- Home
- Conferences
- Conference Proceedings
- Conferences
Fifth EAGE Arabian Plate Geology Workshop 2015
- Conference date: 08 Feb 2015 - 11 Feb 2015
- Location: Kuwait City, Kuwait
- ISBN: 978-94-6282-113-2
- Published: 08 February 2015
1 - 20 of 25 results
-
-
Spatial Organization, Heterogeneity and Complexity of Triassic and Early Jurassic Deposystems of the Arabian Plate
By A.D. HorburyThe Triassic - Early Jurassic stratigraphy of the Arabian Plate is notably different to all underlying and overlying units. Several unique features include an often thick, very strongly vertically heterogeneous and often thin-bedded stratigraphy dominated by evaporites, restricted facies carbonates, and paralic siliciclastics. MFS are marked by open marine carbonates, and may be traced laterally across the plate. In general these record very low energy environments that are faunally impoverished; carbonates dominate intrabasinal and basin flank highs. Evaporites are concentrated in depocentres and are dominated by sulphates. Siliciclastics fringe the basin system. This is the least prospective of the post-Carboniferous units; sporadic carbonate reservoirs are usually thin, high-energy dolomitized oolites. Other reservoirs are thicker continental clastics. Source rocks have an evaporitic to locally lacustrine signature and yield generally light oils, but are mostly localised in depocentres where reservoir rocks are often lacking; whilst sealing evaporites are also often restricted to basinal areas whilst being absent on paleohighs. Future success within this stratigraphy will mainly depend upon our ability to predict the distribution and thicknesses of reservoir units within areas of reasonable burial depth; whilst the complex stratigraphy and regional thickness changes offer the possibility of locating stratigraphically trapped reserves.
-
-
-
Sequence Stratigraphic Framework, Depositional Environments and Reservoir Quality of the Triassic Jilh Formation, Eastern Saudi Arabia
More LessThe Middle to Upper Triassic Jilh Formation is a thick predominantly carbonate-evaporite succession extending across much of the central Arabian Basin in eastern Saudi Arabia. The Jilh Dolomite Member shows the best reservoir potential forming a 90-100 ft. thick blocky and laterally persistent unit in the upper part of the Jilh succession. It is dominated by very fine to medium grained fabric destructive dolomite originally deposited in lagoon to shoal settings following a period of transgressive flooding and backstepping of the depositional facies. Thinner beds of dolomite, anhydrite, shale and dolomitic limestones occur above and below the Jilh Dolomite suggesting deposition within restricted peritidal settings. Measured porosities in the Jilh Dolomite range from poor to excellent with permeabilities ranging from poor to very good. Macropores are dominated by relatively large mouldic/vuggy pores and finer intercrystal pores that show a complex patchy or non-uniform distribution. The origin of the pores is difficult to determine; some pores may be relicts of the precursor limestone, some may have formed during the dolomitisation process and some may postdate dolomitisation. The Jilh Dolomite was probably dolomitised during relatively early burial by descent of magnesium-rich fluids from overlying anhydrites. Growth zonation, seen mainly within euhedral dolomite rhombs closely associated with macropores, suggests multiple phases of dolomite precipitation. This has led to a significant loss of porosity within the Jilh Dolomite Member. In contrast, facies within the rest of the Jilh Formation are likely to have been dolomitised by seepage reflux due to their close association with laminated anhydrites. This type of dolomite tends to be fabric preserving.
