Effect Of Stress Sensitivity Research Articles

Productivity Model for Water-Producing Gas Well in a Dipping Gas Reservoir With an Aquifer Considering Stress-Sensitive Effect

The development process of a dipping gas reservoir with an aquifer considering stress sensitivity is complex. With gas development, formation pressure decreases, stress-sensitive effect decreases permeability and porosity, and formation water could flow into the development gas well and gather in the wellbore. The accumulation of water may lead to a lower gas rate. Simultaneously, the gravity action of fluid caused by formation dip angle affects gas well productivity. However, few studies have investigated a deliverability model for a water-producing gas well with a dipping gas reservoir considering stress sensitivity. For this reason, it is important to determine the relationships between gas well productivity and stress sensitivity, formation angle, and water production. In this research, a new mathematical model of deliverability was developed for a water-producing gas well with a dipping gas reservoir considering stress sensitivity. Additionally, a new equation was developed for gas well productivity. By analyzing a typical dipping gas reservoir with an aquifer, the level of influence on gas well productivity was determined for stress sensitivity, formation angle, and water–gas ratio (WGR). The work defined the relationships between gas well productivity and stress sensitivity, formation angle, and WGR. The results indicate that deliverability increases with an increase in formation angle, and growth rate hits its limit at an angle of 40 deg. Due to the influence of formation angle, fluid gravity leads to production pressure differences in gas wells. When bottom-hole flow pressure equaled formation pressure, gas well production was not 0 × 104 m3/d, the angle was large, and gas well production was greater. Deliverability and stress sensitivity hold a linear relationship: the stronger the stress sensitivity, the lower the deliverability of the gas well, with the stress sensitivity index from 0 to 0.06 MPa−1 and the deliverability decrease rate at 37.2%. Deliverability and WGR hold an exponential relationship: when WGR increased from 0.5 to 15.0 m3/104 m3, the deliverability decrease rate was 71.8%. The model and the equations can be used to predict gas deliverability in a dipping gas reservoir with an aquifer considering stress sensitivity. It can also be used to guide the development process for a dipping gas reservoir with an aquifer.

Transient Pressure and Rate Decline Analysis for Horizontal Well in Stress-Sensitive Composite Reservoir

The existence of stress sensitivity effect made the percolation mechanism of low-permeability reservoirs significantly complex. Further, numerous reservoirs have composite stratum properties in actual development procedure. This paper based on the concept of permeability stress sensitivity presents an unsteady flow model for horizontal well taking both stress sensitivity and composite reservoir into account. Analytic solutions for the transient pressure and the rate decline behaviors are obtained by comprehensive utilization of regular perturbation method, Laplace transformation, orthogonal transformation, and Stehfest numerical inversion. The example analysis verifies that the proposed model is reliable and practical. Likewise, there is a discussion of the influence of permeability modulus and other relevant parameters on the transient pressure and the rate decline for horizontal well in stress-sensitive composite reservoir. The work of this paper improved the previous researches and provided a more accurate basis for transient flow analysis and formation evaluation of this typical reservoir.

A Practical Methodology for Production-Data Analysis of Single-Phase Unconventional Wells With Complex Fracture Geometry

Summary Forecasting coalbed-methane well performance in the Qinshui Basin is a key task for predicting future gas production. There is evidence suggesting that complex fracture geometry and multiple hydraulic-fracture networks might develop. Unfortunately, very limited work has been published on the production analysis of multiple-fractured vertical wells (MFVWs) in coalbed-methane reservoirs. To better understand the production performance of the MFVWs, a new, fast, and reliable methodology is presented in this paper. This semianalytical methodology is derived from an analytical reservoir solution and a numerical fracture solution. Dual-porosity, gas-diffusion, gas-adsorption, and stress-sensitivity effects are considered. Verification of the methodology is accomplished through comparison with synthetic-reservoir-simulation cases and with field-performance data. Good agreement is shown between results from the proposed methodology and those from a reservoir-simulation model. Results from this study indicate increasing transient-gas-production rate and cumulative gas recovery with increasing natural-fracture permeability, gas-storage coefficient, Langmuir volume, fracture conductivity, and fracture length. The transient gas-production rate and cumulative gas recovery were found to decrease with increasing stress-sensitivity coefficient. The parameters found to have the strongest and weakest effects on the gas-production rate were the natural-fracture permeability and the fracture conductivity, respectively. Results from this study on MFVWs in coalbed-methane reservoirs indicate fracture length is more important than fracture conductivity in terms of its effect on gas productivity.

