Pabdeh Formation Research Articles

Study of hydrocarbon generation and 1D-2D modeling of hydrocarbon migration at the Karanj and Parsi oilfields, Southern Dezful Embayment, SW Iran

Abstract This study is a 2D basin modeling to determine the petroleum system (i.e. Cretaceous-Neogene play) of the Karanj and Parsi oilfields in the Southern Dezful Embayment, SW Iran. This system is characterized by occurrence of source rocks of Middle Cretaceous, Late Cretaceous and Paleocene to Eocene (Kazhdumi, Pabdeh and Gurpi Formation), reservoirs of Upper Cretaceous and Late Oligocene–Early Miocene (Ilam-Sarvak and Asmari formations), and seals of Paleocene and Miocene (Pabdeh and Gachsaran Formation). Considering temperature, transformation ratio and vitrinite reflectance, the maturity of source rocks (Kazhdumi, Pabdeh and Gurpi Formation) was investigated. A maturity history analysis showed that the maturity of Kazhdumi, Pabdeh and Gurpi Formation started during 70–60 and 4 Ma, respectively. Generation and expulsion of hydrocarbons started ~16 Ma in the Kazhdumi Formation and ~3 Ma in the Pabdeh Formation that continued up to the present. The analysis of the transformation ratio indicates transformation of significant amounts of Kazhdumi source rocks for generating hydrocarbons. Migration of hydrocarbons from the Kazhdumi Formation is mainly vertically upward. From Pabdeh Formation migration is both vertically upward (to the Asmari reservoir) and downwards (to the Ilam-Sarvak reservoir). However, some local traps have formed due to the hydrocarbon accumulation above the faults. Our results reveal that petroleum generation, migration and entrapment occurred at proper timing which facilitated the migration of hydrocarbons and their accumulation in the reservoirs.

Biostratigraphy and lithostratigraphy of Late Cretaceous–Early Palaeogene deposits in Tang-e-Abolhayat, Zagros basin (SW Iran)

In this study, to consider microbiostratigraphy of Cretaceous and Palaeocene planktic foraminifera, a stratigraphic section of the Gurpi and Pabdeh formations named Tang-e-Abolhayat was selected. On the basis of the identified planktic foraminiferal assemblages, seven biozones and two sub-biozones have been recorded (four biozones from the uppermost part of the Cretaceous, (Gurpi Formation), and three biozones from the lower part of the Lower Palaeocene (Pabdeh Formation). The biostratigraphic correlations based on planktic foraminiferal zonations showed a comparison between the biostratigraphic zones in this study and other equivalents of the commonly used planktic zonal scheme around the Cretaceous–Palaeogene in and outside Iran. Biostratigraphic analysis confirms that the studied section is incomplete across the Cretaceous–Tertiary boundary and a hiatus is suggested by the absence of the Plummerita hantkeninoides, Guembelitria cretacea, Parvularugoglobigerina eugubina Zones and Parasubbotina pseudobulloides Subzone (CFl to Pla zones). These absences could reflect the restriction of the above-mentioned zones to shallower settings, slow sedimentation rates or an interval of erosion or no deposition. There is no obvious evidence of erosion. On the other hand, the Pabdeh Formation overlies Gurpi Formation paraconformably.

Evidence of high-energy storm and shallow water facies in Pabdeh sedimentary phosphate deposit, Kuhe-Lar-anticline, SW Iran

