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Mixed siliciclastic-carbonate systems are regulated interactively by factors such as siliciclastic sediment supply, carbonate production, sea-level change, tectonism, and climate conditions. These systems record vital information that aids in understanding ancient environments. This study used a merged 3D seismic volume, in conjunction with over 100 industrial wells, to systematically investigate the stratigraphic-sedimentary evolution of such a system within the Huizhou Sag of the Pearl River Mouth Basin, located on the northern continental shelf of the South China Sea. In total, six major sequence boundaries were identified for the Zhujiang Formation within the area, thus subdividing the interval into five typical third-order depositional sequences. Each of these sequences can be divided into a transgressive and a highstand systems tract. Lowstand or falling stage systems tracts were also recognized, the deposition of which was potentially in response to the uplifting process of the Dongsha Rise. During the deposition of the Zhujiang Formation, the Huizhou Sag may have undergone a sequential evolutionary history from delta-shore, to delta-shore-tidal-lagoon, to delta-shore-carbonate, and finally to delta-shore-shallow marine systems. This evolution responded to a varying degree of mixing processes, which was mainly regulated by siliciclastic sediment supply, confined paleomorphology, and local oceanic currents. Furthermore, the deposition of the Zhujiang Formation in the Huizhou Area was time-equivalent with the spreading process after the ridge jump of the South China Sea (23-16.5 Ma), providing valuable insights into sea-level fluctuations, provenance changes, and tectonic evolution. Our results may also shed light on the evaluation of lithologic traps and hydrocarbon sweet spots within mixed siliciclastic-carbonate systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Enormous and inherent heterogeneity of carbonate reservoirs causes problems in the estimation of their geological and petrophysical attributes. The major part of this heterogeneity is due to the various pore types and structures of these reservoirs. Water saturation is economically one of the most important characteristics of any producing reservoir. Archie introduced practical exponents, which are fundamental parameters for saturation calculation. In this research, the effect of geological factors controlling Archie's exponents including depositional and diagenetic characteristics in a sequence stratigraphic framework in Permian–Triassic carbonates of Persian Gulf Basin was carried out. Rock typing approach has been used for assigning reservoir characteristics to geological parameters. Five digenetic facies that were determined according to petrographic studies, wire line logs, SEM and conventional core analysis as well as mercury injection tests, were grouped into four rock types using Lucia diagram. Archie's exponents were calculated for different rock types. Results showed that porosity value and pore type have an important effect on the exponents. This effect could be traced vertically in macro-scale using sequence stratigraphic concept. Grainstone facies with high m values are located in early HST and late TST. Tight grainstone or mud-dominated facies with low m values are located in early TST and late HST. Graphical abstract Image 1 Highlights • Archie's exponents in Iran's Permian–Triassic reservoirs considered here. • The effect of geological parameters on Archie's exponents was examined. • Using facies characteristics and their stacking pattern, 4 third-order sequences were recognized. • Archie's exponents are more controlled by the porosity variation rather than permeability changes. • Grain-dominated rock types 3 and 4 are located in late TST and early HST stages. [ABSTRACT FROM AUTHOR]

The application of gamma ray data as a non-destructive, inexpensive geophysical survey tool with a very high resolution and coverage provides the potential for a better understanding of sequence stratigraphic boundaries in carbonate strata in this study. Three wells’ GR data from Permian–Triassic Kangan and upper Dalan formations in one of the central Persian Gulf Iranian hydrocarbon fields have been used for this purpose. The difference between each data point with the well average GR shows the deviation of each measurement from the base value. Regarding the same physical, chemical and biological conditions (genetic relationship) in each sequence, GR deviations show the same deviation trend within each sequence. The cumulative distribution of these deviations is therefore increasing or decreasing constantly in each sequence. Calculation of GR deviation cumulative distribution exactly showed the Kangan-Dalan (Permian–Triassic) boundary. The average GR value of each sequence then used for the new deviation calculation and new boundaries detected in second level analysis. The turnovers determined in this method were correlated with the sequence stratigraphic boundaries of the studied formations provided by the core analysis, sedimentological methods. The new method applied successfully to the 10 wells in the field and provided the same results. The results demonstrate the applicability of the method in carbonate strata for sequence stratigraphic purposes. [ABSTRACT FROM AUTHOR]

In this research, an integrated geological and petrophysical approach was applied to understanding the most critical factors affecting the water saturation exponent in the Permian–Triassic Kangan and Dalan carbonate formations in the central Persian Gulf in Iran. Economically, water saturation has a fundamental role in reservoir characterisation. A total of 8 sedimentary facies were recognised with multiple diagenetic phases. Diagenetic processes include marine cementation, moldic dissolution, early dolomitisation, recrystallisation, anhydrite cementation, compaction, and fracturing, which have influenced reservoir properties. Four third-order sequences were distinguished in the study area accompanied by nine fourth-order sequences. Petrographic analysis, scanning electron microscopy, petrophysical core analysis, wireline log data as well as mercury injection tests integrated through flow zone indicator, Lucia classes, and Lorenz plot approaches. Consequently, 4 integrated rock types (IRTs) were identified with particular depositional and diagenetic features. IRT1 with dominant interparticle pore type and strong porosity–permeability correlation (average 9.1% porosity and 27 mD permeability, R2 = 0.98), has a high saturation exponent (n = 2.2). IRT4 with grain-to mud-dominated facies, low porosities (average 1.4%), and a mean value of 4.54 mD permeability has the lowest saturation exponent (n = 1.07). Moldic dissolution with low pore connectivity is the dominant pore type in IRT2 and IRT3 which have a medium and relatively high saturation exponent, respectively (IRT2 n = 1.53 and IRT3 n = 1.78). Accordingly, a conceptual model was suggested for saturation exponent variations in a high-frequency sequence stratigraphic framework. In order to evaluate the heterogeneity of the studied formations and its impact on the reservoir properties, the characteristics of the determined rock units were studied. This study integrates microscopic to macroscopic geological and petrophysical factors to understand the saturation exponent distribution in a heterogeneous carbonate reservoir, leading to obtaining a more accurate water saturation estimation of such reservoirs. [Display omitted] • A total of 8 depositional facies were deposited in a ramp environment. • Moldic dissolution and early dolomitisation changed the reservoir properties. • By integration of FZI values and Lucia plot, four IRTs were identified. • Hydraulic flow units and Lorenz plots were correlated with depositional sequences. • A conceptual model has proposed to predict distribution of saturation exponent. [ABSTRACT FROM AUTHOR]

