CN111006985A - Method for quantitatively evaluating pore throat effectiveness of compact reservoir of continental lake basin under geological conditions - Google Patents
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Abstract
The invention provides a quantitative evaluation method for the pore throat effectiveness of a compact reservoir of a continental lake basin under geological conditions. The method comprises the following steps: establishing a relational expression between the nuclear magnetic resonance signal intensity and the porosity; t of reservoir core to be measured in normal pressure environment after saturated water is measured2A spectrum; sequentially applying confining pressure with different pressure values to the reservoir core to be tested after saturated water to simulate the pressure-bearing change condition of the rock pore structure in the stratum burying process, and respectively measuring the T of the reservoir core to be tested after saturated water under the confining pressure with different pressure values2A spectrum; measured T2And determining the pore diameter-porosity distribution of the rock core of the reservoir to be detected under different pressure values by combining the spectrum with the established relation between the nuclear magnetic resonance signal intensity and the porosity, and quantitatively evaluating the change of the effective pore throats of different scales of the compact reservoir under the geological condition, thereby realizing the quantitative evaluation of the effectiveness of the pore throats of different scales of the compact reservoir of the continental lake basin under the geological condition.
Description
Technical Field
The invention relates to an evaluation method for oil content of a compact reservoir of a continental lake basin, in particular to a method for quantitatively evaluating the oil content of connected and unconnected pores of the compact reservoir.
Background
In recent years, tight (shale) oil resources have become a hot spot for global oil-reservoir upgrading as a successor resource to conventional oil fields. The nanometer pore throat in the oil and gas reservoir of China is found for the first time and the scientific value thereof [ J ] in the institute of rock, 2011,27(6): 857-1864). Compared with the conventional oil gas focusing on the matching relation of six elements, the microscopic pore throat structural feature fine research and quantitative evaluation of the reservoir body are the key points of the exploration and development of the compact oil resources. The micro-pore throat structural characteristics comprise the geometric shapes, sizes, distributions and mutual connectivity relations of pores and throats (Wusheng and Qi Hua. gas reservoir geology [ M ]. Beijing: oil industry publishers, 1998:20-65), which are the basis for establishing the evaluation standard of unconventional oil and gas reservoirs and disclosing the formation factors of compact oil and gas, the reservoir performance and the enrichment rule. The deep understanding of the microscopic pore throat characteristics of the tight reservoir and the quantitative evaluation structure are significant for effectively utilizing tight (shale) oil resources.
The method is characterized in that land phase deposition, relatively small distribution area, poor physical property, micro-nano-scale pores, strong heterogeneity and the like are taken as main characteristics of the Chinese compact oil reservoir (Dujin tiger, Liu He, Madein Sheng and the like. trial study on the Chinese land phase compact oil effective development technology [ J ]. oil exploration and development, 2014,41(2): 198-. Scholars at home and abroad actively explore a compact (shale) reservoir microscopic pore throat characterization technology, and a plurality of testing methods such as constant-speed mercury intrusion, a Maps imaging analysis technology, a digital core technology and the like are formed. In the aspect of pore throat shape, size and distribution analysis, high-resolution observation technologies such as argon ion polishing sample preparation equipment, field emission scanning electron microscope image observation, small-angle X-ray scattering and the like and testing technologies such as high-pressure mercury pressing, constant-speed mercury pressing, nuclear magnetic resonance, gas adsorption and the like are formed, and information such as pore throat shapes, pore diameter distribution and the like of samples of different grades is obtained (baibin, zhu as kay, Wu Song and the like. In the research aspect of crude oil occurrence state, the adsorption and free state of organic matters (Zhouacai, Yanzhi, Cujing, etc.) is mainly judged by combining field emission, environmental scanning electron microscope and energy spectrum analysis, shale oil formation mechanism, geological characteristics and development strategy [ J ] oil exploration and development, 2013,40(1): 14-26). In the aspect of the croup morphology and connectivity, methods such as a laser scanning confocal reconstruction three-dimensional image method, a three-dimensional nano imaging CT (computed tomography) technology, a focused ion beam imaging technology and the like are mainly adopted.