Kuhe-Lar sedimentary phosphate deposit is a major phosphate prospect located in Zagros folded basin in the flank of the Kuhe-Lar-anticline in the southeast of Iran. Phosphate deposits in the Middle East extend in Neo-Tethys basin rim through several countries from North Africa, Syria, Iraq, Turkey, Iran, and Oman. The sedimentary phosphate mineralization occurred in the Pabdeh Formation, which is comprised of a marl, limestone, and shale sequence. Based on comprehensive field and laboratory studies, facies zones, standards microfacies, and standard ramp microfacies were recognized in the Pabdeh Formation. Sedimentary features such as tempestite, hummocky cross stratification, ripple marks, couplets of fine and coarse laminae, erosional surface, graded bedding, and shell lag features strongly supported a high-energy storm and shallow water depositional conditions. The main evidence of storm origin for the Pabdeh Formation is the occurrence of sandstones interbedded with bioturbated mudstones commonly as upward fine grade forms. Negative carbon isotopic composition (δ13C, − 1.85 to − 4.89) of bulk phosphatic rock shows that it may be formed within the suboxic-to-anoxic zone, almost 100-cm depths (under seafloor). These values are within the range of recent and ancient phosphorites, suggesting their good preservation.

Palaeoecology and microfacies correlation analysis of the Oligocene–Miocene Asmari formation, in the Gachsaran oil field, Dezful Embayment, Zagros Basin, Southwest Iran

The Asmari formation is a thick carbonate succession of Oligocene–Miocene age in the Zagros Basin, southwest Iran. This research is focused on the microfacies analysis and paleoecology interpretation (based on the distribution of benthic foraminifera) of carbonate sediments of the Asmari formation. Three sections of this formation studied in the Gachsaran oil field (wells 25, 31 and 37), Dezful Embayment, Zagros Basin (southwest Iran). These sections are composed of limestone, dolomite, and limy dolomite. The Asmari formation has a conformable contact with the overlying (Gachsaran formation) and the underlying (Pabdeh formation) units. Based on petrologic studies, identification of larger foraminifera and facies analysis of the Asmari formation allowed the recognition of 14 facies types. There are grouped into four depositional environments which correspond to the inner, middle, outer ramp, and intrashelf basin. According to this study, deposition of the Asmari formation with association of hyaline, lamellar, perforate large, and flat foraminifera first started in the intrashelf basin environment during the Early Oligocene. In the latest Oligocene–earliest Miocene time, the Asmari platform margin prograded basinward, sediments of shallow water were deposited.

Geochemistry of trace elements and their relations with organic matter in Kuh-e-Sefid phosphorite mineralization, Zagros Mountain, Iran

The Kuh-e-sefid phosphorite is located in Zagros fold-thrust belt, in the Ramhormoz area, northeast of Khuzestan province. Phosphorite mineralization occurred as phosphorite lenses of Eocene age hosted by the Pabdeh Formation. The aim of this study is to investigate the role of organic matter in trace metal portioning during phosphorite mineralization in the Kuh-e-Sefid deposit. Field observations and petrographic studies indicate that the host-rock of mineralization is mainly consists of shale, marl, and limestone with textures varying from wackestone to packestone. Phosphoritic components, such as authigenic apatite, pellets, intraclasts, fish skeletal fragments, and micro-fossils are present. Moreover, non-phosphorite minerals including calcite, glauconite, pyrite, iron-oxide and to a lesser extend montmorillonite with microcrystalline quartz occurred in phosphorite lenses. NASC-normalized patterns of REEs showed the enrichment of Heavy Rare Earth elements (HREE) and negative Ce anomaly with co-existence of slightly negative and positive Eu anomalies represent a transitional change from oxic to anoxic sedimentation conditions during mineralization. Importantly, Ni/Co versus V/Cr ratios and V/(V + Ni) diagrams confirmed dysoxic to anoxic conditions for the hydrocarbon-bearing phosphorite and hosted shales, while non-hydrocarbon-bearing phosphorites exhibit oxic conditions. The FTIR studies revealed qualitative information about the component bonds and nature of the organic matter and mineral-organic bonds like OH, carboxylic OH, carboxylic acid CO, CC alkaline, group CH2, CC aromatic, CH aliphatic, and aromatic stretching associated with phosphate mineralization. It seems that there is a link between a relatively high concentration of trace metals (i.e., REEs, U, Co, Zn, Ni, V, Sr and Mo) and phosphorites enriched in organic matter especially those of aromatic hydrocarbon groups.

