Prospects and challenges in unlocking natural-gas-hydrate energy in India: Recent advancements

Natural gas hydrate deposits hold huge potential as a future energy resource of the world including India. To help realize these resources, India carried out two dedicated research expeditions (NGHP-01 and 02) to identify, characterize and analyze natural gas hydrate resource potential in its maritime boundaries. This work presents a review of the current status of research and development activities in the area of natural gas hydrate systems in India taking a cue from the NGHP-02 research findings. The NGHP-02 is considered one of the most extensive research programs to date for drilling and pressure core collection. This program resulted in minimally disturbed and well-preserved core samples collected from pressure-coring. Logging while drilling, wireline logging, formation pressure testing, vertical seismic profiling, and pressure core analysis confirmed one of the highly saturated similar to 40%-100%), sand-based, hydrate accumulation in three ultradeep locations, Area B, C, and E, eastern offshore India. The shipborne evaluation helped in the collection of the most suitable core samples to perform the first-ever comprehensive post-cruise triaxial testing, to obtain key petrophysical and geomechanical properties of interest. Further, a suitably designed experimental strategy helped to collect multiple sets of data from utilizing a lesser number of pressure core samples. The most prominent experiments included drained-undrained consolidation and compression, multistage compression and consolidation, alternating strain-rate compression, and permeability evaluation tests. The seal overlying hydrate layer are primarily made of clay rich sediments. The permeability measurements findings of the tested samples were reported in the range of 0.01 to tens of mD depending upon hydrate saturation, sand particle distribution, and range of applied effective stress. Significant permeability loss (similar to 90%) with increasing effective stress (up to 10 MPa) was noted. Further, permeability anisotropy, a ratio of horizontal to vertical permeability = 4, is reported to be consistent with the values reported for other marine hydrate-bearing sediments. The geochemical analysis put the natural gas to be primarily composed of methane mostly from microbial sources however part contribution from deeper sources was not ruled out. Moreover, numerical modeling of sand migration, thermal characterization, hydrate morphology, and extensive reservoir simulations was also used to obtain greater insight into the nature of the hydrate deposition system and its resource potential. Hydrate occurrences in an ultradeep and shallow subseafloor environment, such as those found in the Krishna Godavari basin, pose challenge to well bore stability and sustained gas production due to the combined effect of high-pressure drawdown and hydrate dissociation induced strength loss and sand migration. Hence, incorporation of a coupled flow, geomechanical and sand migration analysis in well bore stability and reservoir simulation are suggested as a way forward. The NGHP-02 program and its findings not only advance India's endeavor to locally produce natural gas from these unconventional resources but also provides valuable information concerning exploitation of other marine gas hydrate accumulations found elsewhere in the world.

Automated summary

India conducted two research expeditions (NGHP-01 and 02) to investigate the natural gas hydrate resource potential in its maritime boundaries. NGHP-02 is considered one of the most extensive research programs to date, providing valuable insights into the hydrate deposition system and its resource potential.