Abstract

We use a simple analytical model to estimate the stress field in and near density-driven, rising salt domes. We show that the salt pressure within such domes varies linearly along the dome but with a magnitude greater than the overburden stress. We also show that the salt dome changes both the magnitude and the direction of stresses in adjacent sediments: the maximum stress increases higher than the overburden stress, and the minimum stress drops below the regional one. The maximum stress lies and the minimum stress lies tangent to the dome boundary in the circumferential direction. The magnitude of the salt pressure and of the sediment stresses is estimated from the density profile of sediments. These predictions are shown to agree with field observations near salt domes. Our results provide critical insight into the stress field perturbation in and near rising salt domes and can be used to assess the accuracy of numerical models and field measurements near these domes.

1. INTRODUCTION

Salt domes can harbor significant oil reservoirs. Salt’s extraordinary ductility makes salt domes an ideal seal to trap hydrocarbons flowing along margins of basins. In the Gulf of Mexico, the reservoirs trapped by salt domes are estimated to contain undiscovered recoverable resources of at least ~ 13 billion boe [1].

It is important to estimate the stress field in and near rising salt domes. Wellbores are often drilled near and through these domes to reach hydrocarbon targets trapped near them [2-5]. The stability of these wellbores depends on the current state of stress near the domes. In contrast to sediments, salt cannot sustain differential stresses. To accommodate an isotropic stress state, salt deforms and causes substantial perturbation of the regional stress field in adjacent sediments. Therefore, well-established approaches used to estimate the sediment stress field often fail near salt domes [6-9] because they have been derived for regional conditions [10-12].

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