2COAL EXPLORATION

F ollowing nationalization of the coalindustry in the early 1970s major strideshave been made in geological exploration work,leading to the current total inventory of nearly246 billion tonne of coal reserves. About2,45,000m of exploratory drilling is being doneannually. Large capacity mechanized mineshave also been started, both opencast andunderground, which call for accurateexploration data so as not to jeopardize highcapital investment because geologicalanomalies, like faults, dykes and presence ofstone bands, can adversely affect miningoperations resulting in delays, unproductiveexpenditure, loss of production and unsafeconditions.

A total of 19 research projects have beencompleted under the Coal S&T Grant in thearea of exploration techniques. Efforts havebeen made through sustained R&D work,mainly at CMPDI, to enhance both the pace andaccuracy of coal exploration for improvedgeological modeling of the coal resources of thecountry. Many of the exploration techniquesintroduced through these R&D efforts are nowemployed on a routine basis. Research projectscompleted in this area are listed in table 2.

Introduction of geophysical techniques, whichwere hardly used for coal exploration beforenationalization of the industry, has resulted insignificant gains by reducing the earlierpractice of 100% core drilling of boreholes forexploration. Core drilling is both timeconsuming and expensive; whereas non-coredrilling, though much more economical,requires high degree of accuracy foridentification and delineation of rock strata bygeophysical techniques. Not only within thecountry, nearly 50% of the drilling carried outby CMPDI in Mchuchuma coalfield of Tanzaniawas of the non-coring type. As a result of thesuccessful application of geophysical methods,demonstrated by the S&T projects, other coalproducing companies also have adopted thishighly cost saving tool for their explorationneeds.

Multi-parametric GeophysicalLogging

One of the S&T projects has enabled multi-parametric geophysical logging for Indiancoal measure strata, which produces a suite ofgeophysical logs consisting of resistance,focused resistivity, natural gamma, density,

Geological Model

3neutron, sonic and caliper records. Multi-parametric geophysical logging is used toprovide accurate information regarding thethickness of coal seam, presence of dirt bandsand lithology of rock strata in the boreholesleading to precise sub-surface information.Interpretation of the logs is done mostlythrough a software called SASLINT developedfor the purpose. The technique is beingregularly employed now for both coring andnon-coring boreholes to identify lithology of thestrata encountered along with ash, moistureand volatile matter contents of the coal seams.CMPDI has so far used this technique forlogging of 7,21,872m in 3848 boreholes tillMarch 2004.

Geophysical equipment on mobile loggers

The system of geophysical logging hasbeen integrated into the routine explorationprogrammes of the coal sector and presently atotal of eight mobile geophysical loggers areused on a regular basis by CMPDI forlogging of about 50,000 depth metresannually, providing useful inputs to mineplanning.

Other projects carried out involved studiesrelated to micro-gravity, seismic and electricalresistivity tomography, in-seam seismictechnique and high-resolution shallow seismicsurvey.

High Resolution ShallowSeismic Survey

In the 1980s through a project funded underCoal S&T Grant CMPDI introduced highresolution shallow seismic survey [HRSS] forthe coal industry in collaboration with ONGCand a UK mining consultant company. A 24channel digital seismic unit was procured fromthe USA and the R&D project involvedextensive field investigations involving dataacquisition, processing and interpretation. Theproject succeeded in generating usefulinformation for detailed mine planning andlater the technique was integrated into theroutine exploration programme for the coalsector. Since 1998 HRSS data processing hasbeen shifted from earlier mainframe computerbased software to a PC based system. Up toMarch 2004 about 160 line km of survey hasbeen done by CMPDI in 30 coal blocks.

Digital seismic equipment for HRSS survey

Digital seismic equipment for HRSS survey

424 Channel Engineering Seismograph

Geophysical ExplorationStrategy

Investigations carried out under Coal S&TGrant have defined the exploration strategyfor application of geophysical techniques fordepicting sub-surface structure, stratasequence, coal seam in-crop, occurrences ofintrusions, etc. A number of exploration toolsare now available for specific applications.

Seismic refraction survey was originally usedfor delineation of coal seam in-crop, but laterthe technique has also been found useful fordetermination of rippability characteristics ofnear-surface rocks to help opencast mineplanners. This method has been successfullyused also to find the thickness of hard cover[15m mandatory requirement] for undergroundmine planning. A total of about 205 line km hasbeen surveyed by this method so far by CMPDIfor various mines.

Two types of electrical resistivity surveys,namely Electrical Resistivity Profiling [EPR]and Vertical Electrical Soundings [VES], areroutinely used by CMPDI. The first method,EPR, has been found useful for delineation ofseam in-crop, demarcation of sedimentary-metamorphic boundaries and delineation offaults. The other method, VES, is being usedfor basement studies and to locate ground waterresources in order to obtain hydro-geologicalinputs. Up to March 2004 approximately 1300

line km of electrical resistivity profiling hasbeen done besides 1142 vertical electricalsoundings for various coalfields.

Gravity survey has been found useful fordemarcation of major faults and sedimentary-metamorphic boundaries. Another method,magnetic survey, has been successfully utilizedfor accurately demarcating location of dykes incoalfields. The combination of the twotechniques has also been successful inexploration of non-coal minerals, likemanganese and iron ore. So far CMPDI hasconducted nearly 800 line km of magneticsurvey and approximately 100 line km ofgravity survey.