-
-
-
A New Reference Section for the Lower to Middle Jurassic Southwest of Riyadh: Detailed Stratigraphic Architecture and Regional Correlation with the Subsurface of Saudi Arabia and Kuwait
Authors C.T. Reid, N. Hooker, W. Hughes, R. Lindsay, A. Dhubeeb, A. Al-Mojel, P. Breuer, A. Henderson and A. BakhietThe Marrat and Lower Dhruma formations were deposited during a period of transition between tectonic inversion and differential subsidence in the Late Triassic, followed by rifting of Gondwana in the early Middle Jurassic. This is reflected by a switch from predominantly fluvio-deltaic clastics of the Minjur Formation, to mixed carbonates and clastics of the Dhruma Formation, and the establishment of platform carbonates of the Tuwaiq Mountain Formation. Note that the Marrat and Dhruma formations were originally defined from field work in Saudi Arabia in the 1950s. These definitions differ from those currently used in the subsurface of Kuwait, where the Lower Dhruma of Saudi Arabia is called the “Upper Marrat.” This is a source of considerable confusion. Within an outcrop belt to the southwest of Riyadh, and within the subsurface of the Rub’ al-Khali Basin, the Marrat and Lower Dhruma formations consist of north-easterly prograding fluvio-deltaic sandstones, alternating with finer grained paralic to shallow marine sandstones, mottled red to purple pedogenic siltstones, dark lagoonal mudstones and sandy dolomitic limestones. Within the Eastern Province of Saudi Arabia, these formations consist of clean shelfal limestone, alternating with thin interbedded argillaceous lagoonal limestones.
-
-
-
Integrated Regional 3D Basin Modeling of Triassic and Jurassic Petroleum Systems, Northeastern Saudi Arabia: Implications for Exploration Potential
Authors R. Schmidt, D.Z. Tang, M. Hamed and A. BhullarThis assessment focuses on regional 3D basin modeling through integration of a stratigraphic framework, newly defined gross depositional environments (GDEs) and lithofacies maps of Triassic and Jurassic source rocks, reservoirs, and seals that were revealed by integrating seismic interpretations and geological and petrophysical mapping in northeastern Saudi Arabia. The Triassic Jilh and Minjur formations represent two separate third-order composite sequences, consisting of proven source rocks, reservoirs (e.g., Jilh Dolomite and Minjur Sandstone), and seals. The Lower Jurassic Marrat Formation and Middle Jurassic Dhruma Formation represent a third-order and a second-order composite sequence, respectively. Proven Dhruma source rocks (equivalent of Sargelu source rocks) and a variety of grainier carbonate reservoir rocks, spanning the Marrat, Faridah, Sharar, and Lower Fadhili reservoirs, were taken into account as inputs. Well-defined depth grids, derived from regional seismic and well-based mapping and integrated GDE/lithofacies maps of Triassic and Jurassic source rocks, reservoirs and seals, have been utilized for constraining this newly built 3D basin model. This integrated 3D basin modeling has resulted in significant insights for hydrocarbon migration and charge of the Triassic and Jurassic petroleum systems. The Triassic hydrocarbon accumulations are primarily self-sourcing from Jilh source rocks, with exceptions where hydrocarbons are charged from Paleozoic source rocks due to breaching at high-relief structures (e.g., Northeastern Arabian Offshore). The Dhruma source rocks (Sargelu equivalent) primarily charged a variety of Lower and Middle Jurassic reservoirs. Additionally, basin modeling results support insights on HC migration and charge for exploration concepts related to stratigraphic traps and new play fairways.
-
-
-
Sudair and Jihl Margin: Development of the Slope and Basinal Deposits in Oman During the Early-Middle Triassic
Authors S. Richoz, L. Krystyn and A. BaudIn Northeast Oman, outcrop equivalents of the Sudair Formation are present and described as Lower Mahil Member, around 250m thick. Its lower part is built mainly of shale, muddy dolomites, microbialite and oncoidal grainstones, whereas the upper part is mainly represented by grainstones. The stratigraphy is poorly constrained and then, mainly by chemostratigraphy. Here we present detailed sections from slope deposits in the Jabal Sumeini area (Wadi Maqam units) to distally tilted blocks (Ba’id), basinal carbonates (Wadi Wasit) and oceanic deep-water deposits (Buday’ah). We present here new result on the stratigraphy and the architecture of the Arabian Platform margin and its interpretation as a slope, oceanic plateau and basin succession, which provides new insights into the evolution of the coeval Sudair and Jihl platforms. It seems that the accumulation rate in the slope and basinal deposits depends on the carbonate export from the platform - high in Smithian and absent or very reduced in Spathian and Anisian time. This infers for the southeastern Arabian platform high carbonate productivity during the Smithian and very reduced during the Spathian and much of the Anisian.
