This study has been undertaken in three oil fields (A-Libya, B-Libya, and C-Libya) in sirte basin located in Libya. Nubian sandstone Formation is the main reservoir in the studied oil fields. Laboratory measurements methods were applied on the core samples that were selected from three different fields of Nubian Sandstone. Some of these measurements were conducted in Libyan Petroleum Institute (LPI Tripoli-Libya) laboratories in order to determine the resistivity parameters of the central graben reservoir cores and to investigate the effect of rock hetrogeneity and wettability on the resistivity parameters of Nubian sandstone reservoir rocks. The pore size distribution was estimated from generated capillary pressure curves. The samples belonged to Nubian sandstone, Sirt basin were selected to perform formation resistivity factor measurements.

The Pore size distribution and type of pores were calculated from mercury injection capillary pressure data. The results indicated that changes had been observed in formation resistivity factor and cementation exponent when overburden pressure was applied (slightly increases in cementation exponent with increasing O.B.P).Wettability played an important role in determining the fluid movement, distribution and electrical conduction during desaturation processes. Resistivity index effect has been observed after wettability measurement showing oil-wet tendency.

From the results obtained, a good relation between resistivity and type of pores (macro and micro pore system) was observed. When oil begins to penetrate micro-pore systems during the measurements, a significant change in slope of the resistivity index relationship occurs.

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