This phase-measured pressure build-up in the underground heat exchanger (reservoir) was a follow-up to a recently completed long-term flow test.

The diagnostic phase of the reservoir testing program showed evidence the two Habanero wells were connected to a highly permeable fracture system, which forms up the underground heat exchanger.

Analyses show that this system has a fluid volume of at least several million cubic metres, according to Geodynamics.

Tests also indicated the underground heat exchanger was connected to a natural fracture system of lesser permeability which many times greater in size, the company said.

This confirms the existence of a “vast” volume of superheated, over-pressured water, trapped within the granite fracture network, according to Geodynamics.

"The findings are highly encouraging as they confirm the feasibility of heat extraction from the target hot rocks on a large scale," said managing director Bertus de Graaf.

But the long-term flow test has shown that the Habanero-2 well is poorly connected to the underground reservoir with restrictions close to or in the well.

The company now aims to use a large pump for hydraulic stimulation tests in Habanero-2 and possibly improve the connection with the reservoir.

More large pumps will be added for the project's enhancement phase.