-
-
-
The Triassic Sudair and Jilh Formations in Outcrops of the Oman Mountains
Authors M. Obermaier and T. AignerThe Triassic Middle and Upper Mahil Members in the Oman Mountains represent outcrop equivalents of the Sudair and Jilh Formations. This study focuses on sedimentologic descriptions, sequence stratigraphic interpretations and correlations of 8 outcrop sections around the area of al Jabal al-Akhdar in the Sultanate of Oman. In the Oman Mountains, the facies were deposited in a predominantly restricted inner ramp setting. In more central parts of the Arabian Plate, the Sudair and Jilh Formations are traditionally known to form important seals for hydrocarbon accumulations in underlying Permo-Triassic sequences. However, along the former basin margin, represented by the outcrops in the Oman Mountains, several potential reservoir units could be identified in the equivalent outcrop formations: Meter-thick oolitic/peloidal shoal grainstones in the Middle Mahil (Sudair equivalent) and intraclastic-rich peritidal grainstones in the Upper Mahil (Jilh equivalent) present new potential targets for future exploration. The cyclic nature of vertical facies changes is well reflected in the outcrop weathering profile permitting sequence stratigraphic interpretations in a hierarchical manner. In order to capture lateral facies and thickness variations within the sequence stratigraphic framework, various wall panels and correlations were constructed on small (meters) and large scale (hundreds of meters/kilometers) and integrated into a 3D facies model.
-
-
-
Seismic and Well Based Sequence Stratigraphy of the Triassic Jilh Formation in the Rub’ al-Khali Basin of Southern Saudi
Authors E. Al-Saqer, J. Afzal, M. Hashim and A. BhullarSeveral efforts have appeared in the last decade to unravel the eustatic control of, and propose sequence stratigraphic models for, the Arabian Plate. These efforts were made because the distribution of reservoir facies and potential stratigraphic trapping mechanisms are mainly controlled by eustacy, which has implications for flow units and hydrocarbon migration along the chronostratigraphic layers. The published work is predominantly based on well and outcrop data. We are trying to explore reservoir levels primarily based on seismic stratigraphy (picking the discontinuities in reflection geometries) and integrating with well data to establish a sequence stratigraphic framework, with an additional intent to identify viable stratigraphic potential. Our primary dataset consists of extensive regional 2D seismic coverage controlled by Triassic well penetrations in the Rub’ al-Khali Basin of southern Saudi Arabia. At the basin scale, this task is highly challenging due to the limited number of wells, poor seismic data quality, scarce biostratigraphic data and, in some cases, uncertainties in the well tops. In central Saudi Arabia, a proven reservoir interval lies within carbonates of the Middle to Late Triassic (Anisian-Norian) Jilh Formation and its time equivalent rock units in the surrounding regions. Substantial oil/gas shows from this formation in the Rub’ al-Khali Basin qualifies its revision in greater stratigraphic detail. The Jilh Formation is a complete petroleum system having reservoir facies (predominantly dolomite, limestone and sandstone), source (interbedded shale layers) and seal (shales and evaporites). A number of EW and NS oriented seismic transects were constructed for consistent interpretation by picking various surfaces (SB, MRS and MFS) to delineate system tracts. Based on this interpretation, Jilh strata is genetically divisible into four third order sequences. A rigorous effort is made to establish a reliable chronostratigraphic framework based on a consistent relationship between seismic and well data (logs and core/cutting) to understand vertical and lateral distribution of rock facies. Several maps (TWT, isochron, etc.) are prepared and integrated with seismic geometries and well data to delineate gross depositional environment (GDE) maps. This study shows that there are opportunities for maturing stratigraphically trapped hydrocarbon accumulations.
