International Journal of Coal Geology 88 (2011) 113–122

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International Journal of Coal Geology

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Mapping of cleats and fractures as an indicator of in-situ stress orientation,Jharia coalfield, India

Suman Paul, Rima Chatterjee ⁎Department of Applied Geophysics, Indian School of Mines, Dhanbad–826004, India

⁎ Corresponding author. Tel.: +91 326 2296658; fax:E-mail addresses: sumanpaul.jugeo@gmail.com (S. P

(R. Chatterjee).

0166-5162/$ – see front matter © 2011 Elsevier B.V. Alldoi:10.1016/j.coal.2011.09.006

a b s t r a c t

a r t i c l e i n f o

Article history:Received 19 June 2011Received in revised form 2 September 2011Accepted 3 September 2011Available online 10 September 2011

Keywords:CleatCleat mappingStress orientationIn-situ stress mappingCBMJharia coalfield

Cleats and fractures in coal of Barakar Formation in Jharia coalfield, India have been mapped from the coalexposures around 21 opencast and 2 underground coal mines. Macro-cleat distribution, observed from thismapping is similar to that of well-developed coalbed methane (CBM) basins. The opencast coal mines are dis-tributed in SE–NW direction along the boundary of the sickle shaped Jharia coal basin. Permeability of CBMthrough coal seams is the most critical property deciding the viability of any CBM field. It is largely controlledby the degree of cleat development. This paper discusses cleat orientation and other structural features, observedin the outcrops of 14 major coal seams in Jharia coalfield and its directional relationship with the in-situ stress(SH) orientation pattern. Cleat orientation is found to vary laterally within same seam at the different locations,distributed from the south-east part to the north-western part of Jharia coalfield. Face cleat orientation of the 21opencast coal mines varies from N45°E to N45°W. Change of orientation of cleat, observed around the miningareas is related the orientation of fault systems and orientation of igneous intrusions occurring within the coalbearing packet. Maximum in-situ horizontal compressive stress (SH) direction is found to be parallel to theface cleat orientation in normal faulted basin like Jharia coalfield. An overall, NNE–SSW and NW–SE orientationof the SH direction is predicted in the coal mines from cleat orientation mapping. SH orientation is locally modi-fied at places, close to the tectonic features and igneous intrusives. Finite element stress modeling is carried outnear Moonidih area. Cleat orientation predicted stress direction matches well with the finite element stressresults.

+91 326 2296563.aul), rima_c_99@yahoo.com

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

The ongoing interest in coalbed methane as an energy source inmany coal basins around the world is leading to increase explorationof prime coking coal in Jharia coalfield, India. Knowledge of the in-situstress field in a CBM reservoir is essential to optimize drilling and pro-duction. Borehole stability, orientations of natural and hydraulicallyinduced fractures, fluid flow anisotropies, among others, all dependcritically on the present-day stress distribution. Several techniquesranging from dipmeter analysis of borehole breakouts to anelasticstrain recovery and shear acoustic anisotropy analysis of core samplescan be used to determine the in-situ stress orientations and relativemagnitudes (e.g., Henk, 2005; Sperner et al., 2003). This valuable in-formation will only become available after the well has already beendrilled. Information on the regional stress orientations can be derivedfrom large-scale data collections like, for example, the world stressmap project (Sperner et al., 2003; Zoback, 1992). The orientation andmagnitude of the stress field in sedimentary basins, however, can be

highly variable and, particularly near faults, the local stress orientationscan differ by up to 90° from the regional trend (e.g., Bell and Bachu,2003). In such cases, inference of reservoir-scale in-situ stress orienta-tions from regional scale maps would inevitably lead to an incorrectpre-drilling prediction. Both the burial history and stress direction con-trol the timing of cleat development in various parts of the basin and thefinal orientation of face cleat.

Cleats are natural fractures in coal that usually occur in two sets,mu-tually perpendicular and also perpendicular to the bedding. The coalsamples observed at different places of studied 21 opencast mines(OCM) and 2 underground mines (UGM) of the Jharia coalfield revealthat the cleat spacing and the length of the cleats vary from one placeto another (Fig. 1). The regular reticular cleat pattern as observed inFig. 2 is the characteristic of the cleat geometry in Jharia coalfield. Thetectonic stress field controls the cleat geometric patterns. The controlof the tectonic stresses on the cleat formation is based on the intrinsictensile forces and fluid pressure in coalbeds. The formation of regularreticular cleat geometries under the in-situ stresses had been discussedby Su et al.(2001). Horizontal maximum principal compressive stress(SH) is greater than horizontal minimum principal compressive stress(Sh). The face cleat extends along the SH direction and the butt cleatalong the direction of Sh, so the regular reticular cleat pattern is formed

Fig. 1. Stratigraphic and structural map of Jharia coalfield (after Sengupta, 1980) showing locations of opencast and underground coal mines under study.

