| Abstract: | In recent years,a series of large low and medium abundance oil and gas fields are discovered through exploration activities onshore China,which are commonly characterized by low porosity-permeability reservoirs,low oil/gas column height,multiple thin hydrocarbon layers,and distribution in overlapping and connection,and so on.The advantageous conditions for large-area accumulation of low-medium abundance hydrocarbon reservoirs include:(1)large(fan)delta sandbodies are developed in the hinterland of large flow-uncontrolled lake basins and they are alternated with source rocks extensively in a structure like"sandwiches";(2)effective hydrocarbon source kitchens are extensively distributed,offering maximum contact chances with various sandbodies and hydrocarbon source rocks;(3)oil and gas columns are low in height,hydrocarbon layers are mainly of normal-low pressure,and requirements for seal rock are low;(4)reservoirs have strong inheterogeneity and gas reservoirs are badly connected;(5)the hydrocarbon desorption and expulsion under uplifting and unloading environments cause widely distributed hydrocarbon source rocks of coal measures to form large-area reservoirs;(6)deep basin areas and synclinal areas possess reservoir-forming dynamics.The areas with great exploration potential include the Paleozoic and Mesozoic in the Ordos Basin,the Xujiahe Formation in Dachuanzhong in the Sichuan basin,deep basin areas in the Songliao basin etc.The core techniques of improving exploration efficiency consist of the sweetspot prediction technique that focuses on fine characterization of reservoirs,the hydrocarbon layer protecting and high-speed drilling technique,and the rework technique for enhancing productivity. |