-
-
-
Carbonate Factory Evolution and Carbon Isotope Stratigraphy Across the T-J Boundary from the Musandam Peninsula (UAE)
By M.R. HoenigTriassic and Jurassic carbonates across the Middle East host large amounts of hydrocarbons and might serve as reservoirs for CO2 storage in the future. The Triassic-Jurassic transition was marked by global changes, including carbon-cycle perturbations and the opening of the Atlantic Ocean. These changes were accompanied by one of the major extinction events of the Phanerozoic. In this study we investigate the evolution of a carbonate ramp across the Triassic-Jurassic boundary on the Musandam Peninsula in a series of wadis approximately 35 km apart (Wadis Naqab, Ghalilah and Al-Ghabbah) in the United Arab Emirates. In the proximal part of the ramp the Triassic benthic carbonate factory dominated by automicrite and microbialites was replaced by an ooidal-bioclastic ramp during the Jurassic. In the more distal part of the ramp, microbialites with abundant siliciclastic detritus are overlain by muddy carbonates with few oolites. The very abundant clastic components are being sourced most likely from the Arabian Craton. The change in the carbonate factory across the Triassic Jurassic transition, especially evident in the proximal part of the studied carbonate ramp is the result of an important change in palaeoenvironmental conditions. The carbon-cycle perturbations across the Triassic-Jurassic boundary have been recorded in carbon isotope curves from bulk carbonates, organic carbon and fossil wood in several Tethyan locations and have been used for chemostratigraphic purposes. Our site was located at the equator and on the southeastern margin of the Tethys throughout the Late Triassic and the Early Jurassic, and this study provides the first constraints of environmental changes at the low-latitudes for the Triassic-Jurassic boundary. Our stable isotope results on micrite show a prominent negative shift in carbon isotope values of approximately 2 ‰ just below the inferred position of the Triassic-Jurassic boundary. A similar isotopic trend is also observed across the Tethys with amplitudes ranging from ~2 ‰ to ~4 ‰. These results seem to indicate that the neritic carbonates from our studied section can be used for chemostratigraphic purposes. We gratefully acknowledge funding from Qatar Petroleum, Shell and Qatar Science & Technology Park.
-
-
-
Sedimentology and Diagenetic History with Reference to Reservoir Quality, Triassic Lower Jilh (Kra Al Maru), Kuwait
By D. A. KhanThe name Kra Al Maru has been assigned to the additional unit at the lowermost part of the Middle Triassic Jilh Formation in Mutriba and Kra Al-Maru area in western Kuwait. Stratigraphically the interval corresponds to the Jilh C Member of Jilh Formation, and it is divisible into a lower (KM-B) and an upper (KM-A) unit. Microfacies comprises anhydrite, dolomudstone, dolowackestone, argillaceous dolostone and dolomitic shales with minor dolopackstone, dolograinstone, lime mudstone, lime wackestone. Carbonaceous matter and terrigenous material is present at places. Anhydrite is present as early nodules and crystals, as well as late cement and vug fillings. Facies associations of both units are bioturbated, highly variable with common organic matters. The distinguishing feature of the lower unit (KM-B) is having less anhydrite than the upper unit (KM-A). The lower unit was deposited in intertidal to subtidal and lagoonal environments, as a shallowing upward sequence that grade upward to algal laminated wackestone and anhydrite. The presence of few sub-aerial exposure surfaces indicate dissolution that might have developed at the end of cycle and are indicative of slightly humid conditions. The upper unit was deposited in an intertidal to supratidal, Sabkha environments under arid climate. Diagenetic events include compaction, dolomitization, and replacement by anhydrite, fracturing and stylolization. Primary porosities were reduced by compaction, overdolomitisation and late stage cementation. Both cemented and uncemented fractures are observed in the core and microfractures are seen in core plugs and have led to increased fracture porosity and permeability. The Lower unit is ranked and pursued as new prospective units within the Jilh Formation.
-
-
-
Depositional Nature of the Triassic Jilh Lower Carbonates: A Proven Hydrocarbon Play in West Kuwait Area
Authors R.T. Arasu, B.V. Rama Rao, S. Das and R.I.A. Abu-TalebJilh carbonate succession represents Middle to Late Triassic stratigraphy in Kuwait. It is deposited in shallow marine inner ramp and restricted settings. Three major lithofacies units are recognized based on well data: Jilh Lower Carbonates which is overlying the Early Triassic Sudair Formation, Jilh Dolomite in the middle and Jilh Upper Carbonates. A thin salt layer, near absent at places, separates the bottom unit from the upper ones. The entire sequence from top to bottom is characterized by numerous thin anhydrite layers, exhibiting prevalence of arid climate. Whereas Jilh Dolomite and Upper Carbonate sequences are regionally consistent with near uniform thickness, the bottom unit occurs with highly varying thickness ranging from 300’ to 800’. Increase in thickness is seen mainly in the western parts of Kuwait where it is also referred to as ‘Kra AlMaru’ Unit. It comprises mainly dolowackestone and dolomudstones. Good amount oil and gas flowed from these reservoirs during initial testing in a couple of wells. Therefore, the depositional pattern may be interesting from the oil exploration point of view.
