scholarly journals Characterization of Permeability Changes in Coal of High Rank during the CH4-CO2 Replacement Process

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
X. M. Ni ◽  
Q. F. Jia ◽  
Y. B. Wang
Keyword(s):  
Effective Stress ◽  
Bituminous Coal ◽  
Gas Adsorption ◽  
Gas Injection ◽  
Testing Machine ◽  
Injection Pressure ◽  
Confining Pressure ◽  
High Rank ◽  
Replacement Process ◽  
Matrix Expansion

The influences of coal matrix expansion/contraction and effective stress on the permeability of coal with different thermal maturities are different during the CH4-CO2 replacement process due to different mechanical properties and gas adsorption capacities. To accurately predict the variation law of coal permeability during the CH4-CO2 replacement process, it is critical to understand how the matrix expansion/contraction and effective stress affect the permeability of coal at different thermal maturities during the CH4-CO2 replacement. In this study, the permeability of two coal specimens with anthracite and high-rank bituminous coal during the CH4-CO2 replacement process under different confining and injection pressures was tested using a CBM replacement testing machine. The results demonstrate that with decreasing gas injection pressure, the permeability of the two coal specimens exhibited a U-shaped correlation under different confining pressures. Under the same gas injection pressure, with increasing effective stress, the permeability presented a negative exponential decrease and the permeability of the anthracite decreased more significantly. Moreover, under the same confining pressure, with increasing gas injection pressure, the decreasing permeability agreed with Langmuir curve and the permeability of high-rank bituminous coal was more significantly reduced.

Control Mechanism of the Effective Stress on Nano-Micro Pores and the Permeability of High-Rank Coals

2021 ◽  
Vol 21 (1) ◽  
pp. 484-494
Author(s):  
Xiaofeng Ji ◽  
Dangyu Song ◽  
Shaokai Yu ◽  
Kaikai He ◽  
Yunbo Li
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Gas Adsorption ◽  
Initial Permeability ◽  
High Rank ◽  
Control Factors ◽  
Reservoir Permeability ◽  
Variation Mechanism ◽  
Coal Reservoir ◽  
The Impact

To study the change and main control factors of the high-rank coal reservoir permeability in deep coal seams, permeability tests under different stresses and gas pressures were carried out in the laboratory. The development and distribution of nano-micro pores and fractures in the coal matrix were analyzed and observed by mercury intrusion porosimetry, gas adsorption, scanning electron microscope and computed tomography to reveal the permeability variation mechanism. The results showed that the initial permeability of the coal samples ranged from 0.0114 mD to 0.2349 mD when the effective stress was 0 MPa, and it clearly varied among different samples. The permeability of all the coal samples was very sensitive to the effective stress and decreased exponentially with the increase of the effective stress. The increase of the pore pressure also led to a decrease of the permeability, whereas the impact of the pore pressure on permeability was less obvious compared with the effective stress. Sub-nanopores, nanopores, micro-fractures and larger fractures are all developed in the coal samples. Connected larger fractures were the main gas migration channels in permeability determination, and the narrowing, disconnection, and closure of the fractures caused by the increase of the effective stress were the most important reasons for significant reduction of permeability.

scholarly journals Gas Permeability Change with Deformation and Cracking of a Sandstone under Triaxial Compression

2021 ◽  
Author(s):  
Yuan-Jian LIN ◽  
Jiang-Feng LIU ◽  
Tao CHEN ◽  
Shi-Jia MA ◽  
Pei-Lin WANG ◽  
...  
Keyword(s):  
Gas Permeability ◽  
Axial Stress ◽  
Triaxial Compression ◽  
Gas Injection ◽  
Injection Pressure ◽  
Confining Pressure ◽  
Loading Path ◽  
Permeability Evolution ◽  
Axial Pressure ◽  
Triaxial Cell

