scholarly journals Facies, sequence stratigraphy, reservoir and seal potential of the Mafraq Formation, Sultanate of Oman: An integrated outcrop analogue study

GeoArabia ◽  
2015 ◽  
Vol 20 (3) ◽  
pp. 17-94
Author(s):  
Daniel Bendias ◽  
Thomas Aigner
Keyword(s):  
Sequence Stratigraphy ◽  
Northwestern Part ◽  
Southeastern Part ◽  
Terrestrial Environment ◽  
Oman Mountains ◽  
Facies Associations ◽  
Potential Reservoir ◽  
Lateral Extent ◽  
Member Sequence ◽  
Mixed Carbonate

ABSTRACT The mixed carbonate-siliciclastic Lower to Middle Jurassic Mafraq Formation unconformably overlies the Triassic Mahil Formation in outcrops of the Oman Mountains (pre-Mafraq Unconformity, known as pre-Marrat unconformity in other regions of Arabia). 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. Twenty-four facies types were established and grouped into five facies associations, which can also be recognized in subsurface core intervals; (2) a detailed sequence-stratigraphic framework of the Mafraq Formation. Facies stacking and log patterns reveal cycle hierarchies on four scales from m-scale cycles, to several m-thick cycle sets, to tens of m-thick, high-frequency sequences, to 100 m-thick composite sequences; and (3) a documentation of potential reservoir and seal units. The study follows an approach from 1-D (outcrop sections) to 2-D (correlations and potential reservoir dimensions). The Mafraq outcrop type section, located in Wadi Sahtan is documented in an integrated way (facies, litho-, bio-, chemo- and sequence stratigraphy), together with additional outcrops of the Mafraq Formation throughout North Oman. 2-D correlation of the Mafraq Formation throughout North Oman is essentially based on cycle sets and provides key information about the lateral paleogeographic development of the formation. A general proximal-distal trend, from south to north, has been proposed by Ziegler (2001); outcrop data from the Oman Mountains confirms this trend and adds an EW-deepening component. The mixed carbonate-clastic Lower Mafraq Member (Sequence) with a coastal/estuarine to shallow-marine environment forms onlaps onto the pre-Mafraq Unconformity below, and thins out completely after some 10s of kilometers towards the southeast. The Upper Mafraq Member (Sequence) seems to be continuous over 10s of kilometers with less thickness decrease. Instead, a transition from a more distal carbonate shoal - backshoal environment in the northwest to a proximal clastic coastal/estuarine/terrestrial environment in the southeast can be observed. On a 100s km-scale significant thinning and a change towards terrestrial clastic facies can be observed southeast of the Oman Mountains area. Combined results from lateral/vertical logging, paleoenvironmental interpretations and correlation provided 3-D information about the dimensions of potential reservoir and seal units. Several potential reservoir/seal intervals and their dimensions in dip direction could be identified: (1) Lower Mafraq Sequence: various types of sandbodies, most of them with a lateral extent ca. 5 km, sealed by shales. (2) Upper Mafraq Sequence, northwestern part: oolitic grainstones, laterally correlative over 10–20 km, sealed by shales. (3) Upper Mafraq Sequence, southeastern part: channelized sandstones units, lateral extent up to km, sealed by shales.

scholarly journals Mid-Permian Khuff Sequence KS6: Paleorelief-influenced facies and sequence patterns in the Lower Khuff time-equivalent strata, Oman Mountains, Sultanate of Oman

GeoArabia ◽  
2013 ◽  
Vol 18 (3) ◽  
pp. 135-178 ◽  
Author(s):  
Daniel Bendias ◽  
Bastian Koehrer ◽  
Michael Obermaier ◽  
Thomas Aigner
Keyword(s):  
Tectonic Activity ◽  
Gulf Region ◽  
Layer Cake ◽  
Oman Mountains ◽  
Stratigraphic Architecture ◽  
Facies Associations ◽  
Potential Reservoir ◽  
Stratigraphic Position ◽  
Lateral Extent ◽  
Reservoir Potential

