Geological characteristics and exploration potential of diamictite tight oil in the second Member of the Permian Lucaogou Formation, Santanghu Basin, NW China

Abstract

Based on the latest exploration data of tight oil, the evaluation of the “seven properties” relation of diamictite tight oil in the second Member of the Permian Lucaogou Formation in Santanghu Basin was carried out. The second Member of the Lucaogou Formation developed a new suit of high-quality hydrocarbon source rocks, which are characterized by wedging distribution, big thickness, high organic content and good organic type, and the overall being in the oil-generating window. Complex in lithology, the second Member of the Lucaogou Formation is a set of laminated structure diamictite combination composed of detrital material of terrigenous origin, dust fall, carbonate rock in variable proportions. With low natural gamma and high electrical resistivity, strong heterogeneity, micropores as main matrix porosity, it has features of ultra-low porosity and extra-low permeability; the fractures in it provide some reservoir space, and make great contribution to permeability. The Member has good oiliness (oil saturation from conventional core analysis is 15%−80%), high content of brittle minerals (80%−90%), clay mineral content of less than 10% in general; core sensitivity test shows that it varies widely in water sensitivity and velocity sensitivity, and is weak in acid sensitivity. Through evaluating the “seven properties” relation, it is concluded that the main control factors of the tight oil layer are the maturity of hydrocarbon source rock and reservoir physical property. The “sweet spots” of diamictite tight oil in the second Member of the Lucaogou Formation were selected, that is, the areas with favorable reservoir physical properties in the mature hydrocarbon source rock of the sag. Key words: Santanghu Basin, Permian Lucaogou Formation, tight oil, diamictite, geological characteristics, exploration potential