Abstract In this paper, a THMC multi-field coupling triaxial cell was used to systematically study the evolution of gas permeability and the deformation characteristics of sandstone. The effects of confining pressure, axial pressure and air pressure on gas permeability characteristics were fully considered in the test. The gas permeability of sandstone decreases with increasing confining pressure. When the confining pressure is low, the variation of gas permeability is greater than the variation of gas permeability at high confining pressure. The gas injection pressure has a significant effect on the gas permeability evolution of sandstone. As the gas injection pressure increases, the gas permeability of sandstone tends to decrease. At the same confining pressure, the gas permeability of the sample during the unloading path is less than the gas permeability of the sample in the loading path. When axial pressure is applied, the axial stress has a significant influence on the permeability evolution of sandstone. When the axial pressure is less than 30 MPa, the gas permeability of the sandstone increases as the axial pressure increases. At axial pressures greater than 30 MPa, the permeability decreases as the axial pressure increases. Finally, the micro-pore/fracture structure of the sample after the gas permeability test was observed using 3D X-ray CT imaging.

scholarly journals Gas Permeability Change With Deformation and Cracking of a Sandstone Under Triaxial Compressiongas Permeability Change With Deformation and Cracking of a Sandstone Under Triaxial Compression

2022 ◽  
Author(s):  
Yuan-Jian LIN ◽  
Jiang-Feng LIU ◽  
Tao CHEN ◽  
Bing-Xiang HUANG ◽  
Kundwa Marie Judith ◽  
...  
Keyword(s):  
Gas Permeability ◽  
Triaxial Compression ◽  
Gas Injection ◽  
Injection Pressure ◽  
Confining Pressure ◽  
Loading Path ◽  
Permeability Change ◽  
Permeability Evolution ◽  
Axial Pressure ◽  
Triaxial Cell

Abstract In this paper, a THMC (Thermal-Hydrological-Mechanical-Chemical) multi-field coupling triaxial cell was used to systematically study the evolution of gas permeability and the deformation characteristics of sandstone. The effects of confining pressure, axial pressure, and air pressure on gas permeability characteristics were fully considered in the test. The gas permeability of sandstone decreases with increasing confining pressure. When the confining pressure is low, the variation of gas permeability is greater than the variation of gas permeability at high confining pressure. The gas injection pressure has a significant effect on the gas permeability evolution of sandstone. As the gas injection pressure increases, the gas permeability of sandstone tends to decrease. At the same confining pressure, the gas permeability of the sample during the unloading path is less than the gas permeability of the sample in the loading path. When axial pressure is applied, it has a significant influence on the permeability evolution of sandstone. When the axial pressure is less than 30 MPa, the gas permeability of the sandstone increases as the axial pressure increases. At axial pressures greater than 30 MPa, the permeability decreases as the axial pressure increases. Finally, the micro-pore/fracture structure of the sample after the gas permeability test was observed using 3D X-ray CT imaging.

scholarly journals Experimental Study on the Effects of Stress Variations on the Permeability of Feldspar-Quartz Sandstone

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-15 ◽  
Author(s):  
Fugang Wang ◽  
Zhaoxu Mi ◽  
Zhaojun Sun ◽  
Xufeng Li ◽  
Tianshan Lan ◽  
...  
Keyword(s):  
Injection Pressure ◽  
Confining Pressure ◽  
Repeated Loading ◽  
Micropore Structure ◽  
Injection Process ◽  
Reservoir Permeability ◽  
Stress Changes ◽  
Cyclic Variations ◽  
Loading And Unloading ◽  
Stress Variations

The multistage and discontinuous nature of the injection process used in the geological storage of CO2 causes reservoirs to experience repeated loading and unloading. The reservoir permeability changes caused by this phenomenon directly impact the CO2 injection process and the process of CO2 migration in the reservoirs. Through laboratory experiments, variations in the permeability of sandstone in the Liujiagou formation of the Ordos CO2 capture and storage (CCS) demonstration project were analyzed using cyclic variations in injection pressure and confining pressure and multistage loading and unloading. The variation in the micropore structure and its influence on the permeability were analyzed based on micropore structure tests. In addition, the effects of multiple stress changes on the permeability of the same type of rock with different clay minerals content were also analyzed. More attention should be devoted to the influence of pressure variations on permeability in evaluations of storage potential and studies of CO2 migration in reservoirs in CCS engineering.

scholarly journals The binary gas sorption in the bituminous coal of the Huaibei Coalfield in China