114 S. Paul, R. Chatterjee / International Journal of Coal Geology 88 (2011) 113–122

in the Jharia coalfield. The extensional stress regime existing in theJharia coalfield (Ghosh and Mukhopadhyay, 1985) developed fracturesand cleats in the coal seams.

These cleated networks in a coal matrix create channels for fluidflow through a CBM reservoir. The orientation of natural fractures thatcontrol coal seam permeability is governed by the regional stress field.Borehole breakouts, earthquake focal mechanism solutions and stressmeasurements can give the direction of the horizontal maximum

Fig. 2. Showing typical reticulate cleat pattern in coals of Jharia coalfield, India.

principal compressive stress. Fracture detection using borehole imaginglogs (Major and Holtz, 1997) and mapping of micro-fractures byscanned cathode-luminescence imaging (Laubach, 1997) are cost-effective and highly reliable method of determining the presence offractures in the subsurface and, more importantly, the orientation offractures that control coal seam permeability.

Unfortunately, no borehole imaging log datawere available adjacentto the studied mining areas to determine the cleat orientation. There-fore, the present study aims to (a) estimate the in-situ stress orientationfrom cleat orientation mapping from 21 OCMs and 2 UGMs distributedover the Jharia coalfield, (b) analysis of cleat orientation in 14 numbersof major coal seams as observed in this coalfield, (c) correlation of cleatorientation with the geological structures in this Jharia basin and(d) comparison of predicted SH orientation with previously establishedstress data.

2. Geology of Jharia coalfield

The Jharia coal basin located in the Singhbhum craton extends forabout 38 km in an east–west direction and maximum of 18 km innorth–south direction, and covers an area of about 456 km2 (Fig. 1).The general stratigraphic succession (Chandra, 1992) is illustratedin Fig. 1. In general beds of Jharia coalfield is dipping southerly(10°). The formations generally follow the boundary of the coalfield,striking E–W and NW–SE and dipping towards the centre of thecoalfield. The sedimentary succession, unconformably overlyingthe Archaean gneissic basement, starts with the Talchir Formationfollowed upward successively by the Barakar, Barren Measures and

Table 1Brief details of mines of Jharia coalfield India.

Area name Mine name Area ofmine(km2)

Presentworkingdepth(m)

Presentworking seam

Seamthickness (m)

Block II Jamunia OCM 0.57 110 E/F/G combined 24.00–38.00Block II OCM 8.52 130 E/F/G combined 22.00–24.00

Barora Shatabdi OCM 1.81 65 F/G–C combined 25.00Muraidih OCM 5.36 90 H–B 04.00

H–A 04.00E/F/G combined 25.00

Govindpur Block IV OCM 1.49 35 E/F/G combined 30.00AkashkinariOCM

3.68 32 I 02.46J 07.62

Katras AKWMC OCM 1.31 110 D 16.00–19.70E/F combined 09.00–10.00G 04.70–05.70H-botton/middle/top

07.90–08.30

GaslitandOCM

0.42 52 N 07.00O-top 02.55O-bottom 02.55

Sijua TentulmariOCM

3.17 90 D 14.00E/F combined 09.50G 03.60

NichitpurOCM

1.50 80 B 09.14C 03.96D 11.28E/F combined 09.14

Kusunda Dhansar OCM 1.74 42 B 08.66Kusunda OCM 2.47 80 E/F/G/H

combined18.97

J 14.79Kustore Ena Fire OCM 1.81 50 K/L combined 11.00

South JhariaOCM

2.08 40 E/F/G/Hcombined

16.00

I 02.10Bastacolla Ghanoodih

OCM0.73 75 J 13.25

Kujama OCM 1.91 80 J 14.00Lodna North Tisra

OCM1.28 95 C 16.00

South TisraOCM

1.29 93 C 15.00

East Jharia Bhowra NorthOCM

3.18 45 N–A 02.60O 08.60

Bhowra SouthOCM

5.70 40 N 05.60–09.50

PatherdihChandan OCM

0.26 75 B 18.00

WestJharia

MoonidihUGM

17.25 600 O 02.40P 02.80

PutkeeBalihari

PutkeeBalihariProject UGM

5.51 340 K 04.60

OCM=opencast mine; UGM=undergroundmine; AKWMC=Amalgamated KeshalpurWest Mudidih Colliery; PBP = Putkee Balihari Project; B/M/T = bottom/middle/top.

