Coal Exploration - COAL EXPLORATION F ollowing...

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Unformatted text preview: COAL EXPLORATION F ollowing nationalization of the coal industry in the early 1970s major strides have been made in geological exploration work, leading to the current total inventory of nearly 246 billion tonne of coal reserves. About 2,45,000m of exploratory drilling is being done annually. Large capacity mechanized mines have also been started, both opencast and underground, which call for accurate exploration data so as not to jeopardize high capital investment because geological anomalies, like faults, dykes and presence of stone bands, can adversely affect mining operations resulting in delays, unproductive expenditure, loss of production and unsafe conditions. Introduction of geophysical techniques, which were hardly used for coal exploration before nationalization of the industry, has resulted in significant gains by reducing the earlier practice of 100% core drilling of boreholes for exploration. Core drilling is both time consuming and expensive; whereas non-core drilling, though much more economical, requires high degree of accuracy for identification and delineation of rock strata by geophysical techniques. Not only within the country, nearly 50% of the drilling carried out by CMPDI in Mchuchuma coalfield of Tanzania was of the non-coring type. As a result of the successful application of geophysical methods, demonstrated by the S&T projects, other coal producing companies also have adopted this highly cost saving tool for their exploration needs. A total of 19 research projects have been completed under the Coal S&T Grant in the area of exploration techniques. Efforts have been made through sustained R&D work, mainly at CMPDI, to enhance both the pace and accuracy of coal exploration for improved geological modeling of the coal resources of the country. Many of the exploration techniques introduced through these R&D efforts are now employed on a routine basis. Research projects completed in this area are listed in table 2. Multi-parametric Geophysical Logging O ne of the S&T projects has enabled multiparametric geophysical logging for Indian coal measure strata, which produces a suite of geophysical logs consisting of resistance, focused resistivity, natural gamma, density, Geological Model 2 neutron, sonic and caliper records. Multiparametric geophysical logging is used to provide accurate information regarding the thickness of coal seam, presence of dirt bands and lithology of rock strata in the boreholes leading to precise sub-surface information. The system of geophysical logging has been integrated into the routine exploration programmes of the coal sector and presently a total of eight mobile geophysical loggers are used on a regular basis by CMPDI for logging of about 50,000 depth metres annually, providing useful inputs to mine planning. Interpretation of the logs is done mostly through a software called SASLINT developed for the purpose. The technique is being regularly employed now for both coring and non-coring boreholes to identify lithology of the strata encountered along with ash, moisture and volatile matter contents of the coal seams. CMPDI has so far used this technique for logging of 7,21,872m in 3848 boreholes till March 2004. Other projects carried out involved studies related to micro-gravity, seismic and electrical resistivity tomography, in-seam seismic technique and high-resolution shallow seismic survey. High Resolution Shallow Seismic Survey I n the 1980s through a project funded under Coal S&T Grant CMPDI introduced high resolution shallow seismic survey [HRSS] for the coal industry in collaboration with ONGC and a UK mining consultant company. A 24 channel digital seismic unit was procured from the USA and the R&D project involved extensive field investigations involving data acquisition, processing and interpretation. The project succeeded in generating useful information for detailed mine planning and later the technique was integrated into the routine exploration programme for the coal sector. Since 1998 HRSS data processing has been shifted from earlier mainframe computer based software to a PC based system. Up to March 2004 about 160 line km of survey has been done by CMPDI in 30 coal blocks. Digital seismic equipment for HRSS survey Digital seismic equipment for HRSS survey Geophysical equipment on mobile loggers 3 line km of electrical resistivity profiling has been done besides 1142 vertical electrical soundings for various coalfields. Gravity survey has been found useful for demarcation of major faults and sedimentarymetamorphic boundaries. Another method, magnetic survey, has been successfully utilized for accurately demarcating location of dykes in coalfields. The combination of the two techniques has also been successful in exploration of non-coal minerals, like manganese and iron ore. So far CMPDI has conducted nearly 800 line km of magnetic survey and approximately 100 line km of gravity survey. 24 Channel Engineering Seismograph Geophysical Exploration Strategy I nvestigations carried out under Coal S&T Grant have defined the exploration strategy for application of geophysical techniques for depicting sub-surface structure, strata sequence, coal seam in-crop, occurrences of intrusions, etc. A number of exploration tools are now available for specific applications. Seismic refraction survey was originally used for delineation of coal seam in-crop, but later the technique has also been found useful for determination of rippability characteristics of near-surface rocks to help opencast mine planners. This method has been successfully used also to find the thickness of hard cover [15m mandatory requirement] for underground mine planning. A total of about 205 line km has been surveyed by this method so far by CMPDI for various mines. Residual magnetic anomaly map Application of powered-support longwall mining requires accurate prediction of structural disturbances within the coal seam so as to avoid unproductive stoppage of capital intensive mining equipment. To this end inseam seismic survey [ISS] has been found to play a key role for demarcation of areas free from geological