Semi-analytical simulation of transient flow behavior for complex fracture network with stress-sensitive conductivity

The main object of this paper is to establish a benchmark model to investigate the transient flow behavior for complex fracture network with stress-sensitive conductivity. An associated semi-analytical solution is proposed by coupling reservoir-fracture flow model and incorporating stress sensitivity of fracture conductivity into coupled model, with sufficient flexibility to account for complex fracture geometry and stress sensitivity. A dimension transformation with multiple source terms is fully developed and extended to the case of complex fracture network, which renders the resulting nonlinear equations fully amenable to the linear treatment. An accurate, closed form iterative algorithm is subsequently provided and verified against numerical reservoir simulator. A set of synthetic simulations is utilized to investigate the physics of transient flow behavior and capture the interaction between fracture-production interference and conductivity decay by performing pressure transient analysis. The results show that the pressure response transitions from the initial condition (constant initial-conductivity) to the limited condition (constant minimum-conductivity) because of the loss of stress-sensitive conductivity, displaying a gradual increasing in the pressure drop. The magnitude of extra pressure drop is dependent on the complexity nature and conductivity decay of fracture network. In the condition of high flow resistance (i.e. low initial conductivity, small area connected to the reservoir), it is of great significance to take the effect of stress sensitivity into account to obtain correct simulation of transient pressure response. The findings in this paper could improve the understanding of flow mechanisms and facilitate the analysis of transient pressure/rate data for complex fracture network with stress-sensitive conductivity.

A general analytical method for transient flow rate with the stress-sensitive effect

The permeability of deep-seated reservoirs and aquifers usually changes with formation pressure; however, the widely used analytical method assumes constant permeability, resulting in significant errors in flow rate prediction. This work extended the conventional analytical method to consider the effect of stress-sensitive permeability. The proposed analytical method was validated by comparing analytical flow-rate solutions for vertical wells with numerical flow-rate solutions. The production rates of a multi-stage fractured horizontal (MSFH) well with and without the effect of stress-sensitive permeability were obtained. A field case of an MSFH well was used to test the applicability of the proposed analytical method. It was found that the stress-sensitive effect negatively affected production rates of the MSFH well for the whole flow period, increasing with increasing drawdown pressure and permeability modulus. The proposed method is appropriate for various well types and reservoir scenarios. Compared with the conventional method, the proposed method can be employed to obtain more accurate production rates with little increase in the computational time.

A mathematical model for gas and water production from overlapping fractured coalbed methane and tight gas reservoirs

With the continuous expansion, exploration and development of unconventional natural gas resources, mainly coalbed methane, shale gas and tight gas, some areas overlapped by two or three types of unconventional natural gas reservoirs are explored, e.g., the Linxing, Shilou and Linfen blocks located in the east margin of the Ordos Basin, China. Gas extraction from an individual reservoir becomes not economic as gas resources are not fully recovered; thus, gas coproduction from two or multiple layers is an effective method for improving gas production. In this work, a mathematical model of gas and water two-phase flow for the coproduction of coalbed methane and tight gas is developed. The adsorption characteristics, stress-sensitive and matrix shrinkage effects on coal permeability, and the stress-sensitive effect of tight sandstone are all considered in the model. The gas production related parameters, such as bottom hole flowing pressure, reservoir pressure differences, reservoir properties (e.g., permeability, cleat compressibility of coal, and Langmuir isotherm parameters) are discussed and compared with different geological conditions. The results show that the gas and water flow from the coalbed and sandstone reservoirs show no interference between each other under a constant pressure drainage system; the sandstone reservoirs show a fast pressure drawdown with a high gas production rate decline, while the coalbed reservoir is slow in pressure drawdown and the gas production rate increases gradually. The properties of a specific reservoir have a great influence on its own gas production performance, but with no influence on the other reservoirs. It was found that a lower constant drainage pressure should be adopted in the case of stress-sensitive effects, and coal with a lower cleat compression coefficient and Poisson's ratio value is better for higher gas production. The production contribution from each layer can be acquired if a specific production rate is set. If the reservoir pressure difference between the two reservoirs is too high (for instance at least > 3 MPa in the cases studied in this work), gas and water intrusion may happen, but the reservoirs would be balanced quickly. Thus, the coproduction of coalbed methane and tight gas from one well bore is feasible, and more work should be conducted on proposing a proper drainage strategy to improve the gas resource recovery efficiency in coal-bearing strata.

