Lithology and pore fluid prediction of a reservoir using density, compressional and shear wave logs: a case study of the Tano basin
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Date
July, 2015
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Abstract
Due to the higher uncertainties associated with the traditional method of determining
lithology and pore fluid using well logs, quantitative rock physics analysis was carried out to
determine the lithology and pore fluid of a reservoir in the Tano Basin. Inaccurate prediction
of lithology and pore fluid, results in the inaccurate determination of other petrophysical
properties such as porosity, permeability, net pay, etc. Rock physics analysis reduces the
uncertainties related to the traditional method of predicting lithology and pore fluid. The
primary objective of this thesis is to predict lithology and pore fluid using rock physics
analysis, however, the oil-water-contact (O.W.C) and reservoir zone were also predicted. In
this thesis, density, compressional wave velocity and shear wave velocity logs were used as
input to calculate elastic parameters such as velocity ratio, Poisson’s ratio, and Lamé
parameters. The calculated velocity ratio log was used to differentiate between sand and
shale. Rock physics analysis of the calculated Lamé parameters was used for comprehensive
lithology prediction. A crossplot of Lamé’s ratio (λ/μ) and difference (λ*⍴ - μ*⍴) using
Goodway (2001) interpretation template was carried out. The gas sand, wet sand, and
carbonate formations were delineated according to the crossplot analysis. Poisson’s ratio and
velocity ratio crossplot was also used to determine the pore fluid content. Oil sand, gas sand,
and brine sand were predicted from the crossplot analysis. Oil-water-contact and reservoir
zone were identified due to the rapid variations observed in the velocity ratio log. This thesis
demonstrates how rock physics analysis can be used to improve lithology and pore fluid
prediction of the Tano Basin.
Description
A thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfillment of the requirements of the degree of Master of Philosophy (Geophysics).