Suez Rift Research Articles

Geomechanical modeling using the depth-of-damage approach to achieve successful underbalanced drilling in the Gulf of Suez rift basin

Typical oil and gas reservoirs producing in the Gulf of Suez are now extensively depleted in terms of recovery of conventional resources and display declining production levels and heterogeneous pore pressure regimes. To continue production on a commercially viable basis and enhance the recovery of remaining oil and gas from the mature reservoirs currently in production, drilling decision-makers can no longer rely on traditional balanced or overbalanced drilling methods. Hence, underbalanced drilling is an essential requirement for such reservoirs. However, inducing underbalanced conditions increases the risk of the borehole instability. In the studied area, three previous wellbore stability studies were performed associated with the Hilal-X platform wells using the breakout-width-failure concept. Nevertheless, several wellbore instability issues were recorded there due to that method determining a mud-weight window that was too conservative. New wellbore stability analysis has been performed using a depth-of-damage approach. This analysis has helped to deliver excellent results during underbalanced drilling, after many attempts in previously drilled wells in overbalanced conditions that resulted in borehole instability and/or formation damage. This study documents how successful underbalanced drilling has been achieved in this basin for the first time by mud weights being guided by depth-of-damage analysis, highlight the requirements of that method using a case study for a specific well. In-situ stresses and an 1D-geomechanical earth model were generated using well log data from offset wells. The modified Lade method was used as a failure criterion, while the depth-of-damage approach was used for wellbore stability analysis in Hilal-X4 well. The study reveals that: 1) the Hilal field reservoirs have variable pore pressure regimes, 2) the breakout-width-failure concept provides misleading results in the studied reservoir formation, 3) the depth-of-damage approach reflects reservoir conditions more effectively and allows for successful underbalanced drilling without any instability events, 4) a new casing design for the Hilal Field wells has led to enhanced production performance, and 5) underbalanced drilling, when downhole pressures are carefully managed, is a safe and reliable technique for the mature fields of the Gulf of Suez rift basin.

Multi-scale characterization of unconventional tight carbonate reservoir: Insights from October oil filed, Gulf of Suez rift basin, Egypt

The thick Eocene carbonate deposits that are newly ascribed as Radwany Formation (previously Thebes Formation) in the October basin within the Gulf of Suez region, are of particular interest for hydrocarbon exploitation. However, no efforts have been directed to investigate their petrophysical characteristics and pore system. This study aims to investigate the petrophysical characteristic, pore system and formation potentiality as a reservoir rock. Thirteen sidewall core samples and sixty thin sections from OCT-X well were studied in order to investigate the lithological characteristics, porosity network. In addition, well logging data and petrophysical and geochemical laboratories measurements including Nuclear Magnetic Resonance (NMR) porosity technique were used to define the petrophysical characteristics. The investigated work revealed that: 1) the pore system is a combination of depositional and diagenetic processes. 2) the dominant porosity types include fracture, inter-particle, intra-particle and moldic porosity; NMR indicates mesopores to macropores, 3) petrophysical evaluation and geochemical analysis indicates a self-sourced unconventional reservoir based on its organic richness characteristics unconventional resource opportunity as tight carbonate reservoir, 4) the basal part of the Radwany Formation has a high potential to store hydrocarbon, and it is a potential conventional resource. 6) The linking trends between the petrophysical parameters with sediment microfacies were defined in the studied section, where a significant increasing trend line has been inferred in the direction from wackestone microfacies to packstone microfacies. Finally, the diagenetic process through time has greatly controlled the petrophysical parameters of the Radwany Formation. The gap between Source and Reservoir rocks has been defined based on integrated geochemical and petrophysical characteristics. The studied section has unique multiscale characterization as unconventional and conventional resource.

