Structure and fracture-cavity identification of epimetamorphic volcanic-sedimentary rock basement reservoir: a case study from central Hailar Basin, China

Abstract

Taking the epimetamorphic volcanic-sedimentary complex basement in Beier Depression, Hailar Basin, China, as an example, the lithology, diagenesis, reservoir characteristics, and vertical zoning structure division are studied by using core, thin sections, cathodoluminescence, SEM, LSCM, well logging, FMI, diplog, and 3D seismic data. The reservoirs including fractures and cavities are identified and predicted separately under the control of vertical zoning structure, by well logging response, seismic reflection features, and multiseismic attributes. The results show that the assemblage of fine siltstone, tuffaceous sandstone, and tuff is the best lithology assemblage for reservoir development. The basement reservoir structure is divided into four zones, and zone II developing both fractures and pores has the best reservoir quality, followed by zone III having fractures dominated. Fracture and pore-cavity reservoirs have decreasing resistivity, density, and other features in conventional well log, and pore-cavity reservoirs have relatively high amplitude and bead or lenticular-shaped seismic reflection. The seismic attributes of curvature, coherence, and amplitude extracted under the control of specific zonation are effective reservoir prediction methods. Reservoir distribution including fracture and pore-cavity is controlled by the palaeogeomorphology of basement buried hill and fault activity and property. For the buried hills with high palaeogeomorphology and long-term structural activity controlled by main faults, developing high-quality reservoirs of fractures as well as pores, are the optimal targets for basement drilling, in the condition of effective hydrocarbon migration path.