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During appraisal, the absence of data from which facies architecture and diagenetic modification can be mapped means multiple scenarios can be envisaged to both explain platform evolution through time, and also the resultant reservoir properties. Stratigraphic forward models and reactive transport models therefore offer an opportunity by which the sensitivity of the platform to particular environmental parameters – and its resultant response – can be analysed.

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During appraisal, the absence of data from which facies architecture and diagenetic modification can be mapped means multiple scenarios can be envisaged to both explain platform evolution through time, and also the resultant reservoir properties. Stratigraphic forward models and reactive transport models therefore offer an opportunity by which the sensitivity of the platform to particular environmental parameters – and its resultant response – can be analysed.

Reservoir models are critical to concept testing and selection for field development, including optimisation of well placement and analysis of full-field economics. In order that the most economically and technically feasible development option is selected, it is imperative that reservoir models are

a) constructed using geologically robust rules sets, providing confidence in interwell permeability prediction

b) have appropriately upscaled petrophysical properties, so that flow controlling layers are not obscured by averaging

c) have assigned dynamic data (e.g. relative permeability) that reflects, rather than obscures, reservoir heterogeneity

d) able to incorporate past and present reservoir performance within the geological interpretation, so that flow-controlling layers (e.g. baffles, barriers and high permeability streaks) are represented in the model, and

e) fundamentally linked to a fracture model

A range of geostatistical methods can be used for modelling carbonate reservoir architecture. None are used consistently by the industry, and the modelling workflow is often driven by corporate workflows (perhaps based on clastic reservoirs), reservoir architectural elements, data type, quality and volume, the timeframe available for model construction and prior experience of the reservoir modeller.

Once faults have been picked, surfaces mapped and the model grid constructed, most carbonate reservoirs should be modelled by a workflow that includes facies modelling, diagenetic modelling, petrophysical modelling and fracture modelling. However, during appraisal, it is unlikely that there will be sufficient data for this workflow to be developed in full. At this point it is more important to undertake a robust risk and uncertainty analysis and thereby assess the impact of these uncertainties by running multiple scenarios. One approach for ensuring that the most appropriate range of scenarios is modelled, taking account of the combined uncertainty of different parameters, is through experimental design (e.g. Hollis et al., 2011).

The rationale for forward modelling at different stages in the project lifecycle are considered below

This section provides a summmary of stratigraphic and seismic forward models produced as part of PD3. Full details are provided in Masiero, PhD in prep.