Petrophysical evaluation of reservoir in a selected well (Z) in an onshore oil field (X) in the Niger Delta Basin, Nigeria using wireline logs

E.J Ighodaro,M.E Okiotor,N Idemudia,P.N Okanigbuan

doi:10.4314/jasem.v23i5.23

Abstract

: The petrophysical properties of a well selected from among the onshore oil fields in the Niger Delta Basin, Nigeria was evaluated using gamma ray log, resistivity log and neutron-density overlay log to analyze for the hydrocarbon potential of the well. Some petrophysical properties of the reservoir rocks and fluid characters such as porosity, shale volume, effective porosity, permeability, and formation resistivity factor, resistivity of water, hydrocarbon saturation, water saturation, and net pay thickness were evaluated. The results show that the volume of shale in each reservoir zone directly affects the effective porosity and the zones. The volume of shale is inversely proportional to the effective porosity, as an increase in the volume of shale will bring about a decrease in effective porosity. On the other hand, permeability is dependent on the effective porosity. Facies type identification of the reservoir sands were also carried out using the wireline log - Gamma Ray Log. Results of the work revealed the presence of hydrocarbon in 10 reservoirs across the well, and the hydrocarbon type was observed to be only oil. Oil/Water contacts occurred at 2288m, 2518mm, and 2989m, and the Net Pay Thickness was calculated to be 238m, that is the total thickness of the hydrocarbon reservoirs.Keywords: Petrophysics, Wireline logs, Facies, Reservoir rocks, Pay thickness.

Highlights

A petroleum system is defined as a natural system that encompasses a pod of active source rock and all related oil and gas, and which includes all the geologic elements and processes that are essential if a hydrocarbon accumulation is to exist
Once the gamma rays are emitted from an isotope in the formation, they progressively reduce in energy as the result of collisions with other atoms in the rock
A sand line is constructed on the left hand side of the log strip, reading the average gamma ray (GR) level of thick sands which is equivalent to sands with the lowest GR level

Summary

Introduction

A petroleum system is defined as a natural system that encompasses a pod of active source rock and all related oil and gas, and which includes all the geologic elements and processes that are essential if a hydrocarbon accumulation is to exist. A petroleum reservoir is a subsurface formation containing gas, oil and water in varying proportions. For the wireline log used as a case study in the evaluation here, shale line was read at 100 API, while the sand line was read at 30 API, making a cut- off line at around 65 API.

Results

Conclusion