Characteristics of Possible Methane Gas Hydrate Reservoirs: The Cretaceous Nanushuk and Colville Groups, National Petroleum Reserve in Alaska

摘要

Methane gas hydrates are known to exist in nature and represent a resource of large potential. Conditions necessary for methane hydrate formation occur in a wide variety of environments, including the permafrost regions of the National Petroleum Reserve in Alaska (NPRA). Water and methane gas are required to form methane gas hydrates, and their presence is dependent, in part, on the porosity and permeability of the potential reservoir rocks in the NPRA. Fifty-two very-fine- to medium-grained sandstone samples from 19 wells and core tests in the NPRA were examined. Gas producing and nonproducing strata from both the Cretaceous Nanushuk and Colville groups strata were sampled. Visual and statistical examinations indicated significant differences in petrologic constituents, grain size, porosity, and permeability between the Nanushuk and Colville samples. Differences also existed between gas producing and nonproducing units. High clay content, severe compaction, and the presence of swelling clays have reduced the porosity, permeability, and reservoir potential of the sampled strata. The inability to test extremely friable material from the Simpson Wells and Core Tests may have reduced the mean values of porosity and permeability of the samples. Further study should be focused on reservoir characteristics of the rocks in the methane gas hydrate stability zone in the Simpson area of the NPRA. Consideration should be given to swelling clays and the possibility that their presence in a well may mimic the characteristics of methane gas hydrate. 36 refs., 9 figs., 12 tabs. (ERA citation 11:053403)