A MULTI-DISCIPLINARY APPROACH DELIVERS QUALITY RESULTS TO A COMPLEX FORMATION EVALUATION PROBLEM

Abstract

This paper illustrates the benefits of a multi-disciplinary approach to formation evaluation in an interbedded sand/ shale reservoir sequence. The Egret–3 appraisal well was drilled to obtain information to evaluate the commercial viability of the Egret oil field. A key objective of the well was to test for the presence of a gas cap and, if present, to confirm the gas-oil contact (GOC).

A number of analytical techniques were employed to distinguish between oil and gas in the reservoir; these included analysis of mudlog gas ratios, evaluation of separation between the density and neutron logs, pressure gradient analysis, formation fluid sampling and PVT and geochemical analyses. Each method confirmed the presence of a gas cap, but indicated a different GOC. It was only by combining the full suite of tools that the uncertainty associated with the GOC could be accurately defined.

Key elements contributing to the success of the program included: clear recognition of the significance of gas cap to commercial viability of the Egret oil development; design and planning of an appropriate formation evaluation program; flexibility in implementation of the program and determination and alignment amongst all disciplines to overcome operational difficulties.