Determination method for real methane adsorption capacity of deep shale reservoir

Abstract

The invention relates to a method for measuring the real methane adsorption capacity of a deep shale reservoir. A target area rock core sample is selected; determining reservoir parameters of the target area; carrying out an isothermal adsorption experiment in combination with reservoir parameters of the target area to obtain excess adsorption curves under different conditions, and preferably selecting an excess adsorption model; fitting isothermal adsorption experiment results by using an excess adsorption model, and respectively establishing calculation models of Langmuir volumes VL and Langmuir pressures PL under different temperatures, water saturations and TOC contents; vL and PL under the experimental temperature condition are corrected into VLT and PLT under the actual temperature condition of the reservoir by utilizing temperature calculation models of the VL and the PL, and VL and PL under the experimental water saturation condition are corrected into VLTSW and TLTSW under the actual water saturation condition of the reservoir by utilizing water saturation calculation models of the VL and the PL. Correcting the VL and the PL under the TOC content of the experimental sample into VLTOCTSW and PLTOCTSW of the actual TOC content of the target reservoir by utilizing a TOC content calculation model of the VL and the PL; a methane isothermal adsorption curve is calculated according to the VLTSW and the PLTSW or the VLTOCTSW and the PLTOCTSW, and the absolute gas adsorption amount VaTSW or VaTOCTSW under the deep real reservoir condition is obtained by combining the target reservoir pressure.

Description

Technical Field

[0001] The invention belongs to the technical field of shale gas exploration and development, and in particular relates to a method for determining the true adsorption capacity of methane in a deep shale reservoir. Background Art

[0002] Shale gas is mainly stored in the reservoir pores in adsorbed and free states. Accurately evaluating the actual amount of gas adsorbed by shale under reservoir conditions is of great significance for geological reserve calculation, development plan formulation, and production system optimization. The adsorption capacity of shale is usually described by an isothermal adsorption line, which generally refers to the relationship curve between adsorption amount and pressure at a constant temperature.

[0003] Isothermal adsorption experiment is widely used to study the adsorption process of methane in shale matrix and is the most important test method for shale gas adsorption characteristics. Isothermal adsorption experiments mainly include gravimetric method and volumetric method. The gravimetric method calculates the adsorption amount by measuring the weight difference of the adsorbent before and after equilibrium. The disadvantage is that it is only applicable to dry rock samples. The volumetric method uses the gas state equation to calculate the amount of free gas before and after adsorption equilibrium, thereby determining the adsorption amount.

[0004] The highest equilibrium pressure of the experimental device reported in the existing literature is about 50MPa. However, the formation pressure of deep shale reservoirs in a certain area is generally higher than 70MPa, and can reach up to 100MPa, which is much higher than the level of existing experimental devices. In addition, logging and experimental data show that there is pore water in the shale reservoir, and the water saturation can reach more than 50%. The presence of pore water will occupy the adsorption sites of methane on the pore surface, which has a great impact on the adsorption capacity of the reservoir. However, due to the influence of factors such as water evaporation at high temperature, the maximum temperature of the existing isothermal adsorption experiment of water-containing shale samples is only 60℃ (the maximum experimental temperature of dry samples is 177℃), while the average formation temperature of deep shale reservoirs is about 140℃, which is also much higher than the existing experimental conditions.

[0005] It can be seen that the existing experimental testing and analysis methods are difficult to meet the testing requirements under high temperature, high pressure and water-containing conditions of deep shale reservoirs, and there is a lack of effective methods for determining the true adsorption capacity of methane under deep shale reservoir conditions. Summary of the invention

[0006] In view of the above problems, the present invention proposes a method for determining the true adsorption capacity of methane under high temperature, high pressure and water-containing conditions in deep shale reservoirs, which solves the shortcomings of traditional isothermal adsorption experimental testing and analysis methods, and provides key input parameters for shale gas reservoir geological reserve calculation, well test interpretation, numerical simulation and production decline analysis.

