Hydrate petroleum system approach to natural gas hydrate exploration

Natural gas hydrate (NGH) is a solid crystalline material composed of water and natural gas (primarily methane) that is stable under conditions of moderately high pressure and moderately low temperature found in permafrost and continental margin sediments. A NGH petroleum system is different in a number of important ways from conventional petroleum systems related to large concentrations of gas and petroleum. The critical elements of the NGH petroleum system are: (1) a gas hydrate stability zone (GHSZ) in which pressure and temperature lie within the field of hydrate stability, creating a thermodynamic trap of suitable thickness for NGH concentrations to form; (2) recent and modern gas flux into the GHSZ along migration pathways; and (3) suitable sediment host sands within the GHSZ. These elements have to be active now and in the recent geological past. Exploration in continental margin sediments includes basin analysis to identify source and host sediment likelihood and disposition, potential reservoir localization using existing seismic analysis tools for locating turbidite sands and estimating NGH saturation, and deposit characterization using drilling and logging. Drilling has validated first-order seismic analysis techniques for identifying and quantifying NGH using rock physics mechanical models.