Biostratigraphy of Early Oligocene-Early Miocene Asmari

In this research, biostratigraphy related to the Asmari Formation at the southern flank of Mish anticline, Izeh Zone, is discussed. In the studied stratigraphic section, the Asmari Formation overlies the Pabdeh Formation and underlies Quaternary sediments. A study of 192 samples of the 328 m-thick Asmari Formation led to identification of 16 species and 26 genera of foraminifera taxa and identification of four Oligocene biozones. The Globigerina spp. and Nummulites intermedius- vascus Assemblages Zones represent the Rupelian age. The Ruplian- Chattian age is also defined by Lepidocyclina- Operculina- Ditrupa Assemblages Zone and Archias asmaricus- Miogyosinoides spp. Assemblages Zones that indicates a Chattian age.

Promoting wellbore stability in active shale formations by water-based muds: A case study in Pabdeh shale, Southwestern Iran

Minimizing water invasion into shales is a critical property for many water-based muds. By improving drilling fluids rheology in HPHT conditions, it is possible to minimize water invasion and maintain true overbalance pressure conditions at near wellbore scale which endorses wellbore stability. In order to propose an inhibitive mud formulation for drilling troublesome swelling Pabdeh formation frequently encountered in southern to southwestern regions of Iran, a comprehensive experimental approach was adopted. After performing rheology and thermal stability tests for 81 different formulations of drilling fluids, 5 high performance salt/polymer solution muds were chosen. They showed good rheology properties and all of them were thermally stable. In order to find the best formulation which accomplishes all requirements pertaining shale stability and wellbore integrity, some complementary analyses were performed. Using a roller oven simulating down hole temperature conditions, physical integrities of shale samples immersed and rolled in these 5 mud formulations were investigated. Pore pressure transmission tests were also carried out using a membrane efficiency screening equipment to evaluate membrane efficiency of the Pabdeh shale and also inhibitive performances of 5 designed mud formulations. Accordingly, pore pressure evolution in shale samples in contact with designed muds were obtained by direct measurements, which resembles the near wellbore pore pressure alterations. According to the obtained results, Pabdeh shale shows negligible membrane efficiency of about 4%. Although all mud formulations show high surface coating capabilities resulting in almost high shale recovery after exposure, pore pressure transmission tests revealed different inhibitive performances. Among them, a combination of polymers and sodium silicate shows promising mud formulation that hinders filtrate invasion into shale samples by either physical or chemical plugging of the shale pore throats. Regarding both environmental and economical aspects of drilling operations, derived mud formulations can also be advantageous for drilling safe and stable wells in Pabdeh formation.

Folding style of the Dezful Embayment of Zagros Belt: Signatures of detachment horizons, deep-rooted faulting and syn-deformation deposition

Defining the governing factors on the geometry of the Dezful Embayment folds, a major oil province in the Zagros Fold-Thrust Belt in SW Iran, reduces the risks inherent in hydrocarbon exploration. The goal of the current study is to find a reasonable relationship between folding and faulting in the northern part of the Dezful Embayment. The role of major and minor detachment horizons and deep-rooted faults on structural style is also a matter of investigations. To achieve these goals, geological surface information and the available well and 2D and 3D seismic data were used to construct a balanced structural cross-section. The area is subdivided into NE and SW sectors based on dissimilar physiographic features of the surface and structural and stratigraphic characteristics. In the both sectors, the Miocene Gachsaran Formation acted as the upper detachment horizon. In the NE sector, the role of the Gachsaran Formation as major detachment horizon in decoupled folding styles of overlying and underlying units is prominent. The Gachsaran Formation becomes less effective as a detachment horizon towards the SW as its thickness decreases and its facies change. The Triassic Dashtak Formation is most probably a major detachment horizon in the study area and evidence of another deeper detachment horizon (such as the pre-Cambrian-Cambrian Hormuz Series) is not apparent based on available data. The Lower Cretaceous Garau, Upper Cretaceous Gurpi and Paleocene-Eocene Pabdeh formations and the Oligocene Kalhur Member are subordinate detachment horizons. The role of major faults in the area, such as the Mountain Front Fault in driving thick-skinned deformation is taken into account along with the dominant thin-skinned deformation in the study area. The Kuh-e Asmari Anticline is the only emergent anticline exposing the Paleocene strata due to the activity of the deep-rooted Lahbari Thrust. This study reveals the commanding role of the upper detachment Gachsaran Formation and the overlying syn-deformation fluvial clastics of the Aghajari (Miocene) and Bakhtyari (Pliocene) formations on disharmonic folding styles.

