Effect of Hydrate Dissociation and Axial Strain on the Permeability of Hydrate-Bearing Sand during the Creep Process

Abstract

Summary The relative permeability (kr) and capillary pressure (Pc) are essential components to predict the gas and water flow in hydrate-bearing reservoirs. In this study, we analyze the dynamic gas and water relative permeability (krg and krw) during the continuous creep process of hydrate-bearing sand (HBS) under conditions of thermal-stimulated hydrate dissociation using computed tomography (CT) and the pore network model (PNM). The dynamic sample region extraction method for CT images is adopted by considering the deformation of HBS in the vertical direction. The pore structure of the HBS was visualized and reconstructed by CT scanning. The 3D pore network is built after image processing; then, gas and water flow processes are analyzed by the PNM. The results show that krw is highly consistent with two main pore structure factors: the pore space size and connectivity variation. krg is greatly affected by an increasing number of narrow flow channels in the HBS during the creep process. In addition, the irreducible water saturation (Swir) during the creep process is mainly affected by the joint effect of the pore size, throat size, and pore space connectivity. The preferential flow directions of the gas and water change from vertical to horizontal along with the progression of creep.