Geomechanical modelling of a gas reservoir in the North German Basin
PhD thesis K. Fischer
DGMK Research Project 721: Prediction of tectonic stresses and fracture networks with geomechanical reservoir models – case study of a Rotliegend gas reservoir in the North German Basin.
The optimal exploitation of deep geothermal, as well as conventional and unconventional hydrocarbon reservoirs is strongly affected by the tectonic stress. Amongst others, wellbore stability and the orientation of hydraulically induced fracs depend on the recent in situ stress. However, the state of stress in a reservoir can be substantially modified by faults as well as vertical and lateral lithological changes, i.e. contrasts in rock mechanical properties.
Such local stress perturbations also existed in the past, while their characteristics are determined by the respective paleo-stress field differing from the present state. These paleo-stress field perturbations at times of fracture formation and reactivation were responsible for the spatial variations in fracture orientation, fracture type and fracture density observed today.
Within the DGMK Research Project 721, the potential of geomechanical reservoir models for a robust prediction of in situ stress fields and fracture networks is examined. These models are based on the Finite Element Method (FEM), which is the preferred numerical technique due to its abilities when dealing with the complexity of real reservoirs. Ideally, a “pre-drilling” prediction is desirable that can be used to optimize drillings and minimize exploration risks.
The case study reservoir of the research project is a mature gas field in the North German Basin. For this reservoir, a field-scale geomechanical FE model is built that comprises a large number of faults interpreted from 3D seismics. A wide range of further input and calibration data is available and provided by the project partners. These are ExxonMobil Production Deutschland GmbH, Gaz de France Suez E&P Deutschland GmbH and RWE Dea AG, whose funding and support is gratefully acknowledged.
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