Semi-analytic subsidence prediction

Subsidence of the surface due to the extraction of gas or oil from hydrocarbon reservoirs can in some cases be considerable. Two places where this is a problem are the Groningen field in The Netherlands and the Ekofisk field offshore Norway. Two approaches have traditionally been used to calculate subsidence: analytical and numerical. This paper presents a semi-analytical method, which has broader applicability than analytical models while calculation times remain very short. This new method can be applied for a multilayer subsurface in which the elastic properties vary per layer. It performed excellently in a validation exercise against analytical and numerical approaches. Further, the flexibility of the method was demonstrated using a field case. The new approach does not yet incorporate the viscoelastic behaviour of salt layers; this is scheduled for the near future.