Estimating source rock parameters using wireline data: An example from Dezful Embayment, South West of Iran

Availability and high potential of wireline data to correlate with geochemical properties convinced petroleum geologists to use them for source rock detection and calculating their richness. In this research, intelligent techniques and mathematical relationships were used to evaluate source rock potential and organic matter type indirectly. Artificial neural networks (ANN) and ΔLogR techniques were successfully used to model the relation between wireline logs and Total Organic Carbon (TOC) content. Furthermore, wireline data and TOC values were used as input data to model a second ANN for S2 parameter (present hydrocarbon potential) calculation. Owing to its great ability in the course of solving non-linear problems with overwhelming complexity, the back propagation method was used to train the networks using 70 points datasets. Predicted TOC contents were validated by Rock-Eval pyrolysis results of which revealed dependency of the ΔLogR accuracy to the organic richness and lithology, and therefore higher precision of the ANN outputs in compare to the ΔLogR results.Hydrogen Index (HI) and kerogen type were also effectively predicted using mathematical relationship between TOC and S2 factors. Reliability of all steps of the methodology was approved using a 16 members retest dataset for which testing predicted parameters against measured data demonstrated good correlation coefficients combined with negligible errors. Finally, applicability of the methodology was checked by applying it on two wells in the Dezful Embayment to evaluate geochemical and depositional properties of the Paleocene-Early Oligocene Pabdeh Formation.

Estimation of thermal maturity from well logs and seismic data in the Mansuri oilfield, SW Iran

Thermal maturity is the primary geological factor in exploration of hydrocarbon resources. Maturity index which is calculated from well-logging information and it is a useful parameter to unravel the burial history and hydrocarbon generation phases of a source rock. This study proposes a new method for estimating maturity index from well logs and seismic data using neural network and ant colony optimization (ACO) approach. The 2D seismic data and petrophysical logs of the Pabdeh Formation from three wells of the Mansuri field are employed to examine the methodology of this study. In the first step, maturity index (MI) was calculated from well logs including neutron, resistivity, sonic and density. The calculated values were used as inputs in a multi-attribute analysis to exploit logical relationships between them and seismic attributes. Seismic inversion was performed and the resulting acoustic impedance was utilized as an external attribute in maturity index estimation. A probabilistic neural network (PNN) was trained by using a set of predictor attributes derived from a multiple regression analysis. Finally, the nonlinear Ant Colony Optimization technique was utilized as an intelligent tool to generate a seismic section of maturity index. Using the Matlab programming environment for math computations and its graphical visualizations the nonlinear ACO section of the maturity index was obtained. The results show that the intelligently derived equation based on the nonlinear ant colony algorithm provides fast and more accurate solutions. The stochastic optimization outperforms the gradient optimization in maturity index estimation from well logs and seismic attributes. The calculated MI values range from 3 to 5 indicating the early stage of the oil window. The simulated MI shows a good agreement with the thermal maturity derived from Rock-Eval pyrolysis.

