A constitutive model for North Sea Chalk. Application to reservoir compaction and to waterflooding

Subsidence of chalk oil reservoirs in North Sea is related to the chalk compaction induced by fluid depletion and by the water – chalk interaction. A constitutive model is developed in order to take into account these two effects. It is based on frictional – cap elastoplasticity and on the Barcelona unsaturated soil model. Oil – water – chalk interaction is modeled through the suction variable. The two saturating fluids flow is also developed. After implementation into a finite element code, these tools allow to simulate a waterflooding experiment on a chalk sample. The model appears to reproduce qualitatively and quantitatively the experimental results.