PETROPHYSICAL PROPERTIES AND FACIES ANALYSIS OF THE LOWER MEMBER OF THE SILURIAN ACACUS SANDSTONES, CONCESSION NC2, GHADAMES BASIN, NORTHWEST LIBYA

Introduction

 The lower member of the Acacus sandstones is considered as the main oil target bed in central and southeast Ghadames Basin. In fact, the control keys of the petroleum system in Ghadames Basin are mainly the topographic “relief,” and the sedimentary process, which is erosion. This study attempts to interpret the petrophysical properties of main reservoir rock in part of concession NC-2. The combination of well data interpretation and thin sections illustrates identical results concerning the petrophysical characteristics and three sandstone facies of the lower member of the Silurian Acacus sandstone. These three facies are quartz-cemented facies, carbonate-cemented facies, and clay-cemented faciesrepresent a change from fluvial sandstone to marine sandstone in the delta system.

In the Lower member of Acacus sandstones, the irreducible water won’t increase because the amount of permeability is more than 0.01md. In addition, BVW shows the irreducible water zone where water will be stuck at uninvaded zone by capillary pressure within the irreducible water zone. Therefore, the hydrocarbon product from this area will be free water. Furthermore, the well log data results determine the high oil saturation at 71%, and oil-water contact at depth 9130 ft and 9136 ft.

The stratigraphic correlation of seven wells from the study area represents the lateral change of different depositional environments, which matched the results of the petrographic study that has been done in the same area.

Methods and results

Cross Plot chart interpretation, Well logs data, Combining Core interpretation with Petrographic study, and Correlation.

Conclusion

The Lower Acacus Formation has undergone three diagenetic facies as well as regional tectonic which created the second porosity. The value of permeability which is 3md was not that good; nonetheless, with this value, the irreducible water won’t increase because the permeability had to be less than 0.01md to give a possibility of the irreducible water to enlarge. Furthermore, the bulk volume water (BVW) was constant for the most of the Acacus Reservoir so that the hydrocarbon product will be free water for the most of this reservoir. As a result, there is certainly a possibility for the second porosity to be connected so that the permeability will enhance for the better reservoir.