Prof. Dr. Andreas Henk
Department of Geology
Institut für Geowissenschaften
Albert-Ludwigs-Universitaet Freiburg

Karsten Fischer
Department of Geology
Institut für Geowissenschaften
Albert-Ludwigs-Universitaet Freiburg

The state of stress in a reservoir is affected by faults as well as vertical and lateral lithological changes, i.e. contrasts in rock mechanical properties. Observations from surface and subsurface studies indicate that such heterogeneities can substantially modify the local magnitudes and orientations of the three principal stresses. In some fault-controlled reservoirs, local stress orientations differing by up to 90° from the regional trend have been reported for individual fault compartments. Such stress perturbations characterize not only the present-day in situ stress regime in a reservoir, but must have existed also during past tectonic stages.Such paleo-stress field perturbations at the times of fracture formation and reactivation were responsible for the spatial variations in fracture orientation, fracture type and fracture density observed today.

Amongst others, wellbore stability, the orientation of hydraulically induced fracs and - especially in fractured reservoirs - permeability anisotropies depend on the recent in situ stress field. Considering this fundamental role of tectonic stresses and fractures for the optimal exploration and production of both conventional and unconventional hydrocarbon reservoirs, numerical tools which allow for a robust prediction of these reservoir properties are highly desirable. Such a tool requires the incorporation of the specific reservoir geometry, the remote stress field, as well as the mechanical properties of all participating lithologies and faults. Prior to other numerical techniques, the Finite Element Method (FEM) is able to meet these demands and deal with the complexity of real reservoirs. Within the DGMK Research Project 721, the potential of such FEM-based geomechanical reservoir models for a robust prediction of stress fields and fracture networks is examined using a gas field in the Rotliegend of the North German Basin as case study. The emerging extensive FE-models are computed in the bwGRiD.

Links

http://www.geologie.uni-freiburg.de/
http://www.dgmk.de/upstream/fbag_pro.html
http://www.ansys.com/de_de

Software

• ANSYS

Publications

• Fischer, K., Henk, A., 2011: Parameterstudien zum Einfluss von Störungen auf das tektonische Spannungsfeld am Beispiel eines norddeutschen Erdgasfeldes, DGMK-Tagungsbericht 2011-1, DGMK-ÖGEW Frühjahrstagung, 11-12 April 2011, Celle. (poster)
• Fischer, K., Henk, A., 2011: Factors controlling stress perturbations in faulted reservoirs - insights from numerical parameter studies. Conference Proceedings, 73rd EAGE Conference & Exhibition, 23-26 May 2011, Vienna. (poster)
• Henk, A. (2009): Perspectives of geomechanical reservoir models - why stress is important. - OIL GAS European Magazine, Vol. 35, 1/2009: 20-24. (paper)
• Henk, A., Fischer, K., 2011: Spannungsfeldperturbationen und geomechanische Lagerstättenmodelle - Methode und Prognosepotential. DGMK-Tagungsbericht 2011-1, DGMK-ÖGEW Frühjahrstagung, 11-12 April 2011, Celle. (oral presentation)
• Henk, A., Fischer, K., 2011: Building and calibrating 3D geomechanical reservoir models - a worked example. Conference Proceedings, 73rd EAGE Conference & Exhibition, 23-26 May 2011, Vienna. (oral presentation)
• Henk, A., Frischbutter, A. & Tawengi, K.S. (2010): Geomechanical reservoir models – a case study from the Sirte Basin / Libya. - OIL GAS European Magazine, Vol. 36, 1/2010: 18-22. (paper)