Abstract

This paper proposes a classification of low-contrast pay and introduces the methodology in evaluating some low-contrast (LC) pay intervals within shaly sands of the Telisa Formation, Central Sumatra. This methodology addresses the cost effectiveness and degree of certainty of the analysis.

In Central Sumatra, low-contrast pay in sandstone can be classified into two types: Type I sands, which have disperesed clay and clay-coated grains. These sands are thinly laminated, thinner than the resolution of wireline logging tools. Proper analysis of Type I sands requires detailed core analysis and fluid analysis prior to additional wireline log runs. Type II sands have thin beds and/or bioturbation which can be resolved by modern logging tools. Analysis of Type II sands requires recognition of the geometric distribtion of discrete shale bodies within the low-contrast shaly sands.

The Telisa sands in Sabak Field represent the Type I model. These very fine grained sands have dispersed caly and exhibit good hydrocarbon indications while drilling. Core analysis is required to ensure producibility of hydrocarbons. Unfortunately, no full diameter cores are available for the studied field. Detailed sidewall core analysis, including Quantitative Fluorescence Technique (QFT^#), was conducted to address this limitation.

Type II sands have been recognized in packages of thinly bedded sandstone of the Telisa Formation in the Petapahan Field. The fine sample increment of the standard logging tools as well as formation scanning tools were used to enhance the resolution and to "gain-up" the resistivity and porosity contrasts. Core analysis has also improved the model and has provided better evaluation of these Type II sands. Additional oil production of 600 BOPD from these sands confirms the analysis.