Sequence stratigraphy of the Burdigalian Rudeis Formation in Ras El-Ush oil field, Gulf of Suez: Application of gamma-ray analysis and biostratigraphy

The Rudeis Formation represents one of the most important oil-producing reservoirs in the Gulf of Suez. This formation exhibits conspicuous lateral facies changes and therefore presents a complex exploration target due to tectonic activity. In the study area, it is composed largely of shale with a few limestone interbeds, but so far composed of fine-grained marl and sandstone. Here, we interpret the sequence stratigraphy of the Rudeis Formation at two onshore wells (Ras El-Ush-7 and Ras El-Ush 8) in the southernmost western shore of the Gulf of Suez via the integration of gamma-ray log and biostratigraphic data, in order to develop a high-resolution sequence stratigraphic model of these syn-rift rocks and determine their viability for hydrocarbon exploration. Using new biostratigraphic analysis of calcareous nannoplankton and planktic foraminifera, we verified the ages of the Rudeis successions. Our results suggest the occurrence of three Burdigalian depositional sequences (SQ1, SQ2 and SQ3), along with six stratigraphic surfaces delineating sedimentation cycles and were mainly deposited in inner shelf to upper slope settings. Each of the sequences typically contains a transgressive systems tract bounded above by a maximum flooding surface and a highstand systems tract bounded above by a sequence boundary. We further demonstrate that the variable timing in deposition and erosion of these depositional sequences were controlled by either local tectonism associated with Gulf of Suez rifting or eustatic sea-level changes.

Stress Path Analysis for Characterization of In Situ Stress State and Effect of Reservoir Depletion on Present-Day Stress Magnitudes: Reservoir Geomechanical Modeling in the Gulf of Suez Rift Basin, Egypt

A reservoir geomechanical modeling has been attempted in the hydrocarbon-bearing Miocene formations in the offshore Badri field, Gulf of Suez, Egypt. Pore pressure established from the direct downhole measurements indicated sub-hydrostatic condition in the depleted mid-Miocene Hammam Faraun and Kareem reservoirs. Vertical stress (Sv) estimated using bulk density data yielded an average of 0.98 PSI/feet (22.17 MPa/km) gradient. Magnitudes of minimum (Shmin) and maximum (Shmax) horizontal stresses were deduced from the poro-elastic model. Relative stress magnitudes (Sv ≥ Shmax > Shmin) reflect a normal faulting tectonic stress in the Badri field. Pore pressure and stress perturbations (ΔPP and ΔSh) in the depleted reservoirs investigated from actual measurements recognized ‘stress path’ values of 0.54 and 0.59 against the Hammam Faraun and Kareem Formations, respectively. These stress path values are far away from the normal faulting limit (0.68), indicating induced normal faulting or fault reactivation to be unlikely at the present depletion rate.

Structure and kinematics of an extensional growth fold, Hadahid Fault System, Suez Rift, Egypt

Abstract. Normal faulting drives extensional growth folding of the Earth's upper crust during continental extension, yet we know little of how fold geometry relates to the structural segmentation of the underlying fault. We use field data from the Hadahid Fault System, Suez Rift, Egypt, to investigate the geometry and kinematics of a large (30 km long, up to 2.5 km displacement), exceptionally well-exposed normal fault system and to test and develop models for extensional growth folding. The Hadahid Fault System comprises eight up to 5 km long segments that are defined by unbreached or breached monoclines. These segments are soft-linked, hard-linked, or defined by a more subtle along-strike transition in overall structural style. High overlap : separation (O:S) ratios between its segments suggest the Hadahid Fault System comprises a single, now hard-linked structure at depth. We demonstrate that a progressive loss of at-surface displacement along-strike of the Hadahid Fault System results in surface-breaking faults and breached monoclines being replaced by unbreached monoclines developed above blind faults. However, shorter along-strike length-scale variations in structural style also occur, with unbreached monoclines developed between breached monoclines. The origin of this variability is unclear, but it might reflect local variations in host rock material properties that drive short length-scale variations in fault propagation-to-slip ratio, and thus the timing and location of fold breaching. We show that folding is a key expression of the strain that accumulates in areas of continental extension, arguing that tectono-sedimentary models for rift development should capture the related structural complexity.