discontinuities, like faults and intrusions. With projected rise in longwall mining the ISS method is going to find much greater application in the Indian coal industry. Two types of electrical resistivity surveys, namely Electrical Resistivity Profiling [EPR] and Vertical Electrical Soundings [VES], are routinely used by CMPDI. The first method, EPR, has been found useful for delineation of seam in-crop, demarcation of sedimentarymetamorphic boundaries and delineation of faults. The other method, VES, is being used for basement studies and to locate ground water resources in order to obtain hydro-geological inputs. Up to March 2004 approximately 1300 Along with the introduction of advanced exploration techniques, development of computer software for data analysis and interpretation has also been an area of intense R&D effort. A PC based software package CEMPGEODOC has been developed, which can 4 be used as a front end for mine planning software like MINEX. The package enables validation of basic lithology and provides output of analytical data, graphic lithologs, seam correlation, seam structure, borehole location plans and graphic correlation charts on PC based plotters. workings under heavily water-bearing strata need to be safeguarded against possible inrush of water, it is also necessary to protect the natural water resource in a mining area, both in terms of quality and quantity. Studies related to the hydro-geological regime of a coalbearing area, therefore, play an important role in planning future mining operations. Hydro-geological investigations have been carried out under Coal S&T Grant for lignite deposits at Merta Road in Rajasthan. Similar studies have also been carried out for modeling and control of water systems in Chandrapur area of Wardha Valley coalfield and in Rajmahal area of Lalmatia coalfield under a UNDP assisted project. The procedures established through these projects have been gainfully employed for a large number of mines in BCCL, ECL and in WCL where underground mining is being carried out under heavily water-bearing aquifers. These studies have led to the development of a strong technological base and know-how for detailed hydro-geological studies, water supply investigations, deep-seated dewatering, well rehabilitation, long duration pumping tests and data analysis through computer based programmes for groundwater modeling and futuristic projections with socioeconomic interface to enable total water resource management. Resistivity distribution from profile data Hydrogeology W ater in sub-surface strata encountered during mining is a part of the hydrogeologic cycle and needs to be managed both for ensuring safe operations and also for preservation of the eco-system. While mine Automated Petrograph Image Analysis System A research project on characterization of Indian coals by use of digital image analysis technique was taken up by CMPDI. Under this project an Automated Petrograph Image Analysis (PIA) system using digital image analysis technique was developed for maceral analysis of coal pellets and for measurement of reflectance of vitrinite in coal pellets. A total of 242 coal samples (borehole coal cores and low volatile high reflectance coals) from the major coalfields of India, viz. Ranigunj, Jharia, East Bokaro, West Bokaro coalfields, and also 18 LVMR coal samples from East Bokaro and Jharia coalfields were studied and validated for maceral analysis. It was observed that the PIA system can speed up maceral analysis to the extent of three samples per day (one shift operation) per person in Well testing under S&T project in Rajasthan 5 comparison to that of one sample per day (one shift operation) per person using the pointcount method of conventional petrography, which would mean a cost saving of 30%. Similarly, reflectance measurements on vitrinite could be performed on six samples per day (one shift operation) per person in comparison to that of two samples per day (one shift operation) per person using the conventional petrography method, which would provide a cost saving of 45%. Thus, the PIA system developed under the project was nearly three times faster and cost saving than manual work. Identification of macerals/minerals using gray-level detection technique Table 2 : S&T projects on coal exploration and hydrogeology Sl. No. 1. 2. 3. Title of the Project Project Code Total Approved Cost (Rs. in lakh) CMPDI 1982 0.80 CE/5 CMPDI 1982 0.80 CE/6 6 Year of completion CE/4 Resistivity survey for estimation of overburden, locating out-crops and mapping bed-rock geology Resistivity survey for estimation of river sand Seismic refraction survey for sub-surface gological mapping Implementing Agency CMPDI 1982 10.15 4. Geophysical strategy to solve coal exploration problem CE/8 CMPDI\ Osmania Univ. 1982 1.50 5. Geophysical logging of boreholes CE/3 CMPDI 1983 41.51 6. Estimation of reserves of coal volume of overburden by electronic data plotter CE/13 CMPDI 1983 13.87 7. Physico-mechanical properties of rocks and coal from exploration data CE/11 CMPDI 1984 8.00 8. Hydrogeological investigation CE/1 CMPDI 1985 36.00 9. Computerisation of geophysical logging data CE/14 CMPDI 1985 2.20 10. Geo-statistical analysis for optimisation of drilling CE/15 CMPDI 1985 2.89 11. Carbolite coke oven CE/2 CMPDI 1986 5.00 . Development of computer based geo-data bank CE/12 CMPDI 1988 34.60 13. Geothermal investigations in Manuguru area of Godavari valley coalfield CE/20 SCCL 1988 10.85 14. Identification and delineation of abandoned underground colliery workings in Raniganj Coalfield CE/22 MGMI 1991 4.50 15. High resolution shallow seismic reflecton survey CE/9 CMPDI 1992 224.63 16. Development of methodology for thermal studies of mine fires using remote sensing technique in Jharia Coalfield CE/23 CMPDI NRSA 1992 179.00 17. Identification and delineation of abandoned and unsurveyed colliery workings in Raniganj Coal Fields - Geophysical Studies CE/24 CMPDI MGMI IDRC (Canada) 1995 57.5 18. In-seam seismic survey CE/21 CMPDI 1999 184.00 19. Development of methodology for characterisation of Indian coal by computer aided petrographic image analysis CE/26 CMPDI 2001 114.50 12 7 ...
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