The objective of this project is to determine the effect of reservoir and fluid properties on fluid circulation and pressures in geothermal operations with production from multiple reservoirs and the implications, associated hazards and mitigation measures.
Fluid circulation in geothermal systems with matrix-dominated flow may involve multiple reservoirs where heat is extracted from two or more reservoirs separated by low-permeability layers. In the Dutch geothermal industry these fluid flows are not separated inside the wells by using multiple injection/production strings, but are commingled. This type of production involves the assumption that the volume ratio between the reservoirs for the extracted fluid is equal to the volume ratio between the reservoirs for the injected fluid. In other words, the distribution of flow in each reservoir is balanced, where the volumes of water that are extracted from and re injected into one reservoir are equal. The average reservoir pressures are expected to be close or equal to initial conditions in such a system. Differences in the reservoir properties between the injection and production well within one reservoir, such as differences in thickness or permeability, could potentially affect the fluid circulation and cause unbalanced flow. Unbalanced flow could also result from differences in well completion between the injector and producer, and/or differences in the connection between the well and reservoir (‘skin factor1 ’) for the injector and producer. Finally, differences in the properties of the fluids between the reservoirs, such as salinity or temperature, could also potentially cause unbalanced flow. The latter could result because the injection fluid is a homogenised fluid in which the produced fluids with different properties are no longer separated but mixed. Possible effects of unbalanced flow are expected to include a change in the reservoir pressures. The effects of unbalanced flow, in turn, may result in hazards such as seismicity or uplift / subsidence.
Specific research questions to be answered are:
1) What is the effect of reservoir and fluid properties on fluid circulation and pressures in geothermal systems with production from multiple reservoirs?
2) What are the possible effects of unbalanced fluid circulation per reservoir and what are the associated hazards?
3) What are potential mitigation measures of the effects of unbalanced flow, such as potential pressure gradients?
The research started in 2025 and is excuted by VITO and Sproule.