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Application of Quantitative Outcrop Analogue Studies in Stratigraphic and Seismic Forward Modelling of Late Cretaceous Carbonate Platform Deposits

Abstract

Variability of small-scale facies architecture and geobodies within carbonate platform deposits poses a challenge in exploration and reservoir characterisation. Such geobodies may include bioherms, biostromes and grainstone clinoforms. At a sub-seismic scale, geobody shape and size are difficult to assess from seismic and borehole data, yet they may substantially contribute to reservoir heterogeneity. With many carbonate reservoirs entering advanced recovery it is crucial to understand how heterogeneity controls water or gas injection and hydrocarbon recovery. Stratigraphic and seismic process forward models that consider both geobody morphology and rock properties, based on actual parameterised analogue data, may be helpful. Digital outcrop models have been constructed from upper Cretaceous carbonate platforms (Turonian-Coniacian, lower Santonian and Campanian) exposed in the Tremp area of the south-central Pyrenees to extract quantitative data for modelling. Some of the platforms are dominated by grainstone and packstone clinoform bodies that are tens of metres thick, and others show alternations between laterally extensive rudist and coral buildups, small patch reefs and grainstone and rudstone clinoforms. Lidar scanning and photogrammetry allow quantification of size and spatial distribution of the exposed elements. Ground-proofing, including logging and sampling, with detailed petrographic studies provides the necessary geological and stratigraphical context. Modal analysis allows petrophysical parameters such as back-stripped porosity and permeabilities to be derived and compared with similar facies in the subsurface. Integrated into a digital outcrop model, the data provides a framework for stratigraphic and seismic forward modelling. Stratigraphic forward modelling is conducted using CarboCAT, which incorporates parameters such as depth-dependant production rates, subsidence, eustatic sea level change and sediment transport to predict 3D spatial distribution of carbonate facies. Simulation of different transportation processes, e.g. bed load transport, suspended plume and their dynamic combinations is conducted to help determine controls on clinoform geometry. Accurate stratigraphic modelling is the basis for developing synthetic seismic algorithms which consider all scale heterogeneities and structures to produce precise seismic response of the outcrops and to allow for safer interpretation and reservoir characterisation.