115S. Paul, R. Chatterjee / International Journal of Coal Geology 88 (2011) 113–122

Raniganj Formations (Dasgupta, 2008), deposited within an intra-cratonic extensional setting (Ghosh and Mukhopadhyay, 1985). Thecoal seams of the present study belong to Barakar Formation of Permianage, which does not show any evidence of high intensity tectonic defor-mation except normal gravity faults of different magnitudes — bothminor (thrown less than 10 m) and major (thrown 10 m to greaterthan 100 m) (Ghosh and Mukhopadhyay, 1985; Sengupta, 1980).

3. Data collection

Cleat orientation data have been collected from the 12 miningareas operated by Bharat Coking Coal Limited (BCCL), India which in-cludes total 21 OCMs and 2 UGMs of Jharia coalfield (Fig. 1). Duringthe measurements, authors have covered the maximum exposedand accessible parts of coal seams. For each seam of each mine, 30to 40 numbers of face cleat, 30 to 40 numbers of butt cleat and 50to 60 numbers of joint orientation data have been recorded. Authorshad already studied the cleat orientation pattern of four major coalseams of two underground mines, i.e., Moonidih UGM of WJ areaand Putkee Balihari UGM of PBP area of Jharia coalfield (Paul andChatterjee, 2011). Table 1 lists brief details of the mining areas andmines of Jharia coalfield.

For cleat orientation measurement at the 21 opencast mines and 2underground mines of Jharia coalfield the following methodology isadopted: (1) magnifying glass has been used for cleat identification,(2) all data are collected either from the roof or from the bottom ofcoal seams as cleat patterns are most prominently exposed in thoseparts, (3) only the coal seams having prominent vitrinite (bright)bands are preferred for the study as cleats are easily identifiable insuch seams and (4) all data are collected wherever both face andbutt cleats could be identified.

Total 14 numbers of major coal seams namely; B, C, D, E, F, G, H, I, J,K, L, N, O and P from 21 OCMs and 2 UGMs have been studied to pre-pare the cleat orientation map of Jharia coalfield. Out of 14 numbersof studied seams the oldest seam, “B”, is exposed to the surface nearthe northern boundary of the Jharia coal basin at Nichitpur OCM(Sijua area), Dhansar OCM (Kusunda area) and Patherdih ChandanOCM (East Jharia area) and the youngest seam, “P”, is encounteredat the inner part of the Jharia coal basin at Moonidih UGM. For an ex-ample, Fig. 3 displays the major coal seams, partings between twocoal seams and overburden in a vertical section from Block IV OCMof Govindpur area.

4. Face cleat/SH orientation in major seams in mining areas ofJharia coalfield

The orientations of cleats and joints have been measured criticallyat the selected mines of Jharia coalfield. Macro cleat spacing variesfrom 0.2 cm to 0.9 cm as observed at the field sites. All the collectedcleat and joint orientation data are assembled in Table 2. It is ob-served that, (1) the orientations of cleats are more of less parallelwith the adjacent joint planes, (2) in most of the cases the orienta-tions of both cleats and joints are changing from one mine to anotherand (3) all the seams of any single mine are showing same cleat ori-entation direction. Cleat orientations for all seams remain unchangedwithin same mines though there are changes in cleat orientation forthe same seam in different mines within same mining area or in dif-ferent mining areas. Table 3 illustrates the change of face cleat orien-tation for each seam from one mine to another mine within Jhariacoalfield. Fig. 4 is showing the orientations of face cleats at differentmines of Jharia coalfield. It has been observed that the twodistinct groupsof face cleat orientations such as: N10°E–40°E and N30°W–45°W, arepresent in the Jharia coalfield. The two average dominant face cleatorientations in this coalfield are towards N25°E and N35°W respectively.The authors in their previous study in the Moonidih UGM (WJ area) andPBUGM(PBP area) have indicated the relation between face cleat and SH

orientation (Paul and Chatterjee, 2011). Therefore, the face cleat orienta-tion in themining areas of Jharia coalfield is serving as the SH orientationduring the cleat formation.

