Search

The sediment samples from Cretaceous sequences, Lower Indus Basin, were investigated using biomarkers approach to predict the source, depositional environment and lithology of organic matter. The Parh and Upper Goru Formations demonstrate the presence of algal organic matter deposited under anoxic and suboxic conditions. The interpretation was supported by relatively high distribution of C27 5α (H), 14α (H), 17α (H) 20R (ααα-20R) steranes. The samples of Lower Goru Formation reveal mixed organic matter, predominantly terrestrial and oxic, as apparent from biomarkers distribution. The Sembar Formation specifies mixed input of organic matter more terrigenous input at intervals, deposited under anoxic and suboxic conditions. Geochemical analyses performed on Cretaceous strata show that hydrocarbons were derived from organic matter of mixed origin, predominantly terrestrial, deposited under anoxic and oxic conditions.

The sediment samples from cretaceous sequences, Lower Indus basin, were analyzed using diagnostic biomarkers to predict the thermal maturity of organic matter. The sediments were tested for aliphatic biomarkers ratios, i.e. homohopanes and steranes isomerization ratios and carbon preference indices. These biomarker maturity parameters reveal that the Lower Goru (including its members Upper shale, Lower shale, and Talhar shale) and Sembar Formations in the Lower Indus Basin of Cretaceous age have reached the maturity level equivalent to the main zone of hydrocarbons generation, whereas Parh and Upper Goru Formations are immature and far from oil window. Geochemical analyses carried out stresses that hydrocarbons derived from the Sembar and Lower Goru Formations (particularly deeper Members) are within the zone of peak oil generation.

Sediment samples from three boreholes namely Paniro-II, North Akri, and Bhadmi of Sembar Formation, Southern Indus Basin were geochemically analyzed. The Soxhlet extracted bitumen were fractionated by column chromatography. The saturate fractions were further analyzed to evaluate type and quality of organic matter (OM). Total organic carbon, determined by a wet combustion titration method, indicates fair-to-good source rock potential. The plot of isoprenoids/n-Alkanes shows a mixed source of OM. Pristane/Phytane values and distribution of hydrocarbons showed dysoxic depositional environment. Carbon preference indices suggested increase in maturity with depth.

This study includes geochemical characterization of source rock samples from the Upper shale, Lower shale, Talhar shale units of Sembar Formation and Badin shale, Turk shale units of Lower Goru For...

In previous studies, Patala-Nammal Composite Total Petroleum System (TPS) was recognized as a potential source of hydrocarbon in the Upper Indus Basin, and Sembar-Goru Composite TPS in the Lower Indus Basin. However, petroleum source-rock potential of Cretaceous strata in the Indus Basin is poorly known. In the current study, Rock Eval and total organic carbon (TOC) analyses were conducted to investigate the thermal maturity and source-rock potential of Cretaceous unit in the Lower Indus Basin. The Parh Formation of the Lower Indus Basin is lean in organic contents (TOC < 0.73%) and consistent with immature type-III/IV kerogen. The Upper Goru Formation is fair in organic contents and presents similar characteristics to the Parh Formation with respect to the hydrocarbon generation zone. The Lower Goru Formation presents fair to very good organic contents. The members of Lower Goru Formation have enough organic matter (OM) and are mature, with the exception of Badin shales. The OM, throughout the fo...

Geochemical analyses of the 10 crude oils from Cretaceous sequences, Lower Indus Basin, Pakistan, are performed to characterize source, depositional environment, biodegradation, and thermal maturity to establish genetic relationship. Low sulfur, high pristane/phytane (Pr/Ph) ratios, and high American Petroleum Institute gravity indicate oxic depositional environment and terreginous input of organic matter (OM). Full suite of n-alkanes, low isoprenoid/n-alkane ratios, elevated saturates/aromatics ratios, and the absence of unresolved complex mixture indicate typical non-biodegraded light crude oils. The carbon preference index, odd even predominance, Pr/n-C17, and Ph/n-C18 ratios reveal that source rocks generating Lower Indus Basin crude oils are thermally mature. Based on geochemical analyses, the source OM input is probably terreginous mixed with marine, deposited under suboxic to oxic depositional environments.