The multi-method and multi-scale matching technology effectively improves the representation precision of the micro pore throat structure of the compact (shale) reservoir, but still has some problems in actually describing the micro pore throat structure characteristics of the compact (shale) oil. For example, different methods differ in test principle, test range, and accuracy; sample handling and experimentation may destroy the original pore structure; pore throat characterization experiments mostly do not take into account actual temperature-pressure conditions in the subsurface, etc. A number of studies have shown that during deposition, the change of temperature and pressure conditions in the processes of diagenesis, mature evolution and the like affects and modifies reservoir pore throat structural characteristics (ginger is in the Xing, Zhang Wen, beam excess and the like, shale oil reservoir basic characteristics and evaluation elements [ J ] Petroleum reports, 2014,35(1): 184-.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a compact reservoir pore throat effectiveness quantitative evaluation method capable of realizing quantitative characterization of the dynamic change of the compact reservoir microscopic pore throat under the geological background.
In order to achieve the purpose, the invention provides a method for quantitatively evaluating the pore throat effectiveness of a compact reservoir of a continental lake basin under geological conditions, wherein the method comprises the following steps:
1) establishing a relational expression between the nuclear magnetic resonance signal intensity and the porosity;
2) determining a T2 spectrum of the reservoir core to be detected after saturated water in a normal temperature and pressure environment; the method is used for representing the condition of the effective pore structure of the reservoir core to be detected;
3) sequentially applying confining pressure with different pressure values to the reservoir core to be detected after saturated water, enabling the reservoir core to be detected to be at the corresponding formation temperature when the confining pressure is applied, simulating the pressure-bearing change condition of the rock pore structure at the corresponding formation temperature in the formation burying process, and respectively measuring the T of the reservoir core to be detected after saturated water under the confining pressure with different pressure values2A spectrum; the method is used for representing the condition of an effective pore structure of the reservoir core to be detected under confining pressures of different pressure values;
4) t determined according to step 2), step 3)2Determining the pore diameter-porosity distribution of the reservoir core to be detected under different pressure values, namely the porosity distribution of pore throats with different diameters, by combining the nuclear magnetic resonance signal intensity and the porosity relation established in the step 1);
5) quantitatively evaluating the change of the effective pore throats of the compact reservoir with different scales along with the pressure change, namely the change of the effective pore throats of the compact reservoir with different scales under the geological condition according to the pore diameter-porosity distribution of the reservoir core to be measured under different pressure values determined in the step 4), thereby realizing the quantitative evaluation of the effectiveness of the pore throats of the compact reservoir of the continental facies lake basin under the geological condition with different scales.
In the quantitative evaluation method, the internal effective pore structure, namely the internal communicated pore structure, can be effectively represented after the saturated water of the reservoir core to be measured is treated.
In the quantitative evaluation method, the rock pore structure change condition in the pressure bearing process in the stratum burying process can be effectively simulated by sequentially applying confining pressure with different pressure values to the reservoir core to be tested after saturated water.
In the above quantitative evaluation method, preferably, step 1) is carried out by: and the calibration of the porosity and the nuclear magnetic resonance signal of the compact reservoir is realized by using the standard scale sample, so that the establishment of a relational expression between the nuclear magnetic resonance signal intensity and the porosity is realized. In a preferred embodiment, the relationship between the nmr signal intensity and the porosity is:
wherein Φ is the porosity of the standard scale sample,
the method comprises the steps of obtaining porosity of a reservoir core to be detected, NS is the accumulation frequency of a standard scale sample, NS is the accumulation frequency of the sample to be detected, RG1 and RG2 are respectively analog gain (RG 1) and digital gain (RG 2) of the standard scale sample, RG1 and RG2 are respectively analog gain (RG 1) and digital gain (RG 2) of the reservoir core to be detected, S is a nuclear magnetic signal intensity value of the standard scale sample, and S is a nuclear magnetic signal intensity value of the reservoir core to be detected; and performing linear fitting on the porosity and the nuclear magnetic resonance signal intensity of the standard scale sample based on the formula, and determining a relational expression between the nuclear magnetic resonance signal intensity and the porosity.