[0007] The technical solution adopted by the present invention is as follows: a method for determining the real adsorption capacity of methane in deep shale reservoirs, the method comprising the following steps: selecting core samples in the target area; determining reservoir parameters in the target area; conducting isothermal adsorption experiments in combination with the reservoir parameters in the target area, obtaining excess adsorption curves under different conditions, and optimizing excess adsorption models; fitting the isothermal adsorption experimental results using the excess adsorption model, and establishing Langmuir volume V under different temperatures, water saturations, and TOC contents. L 、Langmuir pressure P L The computational model of

[0008] Using V L , P L The temperature calculation model takes V under experimental temperature conditions as L , P L Corrected to V under actual reservoir temperature conditions L_T , P L_T , using V L , P L The water saturation calculation model uses V under experimental water saturation conditions L , P L Corrected to V under the actual water saturation of the reservoir L_TSW , P L_TSW , using V L , P L The TOC content calculation model uses the V L , P L V corrected to the actual TOC content of the target reservoir L_TOCTSW , P L_TOCTSW According to V L_TSW and P L_TSW The methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; or according to V L_TOCTSW , P L_TOCTSW The methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW .

[0009] Further, according to V L_TSW and P L_TSW The methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; or according to V L_TOCTSW , P L_TOCTSW The methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW include:

[0010] When the isothermal adsorption experiment has been carried out and needs to be corrected to the actual reservoir temperature and pressure conditions, V L_TSW , P L_TSW Substituting into the Langmuir isotherm adsorption equation, the methane isotherm adsorption curve under the real deep reservoir conditions is calculated, and the absolute adsorbed gas volume V under the real deep reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ;

[0011] Or, when the isothermal adsorption experiment is not carried out and prediction is required, V L_TOCTSW , P L_TOCTSW Substituting into the Langmuir isotherm adsorption equation, the methane isotherm adsorption curve under the corresponding TOC, temperature, pressure and water saturation conditions is calculated, and the absolute adsorbed gas volume V under the real deep reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW .

[0012] Furthermore, selecting core samples in the target area includes: selecting core samples from different wells and different layers in a single well in the target area, crushing the cores, drying them in an oven for a period of time, and testing the porosity of the core samples. core , density ρ core 、Mass m core TOC core .

[0013] Furthermore, the reservoir parameters of the target area include temperature, pressure and water saturation; the temperature is determined by the well temperature logging interpretation results; the pressure is determined by the fluid injection diagnostic test results; the water saturation is calculated by the Simandoux formula or determined by distillation extraction using fresh rock samples drilled on site.

[0014] Furthermore, the parameter free gas density ρ in the excess adsorption model free Calculated using the gas state equation; adsorbed gas density ρ a The results were obtained by establishing a molecular simulation model of typical inorganic minerals and kerogen in the target area and simulating the methane adsorption behavior under different temperature and pressure conditions.

[0015] Furthermore, the isothermal adsorption experiment is carried out in combination with the reservoir parameters of the target area to obtain excess adsorption curves under different conditions, and the preferred excess adsorption model includes: carrying out isothermal adsorption experiments under different temperatures, water saturations and TOC contents, fitting the isothermal adsorption experimental data using the excess adsorption model, and using the adsorption gas density ρ obtained by molecular simulation a The fitting result is constrained as the fitting upper limit of the adsorbed gas density, and the excess adsorption model is optimized according to the fitting accuracy.

[0016] Furthermore, the isothermal adsorption experiments carried out at different temperatures, water saturations and TOC contents include: selecting a volumetric isothermal adsorption experimental device, setting the maximum air inlet pressure and the maximum experimental temperature of the device, and determining the experimental test temperature range, water saturation range and TOC content in combination with the reservoir parameters of the target area.

