The mechanical behavior of chalk under laboratory conditions simulating reservoir operations

Abstract

This work has been carried out with the chalk mechanics research society at the University of Stavanger. The PhD thesis is thus a continuation to the long line of experimental chalk research carried out honoring the academic principles investigating fundamental mechanisms of chalk mechanical behavior. Simultaneously, the work and objectives have been a joint project with the Ekofisk license (the COREC program) and the Valhall license ensuring a strong link to important operating challenges associated with hydrocarbon production from chalk reservoirs. The overall goal has been to address fundamental chalk behavior in a controlled laboratory environment and simultaneously approach conditions as close as possible as those in-situ. The focus in this thesis may be subdivided into five main categories: 1) Experimental challenges regarding the effective stress relations. 2) Time and rate effects during depletion close to in-situ conditions. 3) Seawater impact on creep close to in-situ conditions. 4) Basic mechanisms for chemical water weakening. 5) Effect of acid injection as a function of various chalk properties. The contribution of the pore fluid pressure to the reduction of the effective stress during loading of fully saturated high porosity chalk (>40% porosity) has often been assumed to be represented by an effective stress coefficient close to unity...