Relationships between mechanical and transport properties in Marcellus shale. (July 2019)

• Record Type: Journal Article
• Authors: Schwartz, B.; Elsworth, D.; Marone, C.
• Is Part Of: International journal of rock mechanics and mining sciences. Volume 119(2019)
• Page Start: 205
• Page End: 210
• Publication Date: 2019-07
• Subjects: Rock mechanics -- Periodicals; Soil mechanics -- Periodicals; Mining engineering -- Periodicals; Roches, Mécanique des -- Périodiques; Sols, Mécanique des -- Périodiques; Technique minière -- Périodiques; 624.151305
• DOI: 10.1016/j.ijrmms.2019.04.020
• Languages: English
• ISSNs: 1365-1609

Abstract

Abstract: We explore relationships among bulk modulus, crack density, and permeability through repetitive loading of Marcellus shale. Cumulative cyclic stressing (22–26 MPa with confinement of 24 MPa) is applied at a frequency of 0.05 Hz over 100, 000 cycles. Changes in acoustic velocities are used to follow changes in dynamic bulk modulus, Poisson ratio, and crack density and to correlate these with bedding-parallel measurements of methane permeability. The shale is represented as an orthotropic elastic medium containing a dominant, noninteracting fracture set separated by thin laminae. An effective continuum model links permeability evolution to the evolution of the bulk modulus and crack density. Bulk modulus is linearly related to crack density by a scaling parameter representing rock fabric and fracture geometry. The Poisson ratio and bulk modulus of the intact, uncracked shale are approximated from our data. We propose a method for tracking permeability evolution of finely laminated shales using acoustic waves. Highlights: Some shales are orthotropic materials with a dominant, noninteracting fracture set oriented parallel to bedding. When a shale exhibits a dominant fracture set, permeability evolution can be tracked with changing acoustic velocities. Changes in bulk modulus and Poisson ratio are inversely related to changes in permeability andcrack density parameter. Abstract : Plain Language Summary : Shales are increasingly important rocks for oil and gas production and carbon sequestration. Due to their tight and often disconnected internal flow paths, it is often difficult to track changes in permeability—how easily a fluid flows through a rock—that arise within the shale itself. This study shows that for some shales sound waves that can originate on the surface or within bore holes can be used to track changes in permeability. Being able to monitor permeability during liquid or gas production/injection will provide useful information to scientists and engineers for a variety of applications.