-
-
-
The Geology of the Middle Jurassic Dhruma Formation in Outcrops of the Oman Mountains (Sultanate of Oman)
Authors M. Schlaich and T. AignerIn outcrops of the Oman Mountains the Sahtan Group consists of the Early to Middle Jurassic Mafraq Formation and the Middle Jurassic Dhruma Formation. It is unconformably overlain by the Early Cretaceous Rayda Formation. Within an outcrop analog study, the Dhruma Formation was logged in several wadi sections of the central Oman Mountains, supplemented by spectral gamma-ray measurements and thin section analyses. A sequence stratigraphic framework and 2D correlations were established. In the type section in Wadi Sahtan, the Dhruma has a thickness of about 240 meters. Twelve facies types can be distinguished ranging from mud- to grainstones. They can be grouped into four lithofacies associations, representing depositional environments on a carbonate ramp. Environments range from a low-energy, mud-dominated lagoon to a high-energy, peloid and ooid dominated environment. While the lower part of the Dhruma is dominated by lagoonal mud- and wackestones, more and more peloidal and oolitic pack- and grainstones, approaching the high-energy environment, can be found towards the top. The Dhruma shows a pronounced cyclicity, recognizable in systematic, vertical lithofacies changes and characteristic gamma-ray patterns. The largest scale of cyclicity is tens of meters thick and can be correlated over a distance of 25 km between the studied sections.
-
-
-
Sequence Stratigraphic Framework and Exploration Potential of the Middle Jurassic Dhruma Formation, Eastern Saudi Arabia
Authors D.Z. Tang, W. Tan, R. Schmidt and A. BakhietThe Middle Jurassic Dhruma Formation is of Bajocian-Bathonian age, and represents a composite second-order sequence in Saudi Arabia. An integration of well log correlations, 3D seismic interpretations, and sedimentological studies has been undertaken to unravel the sequence stratigraphic framework. The Lower Dhruma Member is interpreted as a transgressive systems tract, with the maximum shale content of the “Dhruma Shale” representing the maximum flooding surface (MFS) of the second-order Dhruma sequence. The highstand systems tract of this second-order sequence consists of an overall shallowing-up interval comprising the Faridah, Sharar and Lower Fadhili members, with each member representing a third-order composite sequence. The Faridah grainy carbonate reservoirs that were deposited in the highstand systems tract of the third-order Faridah sequence can be subdivided into the following fourth-order sequences: Lower-, Middle- and Upper-Faridah subunits. The grainier facies of the Faridah highstand changes laterally to muddy limestone and organic-rich mudstone facies (Sargelu-equivalent source rocks) in basinal areas. The top of the Faridah sequence represents a subaerial exposure surface across most of the Arabian carbonate platform, in response to a significant base-level fall. The Sharar third-order sequence comprises a basal lowstand wedge (reworked sediments from carbonate shoaling complexes), transgressive deposits with muddy facies and possible organic-rich facies in the distal and basinal setting; and also a highstand grainy reservoir facies. The third-order Lower Fadhili sequence is dominated by widespread grainier carbonate facies, indicating infilling of most of the accommodation space. The top of the Dhruma Formation (i.e., the top of the Lower Fadhili Member) represents a significant subaerial exposure surface (hiatus). Gross depositional environment (GDE) maps of the Dhruma Formation have been reconstructed by integrating core/drill cutting sedimentology, well log electrofacies, and seismic attributes. These GDE maps depict evolving depositional environments that span the Faridah, Sharar and Lower Fadhili third-order sequences. A variety of new exploration opportunities have emerged through building a robust stratigraphic framework and reconstruction of gross depositional environments, and detailed play fairway mapping.
