Core-log Data Integration for Improved Formation Evaluation in the Dulang Field, Offshore Peninsular Malaysia

Abstract

One of the most challenging tasks of a log analyst is to understand logresponses. In order to achieve this it is essential to establish an accurate Bulk Volume Model for the reservoir. This includes mineralogy, porosity and saturations. Unfortunately, in the case of Dulang field, log data alone cannotbe used to derive accurately the Bulk Volume Model due to insufficient log dataand the presence of special minerals. These minerals which affect log responses significantly are Potassium-Feldspar, Siderite and Fe-Dolomite. Dulang field is a complex shaly-sand reservoir situated 130 kilometres offshore Peninsula Malaysia. This paper illustrates how results of core analysis have helped usunderstand log responses in the Dulang field. A special core recovery programwas carried out in three wells, namely, Dulang-A17, B20 and B21, which penetrated all the major reservoirs that contributed the bulk volume of STOIIP in the Dulang field. A low toxicity oil-based mud was used in well Dulang-B21to establish accurately the connate water saturation for quantitative calibration of log derived parameters. A bland water-based mud was used in theother two wells to preserve the rock wettability. The results of the coreanalysis enabled us to better refine our petrophysical model of the reservoir which led to a more accurate computation of reserves. Components of core analysis used in this study are Fourier Transform Infra-Red spectroscopy, Core Layering and conventional core measured petrophysical parameters (porosity, permeability, grain density and saturations). Introduction One of a log analyst's nightmare is looking at a bare minimum number of logcurves in a complex shaly sand reservoir to compute meaningful Net Pay (h), Porosity () and Water Saturation (Sw) for volumetric purpose. In the case of Dulang field, wireline log interpretation approach alone is insufficient to describe completely the formation. P. 107