bluuebunny/crossref_metadata_2025 huggingface dataset:
Inovando no Desenvolvimento de Profissionais da Gestão Pública: O Caso do Programa de Desenvolvimento de Lideranças da Escola Nacional de Administração Pública – Enap
Authors: Barzelay Michael , Martins Humberto Falcão , Vilela Pedro , Marques Paulo
Published: October 2021

Este trabalho trata de uma nova abordagem, na forma e no conteúdo, de desenvolver a prática profissional de gestores públicos orientada por design, elaborada pelo prof. Michael Barzelay, objeto de seu último livro “Public management as a design-oriented professional discipline” (2019). Relata a forma como esta abordagem foi colocada em prática na Escola Nacional de Administração Pública (ENAP) do Governo Federal do Brasil entre 2016 e 2019 e os resultados positivos decorrentes para os participantes. Foi possível comparar os efeitos da abordagem nas turmas que a adoraram com os das turmas que não a adotaram. Uma avaliação econométrica e qualitativa do programa revelou efeitos positivos da abordagem relacionados à transferência de aprendizados, capacidade de estruturar problemas complexos e desenvolvimento de soluções colaborativas.
Gestão Pública no Brasil, Conquistas Recentes e Dilemas Presentes
Authors: Levy Evelyn
Published: October 2021

Pensata escrita pela Prof. Evelyn Levy, coeditora da edição especial da APGS com a SBAP.
Degradation of Reservoir Quality by Clay Content, Unayzah Formation, Central Saudi Arabia
Authors: Polkowski George R.
Published: October 2021

Reservoirs in Central Saudi Arabia are important new sources of light sulfur-free crude oil. Development work on these wells has shown the adverse effect of authigenic clay minerals on their productivity or injectivity. The clay minerals may be affected during drilling of the well, during completion, during production, and/or injection. Kaolinite, chlorite, illite, and ordered and random mixed layer illite/smectite are commonly occurring authigenic clay minerals within the Permian Unayzah reservoir rock. As little as 2 weight percent clay causes permeability to be drastically reduced. Formation damage due to clay minerals results from: (1) swelling of smectite caused by injection water or drilling fluids of low salinity; (2) clay mineral migration and subsequent pore blockage; (3) precipitation of gelatinous pore-blocking iron hydroxides caused by the dissolution of chlorite by acid; (4) high water saturations; and (5) disaggregation of poorly consolidated parts of the reservoir into its component sand grains if the weak clay cements are disturbed. The implementation of clay control measures has resulted in increased production while minimizing formation damage.
Thermal History of the Lower and Middle Cretaceous Source Rocks in Kuwait
Authors: Abdullah Fowzia H.A. , Nederlof Peter J.R. , Ormerod Mark P. , Kinghorn Robert R.F.
Published: October 2021

The thermal history of Kuwait was reconstructed with Shell’s “Cauldron” basin modeling software and calibrated with maturity indicators from four wells. Maturity measurements were carried out on source rock samples from wells in the Ash-Shaham, Minagish, Raudhatain and Riqua (offshore) fields. The analytical data indicate that ‘top oil window’ is located at a depth of around 2,500 meters (8,250 feet). Due to the low structural dips of the sequences in Kuwait, thermal modeling in one-dimension was found to be adequate. The Cretaceous source rocks subsided without major anomalies in burial rate or heatflow. Modeling results indicate that the Cretaceous Sulaiy, Minagish and Zubair formations entered the oil window during the Late Cretaceous and Early Tertiary, whereas oil expulsion occurred throughout Tertiary time. Quantification of expelled oil volumes suggests that the Sulaiy Formation is the most productive source rock in Kuwait, whereas the Upper Cretaceous Burgan and Maudud formations are presently at the top of the oil window.
Recent Developments in 3-D Acquisition Techniques in Oman
Authors: Wams Jan , Rozemond Justus
Published: October 2021

Acquisition of 3-D seismic surveys in Oman commenced in earnest in 1987 and has been continuous until today. Improvements in data acquisition have been made over the years, be it in small steps and based on similar geometries. A study was carried out to try to further improve data quality and/or efficiency. Two alternative acquisition techniques, ‘wide-line’ and ‘slip-sweep’, were identified and have been the subject of field tests. The results indicate that efficiency of vibroseis seismic acquisition can be substantially increased without, as far as the limited tests indicate, an appreciable impact on quality.
Pleistocene Carbonate Seif Dunes and their Role in the Development of Complex Past and Present Coastlines of the U.A.E.
Authors: Kirkham Anthony
Published: October 2021

Isolated outcrops of Pleistocene carbonate aeolianites and their cappings of shallow water Pleistocene marine limestones are described largely from Al Dabb’iya on the eastern end of the Great Pearl Bank, Abu Dhabi. Their sedimentological characteristics and depositional settings are discussed in relation to mainland Pleistocene aeolianite trends observed from satellite images. A comparison of the internal dune cross-bedding with dune morphologies suggests changing wind regimes that probably resulted from meteorological changes induced by the onset of a Pleistocene glacial period. The complex palaeo-geomorphology imposed by the dunes strongly influenced later Pleistocene coastal marine sedimentation that was concentrated in a series of shallow embayments separated by low-relief seif dunes forming peninsulas. Similar marine settings extended into the Holocene along parts of the United Arab Emirates coastline and still persist locally.
Paleozoic Stratigraphy and Petroleum Systems of the Western and Southwestern Deserts of Iraq
Authors: Aqrawi Adnan A.M.
Published: October 2021

A stratigraphic scheme for the Paleozoic of the Southwestern Desert of Iraq is proposed based upon the review of recently published data from several deep wells in the western part of the country and from outcrops in other regions in Iraq. The main formations are described in terms of facies distribution, probable age, regional thickness, and correlations with the well-reported Paleozoic successions of the adjacent countries (e.g. Jordan and Saudi Arabia), as well as with the Thrust Zone of North Iraq. The Paleozoic depositional and tectonic evolution of the Western and Southwestern Deserts of Iraq, particularly during Cambrian, Ordovician and Silurian, shows marked similarity to those of eastern Jordan and northern Saudi Arabia. However, local lithological variations, which are due to Late Paleozoic Hercynian tectonics, characterize the Upper Paleozoic sequences.