-
-
-
Decrypting Carbonate Complexity: Key for Effective Exploration of Middle Marrat in Kuwait
Authors R. Husain, S.M. Ahmed, R. Mulyono, A. Prakash, G. Gega and D. DjanawirMarrat Formation of Toarcian age is one of the major reservoirs in Kuwait. Middle unit of the formation, the Middle Marrat, has the greatest reservoir potential and is commercially producing in many areas scattered over the country. Available biodata indicate that the Middle Marrat is probably early Toarcian to possibly middle Toarcian in age, with the likelihood of a moderate duration hiatus at the top, resulting in the absence of late Toarcian and possibly part of the middle Toarcian. The unit is dominantly composed of limestone with sub-ordinate dolomite and anhydrite. The carbonate microfacies consist of mudstone, wackestone, packstone to grainstone with occasional algal boundstone. Reservoir quality ranges from nil in lime mudstone facies to very good in the oolitic grainstones. These grainstones contain moderately well interconnected interparticle porosity. Sourced by the Najmah Shales, grain-prone facies developed in different sequences of the unit in structurally favourable locales provide the avenues for the hydrocarbon accumulations. The reservoirs are capped by thin intraformational anhydrites. Key for successful exploration lies in developing a predictive facies model for pinpointing areas of reservoir development. In a synergistic approach employing core, log and seismic data, high-resolution sequence stratigraphic studies have been carried out. The Middle Marrat represents a third order sequence comprising a total of eight high resolution transgressive and regressive cycles. Core data has been utilized for understanding of gross depositional patterns of individual sequences. Country-wide isopach maps of the depositional sequences were calibrated with lithofacies data deciphered from the cores to prepare paleogeographic maps. The gross depositional environments cover an entire spectrum of environments of a typical carbonate ramp ranging from sabkha, tidal flats, lagoon, barrier / shoal, outer ramp to basin. Mostly, the transgressive systems tracts are represented by muddier facies. Coarser facies with well-developed interparticle porosity preferentially occur in highstand systems tracts corresponding to the progradation of the clinoforms sloping towards the basin. Successively younger sequences show gradual basinward shift of the facies belts in an overall regressive phase. Basinward shift of potential reservoir facies can be linked to shift in prospective locales and provide a predictive tool for identification of prospective areas for future exploration.
-
-
-
Complex Carbonate Evaporite Reservoir Description Using Isotope Geo-chemistry and Ichno-facies to Fine-tune a High Resolution Sequence Stratigraphic Framework Model of Marrat Reservoirs
Authors N. Neog, N.S. Rao, A. Al. Darmi, M.Y.M. Al.Dousiri, T. De Keyser and C.G.S.C. KendallField development in complex carbonate evaporite reservoirs has been a challenge for geoscientists by using simple sedimentology based geological models. A high resolution sequence stratigraphic framework has been designed from a conceptual 3D depositional model to a deterministic predictable model. In this process framework boundaries have been fine-tuned with carbon and oxygen isotope signals and defining ichno-facies associations to map lateral continuity of member formations within Marrat sequence. As dolomites and porous grain stones are the key reservoir quality rock types for Marrat Group of formations, position of precursor lithofacies in sequence stratigraphic frame work is found to be crucial. Dolomite samples are analyzed for d13C and d18O. Upper and Lower Marrat members are characterized by thinly laminated, micro crystalline exposure dolomites and high in d18O signal which are associated to low stand packages, whereas Middle Marrat dolomites are relatively low in d18O and high in d13C are associated to high stand precursor facies. Moreover, typical ichnofacies association of porous dolomites defines vertical and lateral connectivity of flow zones in Middle Marrat reservoirs. The reliability of this model has been established through recent tested intervals, with PLT and MDT data integration demonstrates predictability of flow zone connectivity.
