Seismic interpretation for Tu Deh-Kah Geothermal

RPS is excited to have provided seismic interpretation services for the historic Tu Deh-Kah Geothermal (TDKG) project. This 7-15 MW geothermal project will serve the Fort Nelson First Nation, one of the most northern communities in British Columbia, Canada. 

Currently, the region relies on fossil fuel-generated electricity as it is not integrated with the provincial electric grid. This renewable energy project involves converting a depleted gas reservoir into a geothermal energy facility. The project is 100% Indigenous-owned and led, and will provide reliable and clean electricity, as well as abundant direct heat for buildings and greenhouses, creating new opportunities for economic growth for this remote community.

From depleted gas reservoir to geothermal energy

The TDKG project is based on converting a depleted gas reservoir in the Presqu'ile Barrier Reef Complex into a new geothermal project and to do so requires a thorough understanding of the sub-surface geology to determine the project's feasibility.

To estimate potential energy output, calculate profit and demonstrate long-term project sustainability, the TDKG team needed to determine the likely flow rates of the water within the reservoir. The higher the flow rates, the faster water would move through the system, producing more energy.  The better the porosity and permeability of the water-bearing reservoirs, the more likely to achieve high flow rates and hence heat to energy conversion.

A first step in understanding any reservoir's deliverability (whether it be of hydrocarbons or hot water) is to delineate the structure and map the distribution of porous zones within that structure in order to maximise the probability of drilling a new well into a zone that would prove the project's potential. Unfortunately, the data available to the TDKG team over the carbonate reef was limited despite the earlier production and previous mapping etc. and was restricted to well-log data only. Historically acquired 3D seismic had been shot but was prohibitively expensive to purchase.

The challenge was to pinpoint the best possible location to drill confidently, cost-effectively and quickly based on limited data. Based on our deep sub-surface expertise, RPS was selected to maximise such data as were available and evaluate if the proposed drilling target was fit for purpose.

RPS delivered the structure maps for the key geological horizons, and likely porosity maps to the TDKG team. The maps were used to confirm the initial geological model and the proposed well's location and model the expected flow rates of the new geothermal system based on mapped porosity extent and hence likely reservoir deliverability.

The enhanced understanding of the risk and uncertainty that one must expect from any well is critical to minimising the risk of making an expensive mistake, particularly early in a project's lifecycle when investment decisions are likely to be made. A balance must always be struck between the cost of data acquisition and the potential value enhancement of early proof of concept and commerciality.

By applying skills and lessons learned in other exploration and development activities and their deep expertise in seismic data manipulation, interpretation and modelling, RPS was able to provide the TDKG team with a fit-for-purpose methodology to gain greater confidence that the well will be drilled in an optimal location with the best chance of early success. The drilling of the test will be completed in 2021.