Nine crude oils and eight source rock samples from Cretaceous sequences, Lower Indus Basin have been characterized by means of diagnostic biomarker parameters in order to establish genetic liaison among them. The biomarker geochemistry indicators such as relative distribution of C27-C28-C29 ααα-20R steranes, C19 and C23 tricyclic terpanes (TT), C24 tetracyclic terpanes (TeT), hopanes distribution, steranes/hopanes ratio, presence of unidentified compound X (C30 pentacyclic triterpane), and pristane (Pr) to phytane (Ph) ratio suggest that the crude oils contain predominantly terrigenous organic matter (OM). Based on these data, the analyzed crude oils from the Lower Indus Basin are genetically associated and could be classified into a single group. Geochemical correlation studies of crude oils and source rock sediments indicate that Lower Goru shales and Sembar could be the probable source rocks for the petroleum generated from Cretaceous strata, Lower Indus Basin, Pakistan.

Eocene sediments from the Potwar Basin Pakistan have been characterized geochemically using liquid chromatography, gas chromatograph–mass spectrometry (GC–MS), GC–isotope ratio MS and metastable reaction monitoring (MRM) GC–MS. Biomarker and non-biomarker parameters have been used to evaluate the origin, paleodepositional conditions, lithology and thermal maturation of organic matter. The n -alkanes distribution profiles observed for the studied samples suggest an abundance of low molecular weight compounds in the Upper Eocene sequence, which is consistent with higher marine input. On the other hand, the bimodal n -alkanes distribution observed with depth may suggest terrigenous contribution. An enrichment of the δ 13 C of low molecular weight n -alkanes ( n -C 18 ) reveals marine origin (algal and bacterial) while depleted 13 C values observed for n -alkanes greater than n -C 22 indicate terrigenous origin of these compounds. Despite ample biomarker parameters as to the noticeable marine origin of the organic matter, presence of oleanane and retene as well as the enrichment of the δ 13 C values of the long chain n -alkanes suggest significant terrestrial contribution in the studied organic matter. An interesting feature of the δ 13 C isotopic profiles of n -alkanes higher than C 25 is so called saw tooth profile, in which the odd carbon number compounds were more depleted in 13 C than the adjacent even numbered compounds. This feature may further support the assumption that the source of these n -alkanes lay in plant waxes. Depositional environment of these sediments were typical marine with oxic to suboxic conditions and showed variation in oxicity with depth. Our results indicate that the Upper Eocene sediments have been deposited under oxic conditions while the lower Eocene strata are more likely to be deposited under restricted suboxic reducing marine conditions. Significantly low concentration of rearranged steranes and hopanes suggested carbonate lithology for these sediments. Aliphatic and aromatic hydrocarbons geochemical data indicate level of maturity corresponding to the onset of oil generation. Therefore, it is suggested that these sediments are more likely to be considered as possible hydrocarbon source rocks within the Potwar Basin.

The study focused on the petroleum geochemistry of crude oils produced from Cretaceous reservoirs. Geochemical portrayal of crude oils has been carried out by means of diagnostic biomarker parameters like relative distribution of steranes (C27–C28–C29 ααα-20R steranes), C19 and C23 tricyclic terpanes (TT), C24 tetracyclic terpanes (TeT) and hopanes. These parameters suggest that the crude oils contain terrigenous organic matter (OM) mixed with small input of marine OM. The OM of the source rocks was deposited in oxic depositional environment. Maturity parameters, C32 22S/(22S+22R) homohopanes and sterane isomerization ratios [20S/(20S+20R), αββ/(αββ+ααα) for C29 steranes] indicate that these crude oil are produced from the source rocks at early mature stage to mature stage.

