CN-121766211-B - Shale gas and coal rock gas output quantitative evaluation method based on gas-water two-phase flow isotope fractionation model

CN121766211BCN 121766211 BCN121766211 BCN 121766211BCN-121766211-B

Abstract

The application relates to a shale or coal gas evaluation method based on a gas-water two-phase flow isotope fractionation model, which comprises the following steps of 1, collecting data, 2, establishing a gas well model, 3, establishing a control equation set, 4, coupling the effects of real gas effect and effective stress, 5, establishing a gas transmission model and a relative permeability model, 6, establishing a relation between capillary pressure and saturation, 7, considering critical desorption pressure, 8, setting initial condition boundary conditions, 9, solving the control equation set, 10, calculating production dynamic parameters and isotope values, 11, performing history fitting, 12, verifying history fitting quality, 13, predicting capacity, 14, calculating gas dynamic yield proportion, 15, identifying fractionation inflection points and gas production mechanism conversion, and realizing yield prediction and quantitative evaluation of deep-layer production aerodynamic proportion of a reservoir by coupling gas-water two-phase flow, multiple gas transmission mechanisms, stress sensitivity and methane isotope competitive adsorption theory.

Inventors

LI WENBIAO
WANG JUN
LU SHUANGFANG
ZHANG PENGFEI
CHEN GUOHUI
ZHOU NENGWU
Wang Zidie

Assignees

东北石油大学三亚海洋油气研究院

Dates

Publication Date: 20260508
Application Date: 20260303

Claims (9)

