Generation and hydrocarbon entrapment within
Gondwanan sediments of the Mandapeta area,
Krishna-Godavari Basin, India
M.S. Raza Khan *, A.K. Sharma, S.K. Sahota, M. Mathur
RCL, ERBC, ONGC, Sibsagar, Assam 785640, IndiaAbstract
The discovery of hydrocarbons (mainly gas) in commercial quantities from Gondwanan sediments in the Mandapeta ®eld of Krishna-Godavari Basin, India, provided impetus for intensi®ed exploration in Mandapeta and the adjoining Kommugudem, Draksharama and Endamuru ®elds. Both oil and gas have been found in the reservoirs of Mandapeta (Triassic) and Golapalli (Early Cretaceous) formations. Mature, localised, basal shales (1.0±1.1% Ro) in the Manda-peta formation have sourced the oils from the MandaManda-peta Sandstone reservoir (Triassic). The oils being produced from Golapalli Sandstone reservoir (Early Cretaceous) are relatively less mature and have been sourced by the underlying shales in the Mandapeta Formation at a maturity level of 0.80±0.85% Ro. The source and maturity data preclude liquid hydrocarbon sourcing from the Kommugudem (Permian) sequence. Permian coals and shales of the Kommu-gudem Formation are the major source rocks for gaseous hydrocarbons in this area. The hydrocarbon generation started in Early Cretaceous in the Kommugudem Formation, but the intermittent tectonic activity (with associated structural developments) has resulted in reorientation and redistribution of the then existing trap con®gurations. The present day maturity level of the Permian sediments in the Mandapeta ®eld is 1.2% Ro or greater, capable of gen-erating gas dominantly. The Raghavapuram shale in the Mandapeta area is adequately mature and has good hydro-carbon potential for oil generation. The probability of ®nding hydrohydro-carbon reserves in the sands of Raghavapuram shales and other suitable traps is high. Modern seismic information together with geologic models can give new exploration leads.#2000 Elsevier Science Ltd. All rights reserved.
Keywords:Gondwanan sediments; Mandapeta ®eld; Petroleum generation; Maturation and isomerisation
1. Introduction
The discovery of gaseous hydrocarbons in commercial quantities from Gondwanan sediments (Golapalli For-mation of Early Cretaceous and Mandapeta ForFor-mation of Triassic age) in the Mandapeta area of Krishna-God-avari onland basin provided impetus for intensi®ed exploration in Mandapeta (MDP) and adjoining areas. The discovery well Mandapeta-1 (MDP-A, Fig. 1) was drilled to a depth of 4302 m and encountered the top of gneissic basement at a depth of 4263 m. It penetrated Permian to Recent sediments and produced gas from Gondwanan sediments in the interval 2804±2740 m (Mandapeta Sandstone).
To date, more than 16 wells have been drilled on the Mandapeta structure (Fig. 1). Out of these about seven are hydrocarbon bearing in Mandapeta Sandstone reservoir and three are hydrocarbon bearing in Golapalli Sandstone reservoir (Fig. 2). As Kommugudem (KMG), Draksharama (DRK) and Endamuru (END) structures like Mandapeta (MDP) structure have also been identi-®ed to possess Gondwanan sediments, they are considered together for this study.
Seven wells KMG-A, MDP-A, -D, -L, -O, DRK-A and END-A have been studied along with oil samples from MDP-A, -C, -I, -L and-O wells for molecular level characterisation (see in Fig. 1 for well locations).
The aim of the present study was to identify source units and areas of generation and to investigate the sub-sequent migration and accumulation of hydrocarbons in relation to the geological framework of the area.
0146-6380/00/$ - see front matter#2000 Elsevier Science Ltd. All rights reserved. P I I : S 0 1 4 6 - 6 3 8 0 ( 0 0 ) 0 0 1 3 2 - 7
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2. Tectonics and stratigraphy
Mandapeta graben, lying in the East Godavari sub-basin, was formed during Early Palaeozoic rift phase. This extensive track of Lower Gondwanan deposition is collinear with Pranhita Godavari Graben, which hosts the complete sequence of Gondwanan Super Group ranging in age from Permian to Lower Cretaceous. The generalised stratigraphic succession of the Mandapeta area based on interpreted lithology and electrolog cor-relation is given in Fig. 2.
