Depositional Environments and Large-Scale Sediment Architecture in the Upper Ordovician of the Murzuq Basin, SW Libya – Melaz Shugran and Mamuniyat Formations

McDougall, Neil; Tawengi, K.; Quin, Jamie G.; Pont, J. Vila

doi:10.3997/2214-4609-pdb.11.p08

Cited by 4 publications

(3 citation statements)

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“…Geological cross section of the Late Ordovician stratigraphic units in Murzuq Bain in Libya shows the transgressive silty‐shaly facies of the Bir Tlacsin appearing underlying the Silurian shales and overlying the Mamuniyat or older units (modified after McDougall et al . ).…”

Section: Geological Backgroundmentioning

confidence: 97%

“…; McDougall et al . ; El Ghali ; Ghnia and Aziz ). The erosion of the ice sheets or sub‐glacial melt water created an undulating topography.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…The Late Ordovician deposits of the Hawaz, Melaz Shuqran, and Mamuniyat siliciclastic facies (Fig. 2) are formed during multiple stages of advancing and retreating ice sheets (Ghienne et al 2003;McDougall et al 2005;El Ghali 2005;Ghnia and Aziz 2006). The erosion of the ice sheets or sub-glacial melt water created an undulating topography.…”

Section: G E O L O G I C a L B A C K G R O U N Dmentioning

confidence: 99%

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Application of amplitude spectrum and genetic inversion to determine shaly facies distribution: a case study: Murzuq Basin, Libya

Abushalah

Serpa

2018

Geophysical Prospecting

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Late Ordovician glacial deposits of the Mamuniyat Formation are the main oil reservoir in the Murzuq Basin in Libya. Autopicking the strong reflection at the base of the Silurian shales can be used to map the top of the Mamuniyat reservoir in the area where it is in direct contact with the Silurian shales. However, in areas where the Bir Tlacsin Formation, a mud‐prone unit, is between the Silurian shales and the Mamuniyat reservoir, the top of the Mamuniyat is difficult to pick because the units juxtaposed across the boundary are too similar to produce a strong reflection. Defining the Bir Tlacsin facies is important because it impacts hydrocarbon accumulation and migration. To predict the distribution of the shaly facies of Bir Tlacsin and enhance mapping of the top Mamuniyat reservoir, we utilized a continuous wavelet transform to identify the distinctive thickness of the Hot Shale and Bir Tlacsin units. We also used genetic inversion to distinguish the bulk density of the Bir Tlacsin facies. A 64 Hz frequency gave good time resolution to the amplitude spectrum and was used to predict the facies distribution of the Bir Tlacsin. In contrast, the 24 Hz frequency showed good frequency resolution of the amplitude spectrum and was used to estimate the temporal thickness of the non‐reservoir unit of Bir Tlacsin and Hot Shale. That estimate was then used to modify the autopick horizon for the base of the Silurian reflector to approximate the top of the Mamuniyat reservoir. Because of the large density contrast between the shaly facies of the Bir Tlacsin and the underlying and overlying units, inverted density also provides a way to predict the distribution of the Bir Tlacsin through estimated temporal thickness and to enhance mapping of the top Mamuniyat reservoir through mapping the base of the inverted density of the Bir Tlacsin. A comparison between mapping of the top reservoir using spectral decomposition and inverted density with respect to autopick shows that both methods improved the top of the Mamuniyat reservoir mapping. Prediction of the presence of Bir Tlacsin and improved accuracy of the top of the Mamuniyat reservoir mapping reduce the risk of drilling the shaly facies of Bir Tlacsin and provide a better estimate of the reservoir reserve.

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Section: Geological Backgroundmentioning

confidence: 97%

“…; McDougall et al . ; El Ghali ; Ghnia and Aziz ). The erosion of the ice sheets or sub‐glacial melt water created an undulating topography.…”

Section: Geological Backgroundmentioning

confidence: 99%

Section: G E O L O G I C a L B A C K G R O U N Dmentioning

confidence: 99%

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Application of amplitude spectrum and genetic inversion to determine shaly facies distribution: a case study: Murzuq Basin, Libya

Abushalah

Serpa

2018

Geophysical Prospecting

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Late Ordovician glaciogenic reservoir heterogeneity: An example from the Murzuq Basin, Libya

Heron

Craig

Sutcliffe³

et al. 2006

Marine and Petroleum Geology

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Using instantaneous frequency and colored inversion attributes to distinguish and determine the sandstones facies of the Late Ordovician Mamuniyat reservoir, R-field in Murzuq Basin, Libya

Abushalah

Serpa

2016

Interpretation

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The Mamuniyat petroleum reservoir in southwestern Libya is comprised of clean sandstones and intercalated shale and sand facies that are characterized by spatial porosity variations. Seismic reflection data from the field exhibit relatively low vertical seismic resolution, side lobes of reflection wavelets, reflection interference, and low acoustic impedance contrast between the reservoir and the units underneath the reservoir, which make mapping those facies a difficult task. In the absence of broadband seismic data, optimizing frequency bands of bandlimited data can be used to suppress pseudoreflectors resulting from side-lobe effects and help to separate the clean sandstone facies of the reservoir. We have optimized the data based on our investigation of seismic frequency bands and used instantaneous frequency analysis to reveal the reflection discontinuity that is mainly associated with the reservoir boundary of the sandstone facies of the clean Mamuniyat reservoir. We also preformed rock-physics diagnostic modeling and inverted the seismic data using spectral-based colored inversion into relative acoustic impedance. The inverted impedance matches the up-scaled impedance from the well data and the inversion of relative acoustic impedance confirms the conclusion that was drawn from the instantaneous frequency results. The interpretation of facies distributions based on the instantaneous frequency was supported by the inversion results and the rock-physics models.

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Depositional Environments and Large-Scale Sediment Architecture in the Upper Ordovician of the Murzuq Basin, SW Libya – Melaz Shugran and Mamuniyat Formations

Cited by 4 publications

References 0 publications

Application of amplitude spectrum and genetic inversion to determine shaly facies distribution: a case study: Murzuq Basin, Libya

Application of amplitude spectrum and genetic inversion to determine shaly facies distribution: a case study: Murzuq Basin, Libya

Late Ordovician glaciogenic reservoir heterogeneity: An example from the Murzuq Basin, Libya

Using instantaneous frequency and colored inversion attributes to distinguish and determine the sandstones facies of the Late Ordovician Mamuniyat reservoir, R-field in Murzuq Basin, Libya

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