Development of material balance equations for coalbed methane reservoirs considering dewatering process, gas solubility, pore compressibility and matrix shrinkage

As one of the important unconventional resources, coalbed methane (CBM) can mitigate energy shortage issue, and its efficient exploitation has received widespread attention globally. The development of CBM is of great significance to coal mine safety and energy supply. CBM reserve evaluation provides a basis for selecting development zones and determining development strategies. However, most existing CBM reserve evaluation methods do not consider the effects of dissolved gas, free gas and the difference between initial reservoir pressure and critical desorption pressure. Thus, the predicted results usually deviate from the actual reserve.In this paper, firstly, the material balance equation (MBE) for early dewatering stage considering the effect of stress sensitivity on porosity is established, and the initial free gas and dissolved gas reserves of undersaturated CBM reservoirs can be obtained. Secondly, the MBE for gas desorption stage is derived, in which the effects of stress sensitivity, matrix shrinkage and dissolved gas are considered. So the original gas in place (OGIP) of CBM reservoirs can be solved. Next, the correctness and rationality of MBEs for early dewatering stage and gas desorption stage are verified against King's MBE method and CBM dynamic analysis software. Finally, this method is applied to actual production wells.The results show that in early dewatering stage, 1−Swiαcp+αSwicwp¯Z¯−pi−p¯p¯Z¯ and WpBw−Weαp¯Z¯+GppscTZscTsc have a linear shape, and the control area of CBM reservoir can be calculated based on the slope of the straight line. In addition, the ratio of the intercept to the slope of the straight line can be used to calculate the initial free gas and dissolved gas reserves of undersaturated CBM reservoirs. During gas desorption stage, p/Z* and Gp have a linear relationship. OGIP of CBM reservoirs can be obtained by the ratio of y-intercept to the slope of the straight line. Using gas and water production data provided by CBM dynamic analysis software, the reserves of undersaturated CBM reservoirs evaluated by the proposed method are in good agreement with those from CBM dynamic analysis software, which proves that the proposed material balance equations and corresponding methods are reasonable and reliable.The material balance equations and methods presented in this paper take into account the effects of various factors such as the difference between initial reservoir pressure and critical desorption pressure, pore compressibility, water compressibility, coal matrix shrinkage, dissolved gas, and free gas. The proposed reserve calculation methods for undersaturated CBM reservoirs can provide an important basis for selecting dominant production area, determining well spacing and guiding development policy.

Advanced production decline analysis of tight gas wells with variable fracture conductivity

Abstract Considering the characteristics that the fracture conductivity formed by hydraulic fracturing varies across space and time, a new mathematical model was established for seepage flow in tight gas fractured vertical wells which takes into account the effects of dual variable conductivity and stress sensitivity. The Blasingame advanced production decline curves of the model were obtained using the finite element method with hybrid elements. On this basis, the effects of fracture space and time dual variable conductivity and stress sensitivity on Blasingame curve were analyzed. The study shows that the space variable conductivity mainly reduces decline curve value at the early stage; the time variable conductivity can result in drops of the production and the production integral curves, leading to a S-shaped curve; dual variable conductivity is the superposition of the effects given by the two variable conductivities; both time and space variable conductivities cannot delay the time with which the formation fluid flow reaches the quasi-steady state. The stress sensitivity reduces the curve value gradually rather than sharply, delaying the time the flow reaching the quasi-steady state. Ignoring the effects of variable conductivity and stress sensitivity will not affect the estimation on well controlled dynamic reserves. However, it can result in large errors in the interpretation of fractures and reservoir parameters. Conventional advanced production decline analyses of a tight gas fractured well in the Sulige gas field showed that the new model is more effective and reliable than the conventional model, and thus it can be widely applied in advanced production decline analysis of wells with the same characteristics in other gas fields.

Pressure transient analysis of multi-fractured horizontal wells in tight oil reservoirs with consideration of stress sensitivity

Multi-fractured horizontal well (MFHW) is an effective technique to develop unconventional reservoirs. Complex fracture network around the well and hydraulic fractures is formed during the fracturing process. Fracture network and hydraulic fractures are the main seepage channel which is sensitivity to the effective stress. However, most of the existing models do not take the effect of stress sensitivity into account. In this study, a new analytical model was established for MFHW in tight oil reservoirs based on the trilinear flow model. Fractal porosity and permeability were employed to describe the heterogeneous distribution of the complex fracture network, and the stress sensitivity of fracture was considered in the model. The Pedrosa substitution and perturbation method were applied to eliminate the nonlinearity of the model. By using the Laplace transformation method, the analytical solutions in Laplace domain were obtained. Then, validations were performed to show that the model is valid. Finally, sensitivity analysis was discussed. The presented model provides a new approach to the estimation of fracturing effect and can be also utilized for recognizing formation properties of tight oil reservoirs.