Diagenetic impacts on hydraulic flow unit properties: insight from the Jurassic carbonate Upper Arab Formation in the Persian Gulf

The Upper Arab reservoir in the central Persian Gulf was examined for depositional, diagenetic, sequence stratigraphic and petrophysical features. This succession is composed of eight sedimentary facies that deposited on a carbonate ramp. Three-third-order sequences prograded across the Late Jurassic Arab Platform. This interval was complicated by multiple diagenetic phases including eogenesis and mesogenesis that strongly influenced reservoir properties. Dolomitization, dissolution, cementation and compaction are major diagenetic processes which played an essential role in increasing or decreasing reservoir quality. Four hydraulic flow units (HFU) were determined by flow zone indicator approach for evaluation of the reservoir quality. In addition to depositional features, diagenetic alterations have changed general HFUs characterizations such as porosity, permeability and pore-throat size. Likewise, via Lucia classification, HFUs of the Arab reservoir were grouped based on the integration of geological and petrophysical attributes in detail. Among diagenetic processes, dolomitization and dissolution have positive effects while cementation and stylolitization have a negative effect on HFUs characteristics in the studied reservoir. Put another way, since diagenetic alterations lead to the intensification of heterogeneity in carbonate reservoir, prediction of the relationship between pore type and pore throat size is a problematic issue. Recognition of the hydraulic flow units considered as a practical tool for grouping reservoir rocks and characterizing heterogeneity using porosity and permeability relationship. Finally, specifying of the contribution of various diagenetic imprints in each hydraulic flow unit in a sequence stratigraphic framework results in a conceptual reservoir model that could predict reservoir quality variations across the field.

Palaeoenvironmental and source rock potential of the Turonian–Miocene sequence in the West Esh El Mellaha (SW margin of the Suez rift, Egypt): Insights from palynofacies, palynology and organic geochemistry

A detailed palynological, palynofacies and geochemical study has been undertaken on cuttings samples selected from wells drilled in the Gulf of Suez, Egypt. Inter alia, the samples yielded marine palynomorphs, non-marine palynomorphs, amorphous organic matter (AOM) and phytoclasts. Deposits of the Matulla Formation are dated as Coniacian–Santonian based on the angiosperm pollen and dinoflagellate cyst content. Angiosperm pollen Areolipollis vespiformis in the Rudeis Formation is taken as a biostratigraphic marker for the early Miocene.Two palynofacies associations were identified. Association-A from the Matulla and upper Rudeis formations consists mainly of Type-III gas-prone kerogen. Association-B contains Type-II and Type-II/III kerogens with mixed oil and gas, and is typical of Duwi, Esna, Thebes and lower Rudeis samples. Samples were deposited under various dysoxic–anoxic and suboxic–anoxic conditions.The peridiniacean assemblage from the Upper Cretaceous Matulla Formation intimates deposition in a tropical to subtropical setting within the Tethyan Realm of the Malloy Suite. Salixipollenites, fern spores, and dinoflagellate cysts suggest successive phases of humidity versus aridity during the early Miocene.Geochemical data show that samples from the Duwi Formation are Type-II and Type-II/III kerogens. Based on low HI values and low abundance of AOM, palynofacies association-A samples indicate Type-III gas-prone kerogen, whereas association-B samples have the greatest values of HI and AOM, indicating oil-prone Type-II to Type-II/III kerogens.

Thermal maturity modelling for the pre-Miocene source rocks in Ras Garra area, Suez rift Basin, Egypt

The main potential source rocks in the Ras Garra area of the Suez rift Basin are thought to be the pre-Miocene formations, Duwi, Esna, and Thebes, from the oldest to youngest. The total organic carbon content (TOC) ranges from 6.0 to 7.0 wt %, suggesting very good hydrocarbon generative potential. The hydrogen index (HI) ranges from 600 to 700 mg HC/g TOC and the kerogen is of type I/II. Burial and thermal maturity modelling indicates that the pre-Miocene source rocks started the oil generation as early mature stage in Langhian (14.3 Ma), and mid-mature stage in Pleistocene (2.4 Ma). The early mature stage is characterized by the depth to maturity of 1400 m, burial maximum temperature up to 87 °C and vitrinite reflectance (VR) up to 0.7% Ro. The mid-mature stage is characterized by the depth to maturity of 3007 m, burial maximum temperature up to 120 °C and vitrinite reflectance up to 0.75% Ro. The hydrocarbon generation and expulsion history is divided into two phases and Duwi source rock passed the second phase of hydrocarbon generation, and expulsion with transformation ratio (TR) of 29%. From 0.8 Ma until the present, the hydrocarbon generation and expulsion rates have been increased and the generated and expelled hydrocarbons are mainly oil with minor gases. The results show that the most important factor affecting the maturity of the source rocks and hydrocarbon generation and expulsion rates is the durations of early and mid-mature stages.