-
-
-
Classification and Environmental Distribution of Microbial Lithofacies: A Key Reservoir Description Tool
Authors N. Neog, T.L. De Keyser, N.S. Rao and M.Y.M. Al DousiriMost of the fossil and sedimentary structures that have been referred to as algal, cryptalgal, or cyanobacterial can now be grouped under the term microbial and are understood to have formed through the activities of this diverse group of prokaryotic organisms. Such photosynthetic biota, by removing CO2 from marine waters, induce the precipitation of carbonate minerals. Microbial lithofacies are extremely common in the mid-Mesozoid Toarcian Series, occurring in many different forms and along nearly all of the depositional profile, down to the base of the photic zone. They may also be transported farther basinward, into slope and basinal environments. Several authors have suggested classifications of microbial fossil forms. Virtually all of these forms can be recognized within the Toarcian of the Arabian Plate. Long cored intervals in more than 40 wells provide complete coverage of the calciclastic shelf depositional profile from tidal flats to at least outer shelf. Microbial forms are particularly abundant in most wells and provide the basis for a morphological classification based on this model. The subdivisions of this morphological classification are described and illustrated in this paper. Their distribution along the depositional profile is summarized, based on lithofacies, interpreted depositional environment, and ichnofacies data.
-
-
-
The Faridah Unit of Central and Northeast Saudi Arabia: Stratigraphy and Depositional Setting
More LessThis core- and log-based analysis provides a depositional and stratigraphic synthesis of the Faridah compartment in the area. It brings together data from a number of cored wells, totaling 1950 feet in length. These wells are located in the onshore and adjacent coastal waters. The Middle Jurassic Dhruma Formation is stratigraphically positioned between the Tuwaiq Mountain and Marrat formations, respectively, and consists predominantly of carbonates and a minor amount of shale. The formation has been subdivided into six members; D1-D6, with D-4 containing the Farida layers. The type section of the Faridah in the study area is the FRDH-A well, where the upper part of the section comprises four stacked and distinct layers, termed the Faridah-D, -C, -B and -A, in ascending stratigraphic order. The grainy-rich layers are considered to represent the upper part of the Middle Dhruma D4 Member. The sedimentologic analysis and lithologic breakdown of the Faridah sediments resulted in the identification of twelve primary lithofacies. These are designated LF1 to LF12 in broadly shallowing upward order. The lateral lithofacies distribution suggests that environments of deposition are in line with platform interior to shelf margin to basin. The stratigraphic architecture and facies stacking patterns suggest that the Faridah spans parts of at least two long-term depositional sequences, together forming a large-scale northward-prograding and thinning shelf-margin succession. This thinning trend is accompanied by a gross change in depositional facies, from (a) thick platform-top peloid-oncoid packstone and grainstone, to (b) shelf-edge micro-gravels, coral boundstones and slumped foreslope facies, to (c) thin bituminous basin-floor laminites in the northern parts. The Dhruma D4 stacking patterns comprise four correlatable high-frequency depositional cycles (Faridah D-A layers), representing a mid- to late-highstand systems tract that is genetically-linked to the underlying Dhruma D3 TST and early HST. These four cycles progressively thin basin-ward, and their correlatability becomes insecured and less distinguishable. The best quality rocks recorded in the area are associated with the Faridah shelf-margin grainstone facies at Faridah, Ash Shihiyah and southern Juraybi’at areas, with excellent porosities and fair to good permeabilities. The northward transition from clean porous shelf-edge facies to tight basin-floor laminites occurs over a distance of just a few tens of kilometers, and provides opportunities for stratigraphic trapping in the area.