The Lower Silurian marine “hot” shale, 65 meters thick in the Akkas-1 well in the Western Desert, is believed to be the main Paleozoic source rock in the Western and Southwestern Deserts. Additional potential source rocks in this region could be the black shales of the Ordovician Khabour Formation, the Upper Devonian to Lower Carboniferous Ora Shale Formation, and the lower shaly beds of the Upper Permian Chia Zairi Formation. The main target reservoirs are of Ordovician, Silurian, Carboniferous and Permian ages. Similar reservoirs have recently been reported for the Western Desert of Iraq, eastern Jordan and northern Saudi Arabia. In addition, two main regional seals (Lower Silurian shales and Permian evaporites) of northeastern Arabia extend over most of the Southwestern Desert, together with several other local seals. These considerations render the unexplored Paleozoic Southwestern Desert of Iraq prospective.
Sequence Stratigraphy of the Arab A to C Members and Hith Formation, Offshore Abu Dhabi
Authors: Azer Samir R. , Peebles Ross G.
Published: October 2021

The Upper Jurassic Hith Formation and Arab members A, B and C, in central and western offshore Abu Dhabi, consist of 450 to over 600 feet of massive to interbedded anhydrites with varying proportions of limestones and dolomites. A high resolution sequence stratigraphic framework for this important petroleum reservoir interval was developed from core and well log data, and various inorganic geochemical analyses. This data was acquired from wells located at 3 locations spread over 100 kilometers. Nineteen shallowing-upward parasequences, corresponding to fourth and possibly fifth-order cycles, were recognized for the Arab members as follows: A (7 cycles), B (5 cycles), and C (7 cycles). Five parasequences were recognized for the Hith Anhydrite Formation.

The Arab parasequences are arranged in a layer-cake stacking pattern and vary in thickness from 6 to 30 feet. These are interpreted to correspond to transgressive-regressive episodes which are driven by low-amplitude sea-level fluctuations (eustacy). The typical parasequence consists of shoal grainstones, representing transgressive system tracts, that pass upward into thin-bedded lagoonal burrowed mud/wackestones, representing the maximum flooding surface. These are overlain by coarse bioclastic grainstones capped by algal laminites and culminate into supratidal anhydrites, which pinchout eastwards. In the west offshore Abu Dhabi the parasequences are thicker and consist of intertidal pack/grainstones overlain by anhydrites.
FORWARD MODELING OF SEQUENCE STRATIGRAPHY AND DIAGENESIS: Application to Rapid, Cost-Effective Carbonate Reservoir Characterization
Authors: Matthews Robley K. , Frohlich Cliff
Published: October 2021

Dynamic forward modeling of carbonate reservoir sequence stratigraphy and diagenetic overprint can yield rapid, cost-effective reservoir characterization. The common practice in reservoir characterization now relies heavily on massive data accumulation and geostatistics to produce the three-dimensional geocellular static model which is the basis for flow simulation. In dynamic forward modeling, reliance on understanding of geological process allows high resolution prediction of the geometry of permeable and impermeable units and horizons within the reservoir. Data requirements are reduced to state-of-the-art information on a relatively small number of control wells which constrain and calibrate the forward model. Sensitivity-testing among formally-stated competing concepts is encouraged. In the long-term, it is the accurate prediction of reservoir response to future production that will afford choice among competing static models and flow simulations. The goal should be to predict future problems and avoid them, rather than wait to observe problems and react to them.
Surface Geology of Jebel Rawdah, Oman Mountains
Authors: Sayed M.G. Salah Abou , Mersal Mohamed A.
Published: October 2021

Jebel Rawdah is a west-northwest to east-southeast trending, post-obduction fold located at the western edge of the Hatta Zone of the Northern Oman Mountains. The main syncline plunges about 5 kilometers to the northwest and it is flanked to the west by a minor anticline. The outcrops in the area consist of: (1) allochthonous Semail Ophiolite, consisting of slices of oceanic crust and upper mantle, together with the Haybi Complex of volcanic rocks and associated metamorphics; (2) the parautochthonous Sumeini Group consisting of shelf edge and slope carbonates and clastics; and (3) the post-obduction neoautochthonous clastics and carbonates of the Qahlah, Simsima and Muthaymimah formations (Maastrichtian to Early Tertiary).

Two stages of folding were detected in the Jebel Rawdah area. The older folds affect the allochthonous rocks and result from shearing deformation along the westward extension of the Hatta Zone. The younger deformation is manifested in drape folds in the neoautochthonous rocks which was caused by differential vertical movements of fault blocks in the underlying allochthonous rocks. Three sets of faults were observed: (1) northwest-southeast trending vertical to steeply-dipping scissor faults; (b) reverse faults which form flower structures; and (c) northeast-southwest trending normal faults.

