Publications

The major impediment to the quantitative formation evaluation of Indonesian reservoirs is the occurrence of high degrees of shaliness in the presence of law salinity, and therefore high resistivity, electrolytes. Under these freshwater conditions shale effects can account for over seventy per cent of the measured log signal, and might render the reservoir invisible. In these cases conventional shaly-sand evaluation procedures can break down and hydrocarbon saturation becomes very difficult to determine reliably. These problems are compounded when the reservoir also contains shale laminations, when the reservoir is tight, or when the constituent shales are kaolinitic.As a contribution towards overcoming some of these difficulties, this paper outlines important new elements of an evaluation strategy for shaly freshwater reservoirs. Firstly, the concept of shale effects is redefined in the light of recent technical advances so that misunderstandings of the past can be eliminated. Secandly, the integrated use of log and core data allows prevailing shale effects to be quantified meaningfully, even in the more hostile freshwater environments. Thirdly, improved account of shale effects in log interpretation can be taken by deploying some of the recently available well logging technology, especially in nuclear geophysics. Finally, the resolution of thin beds is promoted through micro-electrical sensing and high frequency dielectric tools.This interpretative scheme is illustrated by drawing upon field examples throughout. The overall objective is an improved strategy for hydrocarbon evaluation in those technically difficult reservoirs which are both very shaly and contain fresh waters. The recommended procedures might also provide an initial basis for the recognition of otherwise invisible reservoirs, for example low resistivity pay sands.