Recent Advances in Coal Seam Sequestration Research in India - Highlighting Multiphase CO2 Flow for Deep Seam Sequestration

Abstract

India is a coal rich nation and has significant volumes of coalbed methane reserves. The recent developments in CBM production show a positive way of further research on understanding the reservoir behavior for carbon sequestration. India has the 3rd largest proven coal reserves and is the 4th largest producer of coal in the world. Moreover, the estimated CBM resources hold significant prospects for commercial recovery of the natural gas. The total CBM resource in India has been estimated to be around 4.6 TCM. Deeper reserves from which recovery of coal after CBM extraction seems less feasible, technologically as well as economically, may be the prime targets for sequestration of anthropogenic CO2. Coal seams that are found at depths which are below the limits of mining are considered suitable for disposal of anthropogenic CO2. Some estimates suggest that huge CO2 storage potential exists in the major coal fields in India and coal at depths more than 1200 m could store CO2 in the order of 345 Mt. Power sector in India is mostly coal based and produce huge quantities of CO2. There are several industries acting as point sources for CO2. The close proximity of deeper coals and location of large point sources of CO2 emission indicate the positives of sequestration in coal. Some basins have been marked with high sequestration potential of 1885 Mt in the Cambay basin while some like Singrauli could offer only 1-2 Mt of storage depending on various parameters.This study is a review of recent developments in the area of coal seam sequestration in India. A detailed analysis of the available literature was conducted along with few experiments on CO2-coal interactions. Few studies have been initiated in India to study the behaviour of Indian coal using CO2 and also to explore the possibility of enhanced recovery of coalbed methane. The trapping of CO2 in the coal seams is related to its capacity as well as the gas injectivity. Coal matrix shrinkage, swelling, gas diffusion and permeability have been significantly investigated over past few years. An important aspect which is yet to be fully understood is the role of phase transformation of CO2 on its hydro-mechanical behavior. Few experiments were conducted in our laboratory using different phases of CO2 in coal, obtained by varying pressure and temperature conditions. The changes in coal permeability due to supercritical CO2 flow were greatly attributed to the high volumetric deformation or the swelling of coal under supercritical CO2 as compared to liquid CO2. The injection pressures were observed to reduce the effective stress behavior, which in turn pushed the permeability evolution at each confinement to a positive trend. However, the permeability of CO2 reduced exponentially with increasing effective stresses.