[0017] Furthermore, before conducting the isothermal adsorption experiments at different temperatures, water saturations and TOC contents, shale samples with different water saturations were prepared by the saturated steam method, including: weighing the water saturation shale samples every 24 hours, and the weight of water entering the shale at different times was:

[0018] m water (i) = m core_dry -m core_wet (i);

[0019] Among them, m core_dry is the weight of the dry shale sample, m core_wet(i) is the weight of the water-bearing shale sample, m water (i) is the weight of water in shale, i represents different test times;

[0020] The water content M(i) of the shale samples at different times is:

[0021]

[0022] According to the porosity of shale samples core , density ρ core and mass m core , the volume of water V water and the apparent volume V core They are:

[0023]

[0024]

[0025] Pore ​​volume of shale samples for:

[0026] V φ =φ cor eV coe ;

[0027] The equivalent water saturation Sw in the water-bearing shale sample is:

[0028] Among them, ρ water Indicates the density of water;

[0029] Considering the effect of water evaporation in the air, when the equivalent water saturation S wAfter reaching the actual water saturation of the formation, saturation is continued until it is 5-10% higher than the actual water saturation of the formation and then saturation is stopped, thereby obtaining a water-bearing shale sample at the corresponding water saturation.

[0030] Furthermore, V under the actual reservoir temperature conditions L_T , P L_T They are:

[0031] V L_T =V L (1-T V );

[0032] P L_T =P L (1-T P );

[0033] Among them, T V 、T P Represents V under experimental temperature conditions L and P L The rate of change of

[0034] V under actual water saturation conditions of the reservoir L_TSW , P L_TSW They are:

[0035] V L_TSW =V L_T (1-S W_V );

[0036] P L_TSW =P L_T (1-S W_P );

[0037] Among them, S w_V , S w_P They represent the experimental water saturation conditions V L and P L The rate of change of

[0038] V under the corresponding TOC content conditions L_TOCTSW , P L_TOCTSW They are:

[0039] V L_TOCTSW =V L_TSW (1-TOC V );

[0040] P L_TOCTSW =P L_TSW (1-TOC P );

[0041] Among them, TOC V 、TOC PRespectively represent V under the experimental TOC content conditions L and P L The rate of change.

[0042] Furthermore, the Langmuir isotherm adsorption equation is: p stands for pressure;

[0043] For reservoirs where isothermal adsorption experiments have been conducted, the absolute adsorbed gas volume V is corrected to the real deep reservoir conditions. a_TSW for:

[0044] For reservoirs where isothermal adsorption experiments have not been conducted, the absolute adsorbed gas volume V corresponding to reservoir conditions is calculated by considering TOC content correction. a_TOCTSW for:

[0045] Furthermore, the excess adsorption model is used to fit the isothermal adsorption experimental results to establish the Langmuir volume V at different temperatures, water saturation and TOC content. L 、Langmuir pressure P L The calculation model includes: using the excess adsorption model to fit the isothermal adsorption experimental results at different temperatures, water saturation and TOC content, and determining the relationship between temperature, water saturation and TOC content and Langmuir volume V L 、Langmuir pressure P L The relationship between V and TOC was established at different temperatures, water saturation and TOC content. L , P L The computational model.

[0046] The present invention selects core samples from different wells and different layers in a single well in the target area, conducts isothermal adsorption experiments under different temperatures, water saturations and TOC contents, selects an isothermal adsorption model suitable for the target area, and combines the molecular simulation method to determine the adsorption gas density, constrains the model fitting results, and establishes V under different temperatures, water saturations and TOC contents. L , P L Based on this model, the isothermal adsorption curves of reservoirs in the target area where isothermal adsorption experiments have not been carried out can be calculated, and the isothermal adsorption curves of reservoirs where isothermal adsorption experiments have been carried out can also be corrected to the actual temperature, pressure and water content of the reservoir. This determination method can determine the true methane adsorption capacity of shale reservoirs under deep high temperature, high pressure and water conditions, solving the problem of lack of effective means for determining the methane adsorption capacity of deep shale reservoirs.

