TITLE:
Evaluation of the Influence of Shale on the Petrophysical Properties of Hydrocarbon-Bearing Reservoir Sand in “CAC” Field in the Niger Delta, Nigeria
AUTHORS:
Charles C. Ugbor, Chinwe Adaobi Obumselu, Jethro O. Ogboke
KEYWORDS:
Petrophysical Properties, Reservoir Quality, Shaliness, Permeability, Cross-Plot, Hydrocarbon
JOURNAL NAME:
International Journal of Geosciences,
Vol.13 No.1,
January
30,
2022
ABSTRACT: This study aims at
evaluating the influence of the presence of shale on the quality of reservoir
sand in “CAC-Field”, Coastal swamp Niger Delta by integrating suites of well
logs and 3D pre-stack seismic data. Shales in the reservoir pose interpretation
challenges as they form baffles to fluid flow and reduce effective porosity.
The data used included well logs (density, gamma ray, neutron, resistivity) and
3D seismic data. Petrel and Interactive Petrophysics software were adopted for
the analyses. The Vclay/effective porosity cross-plots were used to determine
the clay distribution patterns hence the influence of shale on the
petrophysical properties of the hydrocarbon reservoir. Result of the well
correlation yielded 12 reservoirs with 4 (RES 4 - RES 7) being hydrocarbon
bearing and laterally continuous across the 4 wells, (CAC-1 - CAC-4) forming
the focus of the study. Evidence of an NW-SE trending delta
progradation in the CAC field is represented by the increasing sandiness
downdip, at both intermediate and the shallow horizons. Thickening of the
reservoir in some instances may be structurally controlled due to faulting. The
results from the petrophysical evaluation show Vclay ranges of 13%-21% and good to very good porosity values that vary
from 15%-25%. The permeability range from 240.49-2406.49 mD except for the sands in RES 7, CAC-3 well
where the permeability was low (91 mD). Additionally, the Vclay/Effective
Porosity cross-plots indicate essentially laminated and structural clay types
with few dispersed clay in RES 7, CAC-3 well. The existence of these 3 clay
types did not significantly influence the quality of the sands containing the
hydrocarbon in the area, except in RES 7, CAC-3. The compartmentalizing effect
of the laminated clay/shale could only possibly affect the vertical flow due to
possible baffles to the vertical flow, but the horizontal flow may not have
been impeded significantly. The study of the type and pattern of clay has
helped to better evaluate the quality and mobility trend of the hydrocarbon in
the CAC field.