Mineralogical and geochemical characteristics of the Paleozoic source rocks, Akkas gas field, Western Desert of Iraq: Implications for their origin, maturation and Ordovician-Silurian transition

Mohammed, Ibrahim Q.; Farouk, Sherif; Baioumy, Hassan; Lotfy, Naira M.; Al-Hadidy, Aboosh H.

doi:10.1016/j.marpetgeo.2020.104432

Cited by 23 publications

(8 citation statements)

References 47 publications

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“…The porosity analysis from the sidewall cores of Risha-6 ranged 3-6% but showed as high as 8% too with almost half percent as secondary in origin (Davies, 1990). The effective porosity for the Risha sandstone at the Risha Field is considered to be more than 5% (Risha Task Force, 1990 (Mohammed et al 2020). Sandstones are particularly significant when fractured (Fig.…”

Section: Proven and Potential Reservoirs Of Sequence: S5-ap2mentioning

confidence: 99%

“…Al-Khafaji et al (2015) concluded that only the Khabour Formation can be regarded as source for the gas and condensate in the Akkas field, whereas the hot shales of the Akkas Formation have not reached a sufficient maturation level in the well investigated. Mohammed et al (2020) concluded that the black shales of Khabour Formation are fair source rocks, highly matured and reached the peak of gas generation. Al-Juboury et al (2019) reported visual porosity in the sandstones from the Akkas-1and -3 wells ranging from 1% to 10%, but pore connectivity was considered often poor, which might affect the reservoir potential.…”

Section: Proven and Potential Reservoirs Of Sequence: S1-ap3mentioning

confidence: 99%

“…The Lower Palaeozoic succession is thus a primary exploration target with some discoveries in Ordovician and Silurian sandstones (e.g. Al-Haba et al 1994;Aqrawi, 1998;Al-Hadidy,2007;Tamar-Agha, 2009;Al-Ameri, 2010;Aqrawi et al 2010;Al-Khafaji et al 2015;Al-Juboury et al 2019;Abdula et al 2020 andMohammed et al 2020) where it is thick in both eastern Jordan and western Iraq ( Figs. 2A & 2B).…”

Section: Introductionmentioning

confidence: 99%

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Review of the Lower-Palaeozoic Reservoir Prospectivity of W. Iraq With Reference to Jordan

Aqrawi

Masri²,

Horbury³

2020

IGJ

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The Palaeozoic basin of Jordan and Iraq occupies the NW part of the Arabian Plate. The Lower Palaeozoic succession is the most under-explored succession in Iraq, particularly in western Iraq where it is the most promising target for future exploration. The western Iraqi subsurface and Jordanian geology are characterized by similar major chrono-stratigraphic rock units. In western Iraq, the Akkas-1 well is the only gas and condensate discovery in sandstone reservoirs of Early Silurian and Late Ordovician age. Lower Silurian sandstones of the Akkas Formation are an oil reservoir characterized by an average porosity of 6.5% and permeability of 0.2 mD. Underlying Upper Ordovician sandstones of the upper part of the Khabour Formation are also reservoir, but for sweet gas and condensate. The latter are comparable to both the Risha and Wadi Sirhan discoveries in Jordan. Several deeper potential sandstone reservoirs (of older Ordovician and Cambrian ages) are also present across the region. Equivalent Ordovician age Jordanian reservoirs are primarily developed in homogeneous, highly mature quartz arenites of storm-dominated clastic-shelf stratigraphies. Within the Risha Field and the Wadi Sirhan area, are also end-Ordovician (Hirnantian) glaciogenic and periglacial sandstones with more variable reservoir quality characteristics compared to the underlying quartz arenites. These often comprise highly immature arkoses (as diamictites), which provide a mineralogically much less stable assemblage in which there is a possibility of developing secondary porosity. Almost similar sandstones were also reported from the upper part of the Khabour Formation in the Akkas Field of western Iraq. Sedimentological and XRD mineralogical studies suggest that diagenesis is an important factor in developing of reservoir quality. Nevertheless, reservoir quality is a major exploration risk where burial was significant that led to quartz overgrowth and clay cementation. It is notable that some sandstone reservoirs have chlorite-clay

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Section: Proven and Potential Reservoirs Of Sequence: S5-ap2mentioning

confidence: 99%

Section: Proven and Potential Reservoirs Of Sequence: S1-ap3mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Review of the Lower-Palaeozoic Reservoir Prospectivity of W. Iraq With Reference to Jordan

Aqrawi

Masri²,

Horbury³

2020

IGJ

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“…They are also present at a similar stratigraphic level in the interior basins of the USA, the Amazon Basin and on the Russian platform (Klemme and Ulmishek, 1991;MacGregor, 1996). Deposition of the "hot" shales is considered by many authors to have occurred during the early stages of the marine transgression which followed the Late Ordovician (Hirnantian) glaciation (Konert et al, 2001;Sharland et al, 2001;Haq and Al-Qahtani, 2005;Le Heron et al, 2009;Mohammed et al, 2020). The distribution of the shales is thought to have been controlled by relief on the underlying depositional surface (Lüning et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

“…In previous studies, TOC values up to 16.6% in the Akkas-1 well and up to 9.5% in the Akkas-3 well have been reported (Al-Haba et al, 1994). Because of their economic significance, these shales have previously been studied in terms of their biostratigraphy, organic geochemistry and hydrocarbon potential (Baban, 1996;Aqrawi, 1998;Al-Juboury and Al-Hadidy, 2009;Al-Ameri, 2010;Alkhafaji et al, 2015a, b;Mohammed et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Organic and Inorganic Geochemical and Mineralogical Assessments of the Silurian Akkas Formation, Western Iraq