In the quantitative evaluation method, preferably, the reservoir core to be measured after saturated water is obtained by performing vacuum pressurization saturated water treatment on the reservoir core to be measured; the time for vacuumizing is preferably 8h, the pressure of the pressurized saturated water is preferably 15MPa, and the time for pressurizing the saturated water is preferably 12 h.
In the above quantitative evaluation method, preferably, the method further comprises: according to step 2), stepT of reservoir core to be measured after saturated water measured in step 3)2Calculating the porosity of the reservoir core to be measured under different pressures by combining the spectrum with the relational expression established in the step 1); and quantitatively evaluating the change of the porosity of the compact reservoir under the geological condition.
In the quantitative evaluation method, preferably, the confining pressure of the reservoir core to be measured after saturated water is sequentially applied with different pressure values in the step 3) is applied by using an external simulation holder.
In the quantitative evaluation method, preferably, the applying of the confining pressures with different pressure values in step 3) in sequence is realized by applying the confining pressures with pressure values from small to large in sequence.
In the quantitative evaluation method, the confining pressure value can be determined according to the actual formation condition of the area where the reservoir core to be measured is located, the pressure value corresponding to the geological age where the reservoir core to be measured is located can be calculated generally according to different basin pressure gradients, and the pressure value corresponding to the depth calculation with research significance is selected as the confining pressure value; for example, the depth corresponding to the key accumulation period may be selected to combine with the formation pressure gradient to calculate a corresponding pressure value as a confining pressure value (the formation pressure gradient × the formation depth is the pressure value of the formation at that depth); for example, the method can be determined by combining the formation depth with the formation pressure gradient in the evolution process of the reservoir to be detected; for example, 3MPa, 6MPa, 9MPa, 12 MPa.
In the above quantitative evaluation method, preferably, the corresponding formation temperature in step 3) is a formation temperature corresponding to a confining pressure value, and the temperature is determined by combining a geothermal gradient with a formation depth corresponding to the confining pressure value (the temperature is the surface temperature + the geothermal gradient × the formation depth). The simulation of the pressure of the reservoir core to be tested in different geological periods and the temperature of the stratum can be realized by using different confining pressure values and corresponding temperatures.
In the above quantitative evaluation method, preferably, the confining pressure value is not higher than the rock fracture pressure.
In the quantitative evaluation method, preferably, the applying process of sequentially applying the confining pressure with different pressure values to the reservoir core to be tested after saturated water in step 3) includes a pressure increasing process and a pressure maintaining process; in this case, the sum of step 3) is measured separatelyT of reservoir core to be measured under different confining pressures after saturated water2The spectrum is specifically the T of the reservoir core to be measured after respectively measuring saturated water of each confining pressure value after pressure maintaining2A spectrum; for example, the application of confining pressure can be accomplished by applying pressure 1h to achieve pressure increase and maintaining pressure for 1 h. This manner of applying confining pressure helps to adequately simulate different pressure environments.
In the quantitative evaluation method, preferably, the step 3) further includes measuring T of the reservoir core to be measured after saturated water for different dwell time periods when the reservoir core to be measured after saturated water is subjected to dwell pressure at different confining pressures2Spectra. In a specific embodiment, a certain confining pressure is applied to the reservoir core to be measured after saturated water, the pressure is maintained for a period of time, and the T of the reservoir core to be measured after saturated water with different pressure maintaining time lengths is measured2A spectrum; then repeating the process under the next confining pressure value until the measurement under all confining pressure values is completed; determination of T at different dwell times2Spectrum avoids adverse effects caused by hysteresis effect of confining pressure applied in experiment, and determines T under different pressure holding times2Whether the pore changes are consistent or not is observed through spectrum, and the influence brought by confining pressure is reflected more truly.
