Study On High Resolution Sequence Stratigraphy And Reservoir Heterogeneity Of Loucaogou Formation Of Middle Permian In Chaiwopu Basin

Chaiwopu basin had more abundant oil-gas resource and good petroleum preservation conditions, but only Well Chaican-1-Cl, which drilled in 1989, had commercial oil/gas flows now, Loucaogou Formation of Middle Permian was one of its mainly production stratas. High-resolution sequence stratigraphy for Loucaogou Formation of Middle Permian, which belonged to Chaican-1(DI) and Well Chaican-1-Cl and Well Da-1, in the middle of Chaiwopu basin, was established for the first time. It supplied the basic data for the petroleum exploration in this basin.The basic concepts of the base-level and the accommodation, which were extremely important in high-resolution sequence stratigraphic study, were elaborated detailedly. On the base of the hypothesis of PAC which presented by Goodwin and Anderson in 1985, the concepts of autocyclicity and allocyclicity, base-level cycle and sedimentary cycle were also studied in depth. Considering the division of base-level cycles was extremely indefinite, the paper attached the autocyclicity and allocyclicity to the concepts of base-level cycle. The concept of the grain-size genetic unit and its research methods were explored to put forward, and applied to establish high-resolution isochronous sequence framework of Loucaogou Formation of Middle Permian in Chaiwopu basin. There totally 2 long base-level cycle sequences, 6 middle-term grain-size genetic units, 5 members which the same as 5 system tracts ,were distinguished from Loucaogou Formation of Middle Permian in Chaiwopu basin. The microcosmic and macroscopic reservoir heterogeneity of Loucaogou Formation of Middle Permian, in Chaiwopu basin, were studied by using the methods of grain-size genetic units. The reservoir of Loucaogou Formation of Middle Permian, in Chaiwopu basin, was a type of low porosity and low permeability reservoir. The grain-size genetic units controlled the microcosmic heterogeneity of reservoir, and the short-term grain-size genetic units controlled the in-layer heterogeneity of reservoir ,and the long-term base level units controlled the heterogeneity of reservoir of the middle-term grain-size genetic units(reservoir interlayer heterogeneity), and oil/gas stratums mainly distributed at the bottom of middle-term grain-size genetic units. The distribution of the reservoir and valuable deposits of oil/gas of Loucaogou Formation of Middle Permian, in Chaiwopu basin ,were given a preliminary prediction. In the part of the higher accommodation space, the reservoir and valuable deposits of oil/gas mainly distributed in the opposite from the paleocurrent direction area where the accommodation space increased. In the part of the lower accommodation space, the reservoir and valuable deposits of oil/gas mainly distributed in the paleocurrent direction area where the accommodation space decreased.