Quantitative Assessment of Resistivity Anisotropy in Evaluation of Laminated Shaly Sand Hydrocarbon Reservoirs–A Case Study in the Barents Sea, Norway

Abstract

Resistivity anisotropy in shaly sand lamination sequences affects the hydrocarbon evaluation in multiple dimensions of petrophysical logs. Currently, vertical resistivity (Rv) and horizontal resistivity (Rh) from 3D triaxial induction measurements can be applied simultaneously to resolve these petrophysical impacts. In this paper, an extensive analysis is offered with a focus on the hydrocarbon evaluation based on advanced petrophysical logs from a well. A critical analysis is done on the three comparable cases including clean formation as a base case, shaly sand case and laminated shaly sand case towards resolving resistivity anisotropy in a typical shaly sand laminated reservoir. The analysis results into potential pay zones of 38.0 m thick of gas and 76 m thick for oil. Furthermore, the results provide an increase in hydrocarbon pore fraction (HCPF) per depth up to 30% in zones with Rv/Rh ratio greater than or equal to 3 compared to conventional evaluation. The study concludes that in a lithology of shale sand laminated sequences, the feasible evaluation technique of hydrocarbon should involve the combination of derived hydrocarbon bearing sand lamina resistivity (Rsand) from horizontal (Rh) and vertical resistivity (Rv) of triaxial induction measurement, refined sand porosity from Thomas Stieber model and associated net to gross using the shaly sand models.

Keywords: Resistivity anisotropy; laminated shaly sand; triaxial induction measurements; density;