Field observations, biostratigraphic studies and petrographic examination suggest three stages in the development of the stratigraphic units in Jebel Rawdah. The first stage occurred during the Early Maastrichtian when the Oman Mountains emerged and were subsequently exposed to subaerial erosion. In the second stage a transgression occurred during the gradual subsidence of the area which led to the deposition of the Qahlah Formation in a fluviatile to shallow-marine environment, and the overlying Simsima in a shallow shelf setting. In the final Tertiary stage the Muthaymimah Formation was deposited in a subsiding basin and slope setting.
Generation and Retention of Hydrocarbon in the Haushi Play, North Oman
Authors: Richard Pascal D. , Nederlof Peter J.R. , Terken Jos M.J. , Al-Ruwehy Nashwa
Published: October 2021

In North Oman, 20 fields, with a combined oil-in-place of 500 million cubic meters (3,145 million barrels), have reserves booked in the Permian-Carboniferous Haushi (Gharif and Al-Khlata formations) reservoirs. In addition, some 150 prospects are recognized with a combined ultimate recoverable reserves expectation of 39 million cubic meters (245 million barrels). Following a successful exploration campaign, the success ratio decreased progressively. An integrated charge and retention study was therefore carried out to revitalize the play. The aim of this study was to establish a framework for predicting fluid content (gas, oil, and water). Components of this framework were a charge study to explain the hydrocarbon distribution on a basin scale and a retention study addressing top and fault seal quality.

The oil in the Haushi has been generated by three different source rocks: ‘Q’, Huqf Group (Shuram Formation) and Haima Group (Safiq Formation). However, oil-typing shows that over 90% of the oil-in-place is derived from the ‘Q’ source rock. This seems to indicate a charge problem for prospects outside the ‘Q’ migration fairways. The ‘Q’ kitchen was defined with the help of chemical odometers (nitrogen compounds whose relative concentrations provide a measure of migration distance). Measurements on 18 ‘Q’ oils suggest a source area on the western margin of the Ghaba Salt Basin, immediately to the east of Ramlat Rawl and Saih Rawl. Seismic lines across this area show salt-filled rim synclines, which possibly contain the ‘Q’ source beds.

The two main sealing lithologies are carbonate (Khuff and Haushi limestone) and shale (intra-Haushi shales), which can act as both top seal and/or fault seal. Based on log response, seal lithologies for gas-only, gas-and-oil and oil-only could not be discriminated. Recent mud logs over the Khuff Formation (top seal of the Gharif reservoirs) showed no evidence for a gas fraction, suggesting that the Khuff is an efficient gas seal. However, it has been observed that gas fields tend to have a thicker Khuff seal and smaller fault throw than the oil fields. This trend is related to the regional westward tilting of the basin during Khuff deposition. Fault seal has been analyzed on across-fault juxtaposition diagrams.

Highly-faulted prospects, above salt domes, are water-bearing. However, apart from these extreme cases, seal breaching is not seen as a general problem. Sand-sand juxtaposition areas along faults were calculated in several Gharif accumulations. Although cross-fault juxtaposition was identified as the critical factor determining the hydrocarbon contacts in some moderately faulted fields (e.g. Burhaan), there seems to be no general relation between hydrocarbon fill and Khuff thickness. An opportunity map was generated for North Oman. A strategy for exploring for stratigraphic traps in the ‘Q’ migration fairways is believed to have the greatest chance of success.
Microporosity in Arab Formation Carbonates, Saudi Arabia
Authors: Cantrell Dave L. , Hagerty Royal M.
Published: October 2021

Microporosity occurs throughout Arab Formation carbonates of Saudi Arabia, and affects the log response, fluid flow properties and ultimate recovery of hydrocarbons in these reservoirs. Qualitative examination of Arab samples indicates that microporosity occurs as four major types: (1) microporous grains, (2) microporous matrix, (3) microporous fibrous to bladed cements, and (4) microporous equant cements. Quantitative estimation of microporosity abundance was measured in two ways: (1) thin section point counts, and (2) pore throat size distributions derived from capillary pressure data. Point count data shows that microporosity can vary widely from sample to sample, ranging from 0% to 100% of the total measured porosity of a sample. Capillary pressure data confirms the volumetric significance of pore throats that are 10 microns or less in size. Variations in microporosity abundance and type appear to be controlled by depositional texture, grain mineralogy and grain microstructure. We suggest that microporosity in Arab Formation carbonates formed diagenetically, via three mechanisms: (1) leaching and incomplete reprecipitation of metastable carbonate, (2) crystal growth contact inhibition, and (3) (locally) endolithic borings of grains.
Best Practices in 3-D Land Seismic Acquisition in the Middle East and North Africa: Cost-Effective Acquisition in a Low Oil Price Environment
Authors: McMahon Neil , Ruitenbeek Kees , Wams Jan , Slawson Steve
Published: October 2021

Increasing expenditure in 3-D land seismic acquisition has driven the need to define Best Practices and improvement areas in the acquisition process. Petroleum Development Oman (PDO) and Arthur D. Little Management Consultants undertook a study to identify these Best Practices in the Middle East and North African regions by interviewing 34 companies and compiling data from 51 recent vibroseis surveys. Acquisition costs and duration from surveys over similar terrains, but with varying geometries, were compared on an equal basis to determine the most cost-effective method for acquiring high-quality (i.e. data density) 3-D data. High-quality surveys acquired using a Zig Zag geometry had lower costs than those acquired using conventional geometries over gravel plain terrain. However, there was no clear best geometry for other terrains. Acquisition performance was also improved by adopting a number of Best Practices covering the design, planning, contracting strategy, execution, processing and post-acquisition elements of the seismic acquisition process.
Depth Imaging Sub-salt Structures: A Case Study in the Midyan Peninsula (Red Sea)
Authors: Mougenot Denis , Al-Shakhis Amir A.
Published: October 2021

