3D fully coupled multiphase modelling of Ekofisk reservoir

During reservoir production, the depletion usually induces a compaction of the reservoir layers. To enhance oil recovery, waterflooding operations are generally performed but, in the North Sea chalk reservoir, they have also induced an additional compaction. This latter phenomenon has a positive impact (improve the ‘Compaction drive’ oil recovery) but endangers the offshore platforms and causes huge extra costs. The coupling effects between mechanical behaviour and fluids flow are thus a key issue in petroleum engineering. Pasachalk program I & II have proposed a constitutive model (referred as Pasachalk model), where the suction is the key parameter to explain the water weakening effect. This model has been used for the modelling of waterflooding experiment on chalk plug and bi-dimensional reservoir. However, as the reservoir modelling is actually a 3D model, the purpose of this paper is to present 3D fully coupled modelling of a simplified Ekofisk reservoir during production and waterflooding phases. In order to exhibit the influence of the constitutive mechanical model, different studies are performed: increasing the complexity of the mechanical model (from an elastic model up to the Pasachalk one with suction effect). The numerical results show the influence of the mechanical law on the oil production and exhibit that only an elasto-plastic law with suction effects succeeds to reproduce compactions during both production and waterflooding.