reservoir sample at various temperatures is determined in combination with the results of ② and ③; ⑤ the reservoir porosity is determined according to the reservoir burial depth and in combination with the overburden porosity, and then the content of the free oil of the reservoir is determined in combination with the content of the adsorbed oil and the pore water of the reservoir.

Description

Technical Field

[0001] This invention relates to the field of petroleum exploration and development technology, and to a method for evaluating the content of adsorbed oil and free oil in tight reservoirs at various temperatures. Background Technology

[0002] Unconventional energy sources, including coalbed methane, tight oil, tight gas, shale oil, and shale gas, are receiving increasing attention.

[0003] International exploration practices have also confirmed the enormous potential of tight oil resources. For this reason, many continental oilfields in my country, especially older oilfields in the east, are currently accelerating research, evaluation, and exploration work on tight oil.

[0004] Tight oil in reservoirs mainly exists in the form of adsorbed oil and free oil. The free oil content represents the maximum recoverable amount under the reservoir's temperature and pressure conditions, and is also the maximum recoverable oil quantity that can be utilized under current development technologies. Clarifying the adsorbed and free oil contents in tight oil reservoirs is of great guiding significance for the selection of sweet spots, resource assessment, and development planning.

[0005] Currently, methods for evaluating the adsorbed and free oil content in tight oil reservoirs include empirical statistical methods, nuclear magnetic resonance (NMR) methods, swelling methods, multi-step pyrolysis methods, molecular simulation methods, capillary condensation theory methods, and displacement methods. These methods each have their own specific applications and advantages / disadvantages in evaluating the adsorbed and free oil content in tight oil reservoirs. For example, empirical statistical methods require a large amount of organic geochemical characteristic data for the target stratigraphic section in the study area to roughly determine the upper limit of saturated adsorption, resulting in relatively coarse evaluation results. NMR methods use one-dimensional and two-dimensional spectra to qualitatively and semi-quantitatively evaluate the adsorbed and free oil content, but quantitative aspects still have certain limitations. Swelling methods mainly evaluate the adsorption of components such as organic matter and clay on crude oil, leading to a relatively high assessment of adsorbed oil content. Multi-step pyrolysis methods quantitatively analyze the content of light, medium, medium-heavy, and heavy oil through segmented pyrolysis, thus roughly evaluating the adsorbed and free oil content, but classifying adsorbed and free oil based on molecular weight has certain shortcomings. Molecular simulation methods use molecular simulation... The first method determines fluid density, identifies free and adsorbed fluids, and then evaluates the content of adsorbed and free oil; however, the evaluation results lack experimental verification. The capillary condensation theory method improves the evaluation model of adsorption and condensation (free) under experimental conditions to a model under geological conditions based on the conversion relationship between porosity, pore volume, and specific surface area, and then evaluates the content of adsorbed and free oil; however, the evaluation results also lack experimental verification. The displacement method uses a displacement-NMR coupled online detection device to physically simulate the process of oil and gas being displaced by heavy water (or nitrogen) and detects the changes in oil signals during the charging process, and then evaluates the content of adsorbed and free oil. However, it is easy to overestimate the content of adsorbed oil and underestimate the content of free oil.

[0006] Therefore, this invention proposes a method for evaluating the adsorbed and free oil content in tight oil reservoirs at various temperatures. This method measures the thickness of the adsorbed oil film on the surface of pure minerals with different particle diameters at various temperatures, approximating it to the thickness of the adsorbed oil film on the inner surface of pores of the same pore size contributed by the pure minerals. This allows for a quantitative evaluation of the adsorbed and free oil content in tight oil reservoirs under different temperature conditions, providing important technical parameters for the selection of sweet spots, resource assessment, and development plan formulation in tight oil reservoirs. Summary of the Invention

[0007] The purpose of this invention is to provide a method for evaluating the adsorbed and free oil content in tight oil reservoirs at various temperatures. This method measures the thickness of the adsorbed oil film on the surface of pure minerals with different particle diameters at various temperatures, approximating it to the thickness of the adsorbed oil film on the inner surface of pores with the same pore size contributed by the pure minerals. This allows for a quantitative evaluation of the adsorbed and free oil content in tight oil reservoirs under different temperature conditions, providing important technical parameters for the selection of sweet spots, resource quantity assessment, and development plan formulation in tight oil reservoirs.

