Pabdeh Formation Research Articles

TOC Determination in Source Rocks Using GR Spectrometry and Neuro-Fuzzy Techniques in a Zagros Basin Oilfield

Due to the high content of gamma ray in hydrocarbon source rocks, it may be detected by gamma ray or computed gamma ray peaks. In this article, the total organic carbon content of (TOC) of Pabdeh and Gurpi formations was calculated using a ΔlogR technique with three methods including cross-plots of resistivity–sonic, resistivity–density, and resistivity–neutron. This approach was applied for Pabdeh and Gurpi formations in wells A and B in an oil field in Zagros basin of Iran. The results were calibrated with core-derived data. The amount of TOC was compared with spectrometry of uranium, thorium, and potassium. All data were predicted by a neuro-fuzzy technique in these wells.

The distribution of calcareous nannofossils in the late Santonian–Late Maastrichtian deposits in the southwest of Iran (Khuzestan Province)

The first data on the distribution of calcareous nannofossils in the Behbehan section, the Kuh-e-Rish, are considered. According to the distribution of nannofossils, the Upper Cretaceous deposits of the section are subdivided into nine biostratigraphic zones. CC17 (Calculites obscurus zone) indicate the Late Santonian. Biozones CC18 (Aspidolithus parcus zone), CC19 (Calculites ovalis zone), CC20 (Ceratolithoides aculeus zone), CC21 (Quadrum sissinghii zone), and CC22 (Quadrum trifidum zone) represent the Campanian. Biozone CC23 (Tranolithus phacelosus zone) indicate the Late Campanian–Early Maastrichtian. Biozones CC24 (Reinhardtites levis zone) and CC25 (Arkhangelskiella cymbiformis zone) suggest the Middle and Late Maastrichtian, respectively. In the late Late Maastrichtian, due to decreasing in water depth at the study area, Nephrolithus frequens zone (CC26) defined in Tethysian domain was not recognized. The boundary between Gurpi–Pabdeh Formations represented a non-depositional period from the late Late Maastrichtian to the end of Early Paleocene. Also, it seems that predominant conditions of the sedimentary environment of Neotethys basin with the presence of index species calcareous nannofossils specified, which itself indicates that the warm climate and high depth of the basin in Late Santonian to Late Maastrichtian, in low latitudes has been prevalent.

Comparing the Potential of Hydrocarbon Generation of Kazhdomi and Pabdeh Formations in Bangestan Anticline (Zagros Basin) According To Rock-Eval Pyrolysis Data

In this study, the Hydrocarbon generation Potential of Kazhdomi and Pabdeh formation in Bangestan Anticline has been studied. In this regard, 10 samples were collected from Pabdeh formation, and 6 samples were collected from Kazhdomi formation that eventually was analyzed by Rock-Eval 6 system. In this system, a temperature raising program in oxygen-free environment was used. This device introduces a series of valuable factors related to Source rock, including: available free hydrocarbon in sample (Peak S1), hydrocarbons emanated From thermal cracking of Kerogen (Peak S2), heat index of organic matter (Tmax), Total Organic Carbon (TOC), Hydrogen Index (HI), Oxygen Index (OI), and Production Index (PI). Applying these factors, there factors of evaluating source rock could be identified, which included amount, type and thermal maturity of organic material. Kerogen of Kazhdomi Formation was type II, and Kerogen of Pabdeh Formation was defined type II and III. Studied showed that Kazhdomi Formation compared with Pabdeh Formation had more oil-generation potential. Sedimentary Facies of Pabdeh Formation was defined C, CD, D and sedimentary Facies of Kazhdomi formation was defined AB, B, BC, and C. The amount of inter organic carbon of Pabdeh formation was estimated 0.9769 weight percent (WP), and this amount for Pabdeh formation was about 0.3957 weight percent (WP). Determination of hydrocarbon absorption by Rock matrix showed that absorption rate in samples of Kazhdomi formation was much more than samples of Pabdeh Formation, which indicates that Rock matrix in Kazhdomi formation involves much more clay mineral compared with Pabdeh formation.