Chemometric Differentiation of Oil Families and Their Potential Source Rocks in the Gulf of Suez

An oil–oil and oil–source rock correlation study was carried out using chemometric methods applied to geochemical data for 123 Upper Cretaceous—Lower Miocene putative source rock and 46 crude oil samples from the Gulf of Suez Rift basin. The Gulf of Suez has many organic-rich intervals. The pre-rift source units, such as the Brown Limestone and Thebes formations, contain very good-to-excellent organic content, whereas the Miocene rocks are rated fair to good. HI and Tmax pyrolysis data indicate variable kerogen type and maturation histories where most of the analyzed samples occur along the Type II and Type II/III kerogen pathways from immature to the main stage of oil window with %Ro < 0.9. Carbon isotope ratios’ biomarker data for the bitumen samples indicate predominantly anoxic source rock depositional conditions with substantial algal/bacterial marine and a minor terrigenous organic matter. The Gulf of Suez oils exhibit a wide range of chemical composition from heavy-to-medium gravity and moderate-to-high sulfur content. These oils originated from carbonate/marl source rocks rich in lipids from phytoplankton/benthic algae and bacteria with less contribution of terrigenous organic debris, deposited under anoxic conditions with different thermal maturity histories equivalent to at least the early oil window. Chemometrics using 16 source-related biomarker and isotope ratios identifies six genetic families in the Gulf of Suez. The oil families share common characteristics where the precursor organic matter was deposited in a restricted marine environment with limited land-derived organic matter. The major factor that greatly modifies oil composition in the Gulf of Suez is thermal maturation. However, migration history and spatial and temporal organofacies’ variations of the presumed source rocks are also important. The overall geochemical similarity of the Gulf of Suez oils confirms the mixed nature of these fluids and suggests that no single source rock horizon is likely to have sourced the oil in this promising province. Based on oil–source correlation data and a decision tree chemometric model, the Brown Limestone, Esna, Thebes, and Nukhul formations are the effective source rocks for oil families III, IV, and V, whereas none of the source rock extracts has been assigned for Family I or VI oils.

Active tectonic structures in northeastern Egypt: a geospatial analysis using structural, remote sensing, and seismic data

The seismotectonic activity in Northeastern Egypt is intimately related to the active tectonic structures (mainly faults) which deform the region and induce intraplate seismicity. The present contribution is a new attempt to integrate structural, remote sensing, and seismic data, and implement a reliable geospatial analysis to investigate and assess the nature of the relation between tectonic structures and seismotectonic activity in the Cairo–Suez district which is an active seismic source zone in Northeastern Egypt. The achieved remote sensing and GIS-based geospatial analysis introduces valuable information on the frequency, orientation, and density of investigated tectonic fault trends. The spatial distribution of earthquakes epicenters which recorded during the period (1997–2016) with magnitude (ML ≥ 3.0) is evidently interrelated with the detected tectonic trends, and normal faulting with subordinate shear component is the most focal mechanisms indicated from the analyzed seismic events. The depth analysis of the studied earthquakes suggests a “hard linkage” between the major rift-boundary faults in the northern Gulf of Suez rift and the tectonic trends in the southern domain of the Cairo–Suez district, and thus indicates seismic activity on relatively deeper crustal levels. Most of the studied earthquakes have occurred on the WNW–ESE to NW–SE oriented faults in predominantly extensional to transtensional stress regime, which indicating the WNW to NW tectonic trend as an active fault trend. The intraplate seismotectonic activity in Northeastern Egypt is highly controlled by two active tectonic boundaries, the Red Sea–Gulf of Suez rift and Aqaba–Dead Sea transform (to the east) and the Pelusium Shear System (PSS, to the west). Any reliable hypothetical model explaining the seismotectonic setting in such region would consider the Cairo–Suez district as a large transfer zone transmitting the “far-field” stresses northwestward to the PSS with an effective mechanism keeping the within-plate WNW–ESE, NW–SE, and E–W tectonic trends highly prone to rejuvenation and seismic rupture.

