Abstract:

The shale oil of Lucaogou formation in Santanghu basin is the key exploration target for Tuha oilfield. The researches on lithofacies characteristics and its relationship between lithofacies characteristcs and shale oil reservoirs are lacking, which directly restricts the progress of exploration. The lithofacies type division, fine lithofacies description and lithofacies distribution in the Lucaogou formation of the Santanghu basin are studied through techniques such as core observation, thin section identification, SEM analysis on field emission environment, whole-rock mineral analysis by X-ray diffraction, high-pressure mercury injection and nuclear magnetic resonance. The results show that the reservoir of Lucaogou formation is mainly composed of carbonate, pyroclast and organic matters, and can be classified into massive tuff, thick stratified dolomicrite, laminated tuffaceous dolomite and laminated dolomitic tuff, most of which are medium-rich in organic matter. There are differences in reservoir physical properties, pore-throat structures and reservoir spaces among different lithofacies types. The massive tuff and thick stratified dolomicrite have well-developed pores and good oil-bearing properties, and high yield and sustainable production can be achieved after fracturing. Fractures are well developed in the stratified tuffaceous dolomite, and high yield can also be obtained after fracturing, but cannot be maintained. It is predicted according to the lithofacies distribution that the southern margin of the Tiaohu sag and the Niujuanhu structure in the Malang sag are favorable areas for shale oil exploration.

Key words: Santanghu basin, Permian, Lucaogou formation, shale oil, lithofacies type, fine-grained mixed sedimentary rock, sedimentary environment