In the Midyan Peninsula (onshore northern Red Sea, Saudi Arabia), the current prospective oil and gas exploration targets are sub-salt structures. In this region, conventional time-migrated seismic sections are distorted due to the presence of salt diapirs, faults, and related lateral velocity variations. As demonstrated in other sub-salt prospects (North Sea, Gulf of Suez, and Gulf of Mexico), pre-stack depth migration can remove these distortions and accurately focus the structural image. Depth migration, however, requires a model which includes both lateral and vertical velocity variations to compensate for ray bending. Building such a velocity model is an iterative process which involves integration of various time/depth processing and interpretation skills. A 2-D seismic line, crossing various extensional structures in the dip direction, is used to illustrate these depth-imaging techniques. At the location of the sub-salt prospect, the depth image is improved and the lateral position of the main fault is shifted by 345 meters. The resulting structural model has refined the target definition and well position. This imaging approach is compared with the different steps of the seismic processing/interpretation flow.
Petrological and Tectonostratigraphic Evidence for a Mid Ordovician Rift Pulse on the Arabian Peninsula
Authors: Oterdoom W. Heiko , Worthing Mike A. , Partington Mark
Published: October 2021

During late Early Ordovician times an increase in the rate of subsidence in the Ghaba Salt Basin and western South Oman Salt Basin is suggested by the thick sequence of continental clastics of the Ghudun Formation. After a phase of rift-shoulder uplift and erosion, related to a renewed pulse of extension which may have initiated diapiric growth of salt structures in the Ghaba Salt Basin, sedimentation resumed again in the Mid Ordovician. During this period, the center of deposition shifted to the Saih Hatat area in North Oman. This paper documents seismic and well data, field investigations and petrological study of potassic mafic rocks from the Huqf area which were intruded in the eastern side of the Ghaba Salt Basin. A Mid Ordovician age of 461 ± 2.4 million years has been established for these rocks by the Argon-Argon step heating method. Analogy with the petrology and setting of similar potassic mafic rocks from the Rio Grande Rift in the western United States of America suggests that they were intruded into the shoulder of an intra-continental rift. The data provide the first clear evidence of a pulse of rift-shoulder uplift in the Huqf area during the Mid Ordovician. The 3-kilometer-thick Mid to Late Ordovician clastic sediments of the Amdeh Formation in North Oman, together with the occurrence of abnormally thick sedimentary sequences and volcanics in the Tabas Graben in Iran, are consistent with a period of break-up of eastern Gondwana. Together, the Ghaba-Saih Hatat and Tabas Basins are considered to be part of a failed rift arm. These observations further improve our regional knowledge of the Early to Late Ordovician tectonic setting of Oman and will assist in unlocking the hydrocarbon potential of classical rift-related structures consisting of early-rift Early Ordovician sand-prone reservoirs sealed by syn-rift Mid to Late Ordovician marine shales.
Jurassic Gastropod Faunas of Central Saudi Arabia
Authors: Fischer Jean-Claude , Le Nindre Yves-Michel , Manivit Jacques , Vaslet Denis
Published: October 2021

Mapping of Phanerozoic rocks at 1:250,000 scale by joint teams from the Saudi Arabian Deputy Ministry for Mineral Resources and the Bureau de Recherches Géologiques et Minières since 1980 has covered most of the Jurassic outcrops in central Saudi Arabia. Stratigraphic, sedimentologic and paleogeographic studies provided a precise framework for collected gastropod faunas that could be calibrated against ammonite zones and sequence-stratigraphic zones. Of more than 600 samples collected, about 440 gastropod specimens could be determined on at least a generic level. Their age range is from Bajocian to Oxfordian–Kimmeridgian. They correspond to 26 genera and 35 species from the Euomphalidae, Ataphridae, Pseudomelaniidae, Coelostylinidae, Procerithiidae, Nerineidae, Purpurinidae, Aporrhaidae, Naticidae, Acteonidae, Retusidae, and Akeridae families. Twelve species are new, and three (Kosmomphalus and Bifidobasis in the Euomphalidae, and Striatoonia in the Pseudomelaniidae) were proposed for new taxa of generic or subgeneric rank. Most of the identified species are of Middle Jurassic age, mainly Bathonian and Callovian and only six are Late Jurassic. All species are typical of an internal platform environment (upper infralittoral), in a lagoonal to back-reef setting, but some also colonized the external platform in the lower infralittoral fore-reef zone. Paleogeographically, most of the species are related to European and Sinai faunas; only seven are equivalent to North African or East African faunas, and one only was reported from Madagascar.
High-resolution Sequence Stratigraphic Architecture of Barremian/Aptian Carbonate Systems in Northern Oman and the United Arab Emirates (Kharaib and Shu’aiba Formations)
Authors: van Buchem Frans S.P. , Pittet Bernard , Hillgärtner Heiko , Grötsch Jürgen , Al Mansouri Abdullah I. , Billing Ian M. , Droste Henk H.J. , Oterdoom W. Heiko , van Steenwinkel Mia
Published: October 2021

A regional sequence stratigraphic model for the Kharaib and Shu’aiba formations (Barremian, Aptian) is proposed based on outcrop and subsurface transects in Oman and the United Arab Emirates. The model shows distinct variations in depositional facies and geometrical patterns in relation to third-order sequences. The sedimentary systems evolved from a low-angle carbonate ramp (Kharaib Formation), to an organic-rich intrashelf basin surrounded by carbonate platforms (Hawar Member and Lower Shu’aiba), to a clay-dominated sedimentation restricted to the intrashelf basin (Upper Shu’aiba). Eustatic sea-level changes and, to a lesser extent, local tectonic controls influenced the development of the systems. This high-resolution sequence stratigraphic model has implications for both exploration and production strategies.