5. Correlation between in-situ stress and geological structures inJharia coalfield

The data, presented in Table 3 and Fig. 4 clearly demonstrate thatthe directions and magnitudes of change in cleat orientations are notuniform at different locations across the basin. This indicates that thecleat orientations have been controlled and modified by some events,which occurred later to the lithification and cleat formation process-es. It is observed during the study that in some places, like BhowraNorth OCM and Patherdih Chandan OCM of East Jharia area, dolerite

Fig. 3. Displaying the major coal seams in Block IV opencast mine, Govindpur area,Jharia coalfield, India.

116 S. Paul, R. Chatterjee / International Journal of Coal Geology 88 (2011) 113–122

dykes have been intruded within coal seams. Fig. 5 illustrates thepatches of dolerite dykes within O seam of Bhowra North OCM of EastJharia area. Random variation of cleat orientations has been observed

Table 2Cleat and joint orientations in major coal seam of Jharia coalfield, India.

Area name Mine name Seam name Maxclea

Block II Jamunia OCM E/F/G combined N15Block II OCM E/F/G combined N15

Barora Shatabdi OCM F/G–C combined N45Muraidih OCM H–B N35

H–A N35E/F/G combined N35

Govindpur Block IV OCM E/F/G combined N25Akashkinari OCM I N35

J N35Katras AKWMC OCM D N15

E/F combined N15G N15H-bottom/middle/top N15

Gaslitand OCM N N25O-top N25O-bottom N25

Sijua Tentulmari OCM D N35E/F combined N35G N35

Nichitpur OCM B N05C N05D N05E/F combined N05

Kusunda Dhansar OCM B N35Kusunda OCM E/F/G/H combined N65

J N65Kustore Ena Fire OCM K/L combined N55

South Jharia OCM E/F/G/H combined N45I N45

Bastacolla Ghanoodih OCM J N25Kujama OCM J N25

Lodna North Tisra OCM C N45South Tisra OCM C N45

East Jharia Bhowra North OCM N–A N35O N35

Bhowra South OCM N N25Patherdih Chandan OCM B N25

West Jharia Moonidih UGM O N20P N15

Putkee Balihari Putkee Balihari Project UGM K N25L N15

OCM = opencast mine; UGM = underground mine; AKWMC = Amalgamated Keshalpur W

close to dykes at Bhowra North OCM and Patherdih Chandan OCM. Itmay be explained by effect of variable lateral stress, generated duringintrusion of the dolerite dyke (Boehm and Moore, 2002; Motoki andSichel, 2008).

To investigate the cause behind the changes in cleat orientationsacross the Jharia coalfield as a whole, the cleat orientation map ofJharia coalfield has been correlated with the fault patterns of Jhariacoalfield (Sengupta, 1980). It was established from the earlier studiesthat during Upper Carboniferous (Talchir Formation), the major partof the Jharia coalfield was a positive area and only the northern andnorthwestern fringes subsided. But during the early Lower Permian(Barakar Formation), the entire Jharia basin subsided. Subsidence inthe initial stages took place by a general downwarping of the meta-morphic basement. The boundaries of this basement are marked byhigh angle normal faults of enchelon type (Sengupta, 1980). In addi-tion to these boundary faults there are several intra-basinal gravityfaults within the basin of varying magnitudes, resulting in dislocationof coal seams (Fig. 6). The pattern of subsidence, from middle Barakaronward, began to be increasingly modified by pene-contemporaneousfaulting (Ghosh andMukhopadhyay, 1985). This syngenetic faultingdur-ing Lower Permian, possibly led to the initiation of cleats and joint planeswithin coal seams of Barakar formation under study. The overall stressfield in the Jharia coalfield is extensional, as confirmed by the predomi-nance of normal faults. Under such tectonic set up, vertical stress is great-er than the horizontal stresses. The variations of face cleat orientation

imum facet orientation

Maximum buttcleat orientation

Maximum jointorientation (two sets)

Cleat spacing(cm)

