With known basement hydrocarbon accumulation, Mumbai High field in Western Offshore, India is a priority area for extending the concept of fracture characterization in metamorphic basement reservoirs. Basement in Mumbai High is hydrocarbon bearing in few areas proximal to major fault damage zones and intersections of major regional tectonic cross trends. The challenge lay in characterizing such basement reservoirs with significant heterogeneities in mineralofacies, in situ stress fields, seismic amplitudes, fracture properties and connectivity, and flow potential. This necessitated development of an integrated static fracture model workflow assimilating structural modeling, seismic and petro-physical interpretations for fracture drivers and geocellular fracture modeling, fine tuned using geological concepts and point data extracted from well data analyses. The deterministic geo-cellular fracture model thus prepared has been calibrated with real time well observations and has been found to satisfactorily explain anomalous hydrocarbon accumulation and flow pattern in basement wells tested in the area. The adopted workflow has helped planning wells for evaluating and exploiting basement reservoir as well for real time monitoring of wells.
Alimuddin, Sultan (Pandit Deendayal Petroleum University) | Kumar, Neeraj (Pandit Deendayal Petroleum University) | Gandhi, Kanan (Pandit Deendayal Petroleum University) | Satyam, Swapnil (Pandit Deendayal Petroleum University)
Spurred by the commercial success of coalbed methane activity in USA, India initiated evaluating its coal bearing basins for their coalbed methane potential in 1992. In a short span of five years it tested and flowed coalbed methane from one of the coal seams of Barakar Formation in Jharia basin. This basin is one of the member basins of the Damodar-Koel coal belt of Eastern India. The basin cover an area of 450 square kilometers and exposes sediments of the Permian, Lower Gondwana Group. It is a half graben with the southern boundary fault being more pronounced than the northern boundary fault. The tectonic setting, physio-chemical, and reservoir characteristics, depth and thickness of coal seams, and production testing of one of the coal seams has resulted in demarcating the southern part of the basin to have an attractive coalbed methane play.
The central portion of this part of the basin has been prioritised for converting about 15 billion cubic meters of coalbed methane resources to reserves. Additional 15 billion cubic meters of methane resources could be converted to reserves from the adjoining areas.
Production of unconventional gas from sources like coal, shales and tight reservoirs is becoming increasingly important. In U.S.A. alone, this gas accounts for 20% of the production. Coalbed methane out numbers the other sources of gas by about 65%. Spurred by the U.S. success, many coal rich countries have launched exploration and production programmes to harness this resource. India, in 1992 embarked on evaluating its coal bearing basins for their coalbed methane potential. In 1997 India tested and flowed coalbed methane for the first time from a well drilled in the Parbatpur block of Jharia basin. Since then, concerted efforts are being made to cost effectively exploit this energy source. The Government of India has announced lucrative terms and conditions to attract investments in CBM exploration and production activities (Kelafant and Stern1).
India, which has the 6th largest coal reserves in the world, is expected to have potential for coalbed methane. About 99% of the coal reserves of India are found in the Gondwana basins while 1% lies within the Tertiary basins (Fig.-1). Some of the Gondwana basins have been prioritised for evaluating their coalbed methane plays. The prioritisation has been done on the basis of parameters suggested by Mandal and Ghosh2, wherein thirteen criterion are ranked from 1-10 with the least numeral having highest priority (Table-1). The priority that has emerged is as follows:
I. Jharia basin
II. East Bokaro basin
III. Raniganj basin
IV. North Karanpura basin
V. South Karanpura basin
VI. Rajmahal basin
VII. Pench-KanhanValley (Satpura Basin)
VIII. Pranhita-Godavari basin
The above prioritisation shows that the Rajmahal and Satpura basins are of the same rank. Priority has been given to the former because it has thicker coal seams.
Since coalbed methane exploration and exploitation activity in India is still in the initial stages these activities are in the R & D phase. Concerted efforts integrating geo-scientific, reservoir and production characteristics to evaluate the coalbed methane play of Jharia basin are discussed in this paper.