In the Mandapeta area Kommugudem formations of Lower Gondwanan comprising coal/shale/sandstone were deposited in the lower deltaic to lacustrine environment over an Archean basement. A major erosional unconfor-mity has been found at the top of the Kommugudem Formation over which Mandapeta Fluvial Sandstone of Triassic age were deposited. The top of this sandstone represents a hiatus overlain by Red Bed interval of Triassic age comprising reddish to dark claystone.
The Mandapeta Sandstone together with the Red Beds belongs to the Lower Gondwanan. At this junc-ture, the NW dip of the basin was reversed to SE because of thermal doming associated with rifting. This led to the erosion of elevated areas and deposition of eroded material mainly as alluvial fans in adjacent lows. Subsequent cooling and simultaneous crustal subsidence part heralded the ®rst transgression where paralic to
marine sediments of Cretaceous age (Golapalli Sand-stone, Raghavapuram Shale and Tirupati Sandstone formations) were deposited. The end of Cretaceous sedimentation is marked by marine regression. This was followed by widespread volcanic activity where basaltic ¯ows with interbedded sediments like limestone, sand-stone and claysand-stone were poured. The Paleocene basalts (Rajahamundry Traps) are unconformably overlain by sandstone, claystone and basal limestone of Eocene age. The sediments are then succeeded by Rajahmundry Sandstone of Mio-Pliocene age followed by Pliestocene to Recent sediments.
3. Experimental
Rock samples were crushed in a shatterbox at room temperature. The crushed samples were soxhlet extracted for 48 h with chloroform. The solvent was removed in a rotary evaporator and the extract separated by column chromatography using alumina and silica gel into three fractions: alkane hydrocarbons, aromatic hydrocarbons and polar compounds. The oils were separated into their respective fractions (alkanes, aromatics and polar com-pounds) by column chromatography following the same procedure. Fractionation of aromatic hydrocarbons into mono-, di- and triaromatic was carried out on Waters 840 HPLC system in a normal phase isocratic mode
using Energy Analysis NH2 columns withn-hexane as
the mobile phase.
The saturated hydrocarbon fractions were analysed on a Shimadzu GC 9A system using a 30 m long, 0.25 mm i.d. OV-101, fused silica column with helium as the carrier gas. GC conditions were: 100C, heating rate 4C/ min, ®nal temperature 280C and injector temperature 280C.
The triaromatic hydrocarbon fractions were analysed on a Shimadzu GC 9A system using a 60 m long, 0.25 mm i.d. SE-54, fused silica column with helium as the carrier gas. GC conditions were : 60C, heating rate 3C/ min, ®nal temperature 260C and injector temperature 280C.
The Rc was calculated as per the scheme of Radke and Welte (1983).
4. Results and discussion
4.1. Occurrence of hydrocarbons
Hydrocarbon accumulations have been found in Mandapeta Formation (Triassic) and Golapalli Forma-tion (Early Cretaceous) in Mandapeta area. Regional cap rock for Golapalli Sandstone reservoir is provided by Raghavapuram shale and the regional cap rock for Mandapeta Sandstone reservoir is provided by the Red Bed.
Hydrocarbons have been found in the Mandapeta Sandstone in seven wells (MDP-A, -C, -E, -F, -H and -K) and in the Golapalli Sandstone in three wells (MDP-K, -L and -O). This is dominantly a gas-prone area. The presence of oil has been indicated in MDP-A, -C (Man-dapeta Sandstone) and MDP-I, -L and -O (Golapalli Sandstone). There is no prominent hydrocarbon ®nd in Draksharama or Kommugudem area.
4.2. Hydrocarbon type and characteristics
The oils from MDP-A and MDP-C (produced from Mandapeta Sandstone) are light coloured with medium API gravities (Table 1). The oils from MDP-I, -L and -O, being produced from Golapalli Sandstone, are also of medium API gravities (Table 1). Oils from MDP-I, -L are dark coloured while the oil from MDP-O is light coloured. All liquid hydrocarbons are paranic in nat-ure. The oils found in MDP-A, -C and -O, though light in colour, have high yields of 300C+ residue (around 40%) and substantial amounts of wax (more than 8%). These types of oils may result from deasphalting.
The oils from Mandapeta Sandstone have values of pristane/phytane (Pr/Ph) and pristane/n-heptadecane (Pr/nC17) ratios 2.4:2.6 and 0.5:0.6, respectively. The
oils from Golapalli Sandstone have Pr/Ph and Pr/nC17
ratios ranging from 3.1 to 3.4 and 0.6 to 0.7 (Fig. 3). The high values of Pr/Ph ratio indicate the generation of
these oils from terrestrial organic matter deposited in oxic environment.