°E N105°E N15°E, N105°E 0.20–0.50°E N105°E N15°E, N105°E 0.20–0.50°W N45°E N45°W, N45°E 0.20–0.50°W N55°E N35°W, N55°E 0.20–0.50°W N55°E N35°W, N55°E 0.20–0.50°W N55°E N35°W, N55°E 0.20–0.50°E N115°E N25°E, N115°E 0.30–0.60°E N125°E N35°E, N125°E 0.30–0.60°E N125°E N35°E, N125°E 0.30–0.60°E N105°E N15°E, N105°E 0.30–0.80°E N105°E N15°E, N105°E 0.30–0.80°E N105°E N15°E, N105°E 0.30–0.80°E N105°E N15°E, N105°E 0.30–0.80°E N115°E N25°E, N115°E 0.30–0.80°E N115°E N25°E, N115°E 0.30–0.80°E N115°E N25°E, N115°E 0.30–0.80°W N55°E N35°W, N55°E 0.20–0.60°W N55°E N35°W, N55°E 0.20–0.60°W N55°E N35°W, N55°E 0.20–0.60°E N95°E N05°E, N95°E 0.20–0.60°E N95°E N05°E, N95°E 0.20–0.60°E N95°E N05°E, N95°E 0.20–0.60°E N95°E N05°E, N95°E 0.20–0.60°W N55°E N35°W, N55°E 0.20–0.70°W N25°E N65°W, N25°E 0.20–0.70°W N25°E N65°W, N25°E 0.20–0.70°E N145°E N55°E, N145°E 0.30–0.90°E N135°E N45°E, N135°E 0.30–0.90°E N135°E N45°E, N135°E 0.30–0.90°W N65°E N25°W, N65°E 0.20–0.90°W N65°E N25°W, N65°E 0.20–0.90°W N45°E N45°W, N45°E 0.30–0.80°W N45°E N45°W, N45°E 0.30–0.80°E N125°E N35°E, N125°E 0.50–0.90°E N125°E N35°E, N125°E 0.50–0.90°E N115°E N25°E, N115°E 0.30–0.90°E N115°E N25°E, N115°E 0.30–0.90°W N70°E N20°W, N70°E 0.20–0.50°W N75°E N15°W, N75°E 0.20–0.50°W N65°E N25°W, N65°E 0.20–0.50°W N75°E N15°W, N75°E 0.20–0.50

est Mudidih Colliery; PBP = Putkee Balihari Project; B/M/T = bottom/middle/top.

Table 3Illustrates the rotations of face cleats for each coal seams from one mine to anothermine of Jharia coalfield, India.

Seams Mine name Maximum face cleat orientation(% of total data collected)

B Nichitpur OCM N05°E (74%)Dhansar OCM N35°W (65%)Patherdih Chandan OCM N25°E (60%)

C Nichitpur OCM N05°E (78%)North Tisra OCM N45°W (74%)South Tisra OCM N45°W (71%)

D AKWMC OCM N15°E (63%)Tentulmari OCM N35°W (62%)Nichitpur OCM N05°E (78%)

E/F/G combined Jamunia OCM N15°E (72%)Block II OCM N15°E (62%)Muraidih OCM N45°W (66%)Block IV OCM N25°E (66%)

E/F combined AKWMC OCM N15°E (66%)Tentulmari OCM N35°W (64%)Nichitpur OCM N05°E (77%)

F/G–C combined Shatabdi OCM N05°W (59%)G AKWMC OCM N15°E (67%)

Tentulmari OCM N35°W (61%)E/F/G/H combined Kusunda OCM N65°W (69%)

South Jharia OCM N45°E (56%)H–B Muraidih OCM N35°W (67%)H–A Muraidih OCM N35°W (59%)H–B/M/T combined AKWMC OCM N15°E (65%)I Akashkinari OCM N35°E (74%)

South Jharia OCM N45°E (62%)J Akashkinari OCM N35°E (71%)

Kusunda OCM N65°W (68%)Ghanoodih OCM N25°W (59%)Kujama OCM N25°W (72%)

K PBP UGM N25°W (57%)K/L combined Ena Fire OCM N55°E (66%)L PBP UGM N15°W (54%)N Gaslitand OCM N25°E 65%)

Bhowra South OCM N25°E (65%)N–A Bhowra North OCM N35°E (70%)O Bhowra North OCM N35°E (61%)

Moonidih UGM N20°W (44%)O-top Gaslitand OCM N25°E (70%)O-bottom Gaslitand OCM N25°E (72%)P Moonidih UGM N15°W (54%)

OCM=opencast mine; UGM=undergroundmine; AKWMC=Amalgamated KeshalpurWest Mudidih Colliery; PBP = Putkee Balihari Project; B/M/T = bottom/middle/top.

