Identification and petrophysical evaluation of thinly bedded low-resistivity pay reservoir in the Niger Delta

Abstract

This study is on evaluation of the thinly bedded reservoirs in the Niger Delta. These reservoirs are thin laminations of sand and shale which contain hydrocarbons. The presence of interbedded shales suppresses resistivity values within the thin sand beds, resulting in low-resistivity log signatures that do not meet conventional cut-offs. Advanced high-resolution log suites are required to accurately evaluate the reservoir properties, but in the absence of such data, conventional log suites can be integrated to evaluate the hydrocarbon saturation and other reservoir parameters of such reservoirs. In this study, an approach was adopted to identify these reservoirs using the low-resolution Thomas–Stieber clay distribution plots and to properly quantify the hydrocarbon saturation with enhanced post processing Techlog software. Reservoir E3 in well K32 was delineated and identified as low-resistivity thinly bedded interval. This reservoir was interpreted as proximal to distal lower shoreface heterolithic deposits, whose volume of shale cut-off could not properly define the net sand value of the reservoir. Conventional Archie’s saturation model also gave pessimistic water saturation (S w) values of 73 %. But the application of the Thomas–Stieber low-resolution approach yielded a more realistic S w of 44 %, which represents an increase of 29 % in the hydrocarbon saturation. From the review of the reservoir, it became much clearer that there is substantial opportunity to increase the hydrocarbon resource base in the Niger Delta by targeting thinly bedded pay opportunities.