Shallow-marine depositional sequences in a transgressive mixed siliciclastic-carbonate system: The Early Jurassic Marrat Formation from central Saudi Arabia

Al-Mojel, Abdullah; Razin, Philippe; Nindre, Yves-Michel Le; Dera, Guillaume

doi:10.1016/j.jafrearsci.2019.02.011

Cited by 14 publications

(7 citation statements)

References 60 publications

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“…At 100% water saturation, the NMR T 2 spectrum distribution of MSR is usually bimodal and the surface relaxation time ranges from 0.1 to 1000 ms. The NMR T 2 spectrum distribution of MCR is usually unimodal, and the surface relaxation time ranges from 0.1 to 15 ms. (4) In this study, the centrifugal method, the T 2 spectral morphological method, and the T 2 parameter method were used to estimate the T 2C values of mixed siliciclastic-carbonate rocks, which can be used along with the T 2 spectrum to distinguish irreducible fluids and movable fluids. The T 2C values determined by these methods agree well.…”

Section: Discussionmentioning

confidence: 99%

“…The curve of 100% irreducible water cumulative porosity represents the accumulation of all porosity values during centrifugation [43]; these values could be used to calculate the T2 cutoff value and the movable fluid's porosity. According to the relationship between T2 relaxation times, larger T2 (T2 > T2C) values usually represent larger pores and pore radii, which store the movable fluids [4]. Figure 6A,B,A1,B1 are the CT images of the pores and throats of Sample B' limestone sandstone rock, respectively.…”

Section: Nmr T2 Distribution Of Different Samplesmentioning

confidence: 99%

“…In 1984, Mount first proposed the term "mixed sediments" to describe the mixed sedimentation of siliciclastic and carbonate rocks [1]. Scholars around the world have successively conducted research on mixed sedimentary conditions [2][3][4], the main controlling factors of mixed sedimentation [3,5], mixed sedimentary sequences [6,7], and mixed sedimentary lithofacies distribution patterns [8,9]. Due to the late start of the study of mixed deposition, siliciclastic rocks and carbonate rocks of mixed deposition have traditionally been studied as independent systems, but such studies cannot effectively guide the exploration and development of oil fields with mixed siliciclastic-carbonate rock reservoirs, and there is a paucity of research on the mechanism of oil-gas migration and the significance of mineral geology in mixed sediments.…”

Section: Introductionmentioning

confidence: 99%

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Determination of NMR T2 Cutoff and CT Scanning for Pore Structure Evaluation in Mixed Siliciclastic–Carbonate Rocks before and after Acidification

Wang

Xie

Guo³

et al. 2020

Energies

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Nuclear magnetic resonance (NMR) is used widely to characterize petrophysical properties of siliciclastic and carbonate rocks but rarely to study those of mixed siliciclastic–carbonate rocks. In this study, 13 different core samples and eight acidified core samples selected amongst those 13 from the Paleogene Shahejie Formation in Southern Laizhouwan Sag, Bohai Bay Basin, were tested by scanning electron microscopy (SEM), micro-nano-computed tomography (CT), and NMR. SEM and CT results revealed a complex pore structure diversity, pore distribution, and pore-throat connectivity in mixed reservoirs. Sixteen groups of NMR experiments addressed changes in these properties and permeabilities of mixed siliciclastic–carbonate rocks before and after acidification to determine its effects on such reservoirs. NMR experimental results showed no “diffusion coupling” effect in mixed siliciclastic–carbonate rocks. Distributions of NMR T2 cutoff values (T2C) are closely related to the pore structure and lithologic characteristics before and after acidification. The T2C index separates irreducible and movable fluids in porous rocks and is a key factor in permeability prediction. Centrifugation experiments showed that, before acidification, the T2C of mixed siliciclastic–carbonate rocks with 60–90% siliciclastic content (MSR) ranged widely from 1.5 to 9.8 ms; the T2C of mixed siliciclastic–carbonate rocks with 60–90% carbonate content (MCR) ranged from 1.8 to 5.6 ms. After acidification, the T2C of MSR ranged widely from 2.6 to 11.6 ms, the T2C of MCR ranged from 1.5 to 5.6 ms, and no significant difference was observed between MCR reservoirs. Based on an analysis of the morphology of NMR T2 spectra, we propose a new T2 cutoff value prediction method for mixed siliciclastic–carbonate rocks based on a normal distribution function to predict various T2C values from morphological differences in NMR T2 spectra and to calculate the irreducible water saturation (Swir), i.e., the ratio of irreducible total fluid volume to effective porosity. The reliability of the proposed method is verified by comparing predicted T2C and Swir values with those from NMR experimental results. New experiments and modeling demonstrate the applicability of NMR for the petrophysical characterization of mixed siliciclastic–carbonate rock reservoirs. Our results have potential applications for identification and evaluation of mixed siliciclastic–carbonate rock reservoirs using NMR logging.

