Geophysical Logging for Coal Exploration and Mine Planning at Singareni Collieries, Telangana, India

The Singareni Collieries Company Limited (SCCL) carries out exploration and exploitation of coal deposits in the 350km long NNW-SSE trending Pranhita Godavari Valley located in the state of Telangana, India. The Early Permian Barakar Formation contains workable coal deposits while the Late Permian Raniganj Formation contains intercalated carbonaceous horizons. In 1985, geophysical logging was introduced by SCCL mainly to substantiate logging core data. However since then, the technology has gone on to establish the correlation of coals, stratigraphic and the depositional history of these formations. More specifically, the identification of structural and sedimentary features are noteworthy contributions of geophysical logging and numerous applications have also been established in geotechnical engineering in underground and open cast mining.

The work on the geotechnical applications was driven by the need for greater productivity and safety in mining. In 2007, sonic and acoustic imaging logging tools were introduced to acquire a continuous spectrum of rock strength parameters and establish the spatial distribution of weak and strong beds. The UCS of sandstones estimated from sonic logs fall into three distinct categories of 3-7 MPa; 7.5-15 MPa and 15-30 MPa. The logs also indicate the locations of occasional lenses of 1-3 m thick, very fine grained silicified sandstones with UCS values of 40-150 MPa. These have the potential to induce periodic weighting. Within coal, the acoustic images are establishing the trends of joints/fractures, coal cleats and stress directions. Coal quality parameters are estimated to some extent from density and natural gamma logs.

Modelling software which establishes coal seams and other marker beds as controlling surface to grid the log data makes it easy to construct stratigraphic, facies and geohazard maps. In summary, geophysical logging is now providing insights into all the important branches of geology for acquiring geological and geotechnical information required for mine planning and design.