Organic geochemistry and petrography of Kazhdumi (Albian–Cenomanian) and Pabdeh (Paleogene) potential source rocks in southern part of the Dezful Embayment, Iran

There are several source rock units in the Zagros Basin, but the Cretaceous Kazhdumi and Paleogene Pabdeh formations probably have produced the majority of the commercial hydrocarbons in this area. Among the hydrocarbon provinces of Iran, the Dezful Embayment, which is located southwest of Zagros Mountains, is one of the most prolific regions in the Middle East. Numerous studies have been made in the northern part of the Dezful Embayment, but relatively few have been done in its southern part. The present study focuses on organic matter characterization of two potential source rocks (Kazhdumi and Pabdeh formations) in southern part of the Dezful Embayment. Cuttings samples (114) were collected from 10 wells and evaluated using Rock–Eval pyrolysis and organic petrography in order to characterize the content and type of organic matter and thermal maturity. The results showed that the average total organic carbon (TOC) content of Kazhdumi and Pabdeh formations are 2.48 and 1.62wt%, respectively. The highest TOC contents for both formations are found in the northern compartment and decreased gradually toward the south. Pyrolysis data reveal that organic matter has a fair to very good hydrocarbon generation potential and are classified as Type II–III and Type III. Rock–Eval Tmax and vitrinite reflectance show that the majority of samples are in the early mature to mature stage of the oil generation window.

Chemical Variation during Pabdeh Formation Deposition, Zagros Basin: Gurpi-Pabdeh-Asmari Boundaries determination and Paleoenvironmental Condition

Determination of the formation of the Pabdeh boundary is a main challenge in Zagros sedimentary basin area. The work on hand is an attempt to clarify those based on chemical changes. The location under observation is the outcrop of the Pabdeh Formation (Paleocene-Oligocene) in Bangestan Anticline, the southern part of Zagros orogenic belt. The Pabdeh Formation stratigraphy linked to Asmari and Gurpi has been introduced as a gradual type and somewhat vague in this respect. To overcome these problems, 12 fresh samples from Gurpi, Pabdeh, and Asmari have been selected and chemically analyzed. Variation on both major and trace elements during this stratigraphy sequence generally reveal the high peaks of their frequencies in the lower and upper borders of the Pabdeh Formation. This border is different to the border which was determined during normal studies. These variations illustrate that the stratigraphy age reduction in the boundary of expected deposition time is based on present data documented that the Cretaceous-Tertiary boundary (K-T) had started lower than the stratigraphy limit. Geochemical ratios, including Ni/Co, V/Cr, and V/(V+Ni) were used to diagnose the Paleo-environmental conditions of Pabdeh Formation in comparison to Gurpi and Asmari formations. These chemical indicators present variable paleoredox conditions for the Pabdeh Formation.

Depositional environments and trace fossil assemblages in the Pabdeh Formation (Paleogene), Zagros Basin, Iran

Depositional environments and trace fossil assemblages in the Pabdeh Formation (Paleogene), Zagros Basin, Iran

Estimating Total Organic Carbon Content and Source Rock Evaluation, Applying ΔlogR and Neural Network Methods: Ahwaz and Marun Oilfields, SW of Iran

Well logging is a useful method for sedimentary basin and source rock evaluation. Source rocks have special responses in porosity and resistivity logs that can make them distinguishable from surrounding rocks. Therefore, well logging data and diagrams can be used as indicators of determination of source rock potential. Characterizations of Kazhdomi, Pabdeh, and Gurpi source rocks have been determined by geochemical analysis in some Iranian oilfields, but no total organic carbon (TOC) zonation and interpretation have been carried out in these formations yet. Several studies have confirmed the petroleum potential of the Kazhdomi formation in Dezful Embayment, but Pabdeh formation (more significant) and Gurpi (less significant) have been always the topics of Iranian petroleum geologist discussions in order to deermine whether these formations have the potential of generating oil and what the organic matter properties of these formations are. The purpose of this article is to calculate TOC values of the Pabdeh formation in Ahwaz and Marun oilfields using a combination of sonic and resistivity logs (ΔlogR method) and a neural network method. Then these TOC values were compared with TOC from geochemical analysis. Finally, the zonations of source rock in terms of TOC richness were carried out and TOC changes in the oilfields were shown by plotting Iso-TOC maps. It was found that due to the high local temperature gradient Pabdeh reaches an oil window level in some parts of Ahwaz and Marun oilfields. Hence, Pabdeh acts as a source rock for these two oilfields in some sections.