[0008] The technical solution adopted in this invention is: a method for evaluating the content of adsorbed oil and free oil in tight reservoirs at various temperatures, characterized in that: Step 1: Perform X-ray diffraction whole-rock analysis and X-ray diffraction clay relative content analysis on the reservoir samples to determine the percentage content of each mineral in the reservoir samples. The unit of mineral content percentage is % (%). Step 2: Conduct low-temperature nitrogen adsorption experiments on the reservoir sample to obtain the specific surface area of ​​pores in different pore size ranges. Combined with the percentage content of each mineral obtained in Step 1, determine the specific surface area of ​​pores in different pore size ranges contributed by each mineral in the reservoir sample according to the following formula. S x, j = M j S x In the formula, S x, j M is the specific surface area contributed by the pores with diameter x of mineral number j in the reservoir sample. j S is the percentage content of mineral number j in the reservoir sample. x It is the specific surface area contributed by pores with diameter x in the reservoir sample. The unit of specific surface area is m². 2 / g, the unit of mineral content percentage is %, x=1,2,...,m, is the number of the pore diameter range obtained by the low temperature nitrogen adsorption experiment, j=1,2,...,n, is the number of the mineral species of the reservoir sample in the X-ray diffraction whole rock analysis and X-ray diffraction clay relative quantity analysis. Step 3: Powder samples of quartz, plagioclase, potassium feldspar, calcite, dolomite, illite, chlorite, and montmorillonite with particle diameters of 60µm, 30µm, 15µm, 7.5µm, 5µm, and 3µm, respectively, were dried at 150℃ for 4 hours and their mass was measured. They were then immersed in an organic solvent and subsequently dried at temperatures of 50℃, 70℃, 90℃, and 110℃. Nuclear magnetic resonance (NMR) T2 spectra were measured for each pure mineral powder sample with different particle diameters every 4 hours of drying until no NMR response signal was observed at the relaxation time corresponding to the large pore size range. The mass of the pure mineral powder sample with each particle diameter was measured, and the thickness of the adsorbed oil film on the surface of each pure mineral at different temperatures was determined using the following formula. h i, j, k = 10 3 (m i, j, k - m i, j ) / ρ k, y / (6m i, j / ρ i, j / D i, j ) In the formula, h i, j, k The thickness of the oil film adsorbed on the surface of the pure mineral (particle number i) at temperature k is given by the particle diameter (m). i, j, k The mass of a pure mineral with particle diameter i and particle number j at temperature k, corresponding to the relaxation time within the large pore size range, is when there is no NMR response signal. i, j ρ is the mass of a pure mineral powder sample (particle diameter i, number j) after drying at 150°C for 4 hours. k, y ρ is the density of the organic solvent at temperature k. i, j D is the diameter of particle i and the true density of the pure mineral j. i, j Here, i represents the particle diameter of the pure mineral powder sample numbered i, j represents the particle diameter of the pure mineral powder sample numbered j, i = 1, 2, 3, 4, 5, 6, and j = 1, 2, ..., n, representing the mineral number, k = 1, 2, 3, 4, representing the temperature number, the unit for adsorbed oil film thickness is nm, the unit for mass is g, and the unit for density is g / cm³. 3 The unit of true density is g / cm³. 3 The unit for particle diameter is µm; Step 4: Using the oil film thicknesses on the surfaces of pure minerals with different particle diameters obtained in Step 3, approximate the oil film thickness on the surfaces of pure minerals with different particle diameters to the oil film thickness on the inner surface of pores of the same pore size contributed by the pure minerals. Fit this to obtain the oil film thickness at different temperatures based on the specific surface area within pores of different pore sizes formed by each mineral. Combined with the specific surface area of ​​pores of different pore sizes contributed by each mineral in the reservoir sample obtained in Step 2, determine the adsorbed oil content of the reservoir sample at each temperature using the following formula.