This study presents a revised sedimentological facies interpretation based on detailed outcrop observations with geological constraints provided by a regional well-log correlation from Oman and the United Arab Emirates. Time control was provided by biostratigraphy (including new nannofossil data), and carbon isotope stratigraphy. Four third-order depositional sequences bounded by regional exposure surfaces were defined that are composed of at least two higher-order sequences (fourth- and fifth-order).

Depositional sequences I and II have a flat ramp setting. The typical ecological succession was orbitolinid and/or miliolid wackestone-packstone deposited in a low-energy, inner ramp environment during early transgression; a mixed-fauna mudstone-wackestone in an open lagoon during maximum flooding and early highstand; and a rudist/miliolid wackestone-packstone-grainstone-framestone of the succeeding late highstand in a high-energy, inner- to mid-ramp environment. The doubling in thickness of the sequences from Oman to Abu Dhabi is attributed to differential subsidence. The Sequence III succession was somewhat similar, but differences were caused by the creation of the intrashelf Bab Basin, and by well-developed microbial boundstones. The basin morphology was primarily due to differential accumulation rates and tectonism was of only minor importance. Rapidly aggrading and backstepping microbial boundstones formed the platform, whereas condensed sedimentation and the accumulation of carbonate source rocks occurred in the basin. Highstand deposits were primarily grainy, high-energy rudist-dominated facies. The sequence ended with a forced regressive wedge along the basin margins. Sequence IV was restricted to the Bab Basin and sedimentation consisted of a clay-rich infill phase. At that time, the Oman and Abu Dhabi platforms were exposed on both sides of the basin. Nannofossils dated this major relative fall in sea level to the early-late Aptian.
Maximum flooding surfaces and sequence boundaries: comparisons between observations and orbital forcing in the Cretaceous and Jurassic (65-190 Ma)
Authors: Matthews Robley K. , Frohlich Cliff
Published: October 2021

We have undertaken a simplified calculation of orbital forcing back through the Cretaceous to the Late to Middle Jurassic from 65 to 190 Ma. So long as the Earth has a continental ice volume, orbital forcing will impose a 400-ky periodicity upon glacioeustasy and thereby on fourth-order sequence stratigraphy cycles. Similarly, third-order cycles were defined by orbital forcing of 2.4 ± 0.4 my (predominately 2.0- and 2.8-my cycles). These concepts greatly simplified the task of unraveling sequence stratigraphy. Our sea-level calculations are comparable with stratigraphic observations and the results are consistent with a persistent continental ice volume throughout the Late to Middle Jurassic and Cretaceous. In general, they compare well with the Arabian Plate Maximum Flooding Surfaces and the Cretaceous and Jurassic stage boundaries, within the limits of the recognized stratigraphic time scales. We used simple Parametric Forward Models (PFMs) for modeling changes in sea level, subsidence, and sedimentation and noted that PFMs can be applied to other tasks. The results will provide for rapid, cost-effective forward modeling on tasks such as reservoir characterization and flow simulation.
Shu’aiba rudist taphonomy using computerised tomography and image logs, Shaybah field, Saudi Arabia
Authors: Hughes G. Wyn ap G. , Siddiqui Shameem , Sadler R. Kumbe
Published: October 2021

Rudist fossils in cored carbonates from the Shu’aiba reservoir in the Shaybah field have been used to aid the interpretation of lithofacies and reservoir facies in uncored horizontal development wells. The rudists are sufficiently large fossils that they provide well-developed and easily identified images on computerised tomography (CT) scans of cores. The CT images provide valuable information on the rudist orientation prior to damage caused by plugging and slabbing procedures. CT images, combined with the core-based fossil information, are then used to interpret the images on the formation micro-imager (FMI) logs. As the various rudist species are known to have preferentially occupied different environments during the deposition of the Shu’aiba carbonates, depositional environments can now be interpreted from the FMI logs. Specimen orientation in the core provides supplementary information on the depositional environment by discriminating between in-situ and displaced assemblages. Rudist identification in FMI images is a new tool in uncored vertical wells. In long horizontal wells, this is a major achievement and will assist in modelling the 3-D lithofacies and associated reservoir facies distribution for improving the reservoir model.
Reservoir quality and K-Ar age dating of the pre-Khuff section of Kuwait
Authors: Strohmenger Christian J. , Al-Anzi Menahi S. , Pevear David R. , Ylagan Robert F. , Kosanke Tobi H. , Ferguson G. Scott , Cassiani Daniel H. , Douban Adel F.
Published: October 2021