Hydrocarbon reserves of Gachsaran oilfield, SW Iran: Geochemical characteristics and origin

Abstract Biomarkers and carbon isotope data were used to depict geochemical properties and to delineate source of the crude oils from Asmari and Bangestan reservoirs of the giant Gachsaran oilfield, SW Iran. Despite the distinct horizons of the reservoirs and severe petrophysical heterogeneity inside each reservoir, all oil samples show an identical level of thermal maturity. Furthermore, similar source-related parameters reflect identical source rock for both reservoirs. They indicate carbonate-marl source deposited in a marine environment under anoxic-suboxic conditions. Strong marine organic matter signatures of predominantly algal origin along with evidence of a terrigenous angiosperm plant contribution were detected. Geochemical evidence suggests that the Gachsaran field Asmari and Bangestan oils being sourced from a mix of organic-rich Kazhdumi and Pabdeh source rocks of Albian and Middle Eocene-Early Oligocene ages, respectively. Carbon isotope composition and V/Ni ratio signatures indicate Kazhdumi Formation as the main source rock. Meanwhile, significant presence of oleanane and less than unity values of C 29 /C 30 hopanes ratio demonstrate a partial contribution of Pabdeh Formation. This contradiction could be explained by two scenarios; 1) incorporating very immature non-expelled Pabdeh oils into the mature Kazhdumi oils during migration or 2) partial charge form low maturity Pabdeh oils that is insufficient to impact a typical mixed signature over the geochemical fingerprint of the reservoired oils. Additionally, geochemical similarities give rise to an assumption of reservoir and trap inter-connection for this giant field.

Palaeogeographical peculiarities of the Pabdeh Formation (Paleogene) in Iran: New evidence of global diversity-determined geological heritage

Unique palaeogeographical peculiarities of sedimentary formations are important for geological heritage conservation and use for the purposes of tourism. The heritage value of the Pabdeh Formation (Paleocene–Oligocene) of the Zagros Fold-Thrust Belt in Iran has been investigated. The uniqueness of its palaeogeographical peculiarities has been assessed on the basis of the literature, field studies of three representative sections in the Fars Province (Kavar, Zanjiran, and Shahneshin sections), and comparison with the similar features known in Iran and globally. The Pabdeh Formation reflects the process of mixed siliciclastic-carbonate ramp progradation and the onset of a typical carbonate platform. The other unique features include representation of mesopelagic palaeohabitat, specific trace fossil assemblages, prehistoric bituminous artefacts (production of which was linked to the Pabdeh deposits), etc. It is established that the palaeogeographical type of geological heritage of the Pabdeh Formation is represented by all known subtypes, namely facies, palaeoecosystem, ichnological, taphonomical, event, and geoarchaeological subtypes. Their rank varies between regional and global. The very fact of co-occurrence of these subtypes determines the global importance of the entire palaeogeographical type in the case of this formation. The establishment of geopark in the Zagros Fold-Thrust Belt will facilitate adequate use of the Pabdeh Formation for the purpose of geotourism development. The aesthetic properties (rocks of different colour and striped patterns of outcrops) increase the attractiveness of this geological body to visitors.

Biostratigraphy of Oligocene and Lower Miocene deposits, Anneh Anticline, Folded Zagros, SW of Iran

One stratigraphic section was selected to study the biostratigraphy of the Oligocene and Lower Miocene deposits in Folded Zagros. The sediments include Asmari Formation (345 m) and the upper parts of Pabdeh Formation (180 m). Lithostratigraphy studies show that the Pabdeh Formation is composed of marls and medium-bedded argillaceous limestone alternation. The Asmari Formation is generally composed of medium- to thick-bedded limestone. Biostratigraphy studies for Pabdeh Formation indicate the four genera and six species of planktonic foraminifers. Based on assessment of foraminifera, one assemblage zone has been proposed for the Pabdeh Formation. The Asmari Formation biostratigraphy studies led to identify 27 genera and 35 species of benthic foraminifers. Based on the distribution of foraminifera, three assemblage zones and one indeterminate zone for Asmari Formation are suggested. Micropaleontology studies are offered Early Oligocene for Upper Pabdeh Formation and Late Oligocene to Early Miocene age for Asmari Formation.

