A Workflow to Address Uncertainties in Frontier Areas and Underexplored Basins by Integrating Palaeo-Environmental and Depositional Models with Stratigraphic Forward Modelling: A Case Study for the Shu'aiba Formation
Authors: Kozlowski Estanislao , Moragas Mar , Gold David , Gill Claire , Ashley Alexandra , Valdes Paul 
Published: November 2020

A new workflow is being developed to improve predictivity of geological models in frontier areas with limited data. In underexplored basins, thicknesses and facies distribution, and resulting reservoir presence, are difficult to estimate, often relying on analogues and conceptual depositional models. To overcome this, we propose combining global palaeo-geographic maps and palaeo-Earth system models (PESM) with stratigraphic forward modelling (SFM). The result is an accelerated process for assessing reservoir presence at a regional scale.

Palaeo-environmental information is derived from various sources. A plate kinematics deformable plate model underpins global palaeo-digital elevation models (DEM) and these define palaeo-drainage. DEM were coupled with PESM (UK Met Office HadCM3 GCM) and palaeo-tidal models (Imperial College, UK, ICOM) to provide quantitative global data such as oceanic currents and wind patterns. The data derived from these models can be fed as input parameters into a stratigraphic forward model. The geological process incorporated in the SFM can be tailored to fit the study's objective, regional framework and geological units of interest. The resulting models can be used to extract reservoir thickness estimates or probability of occurrence of particular facies through multiple realisations in order to assess risks associated with reservoir presence in the area.

To showcase this approach, the depositional system of the Rub Al Khali basin during the Aptian (Shu'aiba Formation) is investigated. The low-angle carbonate ramp developed through the Berremian is replaced by a flat-topped platform with intra-platform basins (such as the Bab) exhibiting progradational clinoforms towards the basin edges. For this exercise, we identified strata dominated by bionconstructed sediment (deposited in high energy, shallow settings) as potential reservoir units. The Shu'aiba SFM sits on the global palaeo-environmental data, either by funnelling it as input parameters, or using it as calibration data. The PESM outputs, such as wind patterns controlling wave action, provide valuable, time-saving constrains when setting up key model parameters affecting carbonate deposition. The model shows that modelling wave action and its effect on carbonate growth and transport is important for replicating the facies distribution observed in palaeo-environmental maps. Uncertainty analysis of different modelled processes and controls is used to assess the model robustness. For example, the interplay between subsidence and carbonate production as the main controlling parameters for mean thickness and volume of potential reservoir units can be quantified.

The use of a global palaeo-environmental database is key to speed up the model setup and validation. The continuous characterization of depositional features achieved in this type of 4D model allows a better understanding of the evolution of an area and implications on reservoir distribution. The model outputs can be used to improve exploration workflows, with the creation of confidence or presence risk maps for selected depositional features.