[0009] In the formula, Q k,a It is the content of adsorbed oil in the reservoir sample at temperature k, ρ k, y h is the density of the organic solvent at temperature k. x, j, k S is the thickness of the oil film adsorbed on the inner surface of the pores of a pure mineral with pore size x and number j at temperature k. x, j This represents the specific surface area contributed by mineral j (numbered j) and pore size x (numbered x), where x = 1, 2, ..., m, is the pore diameter range analyzed in the low-temperature nitrogen adsorption experiment, j = 1, 2, ..., n is the mineral number, and k = 1, 2, 3, 4 is the temperature number. The unit for adsorbed oil content is mg / g, and the unit for density is g / cm³. 3 The unit for adsorbed oil film thickness is nm, and the unit for specific surface area is m². 2 / g; Step 5: Based on the reservoir depth, combined with the results of pore water content, free gas content, and overburden porosity, obtain the reservoir porosity. Combined with the adsorbed oil content obtained in Step 4, determine the free oil content of the reservoir sample at various temperatures.

[0010] In the formula, Q k,f It is the free oil content, ρ, of the reservoir sample at temperature k. k, y ρ is the density of the organic solvent at temperature k, Φ is the porosity of the reservoir sample obtained using overburden porosity analysis, ρ is the density of the reservoir sample, and Q is the density of the reservoir sample. k, a Q k, w and Q k, g These represent the adsorbed oil content, pore water content, and free gas content of the reservoir sample at temperature k, respectively. k, w and ρ k, gThese are the densities of pore water and free gas at temperature k, respectively. x = 1, 2, ..., m is the pore diameter range analyzed in the low-temperature nitrogen adsorption experiment, and k = 1, 2, 3, 4 is the temperature number. The units for adsorbed oil content, free oil content, pore water content, and free gas content are all mg / g, and the unit for density is g / cm³. 3 Porosity is measured in percent.

[0011] The beneficial effects of this invention are as follows: This invention proposes a method for evaluating the adsorbed oil and free oil content in tight oil reservoirs at various temperatures. This method can quantitatively evaluate the adsorbed oil and free oil content in tight oil reservoirs under different temperature conditions, providing important technical parameters for the selection of sweet spots, resource quantity assessment, and development plan formulation in tight oil reservoirs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a method for evaluating the content of adsorbed oil and free oil in tight reservoirs at various temperatures, according to the present invention.

[0013] Figure 2 It represents the characteristics of the thickness of the adsorbed oil film on the surface of pure mineral particles with different particle diameters under various temperature conditions. Detailed Implementation

[0014] Example 1: As Figure 1 The method for evaluating the content of adsorbed oil and free oil in tight reservoirs at various temperatures includes the following steps: Step 1: Perform X-ray diffraction whole-rock analysis and X-ray diffraction clay relative content analysis on the reservoir samples to determine the percentage content of each mineral in the reservoir samples. The unit of mineral percentage content is %. The percentage content of each mineral in the reservoir samples is shown in Table 1.

[0015] Table 1

[0016] Step 2: Conduct low-temperature nitrogen adsorption experiments on the reservoir samples to obtain the specific surface area of ​​pores in different pore size ranges. Combined with the percentage content of each mineral obtained in Step 1, determine the specific surface area of ​​pores in different pore size ranges contributed by each mineral in the reservoir samples according to the following formula. The specific surface areas of pores in different pore size ranges contributed by each mineral in the reservoir samples are shown in Table 2.

