Laboratory characterisation of fracture compressibility for coal and shale gas reservoir rocks: A review

Tan, Yunliang; Pan, Zhejun; Feng, Xia‐Ting; Zhang, Dongxiao; Connell, Luke D.; Li, Shaojun

doi:10.1016/j.coal.2019.01.010

Cited by 126 publications

(50 citation statements)

References 66 publications

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“…This assumption is supported by the literature which shows the matrix compressibility is three to four orders of magnitude lower than cleat compressibility: hence matrix strain can be assumed negligible under all but the most severe stresses. For example, Guo, et al (2014) reported the matrix compressibility for 21 different ranks bituminous coals between 0.3451×10 -4 MPa -1 to 2.9060×10 -4 MPa -1 compared to cleat compressibilities of 0.1122 MPa -1 , 0.15 MPa -1 , 0.1017 MPa -1 and 0.79591 MPa -1 as reported by Zheng, et al (2012), Peng, et al (2017), Connell (2016) and ), respectively, any many other reviewed in (Tan, et al 2019)…”

Section: Mechanistic Approachmentioning

confidence: 90%

“…the face and butt cleats since in practice these dominate the transport of fluid to the well. We reduce our experimental results as follow: First, the measured strain is scaled using equation (11) to provide the change over the whole length of the 40 mm wide face of the coal (11) where ε is the strain perpendicular to the face cleat (ε F ) and butt cleat (ε B ) directions, L gauge = 5 mm is the length of the strain gauge, n=8 is the number of strain gauges (40/L gauge ) that can be mounted in series on a 40 mm wide face of coal sample.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Raza

Rufford

et al. 2019

International Journal of Coal Geology

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This paper presents a novel method to calculate the anisotropic and stress-dependent coal permeability by determining cleat compressibility using the Mercury Intrusion Porosimetry (MIP) and stress-strain measurements. Cleat compressibility is often assumed isotropic and constant in the literature and is usually obtained by numerical fitting to a matchstick permeability model e.g. the model by Seidle, et al. (1992) despite the gross simplification of this representation of the coal pore network. This paper provides a method to calculate anisotropic cleat compressibility using only MIP and stress-strain measurements which are easy to conduct, and without permeability information, which is harder to come by, requiring laboratory experiments on the core or through fitting field data. We report the measured stress-strain behaviour of a coal sample, with hydrodynamic loading/unloading over the range 0.5-4.0 MPa, and the permeability in face cleat (k F ) and butt cleat (k B ) directions using the Triaxial Stress Permeameter (TSR). The stress-strain measurement is used to calculate the anisotropic modulus of elasticity (E F , E B, and E V ) in face cleat, butt cleat and bedding plane directions, and cleat compressibility in the face cleat (C fF ) and butt cleat (C fB ) directions using the fractal dimension analysis with MIP measurement. Finally, the cleat compressibilities are used to calculate the anisotropic coal permeability by Seidle, et al. (1992) permeability model and compared with the measured permeability of the coal sample.

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Section: Mechanistic Approachmentioning

confidence: 90%

Section: Accepted Manuscriptmentioning

confidence: 99%

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Raza

Rufford

et al. 2019

International Journal of Coal Geology

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“…Evolution. Extensive experimental results show that gas adsorption-induced matrix swelling has a significant impact on the dual-porosity structure of coal and its permeability [56]. Laboratory measurement permeability results are usually interpreted by a matchstick or cubic geometry model that the coal matrix blocks are assumed to be completely separated by through-going fractures.…”

Section: Implication Of Cleat-matrix Interaction On Permeabilitymentioning

confidence: 99%

Interaction of Cleat-Matrix on Coal Permeability from Experimental Observations and Numerical Analysis

et al. 2019

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Gas transport through porous coal contains gas laminar flow in the cleat network and gas adsorption/diffusion in the matrix block. Since permeable capacity of the cleat is greater than that of the matrix, change of the matrix pressure readily lags behind change in the cleat pressure. Such unsynchronized pressure changes can result in a complex compatible deformation of a cleat-matrix system, significantly affecting the coal permeability. In this paper, we investigated the cleat-matrix interaction on coal permeability by using a modified pressure pulse decay method integrated with numerical analysis. The experimental results indicate that the bulk volume of the coal sample rapidly expanded at the beginning of gas injection, and then the volume expansion rate of the coal sample slowed down as the downstream pressure of the coal sample gradually equilibrated with the upstream pressure. During this process, the coal permeability was observed to gradually decrease with time. Numerical analysis results indicate that gas transport from the cleat to the matrix can attenuate the differential pressure between the cleat and the matrix. A smaller ratio of initial matrix permeability to initial cleat permeability can prolong decay duration of the differential pressure inside the cleat-matrix system. Although the coal sample is subjected to a stress-controlled condition, the coal permeability response to gas diffusion is closer to the case using a constant volume boundary. The dynamic change of coal permeability is significantly affected by the cleat-matrix interaction, in cases where the short-term change is mainly attributable to the cleat network and the long-term change is controlled by matrix swelling/shrinkage.

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“…Therefore, C f is one of the key parameters to describe the dynamic change in reservoir permeability, which is difficult to be obtained directly in the field. 25 Coal has a typical dual pore structure, and its fracture system determines reservoir permeability. However, directly measuring fractures and their compressibility by conventional experiments was time consuming and inaccurate.…”

Section: Introductionmentioning

confidence: 99%

Physical Experiment and Numerical Simulation of the Depressurization Rate for Coalbed Methane Production

et al. 2020

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The influence of the depressurization rate on coalbed methane desorption and percolation was studied using physical experiment and numerical simulation. First, low-field nuclear magnetic resonance technology provided a new approach to conduct desorption experiments with different depressurization schemes and obtain the compressibility ( C f ) of coal samples. Then, the productivity calculation of different depressurization schemes was carried out via numerical simulation. The results showed that the first-slow-then-fast (FSTF) depressurization scheme had the highest desorption efficiency (94%), followed by one-stop desorption (85%), first-fast-then-slow desorption (79%), and uniform depressurization desorption (61%). T 2 cutoff values and the corresponding compressibility were obtained by the saturation–centrifugation method and spectral morphology method, and a high-precision permeability expression for dynamic evaluation of numerical simulation was established by the historical production data fitting approach. Through numerical simulation, high production efficiency can be achieved using depressurization rates of medium (15 kPa/d) and FSTF schemes (8 & 50 kPa/d), and depressurization funnel expansion in the single-phase water flow stage plays a decisive role in stable and high-yield production in the later stage. Thus, the FSTF pressure reduction strategy could be advocated to promote gas production. Slow depressurization should be applied in ineffective desorption and the slow desorption stage for saturated coal seam or single-phase flow stage for undersaturated coal seam, given the higher single-phase water permeability. During the rapid and sensitive desorption stage, rapid depressurization is recommended because of large desorption capacity and low water phase permeability. This paper provides a possibility for the optimization of coalbed methane field production management.

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Laboratory characterisation of fracture compressibility for coal and shale gas reservoir rocks: A review

Cited by 126 publications

References 66 publications

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Anisotropic coal permeability estimation by determining cleat compressibility using mercury intrusion porosimetry and stress–strain measurements

Interaction of Cleat-Matrix on Coal Permeability from Experimental Observations and Numerical Analysis

Physical Experiment and Numerical Simulation of the Depressurization Rate for Coalbed Methane Production

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