Modeling and Optimizing Rate of Penetration Using Intelligent Systems in an Iranian Southern Oil Field (Ahwaz Oil Field)

For drilling optimization, an equation for the rate of penetration (ROP) is necessary. The rate of penetration depends on many factors such as formation properties, mud properties, weight on the bit, rotary speed, mud hydraulics, and size/type of bit. Due to the difficulty of mathematical modeling of ROP, researchers have used experimental results or field data to develop a correlation for ROP. In this study, a new model based on artificial neural networks (ANNs) is designed that is able to predict the ROP using real field data gathered in an Iranian oilfield (Ahwaz oilfield). The new model was successful in predicting ROP. To obtain operating parameters that lead to maximum ROP, the corresponding mathematical equation of an ANN model was implemented in a procedure using a genetic algorithm, which is one of the most reliable methods of optimization, and at different depths the parameters leading to maximum ROP were obtained. This model and its results can be used in Pabdeh and Gurpi formations in all Iranian oilfields and similar shaly formations in the Middle East such as the Iraq, Jaddia, and Aaliji formations corresponding to the Pabdeh formation and the Shiranish formation corresponding to Gurpi.

High Resolution Sequence Stratigraphy and Depositional Environment of Pabdeh Formation in Dashte – Arjan Area (Shiraz, Fars, Zagros, Iran)

Pabdeh shaly formation (Paleocene-Oligomiocene) has been expanded in Fars, Khozestan and Lorestan. The lower lithostratigraphic limit of this formation in Shiraz area is distinguished from Gurpi formation by purple shale. Its upper limit is gradational and conformable with Asmari formation. In order to study sequence stratigraphy and microfacies of Pabdeh formation in Shiraz area, one stratigraphic section have been chosen (Zanjiran section). Petrographic studies resulted in the identification of 9 pelagic and calciturbidite microfacies. The calciturbidite microfacies have been formed when the sea level was high, the rate of carbonate deposition was high and it slumped into the deep marine. Sequence stratigraphy studies show that Pabdeh formation in the studied zone consists of two depositional sequences (DS) that the lower contact is erosional (purple shale - type one, SBI or type two, SB2) and the upper contact is correlative conformity (type two, SB2).

Biostratigraphy of the Danian/Selandian transition: A case study from Kamestan anticline section, northwest of Izeh city in Khuzestan province, Southern Iran

AbstractThe planktonic foraminifera turnover across the Danian-Selandian boundary (early to late Paleocene, ~60 Ma) has been studied in the Kamestan anticline section. The studied interval span planktonic foraminifera zones P2-P3. In this section Danian-Selandian boundary is located in Pabedeh – Gurpi Formations transition. Here, the boundary of Pabeh and Gurpi Formations is a transitional one and identified by with color change of from grey shale to purple shale of Gurpi Formation to Pabdeh Formation .

Regional stratigraphic architecture and reservoir types of the Oligo-Miocene deposits in the Dezful Embayment (Asmari and Pabdeh Formations) SW Iran

Abstract A regional sequence stratigraphic model is proposed for the Oligo-Miocene Asmari and Pabdeh Formations in the Dezful Embayment of SW Iran. The model is based on both new detailed sedimentological observations in outcrops, core and well logs, and an improved high-resolution chronostratigraphic framework constrained by Sr isotope stratigraphy and biostratigraphy. A better understanding of the stratigraphic architecture distinguishes four, geographically separated types of Asmari reservoirs. Three Oligocene sequences (of Rupelian, early Chattian and late Chattian age) and three Miocene sequences (of early Aquitanian, late Aquitanian and early Burdigalian age) have been distinguished, representing a period of 15.4 Ma. The stratigraphic architecture of these sequences is primarily controlled by glacio-eustatic sea-level fluctuations, which determined the distribution of carbonates, sandstones and anhydrites in this sedimentary system. Tectonic control became important in the Burdigalian with a regional tilt down towards the NE. The lithological heterogeneity, the complex geometries, and both early and late diagenetic alterations are the basis for a classification of four main stratigraphic reference types for the Asmari Reservoirs: Type 1, sandstone dominated; Type 2, mixed carbonate-siliciclastic; Type 3, mixed carbonate-anhydrite; and Type 4, carbonate dominated. The sequence stratigraphic model predicts how and when these types change laterally from one to another.