[0017] S x, j = M j S x In the formula, S x, j M is the specific surface area contributed by the pores with diameter x of mineral number j in the reservoir sample. j S is the percentage content of mineral number j in the reservoir sample.x It is the specific surface area contributed by pores with diameter x in the reservoir sample. The unit of specific surface area is m². 2 / g, the unit for mineral content percentage is %, x=1,2,…,m, is the number of the pore diameter range obtained by the low temperature nitrogen adsorption experiment, j=1,2,…,n, is the number of the mineral species of the reservoir sample in the X-ray diffraction whole rock analysis and X-ray diffraction clay relative quantity analysis.

[0018] Table 2

[0019] Step 3: Powder samples of quartz, plagioclase, potassium feldspar, calcite, dolomite, illite, chlorite, and montmorillonite with particle diameters of 60µm, 30µm, 15µm, 7.5µm, 5µm, and 3µm, respectively, were dried at 150℃ for 4 hours and their mass was measured. They were then immersed in an organic solvent and subsequently dried at temperatures of 50℃, 70℃, 90℃, and 110℃. Nuclear magnetic resonance (NMR) T2 spectra were measured for each pure mineral powder sample with different particle diameters every 4 hours of drying until no NMR response signal was observed at the relaxation time corresponding to the large pore size range. The mass of the pure mineral powder sample with different particle diameters was measured, and the thickness of the adsorbed oil film on the surface of each pure mineral at different temperatures was determined according to the following formula. The thickness of the adsorbed oil film on the surface of each pure mineral at different particle diameters at different temperatures is shown in Table 3.

[0020] h i, j, k = 10 -3 (m i, j, k - m i, j ) / ρ k, y / (6m i, j / ρ i, j / D i, j ) In the formula, h i, j, k The thickness of the oil film adsorbed on the surface of the pure mineral (particle number i) at temperature k is given by the particle diameter (m). i, j, k The particle with diameter i and the pure mineral with diameter j are mass at temperature k when there is no NMR response signal in the large pore range, m. i, j ρ is the mass of a pure mineral powder sample (particle diameter i, number j) after drying at 150°C for 4 hours. k, y ρ is the density of the organic solvent at temperature k. i, j D is the diameter of particle i and the true density of the pure mineral j. i, jHere, i represents the particle diameter of the pure mineral powder sample numbered i, j represents the particle diameter of the pure mineral powder sample numbered j, i = 1, 2, 3, 4, 5, 6, and j = 1, 2, ..., n, representing the mineral number, k = 1, 2, 3, 4, representing the temperature number, the unit for adsorbed oil film thickness is nm, the unit for mass is g, and the unit for density is g / cm³. 3 The unit of true density is g / cm³. 3 The unit for particle diameter is µm.

[0021] Table 3

[0022] Step 4: Using the oil film thicknesses on the surfaces of pure minerals with different particle diameters obtained in Step 3, approximate the oil film thickness on the surfaces of pure minerals with different particle diameters to the oil film thickness on the inner surface of pores of the same pore size contributed by the pure minerals. Fit the results to obtain the oil film thickness at different temperatures due to the specific surface area within pores of different pore sizes formed by each mineral. Combine this with the specific surface area of ​​pores of different pore sizes contributed by each mineral in the reservoir sample obtained in Step 2, and determine the adsorbed oil content of the reservoir sample at each temperature according to the following formula. The oil film thickness at different temperatures due to the specific surface area within pores of different pore sizes formed by each mineral is shown in the figure. Figure 2 The adsorbed oil content of reservoir samples at different temperatures is shown in Table 4.

[0023]

[0024] In the formula, Q k, a It is the content of adsorbed oil in the reservoir sample at temperature k, ρ k, y This is the density of the organic solvent at temperature k. In this example, the organic solvent is n-dodecane, and the density of n-dodecane at temperatures of 50℃, 70℃, 90℃, and 110℃ is 0.719 g / cm³. 3 0.703 g / cm 3 0.691 g / cm 3 and 0.681 g / cm 3 h x, j, k S is the thickness of the oil film adsorbed on the inner surface of the pores of a pure mineral with pore size x and number j at temperature k. x, j This represents the specific surface area contributed by mineral j (numbered j) and pore size x (numbered x), where x = 1, 2, ..., m, is the pore diameter range analyzed in the low-temperature nitrogen adsorption experiment, j = 1, 2, ..., n is the mineral number, and k = 1, 2, 3, 4 is the temperature number. The unit for adsorbed oil content is mg / g, and the unit for density is g / cm³. 3 The unit for adsorbed oil film thickness is nm, and the unit for specific surface area is m².2 / g.

