PERMO-CARBONIFEROUS SEDIMENTATION AND RESERVOIRING IN THE BOHAI BAY BASIN

The focus of oil and gas exploration in the Bohai Bay basin has been turned to the deep plays at present as the shallow ones have been basically proved.Studies are carried out on the distribution and physical properties of the deep reservoirs in the Bohai Bay basin in respect of sedimentary control factors,so as to lay a geologic foundation for deep oil and gas exploration.Various log and core data are used to estimate the petrophysical parameters such as porosity and permeability,and to define the distribution and petrophysical properties of the framework sandbodies in each formations of the Permo-Carboniferous in the Bohai Bay basin.Analogy mapping method is used to reconstruct the Carboniferous and Permian lithofacies palaeogeography in the Bohai Bay basin,and to study the controlling effects of sedimentary facies on reservoirs and their petrophysical properties.The following understandings are obtained.The reservoirs in the Lower Shihezi and Upper Shihezi formations are most favorable for hydrocarbon accumulation.The sandbodies are controlled most strongly by the marginal bank facies and channel bar facies of fluvial systems,followed by distributary channel facies of delta plain and tidal flat facies.The poroperm characteristics of the reservoirs get poorer progressively in the sequence of meander river sandbody-delta sandbody-varrier bar sandbody-tidal flat sandbody.