Integrated Dielectric and NMR Measurements in a Solution Workflow to Meet Fluid Typing Challenges in Clastic Reservoirs Drilled Using Synthetic Oil-Based Mud: A Case Study from the Malay Basin

Abstract

Characterization of conventional clastic reservoirs can be very challenging because of issues related to the nature of the reservoir, logging environment, and/or production enhancement projects being performed within the field. In the subject reservoir, the primary challenge was typifying hydrocarbon, in terms of gas or oil, in a well drilled using synthetic oil-based mud (SOBM) as well as in a relatively fresh formation water-bearing reservoir in which a waterflooding project was being performed. Furthermore, the shaly and silty nature of the reservoir and the uncertainty of the resistivity (Rw) value and other saturation equation parameters added to the complexity of this task. Another challenge was calculating residual oil saturation in one zone with the presence of SOBM filtrate containing a 20% water phase and incomplete information about the saturation exponent, n, in the imbibition process because of water injection in the field. To meet such a challenging reservoir situation, nuclear magnetic resonance (NMR), in multi-Te activation, and dielectric logs were acquired along with quadcombo, wireline formation tests (WFTs), and oil-based mud imaging (OBMI). As a normal practice, formation evaluation was performed using the NMR T2D technique and dielectric complex refractive index modeling (CRIM) along with quadcombo and WFT for (1) mineralogy and porosity calculations, (2) fluid typing and quantification, and (3) permeability estimation. A slight viscosity difference between the formation oil and SOBM filtrate was evident on the T2D map, and differentiating the various oils and quantifying residual oil was possible. Dielectric shallow resistivity, water filled porosity, and the estimated cementation exponent, m, all played major roles supporting the NMR T2D processing, particularly when restricted diffusion was experienced as well as to fill gaps across intervals where NMR was not acquired. This paper discusses the reservoir challenges experienced and the solution workflow, with emphasis on the pros and cons of the different techniques used and recommendations for future projects. Data used in this study were acquired from a well offshore Peninsular Malaysia.