Sedimentological and diagenetic characterisation of Paleozoic carbonate platforms

The objective of this project is to build workflows that demonstrate the processes governing interaction of depositional architecture, deformation and diagenesis in controlling fluid flux and diagenesis in carbonate rocks in rifts basins using existing field data from Eocene carbonates in the Gulf of Suez, Egypt, outcrop data from humid-climate platform Permo-Carboniferous carbonates of the Carboniferous of northern England and Wales, and arid-climate Permian carbonates of and Svalbard. The results will be tested on a subsurface dataset of partially dolomitised Devonian carbonates in the Western Canadian Sedimentary Basin.

Fault controls on carbonate platform growth and diagenetic modification

Faults strongly controlled the location, growth and geometry of carbonate platforms, but few studies have linked how the interaction of structural, sedimentological and diagenetic processes controls rock properties in rift basins. The combination of these elements is key to a fundamental understanding of the localization of fluid-rock-interactive focal points. Such an understanding has scientific merit since it will better constrain how fluids migrate within and away from faults during rift evolution. This project will focus specifically on determination of the fundamental relationship between normal faulting, carbonate platform growth and diagenetic modification.

Faults play a profound role in the growth and diagenetic alteration of carbonate platforms. Fault growth may exert strong controls on the location and distribution of carbonate platforms and fault-controlled fluid flow can exert a strong preferential control on the distribution of diagenetically altered bodies. Conversely, stratigraphic architecture exerts strong controls onthe distribution of faults and fractures, and how which diagenetic reactions occur within the surrounding host rocks. The importance of normal fault geometry and permeability structure is still poorly understood.

This project will couple the understanding of how depositional stratigraphic elements and deformation interact, to constrain the processes governing fault- and fracture distribution and fluid flux by

Structural characterisation of normal faults and segment boundaries within the study areas, with simultaneous mapping of sedimentary architecture
Quantitative characterization of the spatial distribution of fractures, veins and stylolites around faults
Description of the diagenetic products associated with normal faults and quantification of their volume to parameterise the relationship between product volume and distance from fault.

Architecture of Palaeozoic carbonate platforms

The focus of this study will initially be Mississippian carbonate platform growth in northern England and Wales. These platforms show an evolution from ramp to steeply dipping, rimmed platforms, the margins of which were strongly influenced by normal faults developed during basin extension. The facies geometry on these platform margins is often complex, whilst gently winnowed platform interior sediments are characterised by stacked, upward shallowing parasequences capped by subaerial exposure surfaces. The platforms have typically undergone by marine cementation of the platform margin, and karstification and meteoric phreatic cementation in the platform interior. Fault-controlled diagenesis is ubiquitous, resulting in differential fault/fracture controlled dolomitisation, calcite cementation, MVT mineralisation and hydrocarbon emplacement.

This field based project will provide an integrated and quantitative description of platform geometry, facies distribution and diagenetic overprint on accessible Mississippian carbonate platforms in the UK, focusing on the platform margin and the role of extensional faulting in governing platform architecture. The data will be used to develop rules-sets for hydrocarbon exploration of carbonate platforms in rift basins and will define length scales that constrain geobody dimensions to populate subsurface reservoir models for appraisal & production. The project will deliver a quantitative description and reconstruction of facies architecture and diagenetic geobodies and determine the relationship between faulting, sedimentation and diagenetic modification. Digital outcrop models will be integrated with field data to constrain the distribution, size and shape of depositional facies, structural elements and diagenetic geobodies. The results will then be compared to Pennsylvanian- Permian platforms that grew in an arid climate, superbly exposed on Svalbard. The data will be compared and the role of climate and relative sea level as well as fault growth on platform architecture considered.

Sedimentation and diagenesis within pre-rift and syn-rift carbonate platforms, Gulf of Suez

This project extends an existing collaborative project between UoM, UoB and UiB.  It is focused upon understanding the relationship between sedimentation, diagenesis, particularly dolomitisation, and normal faulting in a syn-rift to early post-rift environment.  The results of this project would have relevance to prediction of the relationship between faulting, sedimentation, fracturing and diagenesis in syn-rift plays, particularly sub-salt plays.  It also has generic application to the prediction of the geometry and reservoir properties of fault/fracture controlled diagenetic geobodies.  The project offers a superb opportunity to model the relationship between mixed carbonate and siliciclastic sedimentation within an active rift setting, and the resultant seismic response.  It also provides an excellent opportunity to evaluate the interrelationship of rifting, thermal convection of hot, fluids of varying composition and dolomitisation, enhancing our understanding of diagenetic processes in rift basins.

