Petrophysical Analysis of Well Logs Data for Sandstone Reservoir Hydrocarbon Evaluation In Niger Delta Sedimentary Basin.

Abstract

The primary function of petrophysics is to provide the necessary parameters for an
accurate establishment of reservoir model, petrophysical analysis is considered as
one of the critical factors in reservoir evaluation. Hydrocarbon exploration in Niger
delta province has been ongoing for many decades with the exercise now been
gradually shifted to the deep offshore, to exhaust the basin petroleum potential, the
sand channel within the deep sea is now targeted as the main exploration point. This
research work reiterated the relevance of petrophysical analysis of open-hole wireline
data as the primary step in establishing the concept of reservoir evaluation during
hydrocarbon exploration, reservoir petrophysical properties of subsurface
sedimentary layers were studied using wireline logs data from three selected wells in
Niger Delta Basin. The electronic copies (LAS file) of the wireline logs data were
obtained for this research work, the quality checks, accuracy, content policy and
confidentiality remained the right of Department of Petroleum Resources (D.P.R.)
Nigeria. The wireline logs data comprised of gamma ray, resisitiviy (deep), sonic, and
neutron logs integrated with calculated field curves; Archies water saturation (SW),
total porosity (PHiT), bulk-volume water (BVW) and shale volume (VSH). Computer
based data interpretation was conducted using Schlumberger’s PETREL E&P software
2013. The results of the petrophysical analysis were presented in bi-plots and log Vs
depth format (log tracks) for convenient interpretation. The various hydrocarbon
bearing zones across studied wells were quantitatively categorized into three
distinctive reservoirs. Reservoir AA, encountered between intervals 2610ft and
3068ft, has an average pay thickness of 40.4ft and laterally extends to across all the
five wells. Reservoir BB, encountered along interval 4011ft to 4690ft has an average
pay thickness of 16ft. The deepest reservoir encountered between interval 5305ft and
6930ft, has an average pay thickness of 61ft. The average hydrocarbon saturation,
effective porosity and bulk-volume water for reservoir AA, BB and CC, are 50%, 30%
and 0.0571; 33%, 26% and 0.2085; and 40%, 20% and 0.1565 respectively. Due to
the limited availability of wireline logs data only two types of fluids; water and
hydrocarbon were delineated, the values of effective porosity and hydrocarbon
saturation calculated for the hydrocarbon bearing zones are good enough for
commercial accumulation and production of hydrocarbon. The direct correlation
between facies and gamma log shapes relationship has evidently supported the
tentative interpretation of paleo-depositional environment of the Niger Delta Basin.