Development of a material balance equation for coalbed methane reservoirs accounting for the presence of water in the coal matrix and coal shrinkage and swelling

Thararoop, Prob; Karpyn, Zuleima T.; Ertekin, Turgay

doi:10.1016/j.juogr.2014.12.002

Cited by 16 publications

(6 citation statements)

References 8 publications

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“…Furthermore, water and gas are different fluids. Water can also cause adsorption deformation of coal, which is similar to the adsorption deformation of gas (Fan et al 2018;Liu et al 2018;Pan et al 2010;Thararoop et al 2015). The adsorption deformation laws of gas are also applicable to the adsorption deformation of water.…”

Section: Introductionmentioning

confidence: 96%

Combined control of fluid adsorption capacity and initial permeability on coal permeability

Wei

et al. 2022

Int J Coal Sci Technol

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The variations of strain and permeability of coal were systematically studied through the physical simulation of N2 and water injection. The effects of fluid adsorption capacity and initial permeability on strain, permeability and the dominant effect of pore pressure were discussed. The adsorption strain and strain rate of coal during water injection are significantly higher than those during N2 injection. An edge of free adsorption exists in the early phase of N2 and water injection, which is related to fluid saturation. Within this boundary, the strain rate and pore pressure are independent. Moreover, the injection time of initial stage accounts for about 20% of the total injection time, but the strain accounts for 70% of the total strain. For water injection, this boundary is about half of water saturation of coal. Besides, the influence of pore pressure on permeability is complex, which is controlled by adsorption capacity and initial permeability of coal. When the initial permeability is large enough, the effect of adsorption strain on permeability is relatively weak, and the promoting effect of pore pressure on fluid migration is dominant. Therefore, the permeability increases with increasing pore pressure. When the initial permeability is relatively low, the pore pressure may have a dominant role in promoting fluid migration for the fluid with weak adsorption capacity. However, for the fluid with strong adsorption capacity, the adsorption strain caused by pore pressure may play a leading role, and the permeability reduces first and then ascends with increasing pore pressure.

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Section: Introductionmentioning

confidence: 96%

Combined control of fluid adsorption capacity and initial permeability on coal permeability

Wei

et al. 2022

Int J Coal Sci Technol

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“…To date, the dynamic pressure of the coal reservoir is mainly calculated by two methods. One method is based on the material balance equation (MBE). − This method not only is simple and efficient but also makes full use of actual geological and production data. However, it only predicts the average reservoir pressure within a production area, which provides incomplete guidance for CBM production.…”

Section: Introductionmentioning

confidence: 99%

A Prediction Model for Pressure Propagation and Production Boundary during Coalbed Methane Development

et al. 2021

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In coalbed methane field development, an accurate understanding of dynamic propagation of reservoir pressure is crucial for predicting production potential, enhancing recovery, and engineering planning. Based on actual reservoir conditions and production data, a semi-analytical mathematical model that considers the self-regulating effects of coal reservoirs was established for both nonstimulated and hydraulically fractured vertical wells in undersaturated coal reservoirs. In the model, undersaturated coal seam is divided into the drainage area and desorption area. Material balance equations (MBE) are deduced based on the unique gas–water production mechanism of coal seams, and pressure profiles are expressed as continuous succession of steady state flow. The pressure propagation can be finally predicted by combining MBE and pressure profiles in different areas. Three hydraulically fractured vertical wells with different production characteristics in the Shizhuangnan Block, southern of Qinshui Basin are taken as examples to verify the applicability of the model. Results show that dynamic pressure propagation of a single well is accurately characterized in the early production stage, and the shape of the pressure propagation area translates from an ellipse into a circle during production; actual interference boundaries or damage boundaries are precisely predicted when interwell pressure interference is formed or a poor production strategy is adopted, respectively. Additionally, mechanism analysis under a mathematic model and orthogonal experiment evaluation are adopted to quantify the sensitivity of various parameters on the prediction results. Results show that coal reservoir physical properties, especially critical desorption pressure and porosity, mainly affect drainage radius expansion, whereas human factors and adsorption performance are the key factors influencing the desorption radius. The proposed model develops an accurate and efficient mathematical method for evaluating dynamic characteristics of pressure propagation in undersaturated coal reservoir and predicting production boundary and finally provides valuable guidance for the formulation of reasonable development plans.

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“…Yin et al [20] studied the influence of different adsorbent gases on coal deformation and permeability and pointed out that the stronger the adsorption under the same gas pressure, the greater the deformation of the coal and the lower the permeability. Based on the double pore structure characteristics of coal and considering the influence of moisture on the adsorption characteristics of coal and rock, the seepage model under the condition of solid-liquidgas coexistence was established [21]. Mitra et al and Gu et al [22][23][24] studied the non-Darcy phenomenon of gas migration in coal seams based on simplified coal seam physical models.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation on Mesoscale Mechanism of Seepage in Coal Fractures by Fluid-Sloid Coupling Method

Peng

Zhao

et al. 2021

Geofluids

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Trying to reveal the mechanism of gas seepage in coal is of significance to both safe mining and methane exploitation. A series of FEM numerical models were built up and studied so as to explore the mesoscale mechanism of seepage in coal fractures. The proposed mesoscale FEM model is a cube with micron fractures along three orthogonal directions. The distribution of velocity and pressure under fluid-solid coupling was obtained, and furthermore, the seepage flow flux and an equivalent permeability of the whole model were calculated. The influences of fracture width, outlet velocity, and in situ stress level on seepage were investigated. The numerical results show that nonlinear Darcy seepage occurs during low velocity zone. The permeability is increased linearly with the increasing of facture width and outlet velocity. A certain change of lateral coefficient of in situ stress also affects seepage. The permeability is increased sharply once deviating the isotropic spherical stress state, but it is no longer changed obviously after the lateral coefficient has been increased or decreased more than 20%. The mesoscale seepage mechanism in coal fractures has been preliminarily revealed by considering fluid-solid coupling effect, and the key factors influencing fluid seepage in coal fractures were demonstrated. The proposed methods and results will be helpful to the further study of seepage behaviour in coal with more complex structures.

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Development of a material balance equation for coalbed methane reservoirs accounting for the presence of water in the coal matrix and coal shrinkage and swelling

Cited by 16 publications

References 8 publications

Combined control of fluid adsorption capacity and initial permeability on coal permeability

Combined control of fluid adsorption capacity and initial permeability on coal permeability

A Prediction Model for Pressure Propagation and Production Boundary during Coalbed Methane Development

Numerical Simulation on Mesoscale Mechanism of Seepage in Coal Fractures by Fluid-Sloid Coupling Method

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