Evaluation of geological-engineering double sweet spots: A case study of laminated shale oil reservoirs in the southern Ordos Basin

ABSTRACT: Shale oil reservoirs in southern Ordos Basin are highly heterogeneous due to developed laminae and interlayers vertically, which presents a challenge to identify geological-engineering double sweet spots (DSS). This paper firstly introduced lamina failure and lamina density coefficients to establish a calculation model for engineering sweet spot (ESS) index. Then, an evaluation model for DSS index was proposed by using correction factors to combine geological sweet spot (GSS) and ESS indices. Weights of models for ESS and DSS indices were calibrated against hydraulic fracture geometries, microseismic data, and production profile to accurately predict the sweet spot distribution. Results show that weights of porosity, clay content, and oil saturation in GSS index model are 0.4, 0.3, and 0.3, respectively. Matching rates of predicted ESS indices against fracture geometries and microseismic event number exceed 80% and predicted DSS index profile shows an 87.1% agreement with the production profile after calibration. Moreover, DSS can be categorized into types I, II, and III with indices of 0.7~1.0, 0.3~0.7, and 0~0.3, respectively. We found that high-productivity wells tend to be situated in types I and II DSS zones. This study provides guidance for well deployment and layout of perforation clusters in laminated shale oil reservoirs.