Regional Structure, Stratigraphic and Facies Studies (including stratigraphic framework, regional mapping and correlation)
The Carboniferous project: Sequence stratigraphy and potential reservoirs
PhD research Laurent Petitpierre, Dr Sebastian Frohlich, Dr Stefan Lubeseder and Professor Jonathan Redfern
Objective:The Carboniferous period remains very poorly studied in North Africa. Despite several oil and gas discoveries, no third order sequence stratigraphic framework is published and facies analyses of potential reservoirs are very limited. In this project we aim to produce a third order sequence stratigraphic framework in order to understand the regional evolution during sedimentation for Carboniferous period. In a second time, we aim to produce a fieldwork base study on a specific area (Western Libya). Finally, we aim to understand the factors controlling the deposition of the potential reservoirs. This project is now in the third phase.
Associate researchers:
Paul Grech, Simon Lang, Trent Rehill (Woodside)
Stephane Bodin, Guy Spence (NARG)
Deliverables:
2 papers accepted
1 paper submitted
Several papers in preparation
A PhD thesis in preparation
Part one (Stefan Lubeseder) completed; The Carboniferous in North Africa
A sequence stratigraphic framework based on a literature review and one fieldwork season in the Murzuq basin was proposed for North Africa.
All the Carboniferous stages are found in North Africa (Tournaisian, Viséan, Serpukhovian, Bashkirian, Moscovian, Kasimovian and Gzhelian) and this fairly continuous record of the sediment archives records a transition from a silicalstic dominated regime during the Tournaisian-Viséan interval to carbonate sedimentation during the Moscovian, Kasimovian and Gzhelian. The transition between these two end members is recorded by a mixed siliciclastic-carbonate regime interval during the Serpukhovian-Bashkirian interval. In terms of depositional environments, both laterally and temporally this homogenous system records marine to shallow marine facies.
However fluvial incursions can occur in incised valley settings and seem to be excellent potential reservoir during the siliclastic regime. Waulsortian-type reefal build-ups occur in Algeria and could be potential targets for exploration during more the carbonate influence phases of the sedimentation.
Paper:
Stratigraphic trapping potential in the Carboniferous of North Africa: developing new play concepts based on integrated outcrop sedimentology and regional sequence stratigraphy (Morocco, Algeria, Libya). S. Lubeseder, J. Redfern, L. Petitpierre, S. Fröhlich. Geol. Soc. Special Publications. Accepted.
Part two (Sebastian Fröhlich and Laurent Petitpierre) finished; The Carboniferous in Western Libya
a) Following the work effectuated during the phase one where the literature based correlation panel of the Carboniferous strata was oriented along an E-W axis. A North-South study was proposed in the area of western Libya where the Carboniferous sediment outcrop along several hundred kilometres in a SW-NE axis that present the advantage of being the generally accepted paleogeographic trend in this area. Two fieldwork seasons in three outcrop locations were undertaken where several kilometres of sections were logged through the entire Carboniferous.
The facies are mostly marine to shallow marine, although thick fluvial sandstones were described for the first time in the Marar and Assedjefar Formation (Tournaisian, Visean, Serpukovian). The thickness generally increases along the regional SW-NE paleogeographic trend.
The regional siliciclastic to carbonate transition described by Lubesder et al. was recognised in this area as well and the onset of the transitional mixed regime seems to be marked by the appearance a very widespread stromatolitic horizon.
b) An original diagenetic study on the potential reservoir sandstones was undertaken using isotopes and mineralogical mappings. It is the first academic case study on sedimentary rocks using the Qemscan® technology.
Papers:
Sedimentological and sequence stratigraphic analysis of Carboniferous deposits in western Libya: recording the sedimentary response of the northern Gondwana margin to climate and sealevel changes. Journal of African Earth Sciences, In Press. Sebastian Fröhlich, Laurent Petitpierre, Jonathan Redfern, Paul Grech, Stéphane Bodin, Simon Lang
Diagenetic evolution of incised channel sandstones: implications for reservoir characterisation of the Lower Carboniferous Marar Formation, Western Libya. Fröhlich, Sebastian; Redfern, Jonathan; Petitpierre, Laurent; Marshall, Jim; Power, Matthew; Grech, Paul. Submitted to Journal of Petroleum Geology
Part Three (Laurent Petitpierre) in progress
Controls on reservoir deposition and preservation in the Lower Carboniferous of Western Libya
a) This part focuses on the Lower Carboniferous (Marar formation) that is composed of the cyclic siliclastic sedimentation. Additional outcrop observations and logged sections are completing the sequence stratigraphic framework that will provide a higher resolution correlation panel of the Lower Carboniferous deposits in western Libya. The potential reservoir facies (shoreface and fluvial sandstones) are analysed with a special attention on the key surface they are intercalated. The potential glacio-eustatic controls on the sedimentation will be investigated although it has been evocated in the past (e.g. Lubeseder et al., Wendt et al. 2009). The stratigraphic and paleogeographic occurrence of the sandstones will be better described in order to understand the reservoir locations on this cratonic, widespread and low topographic gradient shelf.
b) The first carbonate occurrence composed of the Collenia stromatolitic horizon is investigated because it represents an excellent stratigraphic marker. A mapping of their extension and a gamma ray based technique to identify them in the subsurface are currently in progress
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