International Journal of Natural and Applied Science

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1 Available online at International Journal of Natural and Applied Science Universal Research Publications. All rights reserved Original Article WELL LOG DATA ANALYSIS FOR COAL SEEMS DELINEATION AND ITS PROXIMITY ANALYSIS IN MAHUAGARHI COAL FIELD, JARKAND, INDIA J. Srinaiah, Dr. G. Udaya Laxmi and Dr.G.Ramadass Center of Exploration Geophysics, Osmania University, Hyderabad-7 Corresponding Author Received 24 January 2014; accepted 03 February 2014 Abstract Well log responses can be used to delineate coal seems from non-potential litho-units by cross plotting techniques (Chatterjee and Paul, 2012). Through these different cross-plots across the study area, different litho units like coal, shaly coal, carbshale, shale, sand/sandstone, shaly sand have been identified. Well logs are an important information source for identifying coal layers and infer their characteristics, e.g. ash and moisture content. Determination of ash content of density log is routine feature. A direct relationship exists between density and ash content. All the coal seams of 2 exploratory wells namely BH No.3 & 4 have been identified from combined signatures of available gamma ray, resistivity and density logs against coal and non-coal litho-units, whereas coal seams and other non coal lithology in well 3 & 4 are marked with the help of available litholog for certain depth using Wellcad Software. The coal horizons are mostly overlain and underlain by shale or sandstone. Cross-plot analysis indicates the various coal lithologies which will important role in coal seems exploration and exploitation strategy. Mahuagarhi basin occupies the south-central part of the Rajmahal group of coal-fields representing approximately North-South trending linear chain of coal basins and is sandwiched between the Brahmani basin in the south and the Pachwara basin in the north-north-east. In coal bed identification, the special physical properties of the coal formation, e.g., low density, high resistivity, low natural gamma cause large impedance contrast between coal seams and inter-seam sediments Universal Research Publications. All rights reserved. Key words: Coal seams, Cross-plot techniques, Ash and Moisture content, Mahuagarhi basin, Coal grade, Wellcad Software INTRODUCTION Geophysical borehole logging is routinely conducted at coal mines for various applications such as strata correlation from borehole to borehole. Geophysical well logs respond to variations in petrophyscial factors, the quality, temperature and pressure of interstitial fluids and ground water flow. The information obtained from a well log can be extrapolated vertically within a well and laterally to other wells for a better understanding of subsurface geology (Fox, 1934). Geophysical logs can be used to identify coal beds and to quantify their resources because coal has several unique physical properties including low natural radioactivity, low density, and high resistance to electrical currents; these properties contrast with those of most other rocks in the coal-bearing sequence. Thus, geophysical logs can provide information on the existence, continuity, thickness, and correlation of shallow to deep buried coal beds unknown coal-bearing areas that have not yet been fully explored and in the future may provide information in areas not previously thought to contain coal. The important basic concepts that are to be understood are the volume of investigation, calibration and extraneous problems (V.V.L.N.Swamy, 1988).The logs normally run to evaluate a coal bed includes resistivity, lithology and auxiliary data. The density data under the lithology are used to determine the coal quality. The resistivity log is used for coal bed thickness measurements and coal bed correlation. The spontaneous potential (SP) under ancillary data is used for indication of permeable zones. Coal seams are relatively easy to identify and correlate on well logs. GEOLOGY OF THE AREA Jharkhand is surrounded by West Bengal on the eastern side, Uttar Pradesh and Chhattisgarh on the western side and by Orissa on the southern side. On the north is the state of Bihar. The state of Jharkhand has a total area of about 79,714 square kilometers, out of which 18,423 square kilometer area is covered by deep forests. The total land available for cultivation in Jharkhand is about 38 lakh hectares. Agriculture is the main source of employment in the state. Much of the state is covered in forests, which helps to conserve a fascinating wildlife. Jharkhand is the richest state in the country as far as the availability of mineral resources is concerned (Dutt and Datta 2000; Chandra,1992).The minerals found in 1