Potential Evaluation and Basin Modeling of the Pabdeh Formation in Zagros Basin: A Case Study

Pabdeh Formation is one of the most important source rocks in Zagros basin. In this study, thermal modeling and comparing of hydrocarbon potential evaluation of Pabdeh Formation in Mish Anticline and Gachsaran oil field have been investigated. For this reason, Rock-Eval pyrolysis was carried out on 21 cuttings samples collected from 2 boreholes (Well No. 55 and 83) of Gachsaran oil field and outcrop of Mish anticline. Accordingly, the Kerogen types of Pabdeh Formation in Gachsaran oil field are II, but in Mish anticline are type II and III. The amount of inert organic carbon determined for the Pabdeh Formation in Mish anticline is about 4.879 wt%, while for Gachsaran oil field, it is estimated at 0.153 (Well. No. 55) and 1.156 (Well. No. 83) wt%. Absorption of hydrocarbon by rock matrix was also determined. The amount of absorption in Mish anticline is more than that of Gachsaran oil field. This is mostly due to the presence of argillaceous matrix in this area, but the clays have not been successful in absorbing organic matter; this is due to the result obtained from small amount of organic matter in the basin. The Rock-Eval data revealed that the sedimentary paleo-environment strongly affected the source potential of this formation as it changed from the continental and Deltaic in the Mish anticline to deeper marine in Gachsaran oil field. In addition, curves of Burial history were drawn for Gachsaran well No. 55, in order to assess the thermal maturity of the Pabdeh formation. The results of the methods indicated that Pabdeh formation in Gachsaran oil field had a good to very good hydrocarbon potential and had entered to oil window.

Microbiostratigrapy of the Paleocene-Lower Eocene Sequences in the Bibi Hakimeh 2 Subsurface Section Located in the SW of Iran

This paper investigates the biostratigraphy of the Palaeocene-Lower Eocene sequences in the Bibi Hakimeh 2 subsurface/subterranean sections located in the Bibi Hakimeh Oil Field. The Palaeocene-Lower Eocene sequences are induced as part of the Pabdeh Formation. They are 49 m in thickness and are made up of clayey limestone with chert intercalations. Biostratigraphic investigations identified 10 genera and 51 species of Planktonic Foraminifera which with respect to the specific planktonic species and according to the newest Wade Biozonation led to the determination of 9 biozones and 4 subzones. The Palaeocene-Early Eocene biostratigraphic boundary determined previously in accordance with the Wynd Biozonation was reviewed with respect to the new biozonation. Moreover, the impression of the PETM on the Planktonic Foraminifera found in the Bibi Hakimeh subsurface section, has been occurred at P/E boundary on global scale was studied. Based on this research we can conclude the P/E biostratigraphic boundary border is occurred ranges between 2125 - 2124 meters in Pabdeh formation.