Two aromatic biomarker ratios (the ratio of the con-centration of 1-methyl phenanthrene to that of 9-methyl phenanthrene and the ratio of the concentration of 1,7-dimethylphenanthrene to that of a peak labelled x, which is due to an unresolved mixture of 1,3-dimethylphenan-threne, 3,9-DMP, 2,10-DMP and 3,10-DMP have been calculated which provide information about the biological origins (Alexander et al., 1992). Alexander et al. (1992), have termed them as age speci®c biomarkers and have reported that these ratios are helpful for correlation stud-ies at moderate maturitstud-ies (the signi®cance of the values of these ratios has been discussed in the following text under sub-title `source rocks'). The values of these ratios for oil samples are shown in Fig. 3. Both the ratios are very much similar for oils from the Mandapeta reservoir as well as the Golapalli reservoir, indicating that the source sequen-ces which have given rise to these ¯uids received the same/ similar type of organic matter (Fig. 3).
4.3. Maturity
The maturity of the oils has been assessed using aro-matic compounds. The aroaro-matic based maturity para-meters are considered quite reliable as these compounds are present in substantial concentration. The assessment is based on the fact that during geological times the thermodynamic less stable methyl phenanthrene isomers are converted into more stable isomers. The Rc was calibrated with Ro by plotting the MPI of rock extracts against the observed Ro. It was found that the equation of Radke and Welte (1983) is valid in this area. The maturity derived from calibrated Rc also matches well with other maturity parameters.
The oils found in the Mandapeta reservoir are more mature than the oils found in the Golapalli Reservoir. The maturity of Mandapeta and Golapalli reservoired oils is 0.95±1.0% Rc and 0.80±0.85% Rc, respectively (Fig. 3).
Table 1
Characteristics of oils of the Mandapeta area
Well no.
MDP-A MDP-C MDP-I MDP-L MDP-O
Depth (m) 2804±2795 2835±2831 2271±2275 2249±2246 2373±2359 Formation Mandapeta Mandapeta Golapalli Golapalli Golapalli Reservoir age Triassic Triassic Cretaceous Cretaceous Cretaceous Density (15C) 0.7814 0.8068 0.8019 0.8204 0.7742
API gravity 49.5 43.8 44.9 41.0 51.2
Gross comp.
Saturates% 83.54 81.24 75.25 74.34 76.62
Aromatics% 12.61 13.61 15.92 18.41 16.91
NSO% 3.85 5.15 8.83 7.25 6.47
4.4. Source rocks
Fair to good, locally rich source rocks occur throughout the Permian, Triassic and Cretaceous units. Source rock pyrolysis logs, maturation, extract data and molecular level parameters have been compiled from many wells throughout the sub-basin. Fig. 4 shows the correlation of dierent stratigraphic units of the KMG-MDP-DRK-END belt.
4.5. Permian source sequence (Kommugudem Formation)
The Permian Gondwanan coal/coaly shale sediments were deposited in ¯uvial-lower deltaic- lacustrine envir-onment. The total organic carbon of these sediments is high but S2 (mg HC/g rock) and HI (mg HC/g TOC)
values indicate hydrogen de®cient organic matter (Fig. 4). The pattern and values of Pr/Ph and Pr/nC17ratios
of Permian section (Kommugudem Formation) are shown in Figs. 5 and 6, respectively.
In the Permian Gondwanan sediments of this basin, the values of the ratios of 1 MP/9 MP and 1,7 DMP/x are less than 0.65 and 0.35 respectively, which show the major contribution of Glossopteris Pteridosperms. This is also supported by palynological information (Prasad et al., 1995).
Alexander et al. (1992) have shown that in Cooper/ Eromanga Basin, low values of 1 MP/9 MP and 1,7 DMP/ x ratios (less than 0.65 and 0.35, respectively) in oils and rock extracts are indicator of Permian ¯ora (mainly Pter-idosperms). The values of these ratios increase remarkably as the ¯ora changes.
