High Resolution Sequence Stratigraphy of the Natih Formation (Cenomanian/Turonian) in Northern Oman: Distribution of Source Rocks and Reservoir Facies

Abstract

The Cenomanian of the Arabian Peninsula comprises a carbonate platform setting with rudists, characterized by gradual lateral facies changes including the interfingering of carbonate reservoirs (Natih and Mishrif formations) and source rocks. In order to be more predictive with regard to the distribution and the geometrical aspects of the reservoirs and source rocks, a high resolution sequence stratigraphic study has been carried out in the Adam Foothills of Northern Oman. Based on detailed field sections a correlation scheme covering a transect of 100 kilometers (km) has been established. Three orders of stacked depositional sequences have been found based on the reoccurrence of facies. During long-term increase of accommodation the depositional environment was separated in basinal and platform facies. In contrast, during longer term sea level fall, i.e. long-term decrease of accommodation space, prograding shelfal units extended platform facies over a large part of the basin. The most heterogeneous facies associations are found in times of minimal accommodation space, when incisions and subaerial exposure produce lateral variable strata (e.g. top Natih E). The organic matter is found at the base of two of the three longer term (3rd order) depositional sequences. The organic carbon is contained in marl-limestone couplets (small-scale cyclicity) with a high abundance of oysters and monospecific brachiopod faunas (coquinas). Rudists are found in the progradational part of these sequences, and occur mostly as reworked rudstone layers in meter to decimeter scale, high frequency cycles. The detailed regional correlation depends on the identification of medium- to small-scale (4th to 5th order) depositional sequences which are bounded by regional shifts of the facies belts. The distinct hierarchical organization of the depositional sequences in the Cenomanian, and the relative stability at that time of the Arabian Peninsula, implies a strong correlation potential and thus a broad regional similarity of the architecture of the petroleum systems at that time.

Sequence Stratigraphy, Palaeogeography and Petroleum Plays of the Cenomanian – Turonian Succession of the Arabian Plate: An Updated Synthesis

“…Characterizing the evolving configuration and depositional evolution of these intrashelf basins through the mid-Cretaceous is paramount for exploration success, as they exert a strong control on the distribution of source, reservoir and seal rocks (see below). Some of these basins such as the Shilaif Basin (centred around the United Arab Emirates: Al-Zaabi et al, 2010;Vahrenkamp et al, 2015) and the Najaf Basin (centred around southern Iraq: Aqrawi and Horbury, 2008;Aqrawi et al, 2010a, b) were relatively long-lived and spanned the entire Cenomanian; others such as the Natih E and Natih B Basins in northern Oman were created and infilled within a single depositional sequence (van Buchem et al, 2002) (locations in Fig. 1).…”

“…The sequence boundary (SB) at the base of this sequence lies close to the Albian-Cenomanian boundary and was followed by a transgression which created intrashelf basins such as the Shilaif Basin in the UAE and the Natih E Basin in Oman. There is varying evidence at the K120 sequence boundary for exposure and erosion of the underlying K110 sequence; it can be clearly demonstrated in Kuwait (Strohmenger et al, 2006;Vincent et al, 2020) but is not evident in Oman (van Buchem et al, 2002). K130 (middle -late Cenomanian): A major sequence boundary occurs around the lower/middle Cenomanian boundary and is associated with erosion and channel incision (e.g.…”

“…Outcrops of the mid-Cretaceous stratigraphic interval occur in the Al Hajar Mountains and the Jebel Akhdar area in northern Oman and in the Zagros Mountains of SW Iran, and provide an opportunity to build a reference model that can be applied in the subsurface and regionally across the Arabian Plate. These outcrops have been studied extensively: in Oman by van Buchem et al (1996van Buchem et al ( , 2002, Grelaud et al, (2006Grelaud et al, ( , 2010; Homewood et al (2008) and Razin et al (2017); and in Iran by Razin et al (2010), Vincent et al (2015), Navidtalab et al (2019), Navidtalab et al (2020) and Kalanat et al (2021). The outcrops are valuable for reference as they enable depositional sequences to be identified in age-constrained sections and correlated into the subsurface, and allow the depositional morphology to be characterized in three dimensions.…”

“…The Cenomanian-Turonian of the Arabian Plate has been extensively investigated at the outcrop scale (e.g. van Buchem et al, 2002;Homewood et al, 2008;Razin et al, 2010;Kalanat et al, 2021), at the field scale (e.g. Jordan et al, 1985;Videtich et al, 1988;Neo, 1996;Cantrell et al, 2020), and at the scale of individual intrashelf basins (e.g.…”

Determination of the mud weight window, optimum drilling trajectory, and wellbore stability using geomechanical parameters in one of the Iranian hydrocarbon reservoirs

“…The Upper Sarvak Formation is equivalent to the Mishrif Formation deposited in the south part of the Persian Gulf. This formation is regarded as a significant hydrocarbon reservoir of this area (Van Buchem et al 1996;Rahimi and Riahi 2020). The lower part of Mishrif is Khatiyah Formation that consists of organic matter-rich mudstone and wackestone.…”