Petrophysical and Hydromechanical Behaviors of Methane Hydrate-Bearing Pressure Cores
Tohoku University, Japan
Yi Fang is an assistant professor of Geological Engineering at South Dakota School of Mines and Technology. He studies flow and deformation in both hard and soft rocks. His research goal is first to understand the coupled multi-physical processes occurring in these rocks, and then address the associated challenges in geoengineering activities. Yi has a multidisciplinary background. He was a research associate in the Institute for Geophysics at the University of Texas at Austin, focusing on laboratory characterization of methane hydrate systems in the deepwater Gulf of Mexico. He earned his Ph.D. degree in Energy and Mineral Engineering from Pennsylvania State University in late 2017, focusing on fluid flow and induced seismicity in fractured rocks. Before that, he received his M.Sc. in Geology from California State University, Long Beach in 2013, working on stable isotope analysis for fluid-rock interactions. He received his B.E. in Civil Engineering from China University of Geosciences (Wuhan) in 2011. Yi is the recipient of 2020 Rocha Medal Runner-up Certificate from ISRM, and he serves as the future leader (2018 class) of the American Rock Mechanics Association (ARMA).
Introduction of the Lecture
Methane hydrate is potentially a source of high energy density fuel. It is a crystalline solid composed of methane molecules trapped in cages of water molecules, stable at low temperatures and/or high pressures. The experimental characterization of the petrophysical and hydromechanical properties of hydrate-bearing core samples are essential for the engineering development of this energy resource. However, the laboratory measurements are incredibly challenging because sub-sampling, sample preparation, and testing must be conducted at high pressure and low temperature. This work develops experimental protocols to accurately and systematically characterize the relationship among porosity, permeability, compressibility, and the ratio of horizontal to vertical effective stress (K0) in hydrate-bearing sandy silts from Green Canyon Block 955 (GC 955) in the deepwater Gulf of Mexico. The samples have an in-situ porosity of 0.38 to 0.40 and in-situ effective permeability (keff) ranges from 0.1 md (1.0×10-16 m2) to 2.4 md (2.4×10-15 m2) in these natural sandy silts cores with hydrate occupying 83% to 93% of the pore space. The hydrate-bearing sediments are stiffer than the equivalent hydrate-free sediments; the K0 stress ratio is greater for hydrate-bearing core samples relative to the hydrate-free core samples. The porosity decreases by 0.01 to 0.02 when the hydrate is dissociated at the in-situ stress. The hydrate in the sediment pores is interpreted to be a viscoelastic material that behaves like a fluid over experimental timescales, yet cannot escape the sediment skeleton. It carries a fraction of the vertical load and transfers the applied stress laterally. This work provides insight into the gas hydrate reservoir formation. It also aids in predicting gas production potential and stress state evolution of hydrate reservoirs in the deepwater Gulf of Mexico.