[0047] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 A flow chart of a method for determining the true adsorption capacity of methane in deep shale reservoirs;

[0050] Figure 2 It is an inorganic mineral-organic matter composite molecular model;

[0051] Figure 3 This is a comparison chart of the fitting results of excess adsorbed gas volume of different models;

[0052] Figure 4a is the Langmuir volume V L The fitting results under different temperature conditions; Figure 4b is the Langmuir pressure P L The fitting results under different temperature conditions;

[0053] Figure 5a is the Langmuir volume V L Fitting results under different water saturation conditions; Figure 5b is the Langmuir pressure P L Fitting results under different water saturation conditions;

[0054] Figure 6a is the Langmuir volume V L Fitting result diagram under different TOC content conditions; Figure 6b is the Langmuir pressure P L Fitting result diagram under different TOC content conditions;

[0055] Figure 7 This is a diagram showing the correction effect of the reservoir isotherm adsorption curve for which isotherm adsorption experiments have been carried out. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] like Figure 1 As shown, a method for determining the real adsorption capacity of methane in deep shale reservoirs comprises the following steps: selecting core samples in the target area; determining reservoir parameters in the target area; conducting isothermal adsorption experiments based on the reservoir parameters in the target area to obtain excess adsorption curves under different conditions and optimize excess adsorption models; fitting the isothermal adsorption experimental results using the excess adsorption model to establish Langmuir volume V under different temperatures, water saturations and TOC contents. L 、Langmuir pressure P L The calculation model of V L , P L The temperature calculation model takes V under experimental temperature conditions as L , P L Corrected to V under actual reservoir temperature conditions L_T , P L_T , using V L , P L The water saturation calculation model uses V under experimental water saturation conditions L , P L Corrected to V under the actual water saturation of the reservoir L_TSW , P L_TSW , using V L , P L The TOC content calculation model uses the V L , P L V corrected to the actual TOC content of the target reservoir L_TOCTSW , P L_TOCTSW According to V L_TSW and P L_TSW The methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; or according to V L_TOCTSW , P L_TOCTSW The methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW .

[0058] Specifically, according to V L_TSW and P L_TSWThe methane isotherm adsorption curve is calculated, and the absolute adsorbed gas volume V under deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; or according to V L_TOCTSW , PL_TOCTSW calculated the methane isotherm adsorption curve, and combined with the target reservoir pressure, the absolute adsorbed gas volume V under deep real reservoir conditions was obtained. a-TOCTSW include:

[0059] When the isothermal adsorption experiment has been carried out and needs to be corrected to the actual reservoir temperature and pressure conditions, V L_TSW , P L_TSW Substituting into the Langmuir isotherm adsorption equation, the methane isotherm adsorption curve under the real deep reservoir conditions is calculated, and the absolute adsorbed gas volume V under the real deep reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ;

[0060] Or, when the isothermal adsorption experiment is not carried out and prediction is required, V L_TOCTSW , P L_TOCTSW Substituting into the Langmuir isotherm adsorption equation, the methane isotherm adsorption curve under the corresponding TOC, temperature, pressure and water saturation conditions is calculated, and the absolute adsorbed gas volume V under the real deep reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW .

[0061] Specifically, the core samples of the target area are selected by crushing the shale samples to 100 mesh (particle size is 0.149 mm), and then drying them in an oven at 200°C for 24 hours to ensure that the water in the shale samples is fully removed. Density (ρ core )、Mass(m core )、TOC content (TOC core ) was tested, the porosity of the samples ranged from 3 to 6%, and the density ranged from 2.5 to 2.7 g / cm 3 , mass range is 90~110g, TOC content range is 1~7.5%.

[0062] Specifically, the formation temperature range of the target area is determined by the well temperature logging interpretation results, the formation pressure distribution range of the target area is determined by the fluid injection diagnostic test results, and the water saturation range of the target area is determined by calculating using the Simandoux formula or performing distillation extraction using fresh rock samples drilled on site; the reservoir temperature range of the target area is 120-140°C, the pressure range is 60-90MPa, and the water saturation range is 20-50%.

[0063] A volumetric isothermal adsorption experimental device was selected with a maximum air inlet pressure of 69 MPa (maximum equilibrium pressure of about 50 MPa) and a maximum experimental temperature of 177 °C. Combined with the above-mentioned range of reservoir parameters in the target area, the experimental test pressure range was determined to be 0-50 MPa, the temperature test range was 60-140 °C, and the water saturation test range was determined to be 0-50%.

