Processes controlling geobody dimensions on carbonate platforms

Carbonate platforms typically do not exhibit a layer-cake distribution of facies, diagenetic modification or reservoir properties (porosity and permeability), but there is relatively little quantitative data available on the lateral extent of flow-controlling geobodies. Furthermore, the processes controlling the shape and size of those geobodies are not well constrained, impeding prediction of interwell reservoir properties. This theme focuses upon the quantitative characterisation of carbonate geobodies from outcrop and seismic data, and development of methods to improve predictability of carbonate body geometry.

Eocene carbonate build-ups established at toe-of-slope of prograding delta systems, Great Australian Bight, offshore Australia

Since dolomitisation often results in a marked contrast in colour and rock strength, its distribution is fairly easy to map within the field.  Furthermore, the distribution of dolomisation provides a useful proxy for understanding the lateral extent of reactive diagenetic fluids on carbonate platforms. Several projects within this theme focus upon understanding the nature and size of dolomite geobodies, and the processes controlling their distribution. Most of this work is within the Upper Cretaceous of the Western Mediterranean, including Tunisia and the Iberian Basin and the Danian of the Pyrenean Basin.  The length scales of depositional geobodies such as clinoforms and carbonate build-ups have been described and imaged using LiDAR in the Upper Cretaceous of the central Pyrenean Basin.  The shape and size of dolomitised remobilised Tertiary slope and basinal sediments on the Hammam Fauran Fault Block have also been mapped.

Digital Outcrop model of Sant Cornelli Formation, Santonian, Pyrennean Basin
Clinoforms in Coniacian platform carbonates, Pyrenean Basin

The results of detailed field mapping and logging are incorporated into digital outcrop and 3D geocellular models.  These models aim to develop workflows that allow optimal representation of depositional and diagenetic  geobodies and fractures within static reservoir models.  Population of these models with petrophysical properties means the relationship between geological data, porosity and permeability can be visualised, creating valuable analogue data for exploration and production of carbonate reservoirs.  

Facies model of Eocene Thebes Formation, Hammam Fauran Fault block, with geobody dimensions derived from field data and using stochastic object modelling

 

Overlay of diagenetic geobdies, dolomitised limestone shown in brown, within Eocene Thebes Formation, Hammam Fauran Fault block, with geobody dimensions derived from field data and using smoothed random function and a probability of distance from fault
Two dimensional fluid flow model for Hamman Fauran Fault block demonstrating geothermal convection of cold seawater at rift initiation, leading to stratabound dolomitisation on the Hammam Fauran Fault Block

Through collaboration with University of Bristol and Royal Holloway, University of London, the processes governing the shape and size of these geobodies can be forward modelled, such that iterative rules sets can be derived by which the likely occurrence, shape and size of geobodies can be predicted.  With the integration of petrophysical data, then these models can be advanced into seismic forward models that inform and constrain seismic interpretation of carbonate platforms., dolomitised limestone shown in brown, within  Eocene Thebes Formation, Hammam Fauran Fault block, with geobody dimensions derived from field data and using smoothed random function and a probability of distance from fault

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