Based on studies of petrographic thin sections from core and cutting samples, the pre-Permian siliciclastics in four deep wells in southern Kuwait were found to be tight. Three of these wells are located on the crestal region of the Burgan Arch, and one on the Umm Gudair anticline. These clastics were encountered beneath a thin brick-red shale of unknown thickness, immediately below the pre-Khuff unconformity at the base of the Permian-Triassic Khuff Formation. The pre-Khuff clastics range in thickness from a few tens of feet to more than 4,000 ft, and overlie a Proterozoic argillite (Economic Basement). Based on Illite Age Analysis (IAA) of samples from cores, the depositional K-Ar age of the pre-Khuff clastics is estimated to be younger than 509 Ma (90 percent confidence interval: 544–481 Ma, i.e. Cambrian-Early Ordovician). The argillite was uplifted through the 300°C isotherm at about 611 Ma (90% confidence interval: 635-588 Ma, i.e Late Proterozoic); its deposition and metamorphism preceded this date. During the Paleozoic, the pre-Khuff clastics were buried to depths of 10,000–15,000 ft, but were subsequently uplifted in the Late Paleozoic. IAA diagenetic K-Ar ages of the Economic Basement (421 Ma; 90 percent confidence interval: 442-397 Ma; Late Ordovician-Early Devonian) and pre-Khuff clastics (369 Ma; 90 percent confidence interval: 404–337 Ma, i.e. Devonian-Early Carboniferous) indicate that by these times the pre-Khuff section was already deposited and undergoing burial diagenesis. The interpretation of gravity data indicates that in Paleozoic basinal regions (e.g. between the Burgan Arch and Umm Gudair Anticline), the Paleozoic sedimentary section is likely to be more complete and may exceed 10,000 ft in thickness.
Predicting the occurrence of bulk bitumen in uncored wells: a core-log calibration method, Uwainat Reservoir, Dukhan field, Qatar
Authors: Shankar Varavur Venkitardr , Trabelsi Ali Miloud Said , Beg Mirza Arshad
Published: October 2021

Most Jurassic reservoirs in the Middle East contain bulk bitumen. Core data from the Middle Jurassic Uwainat reservoir in the Dukhan field of Qatar show that bulk bitumen predominantly occurs in grainstones, and to a lesser degree, in bioclastic packstone and wackestone intervals. Bitumen fills interparticle and intraparticle porosities, hairline fractures, and stylolites. The thickness of the bitumen varies, generally in response to the distribution of the porous-permeable lithologies. For this study a learning dataset was constructed, from which numerical estimations were made to isolate petrophysical characteristics of bitumen. Then qualitative estimates were made to predict the occurrence of bitumen. Data from cores and thin sections were integrated with porosity and resistivity logs of twenty cored wells to develop a technique for determining the presence of bulk bitumen in the uncored wells. As this methodology is largely qualitative, a binary flag system was employed to indicate bitumen. The technique involves cross-plotting of bulk density versus thermal neutron porosity, across zones where bulk bitumen has been identified in cores. A transform of the form y=abxxc relates the neutron porosity to the bulk density. This transform is then applied to the neutron data to arrive at a calculated bulk density, theoretically predicting a bulk density response to bitumen. When the difference between the calculated and the actual bulk density is within ± 0.03 gm/cc, a positive flag is generated (suggesting that bulk bitumen is present). Using cut-offs based on calculated bulk density values and the microresistivity log further refines this flag. This method is useful in detecting bulk bitumen in uncored wells, when bulk bitumen forms in intervals more than 2 feet thick. The zones identified as having bulk bitumen in cores were correctly identified by the log data. This technique has about 80 percent reliability when the rock interval containing bulk bitumen is more than 10 feet thick. The approach however, has limitations where bitumen occurs in low porosity rocks, as it becomes difficult to differentiate resistivity increases due to reduction in porosity from those due to bitumen filling the pore spaces. The agreement between core and log requires an accurate depth matching between core and logs.
Fault characterization by seismic attributes and geomechanics in a Thamama oil field, United Arab Emirates
Authors: Tamura Yoshihiko , Tsuneyama Futoshi , Okamura Hitoshi , Furuya Keiichi
Published: October 2021

Faults and fractures were interpreted using attributes that were extracted from a 3-D seismic data set recorded over a Lower Cretaceous Thamama oil field in offshore Abu Dhabi, United Arab Emirates. The Thamama reservoir has good matrix porosity (frequently exceeding 20%), but poor permeability (averaging 15 mD). Because of the low permeability, faults and fractures play an important role in fluid movement in the reservoir. The combination of the similarity and dip attributes gave clear images of small-displacement fault geometry, and the orientation of subseismic faults and fractures. The study better defined faults and fractures and improved geomechanical interpretations, thus reducing the uncertainty in the preferred fluid-flow direction. Two fault systems were recognized: (1) the main NW-trending fault system with mapped fault-length often exceeding 5 km; and (2) a secondary NNE-trending system with shorter faults. The secondary system is parallel to the long axis of the elliptical domal structure of the field. Some of the main faults appear to be composed of en-echelon segments with displacement transfer between the overlapping normal faults (relay faults with relay ramps). The fault systems recognized from the seismic attributes were correlated with well data and core observations. About 13 percent of the fractures seen in cores are non-mineralized. The development of the fault systems was studied by means of clay modeling, computer simulation, and a regional tectonics review. The existing fluid-flow characteristics of individual faults and fractures in the field can be modeled using the present-day stress regime, with the maximum horizontal stress oriented north-northeast. Slip-tendency and dilation-tendency analyses simulating present-day regional stress conditions are indicators of fault and fracture transmissibility. The NNE-striking secondary fault system is parallel to the present-day maximum horizontal stress and could act as a flow conduit in the reservoir.
Sedimentology and play potential of the late Neoproterozoic Buah Carbonates of Oman
Authors: Cozzi Andrea , Al-Siyabi Hisham A.
Published: October 2021

The search for new exploration plays in Oman, and recent successes in the Ara Group, has rejuvenated the interest of Petroleum Development Oman (PDO) in the stratigraphy of the pre-Ara Group. Below the Ara Group, the late Neoproterozoic Nafun Group comprises five formations. The Buah is the youngest of these formations, and represents the most promising exploration target. Accordingly, an integrated outcrop and subsurface study was initiated to better understand the distribution of the Buah depositional facies. High-resolution chemostratigraphy and field gamma-ray surveys were used to correlate outcrop data with the PDO subsurface database. These studies resulted in the reconstruction, with an unprecedented accuracy, of the distribution of the depositional environments at Buah time throughout Oman.