Sedimentary evolution of a shallow carbonate ramp (Kimmeridgian, NE Spain): Unravelling controlling factors for facies heterogeneities at reservoir scale

Abstract The facies evolution of a Late Jurassic (latest Kimmeridgian) shallow carbonate ramp was reconstructed after the analysis and correlation of 21 logs in a 20 × 30 km outcrop area located south of Zaragoza (northeast Spain). The studied succession belongs to the Higueruelas Formation, which is of potential use as an analogue for understanding facies heterogeneities in certain hydrocarbon carbonate reservoirs (e.g. the Arab Formation, Persian Gulf). The studied succession is arranged in nine sedimentary units bounded by discontinuity surfaces that can be traced over kilometres. Facies analysis permitted the reconstruction of two sedimentary models showing the transition from inner ramp subenvironments (i.e. intertidal, lagoon, backshoal/washover, shoal-sand blanket) to the mid-ramp foreshoal and offshore domains: an oncolitic-peloidal-oolitic and an oolitic-peloidal-dominated ramp. The oncolitic-peloidal-oolitic-dominated ramp is characterized by peloidal-oolitic and oncolitic-dominated shoal-sand blankets that developed in higher-energy inner areas, protecting peloidal-oolitic backshoal and oncolitic lagoon domains including a mosaic of stromatoporoid carpets. Peloidal facies with fenestral porosity accumulated in an intertidal belt or as patches on top of the shoal-sand blankets and washover deposits. Offshore from the shoal-sand blankets, chaetetid/stromatoporoid/coral-rich buildups grew on the more proximal mid-ramp, surrounded by peloidal and peloidal-bioclastic grain- to mud-supported facies. An oolitic-peloidal-dominated ramp developed in a second stage of the evolution of the platform, characterized by the presence of a wide restricted peloidal-bioclastic-oolitic lagoon on the inner ramp grading into a backshoal area dominated by storm-related intraclastic-peloidal deposits. Stromatoporoid carpets disappeared and oncolitic-dominated deposits were constrained to the foreshoal and backshoal domains, and locally to local ponds that developed in the intertidal belt or the restricted lagoon. Internal and external factors controlling facies heterogeneity and the sedimentary evolution of the carbonate ramp include resedimentation, topographic relief, and long- to short-term sea-level fluctuations.

Oil-source correlation in the West Esh El Mellaha, southwestern margin of the Gulf of Suez rift, Egypt

There are several source rock units in the Gulf of Suez graben, but the Upper Cretaceous–Miocene sequence has probably produced most of the commercial hydrocarbons in this petroleum province. One hundred and nine shale, marl and marly shale samples collected from five wells in the West Esh El Mellaha Concession and surrounding area were studied by petrographic and organic geochemical methods to determine organic facies, depositional paleoenvironment, and thermal maturity. We also investigated the molecular and stable carbon isotopic compositions of nine oil samples to establish genetic relationships with the source rock samples.Pyrolysis data for samples from the Cenomanian–Santonian Matulla, Paleocene Esna, Eocene Thebes, Oligo-Miocene Nukhul and Lower–Middle Miocene Rudeis formations contain hydrogen-poor terrigenous Type-III to II/III kerogen. However, the Campanian–Maastrichtian Brown Limestone samples contain Type-II and Type-II/III kerogens indicating very good to excellent generation potential. The acyclic isoprenoids and normal alkane distributions and biomarkers in the source rock extracts indicate derivation from bacteria and algae, with varying contributions from land plants, deposited under suboxic to anoxic conditions in normal marine to higher salinity waters.The oil samples have high sulfur content and low to moderately high API gravity, typical of mature oils from pre-rift marine carbonate or calcareous shale lithofacies. Hierarchical cluster analysis (HCA) of 18 source-related biomarker ratios revealed four genetic families of oil samples. The two South Malak-1 oils (Family-4) are substantially different from the Rabeh E−8 and Rabeh E−10 (Family-1), Rabeh-1 and Hurghada-1 (Family-2) and Abu Marwa-1 and Wadi El Sahl-1 (Family-3) oil families, which are more closely related. Principal component analysis (PCA) and HCA based on the 18 ratios for the total data from extracts and oils indicate three groups. The South Malak-1 oils seem to be most closely related to the two Brown Limestone extracts. Group-1 oils appear to represent mixtures with one end member consisting of the South Malak-1 oils and the Brown Limestone source rock, but the other end member is not in the dataset.

