Thermally Induced Fracturing: Analysis of a Field Case in North Sea

Thermally Induced Fracturing (TIF) is often observed on injection wells. In this paper a well documented TIF case is presented and analysed. A numerical model is first presented where waterflooding is computed in two steps. In the first step, radial flow is considered and stress changes are computed. Depending on rock characteristics and flow rate the thermal effect (stress decrease) dominates over the pressure effect (stress increase). In the second step, as soon as the fracturing criterion is reached, the model automatically switches to a coupled two-phase flow option where a PKN type fracture has been incorporated. The main features of the model are summarized. To validate the model a field case has been analyzed where bottom hole pressure and temperature have been recorded. From field data it is shown that in the initial stage the height of the fracture varies and is thus different from the pay zone thickness. Use of Perkins and Gonzalez solution together with Prats formula allows to assess height and length evolution of the fracture. From this information, a mean fracture height can be assessed for the test duration. It is then shown that the pressure profile versus time is well given back using the numerical model, thus confirming the previous estimation of fracture dimensions.