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Carbonate-Evaporite Sequences of the Late Jurassic, Southern and Southwestern Arabian Gulf
Abstract
The carbonate-evaporite sequences of the Upper Jurassic Arab and overlying Hith formations in the southern and southwestern Arabian Gulf form many supergiant and giant fields that produce from the Arab Formation and are excellent examples of a classic reservoir/seal relationship. The present-day sabkha depositional setting that extends along most of the southern and southwestern coasts of the Arabian Gulf provides an analog to these Upper Jurassic sedimentary rocks. In fact, sabkha-related diagenesis of original grain-supported sediments in the Arab and Hith formations has resulted in five distinct lithofacies that characterize the reservoir/seal relationship: (1) oolitic/peloidal grainstone, (2) dolomitic grainstone, (3) dolomitic mudstone, (4) dolomitized grainstone, and (5) massive anhydrite. Interparticle porosity in grainstones and dolomitic grainstones and intercrystalline porosity in dolomitized rocks provide the highest porosity in the study area. These sediments accumulated in four types of depositional settings: (1) supratidal sabkhas, (2) intertidal mud flats and stromatolitic flats, (3) shallow subtidal lagoons, and (4) shallow open-marine shelves. The diagenetic history of the Arab and Hith formations in the southern and southwestern Arabian Gulf suggests that the anhydrite and much of the dolomitization are a result of penecontemporaneous sabkha diagenesis. The character and timing of the paragenetic events are responsible for the excellent porosity of the Arab Formation and the lack of porosity in the massive anhydrites of the Hith, which together result in the prolific hydrocarbon sequences of these formations.
... Alsharhan and Scott (2000) describe the Hith Formation as the final regressive, supratidal stage of the last major Jurassic cycle. Alsharhan and Whittle (1995) and Alsharhan and Kendall (1994) characterized the Dahl Hit type locality as follows: "The anhydrite has a chickenwire texture with some dolomite in the lower part of the section, grading upward to a similar nodular texture and becoming laminated at the top including some fine-grained carbonate material." However, the overall increase of carbonate layers (from anhydrite to transitional and carbonate member) can also be interpreted as increasing transgressive events, where a permanent trend of sea-level rise leads to an end of the marine isolation and the dominance of evaporite deposits of the Arabian Intrashelf Basin (Wilson 2020; Hughes et al. 2009, Le Nindre et al. 1990). ...
The Dahal Hit cavern in Central Saudi Arabia is the only locality where the Tithonian Hith Anhydrite Formation is exposed in the Middle East. In 2010, a 28.5-m interval in the 90-m-thick Hith Formation was logged and described in the cavern as part
of a study to evaluate its sedimentological and sequence-stratigraphic architecture and to identify potential high-permeability layers within the seal of the world’s most prolifc petroleum system. Seven facies types were interpreted as refecting sabkha
(subaerial) or salina (subaqueous) settings, and their vertical stacking patterns revealed that the logged interval consists of three transgressive–regressive cycles and part of a fourth cycle. The cavern was revisited in 2016 but only to fnd that the
water level had risen by about 50 m rendering further geological studies impossible. The higher level of the water suggests that the cavern was fooded by the fow in the subsurface of treated sewage water released into a former quarry. The quarry
is situated about 10 km southeast of the cavern, and the storage of water in it started in 2008. The fow pathways to the Dahal Hit cavern are apparently well-connected karsts, caverns, and high-permeability fow zones present in dolomite layers.
... This barrier formed paleotopographic highs along the edge of the Hith Formation. Indeed, this is best illustrated in eastern Abu Dhabi where the Hith Formation terminates against the Asab Formation ooid shoals (Alsharhan and Whittle, 1995;Al Silwadi et al., 1996;Al Suwaidi et al., 2011). A similar case is documented from the Zagros Fold-Thrust Belt in Iran. ...