117S. Paul, R. Chatterjee / International Journal of Coal Geology 88 (2011) 113–122

throughout the coalfield provide a clue to correlate the in-situ stressorientation with the geological structures of the basin. In-situ stressorientation map (Fig. 7) is prepared for the Jharia coalfield from themaximum average face cleat orientation data of each mine. Predomi-nant fault directions in different zones, as observed from the structuralmap (Sengupta, 1980) and the orientation of the face cleats and SH inthe same zones (Fig. 7) are summarized in Table 4 to show the correla-tion between these elements.

Observations, presented earlier, unambiguously demonstrate therelationship between SH and discordant structural elements like facecleat, faults and dykes. High-resolution lineament studies carriedout in Jharia basin had indicated the presence of three lineamentsmainly: NNE–SSW, NE–SW and NW–SE in their order of dominance(Mazumder and Wolf, 2004). The variability of SH orientation is sim-ilar to that reported from other areas of the coalfield around theworld where cleat is seen to vary with position with respect to faultsand other structures in the mine (Bachu and Michael, 2003; Bell,2006; Bell and Bachu, 2003; Laubach et al., 1998; Pashin, 1998;Wolf et al., 2008). This also leads to inference that the mechanismfor generation of the tectonic features like faults, dykes etc. have sig-nificant control in generation and variation of the cleat patterns andin-situ stress orientation in Jharia coal basin.

6. Comparison of predicted stress orientation with the otherstress data

Cleats are believed to represent the tensional failure of the develop-ing coal, and should reflect the regional stress patterns at the time ofcoal formation in the same way that other tensional joints do (Mills,1986). In-situ stress orientation map (Fig. 7) is prepared for the Jhariacoalfield from the maximum average face cleat orientation data ofeach mine. Fig. 7 is displaying the SH orientation at the site of measure-ment inside the mines along with the prominent geological structures.The total numbers of face cleat orientation data (1782) are plotted inthe rose diagram to indicate the mean orientation of SH in the Jhariacoalfield (Fig. 7). Themeanorientation of SH of the total face cleat azimuthgives almost N–S with two dominant orientations of NNE and NNW.

The previous authors (Ali et al., 2008) had observation of face cleatorientation from FMI log for a single well in the Parbatpur area, locatedat the southern part of the Jharia coalfield. The orientation of SH predictedfrom FMI log is directed towards NW–SE, varying between N30°W andN60°W. Recording of borehole image log like FMI fromdrilledwell at dif-ferent locations is very expensive and time consuming,whereas the cleatdata collections in the field are less expensive. Therefore in the absenceof borehole image log data, SH orientation predicted from face cleat andfracture mapping is more useful as a whole than the estimated orienta-tion provided by Ali et al.(2008) from a single well data.

Although ancient stress directions might be implied from cleat ori-entations in coalbeds of Barakar Formation in Lower Permian time,the information regarding contemporary tectonic stress also may begleaned from nearby earthquakes and their focal mechanisms. A re-view of local earthquake activity near the study area under Singh-bhum craton revealed that a magnitude of lower than 3.0 seismicevent occurred twice in the month of November, 2007 within 8 kmto 10 km from Jharia coalfield. A source solution study indicates thatthis earthquake originated from a depth of about 26 km and definesa strike slip faulting environment with dominant N–S compressionaland E–W tensional stresses (Kayal et al., 2009). Based on the seismicity,Chandra (1977) inferred a NNE–SSW Singhbhum seismic zone beneaththe Singhbhum craton. Mean SH orientations in three zones, A, B and D,in Table 4match well with the regional compressive stress direction.Thus, corroborating information derived from cleat orientation in thecoalbeds and from focal plane solutions of two recent earthquakes im-plies that the orientation of in-situ stresses has not been changedmuch over time, from mean SH direction of about N–S during Permiandeposition and coalification to a present day N–S direction. The conti-nentalmovement of Indian Plate towardsNNE direction is also support-ing the present day stress orientation.

7. Stress orientation modeling

Two-dimensional (2-D) finite element stress modeling for theJharia basin aims to illustrate the effect of the applied stress in theSH direction (N–S) and the variations in mechanical rock propertiesfor the available section: X–Y (Fig. 7) in the study area. The 4545 mlong X–Y section paralleling the N–S direction passes through theMoonidih area where sediment depth exceeds 1.4 km (Sengupta,1980). For the generalized finite element modeling (FEM) purposes,the sedimentary column underlying the section X–Y is broadly divid-ed into 9 layers including four coal seams (L, M, N and O), overlyingand underlying sediments (Fig. 8). An average horizontal compres-sive stress of 15 MPa has been applied at the vertical boundary ofthe solid FEM model with constraining the top boundary. The me-chanical rock properties for the coal seam and overlying/underlyingsediments for the FEM model have been assumed (personal reliablesource) as provided in Table 5. Finite element grids for the underlyingX–Y section consisting of 8777 numbers of 6-noded triangular ele-ments are generated and stress trajectories are calculated usingANSYS (University Intermediate version 7.1) finite element software.