2018 ◽  
Vol 36 (9-10) ◽  
pp. 1612-1628 ◽  
Author(s):  
Lei Zhang ◽  
Zhiwei Ye ◽  
Mingxue Li ◽  
Cun Zhang ◽  
Qingsheng Bai ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Sorption Capacity ◽  
Bituminous Coal ◽  
Gas Adsorption ◽  
Langmuir Equation ◽  
Separation Coefficient ◽  
Gas Sorption ◽  
Langmuir Adsorption ◽  
Gas Molecules ◽  
Huaibei Coalfield

Knowledge of the gas sorption characteristics of a coal not only helps to explain the mechanism of enhanced coalbed methane recovery but also provides an important basis for simultaneous coal and gas extraction. In consequence, the pure and binary gas excess sorption capacity of methane, carbon dioxide, and nitrogen of bituminous coal samples derived from the Xutuan Coal Mine in Huaibei coalfield, in Anhui Province in China, was measured using the volumetric method. The fitting analysis of the pure gas Langmuir adsorption model was carried out. The binary gas excess sorption measurement showed that the final sorption capacity of bituminous samples was the same no matter what the gas adsorption order of competitive adsorption and displacement adsorption. Hence, coal gas adsorption is physical adsorption, i.e. the different adsorption and desorption process of gas molecules does not affect the final adsorption amount of coal to each component of gas. Using the fitting parameters obtained by the Langmuir equation, the extended Langmuir equation was used to predict the adsorption capacity for each component of the binary gas. The comparison between predicted adsorption capacity and measured adsorption capacity showed that the extended Langmuir equation can better describe the trend of the adsorption isotherm curves of a binary gas under different pressures. The separation coefficient and displacement coefficient were defined from Langmuir adsorption theory. The separation coefficient involves the proportion of each component in the free phase and the proportion of each component in the adsorption phase. The displacement coefficient involves the displacement ability of gas molecules at adsorption sites by free gas molecules.

Fluid pressure response to undrained compression in saturated sedimentary rock

Geophysics ◽  
1986 ◽  
Vol 51 (4) ◽  
pp. 948-956 ◽  
Author(s):  
Douglas H. Green ◽  
Herbert F. Wang
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Wave Attenuation ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Pressure Response ◽  
Additional Parameter ◽  
Seismic Wave Velocity ◽  
Specific Storage ◽  
Order Of Magnitude

The pore pressure response of saturated porous rock subjected to undrained compression at low effective stresses are investigated theoretically and experimentally. This behavior is quantified by the undrained pore pressure buildup coefficient, [Formula: see text] where [Formula: see text] is fluid pressure, [Formula: see text] is confining pressure, and [Formula: see text] is the mass of fluid per unit bulk volume. The measured values for B for three sandstones and a dolomite arc near 1.0 at zero effective stress and decrease with increasing effective stress. In one sandstone, B is 0.62 at 13 MPa effective stress. These results agree with the theories of Gassmann (1951) and Bishop (1966), which assume a locally homogeneous solid framework. The decrease of B with increasing effective stress is probably related to crack closure and to high‐compressibility materials within the rock framework. The more general theories of Biot (1955) and Brown and Korringa (1975) introduce an additional parameter, the unjacketed pore compressibility, which can be determined from induced pore pressure results. Values of B close to 1 imply that under appropriate conditions within the crust, zones of low effective pressure characterized by low seismic wave velocity and high wave attenuation could exist. Also, in confined aquifer‐reservoir systems at very low effective stress states, the calculated specific storage coefficient is an order of magnitude larger than if less overpressured conditions prevailed.

Sonic properties as a signature of overpressure in the Marcellus gas shale of the Appalachian Basin

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. D235-D249 ◽  
Author(s):  
Yaneng Zhou ◽  
Saeid Nikoosokhan ◽  
Terry Engelder
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Gamma Ray ◽  
Confining Pressure ◽  
Appalachian Basin ◽  
Burial Depth ◽  
Regression Analyses ◽  
Gas Shale ◽  
Stress Coefficient ◽  
Heterogeneous Rock