Unlike the Tethys Realm, the carbon isotope record from the Boreal Realm exhibits a prominent negative excursion before the Jurassic-Cretaceous boundary referred to as the Volgian Isotopic Carbon Excursion (VOICE). The VOICE has been ascribed to restricted-circulation conditions in northern high latitude basins, which decoupled these basins from the global carbon pool. Similar isotopic signal has been identified in the southern hemisphere where it has been attributed to humid conditions and influx of organic matter. The restricted circulation hypothesis is tested here by examining the depositional record of the Tethyan Late Jurassic–Early Cretaceous succession from central Saudi Arabia. A multi-disciplinary approach, involving sedimentology, sequence stratigraphy, biostratigraphy, and geochemistry, was adopted for studying a composite section covering the Hith, Sulaiy, Yamama, and Buwaib formations. The succession is characterized by restricted salina and sabkha depositional settings at the base that transition upward into an open-marine depositional system. This trend records a long-term sea-level rise during the Early Cretaceous. The carbon isotope record for this succession illustrates two prominent positive excursions of 5.2‰ and 2.6‰ amplitudes at the base and top of the succession, respectively. The larger positive excursion coincides with the restricted-environment facies and shows similarities, in terms of magnitude and trend, to the recovery phase of the VOICE. The upper positive excursion is manifested after a steady drop in the carbon isotope values, and it corresponds to the globally recognized Weissert event. The results indicate that restricted circulation in the Arabian shelf interior during the Late Jurassic duplicated the VOICE signal. The recognition of the Weissert event signal, on the contrary, denotes restored circulation of the shelf interior with the Tethys. The novelty of this study is demonstrated by the findings that the VOICE might indeed be a global signal and restricted circulation driven by eustasy is the main controlling factor for the VOICE signal.
... Leaching is one of the most important processes giving rise to secondary porosity through dissolving the weakly resistant grains and forming secondary voids within the groundmass or event within grains [11]. Anhydrite is found associated with the secondary voids resulting by dissolution and this association caused closing these voids and reducing the porosity [12]. Neomorphism can lead to either increasing or unaltered porosities [11]. ...
The Upper Palaeogene-Lower Neogene succession represent subsurface sections from Kirkuk, Bai Hassan, and Khabaz oilfields were divided to many reservoir units dependent on information derived mainly from petrographical description, well log analysis, and related microfacies. In Khabaz oil Field, the hydrocarbon reservoir includes three reservoir units covered the Jeribe Formation, Anah Formation with its interfingering zone with Azkand Formation and Azkand Formation, the total thickness of this reservoir reaches up to (128 m) with net pay thickness of about (85.7 m) and net average porosity of (0.096) while the net water saturation is (0.185), the volume of shale is (7.130). The hydrocarbon reservoir in Bai Hassan was represented by three reservoir units comprised from the Bajwan and Baba formations, the total thickness of this reservoir is (178 m) with net pay thickness of (154.2m) and net average porosity of (0.121) while the net saturation is (0.156), the volume of shale is (36.837). Four reservoir units comprised the hydrocarbon reservoir in Kirkuk Field where they covered the Bajwan, Baba, Shurau and Sheikh Allas formations. The total thickness of these reservoirs is (136 m) with net pay thickness (124.5m) and net average porosity (0.178) while the net water saturation is (0.159), the volume of shale is (5.82). Many types of porosity were associated with these reservoirs such as the interparticles, intraparticles, intercrystaline, fracture, channel, moldic, vug, and cavern porosities. These porosities are attributed to a combination of dolomitization, fracturing, and dissolution.
... The Hith Formation overlies the Surmeh Formation and forms the regional caprock of the Surmeh reservoirs (Powers, 1962). The upper Surmeh Formation (Kimmeridgian-Tithonian age) in the Persian Gulf investigated in this study containing limestone and dolomitic with interbedded anhydrite rocks (Alsharhan and Whittle, 1995). The Arab Formation sequence with Upper Jurassic age in the Persian Gulf is divided into four members A, B, C, D (Fig. 1). ...
Machine learning methods are increasingly employed in different seismic and petrophysical methods for parameter estimation, interpretation, prediction, and classification. Reservoir facies classification assists the interpretation of seismic data as an important step in petroleum exploration and production monitoring. In this study, we estimate a reservoir facies model by integrating random forest (RF) algorithms and geostatistics modeling. The Surmeh Formation with Jurassic age is known as one of the most important hydrocarbon reservoirs in the Middle East. The upper part of the Surmeh Formation is equivalent to the Arab Formation, which includes sequences of evaporitic carbonate facies in the study area. Well log data including DT, GR, RHOB, and PHI are used in the RF method for reservoir facies classification. Cross-validation verifies the high accuracy of our classification, with an average accuracy of 95%. The predicted reservoir facies consistently describe the carbonate and evaporitic facies with the geological information of this formation. The decision tree diagrams of the RF algorithm give valuable information on decision limitations and how to select features for efficient computation. We use the classification results for facies modeling. The comparison between facies models and drilling core data shows that the APE value of the sequential indicator simulation model is less than that of the indicator kriging model.