Improvements of the permeability experiment in coalbed methane

Although the coalbed methane’s (CBM) production is influenced by many factors, the reservoir permeability is the main parameter of coalbed methane seepage analysis. However, the experiment of CBM is still based on the experiment of conventional reservoir. In the experiment of conventional reservoir, the core will be cemented, cut, and polished, the high pressure will be used, and the nitrogen will be used as the displacement fluid. This means that the experiment is adapted to the weak stress sensitivity, high permeability, and no adsorption effect situation. But the coal has strong stress sensitivity, low permeability, and adsorption effect. This paper analyzed the common methods of CBM permeability experiment, pointed out the current problems existing in the CBM permeability experiment with the analysis of the coal character, and established a new permeability experiment equipment and method considered for the features of coal, which can reduce the experimental error caused by the limitation of experimental samples and device and improve the accuracy of the experiment.

The Effect of MAOA and Stress Sensitivity on Crime and Delinquency: A Replication Study

Across several meta-analyses, MAOA-uVNTR genotype has been associated with an increased risk for antisocial behavior among males who experienced early life adversity. Subsequently, early life stress and genetic susceptibility may have long-term effects on stress sensitivity later in life. In support of this assumption, a recent study found evidence, in two independent samples, for a three-way interaction effect (cG × E × E) such that proximate stress was found to moderate the interactive effect of MAOA-uVNTR and distal stress on crime and delinquency among males. In light of recent developments in cG × E research, we attempted to replicate these findings in an independent sample of university students. Our results failed to support any cG × E or cG × E × E effects reported in the original study. Implications of a failed replication and general concerns for future cG × E research are discussed.

Analytical model for pressure and rate analysis of multi-fractured horizontal wells in tight gas reservoirs

Multi-fractured horizontal wells (MFHWs) are effective for developing unconventional reservoirs. A complex fracture network around the well and hydraulic fractures form during fracturing. Hydraulic fractures and fracture network are sensitive to the effective stress. However, most existing models do not consider the effects of stress sensitivity. In this study, a new analytical model was established for an MFHW in tight gas reservoirs based on the trilinear flow model. Fractal porosity and permeability were employed to describe the heterogeneous distribution of the complex fracture network. The stress sensitivity of fractures was also considered in the model. Pedrosa substitution and perturbation method were applied to eliminate the nonlinearity of the model. Analytical solutions in the Laplace domain were obtained using Laplace transformation. The model was then validated and applied. Finally, sensitivity analyses of pressure and rate were discussed. The presented model provides a new approach to estimate the effect of fracturing. It can also be utilized to recognize formation properties and forecast the dynamics of pressure and the production of tight gas reservoirs.

Analysis of Two-Phase Gas–Water Flow in Carbonate Reservoirs

Gas–water relative permeability (GWRP) is measured in the tests of full-diameter cores. Based on the obtained GWRP curves, the standard normalized curves are plotted for three types of carbonate reservoirs: matrix pore, fracture and solution pore. The corresponding gas and water two-phase flow model was deduced by considering stress sensitivity and non-Darcy effect, and the IPR curve calculation and analysis of gas wells of the three types were carried out. Based on huge gap between the matrix and fracture permeability, the phenomenon of gas drive water mainly exists in the cracks. So the conventional gas–water relative permeability of fractured gas reservoirs was modified.

Dynamic and quantitative Sensitivity analysis on the efficient development of tight oil

The aim of this paper is to present dynamic and quantitative sensitivity analysis for the tight oil development with horizontal fracturing well. And a set of correlations predict the oil production and effective swept scope are built correspondingly. In this paper, a group of orthogonal schemes were designed and simulated with the CMG IMEX Simulator. And 11 parameters are filtered after extensive investigation of typical characteristics of tight oil in China and abroad. The parameters include reservoir characteristics, threshold pressure gradient and stress sensitive effect, fracturing parameters etc. And analysing each five years’ simulation results including cumulative production, oil recovery and effective flow area. The analysis result shows that the initial reservoir pressure and well bottom hole pressure, which decides whether the energy is sufficient to drive oil flow, is the most significant factor to influence the tight oil cumulative production. Secondly, reservoir thickness and porosity influence whether the reservoir oil is rich. However, for the oil recovery, the contribution of fracturing is more essential, which directly determines whether it has industrial oil production. In addition, threshold pressure gradient and stress sensitivity, the distinct seepage characteristics between tight oil and traditional reservoirs, will further exacerbate the ultra-low permeability and seepage process. The most immediate effect is that the swept scope range becomes smaller. In addition, a series mathematical model are also established for the development effect estimation through the use of multivariate regression, Through data validation, the quantitative model error ranges 5.45% from 9.29%.

