Estimated Original Oil in Place Variation due to Porosity Determination Technique

Abstract

Original oil in place underpins field appraisal, development, and management and at early appraisal stage, static volumetric technique had been used for estimation. One of the key variables in this technique is porosity; therefore the technique use for porosity determination will influence the estimated original oil in place magnitude. The evaluations of zone-average porosity in the net-pay intervals in a single well have accuracy of approximately 5 to 25 % of total porosity. This is largely the result of systematic uncertainty. Through this research paper, it is inferred that, the effect of averaging the porosity is more imminent on an inter-bedded reservoir rather than a clean sand reservoir. This is because the averaging effect is not accounting the porosity changes in smaller scale, as it is wrongly assumed; changes in smaller area of reservoir are negligible. This fundamental approach is proven to be incorrect. Though in clean sand this averaging method is still applicable, it is proven that an averaging method is not suitable to be used in a laminar or inter-bedded reservoir. The difference that may be introduced is almost 25% of the original oil in place, which may affect the economic model as the potentially producible and sub-economic field or discovery.