2 abundance in Jharkhand are bauxite, coal, iron ore, pyrite, limestone, copper ore, china clay, fine clay, graphite, soap stone, silica sand and quartz sand( Bose, 1968). The Kayada block covers an area of 1.82 Sq.Km and forms integral part of Mahuagrahi basin. The Mahuagrahi basin occupies south central Part of Rajmahal Group of coal fields. The Kayada block is bounded by Latitudes , and Longitudes , falling in the Survey of India Top sheets No 72 P/7, extending over a strike length of 5.07 km & dip length of 2.68 km. The geology map of study area shown in figure-1. Jackson,1986c).The physical parameters logged are density, caliper, resistivity, resistance, natural gamma. Qualitative analyses of geophysical logs are interpretation software is wellcad version 6.3. Qualitative analysis of geophysical logs comprises of three main stages following. i) Delineation of well section The delineation of well section consists (Hoffman et al., 1982) in differentiating the sequence of formations with varying Geophysical parameters. From delineation we can establish the boundaries of different formations and their thicknesses and lithology. ii) Characteristics of Geophysical Responses Based on the study of the several geophysical log responses ( Gochioco, 2002) described above typical or characteristic responses for certain important geological formation and under varying geological condition have been identified from the present work. For the purpose of study, formation can be conveniently divided into those occurring in Rajmahal formation and Barakar formation. Such logs were recorded with the present data Resistivity log,natural log, Sp log, Caliper log, Formation Density log. The resistivity log shows in coal seams very high value and rajmahal formation shows medium values. natual gamma curve shows in coal seams very low value and Rajmahal formation shows medium and against shale formation shows very high value observed.formation density log very import role in coal seams and accurate lithology thickness identification. The formation density log shows very low value in coal seams and in sandstone shale responds density is 2.2 gm/cc to 2.8 gm/cc. caliper log is shows borehole diameter. In this all bore hole diameter is 80mm to 120 mm. The SP curve is a recording versus the depth of the difference between the potential of a movable electrode in the borehole and fixed potential of a surface electrode (Saha, et al 1992). Figure 2, 3 shown the characteristic of geophysical response of borewells 3 & 4 respectively. Figure 1: Geology map of study area GEOPHYSICAL WELL LOGGING DATA ACQUISITION The geophysical well log data acquisition in the two boreholes consist of qualitative analysis for identifying coal seams and its thickness of lithology and compare with the available lithologs. The relation of particular geophysical log parameter of the section with the coal seams of the wells and correlation. (Reaves, 1971; Kayal and Das, 1981; Akhauri et al.1988) The result of two boreholes presented on scales of 1:1000 m. Individual logs in multiparameters logging are presented as parallel traces showing the variation with depth,which is helpful in the delineation of lithology penetrated by the boreholes (Buchanan and Figure 2: Geophysical Log response of Bore well No. 3. 2

3 Figure 4: Plot Ash Vs Density, Moisture Vs Density, Ash vs Natural Gamma density. The Natural gamma and Density log also used for identification and correlation of coal and its quality evaluation. Ash or dirt/shale content is denser than coal and naturally exhibits greater gamma ray activity also. Figure 3: Geophysical Log response of Bore well No. 4. Therefore Ash content (%) has positive correlation with density as well as gamma ray responses. This is true for iii ) Coal seams Mahaugrahi coal field, Kayada block. Mahuagrahi coal field in coal seams has been The density and natural gamma are increases with encountered in the boreholes drilled in this area. Most of increased of percentage ash of where as moisture increase the coal seams are inter banded in nature and exhibit split density decreased. section development pattern both along strike and dip Conclusions direction. Moreover, coal seams show considerable Borehole logging, employing geophysical variation in thickness and lithological characters of methods is one of the most widely utilized geophysical interseam parting sediments. In view of such variation in techniques in coal exploration. Multiparameter geophysical facies characteristics of the coal seam sections, zone wise logging of boreholes is very important, among the grouping and their correlation have been made where each subsurface methods, in all stages of exploration. The Utility zone comprises a number of coal seam sections having an of different well logging methods of interpretation of the identifiable facies development cycle. The in crops of coal well log data and other application of log data for seams projected from interpolation and extrapolation of evaluating coal properties are problem of great subsurface data generated from boreholes, which are significance. Some of these problems has been tackled in sometimes widely spaced, are somewhat tentative. the present work by way of obtaining actual field logging Exploration in this block reveals the occurrence of nine data from boreholes. regional coal seam zones and these have been numbered I The geophysical well logs are used qualitative text in ascending order. Each coal seam zone barring Seam analyze for identifying coal seams, evolution of lithology Zone- IX is composite one comprising more than one coal (sandstone, shale, carbshale, shaly coal and basalts) and it seam sections with shaly and sandy interbands. thickness, compared with the geological core logs. QUALITY OF COAL The quality of the coal evaluated from the It is well known that quality is grade of coal is parameters comprising ash content, moisture presence, evaluated from the parameter, comprising ash, and volatile matter and fixed carbon in coal in the laboratory. moisture determined from proximate two boreholes 3 & 4 Coal quality can be determined from geophysical logs by analysis of coal in laboratory CFRI Ranchi. Nine coal means of cross plots of various log responses observed for seams shown in table-1 &2. coal. Therefore, the quality of the coal seams can be Figure-4 illustrate and support correlation deduced evaluated in the case of non- core holes too. theoretically these correlation can be explained by taking Study of coal quality parameters indicates wide into account the physico-chemical properties responsible variation in quality of coal in different seams from I to IX. for the log responses and sudden variation at increasing The coal seam developed in the area is non cooking with 3

