Research On Gas Accumulation In Northern Tianhuan Depression, Ordos Basin

Tianhuan depression is located in northwestern of Ordos bason,Spring exploration expresses that Tianhuan depression and Sulige gas field in easten which have similar condition of deposit structural evolution,can form lithological characters gas reservoir. In this area,prospecting wells to the Palaeozoic group show gas commonly,gas test in part of interval intvl can gain industry gas current.It's favorable zone of natural gas accumulation.The research is based on these theory:area field outcrops,core observation, slice observation, geochemical analysis, logging interpretation and property based on analysis,Combining previous research results, the integrated use of sedimentology, source rocks organic geochemistry, reservoir geology basic science knowledge and theory,we do a combination system analysis and evaluation to the north of tianhuan depression in the formation of the hydrocarbon source rocks, reservoir and Reservoir-cap combination.Through the research we think:The study area was a set of Clastic rock series of the sea land transition phase in upper Palaeozoic. The bottom Carboniferous system Taiyuan formation and Dyas Shanxi formation were coal series source rocks, it wide of hydrocarbon generation. The Dyas Shanxi formation and up and down Shihezi formation growthed a set of rivers-delta facies deposits. Sand body developed, but reservoir physical property weak, had low permeability and low porosity characteristics. The entrapment was priority to large-sized lithologic trap, natural gas accumulation conditions is superior, exploration areas was broad, Still has found large gas field geological conditions; Lower palaeozoic era developed marine carbonate deposits Karst reservoir thickness, physical property was good, it can accept two sets of source supply from up and lower Palaeozoic era, had characteristics with mixed source gas, riched air source. Carbonate karst development mainly pore-cave reservoirs and crack-porous type reservoir in Kelimoli formation; Zhuozishan mountain group dolostone section main growth hidden holes-porous type, cloud limestone karst, crystal pore-cave between pore type and dolomite intercrystal pore-pore-cave reservoirs karst. The entrapment be priority to ancient karst-lithology combined trap, exploration potential. The study area growth well cap rocks in up and lower Palaeozoic era, block conditions were good. The study area's source rock-reservoir-cap rock, its can form three favorable reservoirforming assemblages and types reservoirforming entrapment, it has good exploration prospects.