The Permian Gondwanan coals/coaly shales formed from relatively simple Glossopteris pteridosperms ¯ora in a cold to cool temperate climate. The Glossopteris are pteridosperms gymnosperms (Gould and Shibaoka, 1980; Prasad et al., 1995), the preserved components of which are rich in cellulose and lignin, which form the hydrogen-poor, woody parts of trees (Cooper and Murchison, 1969). Permian ¯ora, itself poor in exinite, was also highly susceptible to dessication and oxidation during the peat forming process. Hence the organic matter, which was mainly hydrogen de®cient initially, was subjected to further degradation in unfavourable sites of deposition (Thomas, 1982). Since the Glassop-teris ¯ora does not seem to have been rich in cuticle or
resin, major oil accumulations of land plant origin are not considered likely. The organic character of the Permian is, therefore, mainly gas prone, possibly with low yields in areas where the primary inertinite content is high.
4.6. Triassic sediments (Mandapeta Formation)
This sequence is sand dominated with little sig-ni®cance as a source rock. These sediments however, contain many thin, non-coal, locally rich source rock intervals. This sequence was deposited in a ¯uvial envi-ronment. The intraformational shales in the Kommugu-dem area are thick and of good quality as compared to the Mandapeta area, there being a great variation in source rock thickness, quality and potential. Inertinite is the main maceral with a subordinate amount of vitrinite. The sequence is absent in Draksharama and Endamuru (Fig. 4). The maturity is around 0.8±1.1% Ro. The values of Pr/Ph and Pr/nC17 ratios of this sequence
(Mandapeta Formation) are shown in Fig. 6. The source parameters (1 MP/9 MP and I,7-DMP/x) based on aromatic biomarkers are dierent from those of the Permian. The explanation is that the ¯ora had changed (Figs. 6 and 7). The palynological data indicates that the Dicroidium Pteridosperms (Pteridospermous gymno-sperms) had become dominant (along with some early conifers) over Glossopteris ¯ora (Prasad et al., 1995). The Triassic sequence contains some exinite fraction
which might have been derived from thick cutinite of Dicroidium (Cook and Taylor, 1963; Cook, 1975) and some early conifers (Prasad et al., 1995).
4.7. Cretaceous sequence
The organic richness in terms of TOC increases from Kommugudem to Mandapeta to Draksharama to Enda-muru (Fig. 4). The quality of organic matter deteriorates from Kommugudem to Mandapeta area, while the organic matter in Mandapeta and Draksharama areas is almost similar in quality. Angiosperms appeared in the Cretaceous. The abundance of resins, cuticle and spores, together with the generally resin rich character of the woody parts has led to high survival rate of organic matter which has a high potential for liquid yield. This sequence was deposited in a shallow marine
environ-ment. The aromatic biomarkers are dierent (1MP/ 9MP>1.2 and 1,7-DMP/x>0.65) from the Triassic and Permian sequences. (Figs. 6 and 7). During this period the ¯ora had the dominance of conifers (Prasad et al., 1995).
4.8. Organic maturity
The degree of maturity of source rocks has been determined from Rc, spore discoloration, Rock Eval Tmax. Solvent extracts of source rocks provide additional
data on chemical maturity as well as providing a means of oil-source correlation. All these methods have practical de®ciencies and integrated approach to maturity estima-tion has been adopted (Fig. 8). As discussed above MPI of the rock extracts has been calibrated with observed Ro to check validity of these parameters in this area.
According to Tissot and Welte (1984), the onset of oil generation occurs between 0.5 and 0.7% Ro depending on the organic type. The transformation ratio derived from hydrous pyrolysis of immature rock sample of this
area indicates that the onset of oil generation has occurred at around 0.65% Ro.
The Permian sequence is post oil mature in the Kommugudem area. The maturity increases towards
Fig. 8. Maturity levels at dierent stratigraphic levels in the KGM-MDP-DRK-END belt.
Mandapeta. The maturity decreases towards Drakshar-ama and Endamuru. In the Triassic sequence, maturity increases from Kommugudem to Mandapeta. Around Kommugudem, the sequence is moderately mature to mature and around Mandapeta the sequence is mature. Signi®cant maturation commenced around 2000 m in Cretaceous sediments in Kommugudem and Manda-peta. The Cretaceous sections are marginal to moderately mature in the studied area. The maturity increases from Kommugudem to Mandapeta and decreases towards Draksharama and Endamuru.