ABSTRACT Khuff Sequence KS6 was studied in the Al Jabal al-Akhdar, Oman Mountains, in an area of 30 x 50 square kilometers by means of detailed sedimentological logging of five time-equivalent outcrop sections of the Saiq Formation. KS6 represents one transgressive-regressive, third-order sequence, and is composed of four facies associations each representing particular environments of deposition (backshoal, shoal, foreshoal and offshoal) with distinct sedimentological characteristics. Facies stack to form cycles and cycle sets that were used for correlation at a subregional scale and to reveal the KS6 stratigraphic architecture. During the initial phase of basin-fill, clastic sediments (“Basal Saiq Clastics”) were deposited in paleolows above the “Sub-Saiq Unconformity”. In contrast to younger Upper Khuff sequences KS4 to KS1, the underlying paleorelief strongly affects the thickness and facies composition of KS6. The correlation strategy to follow paleolandscape surfaces using all available sedimentological, biostratigraphic and lithostratigraphic data resulted in a stratigraphic architecture with subtle shingle geometries. Sequence KS6 shows a strong facies partitioning resulting in the necessity of two separate facies models for the transgressive (crinoidal ramp) versus regressive hemisequence (oolitic/peloidal carbonate ramp). This study revealed potential reservoir units in KS6, commonly regarded as non-reservoir in the subsurface of Oman and other parts of the Gulf region. The abundance, nature and lateral extent of reservoir facies strongly varies with stratigraphic position. In the transgressive part of KS6, crinoidal grainstones are concentrated around the margin of a gentle paleohigh. They might have the best reservoir potential, although early diagenetic cementation is common in most settings. Oolitic/peloidal grainstones in the upper regressive part have a much higher diagenetic reservoir potential and are laterally much more widespread. Thus, Khuff Sequence KS6 differs profoundly in its stratigraphic architecture from the more “layer-cake”-like KS4 to KS1 sequences. Facies and thickness patterns are controlled by a marked paleohigh to paleolow configuration, resulting from the antecedent uneven topography during the Neo-Tethyan syn-rift setting, in contrast to the post-rift setting with low tectonic activity during KS4 to KS1.

scholarly journals Outcrop sedimentology of the Natih Formation, northern Oman: A field guide to selected outcrops in the Adam Foothills and Al Jabal al Akhdar areas

GeoArabia ◽  
2008 ◽  
Vol 13 (3) ◽  
pp. 39-120 ◽  
Author(s):  
Peter Homewood ◽  
Philippe Razin ◽  
Carine Grélaud ◽  
Henk Droste ◽  
Volker Vahrenkamp ◽  
...  
Keyword(s):  
Sequence Stratigraphy ◽  
Three Dimensional ◽  
Depositional Environments ◽  
Field Guide ◽  
Sequence Stratigraphic ◽  
Oman Mountains ◽  
Facies Associations ◽  
Al Jabal Al Akhdar ◽  
General Section ◽  
Petroleum Development

ABSTRACT This field guide describes eleven outcrops of the Natih Formation in the Al Jabal al Akhdar-Jabal Shams and Adam Foothills areas, not far from Nizwa, at the foot of the Oman Mountains. The outcrops have been chosen for their accessibility, as well as for the fairly complete picture of the Natih Formation, which they piece together. To visit all eleven outcrops requires several days and the use of 4-wheel-drive vehicles, but the locations offer no serious physical difficulty, nor long hiking, to gain access. The outcrop descriptions follow in stratigraphic order from the lower to the upper Natih members, roving back-and-forth across the outcrop area. Much of the detailed account of the sedimentology and stratigraphy of the Natih that has been used as the basis of this field guide, has been given previously by van Buchem et al. (1996, 2002), Grélaud (2005), Schwab et al. (2005) and Grélaud et al. (2006). The observations and interpretations given here come in part from those studies, but this paper is also largely the product of a subsequent project that was carried out for the Fahud Studies Team of Petroleum Development Oman (PDO), to provide detailed sedimentology and high-resolution sequence stratigraphy of the Natih Formation for further development of the Fahud field (Homewood et al. 2006). In this respect, this field guide is not so much intended to be an original contribution in terms of the science concerning the Natih Formation. The intent is to provide the ways-and-means for all to gain a first-hand personal understanding of the rocks we have enjoyed working on. Following the outcrop descriptions, a general section provides a discussion on facies and facies associations in terms of the constraints of sequence stratigraphy, sea-level change and clay influx on the carbonate factory. With the incorporation of limited subsurface seismic and well data, geobodies and depositional assemblages, the three-dimensional objects that form the stratigraphic packages at outcrop and seismic scales, respectively, are also discussed. Facies are thus interpreted not only in terms of depositional environments, but are also placed within both geometrical (geobody, depositional assemblage) and sequence-stratigraphic frameworks. In the conclusion, it is argued that a deeper understanding of the Natih Formation has been gained by comparison of outcrop data with subsurface data, and by contrast with modern analogs. The detail required to apply what was learned from outcrop to the nearby subsurface, in a practical manner (but also properly to reconstruct the successive Natih scenarios), requires building several facies models. This is in contrast to giving a single composite picture of Natih facies distribution in space and time, under one single facies model.

