Uncertainty in Petrophysical Evaluation of Thin-Bed Reservoirs in Greater Dolphin Area, Trinidad & Tobago

Abstract

Abstract Acceptable data quality for formation evaluation forms the foundation for understanding the reservoir characterization, Petrophysical properties and pay zones identification. The data quality becomes more challenging in the thin-bed reservoirs (also known as ‘Low resistivity pay’ often abbreviated as LowReP), which poses a significant trial for field development to quantify the volumes in place and producibility. "Greater Dolphin Area" (GDA) located within the East Coast Marine Area (ECMA) off Trinidad consists of several fields out of which this paper will be focusing on the Dolphin and Starfish fields. The reservoirs consist of a series of stacked Pleistocene sands with good porosity and permeability within a three-way-dip closure against a large growth fault. Thin-beds have been observed, verified and documented throughout this area via core acquisition, core photographs and PLT analysis. As aforementioned, due to the low resistivity pay reservoirs characteristics in Starfish and Dolphin fields, these often been overlooked or interpreted to be water-bearing, when surveyed with conventional resistivity logging tools. These thinly bedded pay section hydrocarbon volumes have significantly been underestimated between 50% – 200% deposits. Several thin-bed methodologies have been employed for the Petrophysical modelling to support the field development planning using conventional legacy approach and Shell "Low Resistivity Pay" (LowReP) based tool response modelling and inversion methods workflow to resolve the issues associated with the presence of thin beds. This paper investigates the different methods of resolving the thin bed analysis problem and demonstrates the uncertainty of the results from each methodology on the Petrophysical properties and hydrocarbon volumes estimation.