Fig. 4. Illustrating the orientations of face cleats at different mines of Jharia coalfield, India.

118 S. Paul, R. Chatterjee / International Journal of Coal Geology 88 (2011) 113–122

FEM predicted SH orientations are displayed in Fig. 9. Stress orienta-tion in three rectangular boxes namely; A, B and C in Fig. 9a hasbeen illustrated in zoomedmode through Fig. 9b, c and d respectively.It is observed from Fig. 9b that SH direction for the four seams at theleft part (box A) of the X–Y section is oriented towards NW–SEwhereas SH direction at the middle (box B) and right part (box C) of

Fig. 5. Showing patches of dolerite dyke within seam “O” of Bhowra North OCM, EastJharia area, Jharia coalfield, India.

the same section is oriented towards NNE–SSW (Fig. 9c and d). TheFEM predicted SH orientation (NW–SE) at coal seam “O” is matchingwellwith the SH orientation (N45°W) at the same seamat theMoonidihUGM (Paul and Chatterjee, 2011 and Table 2). FEM results also indicaterotation of SH directionwithin coal seams though it is aligned N–S at thedeeper part.

Fig. 6. Indicating a faulted coal seam in Jamunia OCM, Block II area, Jharia coalfield,India.

Fig. 7. In-situ stress orientation map of Jharia coalfield, India. Mean SH orientation displayed in rose diagram is mostly N–S varying NNE to NNW.

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8. Discussion

Sub-surface data on cleat orientation/fracture, is exceedingly sparse,hindering well planned development through optimized well place-ment or directional drilling for CBM exploration in this coalfield. Asthe fractures act as release paths for the CBM, trapped in the coalseams i.e CBM reservoirs, knowledge of the preferred orientation ofthose natural fractures is key to cost-effective and successful CBM ex-ploration and exploitation (Bachu and Bell, 2001; Bachu and Michael,2003; Beekman et al., 2000; Bell and Bachu, 2003). In the CBM

Table 4Orientation of geological structures and in-situ stress in Jharia coalfield, India.

Locationwithin basin

Faulttrend

Intrusivetrend

F(

Zone A NNE–SSW NE–SW

Zone B NNE–SSW NNE–SSW

Zone C NNW–SSE NNW–SSE

Zone D NNE–SSW NNW–SSE

reservoirs, permeability is controlled by cleat network/natural fractures.Therefore, evaluation of such reservoirs needs accurate information on(1) the spatial distribution of faults and fractures, (2) orientation ofthose structures, and (3) quantitative estimation of permeability, provid-ed by those faults and fractures. Locally, however, the stress field canvary in magnitude and direction, the major influence being faults andbasement relief (Laubach et al., 1998; Moon and Roy, 2004). It requiresascertaining the correlation of the variation of SH direction with the pre-dominant fault/fracture orientation. The in-situ stress regime can have astrong influence on CBM production, coal permeability, hydraulic

ace cleat orientationrose diagram)

Mean face cleatorientation

SHorientation

N15°E N15°E

N10°E N10°E

N20°W N20°W

N35°E N35°E

Fig. 8. 2-D model for the X–Y section. Four coal seams (L, M.N and O) are identified. Solid arrow indicates the applied stress, model is constrained at the top boundary.

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fracturing pressure and the borehole stability while drilling horizontalwells. Knowledge of these features is essential to effective developmentof CBM resources. The stress trajectories indicated on the map (Fig. 7)as well as FEM predicted results (Fig. 9) can be used for predicting theorientation of induced hydraulic fractures in different parts of Jhariabasin.