4 Table 1: B. H. No. 3 Ash%, Moisture%, UHV and Grade values BH No.3 From To Thickness Seam No. Moisture% Ash% IX Carb shale Carb shale 4 UHV K.cal/kg VIII E VII E VI F VB F V A F IVB E IV A F IIIF F IIIE E IIID E III C D III B E IIIA E IIB E IIA C IC D IB E IA E Table 2 : B.H.No. 4 Ash%, Moisture%, UHV and Grade values BH. No.4 From To Thickness Seam No. Moisture% Ash% UHV K.cal/kg Grade IX E VIII F VII Carb shale Carb shale VI E VB E V A F IV A G IIIF E IIIE Carb shale Carb shale IIID D IIIC E III B E IIIA F IIB C IIA F IC E IB F IA E Grade

5 generally high moisture (1.8to 9.44%), moderate to high ash content (18.5to 52.80%). The problem has a large scope for further studies. The usefulness of the geophysical logging methods like sonic log and neutron logs needs to be established. Detailed theoretical and modeling studies, and interrelationship between various geophysical parameters logged is an important point to be studied. Acknowledgements: The authors are also extremely thankful to Sri. G. Jawahar, GM - Geophysics Division, GSI, Hyderabad, for his valuable suggestions in the processing and analysis of the study. References: 1. Akhauri H.M., Satikari A., Gupta, O.P., Sinha A.S. and Savanur, R.V. (1988). Estimation of in situ ash in Indian coal seams from gamma-gamma log, In B.B 2. Bose, J : Geological investigation by drilling in the Chuperbhita and Mahuagarhi Coalfields, Rajmahal Hills, Santhan Parganas district, Bihar. Goel. Surv.Ind., Unpublished progress Rep. From Buchanan, D.J and Jackson, L.J (1986c) Boreholes logging of coal deposits: Editor s commentsin: Coal Geophysics, Geophysics Reprint Series No: 6, SEG Publn, pp Chatterjee. R, Paul. S, Application of cross plotting Techniques for Delineation of Coal and Non-Coal Litho-Units from Well logs Geomaterials, 2012, 2, Dutt, A.B and Datta, R.K (2000) Indian coal resources spectrum, Proc. Sem on New Challenges for Indian Coal, Coal resources of India. Mem. Geol. Survey of India. pp D.Chandra, Jharia Coalfield,Mineral Resource of India, Geological Society of India, Bangalore, Harpalani, S.and G. Chen, 1995, Estimation of changes in fracture porosity of coal with gas emission; Fuel, 74, FOX, C.S. (1934) The Lower Gondwana coal field of India, Mem, Geo. Surv.of India.v.LIXpp Hoffman G.L., Jordan G.R., and Wallis G.R., Geophysical Borehole Logging Handbook for Coal Exploration. Coal Mining Research Center, Edmonton, 270 pp. 9. Kayal, J.R.and Das Christoffel, D.A (1989) Coal quality from geophysical logs; Sounth land lignite region, NewZealand. The log analysist, v30. pp M.Gochioco Recent role of Geophysics in US Coal and CBM Development The Leading Edge, Vol.21, No.5, 2002, pp Reeves, D.R.(1971) In-situ analysis of coal by borehole logging techniques, The Canadian Mining and Metallurgical Bulletin, v.64, pp Robertson Geologging 2009: Winlogger software version Robertson Geologging 2009: Wellcad software version Saha, S. N., Roy, A.K., Brahman, C.V., Sastry, C. B. K.And M. K.(1992) Geophysical exploration for Coalbearing Gondwana basin in the state of West Bengal and Bihar in northeast India. Tectonophysics, v. 212, pp V. V. L. N. Swamy, 1988 Computer interpretation of well logging data. Source of support: Nil; Conflict of interest: None declared 5