4.9. Oil±source rock correlation
Fig. 3 shows values of the aromatic hydrocarbon based maturity indicators on oils recovered from the Mandapeta ®eld. The striking feature of this data is the progressive increase in maturity of oils with increasing age (depth) of the reservoir formation based on Rc from methyl phenanthrenes. The maturity indicators show that the oils in the reservoir have similar maturities to those of indigenous hydrocarbons contained in shales in similar stratigraphic locations (Figs. 3 and 8).
The oils found in the Mandapeta and Golapalli reservoirs have been derived from a similar type of source organics based on aromatic biomarker ratios (1 MP/9 MP and 1,7-DMP/x). The oils from the Golapalli reservoir are slightly less mature than the oils from the Mandapeta reservoir.
A detailed study on oil to source correlation suggests that the underlying shales at the depth interval of 2700± 2800 m in the Mandapeta Formation, of moderate maturity, have sourced the oils reservoired in the Gola-palli sandstone based on source and maturity parameters shown in Fig. 9.
Mandapeta sandstone oils (from wells A and C) have been generated by underlying and comparatively more mature source rocks at the depth interval 2850±3150 m in the Mandapeta Formation as evident from the close values of pristane/phytane ratio and aromatic parameters (1 MP/9 MP and 1,7-DMP/x) of Mandapeta reservoir oils and probable rock extracts shown in Figs. 10 and 11. The maturity of ¯uids is around 0.95±1.0% Rc which matches well with the maturity of basal shales in Mandapeta For-mation (Figs. 10 and 11). The origin of these oils from underlying Permian sequence is ruled out on the basis of
maturity as well as aromatic biomarker dierences (Figs. 6 and 7). Moreover, Permian sequence is post oil mature and hydrogen-de®cient which can generate only gaseous hydrocarbons. The ¯ora available during Permian time was of poor quality (as discussed earlier) and must have generated only gaseous hydrocarbons during peak oil generation as evident from a number of gas occurrences in the sands of Kommugudem (Permian) Formation.
4.10. Gas composition and source
The composition of gases recovered from the Gola-palli and Mandapeta sandstone reservoirs is given in Table 2 and Fig. 3. The simple composition of gases and factors such as multiple source, maturity and fractiona-tion during migrafractiona-tion make it dicult to correlate them with their source rocks. The gas generating potential of
Fig. 11. Probable source rocks of the oils found in well MDP-A. Source and maturity data, as shown in the ®gure, indicate that source rocks in Mandapeta Formation have sourced MDP-A and-C oils.
Table 2
Characteristics of gases of the Mandapeta area
Well no.
MDP-A MDP-C MDP-G MDP-L
Depth (m) 2804±2795 2835±2777 2925±2895 2249±2246 Formation Mandapeta Mandapeta Mandapeta Golapalli
Age Triassic Triassic Triassic Cretaceous
d13C1 ÿ32.6 ÿ32.6 ÿ32.5 ÿ38.9
d13C2 ÿ25.6 ÿ24.1 ÿ25.0 ÿ29.0
C1(vol. %) 89.13 85.18 85.2 53.13
C2+ (vol. %) 10.3 9.32 11.1 41.15
C1/C2+C3 9.66 9.68 8.67 1.77
C2/C3+ 2.42 3.63 2.17 0.39
iC4/nC4 0.80 0.81 1.12 0.49
Permian sediments in the Mandapeta sub-basin has long been recognized (unpublished work).
Gas reservoired in Mandapeta sandstone is moderately wet with low C4+hydrocarbon content (Fig. 3). The gas
composition and stable carbon isotopic studies point to a mixed maturity source (catagenetic and metagenetic) with a methane stable carbon isotope ratio of ÿ32.5 to
ÿ32.6%. The bulk of the gas is from the metagenetic
stage and appears to be sourced by Kommugudem Formation. The maturity of these gases is equivalent to 1.2% Ro.
Gas reservoired in the overlying Golapalli Formation is dierent from the Mandapeta Sandstone gas, in that it is wetter and isotopically lighter, the gas composition suggests the gas to be a typical oil-associated gas.
4.11. Origin, migration and entrapment of hydrocarbons
The Triassic reservoir (Mandapeta sandstone) is over-lying the Permian coal-shale sequence (Kommugudem Formation), resulting in extremely favourable entrap-ment conditions with the Red Bed being the regional cap rock. Vertical and lateral migration is facilitated by communication of the predominantly channel point bar sandstone and local syndepositional faulting of the Kommugudem Formation.