Residual magnetic anomaly map

Application of powered-support longwallmining requires accurate prediction ofstructural disturbances within the coal seamso as to avoid unproductive stoppage of capitalintensive mining equipment. To this end in-seam seismic survey [ISS] has been found toplay a key role for demarcation of areas freefrom geological discontinuities, like faults andintrusions. With projected rise in longwallmining the ISS method is going to find muchgreater application in the Indian coalindustry.

Along with the introduction of advancedexploration techniques, development ofcomputer software for data analysis andinterpretation has also been an area of intenseR&D effort. A PC based software packageCEMPGEODOC has been developed, which can

5be used as a front end for mine planningsoftware like MINEX. The package enablesvalidation of basic lithology and provides outputof analytical data, graphic lithologs, seamcorrelation, seam structure, borehole locationplans and graphic correlation charts on PCbased plotters.

Resistivity distribution from profile data

Hydrogeology

Water in sub-surface strata encounteredduring mining is a part of the hydro-geologic cycle and needs to be managed bothfor ensuring safe operations and also forpreservation of the eco-system. While mine

Well testing under S&T project in Rajasthan

workings under heavily water-bearing strataneed to be safeguarded against possible inrushof water, it is also necessary to protect thenatural water resource in a mining area, bothin terms of quality and quantity. Studiesrelated to the hydro-geological regime of a coal-bearing area, therefore, play an important rolein planning future mining operations.

Hydro-geological investigations have beencarried out under Coal S&T Grant for lignitedeposits at Merta Road in Rajasthan. Similarstudies have also been carried out for modelingand control of water systems in Chandrapurarea of Wardha Valley coalfield and in Rajmahalarea of Lalmatia coalfield under a UNDPassisted project. The procedures establishedthrough these projects have been gainfullyemployed for a large number of mines in BCCL,ECL and in WCL where underground miningis being carried out under heavily water-bearingaquifers. These studies have led to thedevelopment of a strong technological base andknow-how for detailed hydro-geological studies,water supply investigations, deep-seateddewatering, well rehabilitation, long durationpumping tests and data analysis throughcomputer based programmes for groundwatermodeling and futuristic projections with socio-economic interface to enable total waterresource management.

Automated Petrograph ImageAnalysis System

A research project on characterization ofIndian coals by use of digital imageanalysis technique was taken up by CMPDI.Under this project an Automated PetrographImage Analysis (PIA) system using digitalimage analysis technique was developed formaceral analysis of coal pellets and formeasurement of reflectance of vitrinite in coalpellets. A total of 242 coal samples (boreholecoal cores and low volatile high reflectancecoals) from the major coalfields of India, viz.Ranigunj, Jharia, East Bokaro, West Bokarocoalfields, and also 18 LVMR coal samples fromEast Bokaro and Jharia coalfields were studiedand validated for maceral analysis. It wasobserved that the PIA system can speed upmaceral analysis to the extent of three samplesper day (one shift operation) per person in

6comparison to that of one sample per day (oneshift operation) per person using the point-count method of conventional petrography,which would mean a cost saving of 30%.Similarly, reflectance measurements onvitrinite could be performed on six samples perday (one shift operation) per person in

comparison to that of two samples per day (oneshift operation) per person using theconventional petrography method, which wouldprovide a cost saving of 45%. Thus, the PIAsystem developed under the project was nearlythree times faster and cost saving than manualwork.

Identification of macerals/minerals using gray-level detection technique

Table 2 : S&T projects on coal exploration and hydrogeology

Sl. Title of the Project Project Imple- Year of TotalNo. Code menting completion Approved

Agency Cost(Rs. in lakh)

1. Resistivity survey for estimation of CE/4 CMPDI 1982 0.80overburden, locating out-crops andmapping bed-rock geology

2. Resistivity survey for estimation of CE/5 CMPDI 1982 0.80river sand

3. Seismic refraction survey for sub-surface CE/6 CMPDI 1982 10.15gological mapping

74. Geophysical strategy to solve coal CE/8 CMPDI\ 1982 1.50exploration problem Osmania Univ.

5. Geophysical logging of boreholes CE/3 CMPDI 1983 41.51

6. Estimation of reserves of coal volume of CE/13 CMPDI 1983 13.87overburden by electronic data plotter

7. Physico-mechanical properties of rocks and CE/11 CMPDI 1984 8.00coal from exploration data

8. Hydrogeological investigation CE/1 CMPDI 1985 36.00

9. Computerisation of geophysical logging CE/14 CMPDI 1985 2.20data

10. Geo-statistical analysis for optimisation CE/15 CMPDI 1985 2.89of drilling

11. Carbolite coke oven CE/2 CMPDI 1986 5.00

12 . Development of computer based geo-data CE/12 CMPDI 1988 34.60bank

13. Geothermal investigations in Manuguru CE/20 SCCL 1988 10.85area of Godavari valley coalfield

14. Identification and delineation of CE/22 MGMI 1991 4.50abandoned underground colliery workingsin Raniganj Coalfield

15. High resolution shallow seismic reflecton CE/9 CMPDI 1992 224.63survey

16. Development of methodology for thermal CE/23 CMPDI 1992 179.00studies of mine fires using remote NRSAsensing technique in Jharia Coalfield

17. Identification and delineation of abandoned and CE/24 CMPDI 1995 57.5unsurveyed colliery workings in Raniganj Coal MGMIFields - Geophysical Studies IDRC

(Canada)

18. In-seam seismic survey CE/21 CMPDI 1999 184.00

19. Development of methodology for characterisation of Indian CE/26 CMPDI 2001 114.50coal by computer aided petrographic image analysis