1. A shale gas and coal rock gas output quantitative evaluation method based on a gas-water two-phase flow isotope fractionation model comprises the following steps: (1) Collecting basic geology and engineering data of a target deep shale or coal-rock gas well, wherein the basic geology and engineering data comprise reservoir basic parameters, fracturing transformation parameters, production dynamic data and wellhead gas isotope data; (2) According to fracturing transformation conditions and reservoir heterogeneity, dividing a shale or coal rock reservoir into three flowing areas, namely a hydraulic fracturing high-permeability area short for an HF area, a reservoir transformation volume area short for an SRV area and an unmodified reservoir area short for USRV area; (3) Establishing a gas-water two-phase flow carbon isotope fractionation control equation set, namely a GWF-CIF model, based on mass conservation, momentum conservation and a state equation, and establishing a gas-water two-phase flow carbon isotope fractionation control equation set considering 12 CH 4 and 13 CH 4 differences; the system of equations applies to the matrix regions of the SRV region and USRV region: (1); Is a bias to time; Equation coefficient in (1) , , , , , And The definition is as follows: (2); (3); (4); in the steps (1) - (4), And Gas phase partial pressures 12 CH 4 and 13 CH 4 , respectively, pa; is the water phase pressure, pa; And Saturation of gas phase and water phase respectively, and ; Is the porosity of the matrix; And Effective diffusion coefficients of 12 CH 4 and 13 CH 4 , m 2 /s, respectively; And Relative permeabilities for aqueous and gas phases; absolute permeability, m 2 ; And The viscosity of the water phase and the gas phase are Pa.s respectively; Is the density of water phase, kg/m 3 ; For the density of the aqueous phase at the reference pressure, 1000 kg/m 3 was taken; Taking 3.84 multiplied by 10 -10 1/MPa as the compression coefficient of water; The capillary entry pressure, pa; is a pore size distribution parameter; And Residual water saturation and residual gas saturation, respectively; And Langmuir adsorption constants of 12 CH 4 and 13 CH 4 , respectively, 1/Pa, in relation to Wherein , ; Is rock density, kg/m 3 ; is Langmuir volume, m 3 /t; Is the reservoir temperature, K; the volume of the gas is 22.4L/mol which is the amount of the unit substance in the standard state; Is a gas constant; For the artificial crack region of the HF region, let And 12 CH 4 and 13 CH 4 are identical in diffusion coefficient, The control equation is reduced to: (5); wherein the subscript F represents an HF-zone parameter, Is the HF region porosity; (4) Coupling real gas effect taking into account temperature and pressure versus methane gas compression factor Density of And viscosity Is a function of (1); (5) The influence of the coupling effective stress evolution on reservoir physical properties is that as a gas well is produced, the effective stress is increased due to the decrease of pore pressure, the porosity and the permeability are reduced, and an effective stress model is established; (6) Establishing a multi-machine gas transmission model; (7) Establishing a gas-water relative permeability model; (8) Establishing a relationship between capillary pressure and saturation; (9) The critical desorption pressure is considered, that is, the desorption of the adsorption gas is controlled by the reservoir pressure, when the reservoir pressure is higher than the critical desorption pressure, the adsorption gas is kept stable, the desorption does not occur, and only when the reservoir pressure is lower than the critical desorption pressure, the desorption is started; (10) Setting initial conditions of a model; (11) Setting model boundary conditions; (12) The established geometric model, the control equation set, variables in the equation, initial conditions and boundary conditions are imported into a numerical simulation soft for solving; (13) Calculating production dynamic parameters and isotope values based on the pressure field obtained by solving, and calculating the production dynamic parameters through volume integration and mass conservation; (14) Constructing an objective function for history fitting, namely accumulating the gas yield obtained by the model calculation in the step (13) Accumulated water yield And methane carbon isotope number Comparing with field actual measurement data to construct a multi-objective optimization function; (15) Verifying history fitting quality, namely substituting optimal parameters obtained by optimization into a model, and drawing a comparison chart of a fitting curve and measured data; (16) Predicting the full life cycle productivity and EUR of a gas well, namely prolonging the calculation time of a model to the economic limit of the gas well based on the optimal parameters determined by history fitting, and predicting the production dynamic of the full life cycle; (17) Calculating the dynamic output ratio of the adsorbed gas and the free gas; (18) And identifying the relation between the isotope fractionation inflection point and the conversion of the gas production mechanism.
2. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1 is characterized in that in the step (2): A. Establishing a horizontal well subsection slotted network geometric model, namely establishing a branch slotted network model under a rectangular coordinate system aiming at a complex slotted network formed by subsection transformation of a horizontal well, wherein a model shaft is parallel to the y direction, an HF (high frequency) area consists of a main slotted hole and a secondary slotted hole, the main slotted hole extends along the x direction and has the length of Width of Two sides of the main crack are provided with a plurality of secondary cracks which are used for simulating the complex shape of the fishbone or dendritic seam net, and the secondary cracks are symmetrical relative to the main crack and have the length of Width of An SRV region is formed around the HF region, the SRV region has a length in the x direction of Length in y direction is Forming USRV region around the SRV region, which is composed of upper and lower regions of SRV region and left region, and the length of upper and lower USRV regions of SRV region in x direction is Length in y direction is The USRV region to the left of the SRV region has a length in the x-direction of Length in y direction is ; B. The method comprises the steps of establishing a vertical well multi-zone composite geometric model, establishing a rectangular coordinate system-based two-dimensional plane geometric model, taking a shaft as a center, dividing a stratum into three elliptic or diamond composite areas with different seepage characteristics, wherein an HF area is a diamond area positioned at the innermost side of the model and represents the artificial main fracture sweep range with high diversion capacity, the half length of the HF area in the x direction is x 1 , the half width of the SRV area in the y direction is y 1 , an SRV area is an elliptic area surrounding the periphery of the HF area and represents a secondary fracture net area formed by fracturing transformation, the half length of the SRV area in the x direction is x 2 , the half width of the SRV area in the y direction is y 2 , the USRV area is an elliptic area at the outermost side of the model and represents an original stratum which is not affected by fracturing, and the half length of the SRV area in the x direction is x 3 , and the half width of the SRV area in the y direction is y 3 .
3. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1, wherein in the step (4): (1) The gas compression factor adopts a polynomial fitting formula to calculate different Wen Yaxia : (6); In the formula, As a function of temperature T: (7) ; (2) Gas density: (8) ; In the middle of 0.016 Kg/mol of methane molar mass; Is a gas constant, 8.314J/mol.K; (3) The gas viscosity was determined using the empirical formula of Lee: (9); in the formula, , And Parameters related to temperature and methane molar mass in the viscosity calculation formula, respectively.
4. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1, wherein in the step (5): (1) Effective stress calculation: (10); (11); In the middle of Pa is the effective stress; Pa is the overburden pressure; taking 1 as a rock correction coefficient; pore pressure, pa; (2) Porosity evolution: The porosity of the matrix under effective stress is expressed as: (12); In the middle of To account for stress sensitive matrix porosity; k' is the rock bulk modulus, pa; is the initial time; is at any moment; the porosity of the matrix under the combined influence of the adsorbent layer and the effective stress is expressed as: (13); Wherein the method comprises the steps of An average pore radius, m, of the matrix pores; The average pore radius under the influence of the adsorption layer, m; is the molecular diameter of methane, is 0.38 nm; And 12 CH 4 And 13 CH 4 coverage, respectively.
5. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1, wherein in the steps (6) and (7): (1) The establishment of a multi-mechanism gas transmission model, namely, in a matrix pore, methane migration involves multiple mechanisms of viscous flow, knudsen diffusion and surface diffusion, and is distinguished by Knudsen number Kn: (14); Wherein Kn is a knudsen number; Three transmission mechanisms and effective stress are combined, 12 CH 4 has an apparent permeability of: (15); wherein c is a mass balance constant, pa; is Langmuir pressure, MPa; Is the inherent permeability of the rock, m 2 ; wherein the first term in brackets is the viscous flow contribution, the second term is the knudsen diffusion contribution, the third term is the surface diffusion contribution, Is the surface diffusion coefficient, which is covered by gas The relation of (2) is: (16); Wherein the method comprises the steps of The surface diffusion coefficient at zero coverage, Is the blocking parameter, apparent diffusion coefficient ratio of 13 CH 4 and 12 CH 4 The range of (2) is 0.97-0.999; (2) The establishment of the gas-water relative permeability model adopts a gas-water relative permeability empirical formula applicable to coal rock/shale: (17); In the middle of And Maximum relative permeabilities of the gas phase and the water phase respectively, , ; And Taking 2 for fitting index; In order to be effective in terms of water saturation, 。
6. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1, wherein in the step (8) Capillary pressure The relationship with water saturation is: (18); In the middle of For the capillary tube to enter into the pressure, The pore diameter distribution parameter is 0.5-2; is the residual gas saturation; Is residual water saturation.
7. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1, wherein in the step (9): 12 CH 4 And 13 CH 4 coverage are respectively: (19); In the middle of Is critical desorption pressure, MPa.
8. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model according to claim 1, wherein in the steps (10) and (11): (1) Setting initial conditions of a model, namely, the specific initial conditions of each region are as follows: (20); Wherein the method comprises the steps of 、 In (a) Is the partial pressure of gas phase 12 CH 4 , pa, in the initial SRV zone, USRV zone, and HF zone reservoirs, respectively; 、 In (a) Is the partial pressure of gas phase 13 CH 4 , pa, in the initial SRV zone, USRV zone, and HF zone reservoirs, respectively; 、 In (a) Is the water phase pressure, pa, in the reservoirs of the initial SRV zone, USRV zone, and HF zone, respectively; is the initial reservoir pressure ,Pa; Is the initial molar ratio 13 CH 4 to 12 CH 4 ; And Initial capillary pressure, pa, of HF and matrix region, respectively; , And The value of (2) can be calculated from the initial methane carbon isotope composition and the initial water saturation: (21); Wherein the method comprises the steps of Is the initial methane carbon isotope value; Carbon isotope values for standard samples; The capillary entry pressure, pa; And Effective water saturation of HF and matrix regions, respectively; And Initial water saturation of HF and matrix region, respectively; And Residual water saturation and residual gas saturation of the HF zone, respectively; And Residual water saturation and residual gas saturation in the matrix region, respectively; (2) Setting a model boundary condition L on the wall surface of a shaft Or surface At this point, a production boundary is set: (22); In the middle of Radius of the horizontal well or the vertical well, m; the method comprises the steps of obtaining an exponential function Pa by fitting measured underflow dynamic pressure data; fitting coefficients of the exponential function; is the pressure Pa corresponding to constant pressure production in the production well.
9. The quantitative evaluation method for shale gas and coal rock gas output based on the gas-water two-phase flow isotope fractionation model of claim 1, wherein in the step (13): the total cumulative gas yield for the HF region, SRV region, USRV region and all regions is given by: (23); In the middle of 、 And Porosity in the HF, SRV and USRV regions, respectively; And The cumulative gas yield of HF region free 12 CH 4 and 13 CH 4 , m 3 , respectively; And The cumulative gas production of SRV regions free 12 CH 4 and 13 CH 4 , m 3 , respectively; And The cumulative gas production in USRV regions free 12 CH 4 and 13 CH 4 , m 3 , respectively; And The cumulative gas yield of 12 CH 4 and 13 CH 4 adsorbed by the SRV region, m 3 ; And The cumulative gas production of 12 CH 4 and 13 CH 4 adsorbed in USRV region, m 3 ; Total cumulative gas yield for all regions, m 3 ; H is the thickness of the reservoir, m; The total cumulative water production in the HF, SRV, USRV and all zones is calculated as follows: (24); In the middle of 、、 And Expressed as total cumulative water production in HF, SRV, USRV and all areas, m 3 , respectively; the density of the aqueous phase at atmospheric pressure is kg/m 3 ; Is the density of water phase, kg/m 3 ; the carbon isotope value of methane in the produced gas of the deep shale/coal-rock gas well is given by the following formula: (25)。