The soluble organic matter (SOM) and kerogen of sediments contain organic molecules, and can be interpreted in terms of source, generative potential, thermal maturity, and depositional environment of the organic matter. Early Cretaceous sedimentary sequence of Sembar Formation comprising five sediments samples was analyzed. Both SOM and hydrocarbons bound to the kerogen terms as pyrolyzed organic matter (POM) were characterized geochemically. Hydrous pyrolysis was carried out to release hydrocarbons from extracted sediments and fractionated by liquid chromatography. Saturated fractions from both SOM and POM were further analyzed by gas chromatography-flame ionization detector. The study suggested that Cretaceous sequence of Sembar Formation has fair to good hydrocarbon source potential. Thermal maturity parameters indicate onset of oil genesis zone. The presence of even carbon numbered n-alkenes, Pr/Ph and Pr/n-C17 versus Ph/n-C18 plots reveal marine algal source and anoxic depositional environme...

A high abundance of ethyl substituted aromatic hydrocarbons (HCs) relative to their methyl counterparts is an unusual feature of some crude oils. Enhanced stability of ethyl aromatic HCs in the presence of tetralin was observed when individual ethylated compounds were heated with activated carbon in sealed tubes over a range of 170–340 °C. In addition, conversion of the common distribution of alkyl aromatic HCs to an unusual distribution, containing a higher relative abundance of ethyl compounds, was demonstrated by way of closed system heating of the aromatic fraction of a crude oil in the presence of activated carbon. The conditions for this unusual process require the presence of hydrogen donor components, which selectively limit the reaction and depletion of ethylated compounds relative to methylated compounds. The phenomenon has been shown to occur for substituted benzenes, naphthalenes, phenanthrenes and biphenyls. Enhanced abundance of ethyl aromatic HCs relative to their methylated counterparts is therefore proposed as an indicator for secondary reactions of migrated crude oil that has undergone thermal alteration after contact with carbonaceous surfaces in sediments. Application of these principles to selected crude oils and sediment extracts from the Carnarvon and Cooper/Eromanga Basins (Australia) indicates that significant secondary reaction of migrated crude oil has occurred.

In a previous study, oils in the Potwar Basin (Upper Indus) of Pakistan were correlated based on the dissimilarity of source and depositional environment of organic matter (OM) using biomarkers and bulk stable isotopes. This study is aimed at supporting the classification of Potwar Basin oils into three groups (A, B and C) using the distribution of alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, alkyldibenzofurans, alkylfluorenes, alkylbiphenyls, triaromatic steroids, methyl triaromatic steroids, retene, methyl retenes and cadalene. The higher relative abundance of specific methyl isomers of naphthalene and phenanthrene and the presence of diagnostic aromatic biomarkers clearly indicate the terrigenous and oxic depositional environment of OM for group A oil. Group B and C oils are of marine origin and the aforementioned heterocyclic and polycyclic aromatic hydrocarbons (HCs) differentiate them clearly into two different groups. The relative percentages of heterocyclic aromatic HCs reveal that the distribution of these compounds is controlled by the depositional environment of the OM. Sulfur-containing heterocyclic aromatic HCs are higher in crude oils generated from source rocks deposited in suboxic depositional environments, while oxygen-containing heterocyclic aromatic HCs in combination with alkylfluorenes are higher in marine oxic and deltaic oils. Biomarker and aromatic HC parameters do not indicate significant differences in the thermal maturity of Potwar Basin oils. Triaromatic and methyl triaromatic steroids support the division of Potwar Basin oils into the three groups and their relative abundances are related to source OM rather than thermal maturity. Significantly higher amounts of C20 and C21 triaromtic steroids and the presence or absence of long chain triaromatic steroids (C25, C26, C27, and C28) indicates that these compounds are probably formed from different biological precursors in each group. Different isomers of methyl substituted triaromatic steroids are present only for short chain compounds (C20–C22) and the origin of these compounds may be short chain methyl steranes from unknown biological precursors.