In the above quantitative evaluation method, preferably, T measured according to step 2) or step 3)2The concrete implementation mode of determining the pore diameter-porosity distribution of the reservoir core to be detected under different pressure values, namely the porosity distribution of pore throats with different diameters, by combining the spectrum with the relational expression established in the step 1) comprises the following steps:
A. the T of the reservoir core to be measured under different confining pressures after saturated water is measured according to the step 3)2Nuclear magnetic signal intensity distribution of spectrum and T of reservoir core to be measured under normal pressure after saturated water determined in step 2)2Calculating the porosity distribution characteristics of the reservoir core to be measured under different pressure conditions after saturated water by combining the nuclear magnetic resonance signal intensity and the porosity established in the step 1);
B. calculating the pore throat diameter distribution under different pressure conditions, namely the nuclear magnetic signal intensity distribution of pore throats with different diameters under different pressure conditions based on the T2 spectrum of the reservoir core to be detected under different confining pressures after saturated water determined according to the step 3) and the T2 spectrum of the reservoir core to be detected under normal pressure after saturated water determined in the step 2);
C. and combining the A and the B to obtain the pore diameter-porosity distribution of the reservoir core to be detected under different pressures.
In a specific embodiment, the method for quantitatively evaluating the effectiveness of the compact pore storage throat of the continental lake basin under the geological condition, provided by the invention, comprises the following steps:
step 1: the method comprises the steps of utilizing a standard scale sample to achieve calibration of the porosity of a compact reservoir and a nuclear magnetic resonance signal, and establishing a relational expression between the nuclear magnetic resonance signal intensity and the porosity;
step 2: carrying out saturated water treatment on the reservoir core to be detected under normal pressure, specifically carrying out saturated water treatment by adopting a vacuum pressurization saturation device, wherein the evacuation time is 8h, the pressure is 15MPa, and the saturation time is 12 h; then, the T of the reservoir core to be measured after saturated water at normal temperature and normal pressure is measured2A spectrum; according to the measured T of the reservoir core to be measured after saturated water at normal pressure2Calculating the porosity of the reservoir core to be measured under normal pressure by combining the spectrum with the relation between the nuclear magnetic resonance signal intensity and the porosity established in the step 1;
and step 3: sequentially applying confining pressure from small to large to a reservoir core to be detected after saturated water by using an external simulation clamp holder, wherein the confining pressure values are 3MPa, 6MPa, 9MPa and 12MPa in sequence; when each pressure value is applied, the pressure is continuously applied for 1h, the pressure is maintained for 1h, and when each pressure value is applied, the core of the reservoir to be tested is at a corresponding temperature (the temperature is the formation temperature corresponding to the confining pressure value, and the temperature is determined by combining the geothermal gradient with the formation depth corresponding to the confining pressure value); and respectively measuring T of the rock core of the reservoir to be measured under different confining pressures after saturated water2A spectrum; according to the measured T of the reservoir core to be measured under different confining pressures2Determining the porosity of the reservoir core to be detected under different confining pressures by combining the spectrum with the relation between the nuclear magnetic resonance signal intensity and the porosity established in the step 1;
and 4, step 4: determining the T of the reservoir core to be measured after saturated water according to the step 3 under different confining pressures2Nuclear magnetic signal intensity distribution of spectrum and T of reservoir core to be measured under normal pressure after saturated water determined in step 22Calculating the porosity distribution characteristics of the reservoir core to be measured under different pressure conditions after saturated water by combining the nuclear magnetic resonance signal intensity and the porosity established in the step 1;
and 5: based on T of reservoir core to be measured after saturated water determined according to step 3 under different confining pressures2Spectrum and T of reservoir core to be measured after saturated water at normal pressure determined in step 22Performing spectrum calculation on the diameter distribution of pore throats under different pressure conditions, namely the nuclear magnetic signal intensity distribution of pore throats with different diameters under different pressure conditions;
step 6: obtaining the pore diameter-porosity distribution of the reservoir core to be measured after saturated water under different pressures according to the porosity distribution characteristics under different pressure conditions determined in the step 4 and the nuclear magnetic signal intensity distribution of pore throats with different diameters determined in the step 5; based on the pore diameter-porosity distribution of the core of the reservoir to be detected after saturated water under different pressures, the change of the effective pore throats of the tight reservoir with different scales along with the pressure change (namely, the change of the effective pore throats of the tight reservoir with different scales under the geological condition) and the change of the effective porosity of the tight reservoir with the pressure change (namely, the change of the effective porosity of the tight reservoir under the geological condition) are quantitatively evaluated, so that the quantitative evaluation of the effective pore throats of the tight reservoir of the continental facies lake basin under the geological condition with different scales is realized.
