Research On The Reservoir Characteristics And Flow Units Of The Chang2 Formation, Ansai Oilfield

The reservoir characteristics and flow unit of the Chang2 Formation, Upper Triassic in Ansai Oilfield, Ordos basin are systematically studied in this paper, using integrated knowledge and techniques of petroleum geology, petrology, reservoir sedimentology, reservoir-physics and reservoir engineering, based on detailed description and observation of drilling cores,and various analytical and measurement methods including identification and quantitative statistics of thin sections under microscope, compute image grain size analysis, analyses of X-ray diffraction (XRD), electron scan microscope (ESM) and capillary pressure measurement.This study shows that the main rock type of the reservoir is feldspar sandstones,with lithicarkose sandstones as the subordinate ones. Pore structure is mainly primary intergranular pores , and dissolution pores, relatively undeveloped, is as the second place among the reservoir pores. The reservoir belongs to strong heterogeneity reservoir, of which the inner layer heterogeneity is relatively weak, the inter layer and the lateral heterogeneity indicates a strong macro heterogeneity. The reservoir can be divided into three kinds of excellent, intermediate and poor reservoirs. The major controlling parameters on the reservoir heterogeneity are sedimentary environment and hydrodynamic conditions, diagenesis and development engineering factors.Reservoir flow unit can be divided into four typesof A, B, C and D. Sandstones in the type A flow unit is characterized by relatively coarser grains, lower argillaceous particle content, better connectivity between pore throats, and with higher porosity and permeability, which occurred mainly in center part of the distributary channels. Sandstones in the type C and D have fine grained particles, poor connectivity between pore throats, and lower porosity and permeability, mostly occurred in the margin of channels. The reservoir quality and lithological characteristics of the type C is between the type A, B and D, mostly occurred between the main part and the margin of distributary channels. The major factors controlling fluid percolation of the reservoir flow unit mainly depend on the nature of fluids, characteristics of the reservoir and and liquid flowing behavior. The research results will provide a scientific basis for deployingand adjusting well network injections, effectively tapping hydrocarbon potentials and enhancing oil recovery.