Investigating geochemical fluid-rock interactions

The analysis of geological systems is essential to enable and improve geothermal production, radioactive waste disposal, and carbon capture and storage. Modern technologies require the engineering of geological host structures which inevitably change in-situ conditions of the rock, including stress state, temperature, geochemistry, and pressure. Fluids injected into rock for these operations can impact hydraulic conductivity, deformation behavior, and chemical interactions.

While numerous geological interactions occur simultaneously in nature, isolating and analyzing individual effects, especially over prolonged periods, can be challenging. Harpers et al. designed a laboratory-scale setup that allows for the analysis of chemical environments and subsurface conditions from rock plugs and powdered samples.

“By combining different functionalities and sensors, we can investigate complex interactions between thermal, hydraulic, mechanical, and chemical effects on rocks,” said author Nick Harpers.

The flow bench consists of four small triaxial cells that can hold confining and pore pressure up to 20 MPa and an axial load of up to 300 MPa. Linear variable differential transducers measure axial deformation. The cells can be heated to 90 C, and gas-saturated brines can be injected into the rock samples. Effluent can be sampled for later analysis of compositions. Each cell can be operated independently allowing for long-term experiments.

“Our setup also shows a way to handle long-term testing of coupled factors and will hopefully inspire new setups to tackle slow mechanisms in rock systems,” said Harpers.

Future work will focus on the addition of pH monitoring to the setup and the effects of the reactions of rocks with complex brines on fracture hydraulics and geometry.

Source: “The Harpers THMC flow bench: A triaxial multi-reactor setup for the investigation of long-term coupled thermo-hydro-mechanical-chemical fluid-rock interaction,” by Nick Harpers, Ming Wen, Paul Miller, Suzanne Hangx, and Andreas Busch, Review of Scientific Instruments (2023). The article can be accessed at https://doi.org/10.1063/5.0160906 .