Aiming at a compact reservoir, the invention develops the evaluation of the microscopic pore throat structure based on the temperature and pressure geological process constraint under the real geological condition, and establishes a set of accurate evaluation method of the multi-scale pore throat structure characteristics of the continental facies compact (shale) oil reservoir. The evaluation method provided by the invention is based on simulating the porosity of the compact reservoir (shale) under different pressure conditions, realizes the quantitative determination of the pore change characteristics of the sample reservoir under different pressure conditions by applying confining pressure, finally fits and establishes the pore change curves of pore throats with different diameters under different pressure conditions, quantitatively predicts the reservoir performance change rule of the compact reservoir (shale) under the geological background (namely the porosity change conditions under different pressure conditions), and provides parameters for evaluation and prediction of continental facies shale (compact) oil desserts.
The invention provides a quantitative evaluation method of microscopic pore throat change under different temperature and pressure geological process constraints based on a real geological background for continental facies compact reservoirs (including shale oil reservoirs), and the quantitative evaluation method can accurately and quantitatively evaluate the pore throat effectiveness change condition of the continental facies compact reservoirs in the change process along with geological evolution. Compared with the prior art, the invention has the following advantages:
1. the technical scheme provided by the invention realizes the simulation of the dynamic evolution of the microscopic pore throat; the micro pore throat structure of the compact reservoir is an important parameter for dessert evaluation, and is an important characteristic for revealing the formation condition and enrichment rule of compact oil, the prior art only focuses on the current surface characteristic of the micro pore throat structure of the compact reservoir, but the micro pore throat structure changes correspondingly along with geological evolution, and the technical scheme provided by the invention realizes the quantitative representation of the dynamic change of the micro pore throat of the compact reservoir.
2. The technical scheme provided by the invention realizes the accurate characterization of the microscopic pore throats with different scales; the diameter distribution range of the micro pore throats of the compact reservoir is large, and the micro pore throats from a few nanometers to a few micrometers form a reservoir space of the compact reservoir.
Drawings
FIG. 1 is a flow chart of a method for quantitatively evaluating the oil content of unconnected pores of a compact reservoir of a continental lake basin.
FIG. 2 is a plot of the porosity calibration for the samples of example 1.
FIG. 3A shows the T2 spectra of the relaxation times of samples at different pressures (0MPa, 3MPa, 6MPa, 9MPa) in example 1.
FIG. 3B is the relaxation time T2 spectrum at 12MPa for the sample of example 1.
FIG. 4A is a graph of nuclear magnetic signal changes of the mesoporous throat of samples of example 1 at different pressures (0MPa, 3MPa, 6MPa, 9 MPa).
FIG. 4B is a graph of nuclear magnetic signal changes of the mesoporous throat of the sample at 12MPa in example 1.
FIG. 5A is a graph of the variation of the nuclear magnetic signals of the macro-pore throat of the samples of example 1 at different pressures (0MPa, 3MPa, 6MPa, 9 MPa).
FIG. 5B is a plot of the change in the macropore throat nuclear magnetic signal of the sample at 12MPa from example 1.
