A new coal-permeability model: Internal swelling stress and fracture-matrix interaction Hui-Hai Liu* and Jonny Rutqvist Earth Sciences Division Lawrence Berkeley National Laboratory Berkeley, CA 94720 USA * Corresponding author. Tel: +1-510-486-6452; fax: +1-510-486-5686. E-mail address: hhliu@lbl.gov

A new coal-permeability model: Internal swelling stress and fracture-matrix interaction

In the case of rock-fluids interaction, numerous studies have mainly focused on field and numerical simulations regarding the existence of toxic gases and investigations about the possibility of gasburst. This paper is related to the development of experimental investigations for granite formations on samples obtained from Creighton mine, Sudbury, Canada. An experimental methodology was developed for intact samples submitted to uniaxial compression for a certain level of temperature, with the monitoring of gas releasing from the rock. A detailed description of the rock-gas interaction apparatus is made. The rock cores were obtained at 2,400 m deep from the mine and results from a sample are presented, as well as theoretical assumptions are discussed. Finally, some conclusions about the investigations on pre-existing fluids in fractured rocks are presented.

Investigations on Gas Flow in Cracked Granite Samples

Shale gas reservoirs like coalbed methane (CBM) reservoirs are promising targets for geological sequestration of carbon dioxide (CO2). However, the evolution of permeability in shale reservoirs on injection of CO2 is poorly understood unlike CBM reservoirs. In this study, we report measurements of permeability evolution in shales infiltrated separately by nonsorbing (He) and sorbing (CO2) gases under varying gas pressures and confining stresses. Experiments are completed on Pennsylvanian shales containing both natural and artificial fractures under nonpropped and propped conditions. We use the models for permeability evolution in coal (Journal of Petroleum Science and Engineering, Under Revision) to codify the permeability evolution observed in the shale samples. It is observed that for a naturally fractured shale, the He permeability increases by approximately 15% as effective stress is reduced by increasing the gas pressure from 1 MPa to 6 MPa at constant confining stress of 10 MPa. Conversely, the CO2 permeability reduces by a factor of two under similar conditions. A second core is split with a fine saw to create a smooth artificial fracture and the permeabilities are measured for both nonpropped and propped fractures. The He permeability of a propped artificial fracture is approximately 2- to 3fold that of the nonpropped fracture. The He permeability increases with gas pressure under constant confining stress for both nonpropped and propped cases. However, the CO2 permeability of the propped fracture decreases by between one-half to one-third as the gas pressure increases from 1 to 4 MPa at constant confining stress. Interestingly, the CO2 permeability of nonpropped fracture increases with gas pressure at constant confining stress. The permeability evolution of nonpropped and propped artificial fractures in shale is found to be similar to those observed in coals but the extent of permeability reduction by swelling is much lower in shale due to its lower organic content. Optical profilometry is used to quantify the surface roughness. The changes in surface roughness indicate significant influence of proppant indentation on fracture surface in the shale sample. The trends of permeability evolution on injection of CO2 in coals and shales are found analogous; therefore, the permeability evolution models previously developed for coals are adopted to explain the permeability evolution in shales.

/pdf/permeability-evolution-in-sorbing-media-analogies-between-4s1lvjaqic.pdf

Permeability evolution in sorbing media: analogies between organic‐rich shale and coal

Complex Process Couplilngs in systems pushed far-from-equilibrium: Applications in CO2 sequestration in carboniferous formation

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Complex Process Couplilngs in systems pushed far-from-equilibrium: Applications in CO2 sequestration in carboniferous formation