The Sinai Rift was initiated in the Miocene, creating NW-SE trending faults that bound crustal-scale tilted fault blocks with eroded crests and hanging wall basins1.  Over the last fifteen years, numerous studies at UoM, UiB and RHUL, have focused on understanding the tectono-stratigraphic evolution of the Sinai Rift, and its impact upon the growth of carbonate platforms.  Since 2010, a high resolution, collaborative project between UoM, UiB and UoB has been underway to describe and model the Hammam Faraun Fault (HFF) Block, which has exceptional pseudo-3D exposure of a complex of fracture-fed and stratabound dolomite bodies 2,3.  Modern hot springs are coincident with the HFF, and delivers meteoric fluids into brine pools at temperatures of around 70oC.  The geometry of the facies within the host pre-rift Eocene Thebes Formation, the dolomite bodies and the associated fracture networks have been described in detail. 

The presence of fault/fracture controlled dolomite bodies that are resemble those of the Hammam Faraun fault block have been noted along the length of the Sinai rift, typically associated with accommodation zones between NE- and SW-dipping normal faults, and the presence of hot springs.  Dolomitisation does not appear to be stratigraphically constrained, and has been noted in pre-rift and syn-rift successions.  In some areas (examples in the Eocene) facies provide a strong control on diagenesis, whilst in others (examples in 

the Miocene) diagenesis cross-cuts facies, though the latter continues to influence reservoir quality.

The aim of this project is therefore to expand and enhance previous studies of the Sinai Rift and the Hammam Faraun Fault Block by understanding the regional controls on carbonate sedimentation and the flux of diagenetic fluids.  This will be achieved through a) constraining the tectono-stratigraphic controls on facies distribution, b) determining the basin-scale controls on patterns of fault/fracture controlled dolomitisation and c) testing conceptual models of fluid flux using nested, multi-scale stratigraphic and diagenetic forward models.  Integration of petrophysical data will allow construction of seismic forward models of the Hammam Fauran Fault Block. 

Multi-scale evaluation of fault-related diagenesis in a rift basin: Lessons from the Gulf of Suez

Predicting the geometry of fault-related diagenetic geobodies, their connectivity and reservoir quality is a fundamental challenge in the characterisation of subsurface reservoirs.  The suite of diagenetic reactions that can take place within carbonate platforms in rift basins includes dolomitisation, dissolution and/or precipitation of calcite, anhydrite and/or quartz, as well as mineralisation (SEDEX and MVT). The variable nature and geometry of diagenetic bodies within syn-rift platforms reflects a range of controlling factors, such as the rate of fluid circulation, source fluid geochemistry, distribution of temperature, pressure and fluid phase and permeability of the rock adjacent to the fault. The complex interactions between these controls over time mean it is difficult to understand the diagenetic system of rift-related settings simply using static conceptual models.

A fully funded PhD studentship (for UK/EU citizens) is now available as part of a new industrially-funded consortium project that links the expertise of four World-leading institutions in carbonate sedimentology diagenesis and structural geology (Universities of Manchester, Bristol, Royal Holloway University of London and Bergen).  The consortium aims to develop a process-based, predictive understanding of deposition, deformation and diagenesis (PD3) in carbonate systems. The studentship will utilise existing data held by the collaborating universities to evaluate the controls on the timing, distribution and character of diagenetic geobodies in an active rift setting using reactive transport models (RTMs). It will develop process-based models that can inform predictive models of diagenetic modification and provide insight into the fundamental processes controlling the characteristics of diagenetic products. The results of the study will be used to improve conceptual and geocellular porosity models for hydrocarbon exploration and production.

The project will be based upon data and pilot fluid flow models developed from spectacular outcrops of Eocene-Miocene carbonate platforms along the Gulf of Suez, where seismic-scale fault-controlled dolomite bodies include massive irregular bodies close to fault zones and stratiform bodies that may extend for several km laterally from the fault zone.  An active and long-lived aquifer system is in place and there is evidence of marine and meteoric diagenesis, sulphate precipitation and non-carbonate mineralisation.  Specifically the study will compare the diagenetic impact of pulsed flow during fault activation and longer-term convection along and around open fault systems during periods of tectonic quiescence.  It will also evaluate the relative importance of regional and local controls on the occurrence and connectivity of diagenetic geobodies, and quantify the sensitivity and hierarchy of geological controlling parameters. 

Training will be provided in basin modelling, geochemical modelling and state of the art reactive transport modelling.  The successful candidate will join an internationally renowned research team in fluid and reactive transport modelling at University of Bristol, and there will be regular contact with lead academics and other PhD students within the consortium.  It is expected that the successful candidate will be highly numerate and have strong communication skills in order to integrate with co-workers at collaborating universities and to present and deliver results to sponsoring companies via oral presentations, written reports and electronic media.  

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