A Workflow to Address Uncertainties in Frontier Areas and UnderexploredBasins by Integrating Palaeo-Environmental and Depositional Models withStratigraphic Forward Modelling:A Case Study for the Shu'aiba Formation

摘要

A new workflow is being developed to improve predictivity of geological models in frontier areas withlimited 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 overcomethis,we propose combining global palaeo-geographic maps and palaeo-Earth system models(PESM)withstratigraphic forward modelling(SFM).The result is an accelerated process for assessing reservoir presenceat a regional scale.Palaeo-environmental information is derived from various sources.A plate kinematics deformable platemodel underpins global palaeo-digital elevation models(DEM)and these define palaeo-drainage.DEMwere 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 derivedfrom these models can be fed as input parameters into a stratigraphic forward model.The geological processincorporated in the SFM can be tailored to fit the study's objective,regional framework and geologicalunits of interest.The resulting models can be used to extract reservoir thickness estimates or probability ofoccurrence of particular facies through multiple realisations in order to assess risks associated with reservoirpresence in the area.To showcase this approach,the depositional system of the Rub Al Khali basin during the Aptian(Shu'aibaFormation)is investigated.The low-angle carbonate ramp developed through the Berremian is replaced bya flat-topped platform with intra-platform basins(such as the Bab)exhibiting progradational clinoformstowards 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 theglobal palaeo-environmental data,either by funnelling it as input parameters,or using it as calibrationdata.The PESM outputs,such as wind patterns controlling wave action,provide valuable,time-savingconstrains when setting up key model parameters affecting carbonate deposition.The model shows thatmodelling 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 modelledprocesses and controls is used to assess the model robustness.For example,the interplay between subsidenceand carbonate production as the main controlling parameters for mean thickness and volume of potentialreservoir 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 betterunderstanding of the evolution of an area and implications on reservoir distribution.The model outputscan be used to improve exploration workflows,with the creation of confidence or presence risk maps forselected depositional features.