[0064] The saturated steam method was used to prepare shale samples with different water saturations. During the preparation process, the water saturation shale samples were weighed every 24 hours. The weight of water entering the shale at different times was:

[0065] m water (i) = m core_dry -m core_wet (i);

[0066] Among them, m core_dry is the weight of the dry shale sample, m core_wet(i) is the weight of the water-bearing shale sample, m water (i) is the weight of water in shale, i represents different test times;

[0067] The water content of shale samples at different times (in %) is:

[0068]

[0069] According to the porosity of shale samples core , density ρ core and mass m core , the volume of water V water and the apparent volume V core They are:

[0070]

[0071]

[0072] Pore ​​volume of shale samples for:

[0073] V φ =φ core Vc ore ;

[0074] Equivalent water saturation S in water-bearing shale samples w for:

[0075]

[0076] According to the above equivalent water saturation S wThe calculation formula can be used to obtain the equivalent water saturation of shale samples at different times. During the experiment, since the sample needs to be moved in the balance water device and the isothermal adsorption device, the influence of water evaporation in the air is considered. After the saturated water saturation reaches the actual water saturation of the formation, saturation is continued until it is 5-10% higher than the actual saturation of the formation and then stopped, thereby obtaining the water-bearing shale sample at the corresponding water saturation. Table 1 shows the water saturation values ​​corresponding to a core at different water specific gravities.

[0077] Table 1 Conversion table of core water content and equivalent water saturation

[0078]

[0079] Establish a molecular model of typical inorganic minerals (illite) and organic matter (kerogen) composite media in the target area (such as Figure 2 shown), Figure 2 The red parts on the left and right sides represent inorganic minerals, the clustered parts in the middle represent organic matter, and the area between organic matter and inorganic minerals represents pores. Simulations of methane adsorption behavior at different temperatures (60-140°C) and pressures (0-90MPa) were carried out to determine the adsorption gas density ρ under different temperature and pressure conditions. a The free gas density ρ under different temperature and pressure conditions was calculated using the Setzmann-Wagner (Se-W) state equation. free .

[0080] The most common excess adsorption models in the existing literature are shown in Table 2 and can be divided into three categories. The first category is the Langmuir model and its modified models (SL model, SLF model and SEL model) based on the monolayer adsorption theory; the second category is the S-BET model and the modified S-BET model based on the multilayer adsorption; the third category is the SDR model and SDA model based on the adsorption potential theory.

[0081] Table 2 Excess adsorption adsorption model and its expression

[0082]

[0083] In order to evaluate the adaptability of different models to deep shale gas, the above models were used to carry out fitting analysis on the isothermal adsorption experimental data. During the fitting process, the adsorbed gas density obtained by molecular simulation was used as the fitting upper limit of the adsorbed gas density to constrain the fitting results in order to reduce the influence of the multi-solution of the fitting and improve the rationality of the fitting results. The fitting results are shown in Figure 2. Figure 3 As shown in Table 3. Figure 3 As can be seen from Table 3, the SL model based on the Langmuir monolayer adsorption theory has the highest fitting accuracy, so this model is selected to analyze the experimental data.

[0084] Table 3 Statistics of fitting results of different models

[0085]

[0086]