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Section: Discussionmentioning

confidence: 99%

Section: Nmr T2 Distribution Of Different Samplesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Determination of NMR T2 Cutoff and CT Scanning for Pore Structure Evaluation in Mixed Siliciclastic–Carbonate Rocks before and after Acidification

Wang

Xie

Guo³

et al. 2020

Energies

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“…It has an unconformable contact with the underlying Triassic Minjur Formation, while the upper contact with the overlying Dhruma Formation is generally found to be conformable [19,20,28,29] . However, some published articles suggest that the Marrat-Dhruma contact is unconformable in some places [19,20,23,30,31] .…”

Section: Geological Settings and Study Areamentioning

confidence: 99%

“…1B) [17,18] , no documentation or attempts have been made to investigate whether this globally recognized event had extended to Arabia. This can possibly be explained by the fact that these red beds have long been viewed as continental deposits [19,20,21,22,23] with the assumption that they cannot yield important geochemical results that can be used for correlation with the reported T-OAE data from the nearby Tethyan basins.…”

Section: Introductionmentioning

confidence: 99%

Expanding our understanding of the Toarcian Oceanic Anoxic Event in the Tethys Ocean: New insights from the Arabian Plate

Alnazghah

Koeshidayatullah

Alhussaini

et al. 2022

Preprint

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The Toarcian Oceanic Anoxic Event (T-OAE) has been reported widely across the Tethyan region and globally. In Arabia, and based on ammonite dating, the T-OAE coincided with the deposition of the reddish siliciclastic unit of the Marrat Formation. However, no evidence of the T-OAE was ever reported from Arabia because these red beds were previously interpreted as continental deposits. Recently, these red beds have been recognized as shallow marine deposits which open an opportunity to assess the occurrence of T-OAE in Arabia. In this study, a multiproxy geochemical characterization was performed on the Toarcian Marrat Formation to infer the chemistry of the paleowater column and identify intervals of possible T-OAE in Arabia. The coupled negative excursion of δ13Corg and enrichment of redox-sensitive elements (Mo, U, V, Cr) indicate a period of marine anoxia during the deposition of Marrat red beds, suggesting that they were deposited in shallow marine settings and under anoxic, potentially ferruginous ocean conditions. The reddening is interpreted to have occurred later due to the stabilization of unstable hydrous iron oxides to hematite under oxic marine conditions. This study records the first documentation of the T-OAE in the Arabian Plate. This will have significant implications for the overall understanding of the T-OAE globally and for exploration of hydrocarbon through realizations of potential new source rocks associated with the OAEs in the Toarcian and other time intervals.

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Sequence stratigraphy and facies analysis of the NE Gondwana Middle Jurassic inner-platform mixed carbonate-siliciclastic succession, Saudi Arabia

Al-Mojel

Razin

2022

Arab J Geosci

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Shallow-marine depositional sequences in a transgressive mixed siliciclastic-carbonate system: The Early Jurassic Marrat Formation from central Saudi Arabia

Cited by 14 publications

References 60 publications

Determination of NMR T2 Cutoff and CT Scanning for Pore Structure Evaluation in Mixed Siliciclastic–Carbonate Rocks before and after Acidification

Determination of NMR T2 Cutoff and CT Scanning for Pore Structure Evaluation in Mixed Siliciclastic–Carbonate Rocks before and after Acidification

Expanding our understanding of the Toarcian Oceanic Anoxic Event in the Tethys Ocean: New insights from the Arabian Plate

Sequence stratigraphy and facies analysis of the NE Gondwana Middle Jurassic inner-platform mixed carbonate-siliciclastic succession, Saudi Arabia

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