A general poro-elasto-plastic model for poorly consolidated sands

Sand failure and production are likely to occur during oil and gas production, especially in poorly consolidated formations. Most past research focuses on either experimental work to understand sanding mechanisms or simple sand production models to estimate the onset of sand production. Such models are usually not enough to capture sanding behavior in complex situations in the field. In this dissertation, a numerical 3D sand production prediction model is developed based on a general poro-elasto-plastic model for multi-phase fluid flow, which can predict both the onset of sanding and the volume of sand produced. The model is thoroughly validated with multiple analytical solutions. It is also validated with experiment data for the onset of sanding, sand production volume, and cavity shape caused by sand production. The model results are shown to agree well with all these experimentally measured quantities and for the first time predict sanding behavior in complex geometries over a wide range of conditions. From extensive sand production experiments, four distinct cavity shapes have been frequently observed: spiral shear band cavity, V-shape cavity, dog-ear cavity, and slit mode cavity. However, the reasons and the sanding mechanisms responsible for this behavior have not been fully articulated. Results presented here show that the model is capable of capturing all the complicated cavity shapes, and provide qualitative guidelines to define the conditions under which each type of cavity will be formed. The effect of different well completions on sand failure and production have been investigated with the model. Results show the potential advantage of using frac-packs for reducing the fluid pressure gradients and redistributing stresses. In addition, the impact of rock and fluid properties on sanding behavior has been studied to show the importance of mechanical failure and fluid erosion on sanding. Wells with multiple oriented perforations are analyzed to study the effect of perforation design on sand production. The application of the model has been further extended to quantitatively explain some field observations, including: delayed sanding in gas wells, sanding caused by water breakthrough, and water hammer effects. Simulation results suggest that rock strengthening by water evaporation and non-Darcy effects in gas flow can delay sand production. On the other hand, sanding after water breakthrough can be explained by accelerating sand failure and fluid erosion due to an increase in the water saturation. The impact of water hammer on sand failure has been investigated to optimize subsurface valve location and shut-in procedure. Finally, the sand production model is applied to a field case for HPHT wells to study sanding mechanisms for different sanding behavior observed in two wells in similar locations in the field. Simulation results show that rock heterogeneity and natural fractures are the most likely reasons for sand production in this field. The difference in onset of sanding from the two wells can be explained by different in-situ stresses, while the difference in severity of sanding can be explained by differences in pressure drawdown and the orientation of perforations. The critical drawdown during reservoir depletion are determined under different conditions from the model to guide drawdown management so as to prevent sanding issues.Petroleum and Geosystems Engineerin