This study indicates that the Buah was deposited on a distally-steepened carbonate ramp, during a highstand systems tract, as a shallowing and upward-coarsening cycle. Good reservoir facies (peloidal-ooidal grainstones) are ubiquitous in the shallow-water Buah sections, making up continuous sheets for tens of kilometers. Karst and fracture development at the top of the Buah may improve the reservoir quality, as in the case of the Makarem gas field in Oman. Buah reservoirs are generally capped by the Ara salt, except on structural highs where the top seal is provided by mudstones of the middle Haima Supergroup. The Buah off-ramp basinal facies represent potential source rocks with total organic carbon values ranging from 2.5–3.5 %.
Two distinct glacial successions in the Neoproterozoic of Oman
Authors: Guerroué Erwan Le , Allen Philip , Cozzi Andrea
Published: October 2021

Neoproterozoic glacial strata in Oman are key to the ongoing Snowball Earth discussion, providing a great opportunity to test the hypothesis. The Abu Mahara Group (Huqf Supergroup) is well exposed in the core of the Jabal Akhdar of northern Oman. It contains two glaciogenic units, the Ghubrah Formation (723+16/−10 Ma) and the Fiq Formation (currently undated), that are separated by the volcaniclastic Saqlah Formation. An angular unconformity is present between the Ghubrah and Saqlah formations, indicating a significant time gap between the deposition of the Ghubrah and Fiq glacial successions. The localised occurrence of pillow basalts and more widespread volcaniclastics of the Saqlah Formation, suggests the initiation of a rifting phase, which is considered to have continued during deposition of the Fiq Formation. Given the available geochronology, the Ghubrah Formation may correlate with other glaciogenic successions worldwide attributed to the Sturtian glacial epoch, and the Fiq Formation with younger glaciogenic successions attributed to the Marinoan glacial epoch. Neoproterozoic glaciations appear to have taken place at times of tectonically generated accommodation, suggesting a link between geodynamics, basin development and climate change.
Devonian Jauf Formation, Saudi Arabia: Orbital Second-order Depositional Sequence 28
Authors: Al-Husseini Moujahed , Matthews Robley K.
Published: October 2021

The Devonian Jauf Formation (Huj Group) froms part of a regional transgressive-regressive depositional sequence that extends more than 1,500 km across the Arabian Platform from the Al Jawf outcrops in northwest Saudi Arabia, to the subsurface of eastern Saudi Arabia and Oman (Misfar Group). The formation ranges in thickness from 200–335 m in eastern Saudi Arabia to about 300–330 m in northwest Saudi Arabia. It disconformably (?unconformably) overlies the continental to shallow-marine Tawil Formation, and is unconformably overlain by the continental Jubah Formation. The Jauf Formation consists of five members that are apparently conformable; from base-up: Sha’iba Shale, Qasr Limestone, Subbat Shale, Hammamiyat Limestone and Murayr. In the Al-Qalibah reference section, it is divided into 21 informal units. The Early Devonian Emsian Hammamiyat Member represents the main marine flooding event; it consists of Hammamiyat units 1–6 each characterized by a clastic section that is capped by limestone.

The Jauf Formation is interpreted as an orbital second-order depositional sequence (denoted DS2 28), which is bounded by two second-order sequence boundaries: SB2 28 = Jauf/Tawil (c. 407.6 Ma) and SB2 27 = Jubah/Jauf (c. 393.0 Ma). The Jauf Formation appears to consist of six third-order depositional sequences (DS3 28.1 to 28.6) that were deposited in the Early Devonian, ?Pragian and Emsian stages The Hammamiyat Member (DS3 28.4) is interpreted to consist of six fourth-order orbital cycles (DS4 28.4.1 to 28.4.6) each deposited in 0.405 million years.
Geophysical reservoir monitoring feasibility study in a Central Saudi Arabian oil field
Authors: Vesnaver Aldo L. , Broadhead Michael K. , Bellaci Isidore J.
Published: October 2021

The Central Arabian field of this study is part of a trend of oil fields primarily producing from Permian sandstone reservoirs. The most productive zone, in the upper part of the reservoir, is characterized with good porosity and permeability, an aeolian depositional environment, and producing zones that tend to be laterally and vertically heterogeneous. The reservoir sandstone lenses are interspersed with low porosity/permeability siltstones. We examined the feasibility of watersaturation surveillance by geophysical means that could help to better produce the field and unravel certain production challenges; hence, time-lapse seismic (4-D) was considered. Using modeling, we argue that time-lapse seismic is a low probability candidate for successful reservoir monitoring of water saturation in this field. We also discuss other techniques that are potential alternatives, such as micro-seismicity, magnetotellurics and borehole gravity, comparing the relative merits and limitations of these methods as applicable to this field. Finally, we conclude with the potential impact of improved reservoir characterization, via integration of more seismic information into the reservoir model.
Strontium (87Sr/86Sr) and calcium isotope ratios (44Ca/40Ca-44Ca/42Ca) of the Miocene Dam Formation in Qatar: tools for stratigraphic correlation and environment analysis
Authors: Dill Harald G. , Henjes-Kunst Friedhelm
Published: October 2021