Evaluation of Hydrocarbon Potential in the Jahrom Area, Interior Fars, Zagros

The study area is located in the Fars area (Interior Fars sub-basin). This area, which is part of the Zagros fold-thrust belt, is located in Zagros simple folded sub zone. It is known as one of the most important regions in the world Gas rich. In this area, anticlinal folds are a different orientation of such as the North Western-South Eastern, East-West and North Eastern-South Western. The Karbasi and Khaftar anticlines are case study anticlines in the interior Fars sub-basin (Fassa area). The anticlines in the Fars region, which are located in the Zagros fold-thrust belt, are valuable because they possess several hydrocarbons. The main aim of this paper is evaluation of hydrocarbon potential in the Jahrom area (Interior Fars) based on interpretation of the Isopach maps and well data. This paper presents part of the results of a regional study of the Coastal Fars area in the Zagros Simply folded belt, based on original fieldwork, satellite images, structural sections, geological maps and well data. In order to investigate of periods Nezamabad fault activity, Isopach maps of the study area has been prepared based on well drilling data and the thickness of the drilled formations. In this study utilizes the thickness of the drilled formations in the study area, for each sedimentary unit was carried out to prepare Isopach maps. The Isopach map prepared based on GIS software method and exploration well data. The Nezamabad fault has been lacked of activity at the deposition time of the Dalan, Kangan, Dashtak, Fahliyan, Gadvan, Dariyan, Kazhdomi, Sarvak, Gurpi and Pabdeh formations within the Khaftar and Karbasi anticline area. Accordingly, changes in basin floor, at the time of sedimentation these formations has not been affected by the Nezamabad fault. Probably the Nezamabad fault has been activated during deposition of the Surmeh, Hith, Laffan and Ilam formations and in this area paleo-basin has been controlled by this fault. In other words, it seems that, activity of the Nezamabad fault in this area have been limited to Jurassic and Cretaceous periods (Coniacian and Senomanian). This can means that in this periods time, the Nezamabad fault have been active sedimentation along with tectonic processes and activities affected on thickness of the Surmeh, Hith, Laffan and Ilam formations. Finally, it seems that the Nezamabad Fault activity has been affected on the source rock, reservoir rock and cap rock and then controlled distributing of hydrocarbon System of the study area in the Khaftar and Karbasi as anticlinal oil traps.

Petroleum source-rock potential of the Piranj oil field, Zagros basin

Zagros basin constitutes one of the most prolific hydrocarbon producing habitats and the second largest basin in the Middle East. The Piranj oil field is part of The Middle Cretaceous–Early Miocene Petroleum System in Zagros basin and southwest of Iran. This study mainly focuses on organic matter characterization and thermal history of two potential source rock's name Gurpi and Pabdeh formations. To evaluate the candidate source rocks, 50 cuttings and core samples of these rock units from well M-11 (the only well drilled up to the probable source rocks) were analysed, using Rock-Eval pyrolysis and organic petrography. In addition, 1D basin modelling and reconstruction of burial history were applied to analyse the thermal history of these source rocks. The green shale, limestone and marls of Pabdeh formation with average 2.52%wt Total Organic Matter (TOC) and Hydrogen Index (HI) higher than 250 is more favourite source rock in comparison with dark shale and limestone of Gurpi formation by 1.8%wt and HI < 300. Moreover, Pabdeh formation can be classified generally as fair to very good source rocks, with kerogens of type II, while Gurpi formation contain mostly kerogens of type II/III. The average values of Vitrinite reflectance (VR) (from 0.44% to 1.23%) indicate that samples from the well M-11 have reached maturities corresponding to early to peak oil generation. Reconstruction of the thermal history suggests various steady heat flow values (53–91 mW/m2) resulted in the best fit between the observed and the calculated bottom hole temperatures (BHT) and Vitrinite reflectance (VR) in the model. Rock-Eval pyrolysis results and Vitrinite reflectance (VR) suggest that the most of samples are in the early mature to mature stage of hydrocarbon generation. Furthermore, according to the modelling results, petroleum generation from the studied source rocks has began after deposition of related seal-rocks and formation of traps which ensures entrapment and preservation of migrated hydrocarbon.

Paleocene-Oligocene dinoflagellate cysts from the Siah Anticline, Zagros Basin, Southwest Iran

A section of the Pabdeh Formation dating back to the Paleocene-Oligocene has been sampled in the Zagros Basin in Southwest Iran for palynological investigations and evaluation of thermal maturity and hydrocarbon generation potential. In total, 125 rock samples were collected and processed palynologically. The samples yielded rich assemblages of dinoflagellate cysts, and 65 cyst species were identified. Some index species allowed us age dating and establishment of seven dinoflagellate cyst zones in accordance with the existing European zonation. The dinoflagellate cyst zones allowed precise age assignment of the formation under study to late Paleocene to early Oligocene. For thermal maturity evaluation, spore and pollen grain color were correlated against the standard color chart prepared by the Shell Oil Company. The properties of the samples, according to palynomorph color changes, suggest that this formation is potentially oil prone and may have produced oil.