Mud-dominated facies distribution of Barremian–Turonian succession in the northeastern Arabian Plate in the central Persian Gulf represents a shallow ramp platform. On the basis of petrographical studies, core analysis data and gamma ray logs, this succession has been studied for facies analysis, defining depositional environment, sequence stratigraphy and reservoir properties. A total of 6 microfacies and 3 petrofacies types are recognized in this succession. Lagoonal environment was dominated during the deposition of Dariyan, Kazhdumi and Sarvak formations. The lagoon rapidly changed to a sand shoal by falling sea-level and increasing energy level of the depositional environment. Sequence stratigraphy of Barremian–Turonian succession shows that mud-dominated facies have been deposited in TSTs and grain dominated facies in HSTs of the sequences. Although grain-dominated facies like packstone to grainstone and algal floatstone were spread during the HSTs of sequences, the changes in the texture and size of the grains had a negligible effect on reservoir quality. During this period (Barremian–Turonian), two major sea-level falls caused considerable environmental changes such as platform emergence, incised valley fills and clastic sediments influx into the carbonate platform. Meteoric diagenesis during the falling sea-level had a major effect on the reservoir properties of the reservoirs, under the sequence boundaries. Grains, matrix and micrite dissolution and subsequent selective blocky and equant calcite cementation, strongly modified the primary reservoir properties. Local dolomitization also enhance the porosity and permeability of the samples. While large pores have been filled by cements, microporosities remained unfilled until the late stages of diagenesis and burial. • Barremian–Turonian succession in the Arabian Plate has been considered. • Facies changes and diagenetic processes linked to sequence stratigraphy. • Depositional setting and reservoir properties evolved by sea-level fluctuations. • Grains and micrites have been dissolved in meteoric diagenetic environment. • The main reservoir parts are HSTs due to the diagenetic processes. [ABSTRACT FROM AUTHOR]

Abstract 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. Graphical abstract Image 1 Highlights • Arab Jurassic Formation is one among most prolific hydrocarbon reservoirs in world. • Composed of 5 facies belts formed on ramp-type platform in arid climate. • Diagenesis (in marine, hypersaline, burial realms) shaped its reservoir properties. • It is mainly controlled by the interplay of eustasy and climate. • So, its reservoir property is predictable in a sequence stratigraphic framework. [ABSTRACT FROM AUTHOR]

During the Albian age, siliciclastic input in the Arabian carbonate-dominated shelf formed important petroleum system elements. Hence, the Albian Burgan-Kazhdumi succession hosts world-class sandstone reservoirs in some Middle East oil fields. Moreover, stratigraphic traps are possible due to changes in facies and structural dips. Accordingly, we used process-based forward stratigraphy modeling as a powerful tool to predict Burgan-Kazhdumi units and de-risking new exploration prospects. A 3D stratigraphic model was constructed in this study for the first time by integrating multi-disciplines and multi-scales of seismic and well data from several countries. The model (324 km × 264 km, 4 km × 4 km grid size) encompasses NW of the Persian Gulf, Kuwait, south Iraq and SW of Iran and is vertically divided into three units based on Albian regional third-order sequences. Results indicated that the lower unit, unit-1, contains onlapping aggradational-retrogradational stacking compounds, high sand bodies thickness and distribution as well as good reservoir quality. This unit was deposited on a tide-dominated delta system. Gradually, with rising sea level, progradational fine-grain marine sedimentation dominated in units 2 and 3. Hence, intra-formational seal facies formed in the proximal and organic-rich facies in the distal intra-shelf areas. The gentle topography of the basin floor seems responsible for the lack of turbidity lobes. The sand bodies of up-dip arches such as Khafji-Norooz and Kharg-Mish highs and pinched out in fine-grained facies provide a significant potential for stratigraphic traps. The model sensitivity analysis showed eustasy, and water-driven diffusion coefficient (Kw) has the most critical impact on the clastic sedimentation of unit-1 and unit-3. Furthermore, tectonic events have the most significant sedimentation effect in unit-2 sedimentation. The findings of this study can help for better understanding of a more precise regional sequence stratigraphic and stratigraphic architecture of the Albian succession of the study area. This study also helps identify elements of petroleum plays as well as stratigraphic trap potential between mixed siliciclastic-carbonate depositional systems. • Construction of paleo-environment characteristics of the Albian Burgan-Kazhdumi succession in the northeastern margin of the Arabian Plate. • Application of multi-disciplinary process-based forward stratigraphy modeling technique for the exploration of subtle traps. • Determination of mixed siliciclastic-carbonate lithotype and thickness of Albian Burgan-Kazhdumi succession in the ∼90,000 km2 for the first time. [ABSTRACT FROM AUTHOR]