Palynological and organic geochemical studies of the Upper Jurassic-Lower Cretaceous successions, Western Desert, Egypt: Implications for paleoenvironment and hydrocarbon source rock potential

The Upper Jurassic-Lower Cretaceous successions in the north Western Desert of Egypt are one of the most prolific hydrocarbon plays in North Africa. However, the source rock characteristics and depositional environments are still poorly understood. The current work assesses these sedimentary sections utilizing an integrated palynofacies and organic geochemical approach for a comprehensive source rock characterization. The investigation was carried out on 70 samples from the OBA. 3-1/1A (interval: 2540 to 3650 m) and OBA. S-C (interval: 2705 to 3782 m) wells. The results obtained are sufficient to categorically establish two types of organofacies linked to depositional environments and kerogen types, namely palynofacies PF I and PF II. The first facies (PF I) is characterized by kerogen type II and III and occurs in the Alamein and Alam El Bueib members of the Lower Cretaceous Burg El Arab Formation. This is further confirmed by pyrolysis results that revealed fair organic richness and gas generation potential in the Alamein Member with TOC ranges from 1.0 to 2.5 wt% and HI from 64 to 112 mg HC/gTOC). The Alam El Bueib Member illustrated better organic richness and quality with TOC ranges from 1.6 to 3.1 wt% and HI from 121 to 318 mg HC/gTOC. The thermal maturity assessment indicates that the Alamein Member is immature and the Alam El Bueib Member is early to oil-mature. PF II occurs in the Jurassic Masajid Formation, which is a transitional mature to overmature, fair to good source rock with mixed kerogen type II and III (TOC 1.3 to 2.4 wt% and HI 148 to 238 mg HC/gTOC). The paleoenvironmental conditions were deduced mainly from the APP ternary plot. The Alamein and Alam El Bueib members were deposited in a suboxic to anoxic basin, whereas the Masajid Formation was deposited under distal, dysoxic to anoxic basinal or proximal, suboxic to anoxic shelf conditions. In summary, it is concluded that the Late Jurassic and Early Cretaceous witnessed deposition of gas-prone source rocks similar to those found in the southern onshore Nile Delta Basin. The results have significant implications for the understanding of the source rock types in the northern onshore and offshore Egyptian basins and the future of the gas exploration.

Cyclo-sequence stratigraphy of the Miocene syn-rift succession, Al Amir and Geyad fields, southwestern part of the Gulf of Suez rift

A cyclostratigraphic analysis is performed using high-resolution well data to study the facies development, characteristics, and patterns of the Miocene syn-rift succession in the Gulf of Suez. The impact of syn-depositional tectonics on the distribution of reservoir units is also highlighted. The study area is in Al Amir and Geyad fields, which are located in the southwestern onshore part of the Gulf of Suez rift. The Cyclolog® software workflow has been applied on nine wells from these two fields using the Gamma Ray log of the Miocene sequences. The Predictive Error Filter Analysis (PEFA) patterns and Integrated Predictive Error Filter Analysis (INPEFA) curves support the definition and distinction of seven 3rd order cycles. These cycles are numbered as 1.4, and 1.5 for Nukhul Formation, 2.1, 2.2, and 2.3 for Rudeis Formation, 2.4 for Kareem Formation, and 2.5 for Belayim Formation. The Kareem Formation is represented by cycle 2.4 and could be divided into higher order subcycles 2.4 (a, b (u and l), c, d and e). The oil reservoir units occur in subcycle 2.4.b (u and l), whereas subcycle 2.4.b (l) is missing in Geyad field and subcycle 2.4.b (u) is missing in Al Amir SE-1X St well. Correlation profiles and isochore maps of the Upper Rudeis and Kareem formations (cycles 2.3 and 2.4 respectively) indicate the relationship between sediment supply and accommodation space which are related to tectonic subsidence of the West Zeit Basin and sediment supply from the Esh El Mellaha range.

