Oil/gas/water distribution is complex in the marine carbonate reservoirs of the Yingshan Formation in ZG-51 wellblock of eastern Tazhong area.Based on analysis of the existing oil and gas exploration results

fault characteristics and reservoir-seal assemblage

we studied the oil/gas distribution and accumulation characteristics of the Yingshan Formation by using various data such as routine logging

image logging

seismic data and geochemical data.The reservoirs of Yingshan Formation in this wellblock are predominantly of vuggy type and fractured-vuggy type

and show quasi-layer distribution along unconformities.The strike-slip faults significantly controlled hydrocarbon accumulation.The distance between oil/gas wells and major strike-slip faults ranges from 0.5 to 4.0 km.The daily oil and gas output decreases away from the strike-slip faults.The geochemical behaviors of oil and gas also changes regularly with the distance to the strike-slip faults.In plane view

the gas reservoirs are near the faults

while oil reservoirs are far from these faults.The 3

rd

to 5

th

members of Lianglitag Formation as well as the high resistive intervals of the Yingshan Formation act as barriers.Vertically

multiple reservoir-seal combinations superimpose each other

resulting in oil/gas accumulation in multiple layers.The early oil pools were influenced by gas invasion in later stage

resulting in the vertical distribution characteristics of "upper oil and lower gas".Hydrocarbons accumulated in favorable structural traps and lithologic traps under the jointly control of cap rocks and strike-slip faults.