[0087] The SL model was used to fit the isothermal adsorption experimental data at different temperatures (60-140°C), water saturation (0-50%) and TOC content (1-7.5%). During the fitting process, the adsorption gas density obtained by molecular simulation was used as the fitting upper limit of the adsorption gas density to constrain the fitting results, so as to reduce the influence of the multi-solution of the fitting and improve the rationality of the fitting results. Finally, the fitting obtained V L and P L The relationship between V and temperature, water saturation and TOC content was established at different temperatures. L and P L The calculation models are as follows: Figure 4a and Figure 4b As shown; Figure 4a The linear fitting equation is: y = -0.0179x + 4.7224, and the correlation coefficient is R 2 =0.9236; Figure 4b The nonlinear fitting equation is: y = -0.0007x 2 +0.1838x-6.1588, the correlation coefficient is R 2 =0.8905; established the V under different water saturation conditions L and P L The calculation models are as follows: Figure 5a and Figure 5b As shown, Figure 5a The linear fitting equation is: y = -0.0328x + 3.1593, and the correlation coefficient is R 2 =0.604; Figure 5b The linear fitting equation is: y = 0.0279x + 3.7424, and the correlation coefficient is R 2 =0.2146; V under different TOC content conditions was established L and P L The calculation models are as follows: Figure 6a and Figure 6b As shown, Figure 6a The linear fitting equation is: y = 0.1867x + 2.4601, and the correlation coefficient is R 2 =0.1938; Figure 6b The linear fitting equation is: y = -0.1457x + 2.7758, and the correlation coefficient is R 2 =0.2206.

[0088] For Well A, where the isothermal adsorption experiment has been carried out, the formation temperature is 142.8℃, the formation pressure is 88.3MPa, the reservoir water saturation is 29.1%, the experimental test temperature is 120℃, the maximum experimental test pressure is 50MPa, and the experimental test water saturation is 0. First, using V L and P L The relationship between V and temperature is as follows: when the temperature rises from 120°C to 142.8°C, L and P L The rate of change T V 、T P , and then the temperature-corrected V L_T , P L_T They are:

[0089] V L_T =V L (1-T V );

[0090] P L_T =P L (1-T P );

[0091] Among them, T V 、T P Represents V under experimental temperature conditions L and P L The rate of change of

[0092] Then use V L and P L The relationship between V and water saturation is as follows: when the water saturation increases from 0 to 29.1%, V L and P L The rate of change S w_V , S w_P ; V under the actual water saturation of the reservoir L_TSW , P L_TSW They are:

[0093] V L_TSW =V L_T (1-S W_V );

[0094] P L_TSW =P L_T (1-S W_P );

[0095] Among them, S w_V , S w_P They represent the experimental water saturation conditions V L and P L The rate of change.

[0096] V under the corresponding TOC content conditions L_TOCTSW , P L_TOCTSW They are:

[0097] V L_TOCTSW =V L_TSW (1-TOC V );

[0098] P L_TOCTSW =P L_TSW (1-TOC P );

[0099] Among them, TOC V 、TOC P Respectively represent V under the experimental TOC content conditions L and P L The rate of change.

[0100] For the reservoirs where isothermal adsorption experiments have been conducted, V L_TSW , P L_TSW Substitute into the Langmuir isotherm adsorption equation p represents pressure, and the methane isotherm adsorption curve under deep real reservoir conditions can be calculated. Further extrapolating the pressure to the reservoir pressure of 88.3 MPa, the absolute adsorbed gas volume V under deep real reservoir conditions can be obtained. a_TSW for: For the reservoirs where no isothermal adsorption experiments were conducted, V L_TSW , P L_TSW Substitute into the Langmuir isotherm adsorption equation Further considering the TOC content correction, the absolute adsorbed gas volume V corresponding to the reservoir conditions is a_TOCTSW for:

