Coal Characterization by Coal Bed Methane Drilling in Tatapani - Ramkola Coalfield, Surguja District, Chhattisgarh, India

Das, Dilip K.; Mahanta, Koushik
CBM, Dart Energy, Gurgaon, India.

Tatapani-Ramkola (TR) Coalfield represents an east-west trending synclinal sub-basin lying in the easternmost segment of South Rewa Gondwana basin. The coal bearing lower Gondwana rocks occur as detached and fault bounded outcrops along the peripheral parts of the sub-basin while the rocks of upper Gondwana occupy the central and western part of the coalfield. There are breaks in the continuity of the coal bearing strata which may be attributed to either structural dislocations or overlapping of younger strata leading to the formation of a number coal bearing locales of limited extent. Three sets of faults have been reported in the coalfield and their interference has resulted in development of a number of horst and graven structures. Dart Energy as an operator in TR block have completed exploration by drilling eight core holes and test wells. The findings presented in this paper are based on the data obtained during the exploration and include gas content/gas saturation, permeability, gas saturation and coal continuity which together decide CBM potential of this area.

The wells were cored for a total of 8212.60 meters of continuous wire line core and logged with a modern wire line logging suite for a total of 3993 meters of new wire line logs. A total of twelve coal seams (I to XII in ascending order) were recorded in Barakar Formation. Seam thickness ranges from 0.75m to 11.67m and were intersected between the depths of 564.50m and 1061.15m. The cumulative net coal content for the main regionally persistent seams III, IV & V varies from 3.00m to 10.20m. Thicknesses of individual seams are almost uniform in nature and maintain uniform inter-seam partings over the area.

Petrographically, the coals are vitrinite rich (67% and 30%) in the upper seams while with more of inertinite (10% and 40%) in the lower coal seams. Unusual very high content of liptinite (6.5% to 16%) may indicate a mixed depositional environment. The coal rank changes from VRo of 0.57% in the western and eastern part to 0.94% in the central deeper part.

The coals desorbed very low quantities of gas over most part of the area with gas saturation of as low as 2%. In the south western part little higher quantities of gas (up to 2.7 m3/t daf) is observed with the maximum saturation about 37%. The reservoir permeability is good (up to 35 mD).

Based on the new drilling results volumetric analysis of the coal volumes, OGIP and potentially recoverable gas can be made.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012