-
-
-
Reservoir and Seal Potential of the Mixed Carbonate-Siliciclastic Mafraq Fm.,Oman: An Integrated Outcrop Analogue Study
Authors D. Bendias, T. Aigner and M. SchlaichThe mixed carbonate siliciclastic Early to Middle Jurassic Mafraq Formation unconformably overlies the Triassic strata in North Oman. Together with the overlying Dhruma Formation, it is part of the Sahtan Group. This study provides: (1) a detailed facies analysis based on sedimentological logging of 12 outcrops. 24 facies types were established and grouped into 5 facies associations which can also be recognized in subsurface core intervals. (2) a detailed sequence stratigraphic framework of the Mafraq Fm. Facies stacking and log patterns reveal cycle hierarchies on four scales from meter-scale cycles, to several meter thick cycle sets, to tens of meter thick high-frequency sequences, to 100 meter thick composite sequences. (3) facies analysis and correlation of the subsurface Mafraq Fm. based on cuttings, cores, well-log and seismic data. (3) a documentation of potential reservoir and seal units of the Mafraq Fm. in North Oman
-
-
-
Digital Outcrop Modeling of Minjur, Marrat and Dhurma Formations: Integrating Sedimentology, Stratigraphy and LiDAR data
Authors M. Osman, O. Abdullatif and M. YassinDigital outcrop models provide important high resolution and quantitative sedimentological data unavailable or difficult to be obtained from the subsurface formations. The Jurassic succession contains several important reservoirs that have excellently exposed stratigraphically equivalent units in central Saudi Arabia. This study provides an outcrop-based case study dealing with Late Triassic to the Middle Jurassic of Minjur, Marrat and Dhurma formations. The study was carried on selected outcrops around Riyadh in central Saudi Arabia. The main objective of the study is to investigate the sedimentological heterogeneity, establish the stratigraphic hierarchy and the reservoir zonation and eventually to build up digital outcrop model. The study was based on sedimentological field observations, Gamma Ray measurements, terrestrial laser scanning or LiDAR data and laboratory analysis. The products of this study are high resolution digital outcrop models for these formations. This final integrated model was capable to reveal detailed description of the sedimentology, the stratigraphic hierarchy, the spatial stacking pattern, distribution of the lithofacies and cyclicity within each formation. The model also helped to characterize and correlate the reservoir and the non-reservoir units and to reveal types of depositional heterogeneity and their lateral continuity and architecture. The models might contribute to understand and reveal micro to macro inter-well sedimentology and heterogeneity and help to and resolve any related uncertainties. The final digital models could act as a geological database and if integrated with subsurface data would enhance our understanding and prediction for the reservoir quality and architecture of these formations.
-
-
-
Use of High Resolution Sedimentological Tools for Core Lithofacies identification and their Grouping of Association
Authors N. Neog, T.L. De Keyser, N.S. Rao and R. Al MayyasDetailed sedimentological core description manifests the heterogeneity in lithofacies distribution and reservoir quality characterization in a complex carbonate-evaporite succession. To produce such detailed core drafts, in addition to routine sedimentogical tools and protocols, polished core slab high-resolution scans have been used to identify surfaces, hardgrounds, ichnotraces and microbial assemblages. A standard lithofacies catalogue has been prepared to guide intrawell facies interpretation and interwell interpolation to build a composite sequence stratigraphic model. 26 core-based lithofacies have been identified and grouped in to 10 depositional facies associations along a depositional profile varying from ramp to calciclastic shelf-setting in an intra-shelf basin with limited syndepositional tectonic relicts. Approximately 15000 ft of core slabs from 75 wells have been processed and interpreted to build profile relays showing changing position along the depositional profile and interpreted vertical stacking pattern. This work flow proves to be a best practice in reservoir modeling where framework- building and distribution of precursor facies between sequence-bounding surfaces is the key for successful field development and reservoir management.
-
-
-
Successful Placement and Testing of a Horizontal Well in an Ultra-thin Mafraq Reservoirs in the Sultanate of Oman
By J. BildsteinThis paper describes the planning, execution, data acquisition and successful completion & well test of a horizontal well into a ultra thin Mafraq carbonate reservoir in the north of Oman. The reservoir spreads laterally like a blanket. Five vertical well tests into the same reservoir had a production range from 0.05 to 0.5 MMm3/d. This range could not be explained. A horizontal well was the only way to access the volume. The learning from a unique outcrop analogue and the vertical appraisal wells have been used to place a successful horizontal well with a stable production at a rate which succeeded the expectations. The key to the success was the integration of all disciplines during the planning and real time monitoring during the execution phase. Without constant interaction and challenging between the disciplines, this would not have been possible. Special core test for stimulation planning, newest LWD tools for steering and formation evaluation are the key novel technologies.
-