Abstract

We studied the stress, temperature, and pore pressure perturbations in proximity of a passive salt dome subjected to given deviatoric far field stresses. Creep relaxation reduces stresses within the salt dome approaching a uniform isostatic stress state. The numerical simulation shows significant changes in stress magnitudes and orientation close to the salt dome. Pore pressure perturbations are small and limited to formations with low permeability. The effect of stress field variation close to the salt dome on borehole stability is discussed.

1 Introduction

Regions of salt uplift are interesting structures for hydrocarbon and also geothermal exploration. The flanks of the salt structures may serve as traps for oil and gas as frequently seen, e.g. in the North German Basin, but also feature local temperature anomalies. Understanding stress and temperature distribution around salt structures is important for successful exploration and production of reservoirs.

This paper discusses the geomechanical implications of a salt dome such as frequently found in the North German Basin (NGB). The focus is on simulation of the stress and temperature perturbations around a passive salt dome, which relaxes under given far field stresses. Stresses around salt structures show temporal evolution and spatial complexity and are referred to as the local stress field. They are affected by updoming of underlying salt formations leading to significant stress changes close to the forming salt structures. Salt movement was reported to lead to formation of normal, reverse and strike-slip faults that develop with varying orientations above and on the flanks of a salt dome, depending on the applied far field stresses (Yamada et al. 2005). The local stress state is thus affected by salt dome formation, associated temperature changes, and induced faulting. Consequently, uncertainties in local stress estimates are large, potentially causing numerous drilling and well stability problems, resulting in increased drilling costs (e.g., Dussault et al. 2004). It is generally assumed that stress within the salt dome at periods of rest is about isostatic (Bräuer et al. 2011), due to viscoelastic relaxation of the deviatoric stress.

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