Geochemical characterisation of 18 crude oils from the Potwar Basin (Upper Indus), Pakistan is carried out in this study. Their relative thermal maturities, environment of deposition, source of organic matter (OM) and the extent of biodegradation based on the hydrocarbon (HC) distributions are investigated. A detailed oil–oil correlation of the area is established. Gas chromatography–mass spectrometry (GC–MS) analyses and bulk stable carbon and hydrogen isotopic compositions of saturated and aromatic HC fractions reveals three compositional groups of oils. Most of the oils from the basin are typically generated from shallow marine source rocks. However, group A contains terrigenous OM deposited under highly oxic/fluvio-deltaic conditions reflected by high pristane/phytane (Pr/Ph), C 30 diahopane/C 29 Ts, diahopane/hopane and diasterane/sterane ratios and low dibenzothiophene (DBT)/phenanthrene (P) ratios. The abundance of C 19 -tricyclic and C 24 -tetracyclic terpanes are consistent with a predominant terrigenous OM source for group A. Saturated HC biomarker parameters from the rest of the oils show a predominant marine origin, however groups B and C are clearly separated by bulk δ 13 C and δD and the distributions of the saturated HC fractions supporting variations in source and environment of deposition of their respective source rocks. Moreover, various saturated HC biomarker ratios such as steranes/hopanes, diasteranes/steranes, C 23 -tricyclic/C 30 hopane, C 28 -tricyclic/C 30 hopane, total tricyclic terpanes/hopanes and C 31 ( R + S )/C 30 hopane show that two different groups are present. These biomarker ratios show that group B oils are generated from clastic-rich source rocks deposited under more suboxic depositional environments compared to group C oils. Group C oils show a relatively higher input of algal mixed with terrigenous OM, supported by the abundance of extended tricyclic terpanes (up to C 41+ ) and steranes. Biomarker thermal maturity parameters mostly reached to their equilibrium values indicating that the source rocks for Potwar Basin oils must have reached the early to peak oil generation window, while aromatic HC parameters suggest up to late oil window thermal maturity. The extent of biodegradation of the Potwar Basin oils is determined using various saturated HC parameters and variations in bulk properties such as API gravity. Groups A and C oils are not biodegraded and show mature HC profiles, while some of the oils from group B show minor levels of biodegradation consistent with high Pr/ n -C 17 , Ph/ n -C 18 and low API gravities.

A suite of six crude oils from Lower Indus Basin, Pakistan, were analyzed for geochemical characterization of source organic matter (OM) and thermal maturity. Distribution of polycyclic aromatic hydrocarbons (PAHs), alkylnaphthalenes, alkylphenanthrenes, alkyldibenzothiophenes, and aromatic biomarkers were reported from aromatic fractions of the crude oils. The aromatic hydrocarbons parameters revealed a higher thermal maturity of OM of source rock-generated Lower Indus Basin oils. Calculated vitrinite reflectance values from the methylphenanthrenes index 1 (MPI-1) and methyldibenzothiophene ratio (MDR) indicate that most of the oils reached a late oil generation window of thermal maturity. PAH distributions revealed the oils of two different origins are present in the Lower Indus Basin; two oil samples indicate aquatic source of OM and the aromatic biomarker distributions of retene, 1-MP, and 1,7-DMP indicate a significant contribution of land plant OM in the other four oils. This is the first s...

The biomarker composition of biodegraded petroleum in an oil seep was determined using GC and GC–MS techniques. The results show that many important biomarker compounds are eliminated or highly altered by biodegradation. In order to establish a correlation between the seep sample and a non-biodegraded crude oil sample from the Dhurnal field, asphaltenes were isolated from the seep and subjected to hydrous pyrolysis. The biomarker composition of the pyrolysate and the Dhurnal oil is similar, suggesting that they are generated by similar source rocks.