Microfacies and Sedimentary Environments of Gurpi and Pabdeh Formations in Southwest of Iran

Problem statement: The Upper Cretaceous Gurpi and lower Tertiary Pabdeh formations as units of folded Zagros Zone were studied in three different regions (Tang-e-Abolhiat, Tang-e-Zanjiran and Maharloo) in Fars Province, Iran. Approach: Gurpi formation consisted of thin to medium sized layers of gray marl and marlstone interbedded with thin layers of argillaceous limestone and shale. The dominant microfacies in this formation biomicrite; Index species of Globotruncana give the age of the Formation from lower companion to upper Maastrichtian. Pabdeh formation consisted of bluish gray, thin to medium sized layers of shale and marl and interlayers of argillaceous limestones with purple shales and thin cherty beds at lower part, dark gray shales and marls with interlayers of argillaceous limestones in the middle andalternative layers of thinly bedded argillaceous limestone, shale and marl at the upper part. The dominant microfacies are biomicrite. Index species of Globorotalia and Hantkenina give the age of formation from upper Paleocene to Eocene. Results: The sedimentary environment of both formations is a bathymetrical carbonate floored basin (deep shelf or basin margin) which had deposited its facies in transgressive stage. The contact between the two formations is of disconformity type. In Tang-e-Abolhiat it lies at the base of purple shale. In this region and also in Tang-e-Zanjiran and Maharloo, in addition to recognition of Globorotalia velascoensis, which was attributed to lower part of the Pabdeh formation, a glauconitic-phosphatic bed separates the two formations. Conclusion/Recommendations: The boundary between Gurpi and Pabdeh formations represented a non-depositional period from the late Maastrichtian to the end of early Paleocene.

Comparison of Asmari, Pabdeh and Gurpi formation's fractures, derived from image log

Small scale fractures around the wellbore, strongly affect the hydrocarbon production. Identification of fracture plays a main role in production and development plans of oil fields. Image logs are one of the powerful tools in fracture study in wells. Image log is a high resolution “pseudo picture” of borehole wall. Using these logs help to identify the exact orientation, depth and type of natural fractures. In this study, image logs of a well in a naturally fractured reservoir were interpreted in order to extract fractures. Statistically analysis has been done to identify the fracturing pattern. Present study shows that pattern of fracturing in Asmari and Pabdeh is similar but, the Gurpi formation is completely different. Fractures density in thin bedded intervals is high hence the maximum fractures density observed is in the upper Asmari and Pabdeh formations. Fracture density log shows two descending trends that are related to mechanism of folding.

Dinoflagellate and foraminiferal biostratigraphy of the Gurpi Formation (upper Santonian–upper Maastrichtian), Zagros Mountains, Iran

A rich dinoflagellate cyst assemblage has been recovered from an outcrop of the Gurpi Formation, the hydrocarbon source rock in the South Iranian Basin. Key dinoflagellates recorded in the section studied provide a means of correlation with zonation schemes for Australasia and north-west Europe. These include Eucladinium kaikourense, Nelsoniella aceras, Odontochitina spp., Cannosphaeropsis utinensis, Palaeocystodinium denticulatum and Dinogymnium spp. The assemblage points to a late Santonian–late Maastrichtian age for the Gurpi Formation. Dinoflagellate and planktonic foraminiferal evidence indicates the presence of a hiatus spanning the uppermost Maastrichtian to at least the lowermost Danian at the base of a glaucony-rich layer separating the Gurpi Formation from the overlying Pabdeh Formation. Palynofacies and lithofacies profiles suggest that the sediments were deposited in an open, relatively deep marine outer ramp environment belonging to ramp facies 8 and 9.

