Tight oil play characterisation: the lower–middle Permian Lucaogou Formation in the Jimusar Sag, Junggar Basin, Northwest China

Abstract

ABSTRACTThe lower–middle Permian Lucaogou (P2l) Formation is a “sandwich-type’’ combination of source rocks and reservoirs that is considered to be a potential tight oil reservoir in the Jimusar Sag (JS). We investigated the P2l Formation using a designated workflow to assess its potential as a viable tight oil reservoir play using geological, petrographical, petrophysical, and geochemical characterisation of core samples. The results showed that the P2l source rocks have a widespread distribution (up to 1500 km2), a huge thickness (up to 160 m), a relatively high abundance of organic matter (averaging 3.12 wt%), a good sapropelic quality, and a moderate thermal maturity. The reservoir consists mainly of dolomites and siltstones, predominantly characterised by secondary dissolved pores, with medium–high porosity (averaging 9.1%) and relative low permeability (averaging 0.26 mD), high abundance of brittle minerals (averaging 87.1%), and low abundance of clay minerals (averaging 11.2%) with low water sensitivity. The results demonstrate that in the JS area the P2l Formation has great potential for tight oil production with its considerable hydrocarbon expulsion quantities, good oil storage capability, and reservoir frackability potential and provide a basis for further evaluation of the tight oil potential of the P2l Formation in the wider Junggar Basin and for identifying similar plays elsewhere.