K. E. Gray Research Projects

Far-field and near-wellbore changes in permeability in depleted, anisotropic formations

Changes in permeability due to changes in the state of stress in the reservoir during depletion arise because of the strain that results from the stress changes. This influences permeability around the producing well, as well as permeability throughout the depleted reservoir that affects future wells. Various models exist for coupling stress, strain, and permeability. The simplest models relate changes in stress relative to some reference value to changes in permeability. More complex models invoke the Kozeny equation in accounting for changes in porosity, tortuosity, and surface area.

Rock properties from resistivity measurements during leak-off tests

During the initial pressure buildup of a leak off test (LOT), the increase in wellbore pressure causes porous flow of drilling fluid into the formation as well as deformation of the formation due to the pressure gradient. When the borehole pressure reaches the fracture initiation pressure, the formation yields and fractures initiate and propagate, allowing drilling fluid to leak off more rapidly into the formation.