[0101] Specifically, Figure 7 As shown, Figure 7 Medium V ex is the excess adsorption volume, V ex_TSW is the excess adsorbed gas volume after correction for temperature and water saturation, V a is the absolute adsorption volume (indicated by the orange solid line in the figure), V a_TSW is the absolute adsorbed gas amount after correction for temperature and water saturation, The experimental data ( Figure 7 The red dots in the middle indicate that the experimental conditions are temperature 120°C and pressure 50MPa. Using SL curve fitting, we get Figure 7 The pink curve in the figure gives the V under the corresponding experimental conditions. L and PL , the pressure is extrapolated using the SL isotherm adsorption equation, and the excess adsorption volume V represented by the blue solid line is obtained when the pressure is extrapolated to 90 MPa. ex , V L , P L Substituting into the Langmuir isotherm adsorption equation and extrapolating the pressure to 90 MPa, the absolute adsorption volume Va (orange solid line) under experimental conditions was obtained; V under different temperature, water content and other conditions was used L and P L The calculation model for V ex After temperature and water saturation correction (correction conditions: temperature 142.8℃, pressure 88.3MPa, reservoir water saturation 29.1%), the excess adsorbed gas volume V is obtained. ex_TSW ( Figure 7 The blue dotted line indicates the absolute adsorption volume V a Substituting into the Langmuir isotherm adsorption equation, we can obtain the absolute adsorbed gas volume V after temperature and water saturation correction. a_TSW ( Figure 7 The orange dashed line indicates that the absolute adsorbed gas volume V after temperature and water saturation correction is a_TSW Compared with the absolute adsorption volume V a Reduced by 35%.

[0102] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the true adsorption capacity of methane in a deep shale reservoir, the method comprising the following steps: Select core samples from the target area; Determine reservoir parameters in the target area; Isothermal adsorption experiments were carried out in combination with reservoir parameters in the target area to obtain excess adsorption curves under different conditions and optimize the excess adsorption model; The excess adsorption model was used to fit the isothermal adsorption experimental results, and the Langmuir volume V at different temperatures, water saturation and TOC content were established. L 、Langmuir pressure P L The computational model of Using V L , P L The temperature calculation model takes V under experimental temperature conditions as L , P L Corrected to V under actual reservoir temperature conditions L_T , P L-T , using V L , P L The water saturation calculation model uses V under experimental water saturation conditions L , P L Corrected to V under the actual water saturation of the reservoir L_TSW and P L_TSW , using V L , P L The TOC content calculation model uses the V L , P L V corrected to the actual TOC content of the target reservoir L_TOCTSW and P L_TOCTSW ; According to V L_TSW and P L_TSW The methane isotherm adsorption curve is calculated, and the absolute adsorption gas volume V under the deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; or according to V L_TOCTSW , P L_TOCTSW The methane isotherm adsorption curve is calculated, and the absolute adsorption gas volume V under the deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW .

2. The method according to claim 1, wherein: According to V L_TSW and P L_TSW The methane isotherm adsorption curve is calculated, and the absolute adsorption gas volume V under the deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; or according to V L_TOCTSW , P L_TOCTSW The methane isotherm adsorption curve is calculated, and the absolute adsorption gas volume V under the deep real reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW include: When the isothermal adsorption experiment has been carried out and needs to be corrected to the actual reservoir temperature and pressure conditions, V L_TSW , P L_TSW Substituting into the Langmuir isotherm adsorption equation, the methane isotherm adsorption curve under the real deep reservoir conditions is calculated, and the absolute adsorbed gas volume V under the real deep reservoir conditions is obtained by combining the target reservoir pressure. a_TSW ; Or, when the isothermal adsorption experiment is not carried out and prediction is required, V L_TOCTSW , P L_TOCTSW Substituting into the Langmuir isotherm adsorption equation, the methane isotherm adsorption curve under the corresponding TOC, temperature, pressure and water saturation conditions is calculated, and the absolute adsorbed gas volume V under the real deep reservoir conditions is obtained by combining the target reservoir pressure. a_TOCTSW .

3. The method according to claim 2, wherein: The core samples selected in the target area include: Select core samples from different wells in the target area and different layers in a single well, crush the cores, place them in an oven to dry for a period of time, and test the porosity of the core samples. core , density ρ core 、Mass m core TOC content core .

4. The method according to claim 3, wherein: The reservoir parameters of the target area include temperature, pressure and water saturation; the temperature is determined by the well temperature logging interpretation results; the pressure is determined by the fluid injection diagnostic test results; the water saturation is calculated by the Simandoux formula or determined by distillation extraction using fresh rock samples drilled on site.

5. The method according to claim 4, wherein: The parameter free gas density ρfree in the excess adsorption model is calculated using the gas state equation; Adsorption gas density ρ a The results were obtained by establishing a molecular simulation model of typical inorganic minerals and kerogen in the target area and simulating the methane adsorption behavior under different temperature and pressure conditions.