Mineralogic and Diagenetic Controls on Reservoir Quality of Paleozoic Sandstones, Gebel El-Zeit, North Eastern Desert, Egypt

Studying the mineral composition and petrophysical properties of the Cambro–Ordovician sequence in Gebel El-Zeit indicates that it can be discriminated into four rock types, namely quartz arenite (RRT1 of the Cambrian Araba Formation, 35 m; RRT2 of the Ordovician Naqus Formation, 320 m), quartz wacke (RRT3) and mudstone (RRT4) of the Naqus Formation. Diagenesis played a major role in reducing or enhancing the studied microfacies. Cementation by silica, compaction and authigenic clay minerals are the main porosity-reducing factors, whereas dissolution and leaching out as well as fracturing are the most important porosity-enhancing factors. For the present study, reservoir quality was determined using reservoir quality index (RQI), flow zone indicator (FZI) and reservoir potentiality index (RPI) based on helium porosity and permeability values, in addition to the mercury injection capillary pressure (MICP) tests. The best reservoir quality was assigned to the quartz arenite microfacies, whereas the least quality was assigned to RRT4. Reservoir quality is mostly controlled by permeability, which in turn is controlled by the helium porosity and the pore radius of the studied samples (r35 of Winland and r10 of Schowalter). The Araba Formation at the bottom of the sequence is characterized by the best hydraulic flow units (best RQI, FZI, RPI and MICP, rank II). In addition, the middle and top parts of the Naqus Formation have good to very good reservoir quality (rank III).

Limited thermochemical sulfate reduction in hot, anhydritic, sour gas carbonate reservoirs: The Upper Jurassic Arab Formation, United Arab Emirates

Abstract Limited thermochemical sulfate reduction (TSR) in hot (130–160°C) and anhydrite-rich sour gas reservoir carbonates of the Arab Formation (Upper Jurassic) is manifested by rare calcitization of anhydrite with slightly lower δ13CVPDB values (−3.2 to −0.1‰) than calcite precipitated in equilibrium with Late Jurassic seawater. Fluid inclusion microthermometry of calcite that has replaced anhydrite indicates that TSR occurred between 130°C and 160°C. The lack of evidence for extensive TSR, despite the suitable current temperatures and abundant sulfates in the gas reservoir, coupled with the relatively more common TSR-related calcite in the flanks (water zone) than crest (gas zone), indicate that: (1) gas emplacement while the reservoir was buried at shallower depth slowed down or inhibited TSR in the crest even when it subsequently reached depths where extensive TSR would occur, and (2) H2S (up to 38 vol%) has migrated from the underlying Permo-Triassic and/or Jurassic sulfate-carbonate deposits. This study demonstrates that constraining the timing of hydrocarbon emplacement within the context of burial-thermal history is crucial for a better understanding of the origin and distribution of H2S in hot, anhydrite-rich, sour gas reservoirs.

Early flank uplift along the Suez Rift: Implications for the role of mantle plumes and the onset of the Dead Sea Transform

The Suez Rift is the northern extension of the Red Sea Rift and is an ideal location to study young continental breakup tectonics. Yet, despite much effort to constrain the timing of rift flank uplift and extensional exhumation in this region, the emerging picture remains uncertain. Here we present new thermochronologic constraints including apatite (U–Th)/He and fission track data from a transect across the eastern flank of the Suez Rift in SW Sinai. The use of two different thermochronometers in conjunction with thermal history modeling and well constrained kinetic parameters delineates a pronounced episode of relatively rapid cooling at 25-18 Ma followed by subdued post ∼18 Ma cooling. In contrast to previous estimates, this cooling pattern suggests that the most rapid uplift and exhumation phase along the Gulf of Suez took place during the early stage of rift formation, prior to the middle Miocene, with over 2.4 km of exhumation occurring during this stage. Uplift and exhumation along the Suez Rift flank slowed substantially post ∼18 Ma, as deformation migrated to the newly formed plate boundary along the Dead Sea Transform. This finding complements and strengthens previous indications for the initiation timing of the Dead Sea Transform plate boundary. The inferred late Oligocene–early Miocene timing of rapid exhumation, associated with tectonic extension and rift flank uplift coincides with the onset of regional alkali-basalt magmatism, suggesting lithospheric heating prior to the rift formation. This observation, along with the elevated topography around the Sinai triple junction and indications for some pre-rifting uplift, supports a more active mantle plume role in the rifting process.

