Speaker
Description
Objectives and Scope:
The Tano basin offshore Ghana is being studied to strategically help achieve net-zero goals within the oil and gas industry across the West African sub region. The Ghana National Petroleum Corporation and the Petroleum Commission of Ghana hold years of subsurface data and knowledge to analyze and choose conducive reservoirs for CCUS project, playing key role in the energy transition in the sub region. Petrophysical and geomechanic properties of three wells A, B, and C were studied and used to characterize basin formation.
Methods, Procedures, Process:
The study employed an integrated workflow to investigate reservoir rock characteristics. We obtained reliable geotechnical data from limited geophysical well logs and results used to describe the geological suitability of three offshore wells in the Tano basin for CO2 sequestration. Data comprising gamma ray, resistivity, neutron, density logs were used. Gamma ray log was used for lithologic discrimination; resistivity log was employed to identify formation fluid based on electrical responses of reservoir formations, while combined density and neutron logs were used to estimate reservoir porosity. The analysis revealed thickness of sand zones and their geotechnical properties such as porosity and permeability.
Results, Observations, Conclusions:
Analysis of Well A indicated net reservoir interval, 56.1m of sandstone zones delimited by shale with porosity (min.9, aver.14 and max. 18) and 0.3-5.8mD permeability range. Well B, 37m, porosity (min.14, aver.16.5 and max. 19) and permeability 1.4 - 13.1mD range. Well C, 43m of alternating sandstone and shale, porosity system (min.14, aver.16.6 and max. 19) and 1.0-9.4mD range of permeability. Average water saturation (Sw) and hydrocarbon saturation (Sh) in each well was 0.88/0.12, 0.70/0.30 and 0.61/0.39 for wells A, B and C respectively. Reservoir permeability and Sw values observed depict suitability of reservoir to enhance CO2 storage as in residual and solubility trappings whereas the several intra-reservoir shale layers act as barriers to trap CO2 deep in the reservoir. The study approach provides useful insights and preliminary evaluations of suitability of the wells for CO2 sequestration.
Significance/Novelty:
The work approach use a deterministic workflow to obtain reliable petrophysical outputs with scarce wellbore data. Deterministic workflows calculate petrophysical parameters sequentially and are easy to use even for non-petrophysicists. This studies workflow can be applied to other reservoirs targeted for CO2 storage offshore Ghana.