Nuclear geophysical logging for Gondwana coal exploration: a case study at Phulbari Coal Basin, northern part of Banglad
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ORIGINAL PAPER
Nuclear geophysical logging for Gondwana coal exploration: a case study at Phulbari Coal Basin, northern part of Bangladesh Md. Ibrahim Khalil & Farhana Islam & Eunuse Akon
Received: 1 June 2011 / Accepted: 11 November 2011 / Published online: 25 November 2011 # Saudi Society for Geosciences 2011
Abstract Different methods of lithology predictions from geophysical data have been developed in the last 15 years, among which the conventional logs are as follows: sonic, neutron–neutron, natural gamma, and density (backscattered gamma–gamma). This article concentrates on the nuclear geophysical suite, in particular, gamma and gamma–gamma logging, which, to date, provide the most accurate geophysical means of identifying coal seams and estimating their thickness. From the gamma and gamma– gamma logs of boreholes AEN 002, 007, 044, 045, 063, 085, and 105, which were carried out at the Phulbari Coal Basin of Bangladesh, two coal seams—upper and main with two lower seams of limited occurrence and of varying thickness—were identified, together with their regional occurrence. Keywords Nuclear geophysical logging . Gondwana coal exploration . Phulbari Coal Basin
Introduction The usual procedure for exploration of coal is to drill a large number of boreholes and undertake analysis of drill core to give all the geological information. However, in many cases, the drill core cannot be fully recovered and core loss poses a problem in determining the depth and the thickness of a coal seam accurately. Geophysical logging is an alternative method to provide the required geological M. I. Khalil (*) : F. Islam : E. Akon Nuclear Minerals Unit, Atomic Energy Research Establishment, Bangladesh Atomic Energy Commission, Ganakbari, Savar, Dhaka 1349, Bangladesh e-mail: [email protected]
information (Kayal 1979; Aizawa et al. 2004). Geophysical logging is the engineering science of downhole measurements of physical and chemical properties of rocks and their constituent fluids and often encompasses either an acoustic, electromagnetic, or nuclear technology (Kerr and Worthington 1988). Nuclear borehole logging methods are either active or passive (Borsaru 2005; Kerr and Worthington 1988). Passive device logging measures natural radiation using a detector, while active device logging uses a radioactive source and detector. Nuclear logging is widely used in the coal mining industry (Borsaru et al. 2001), particularly natural gamma, gamma– gamma, and both, and can provide information about coal seams. They are used in coal exploration or in the mining stage and can significantly reduce exploration and development costs (Borsaru et al. 2002; Charbucinskia et al. 1985). Wireline logs not only provide valuable information on seam continuity, interseam lithologies, and overburden type but also enable accurate seam thickness determination and depth correction of cores (Kempton et al. 1977). The prime benefit of geophysical logging is that it allows detailed interpretation of noncored holes, permitting either substitution of dia
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