The Dam Formation in Qatar is a series consisting of calcareous (calcite, dolomite) and evaporitic sediments (gypsum, celestite) that developed under subtidal through supratidal conditions passing towards younger and older series in an environment of deposition more akin to modern beach deposits. In the present study 87Sr/86Sr ratios, δ44/40Ca and δ44/42Ca data are discussed together with δ13C and δ18O values obtained during an environmental analysis carried out previously. Rather uniform isotope curves of the Sr, Ca and O isotopes for tidal deposits are replaced by more oscillating ones when these tidal-influenced regimes became substituted for by a more wave-dominated regime. Calcium isotope ratios still at its infancy and not fully understood seem to provide a new tool in carbonate petrography when it comes to an interpretation of the environment of deposition and calcification of dolomitic series. The Sr isotopes not only indicate an influx of more primitive Sr from the hinterland but also allow for a refinement of the stratigraphy, which yields a late Aquitanian to early Burdigalian age of sedimentation for the Dam Formation in Qatar.
Hydrocarbon plays and prospectivity of the Levantine Basin, offshore Lebanon and Syria from modern seismic data
Authors: Roberts Glyn , Peace David
Published: October 2021

The Levantine Basin is located in the easternmost region of the Mediterranean Sea between Cyprus and the Nile Delta marine cone in Egypt. Based on an analysis of more than 20,000 line-km of 2-D seismic data, the basin appears to contain up to 10,000 metres of Mesozoic and Cenozoic rocks above a rifted Triassic-Lower Jurassic terrain. Although many hydrocarbon discoveries have been made in the Nile Delta and the near-offshore areas in the southeastern Mediterranean Sea, no exploration wells have been drilled in its deep offshore or anywhere offshore Lebanon, Syria and Cyprus. Widespread occurrence of oil seeps (over 200) that closely correlate to hydrocarbon indication on seismic (e.g. bright spots and gas chimneys associated with possible migration pathways) suggest that the undrilled parts of the Levantine Basin can be prospective. Thirteen potential exploration plays are identified in this study and illustrated with seismic examples. The plays range in age from the Triassic to the Neogene-Pliocene.
Microfacies and sequence stratigraphy of the Late Campanian Bekhme Formation in the Dohuk area, north Iraq
Authors: Al-Mutwali Majid M. , Al-Banna Nabil Y. , Al-Ghrear Jamal S.
Published: October 2021

The Bekhme Formation represents the lower part of a regional Upper Cretaceous (Campanian - Maastrichtian) succession that was deposited over most of Iraq and adjacent regions. The formation unconformably overlies the Qamchuqa Limestone Formation (Hauterivian-Albian) and is overlain by the Shiranish Formation (Upper Campanian - Maastrichtian). Northeast of the city of Dohuk, an incomplete, but well-exposed, section of the Bekhme Formation crops out in a 75-m-thick section that formed the basis for our study. Twenty-five samples were collected from the section and used for biostratigraphic and microfacies analysis. The study of planktonic foraminifera resulted in the recognition of two Campanian biozones: the Globotruncanita calcarata Zone and the Globotruncanita stuartiformis–Globotruncanita stuarti Zone, both considered to be of Late Campanian age. Three main microfacies were distinguished throughout the formation, which represent middle-shelf, outer-shelf and upper-bathyal environments. Sequence stratigraphic analysis, as calibrated by microfacies, delineated five depositional sequences of probable fourth-order, thus suggesting the studies section was deposited in about 2.0 million years and represents an overall third-order sequence.
A new upper Oligocene marine record from northern Sinai (Egypt) and its paleogeographic context
Authors: Kuss Jochen , Boukhary Mohamed A.
Published: October 2021

The upper Oligocene Wadi Arish Formation is composed of a carbonate-dominated succession at Gebel Risan Aneiza (Sinai). The 77-m-thick unit disconformably overlies Jurassic to lower Cretaceous carbonates and is subdivided into three members, comprising six lithofacies units. The lower Wadi Arish member contains three units, a gypsiferous sandstone unit (Oa), overlain by two limestone units (Ob and Oc). The middle Wadi Arish member is represented by a conspicuous marl unit (Od) that is overlain by two upper limestone units (Oe and Of) of the upper Wadi Arish member. We discuss the euphotic subtidal depositional environments in conjunction with macro- and microfacies characteristics. Six microfacies types are defined, dominated by grain associations of rhodoliths, larger benthic foraminifera (rotaliids), corallinaceans, bivalves, peloids, few corals, and bryozoans. They characterize rhodalgal associations, common in non-tropical warm-temperate settings. Biostratigraphy is based on larger foraminifera. The middle Wadi Arish member corresponds with SB 23 (Chattian) and may correlate with Pg50, a regional maximum flooding surface. Our sequence stratigraphic interpretations define a late lowstand to early transgressive systems tract (lower Wadi Arish member), a late transgressive systems tract (middle Wadi Arish member), while the upper Wadi Arish member reflects highstand conditions. The paleogeographic setting and sequence stratigraphic interpretation of this unique upper Oligocene outcrop is placed in context of the northeast African-Arabian region.