Geophysical Well Log Appraisal of Okpella Field within Offshore Niger Delta Basin of Nigeria
E. U. Waziri *
Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria.
E. E. Udensi
Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria.
C. I. Unuevho
Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria.
M. O. Jimoh
Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria.
U. D. Alhassan
Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria.
K. A. Salako
Department of Physics, Federal University of Technology, Minna, Niger State, Nigeria.
A. A. Solomon
Department of Geosciences, University of Lagos, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
The Production data of Okpella Field, located within the Offshore Niger Delta Basin, Nigeria, revealed that the Okpella Field attained peak annual hydrocarbon production of 430175 MBO (Million Barrel of Oil) in 2008, and the production has presently dropped to 7839 MBO per annum. Therefore, an appraisal study was conducted to identify opportunities for reversing the low production. The sought opportunities were bypassed reservoirs with pay zones. This study uses geophysical Well log data, Biostratigraphic data, and Production data to appraise Okpella Field. The hydrocarbon production data were analyzed for the produced reservoirs to establish the positive effects of the Bypassed hydrocarbon reservoirs zone within Okpella Field Offshore Niger Delta Basin. Before this study, the operating company had previously identified six reservoirs. They were named major reservoirs Sand A to F, of which major reservoirs B, C, and E are gas-bearing, major reservoir D bears gas and oil, and major reservoir F bears condensates. Three additional reservoirs with pay zones were identified within this study, and they were named Bypassed A to C. Bypassed A is gas bearing, Bypassed B is oil and gas and Bypassed C is oil-bearing. The petrophysical analysis of the wells within Okpella Field determined the various reservoir properties such as the gross thickness, net thickness, net to gross ratio, the volume of shale, porosity, and hydrocarbon saturation of the major reservoir and bypassed reservoir zones. Some of the reservoirs are amalgamated upward coarsening sand bodies of distal fan lobes within the Low-stand systems tract. Others are leveed channel proximal. The Biostratigraphy data were integrated with the stacking pattern of the Gamma-ray log motif, revealing the sequence boundaries and inferring the possible depositional environment. The reservoirs within the Okpella Field were deposited within the Low-Stand System Tract (LST), reflecting a high energy environment, possibly the shoreface depositional environment.
Keywords: Major reservoir, bypassed reservoir, net pay, hydrocarbon saturation, fluid types