FIG. 6 is a plot of pore size versus porosity for samples of example 1 at different pressures.
FIG. 7 is a graph of pore throat versus porosity for different dimensions for the samples of example 1 at different pressures.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
Example 1
The embodiment provides a method for quantitatively evaluating pore throat effectiveness of a compact reservoir of a continental lake basin (shown in figure 1), wherein the method comprises the following steps:
step 1: the method comprises the steps of utilizing a standard scale sample to achieve calibration of the porosity of a compact reservoir and a nuclear magnetic resonance signal, and establishing a relational expression between the nuclear magnetic resonance signal intensity and the porosity;
specifically, the relationship between the nuclear magnetic resonance signal intensity and the porosity is:
wherein Φ is the porosity of the standard scale sample,
the porosity of the reservoir core to be detected is shown, NS is the accumulation frequency of the standard scale sample, NS is the accumulation frequency of the standard scale sample to be detected, RG1 and RG2 are respectively the analog gain and the digital gain of the standard scale sample, RG1 and RG2 are respectively the analog gain and the digital gain of the reservoir core to be detected, S is the nuclear magnetic signal intensity value of the standard scale sample, and S is the nuclear magnetic signal intensity value of the reservoir core to be detected; based on the formula, the porosity and the nuclear magnetic resonance signal intensity of the standard scale sample are subjected to linear fitting to determine the nuclear magnetic resonance signalThe relationship between strength and porosity is shown in fig. 2, y is 360.72x + 123.06; x is porosity and y is nuclear magnetic resonance signal intensity;
step 2: performing saturated water treatment on the reservoir core to be detected under normal pressure, specifically performing saturated water treatment by adopting a vacuum pressurization saturation device, wherein the vacuumizing time is 8h, the pressure is 15MPa, and the saturation time is 12h (the core data is shown in a table 1); then, the T of the reservoir core to be measured after saturated water at normal temperature and normal pressure is measured2A spectrum; according to the measured T of the reservoir core to be measured after saturated water at normal pressure2Calculating the porosity of the reservoir core to be measured under normal pressure by combining the spectrum with the relation between the nuclear magnetic resonance signal intensity and the porosity established in the step 1;
TABLE 1 porosity values of samples under saturated water conditions at ambient temperature and pressure
| Original mass (g) | Saturated mass (g) | Density (g/cm)3) | Volume (cm)3) | Nuclear magnetic porosity (%) |
| 54.1452 | 55.1094 | 2.52 | 21.87 | 5.42 |
And step 3: sequentially applying the reservoir rock core to be detected after saturated water from small to large by using an external simulation clamp holderThe confining pressure of the system is 3MPa, 6MPa, 9MPa and 12MPa in sequence (the confining pressure value is obtained by calculating the depth corresponding to the key accumulation period and combining with the pressure gradient of the stratum, wherein the pressure gradient is 0.88MPa/100m, and the ground temperature gradient is 2.5 ℃/100 m); when each pressure value is applied, the pressure is continuously applied for 1h, the pressure is maintained for 3 hours and 15 hours, and the core of the reservoir to be tested is at a corresponding temperature when confining pressure is applied (see table 2 specifically); t of reservoir rock core to be measured under different confining pressures after respectively measuring saturated water2Spectrum (measured T)2The spectra are shown in FIGS. 3A-3B, where only 12MPa has porosity change at different holding times, and T at different holding times under the confining pressure of 3MPa, 6MPa, and 9MPa2Spectral curve coincidence); determining that the rock fracture pressure P of the reservoir core to be detected is near, and all applied confining pressure values do not exceed PFace(ii) a According to the measured T at different confining pressures2Calculating the porosity of the reservoir core to be detected under normal pressure by combining the spectrum with the relation between the nuclear magnetic resonance signal intensity and the porosity established in the step 1, wherein the porosity corresponding to 3MPa, 6MPa, 9MPa and 12MPa is respectively 7.10%, 5.36%, 5.43% and 5.42%;
TABLE 2 values of confining pressure and corresponding temperatures
| Depth (m) | 300 | 700 | 1022 | 1500 |
| Confining pressure (Mpa) | 3 | 6 | 9 | 12 |
| Temperature (. degree.C.) | 7.5 | 18 | 25 | 38 |