6. The method according to claim 5, wherein: The isothermal adsorption experiment is carried out in combination with the reservoir parameters of the target area to obtain excess adsorption curves under different conditions. The preferred excess adsorption model includes: Isothermal adsorption experiments were carried out at different temperatures, water saturations and TOC contents. The excess adsorption model was used to fit the isothermal adsorption experimental data. The adsorption gas density ρ obtained by molecular simulation was a The fitting result is constrained as the fitting upper limit of the adsorbed gas density, and the excess adsorption model is optimized according to the fitting accuracy.

7. The method according to claim 6, wherein: The isothermal adsorption experiment under different temperatures, water saturations and TOC contents includes: selecting a volumetric isothermal adsorption experimental device, setting the maximum air inlet pressure and the maximum experimental temperature of the device, and determining the experimental test temperature range, water saturation range and TOC content in combination with the reservoir parameters of the target area.

8. The method according to claim 7, wherein: Before conducting the isothermal adsorption experiments at different temperatures, water saturations and TOC contents, shale samples with different water saturations were prepared using a saturated steam method, including: The water saturation shale samples were weighed every 24 hours, and the weight of water entering the shale at different times was: m water (i)=m core_dry -m core_ wet(i); Among them, m core_dry is the weight of the dry shale sample, mcore_wet(i) is the weight of the water-containing shale sample, m water (i) is the weight of water in shale, i represents different test times; The water content M(i) of the shale samples at different times is: According to the porosity of shale samples core , density ρ core and mass m core , the volume of water V water and the apparent volume V core They are: Pore ​​volume of shale samples for: V φ =φ core V core ; Equivalent water saturation S in water-bearing shale samples w for: Among them, ρ water Indicates the density of water; Considering the effect of water evaporation in the air, when the equivalent water saturation S w After reaching the actual water saturation of the formation, saturation is continued until it is 5-10% higher than the actual water saturation of the formation and then stopped, thereby obtaining a water-bearing shale sample at the corresponding water saturation.

9. The method according to any one of claims 1 to 8, wherein: V under actual reservoir temperature conditions L_T , P L_T They are: V L_T =V L (1-T V ); P L_T =P L (1-T P ); Among them, T V 、T P Represents V under experimental temperature conditions L and P L The rate of change of V under actual water saturation conditions of the reservoir L_TSW , P L_TSW They are: V L_TSW =V L_T (1-S W_V ); P L_TSW =P L_T (1-S W_P ); Among them, S W_V , S W_P They represent V under the experimental water saturation conditions. L and P L The rate of change of V under the corresponding TOC content conditions L_TOCTSW , P L_TOCTSW They are: In L_TOCTSW =V L_TSW (1-TOC V ); P L_TOCTSW =P L_TSW (1-TOC P ); Among them, TOC V 、TOC P Respectively represent V under the experimental TOC content conditions L and P L The rate of change.

10. The method according to claim 9, wherein: The Langmuir isotherm adsorption equation is: p stands for pressure; For reservoirs where isothermal adsorption experiments have been conducted, the absolute adsorbed gas volume V is corrected to the real deep reservoir conditions. a_TSW for: For reservoirs where isothermal adsorption experiments have not been conducted, the absolute adsorbed gas volume V corresponding to reservoir conditions is calculated by considering TOC content correction. a_TOCTSW for:

11. The method according to claim 10, wherein: The excess adsorption model is used to fit the isothermal adsorption experimental results to establish the Langmuir volume V at different temperatures, water saturation and TOC content. L 、Langmuir pressure P L The computational models include: The excess adsorption model was used to fit the isothermal adsorption experimental results at different temperatures, water saturation and TOC content to determine the relationship between temperature, water saturation and TOC content and the Langmuir volume V. L 、Langmuir pressure P L The relationship between V and TOC was established at different temperatures, water saturation and TOC content. L , P L The computational model.

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