Hydromechanics Model of Natural Gas Transport in Stress-sensitive Dual-porosity Medium

The assumption of constant permeability is not strictly applicable to porous media where rock properties undergo changes, such as stress-sensitive gas reservoirs. This study developed a hydromechanics model of a horizontal well in dual-porosity media considering the stress-sensitivity effect. The solution methods include variable substitution, perturbation technique, Laplace transformation, Sturm-Liouville eigenvalue theory, orthogonal transformation and numerical inversion. The results showed that the production rate decreases with the increasing of permeability modulus and the derivative curve will be warped up during the whole system late radial flow stage. The research has both theoretical and practical significance in predicting production performance and evaluating underground fluid transport in such formations.

Pressure-Transient Analysis of a Vertically Fractured Well in a Tight Oil Reservoir With Rectangular Stimulated Reservoir Volume

Summary The technique of stimulated reservoir volume (SRV) is becoming a key measure to enhance vertical-well productivity and ultimate recovery in tight oil reservoirs. After the SRV treatment, microseismic monitoring results strongly show approximately rectangular stimulated reservoir volumes with a single biwing fracture. However, most published works assumed that the SRV is approximately circular, and few works have considered a rectangular SRV. In this paper, a new analytical pressure-transient solution for vertically fractured wells (VFWs), with rectangular SRV and a single biwing fracture, is derived under constant rate. First, a two-region composite model is established to model the VFW. The inner region is simplified as rectangle dual-porosity with a single biwing fracture. In addition, this model also considers the effect of other multiple factors including stress-sensitivity effect of permeability and unsteady crossflow between matrix and fracture. Then, the trilinear flow model is extended to handle the rectangle boundary and biwing fracture; the Pedrosa's perturbation and Laplace transformation are used to solve the nonlinear equation; the Kazemi's method is adopted to simulate the unsteady crossflow; and the pressure equation for VFW is solved. After that, this analytical solution is applied to a real case from Ordos Basin to conduct equation validation. Finally, sensitivity studies are conducted to evaluate the effect of some critical parameters on the pressure behavior of VFW. The results of model validation show that there is close agreement. Results from this study show that the special flow regimes for a VFW are: (1) linear flow dominated by the biwing fracture with high conductivity, (2) SRV-width-effect flow, and (3) inner boundary-dominated flow. The linear flow is stronger with the increase of biwing-fracture length, biwing-fracture conductivity, and SRV width. As the permeability of SRV increases, the inner boundary-dominated flow becomes more dominant. Moreover, the SRV linear flow will become stronger as the SRV volume increases. This work provides a significant reference for reservoir engineers in pressure-transient analysis as well as fracturing evaluations of vertically fractured wells in tight oil reservoirs.

A Study of Nonlinear Elasticity Effects on Permeability of Stress Sensitive Shale Rocks Using an Improved Coupled Flow and Geomechanics Model: A Case Study of the Longmaxi Shale in China

Gas transport in shale gas reservoirs is largely affected by rock properties such as permeability. These properties are often sensitive to the in-situ stress state changes. Accurate modeling of shale gas transport in shale reservoir rocks considering the stress sensitive effects on rock petrophysical properties is important for successful shale gas extraction. Nonlinear elasticity in stress sensitive reservoir rocks depicts the nonlinear stress-strain relationship, yet it is not thoroughly studied in previous reservoir modeling works. In this study, an improved coupled flow and geomechanics model that considers nonlinear elasticity is proposed. The model is based on finite element methods, and the nonlinear elasticity in the model is validated with experimental data on shale samples selected from the Longmaxi Formation in Sichuan Basin China. Numerical results indicate that, in stress sensitive shale rocks, nonlinear elasticity affects shale permeability, shale porosity, and distributions of effective stress and pore pressure. Elastic modulus change is dependent on not only in-situ stress state but also stress history path. Without considering nonlinear elasticity, the modeling of shale rock permeability in Longmaxi Formation can overestimate permeability values by 1.6 to 53 times.