scholarly journals Khuff Sequence KS5 outcrop-equivalents in the Oman Mountains, Sultanate of Oman: Variations to the simple “layer-cake” stratigraphy

GeoArabia ◽  
2013 ◽  
Vol 18 (4) ◽  
pp. 179-218 ◽  
Author(s):  
Lisa Walz ◽  
Thomas Aigner ◽  
Bastian Koehrer
Keyword(s):  
Lower Triassic ◽  
Sultanate Of Oman ◽  
Associated Gas ◽  
Layer Cake ◽  
Oman Mountains ◽  
Facies Associations ◽  
Potential Reservoir ◽  
Stratigraphic Position ◽  
Thickness Variations ◽  
Facies Types

ABSTRACT The Khuff Formation is a major producer of non-associated gas and an exploration target in the Middle East. The Middle Permian to Lower Triassic Khuff carbonates were deposited on a gently inclined epeiric carbonate ramp, which formed on the margin of the Neo-Tethys Ocean. The formation represents a supersequence consisting of transgressive-regressive sequences KS6 to KS1 from oldest to youngest. This paper focuses on a detailed sedimentological analysis of Khuff Sequence KS5 in outcrops in Al Jabal al-Akhdar in the Oman Mountains, Sultanate of Oman. Based on the sedimentological analysis of five outcrop sections, 11 facies types were identified in KS5. These were grouped into six facies associations, which represent environments ranging from a tidal flat to offshoal. Based on the 1-D analysis of sequences and their stacking patterns, 2-D correlations were constructed on a scale of several tens of kilometers. These correlations were used to build the framework for 3-D facies models. In contrast to the typical “layer-cake”-type Upper Khuff sequences KS4 to KS1 in terms of facies associations and cyclicity prominent lateral facies association changes and thickness variations are common in KS5, which makes correlation challenging. Different correlation strategies were tested, all resulting in complex cycle and stratal geometries with cycle pinch-outs and apparent cycle set downlaps/onlaps. Due to the dynamic depositional changes throughout KS5, the lateral extent of shoal-associated grainstones is limited. The appearance of these potential reservoir bodies is mainly governed by paleogeography and stratigraphic position. The observed depositional patterns represent significant variations from a rather simple “layer-cake”-type stratigraphic architecture and are possibly due to effects of differential subsidence on a subregional scale. This study contributes to a more detailed understanding of the Lower Khuff’s reservoir distribution and continuity, which is a key to ensuring future success in Khuff exploration and the efficient recovery in producing fields.

The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada

1990 ◽  
Vol 27 (10) ◽  
pp. 1359-1370 ◽  
Author(s):  
Eva M. Klaper
Keyword(s):  
Large Scale ◽  
Ellesmere Island ◽  
Small Scale ◽  
Northwestern Part ◽  
Fold Belt ◽  
Southeastern Part ◽  
Lower Paleozoic ◽  
Slip Mechanism ◽  
Fold Belts ◽  
Surface Geology

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.

Novel geometric classification of 3D seismic and its application to the Habshan clinoforms of Western Oman

2021 ◽  
Vol 40 (3) ◽  
pp. 186-192
Author(s):  
Thomas Krayenbuehl ◽  
Nadeem Balushi ◽  
Stephane Gesbert
Keyword(s):  
Sequence Stratigraphy ◽  
Seismic Data ◽  
Northwestern Part ◽  
Full Potential ◽  
Seismic Sequence ◽  
3D Seismic ◽  
Level Curve ◽  
Seismic Sequence Stratigraphy

The principles and benefits of seismic sequence stratigraphy have withstood the test of time, but the application of seismic sequence stratigraphy is still carried out mostly manually. Several tool kits have been developed to semiautomatically extract dense stacks of horizons from seismic data, but they stop short of exploiting the full potential of seismo-stratigraphic models. We introduce novel geometric seismic attributes that associate relative geologic age models with seismic geomorphological models. We propose that a relative sea level curve can be derived from the models. The approach is demonstrated on a case study from the Lower Cretaceous Kahmah Group in the northwestern part of Oman where it helps in sweet-spotting and derisking elusive stratigraphic traps.

