Gas Hydrate Multistress Permeability-Testing Apparatus: A Hydrate Formation and Dissociation Study

The world is transitioning from conventional to unconventional energy sources due to climate change and the increasing demand for energy. To minimize the CO2 footprint of coal- or oil-based energy, the scientific community is exploring energy sources that emit lower levels of CO2. One such source of energy is methane hydrates, which are abundant across the globe and are a dense form of energy. India has an estimated 1900 TCM of methane-gas-hydrate (MGH) reservoirs in the KG Basin of the eastern economic zone, and developing this resource may play a vital role in driving its energy self-sufficiency. However, the geomechanical response of these reservoirs is yet to be understood from the perspective of production, and therefore, the associated risks remain to be ascertained. Therefore, it is necessary to develop an experimental facility that can replicate the conditions of Indian subsurface MGH reservoirs. Triaxial testing is considered to be the best method to study the geomechanical response of hydrate-bearing sediments. A triaxial facility, which was developed at the Indian Institute of Technology, Bombay (IITB), can recreate the thermodynamic conditions of the hydrate reservoir. The apparatus is also equipped for the control of a complex multiphase fluid flow. This instrument can form gas hydrates in field sediments. Additionally, it enables triaxial testing at a constant stress or strain rate. The multistress gas hydrate triaxial can apply a maximum confining pressure of 30 MPa and backpressure of 30 MPa, and it can regulate the temperature from −35 to 40 °C. It is also capable of applying a maximum axial load of 150 kN on a sample diameter of 50 mm and height of 100 mm. The system logs data continuously to record axial and radial strains, confining and backpressures, temperature, P–S wave velocity, and electrical resistivity tomography (ERT). The system was successfully tested for leakage at its maximum pressure capacity. The CH4 hydrates were formed in the synthetic sand sediment at 9 MPa of confining and 8.8 MPa of backpressures at a temperature of 3–5 °C. The hydrate formation event was marked by temperature and validated by changes in P–S velocity and electrical resistivity. A detailed methodology covering sample preparation is also presented.