Laboratory experiments simulating poroelastic stress changes associated with depletion and injection in low‐porosity sedimentary rocks. Issue 4 (1st April 2017)

• Record Type: Journal Article
• Authors: Ma, Xiaodong; Zoback, Mark D.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 4(2017)
• Page Start: 2478
• Page End: 2503
• Publication Date: 2017-04-01
• Subjects: Bakken -- Biot coefficient -- depletion -- injection -- poroelasticity -- low‐porosity rocks; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB013668
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: We characterized the poroelastic deformation of six cores from three formations associated with the Bakken play in the Williston Basin (the Lodgepole, Middle Bakken, and Three Forks formations). All are low‐porosity, low‐permeability formations, but vary considerably in clay, kerogen, and carbonate content. The experimental program simulated reservoir stress changes associated with depletion and injection via cycling both the confining pressure ( Pc ) and pore pressure ( Pp ). We measured volumetric strain, derived the corresponding bulk modulus, and calculated the Biot coefficient ( α ). We found α, which generally ranges between 0.3 and 0.9, to vary systematically with Pc and Pp for each of the specimens tested. The effect of pore pressure on α is much larger at low simple effective stress ( σ = Pc ‐Pp ) during depletion than injection. The α decreases with σ for all pore pressures. For the same Pc and Pp, the Biot coefficient is consistently higher during injection than during depletion. Given the observed variations of α with Pc and Pp, the modeling of reservoir stress changes using a constant α could be problematic as poroelastic stress changes during depletion and injection are not likely to follow the same path. Scanning electron microscope examination of microstructures suggests that the variations of the bulk modulus and the Biot coefficient can be attributed to the abundance of compliant components (pores, microcracks, clays, and organic matter) and how they are distributed throughout the rock matrix. Key Points: Volumetric strain variations with Pc and Pp enabled the determination of the Biot coefficient ( α ) for six Bakken lithologic units The pore pressure effect on α is much larger at low ( Pc ‐Pp ) during depletion than injection. The α decreases with σ for all pore pressures For the same Pc and Pp, the Biot coefficient is generally higher during injection than during depletion