... Various origins have been proposed for disseminated evaporites, including the following: (1) In sabkhas of arid tidal flats (Kinsman, 1969;Dean et al., 1975;West et al., 1979). These evaporites are precipitated from concentrated saline water derived from preexisting porous sediments by capillary pressure generated from strong evaporation (Friedman and Sanders, 1967) and can also form in porous strata and karst systems of the vadose or phreatic zone in sabkha environments through seepage reflux (Schreiber et al., 1976;Alsharhan and Whittle, 1995;Kasprzyk and Orti, 1998). This is the most important and common origin. ...
The development of evaporite–carbonate assemblages is a common sedimentary process in restricted evaporitic marine environments. These assemblages provide important reservoir spaces for oil and gas. To establish a systematic understanding of, and scientific basis for, oil and gas exploration, this paper reviews the major genetic environments of evaporite–carbonate assemblages and associated reservoirs. Based on the review, carbonate reservoir-forming marine evaporite sequence worldwide can be categorized into four major settings: marginal-marine sabkhas, marginal-marine evaporative lagoons, coastal salinas and regional evaporite basins. In addition, a new type of reservoir that developed in the Ordos Basin of China during the Ordovician greenhouse is proposed based on a synthesis of new and existing chemical and physical data. This new model is identified in the supra-salt reservoir in the fifth member of the Middle Ordovician Majiagou Formation in the Ordos Basin and is termed an “epeiric basin-scale disseminated evaporite deposition”. In this newly identified type of dolomite reservoir, irregular–circular moldic pores and vugs that are uniformly distributed in micritic dolomite matrix formed high-quality reservoir spaces, examples of which are rare worldwide to date. The primary evaporitic mineral in these molds is halite crystal, which formed in a restricted evaporitic epeiric basin environment. The selective dissolution of disseminated halite crystals and enlargement of its surrounding rocks in the upper part of the sedimentary cycle by meteoric water during late highstand system tract formed the unique distribution of halite-moldic pores and vugs. Within the evaporitic epeiric basin, high-frequency sea-level fluctuation and syngenetic exposure are also likely to have occurred, conditions that have been neglected in the classic models. Coupling of the extremely high atmospheric CO2 content, low-amplitude location and high-frequency sea-level fluctuations during the Middle Ordovician greenhouse, together with the flat and broad restricted evaporative environment, controlled the formation of this rare end-member sedimentary assemblage and associated reservoirs. The reservoirs were developed within the sedimentary framework of the North China Platform. which was characterized by a depression surrounded by three uplifted areas. The epeiric basin-scale disseminated evaporites model allowed the formation of reservoirs with high exploration potential. Exploration of this type of reservoir requires that attention is paid to hydrocarbon sweet spots generated by later diagenesis and to heterogeneous hydrocarbon accumulation.
... In contrast to these shallow-water facies, the evidence belonging to the deep marine (off-shore) conditions, rimmed shelves and turbidity currents were not recorded in the Surmeh carbonates reservoir. These evidence beside the lack of considerable barrier reef structures and the facies gradational pattern in a literature framework of Arab-D reservoir depositional setting (e.g., Alsharhan and Kendall, 1986;Alsharhan and Whittle, 1995;Lindsay et al., 2006) proposed that the studied sequence in well 2S-2 (Salman Field) was deposited in inner parts of a low steep carbonate ramp (Fig. 6). ...
The Upper Jurassic Surmeh reservoir in the northern Persian Gulf is a stratigraphic equivalent of Arab-D reservoir that is one of the best Jurassic reservoir rocks of the Arabian Peninsula. In this study, in the first step the palaeontology, sedimentary environment, sequence stratigraphy and reservoir quality of the Surmeh reservoir was investigated in a core-bearing well in Salman oil field. The palaeontological studies reveal a moderately diverse assemblage of benthic foraminifera. Dominated foraminifera include the agglutinated forms and miliolids and there are also fragments of alga, stromatoporoids, corals, bivalves, gastropods and echinoderms. These recorded fauna and flora resulted in distinction of three zones that characterize the age of undifferentiated Kimmeridgian-Tithonian. Based on petrographic observations, along with palaeontological materials, eight microfacies were identified that represent four sub-environments of a carbonate inner ramp including supratidal, intertidal, lagoon and shoal. These studies combined with well log responses resulted in identification of a 3rd order sequence and parts of an incomplete one that is composed of an incomplete HST. These 3rd order sequences comprise four 4th order subordinate sequences.
