Sanding Prediction in a Gas Well Offshore Mexico Using a Numerical Simulator

Abstract

Sand production is a problem that plagues many reservoirs and has strongly affected benefit-cost relationships in the oil industry for years. Research dating as far back as the early 1930s has documented sand-production problems in unconsolidated formations.These problems are not related to one specific location or area, and although sand production is a worldwide problem, the major documented areas of sand production are in the USA, Canada, the North Sea, Europe, Venezuela, Bolivia, Brazil, and Colombia. Major causes of sand production include depletion, a change in flowing fluids, a change in stresses, and wellborestability failure.Failure to manage sand production can have a significant impact on the productivity of the well with the possibility of causing an eventual well collapse.In this paper, the application of a numerical simulator used for sand prediction in a gas well is presented. The simulator predicts the amount of produced sand and its effect on the productivity of the well. The model is based on the hydro-erosion model, first proposed by Vardoulakis in 1996(Vardoulakis et al. 1996. The model is based on rigid, porous media (no skeleton deformation), in which mass balance is applied to a three-constituent system comprised of solid, fluid, and fluidized solid using the homogenization-mixture theory. Subsequently, Wan and Wang (2002) extended this pure-erosion model to include the effects of the deformation of porous media in a consistent manner. A single-phase flow is iteratively coupled with geomechanics within a continuum mechanics framework. Furthermore, Wang (2004) extended previous work to develop a fully coupled reservoir-geomechanics model to account for the effects of multiphase flow and geomechanics in a consistent manner.By using this numerical simulator application, the severity and quantification of the problem of sand production were resolved, resulting in an acceptable economical return. The results of this field case are documented below in further detail. The Sand-Production ProcessSand production occurs when the stresses of the formation exceed the strength of the formation. The formation strength is derived from the natural cementing material that bonds the sand grains together. Sand grains are also held together by the cohesive forces caused by the immobile formation water.The stress of the formation-sand grains is caused by many factors, such as tectonic actions, overburden pressure, pore pressure, stress changes from drilling, and the drag forces of the producing fluids.Sand production is rate-sensitive in that there is a rate below which no sand production occurs. This reduced producing rate can be uneconomical because some formation sands might be produced with a fairly low fluid velocity. In some unconsolidated sands, the cementing agent is clay and mud that forms a weak material that provides little or no strength to withstand the formation stresses. In such a case, a wellbore might produce sand even during the production tests. Other formations might initially produce sand-f...