And 4, step 4: based on T of reservoir core to be measured after saturated water determined according to step 3 under different confining pressures2Spectrum and T of reservoir core to be measured after saturated water at normal pressure determined in step 22Calculating a porosity distribution characteristic diagram under different pressure conditions by combining the nuclear magnetic signal intensity distribution in the spectrum with the relation between the nuclear magnetic resonance signal intensity and the porosity established in the step 1;
based on T of reservoir core to be measured after saturated water determined according to step 3 under different confining pressures2Spectrum and T of reservoir core to be measured after saturated water at normal pressure determined in step 22Performing spectrum calculation on the pore throat diameter distribution under different pressure conditions, namely the nuclear magnetic signal intensity distribution of pore throats with different diameters under different pressure conditions (as shown in figures 4A-4B and figures 5A-5B);
and 5: obtaining a porosity value, namely a pore-porosity distribution (shown in fig. 6, for pore diameters with different diameters) corresponding to the actually measured pore size distribution characteristics of the reservoir core to be tested after obtaining saturated water under different pressures from the porosity distribution characteristics under different pressure conditions and the nuclear magnetic signal intensity distribution of pore throats with different diameters determined in the step 4; based on the porosity values corresponding to the measured pore size distribution characteristics of the rock core of the reservoir to be measured after saturated water under different pressures, the effectiveness of pore throats of compact reservoirs with different scales along with the pressure change is quantitatively evaluated (see table 3 and fig. 7 for details), so that the quantitative evaluation of the effectiveness of the pore throats of compact reservoirs of continental lake basins with different scales is realized.
TABLE 3 pore throat variation characteristics of samples of different dimensions under different pressure conditions
| Item | 0MPa | 3MPa | 6MPa | 9MPa | 12MPa | 12MPa-3h | 12MPa-15h |
| Amplitude of mesoporous signal | 56746.10 | 56679.98 | 54732.25 | 54607.54 | 54568.41 | 53343.96 | 52660.79 |
| Amplitude of the macro-aperture signal | 10332.42 | 10377.14 | 10584.35 | 10740.21 | 10843.64 | 10775.71 | 10768.63 |
| Relative change of |
0％ | -0.12％ | -3.55％ | -3.77％ | -3.84％ | -6.00％ | -7.20％ |
| Relative change in |
0％ | 0.43％ | 2.44％ | 3.95％ | 4.95％ | 4.29％ | 4.22％ |
The mesopores are pores with the aperture of 2-50nm, and the macropores are pores with the aperture of more than 50 nm.
According to test data (shown in table 3) under different confining pressures, the reservoir core to be tested does not change significantly below 3MPa after confining pressure is applied, and relatively large changes occur when the pressure gradually rises to a certain pressure (about 6 MPa). The mesopores are gradually reduced along with the increase of confining pressure, and the later period is gradually gentle. The macro-pores are gradually increased along with the increase of the pressure, and the late stage is gradually gentle.
Claims (12)
1. A method for quantitatively evaluating pore throat effectiveness of a compact reservoir of a continental lake basin under geological conditions comprises the following steps:
1) establishing a relational expression between the nuclear magnetic resonance signal intensity and the porosity;
2) t of reservoir core to be measured in normal temperature and pressure environment after saturated water determination2A spectrum;
3) sequentially applying confining pressure with different pressure values to the reservoir core to be detected after saturated water, enabling the reservoir core to be detected to be at the corresponding formation temperature when the confining pressure is applied, simulating the pressure-bearing change condition of the rock pore structure at the corresponding formation temperature in the formation burying process, and respectively measuring the T of the reservoir core to be detected after saturated water under the confining pressure with different pressure values2A spectrum;
4) t determined according to step 2), step 3)2Determining the pore diameter-porosity distribution of the reservoir core to be measured under different pressure values, namely the porosity distribution of pore throats with different diameters by spectrum and combination of the relational expression established in the step 1);
5) quantitatively evaluating the change of the effective pore throats of the compact reservoir with different scales under the geological condition according to the pore diameter-porosity distribution of the reservoir core to be measured with different pressure values determined in the step 4), thereby realizing the quantitative evaluation of the effective pore throats of the compact reservoir with different scales of the continental lake basin under the geological condition.