The Marcellus Formation, a Devonian gas shale in the Appalachian Basin, is a heterogeneous rock as the result of a complex depositional, diagenetic, and deformational history. Although it is overpressured over a large portion of its economic area, the origin and distribution of pore pressure within the gas shale are not well-understood. We have used the sonic properties of the Marcellus and statistical analyses to tackle this problem. The sonic data come from a suite of 53 wells including a calibration well in the Appalachian Basin. We first analyze the influence of various extrinsic and intrinsic parameters on sonic velocities with univariate regression analyses. The sonic velocities of the Marcellus in the calibration well generally decrease with an increase in gamma-ray american petroleum institute (API) and increase with density and effective stress. Basin-wide median sonic velocities generally decrease with an increase in median gamma-ray API and pore pressure and increase with burial depth (equivalent confining stress), effective stress, and median density. Abnormal pore pressure is verified by a stronger correlation between the median sonic properties and effective stress using an effective stress coefficient of approximately 0.7 relative to the correlation between the median sonic properties and depth. The relatively small effective stress coefficient may be related to the fact that natural gas, a “soft” fluid, is responsible for a basin-wide overpressure of the Marcellus. Following the univariate regression analyses, we adopt a multiple linear regression model to predict the median sonic velocities in the Marcellus based on median gamma-ray intensity, median density, thickness of the Marcellus, confining pressure, and an inferred pore pressure. Finally, we predict the pore pressure in the Marcellus based on median sonic velocities, median gamma-ray intensity, median density, thickness of the Marcellus, and confining pressure.

scholarly journals Experimental study of the moisture content influence on CH4 adsorption and deformation characteristics of cylindrical bituminous coal core

2018 ◽  
Vol 36 (7-8) ◽  
pp. 1512-1537 ◽  
Author(s):  
Dingyi Hao ◽  
Lei Zhang ◽  
Mingxue Li ◽  
Shihao Tu ◽  
Cun Zhang ◽  
...  
Keyword(s):  
Moisture Content ◽  
Adsorption Capacity ◽  
Exponential Decay ◽  
Coal Mine ◽  
Bituminous Coal ◽  
Gas Adsorption ◽  
Decay Function ◽  
Exponential Decay Function ◽  
Adsorption Deformation ◽  
Original Moisture

Moisture content in coal is an important factor affecting the coal seam gas extraction. It directly affects the storage and flow of gas in bituminous coal. In this paper, the cylindrical bituminous coal cores of Xutuan coal mine in Huaibei coal mine group were studied as experimental objects, using the laboratory self-designed experimental device Gas Adsorption and Strain Testing Apparatus system. The influence of the bituminous coal moisture content on gas adsorption characteristics was studied. Drying experiments of coal samples showed that they lose the original moisture content following the exponential decay function of time. At wetting, the saturated moisture content in coal samples increased following the Exponential Association function of time. The experimental results show that the average original moisture content and average saturated moisture content of raw coal samples are 1.3 and 2.4%, respectively. On this basis, the gas adsorption experiments on samples with different moisture contents under different gas pressures were carried out. With the moisture content increase, the gas adsorption capacity and saturation value decreased and the decrease rate gradually reduced. The single exponential decay function describes the gas adsorption capacity dependence on moisture content. Moisture content also affects the adsorption deformation of bituminous coal. At high moisture content, the adsorption deformation of bituminous coal is less.

Study on Minimum Miscible Pressure and Oil Displacement Law for CO2 Flooding

2011 ◽  
Vol 391-392 ◽  
pp. 1051-1054
Author(s):  
Shu Li Chen ◽  
Wen Xiang Wu ◽  
Jia Bin Tang
Keyword(s):  
Oil Recovery ◽  
Gas Injection ◽  
Injection Pressure ◽  
Water Flooding ◽  
Tube Model ◽  
Gas Oil ◽  
Core Flooding ◽  
Oil Displacement ◽  
Gas Flooding ◽  
Cumulative Recovery

In laboratory, the minimum miscible pressure (MMP) of oil and CO2 was studied by using a slim tube model. The results showed that the greater the gas injection pressure, the higher the cumulative recovery. The gas breakthrough when the gas was injected with a volume of 0.7~0.8PV, the trend of cumulative recovery increase slowed down and the produced gas-oil ratio increased dramatically. Core flooding experiments were carried to compare the effects of CO2 and water flooding. As a result, the ultimate oil recovery of CO2 flooding increased with the increase of gas injection pressure. If the gas flooding was miscible, the ultimate recovery of CO2 flooding was generally higher than that of water flooding.

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