Description

Shale gas and coal rock gas output quantitative evaluation method based on gas-water two-phase flow isotope fractionation model Technical Field The invention relates to the technical field of unconventional shale oil and gas field exploration and development, in particular to a dynamic evaluation method of deep shale gas or coal and rock gas wells based on a gas-water two-phase flow isotope fractionation model (GWF-CIF). Background The deep shale gas and the coal rock gas in China are rich in resources, the geological resources of the deep shale gas reach 21.8X10 12m3 and the geological resources of the deep coal rock gas reach 30.05X10 12m3 by 2025, and the deep shale gas has huge resource potential and is expected to become an important field of stable production and yield increase of natural gas in China. Along with the continuous perfection of exploration and development technology and theory, the exploration and development of deep shale gas and coal gas in China are gradually advanced. The method has the advantages that the deep coal-rock gas field of Daning-Ji county is built on the Ordos basin in 2019, the available resource amount is up to 1664.1 hundred million square, the deep shale gas development bottleneck is broken through by the Fuling shale gas field focal page 42-1HF well of the Sichuan basin in 2020, the daily gas yield is up to 20.1 multiplied by 10 4m3, the important breakthrough is realized by the Xue-Ji county male coal 1HF well in 2023, and the predicted reserve amount is 1226 hundred million square. The series of breakthrough progress marks the deep shale/coal gas exploration and development of China to enter a rapid development stage. The energy structure is gradually transformed to low-carbon green, deep shale/coal gas is used as clean energy, and the acceleration of large-scale development of the deep shale/coal gas provides key support for reducing greenhouse gas emission. Compared with a middle shallow reservoir stratum, the deep shale/coal rock reservoir stratum has the characteristics of high ground stress, high fluid pressure and high stratum temperature, and the characteristics of low porosity and low permeability, such that obvious differences exist in the aspects of pore structure, gas occurrence state, fluid flow mechanism and the like. The deep shale/coal gas reservoir has the common gas-water two-phase flow phenomenon in the development process, the existence of the water phase obviously changes the migration behavior of the gas, and the gas output is influenced by occupying the effective pore space, generating mass transfer resistance and the like. At present, EUR evaluation and adsorption/free gas output mechanism research under the gas-water two-phase flow condition of a deep shale/coal-rock gas well are in a starting stage, the gas occurrence state is complex, the water phase influence mechanism is not clear, and therefore, great disputes exist on the adsorption/free gas output ratio and the final recoverable reserves in the production process, and accurate understanding and optimization decision on deep shale/coal-rock gas development are limited to a certain extent. The current method for quantitatively evaluating the EUR of the deep shale/coal-rock gas well and the dynamic yield ratio of the adsorbed/free gas in the production process mainly comprises an experience decreasing curve method, a material balance method, a numerical simulation method and a nuclear magnetic resonance method. The empirical decreasing curve method such as Arps decreasing method, SEPD method and Duong method establishes decreasing behavior based on historical production data fitting, and the reservoir physical property is assumed to be relatively stable, but dynamic influence of physical processes such as effective stress change, gas-water two-phase relative permeability evolution and the like on the reservoir physical property is not considered, so that long-term prediction has larger uncertainty. The material balance method is based on the constant volume gas reservoir assumption, and the adsorption/free gas ratio under different time is calculated through fitting measured pressure and accumulated gas production data, but the method can only evaluate the adsorption/free gas amount in the existing production period, can not predict the future gas yield ratio and EUR, and under the gas-water two-phase flow condition, the water phase volume change can influence the calculation precision of the effective gas volume. The numerical simulation method carries out EUR prediction by constructing a mass transfer model for coupling gas diffusion, adsorption/desorption and percolation processes, but the traditional model mainly aims at single-phase gas flow, the influence of water on gas migration is not fully considered, and too many unknown parameters exist in the model, so that different results can be caused by different optimization algorithms. The nuclear magnetic resonance method acquires a