[0025] Table 4

[0026] Step 5: Based on the reservoir depth, combined with the results of pore water content, free gas content, and overburden porosity, the reservoir porosity is obtained, along with the adsorbed oil content obtained in Step 4. The free oil content of the reservoir sample at each temperature is then determined. The results of pore water content, adsorbed oil content, and free oil content of the reservoir sample at each temperature are shown in Table 5.

[0027]

[0028] In the formula, Q k, f It is the free oil content, ρ, of the reservoir sample at temperature k. k, y This is the density of the organic solvent at temperature k. In this example, the organic solvent is n-dodecane, and the density of n-dodecane at temperatures of 50℃, 70℃, 90℃, and 110℃ is 0.719 g / cm³. 3 0.703 g / cm 3 0.691 g / cm 3 and 0.681 g / cm 3 Φ is the porosity of the reservoir sample obtained using overburden porosity-permeability analysis, with a value of 1.67%, and ρ is the density of the reservoir sample, with a value of 2.55 g / cm³. 3 Q k, a Q k, w and Q k, g These represent the adsorbed oil content, pore water content, and free gas content of the reservoir sample at temperature k, respectively. k, w and ρ k, g These are the densities of pore water and free gas at temperature k, respectively, with values ​​of 1.01 g / cm³. 3 and 0.09 g / cm 3 x = 1, 2, ..., m are the pore diameter ranges analyzed in the low-temperature nitrogen adsorption experiment; k = 1, 2, 3, 4 are the temperature numbers; the units for adsorbed oil content, free oil content, pore water content, and free gas content are all mg / g; and the unit for density is g / cm³. 3 Porosity is measured in percent.