2. The quantitative evaluation method according to claim 1, wherein step 1) is achieved by: and calibrating the porosity of the compact reservoir and the nuclear magnetic resonance signal by using the standard scale sample, so as to establish a relational expression between the nuclear magnetic resonance signal intensity and the porosity.
3. The quantitative evaluation method according to claim 1, wherein the reservoir core to be tested after saturated water is obtained by performing vacuum pressurization saturated water treatment on the reservoir core to be tested.
4. The quantitative evaluation method according to claim 1, wherein the method further comprises:
according to the T of the reservoir core to be measured after saturated water measured in the step 2) and the step 3)2Calculating the porosity of the reservoir core to be measured under different pressures by combining the spectrum with the relational expression established in the step 1); and quantitatively evaluating the change of the porosity of the compact reservoir under the geological condition.
5. The quantitative evaluation method according to claim 1, wherein the pressure value of the confining pressure in step 3) is determined by calculating a corresponding pressure value through combining the depth corresponding to the key reserve stage of the reservoir to be tested with the formation pressure gradient.
6. The quantitative evaluation method according to claim 1, wherein the confining pressure value in step 3) is 3MPa, 6MPa, 9MPa, 12 MPa.
7. The quantitative evaluation method according to any one of claims 1, 5 and 6, wherein the corresponding temperature in step 3) is the formation temperature corresponding to the confining pressure value, and the temperature is determined by combining the geothermal gradient with the formation depth corresponding to the confining pressure value.
8. The quantitative evaluation method according to claim 1 or 5, wherein the applying of the confining pressures of different pressure values in sequence in step 3) is realized by applying the confining pressures of the pressure values from small to large in sequence.
9. The quantitative evaluation method according to claim 1, wherein the applying process of sequentially applying the confining pressure with different pressure values to the reservoir core to be tested after saturated water in step 3) comprises a pressure increasing process and a pressure maintaining process.
10. The quantitative evaluation method according to claim 9, wherein the step 3) further comprises: when the reservoir core to be measured after saturated water is subjected to pressure maintaining under different ambient pressures, the T of the reservoir core to be measured after saturated water with different pressure maintaining time lengths is measured2Spectra.
11. The quantitative evaluation method according to any one of claims 1, 9 and 10, wherein the step 3) of sequentially applying the confining pressure of different pressure values to the reservoir core to be tested after saturated water is performed by applying the confining pressure by using an external simulation gripper.
12. The quantitative evaluation method according to claim 1, wherein the implementation of step 4) comprises:
A. the T of the reservoir core to be measured under different confining pressures after saturated water is measured according to the step 3)2Nuclear magnetic signal intensity distribution of spectrum and T of reservoir core to be measured under normal pressure after saturated water determined in step 2)2Calculating the porosity distribution characteristics of the reservoir core to be measured under different pressure conditions after saturated water by combining the nuclear magnetic resonance signal intensity and the porosity established in the step 1);
B. based on the T of the reservoir core to be measured after saturated water determined according to the step 3) under different confining pressures2Spectrum and T of reservoir core to be measured after saturated water determined in step 2) under normal pressure2Performing spectrum calculation on the diameter distribution of pore throats under different pressure conditions, namely the nuclear magnetic signal intensity distribution of pore throats with different diameters under different pressure conditions;
C. and combining the A and the B to obtain the pore diameter-porosity distribution of the reservoir core to be detected under different pressures.
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