THE INFLUENCE OF TECTONICS ON THE ENTRAPMENT OF OIL IN THE DEZFUL EMBAYMENT, ZAGROS FOLDBELT, IRAN

The timing of the orogenic events associated with the closure of South Tethys significantly influenced the generation, migration and entrapment of petroleum in the Zagros Foldbelt of Iran. This influence was particularly important in the Dezful Embayment, which is one of the world's richest oil provinces, containing some 8% of global oil reserves in an area of only 60,000 sq. km. In the Dezful Embayment, oil and associated gas occur in two carbonate reservoirs - the Sarvak Formation of Cenomanian to Turonian age, and the Oligocene - Early Miocene Asmari Formation, sealed by the evaporites of the Gachsaran Formation. The oil and associated gas are trapped in large “whaleback” anticlines which formed during the Neogene Zagros orogeny. Two excellent source rocks, the Albian Kazhdumi Formation and the upper part of the Pabdeh Formation (Middle Eocene to Early Oligocene), supplied the Asmari and Sarvak reservoirs and with them form the Middle Cretaceous to Early Miocene Petroleum System. This system was found to be independent of older petroleum systems. Two particular problems are addressed in this paper. The first is the relative timing of trap formation versus oil expulsion from the source rocks. If oil expulsion occurred prior to Zagros folding, the oil would have migrated along gently dipping ramps towards the Persian (Arabian) Gulf and Southern Iraq, and would have been trapped a long way from the source kitchen. By contrast, if oil expulsion took place when the whaleback anticlines already existed or had at least begun to develop, the oil generated would have moved almost vertically towards the nearest anticline. Secondly, we assess the type of heatflow to be used for modelling. This could be either variable or constant, depending on the stability or instability of the Arabian Platform and on subsidence variations during source rock maturation. Our conclusions can be summarized as follows. First, the paroxysmal phase of Zagros folding commenced in the Dezful Embayment towards the end of the Middle Miocene around 10 Ma ago and continued throughout the Late Miocene and Pliocene. Second, bearing in mind the remarkable stability of the Arabian Platform for some 260 Ma, during which there was almost continuous gentle subsidence between the Permian transgression and the Early Miocene, a constant heatflow was used for modelling. Burial profiles and maturity indices, such as vitrinite reflectance and Rock-Eval parameters, demonstrate that the Kazhdumi and Pabdeh source rocks reached the onset of oil expulsion during deposition of the Agha Jari Formation between 8 and 3Ma, depending upon the location. This chronology means that oil migrated from source rocks into preexisting Zagros structures. Therefore, oil migrated over short distances to nearby traps within well-defined drainage areas, the geometry of which can be deduced from seismic data. Moreover, the Zagros folding induced prominent fracturing which can be observed both at outcrop and in wells. This fracturing, which affects lime-stones as well as marls, enhanced subvertical migration of hydrocarbons towards the reservoirs. As a result of this short distance migration, oils can directly be linked to the source rocks which generated them by oil-oil and oil-source rock correlations based on stable isotope (σ13C, σ34S) and biomarker data. Modelling of each drainage area provides estimates of the amount of oil expelled by each source rock. Calculated estimates can then be compared to the actual oil-in-place of the corresponding field. An example of this modeling procedure is given in this paper.

Depositional environment and sequence stratigraphy of the Oligo-Miocene Asmari Formation in SW Iran

The Asmari Formation, a thick carbonate succession of the Oligo-Miocene in Zagros Mountains (southwest Iran), has been studied to determine its microfacies, paleoenvironments and sedimentary sequences. Detailed petrographic analysis of the deposits led to the recognition of 10 microfacies types. In addition, five major depositional environments were identified in the Asmari Formation. These include tidal flat, shelf lagoon, shoal, slope and basin environmental settings and are interpreted as a carbonate platform developed in an open shelf situation but without effective barriers separating the platform from the open ocean. The Asmari carbonate succession consists of four, thick shallowing-upward sequences (third-order cycles). No major hiatuses were recognized between these cycles. Therefore, the contacts are interpreted as SB2 sequence boundary types. The Pabdeh Formation, the deeper marine facies equivalent of the Asmari Limestone is interpreted to be deposited in an outer slope-basin environment. The microfacies of the Pabdeh Formation shows similarities to the Asmari Formation.

