ESTIMATE OIL IN PLACE IN SHALY SAND USING A SUITE OF WELL LOGS

Abstract

Estimation of oil in place depends on water saturation, porosity and volume of reservoir rock. Water saturation depends on resistivity of water, resistivity and porosity of formation and in addition it depends on whether the shale volume in the reservoir rock is appreciable or not. When the reservoir rock is composed of reasonably clean sand, Archie's relation can be used. If shale constitute a significant part of the reservoir rock, use of Archie's relation will give erroneous results because shale affect the porosity and resistivity of formation. A number of relations have been suggested to compute water saturation when shale are present. In the present work log data S from 4 wells have been used to compute shale volume, porosity, water saturation and then the volume of oil in place. It has been found, on the basis of present work, that present of shale should be taken into account if the shale volume exceeds 40% since the volume of oil computed shows large variation from that computed using Archie's relation only. When shale volume is less than 40%, the estimates of oil in place do not differ significantly from those made using Archie's relation and presence of shale could be ignored. Further use of effective porosity in all relations give acceptable results.