In fluvio-deltaic sediments of East Kalimantan, Indonesia, coal commonly occurs and poses serious problems in reservoir evaluations. Thick coal seams can easily be identified, but it is often difficult to identify and quantify coal within sandstones using the conventional well logs. This can lead to inaccurate computation of reservoir parameters such as porosity, permeability and water saturation. In this paper, it is shown how petrophysical interpretation can identify these coals and improve decision making.

In order to understand the "coaly" response on well logs, a number of core slabs were studied. It was found that the coal within the sandstones mostly occurs as thin layers interbedded with sands, not "dispersed" as often thought.Previous petrophysical analyses were reviewed where coals were not interpreted properly and resulted in over and under-estimation of coals. The new petrophysical model (ElanPlus) is based on local knowledge and extensive core data, and overcomes earlier problems. Also, the application of new logging technology (Combinable Magnetic Resonance CMR) validated the new petrophysical model and a better insight was gained. Uncertainty in quantification of coals under unfavorable situations such as, hole wash out and lack of log resolution, is now better understood.

The new petrophysical interpretation accurately quantifies coals from the conventional well logs and addresses the long standing problem in East Kalimantan sandstones. Accurate reservoir parameters can be computed and better decisions on completions can be made.

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