Estimation of petrophysical data for assessing hydrocarbon potential in Western Ghana Oilfield (Tano Basin)
Well log data were obtained from Ghana National Petroleum Corporation for each of the six exploratory wells studied. For each well, the following logs were collected; resistivity log, sonic log, formation density compensated log, compensated neutron log and gamma ray log. These in situ well logs were subjected to well log analysis and interpretation methods. The following Petrophysical parameters; porosity, permeability, water saturation, reservoir thickness and volume of shale were estimated for each hydrocarbon-bearing zone delineated for each well. The data obtained have been analyzed and interpreted quantitatively, to assess the hydrocarbon potential of each well. The mean estimates for porosity and permeability of all the oil-bearing zones delineated, range from 23.75 % to 34 % for porosity and 65 md to 714.7 md for permeability, compared to mean porosity range of 8.5 – 23.15 % and permeability range of 6.83 × 10-2 md to 5.99 md of the gas zones. The results of the well logs interpretation suggest that oil- bearing zones are much more porous and permeable than the gas-bearing zones. This was evident throughout the wells. The estimates for the water saturation of hydrocarbon-bearing zones range from 6 % to 63.6 % indicating good hydrocarbon saturation potential. The reservoir thickness estimated for all the oil-bearing zones delineated range from 2 m to 40 m while the gas-bearing zones range from 4 m to 10 m. The Western Basin low estimated reservoir thicknesses for hydrocarbon-bearing zone suggests that reservoir reserves potentials are not sufficient, but the range 8 % to 36.8 % of volume of shale estimated for the hydrocarbon-bearing zones of the wells suggests that sandstone lithology of the Western Basin is clean. The Western Basin proved to be a high capital venture, as far as drilling is concern due to abnormal high pressure zones detected in almost all the wells studied.
A report submitted to the school of Graduate Studies, Kwame Nkrumah University of Science and technology (KNUST), Kumasi, in partial fulfillment of the Degree of Msc. Geophysics, 2008