Organic Facies and Hydrocarbon Potential of Narrow-Long Fault Basin

Abstract

Yishu basin is one of a great group of Mesozoic-Tertiary fault basins in Northeast China. It is a narrow-long oil-producing basin with a 7:1 ratio of length to width. The basin is filled by 2-6 km of Eocene to Miocene and is confined by two parallel normal faults. Its geometry and unsymmetry determine the spatial distribution and evolution of organic facies. Eocene dark mudstone of deep lake is the source rock, and interfan or filled lake swamps facies contain coal. Because of development of short transversal alluvial series and plentiful terrestrial matter, frequent gravity current disturbs the stagnant reducing environment and deteriorates organic matter. As a result, humic matter is dominant in source rock with TOC 0.7-1.3%, H/C ratio 0.6-1.1, IH less than 120 mg/g{sub TOC}, and high Pr/Ph, {delta}{sup 13}C {minus}25.40% (PDB). Products of kerogen pyrolysis have rich aromatics. This basin produces light oil with API 40-60{degree} and heavy gas with 20-40% of C{sub 2}-C{sub 5}. Important implications for further exploration are evident. Though this group of lacustrine fault basins is located within the same climatic plant zone, only those having enough subsidence rates with buried depth greater than 3 km tend to be oil-generating basins, of which themore » narrow-long one is inclined to produce light oil and condensate.« less