TEMPESTITE DEPOSITS ON A STORM‐INFLUENCED CARBONATE RAMP: AN EXAMPLE FROM THE PABDEH FORMATION (PALEOGENE), ZAGROS BASIN, SW IRAN

The Pabdeh Formation is part of a thick carbonate‐siliciclastic succession in the Zagros Basin of SW Iran which includes carbonate reservoirs of Cretaceous and Cenozoic ages. From field observations and petrographic and facies analysis of exposures in the type section of the Pabdeh Formation, four lithofacies were recognized. These are from oldest to youngest: (i) a mottled, bioturbated bioclastic wackestone/mudstone facies; (ii) a wackestone/packstone facies with horizontal burrows on bedding planes; (iii) a thin‐bedded bioclastic wackestone/mudstone facies alternating with thin bioclastic‐oolitic‐intraclastic intervals; and (iv) a bioclastic foraminiferal / algal / peloidal packstone facies. These observations indicate that facies evolved upwards from deep outer‐ramp deposits to inner‐ramp deposits within a shoal complex, suggesting progradation of the ramp depositional system.Storm events significantly influenced the ramp system. Storm‐generated surges transported sediments from nearshore to the deeper outer‐ramp environment where they were deposited as shell‐lags, composed mostly of bioclastic packstones, rich in pelagic microfauna with sharp, undulatory erosional basal contacts. The packstones rest on outer ramp mudstones deposited below storm base level. Sedimentary structures in the Pabdeh Formation are those typical of storm deposits, such as hummocky cross‐stratification, ripple cross‐lamination, ripple marks, escape burrows on the tops of the beds, couplets of fine‐ and coarse‐grained laminae and mixed fauna, as well as intraclasts derived from underlying facies. These distinctive sequences are interpreted to have been generated by waning storm‐generated currents. The dominance of fine‐grained sediments (medium to fine sand); the lack of large‐ scale hummocky cross‐stratification; the minor amounts of intraclasts derived from underlying facies; the paucity of amalgamated tempestite beds; and the finely‐laminated (mm to cm scale) couplets of coarse and fine lamina all suggest a distal tempestite facies. Palaeogeographic reconstruction of the Zagros Basin during the Eocene indicates that the study area was situated in tropical, storm‐dominated palaeolatitudes.

Biostratigraphy of the Baba Heydar section, Iran

A section of pelagic limestones and marls of the Pabdeh Formation, containing vertebrate remains was investigated for calcareous nannoplankton and planktic foraminifera. It is located in the Zagros Mountains near the town Baba Heydar, Iran. The microfossils of the marls are indicative for an eutrophication in the photic zone of the sea with the bloom of r-strategists of calcareous nannoplankton. Planktic foraminifera are abundant and compare with assemblages of Tanzania and the Caucasus. The benthic foraminifera are of Midway type assemblages at a deposition depth of upper bathyal. Biostratigraphically the sequence belongs to nannoplankton zone NP 24 or planktic foraminifera zone P 20, upper Rupelian.

ORGANIC GEOCHEMISTRY AND SOURCE ROCK CHARACTERISTICS OF THE ZAGROS PETROLEUM PROVINCE, SOUTHWEST IRAN

The Zagros of SW Iran and its continuation into N Iraq forms the tectonised NE margin of the Middle East basin. Sedimentation in the Zagros began in the late Precambrian and continued with comparatively few interruptions until the Pliocene, when strong earth movements affected the area and gave rise to the present day large. elongated NW‐SE trending structures. Some of the world's largest structurally‐controlled oil fields are located in the Zagros. The most productive pay zone is the Oligo‐Miocene Asmari Formation, although significant oil pools are present also in the Cenomanian‐Turonian Sarvak limestone and in the Neocomian‐Jurassic Khami Group carbonates. Recently, large gas deposits have been discovered in the Permo‐Triassic carbonates assigned to the Deh Ram Group. Geochemical studies were carried out five potential source beds of Eocene‐Palaeocene (Pabdeh Formation). Coniacian‐Neocomian (Garau Formation) and Silurian (Ghakum Formation) age. The results showed that the organic matter in these formations is almost exclusively of marine algal origin, and that the Kazhdumi is the major source of the hydrocarbons in the Asmari and Sarvak reservoirs. The origin of the hydrocarbons in the Khami and Deh Ram reservoirs is at present speculative.