Al-Juboury

Howard²,

Vincent³

et al. 2020

Journal of Petroleum Geology

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The Silurian Akkas Formation has been reported and described only in the subsurface of western Iraq. The formation is divided into the lower Hoseiba Member, which contains two high‐TOC “hot” shale intervals that together are around 60 m thick, and the overlying Qaim Member that is composed of lower‐TOC “cold” shales. This study investigates the source rock potential of Akkas Formation shales from the Akkas‐1and Akkas‐3 wells in western Iraq and assesses the relationship between their mineral and elemental contents and their redox depositional conditions and thermal maturity. Twenty‐six shale samples from both members of the Akkas Formation from the Akkas‐1and Akkas‐3 wells were analysed. The results showed that the upper, ~20 m thick“hot” shale interval in the lower Hoseiba Member has good source rock characteristics with an average TOC content of 5.5 wt% and a mean Rock‐Eval S2 of 10 kg/tonne. Taken together, the two “hot” shale intervals and the intervening “cold” shale of the Hoseiba Member are ~125‐150 m thick and have an average TOC of 3.3 wt% and mean S2 of 6.2 kg/tonne. The samples from the Hoseiba Member contain mixed Type II / III or Type III kerogen with an HI of up to 296 mgS2/gTOC. Visual organic‐matter analysis showed that the samples contain dark brown, opaque amorphous organic matter with minor amounts of vitrinite‐like and algal (Tasmanites) material. Pyrolysis – gas chromatography undertaken on a single sample indicated a mature (or higher) algal‐dominated Type II kerogen. High spore and acritarch colour index values and weak or absent fluorescence similarly suggest that the lower part of the Akkas Formation is late mature to early post‐mature for oil generation. “Cold” shales from the Qaim Member in the Akkas‐3 well may locally have good source rock potential, while samples from the upper part of the Qaim Member from the Akkas‐1 well have little source rock potential. Varied results from this interval may reflect source rock heterogeneity and limited sample coverage.Mineralogically, all the shale samples studied were dominated by clay minerals – illite and kaolinite with minor amounts of chlorite and illite mixed layers. Non‐clay minerals included quartz, carbonates, feldspars and pyrite along with rare apatite and anatase. Palaeoredox proxies confirmed the general link between anoxia and “hot” shale deposition; however, there was no clear relationship between TOC and U suggesting that another carrier of U could be present. Rare Earth Element (REE) contents suggested a slight change in sediment provenance during the deposition of the Akkas Formation. The presence of common micropores and fractures identified under SEM indicates that these shales could become potential unconventional reservoirs following hydraulic fracturing. Evidence for the dissolution of carbonate minerals was present along fractures, suggesting the possible passage of diagenetic fluids.Palynological analysis combined with existing graptolite studies support a Wenlock ‐ Pridoli/Ludlow age for the Akkas “hot”shales. This is younger than many other regional “hot shale” age estimates and warrants further detailed investigation.

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Geochemical characteristics and the significance of two major coal‐bearing strata claystones from the Datong Coalfield (North China)

Liu

Zhang

et al. 2022

Geological Journal

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This study aims to investigate the significance of the geochemical differences and the factors that control the geochemistry of two major types of coal‐bearing stratum claystones (sedimentary kaolinitic claystone [SK‐claystone] and tonstein). The SK‐claystone and tonstein derived from the Taiyuan Formation of the Upper Carboniferous coal‐bearing strata in the Datong Coalfield of North China have been comprehensively analysed using X‐ray powder diffractometer, scanning electron microscopy, X‐ray fluorescence, and inductively coupled plasma mass spectrometry. The results showed that the SK‐claystones and tonsteins exhibit similar SiO2 content; however, the content of Al2O3 in tonsteins is higher than that in SK‐claystones, whereas the TFe2O3 and K2O content in tonsteins are lower than those in SK‐claystones. These findings are consistent with the mineral composition analysis of the samples. The SK‐claystones and tonsteins have different parent rocks, as shown by the Al2O3/TiO2 ratios, diagram of Zr/TiO2 versus Nb/Y, and chondrite‐normalized rare earth element patterns. The palaeosalinity indexes (B/Ga and Sr/Ba) and palaeoredox proxies (Mo and U enrichment factors as well as U/Th ratios) indicate that both SK‐claystones and tonsteins were formed in freshwater suboxic–oxic environments. The kaolinite in SK‐claystones and tonsteins is formed via the deposition or crystallization of aluminium‐rich weathering products and alteration of volcanic ash, respectively. In summary, the different parent rocks and diagenetic processes are the main factors differentiating the geochemical characteristics of the two types of claystones. Our study links the different types of elemental enrichment features to the geological genesis of the two types of claystones, indicating that the trace elemental enrichment characteristics can be used as indicators for distinguishing the SK‐claystone and tonstein in the Datong Coalfield as well as other similar coalfields.

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Mineralogical and geochemical characteristics of the Paleozoic source rocks, Akkas gas field, Western Desert of Iraq: Implications for their origin, maturation and Ordovician-Silurian transition

Cited by 23 publications

References 47 publications

Review of the Lower-Palaeozoic Reservoir Prospectivity of W. Iraq With Reference to Jordan

Review of the Lower-Palaeozoic Reservoir Prospectivity of W. Iraq With Reference to Jordan

Organic and Inorganic Geochemical and Mineralogical Assessments of the Silurian Akkas Formation, Western Iraq

Geochemical characteristics and the significance of two major coal‐bearing strata claystones from the Datong Coalfield (North China)

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