Time-dependent shape factors for fractured reservoir simulation: Effect of stress sensitivity in matrix system

Matrix-fracture transfer functions are the backbone of any dual-porosity or dual-permeability formulation in the modeling of fluid flow in fractured porous media. The chief feature within them is the accurate definition of shape factors. To date, there is no commonly accepted formulation of a matrix-fracture transfer function and shape factor. Many unsteady transfer formulations of shape factors for incompressible reservoirs have been presented and used. However, the assumption of incompressible reservoirs for these formulations is not consistent with the in-situ reservoir conditions, and a few have been reported on the application of time-dependent shape factor on dual-porosity numerical reservoir simulation. The focus of this study is, therefore, to find the time-dependent shape factor for the single-phase flow of stress-sensitive reservoirs. In this paper, the stress sensitive curves and corresponding fitting equations of a fractured reservoir are obtained based on the laboratory physical simulation; and, a model for the determination of the time-dependent shape factors that considers the stress sensitivity is presented; then the solution of nonlinear pressure diffusivity equation is used to derive the shape factor; finally, the shape factor obtained in this paper is segmented by time and applied to the dual-porosity numerical reservoir simulation. The Boltzmann transform, the separation variable method and the method of power series are used to solve the nonlinear governing equation by considering the stress sensitivity in matrix system. The approximate analytical model for the shape factor presented in this paper is verified using fine-grid, finite element numerical simulation. The dependency of the shape factor on the matrix stress sensitivity is also investigated. The theoretical analysis presented improved our understanding of transfer flow in fractured porous media, and provides a new method for dual-porosity numerical reservoir simulation of fractured reservoirs.

Study on stress sensitivity of lignite reservoir under salinity and pH composite system

The stress sensitivity of a coal reservoir is an important factor affecting the productivity of the coalbed methane well. Determining methods to reduce the stress sensitivity of coal reservoirs in the process of coalbed methane well drainage and recovery is of significance for the efficient development of coalbed methane. Based on a multiindex comprehensive evaluation of the stress sensitivity of a lignite reservoir under different pH and salinity, a permeability prediction model and productivity model of the coalbed methane well are established in consideration of the stress sensitivity under the influence of pH and salinity. Analysis is conducted on changes in permeability with effective stress and the mechanism involved in the stress-sensitive effect in a lignite reservoir under these two influencing factors. Results show that the relation between dimensionless permeability and effective stress is in good agreement with a negative exponential relationship. In addition, the relation between the stress-sensitive coefficient and effective stress can be divided into a fluctuation stage and a stabilization stage using 15–17 MPa as the boundary. It is also apparent that an increase in salinity is beneficial for decreasing the stress sensitivity of a reservoir under alkaline conditions, but this effect gradually decreases with an increase in the pH. Salinity has less influence on stress sensitivity under acidic conditions. In terms of pH, which is bounded by critical salinity, a lower pH is beneficial for reservoir protection in low to intermediate salinity conditions. In contrast, when the pH is higher, the reservoir is better protected. Acidic conditions involve inorganic chemical reactions, whereas alkaline conditions involve organic–inorganic reactions, and the influence of salinity on permeability sensitivity is affected by the amount of H+.

Feasibility and Applicability Analysis of CO2-ECBM Technology Based on CO2–H2O–Coal Interactions

In view of the failed field testing of CO2-ECBM technology, the feasibility and applicability of the CO2-ECBM process were analyzed based on interactions among CO2, H2O, and minerals in the coal reservoir by conducting flooding experiments of coal samples using nuclear magnetic resonance (NMR) technology. CO2 can change the wettability of the coal surface, and adsorbed water can be changed into free water. CO2 is adsorbed constantly on the coal surface, leading to the swelling of the coal matrix. The effects of the dissolution of minerals and flooding pressure can, to some extent, improve the permeability of reservoir, but the improvement of permeability is not obvious with increasing effective stress. Because of severe stress sensitivity, fluid in the ultralow-permeability and deep coal reservoir flows with difficulty. Furthermore, the swelling of the coal matrix leads to an increase of the effective stress, which, in turn, quickly reduces the permeability. It is difficult to compensate the negative effects of stress sensitivity and swelling of the coal matrix with the positive effects of CO2-ECBM technology. Therefore, the application of CO2-ECBM technology should be taken into consideration in the exploitation of ultralow-permeability and deep coal reservoir.