Minimising the Uncertainty in Laminated Shaly Sand Evaluation Using MCI-NMR-OMRI Technologies: A Case Study in Offshore Terengganu, Malay Basin

Abstract

Micro and macroscopic-anisotropic reservoir characterization has, recently, been dealt with by two main approaches, 1) applying the Thomas-Stieber technique on uniaxial resistivity, or 2) applying the Tensor Model technique using multicomponent induction measurements.The output from either technique is sand resistivity (R Sand ) and sand volume (V Sand ) with accurate water saturation (Sw) as a result of overcoming the effect of laminated shale on the resistivity measurement which will, eventually, translate into an enhanced hydrocarbon recovery and optimized reservoir development.Some of the key challenges in both techniques are the proper understanding of total porosity and volume and the distribution of shale in the reservoir in terms of laminated and dispersed forms which if used in error will increase the uncertainty on processing results drastically. Additionally, the dependence of fluid density on saturation and the dependence of the saturation and cementation exponents (m and n) on the total porosity as well as the silty nature of the sand all add to the complexity.The use of Oil Mud Resistivity Imager and Nuclear Magnetic Resonance logs as well as elemental analysis (if available) helped in confirming the laminated nature of the shale in the reservoir, minimizing the uncertainty in estimating total porosity and calculating clay-bound water (CBW). They also helped in accounting for the presence of silt-size sand.This paper provides a complete rock model and a comprehensive workflow that takes into account all the necessary steps used to estimate water saturation in a thinly bedded sand-shale sequence, where both laminated and dispersed shale types can exist.Also, the paper presents a simple sensitivity analysis done to understand the uncertainty of the processing parameters and estimated volumetrics on the results when using different techniques as compared to the proposed technique in this study.Data used in this paper are from a well drilled in the Malay Basin, offshore Malaysia.