The optimization of a potential geothermal reservoir using abandoned wells: a case study for the forest reserve field in Trinidad
The worldwide dependence on non-renewable energy sources continues as existing energy systems have been built on these supplies. There is an established link between these conventional energy resources, greenhouse gas (GHG) emissions and climate change and its associated negative effects. As a signatory to the Paris Agreement, Trinidad and Tobago (TT) has been exploring strategies to reduce GHG emissions and the use of geothermal energy is one potential option. Through enhanced geothermal systems, TT, even without extensive volcanic heat reservoirs, can still develop this renewable source by utilizing oil reservoirs. This study evaluates the possibility of designing and evaluating geothermal systems using wells from the Forest Reserve felds in South-western Trinidad as a case study. The Forest Reserve fields have a high number of abandoned oil and gas wells which can be re-used for tapping the required heat and reducing the requirement for drilling of new injection and production geothermal wells. Key information and data from these wells and reservoirs were used as input for CMG software to model, design and evaluate the feasibility of the geothermal reservoir and wells as being possible and viable for geothermal production. A base model was constructed in the CMG software which was subjected to three essential manual sensitivity analyses (well distance, stream temperature, and injection pressure) to obtain an optimized model which was then subjected to hydraulic fracturing. The optimal model of the retrofitted geothermal systems demonstrated to be the best case scenario due to the shallow nature of the reservoir in the area of interest. Six retrofitted geothermal systems (3 injector wells and 3 producer wells) showed that capable capacity of 3.3721 MWe for a 25-year period with an Internal Rate of Return of 190% and an Net Present Value of US$1,431,263,840.00 utilizing a Minimum Acceptable Rate of Return of 10%, Capital Expenditure of US$12MM, Operating Expenditure of US$2MM and a cost of geothermal electricity at US$0.05 per kWh. These results were then used in Crystal Ball to apply Monte Carlo simulations where it confirmed that the project is 100% economically feasible. The cumulative carbon dioxide reduction after the 25-year period was 50,062,500 tons of CO2.
