Integrated Petrophysical Study of Acacus Reservoir (South of Tunisia)

Abstract

The Silurian is subdivided in the Tannezuft (shale dominated) and Acacus (sand dominated) formations. The Acacus itself is subdivided in Acacus A, B & C, of which the Acacus B includes more shale than the others. During Acacus A, a time span of ~1–1.5 million years (Gorstian & lower Ludfordian), sediments of ~250 m were deposited. Petrophysical properties are quite variable and inhomogeneous since the reservoir shows layer heterogeneity and complex mineralogy related to diagenesis process, mainly chloritization and siderite cementation that deacrease the quality of the reservoir. The water saturation estimation is a critical task, the presence of chlorite and ferruginous mineral affects the logs resistivity responses that appear to be too low, conducting to an overestimation of the water saturation. For this purpose we did this integrated petrophysical study on the acacus that include more than 25 wells and it began by: Stratigraphic correlation, petrophysical interpretation using IP software, then an advanced petrophysical interpretation using the mineral solver, comparaison between the two methods of interpretation. After doing this tasks we conclude that scale data, rock typing and NMR data can reduce the petrophysical interpretation uncertainty.