Abstract
Four core samples of outcrop type shale from Mancos, Marcellus, Eagle Ford, and Barnett shale formations were studied to evaluate the productivity performance and reservoir connectivity at elevated temperature and pressure. These laboratory experiments were conducted using hydrostatic permeability system with helium as test gas primarily to avoid potential significant effects of adsorption and/or associated swelling that might affect permeability. It was found that the permeability reduction was observed due to increasing confining stress and permeability improvement was observed related to Knudsen flow and molecular slippage related to Klinkenberg effect. Through the effective permeability of rock is improved at lower pore pressures, as 1000 psi. The effective stress with relatively high flow path was identified, as 100-200 nm, in Eagle Ford core sample. However other three samples showed low marginal flow paths in low connectivity.
Highlights
A common characteristic of all shale gas reservoirs is their extremely low intrinsic permeability
When describing how volumetric strain varies with effective stress, the appropriate coefficient is defined as the Biot coefficient, α [9,10,11,12] and effective stress law defined as confining pressure and pore pressure combination identify the permeability of the rock through effective stress law as below: σeff = Cp - χPp
Permeability was measured at pore pressures from 1000-4000 psi (6.9-27.6 MPa), confining pressures from 2000-8000 psi (13.8-55 MPa), and simple effective stresses ranging from 1000-4000 psi (6.9-27.6 MPa)
Summary
A common characteristic of all shale gas reservoirs is their extremely low intrinsic permeability. Researchers [1,2] have studied the sensitivity of permeability to confining pressure at a single pore pressure. As gas is produced and reservoir pressure declines, two different processes alter the permeability of the rock. These processes can be categorized as stress effects and flow regime effects. The variation of permeability with effective stress has been studied fairly extensively for sandstones and carbonates [5,6,7]. This is sometimes referred to as slippage flow, in reference to molecules slipping past one another. Mehran University Research Journal of Engineering & Technology, Volume 37, No 1, January, 2018 [p-ISSN: 0254-7821, e-ISSN: 2413-7219] 159
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