Well modeling: An overview

Abstract

The conditions prevailing at the wall, or in the neighborhood of a borehole, often influence the selected development scheme of a field, as well as the completion procedures used for each well. The stress concentrations generated by the drilling operation are not only a function of the geometry of the borehole, the magnitude and orientation of the in situ stresses and the reservoir rock behavior, but are also affected by the engineer's intrusion. This keynote address first succinctly reviews the classical potential failure mechanisms of a circular hole drilled in an elastic isotropic formation, pointing out the associated field problems. This introductory discussion includes stability considerations of far-reaching, as well as horizontal, completions. We then consider the extreme case of a borehole drilled in an environment leading to irremediable failure of the surrounding rock, due either to the low strength of the formation or to adverse in situ stress conditions. The extent of the broken zone is computed and the practical applications discussed in detail. The communication expands then further to include effects of anisotropy, pre-existing discontinuities, as well as coupling phenomena, such as poroelasticity and thermoporoelasticity. Finally, a number of potential aspects throughout the life of the reservoir are considered. The coupled simulations provide, indeed, insight into wellbore stability, sand production, casing design and time-dependent collapse, hydraulic fracturing and naturally fractured reservoirs. Many of those aspects are covered throughout this keynote address.