Probe into natural gas reservoir-forming regularities and exploration direction of Bohai Bay basin

摘要

i bay basin is a rifting basin evoluted and developed mainly in Cenozoic era. The most outstanding characteristics of this kind of hydrocarbon-bearing basin is that it has plenty of crude oil, and short of natural gas relatively, anyhow, some gas fields and gas-bearing structures have been discovered. By a thorough analysis and comparative study of the natural gas genetic type and reservoir-forming control factor of the gas field within two large oil-gas accumulating areas onshore and offshore Bohai bay basin, the major geologic conditions and regularities of the abundant natural gas areas are found out: (1) Larger natural gas fields mainly distributed nearly the strike-slip fault belt whose strike is near north-east, especially the depression (sag) whose axial approximately parallel to or intersect at a small angle with the strike of the strike-slip fault belt are rich in natural gas relatively, and whose axial approximately intersect at a right angle or a bigger angle with it arc short of natural gas relatively; (2) The depression (sag) whose hydrocarbon-source rock with more abundant terrigenous organic matter and have a higher extent of thermal evolution, or combination with the biological action, are rich in natural gas relatively; (3) The Paleogene and pre-paleogene which located under the good regional seal distributed steadily and adjacent the hydrocarbon-source rock are major natural gas-bearing strata; (4) The superposition areas of relative low structural high which are adjacent the gas source area and a favorable sedimentary facie belts are enrichment areas of natural gas. According to knowledge, and integrating the comparative analysis of the concrete geologic condition of the major hydrocarbon-generating sag in Bohai area with the synthetical evaluation, the predicted favorable natural gas-exploring prospects in Bohai area are mainly concentrated in "two areas and three belts "-. the skits along the south edge of Shijiutuo Uplift in Bozhong area, the belt of Bodong Uplift and its surround apron area, the north low-lying belt in Liaozhong area.