石油および環境バイオテクノロジージャーナル

概要

State of Stresses: How to Simulate it Correctly in the Lab?

Vamegh Rasouli

The state of stresses is significantly important in terms of its impact on oil and gas upstream activities. From practical point of view three principal stresses are assumed in a field. The vertical stress is due to the weight of overburden rocks. As the rocks are constrained in their movement underground horizontal stresses will be imposed to an element of rock: this is related to the vertical stress and its magnitude is a function of formation properties. The horizontal stress is unlikely to be equal in different directions due to the existence of fractures at different scales and different geological structures such as folds or anticlines. Therefore it is anticipated that the horizontal stress is maximum in one specific direction, perpendicular to which the minimum horizontal stress acts in the same plane. This is while most of the lab experiments, such as hydraulic fracturing and sanding studies are carried out on cylindrical shaped samples where horizontal stresses are identical: this is contrary to the real state of stresses as applies to the rock. To correctly perform lab experiments a cube of rock is to be used to which three independent stresses can be applied.