Palladium(II) complexes with triphenylphosphine (PPh3) and thioamides of the general formulae, [Pd(L)2(PPh3)2]Cl2 and [Pd(L)2(PPh3)2] have been prepared and characterized by elemental analysis, IR and NMR (1H, 13C and 31P) methods, and two of them (trans-[Pd(PPh3)2(Dmtu)2]Cl2·(H2O)(CH3OH)0.5 (1) and trans-[Pd(PPh3)2(Mpy)2] (2)) by X-ray crystallography; where L = thiourea (Tu), methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu), tetramethylthiourea (Tmtu), 2-mercaptopyridine (Mpy), 2-mercaptopyrimidine (Mpm) and thionicotinamide (Tna). The spectral data of the complexes are consistent with the sulfur coordination of thioamides to palladium(II). The crystal structures of the complexes show that (1) has ionic character consisting of [Pd(PPh3)2(Dmtu)2]+2 cations and uncoordinated Cl− ions, while (2) is a neutral complex with Mpy behaving as anionic thiolate ligand. The coordination environment around palladium in (2) is nearly regular square-planar, while in (1) the trans angles show significant distortions from 180°. The complexes were screened for antibacterial effects, brine shrimps lethality bioassay and antitumor activity. These complexes showed significant activities in most of the cases against the tested bacteria as compared to that of a standard drug. Their antitumor activity against prostate cancer cells (PC3) is comparable with doxorubicin, together with no cytotoxic effects in brine shrimps lethality bioassay study.

Laboratory experiments have shown that activated carbon catalyses the reactions of biphenyls (BPs) with surface adsorbed reactants incorporating either S, O, N or methylene, leading to the formation of some common constituents reported in sedimentary organic matter (OM) namely, dibenzothiophene (DBT), dibenzofuran (DBF), carbazole (C) and fluorene (F). A relationship between the % abundance of the hetero element in the kerogen and the abundance of the related heterocyclic compound in the associated soluble OM supports the hypothesis that these reactions occur in Nature. More specific supporting evidence was obtained from the good relationship observed between methyl and dimethyl isomers of the reactant BPs and the methyl and dimethyl isomers of the proposed heterocyclic products. It is suggested that these aromatic compound distributions reported in sediments and crude oils from the Upper Indus Basin (Pakistan) and the Carnarvon Basin (NW Australia) are the result of a surface reactions of compounds with BP rings and surface adsorbed species of the hetero element on the surface of carbonaceous material.

The hydrocarbon source rock potential of five formations in the Potwar Basin of northern Pakistan – the Sakesar Formation (Eocene); the Patala, Lockhart and Dhak-Pass Formations (Paleocene); and the Datta Formation (Jurassic) – was investigated using Rock-Eval pyrolysis and total organic carbon (TOC) measurement. Samples were obtained from three producing wells referred to as A, B and C. In well A, the upper ca. 100 m of the Eocene Sakesar Formation contained abundant Type III gas-prone organic matter (OM) and the interval appeared to be within the hydrocarbon generation window. The underlying part of the Sakesar Formation contained mostly weathered and immature OM with little hydrocarbon potential. The Sakesar Formation passes down into the Paleocene Patala Formation. T max was variable because of facies variations which were also reflected in variations in hydrogen index (HI), TOC and S2/S3 values. In well A, the middle portion of the Patala Formation had sufficient maturity (T max 430 to 444°C) and organic richness to act as a minor source for gas. The underlying Lockhart Formation in general contained little OM, although basal sediments showed a major contribution of Type II/III OM and were sufficiently mature for hydrocarbon generation. In Well B, rocks in the upper 120 m of the Paleocene Patala Formation contained little OM. However, some Type II/III OM was present at the base of the formation, although these sediments were not sufficiently mature for oil generation. The Dhak Pass Formation was in general thermally immature and contained minor amounts of gas-prone OM. In Well C, the Jurassic Datta Formation contained oil-prone OM. T max data indicated that the formation was marginally mature despite sample depths of > 5000 m. The lack of increase in T max with depth was attributed to low heat flows during burial. However, burial to depths of more than 5000 m resulted in the generation of moderate quantities of oil from this formation.