Discriminating intra-parasequence stratigraphic units from two-dimensional quantitative parameters

2021 ◽  
Vol 91 (8) ◽  
pp. 887-911
Author(s):  
Manuel F. Isla ◽  
Ernesto Schwarz ◽  
Gonzalo D. Veiga ◽  
Jerónimo J. Zuazo ◽  
Mariano N. Remirez
Keyword(s):  
High Frequency ◽  
Two Dimensional ◽  
Facies Associations ◽  
Different Types ◽  
Lateral Extent ◽  
Successive Wave ◽  
Shell Bed ◽  
Definition Of ◽  
High Resolution Sequence Stratigraphy ◽  
Bounding Surfaces

ABSTRACT The intra-parasequence scale is still relatively unexplored territory in high-resolution sequence stratigraphy. The analysis of internal genetic units of parasequences has commonly been simplified to the definition of bedsets. Such simplification is insufficient to cover the complexity involved in the building of individual parasequences. Different types of intra-parasequence units have been previously identified and characterized in successive wave-dominated shoreface–shelf parasequences in the Lower Cretaceous Pilmatué Member of the Agrio Formation in central Neuquén Basin. Sedimentary and stratigraphic attributes such as the number of intra-parasequence units, their thickness, the proportions of facies associations in the regressive interval, the lateral extent of bounding surfaces, the degree of deepening recorded across these boundaries, and the type and lateral extent of associated transgressive deposits are quantitatively analyzed in this paper. Based on the analysis of these quantified attributes, three different scales of genetic units in parasequences are identified. 1) Bedset complexes are 10–40 m thick, basin to upper-shoreface successions, bounded by 5 to 16 km-long surfaces with a degree of deepening of one to three facies belts. These stratigraphic units represent the highest hierarchy of intra-parasequence stratigraphic units, and the vertical stacking of two or three of them typically forms an individual parasequence. 2) Bedsets are 2–20 m thick, offshore to upper-shoreface successions, bounded by up to 10 km long surfaces with a degree of deepening of zero to one facies belt. Two or three bedsets stack vertically build a bedset complex. 3) Sub-bedsets are 0.5–5 m thick, offshore transition to upper-shoreface successions, bounded by 0.5 to 2 km long surfaces with a degree of deepening of zero to one facies belt. Two or three sub-bedsets commonly stack to form bedsets. The proposed methodology indicates that the combination of thickness with the proportion of facies associations in the regressive interval of stratigraphic units can be used to discriminate between bedsets and sub-bedsets, whereas for higher ranks (bedsets and bedset complexes) the degree of deepening, lateral extent of bounding surfaces, and the characteristics of associated shell-bed deposits become more effective. Finally, the results for the Pilmatué Member are compared with other ancient and Holocene examples to improve understanding of the high-frequency evolution of wave-dominated shoreface–shelf systems.

Dynamics of evapotranspiration and variations in different land-cover regions over the Tibetan Plateau during 1961-2014

2021 ◽  
Author(s):  
Shan Lin ◽  
Genxu Wang ◽  
Zhaoyong Hu ◽  
Kewei Huang ◽  
Xiangyang Sun ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Land Cover ◽  
Northwestern Part ◽  
The Tibetan Plateau ◽  
Southeastern Part ◽  
Available Energy ◽  
Forest Region ◽  
Energy Factors ◽  
Term Change ◽  
Increasing Trend

AbstractIn this study, the spatiotemporal changes and driving factors of evapotranspiration (ET) over the Tibetan Plateau (TP) are assessed from 1961-2014, based on a revised generalized nonlinear complementary (nonlinear-CR) model. The average annual ET on the TP was 328 mm/year. The highest ET value (711 mm/year) was found in the forest region in the southeastern part of the TP, and the lowest value (151 mm/year) was found in the desert region in the northwestern part of the TP. In terms of the contribution of different sub-regions to the total amount of ET for the whole plateau, the meadow and steppe regions contributed the most to the total amount of ET of TP, accounting for 30% and 18.5%, respectively. The interannual ET presented a significant increasing trend with a value of 0.26 mm/year from 1961 to 2014, and a significant positive ET trend was found over 35% of the region, mainly in the southeastern part of the plateau. The increasing trend of ET in swamp areas was the largest, while that in the desert areas was the smallest. In terms of the seasonality, the ET over the plateau and different land-cover regions increased the most in summer, followed by spring, while the change in ET in winter was not obvious. The energy factors dominated the long-term change in the annual ET over the plateau. In addition, the available energy is the controlling factor for ET changes in humid areas such as forests and shrublands. Energy and water factors together dominate the ET changes in arid areas.

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