Linking diagenetic history to depositional attributes in a high-frequency sequence stratigraphic framework: A case from upper Jurassic Arab formation in the central Persian Gulf

The carbonate Arab Formation (Kimmeridgian-Tithonian) is one of the most prolific hydrocarbon reservoirs in the world. Petrographic studies of this unit in the central Persian Gulf led to identification of eleven sedimentary facies, and facies are grouped into 5 shore-parallel facies belts (supratidal, tidal flat, lagoon, shoal and mid-ramp). Evidences such as the absence of barrier reefs and the low diversity of facies reveals that these facies formed in a ramp-like platform. Postdepositional processes (diagenetic evolution) considerably influenced reservoir properties of sedimentary facies. Depositional and diagenetic features in this formation are strongly controlled by the interplay of glacio-eustasy and climate leading to sea-level fluctuations during the Late Jurassic. Based on the petrographic analyses and previous studies, four third-order sequences are recognized and all sequence boundaries are capped by evaporites. The main diagenetic processes impacting the Arab Formation occurred under marine and hypersaline conditions and burial realms. The hypersaline conditions correspond to sea-level fall and development of brines and are characterized by dolomitization and moldic dissolution in the Upper Arab Formation. Vuggy dissolution is another major reservoir improving factor. Generally, vuggy dissolution along with anhydrite cementation, occurred extensively in the Upper Arab Formation, while in the Lower Arab Formation, these processes are limited to just beneath of the sequence boundary (nodular anhydrite form). Diagenetic features (eogenetic and mesogenetic environments) appear to correlate to depositional environments in the Arab Formation and are controlled by sea-level changes. Consequently, diagenetic processes and reservoir properties can be predicted within a sequence stratigraphic framework.

REMOVED: The stress dependence of velocities and its influencing factors for carbonate rocks in Arab formation, Saudi Arabia

REMOVED: The stress dependence of velocities and its influencing factors for carbonate rocks in Arab formation, Saudi Arabia

Depositional facies, diagenetic overprints and sequence stratigraphy of the upper Surmeh reservoir (Arab Formation) of offshore Iran

This study uses petrography, stable isotopes, petrophysics and wireline logs to constrain depositional facies, diagenesis, reservoir quality and sequence stratigraphy of the late Jurassic Upper Surmeh Formation (Arab Formation), in one of the northern Persian Gulf oil fields.Petrographic studies led to discrimination of nine microfacies which represented supratidal, intertidal, lagoon and shoal sub-environments of a carbonate ramp. In the un-cored wells five electro-facies were distinguished using Hierarchical Cluster Analysis (HCA) method. These electro-facies were correlated with the microfacies in a well which had both cores and logs data. Reservoir quality of the facies was determined by porosity and permeability data available from the cores.Among recognized diagenetic phenomena, fracturing, dissolution and dolomitization had an enhancing effect, but cementation, anhydritization and compaction had a deteriorating effect on reservoir quality. Stable isotope data were used to decipher the dolomitization process which is the most effective diagenetic process on the reservoir quality.For temporal and spatial reservoir quality prediction, the studied formation is investigated in the sequence stratigraphic framework. In this regard, four 3rd order sequences were determined which include a deepening-up transgressive systems tract (TST) in their lower part and a shallowing-up highstand systems tract (HST) in their upper part. Correlation of the identified sequences with those of equivalent formation in the Arabian plate is carried out to discuss the order of sequences and their major controls.