Correlation of source rocks and crude oils in Kupal and its near oil fields, SW of Iran

ABSTRACTThe Kupal oil field is located in the north of Dezful Embayment in southwest of Iran. The purposes of this study were correlations between the Sarvak and Asmari reservoirs oils in the Kupal oil field and determining the source of oil in this field. In order to achieve these objectives, different geochemical methods, including Rock Eval, gas chromatography, gas chromatography-mass spectrometry, and carbon isotope analyses of asphalthene in oils and source rocks, were used. The results of pyrolyzed possible source rocks of the Kupal and its near fields by the Rock Eval apparatus indicated good source rock potential for the Kazhdumi and Pabdeh formations. In addition, Kazhdumi formation in the Haft-Kel oil field indicated gas production potential while the samples of the Gurpi formation were in a non-source rock zone. The Asmari and Bangestan reservoir oils had the same components and geochemical characteristics, except the Sarvak (Bangestan) reservoir oil in the Kupal field contained Oleanane biomarkers, whereas Asmari reservoir oil had no Oleanane biomarker. This fact was attributed to the fault in the southwestern part of the Kupal oil field, which moved the Pabdeh formation (in which its oil contains Oleanane biomarkers) to more depths and near the Sarvak formation. This movement caused the maturation of Pabdeh formation and migration of the produced oil to the Sarvak reservoir.

Geochemical evaluation and thermal modeling of the Eocene–Oligocene Pabdeh and Middle Cretaceous Gurpi Formations in the northern part of the Dezful Embayment

Rock–Eval pyrolysis analysis, burial history, and 1D thermal maturity modeling have allowed the evaluation of the source rock potential, thermal maturation state, and impacts of the Pabdeh and Gurpi Formations in Cretaceous–Miocene petroleum system in the Naft Safid (NS) and Zeloi (ZE) oilfields, North Dezful Embayment. The total organic carbon (TOC) content of the Pabdeh and Gurpi Formations ranges from 0.2 to 4.7 wt% and 0.3 to 5.3 wt%, respectively. S2 values of the Pabdeh Formation in the ZE and NS oilfields vary from 0.41 to 13.77 and 0.29 to 14.5 mg HC (Hydrocarbon)/g rock, with an average value of 4.48 and 4.14 mg HC/g rock, respectively. These values for the Gurpi Formation in the ZE and NS oilfields range from 0.31 to 16.96 and 0.26 to 1.44 mg HC/g rock, with an average value of 8.54 and 2.43 mg HC/g rock, respectively. The S2 versus TOC diagram reveals a fair to good hydrocarbon generation potential of the Pabdeh Formation and poor to fair potential of the Gurpi Formation. The high values of S2 (S2 > S1) for samples of the both formations in the ZE and NS oilfields show that the samples are not contaminated with petroleum generated from underlying source rocks. The samples of the Pabdeh Formation in the ZE oilfield are characterized by a relatively narrow range of activation energy values with principal activation energy of 46 kcal/mol and frequency factor of 5.27 × 10+11 s−1. It seems that the high sulfur content of the Pabdeh organic matter probably caused the frequency factor and principal activation energy to be lower than usual. Hydrogen index (HI) values of the Pabdeh and Gurpi Formations in the ZE oilfield vary from 71 to 786 and 97 to 398 mg HC/g TOC, with an average value of 310 and 277 mg HC/g TOC, respectively. These values in the NS oilfield range from 66 to 546 and 51 to 525 mg HC/g TOC, with an average value of 256 and 227 mg HC/g TOC, respectively. Plot of HI vs. Tmax value indicates that the majority of the Pabdeh and Gurpi samples contain predominantly type II kerogen and their organofacies are directly related to the more homogeneous precursor materials. Based on thermal maturity modeling results, kinetic parameters, and Rock–Eval analysis, both formations in the ZE and NS oilfields are thermally mature and immature or early mature stage, respectively.