The Lower Cretaceous (Golapalli) reservoir is overlying the Red Bed. The observed migration of hydrocarbons from underlying source rocks will have occurred due to erosion or non-deposition of the regional seal over these trends, together with faulting.
The basin has experienced (Fig. 2) continuous sub-sidence interrupted by episodes of non-deposition (example of heating with a constant rise in temperature punctuated by isothermal heating). The two commonly used methods of maturity modeling, namely TTI method and Easy Ro method, have been applied in this basin. It has been found that Waples TTI method (Waples, 1980) overestimates maturation while the Ro values calculated from Easy Ro of Sweeney and Burn-ham (1990) are in close agreement with the observed ones in marginal to high maturity range (0.5±1.35% Ro). Fig. 12 depicts the source rock potential and maturity level of dierent layers in the KMG-MDP-DRK-END belt. It has been argued that the Permian coals and shales of the Kommugudem Formation are the major source rocks for gas in this area. The hydro-carbon generation started in Early Cretaceous in the Kommugudem Formation as estimated by Easy Ro of Sweeney and Burnham (1990). The traps were available during this time, but the intermittent tectonic activity has resulted into reorientation and redistribution of the original trap geometries. The present day maturity level of the Permian in the Mandapeta area is Ro 1.2% or greater, which is consistent with the maturity of gases encountered in this area. They are thermogenic (mixed i.e. derived at late catagenetic as well as early metagen-etic stages) in origin.
Localised shales in the Mandapeta Formation have sourced the Mandapeta and the Golapalli oils. The oils being produced from Golapalli Formation have been generated at lower maturity levels.
4.12. Hydrocarbon occurrence and fault blocks
The fault blocks in the Mandapeta area are the result of tectonic activity, which was probably initiated prior to the Permian and has continued intermittently. This has in¯uenced the generation and entrapment of hydro-carbons by:
1. Providing conditions conducive to the deposition of potential Permian, Triassic and Cretaceous source rocks, sometimes in considerable thickness, in close proximity to potential reservoir/seal pairs. 2. The formation of a signi®cant number of proven structural traps and probably stratigraphic traps. 3. A favourable timing of trap development relative
to hydrocarbon expulsion.
4. Possibly allowing hydrocarbons to migrate up faults to reservoirs.
5. Conclusions
Land plant rich source rocks are widely distributed throughout the Permian and Triassic sections of the basin. The Cretaceous sequence deposited in shallow marine environment has substantial contribution of marine organic matter. The Permian section is post mature for oil generation in the Kommugudem and Mandapeta area of the belt. The Triassic section is oil mature and the Cretaceous section is early to moderately mature.
Hydrocarbon accumulations are mainly gas and gas/oil. Gas in the Golapalli and Mandapeta reservoirs has been generated from both the Triassic shales (Mandapeta For-mation) and Permian coals/coaly shales (Kommugudem Formation), although there is evidence that the Permian is the principal source.
The associated small accumulations of oils encountered in parts of this belt are attributed to the oil-prone shales in the Mandapeta Formation. Most of the oils discovered are paranic in nature and have mature character. The oil to source correlation and the basin con®guration suggest vertical and short distance migration.
The study indicates that Raghavapuram shale in the Mandapeta area has adequate maturity and hydro-carbon potential for oil generation. Oil has been dis-covered in the interbedded sands of one well recently. The probability of ®nding hydrocarbon reserves in sands of Raghavapuram shale and other suitable traps is high. Modern seismic information together with geo-logic models can give new exploration leads.
Acknowledgements
The authors are grateful to Director (Exploration) Shri T.K.N. Gopalaswami, for according permission to
pub-lish this work. Profound thanks are due to Shri Kuldeep Chandra, Executive Director and Head, KDMIPE, for his valuable guidance and suggestions during the pre-paration of this manuscript. Thanks are due to Shri K.N. Misra, G.M. (GRG), KDMIPE, Dehradun, for his valuable guidance and encouragement. The authors are also grateful to Shri Lehamber Singh, G.M. (Exp), ERBC, and Dr. B.K. Sharma, G.M. (Chem), ERBC, for providing valuable guidance and a wonderful environ-ment to complete this work. The authors are also grateful to Dr. Rajiv Sharma, Sr. Chemist, for his contribution in the preparation of this report. We thank the review-ers, Drs. R.G. Schaefer and C. Clayton, for their valu-able criticism and suggestions.
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