Stability and flux of methane in the deep crust - a review
- Geological Survey, Denver, CO (United States)
Empirical observations and theoretical calculations demonstrate that methane is stable in the crust to temperatures of 800[degrees]C and pressures of 10 kbar or greater. These conditions are equivalent to depths of at least 35 to 40 km. Methane is most stable in metasedimentary crustal rocks that contain graphite. The concept of a [open quotes]deadline[close quotes] for methane is clearly irrelevant in graphitic metasediments. Based on the volume of fluid necessary to form quartz veins, the estimates of the possible flux of methane from depth in the crust are large, on the order of 10's to 100's of Tcf (3 to 30x10[sup 11] m[sup 3]) from single giant vein systems or from areas of focused flow in metamorphic terranes. Crustally generated methane can accumulate through phase separation and buoyant rise of a separate gas phase but may be accompanied by significant amounts of carbon dioxide and nitrogen. The estimated fluxes of methane needed for accumulation of natural gas resources are difficult to assess. Methane can be lost from crustal gases by oxidation in nongraphitic rocks at high temperatures. Methods are needed to chemically identify and ultimately quantify crustally generated methane accumulations that are accessible to drilling and production. 43 refs., 4 figs.
- OSTI ID:
- 6877271
- Journal Information:
- United States Geological Survey, Professional Paper; (United States), Vol. 1570
- Country of Publication:
- United States
- Language:
- English
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