[0029] Table 5

Claims

1. A method for evaluating the content of adsorbed oil and free oil in tight reservoirs at various temperatures, characterized in that: Step 1: Perform X-ray diffraction whole-rock analysis and X-ray diffraction clay relative content analysis on the reservoir samples to determine the percentage content of each mineral in the reservoir samples. The unit of mineral content percentage is % (%). Step 2: Conduct low-temperature nitrogen adsorption experiments on the reservoir sample to obtain the specific surface area of ​​pores in different pore size ranges. Combined with the percentage content of each mineral obtained in Step 1, determine the specific surface area of ​​pores in different pore size ranges contributed by each mineral in the reservoir sample according to the following formula. S x, j = M j S x In the formula, S x, j M is the specific surface area contributed by the pores with diameter x of mineral number j in the reservoir sample. j S is the percentage content of mineral number j in the reservoir sample. x It is the specific surface area contributed by pores with diameter x in the reservoir sample. The unit of specific surface area is m². 2 / g, the unit of mineral content percentage is %, x=1,2,...,m, is the number of the pore diameter range obtained by the low temperature nitrogen adsorption experiment, j=1,2,...,n, is the number of the mineral species of the reservoir sample in the X-ray diffraction whole rock analysis and X-ray diffraction clay relative quantity analysis. Step 3: Powder samples of quartz, plagioclase, potassium feldspar, calcite, dolomite, illite, chlorite, and montmorillonite with particle diameters of 60µm, 30µm, 15µm, 7.5µm, 5µm, and 3µm, respectively, were dried at 150℃ for 4 hours and their mass was measured. They were then immersed in an organic solvent and subsequently dried at temperatures of 50℃, 70℃, 90℃, and 110℃. Nuclear magnetic resonance (NMR) T2 spectra were measured for each pure mineral powder sample with different particle diameters every 4 hours of drying until no NMR response signal was observed at the relaxation time corresponding to the large pore size range. The mass of the pure mineral powder sample with each particle diameter was measured, and the thickness of the adsorbed oil film on the surface of each pure mineral at different temperatures was determined using the following formula. h i, j, k = 10 3 (m) i, j, k - m i, j ) / ρ k, y / (6m i, j / ρ i, j / D i, j ) In the formula, h i, j, k The thickness of the oil film adsorbed on the surface of the pure mineral (particle number i) at temperature k is given by the particle diameter (m). i, j, k The mass of a pure mineral with particle diameter i and particle number j at temperature k, corresponding to the relaxation time within the large pore size range, is when there is no NMR response signal. i, j ρ is the mass of a pure mineral powder sample (particle diameter i, number j) after drying at 150°C for 4 hours. k, y ρ is the density of the organic solvent at temperature k. i, j D is the diameter of particle i and the true density of the pure mineral j. i, j Here, i represents the particle diameter of the pure mineral powder sample numbered i, j represents the particle diameter of the pure mineral powder sample numbered j, i = 1, 2, 3, 4, 5, 6, and j = 1, 2, ..., n, representing the mineral number, k = 1, 2, 3, 4, representing the temperature number, the unit for adsorbed oil film thickness is nm, the unit for mass is g, and the unit for density is g / cm³. 3 The unit of true density is g / cm³. 3 The unit for particle diameter is µm; Step 4: Using the oil film thicknesses on the surfaces of pure minerals with different particle diameters obtained in Step 3, approximate the oil film thickness on the surfaces of pure minerals with different particle diameters to the oil film thickness on the inner surface of pores of the same pore size contributed by the pure minerals. Fit this to obtain the oil film thickness at different temperatures based on the specific surface area within pores of different pore sizes formed by each mineral. Combined with the specific surface area of ​​pores of different pore sizes contributed by each mineral in the reservoir sample obtained in Step 2, determine the adsorbed oil content of the reservoir sample at each temperature using the following formula. ， In the formula, Q k,a It is the content of adsorbed oil in the reservoir sample at temperature k, ρ k, y h is the density of the organic solvent at temperature k. x, j, k S is the thickness of the oil film adsorbed on the inner surface of the pores of a pure mineral with pore size x and number j at temperature k. x, j This represents the specific surface area contributed by mineral j (numbered j) and pore size x (numbered x), where x = 1, 2, ..., m, is the pore diameter range analyzed in the low-temperature nitrogen adsorption experiment, j = 1, 2, ..., n is the mineral number, and k = 1, 2, 3, 4 is the temperature number. The unit for adsorbed oil content is mg / g, and the unit for density is g / cm³. 3 The unit for adsorbed oil film thickness is nm, and the unit for specific surface area is m². 2 / g; Step 5: Based on the reservoir depth, combined with the results of pore water content, free gas content, and overburden porosity, obtain the reservoir porosity. Combined with the adsorbed oil content obtained in Step 4, determine the free oil content of the reservoir sample at various temperatures. ， In the formula, Q k,f It is the free oil content, ρ, of the reservoir sample at temperature k. k, y ρ is the density of the organic solvent at temperature k, Φ is the porosity of the reservoir sample obtained using overburden porosity analysis, ρ is the density of the reservoir sample, and Q is the density of the reservoir sample. k, a Q k, w and Q k, g These represent the adsorbed oil content, pore water content, and free gas content of the reservoir sample at temperature k, respectively. k, w and ρ k, g These are the densities of pore water and free gas at temperature k, respectively. x = 1, 2, ..., m is the pore diameter range analyzed in the low-temperature nitrogen adsorption experiment, and k = 1, 2, 3, 4 is the temperature number. The units for adsorbed oil content, free oil content, pore water content, and free gas content are all mg / g, and the unit for density is g / cm³. 3 Porosity is measured in percent.

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