Though opening-mode fractures (including face cleats) form per-pendicular to the minimum compressive principal stress (Lawn andWilshaw, 1975) subsequent shifts in tectonic loading directions maycause opening-mode fractures to be misaligned with the current stressfield (Laubach et al., 2004). For coals, however, the compliance of thecoal and the potential for annealing of early formed cleats (Laubach etal., 1998) suggests that it may be possible that some (or all) cleats in agiven areamay track themodern day stressfield. The effects of cleat ori-entation and confining pressure on coal properties have been studied inmany coal basins worldwide. Some important or pathbreaking studieshave been made in La Plata mine in San Jun Basin of New Mexico(Gash et al., 1992), Mine in Kushiro Coalfield in Japan (Li et al., 2004),mines at Zonguldak Basin located on the Black Sea coast of Turkey(Karacan and Okandan, 2000), RECOPOL project in the Upper SilesianCoal Basin, Poland (Wolf et al., 2008), mines in the Pittsburgh coalbedPennsylvania (Diamondet al., 1975), coalmines in southwestern Indiana(Acosta et al., 2007), as well as many coal basins including Appalachian,San Juan, Powder River andBlackWarrior Basins inUnited States (Ayers,2002; Flores et al., 2008; Pashin, 1998; Pitman et al., 2003). There wereseveral case studies in Britain, Canada, Mexico, Australia, China and USAwhere maximum horizontal stress orientation has been correlated withthe coal cleat orientation in coalbasins (Bell, 2006; Enever and Clark,1994; Gentzis et al., 2006, 2007; Meng et al., 2011; Rippon et al., 2006).

9. Conclusions

In this study, cleat and joint orientation data have been collectedfrom 14 major coal seams from the area around 21 opencast mines

Table 5Rock mechanical properties assumed in the 2-D FEM for X–Y section of the Jhariacoalfield, India.

Layers Young's modulus(MPa)

Poisson'sratio

Average density(kg/m3)

Coal seams 2000 0.32 1450Overlying/underlying sediments 20,000 0.26 2350

and 2 underground mines across the Jharia coalfield. Face cleat orien-tation varies from NE–SW to NW–SE within the same seam, as ob-served for the whole strata packet containing the B, C, D, E/F/G, H, I,J, K/L, N and O, occurring in different mining areas, distributed fromNW to SE of the basin. When the basin in sub-divided in four zones,based on the preferred orientation of the major fault systems anddykes, dominant face cleat orientation is matches well with the pre-dominant fault direction in each of the identified zones. In-situ stress(SH) orientation is parallel to the face cleat direction and has twoprominent directions of N25°E and N25°W respectively. The orienta-tion of SH is strongly related with the orientation of faults in thisbasin, as shown by overall parallelism between the major regionallineations, the face cleat and the joint direction.

An overall NNE–SSW oriented SH measurement in mines and in-ferred from earthquake events at depth of 26 km is a regional phe-nomenon which locally modified close to the geological structures.The FEM predicted SH orientations agrees well with the cleat orienta-tion predicted SH direction at the Moonidih UGM. The observations,reported from this study, clearly demonstrates that surface mappingof the preferred orientations of the planar structures like cleats, faults,joint and dyke systems in and CBM field can be used as a reliable toolto predict SH directions in sub-regional scale with moderate confidencelevel. This in turn shall facilitate preliminary planning of effective and op-timumwell pattern for CBM exploration, even prior to initiating drillingand collecting sub-surface data.

It is very important to emphasize here that finding of this studydoes not replace or reduce the need for detail drilling investigation,which would provide additional data to map the local variation andfine tune the well designs for CBM production.

Acknowledgements

The authors express their sincere gratitude to Coal India Limited(CIL) and CentralMine Planning andDesign Institute Limited (CMPDIL),Ranchi for the financial assistance under its R&D scheme. Support ex-tended by Mr. A. K. Singh, CMPDIL and Mr. A. N. Sahay, Director(RD&T), CMPDI Ranchi; Chief General Manager (Exploration),CMPDI Ranchi; Mr. A. Saha, Manager (Geology), CMPDI Ranchi; Mr.P. K. Hazra, General Manager (Geophysics), CMPDI Ranchi is grate-fully acknowledged. Authors are thankful to Sri P. K. Pal, Ex-CGM(Exploration), CMPDI, Ranchi for his kind support in editing themanuscript. Kind help by the General Manager (P&P), BCCL; GeneralManager of the mining areas, BCCL are acknowledged, as withoutsuch help the work could not be carried out.

Fig. 9. (a) SH orientations are illustrated in the finite element gridded model. A, B and C are indicating the three rectangular boxes, (b) SH orientation for the box A at the zoomedmode, (c) SH orientation for the box B at the zoomed mode and (d) SH orientation for the box C at the zoomed mode.

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