In addition by integration of petrographic analyses, sub-environments energy regimes and petrophysical data, five reservoir zones were identified. Also, based on core porosity and permeability 6 Hydraulic Flow Unit (HFU) with poor to excellent reservoir quality in ascending trend were identified. The reservoir zone I, which belongs to the sabkha and littoral facies, represents the worst reservoir quality (includes HFU1 to HFU3), while the reservoir zone III with best reservoir quality (includes HFU4 and HFU5) comprises the back shoal grain-supported facies. The introduced sequences and reservoir zones in the studied well were propagated to three other wells throughout the Salman Field via using log responses. Also they were correlated with those introduced for Arab-D reservoir in the southern parts of the Persian Gulf providing a correlation framework. This pattern can be used in the next exploration wells which are going to be drilled especially in the northern parts of the Persian Gulf.
... Due to the age revision, the Sargelu Limestone unit has now been recognized as the lateral continuation of these members into Kuwait and Iraq. The Uwainat Member in the UAE and Qatar is characterised by a grainy, peloidal, skeletal, oolitic facies of grainstones and packstones, with local cross-bedding, and an estimated water depth of 5-10m (Alsharhan & Whittle, 1995;de Matos, 1997). The age equivalent Sargelu Limestone unit, present in Kuwait and Iraq, is less grainy in character and interpreted to be deposited in slightly deeper water of up to 30m depth in Kuwait (Crespo de Cabrera et al., 2019) with further deepening water depths toward more open marine environments in Kurdistan (Lui et al., 2017). ...
The Jurassic stratigraphy of the Middle East includes the world's most economically significant petroleum systems, containing multiple world-class source, reservoir and seal packages. Yet in a regional context, these depositional systems are still not fully understood, leading to inconsistencies in lithostratigraphic nomenclature across international boundaries and misconceptions in the stratigraphic architecture limiting exploration and production success. We have applied sequence stratigraphic principles across the Jurassic strata of the eastern Arabian Plate to increase stratigraphic understanding and resolve some of the common misconceptions. This provides a robust age-based framework to reduce lithostratigraphic uncertainty across international boundaries and provides predictive capabilities into the temporal and spatial distribution of source, reservoir, and seal facies.
Herein, we focus on one of these stratigraphic misconceptions, which deals with the development and sedimentary infill of the Late Jurassic Gotnia Basin, and its relationship with the aggrading platform of the Rimthan Arch. Our literature based re-interpretation proposes a mostly eustatically driven control, whereby the shallow water platform of the Rimthan Arch followed sea level rise, and the Gotnia Basin became a starved intra shelf basin. This revised stratigraphic interpretation has important consequences for the lateral facies relationships, and overall tectono-sedimentary understanding of the area, as well as for the petroleum habitat.
Various petroleum systems existing in the Zagros fold and thrust belt of Iran are introduced and systematically characterized in this paper.
Structural analogs. These comprise analogs assisting the interpretation for regional structural styles such as rifting and pull-apart settings and delineation of regional faults through the alignment of karst features. Structural trap risking analogs comprise relay ramps and extensional fault settings. Salt tectonic analogs can be used for both, potential trap delineation as well as trap risking.
The use of key beds in the cap rocks of the oil reservoirs is crucial. Lack of awareness of these key beds will have serious risks and damages. The Gachsaran oil field is located 220 km southwest of Ahwaz-Iran. The former caprock consists of six key beds (A, B, C, D, E, and F). At the time of writing this paper these key beds are being used during excavations and drilling to determine the site of casing points. What has made utilizing these key beds during excavations difficult however, is use of diamond drill bits which results in the shattering of excavated samples. As such, it has become challenging to learn more about these key beds through studying petrographic thin sections in microscopy. These key beds were observed during the investigation at the drill sites. Later, the excavated samples were studied in the Energy-Dispersive X-ray Spectroscopy (EDS) machine, using a semi-quantitative method to analyze the elemental differences in those key beds. In addition to the identification of various lithological and diagenetic properties of the caprock, this study leads to the introduction of four new key beds based on geochemical properties. Some of the most important differences within the formation include those between the caprock anhydrite and the non-caprock anhydrite, namely the presence of potassium and titanium and the absence of chlorine and sodium in the caprock section. The four new key beds introduced from this study using elemental differences were named as key beds-1, 2, 3, and 4.
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