Sediment extracts and crude oils have been shown to contain methyl substituted biphenyls and dibenzothiophenes, with isomer distributions suggesting a geochemical relationship between the two compound classes. Laboratory simulation experiments have shown that carbon catalyses the reaction between surface adsorbed sulfur and biphenyl to form dibenzothiophene. Similarly, the methyl substituted biphenyls reacted to yield corresponding methyl dibenzothiophenes. We suggest that the widespread distribution of dibenzothiophene and alkylated dibenzothiophenes in sediments and crude oils is the result of a catalytic reaction of biphenyl ring systems and surface-adsorbed sulfur on the surface of carbonaceous material.

The stable hydrogen isotopic compositions (δD) of selected aliphatic hydrocarbons (n-alkanes and isoprenoids) in eight crude oils of similar source and thermal maturity from the Upper Indus Basin (Pakistan) were measured. The oils are derived from a source rock deposited in a shallow marine environment. The low level of biodegradation under natural reservoir conditions was established on the basis of biomarker and aromatic hydrocarbon distributions. A plot of pristane/n-C17 alkane (Pr/n-C17) and/or phytane/n-C18 alkane (Ph/n-C18) ratios against American Petroleum Institute (API) gravity shows an inverse correlation. High Pr/n-C17 and Ph/n-C18 values and low API gravity values in some of the oils are consistent with relatively low levels of biodegradation. For the same oils, δD values for the n-alkanes relative to the isoprenoids are enriched in deuterium (D). The data are consistent with the removal of D-depleted low molecular weight (LMW) n-alkanes (C14–C22) from the oils. The δD values of isoprenoids do not change with progressive biodegradation and are similar for all the samples. The average D enrichment for n-alkanes with respect to the isoprenoids is found to be as much as 35‰ for the most biodegraded sample. For example, the moderately biodegraded oils show an unresolved complex mixture (UCM), loss of LMW n-alkanes (

The branched and cyclic alkane fractions from a biodegraded crude oil and the solvent extract of a mature sediment were analysed for extended 17α-hopanes/moretanes and extended 8,14-secohopanes using gas chromatography-mass spectrometry techniques. The biodegraded crude oil contained abundant 8,14-secohopanes in the form of pseudohomologous series with carbon numbers ranging from 31 to 35. Comparison of the chromatograms of the extended 8,14-secohopanes with those of the extended 17α-hopanes and moretanes from the sediment extract revealed some interesting similarities. Firstly, the C31 moretanes (22S, 22R) were not resolved but the corresponding C31 17α-hopanes were well resolved. In the case of the 8,14-secohopanes three of the six groups of C31 compounds were either poorly resolved into doublets or appeared as single peaks while the other three compound groups were well-resolved into doublets. This suggests that one group of 8,14-secohopanes behave in a similar manner to the moretanes and another group have a behaviour similar to that of the 17α-hopanes. Another feature of the distribution of extended moretanes, namely the greater relative abundance of the second eluting isomer of each pair (22S and 22R diasteromers), was also observed in the “moretane-like” 8,14-secohopanes. These similarities in GC behaviour and in the relative abundances of isomers has been interpreted as evidence for “hopane-type” and “moretane-type” extended 8,14-secohopanes.

An alkane fraction isolated from Pakistani oil seep samples using liquid chromatography on US-Y molecular sieves has been shown to contain six pseudohomologous series of tetracyclic compounds that have mass spectral characteristics of 8,14-secohopanes with carbon numbers extending to 35. This is the first report of extended 8,14-secohopanes in a crude oil, although extended 8,14-secohopanes with up to 32 carbon atoms have previously been reported from a Chinese coal of Jurassic age. The Kovats indices of these extended 8,14-secohopanes are reported from measurements using capillary gas chromatography columns with nonpolar and polar stationary phases.