Abstract
Predicting sand production accurately is a difficult task; many techniques have been previously investigated such as production history, mechanical property analysis using electrical log data, laboratory testing and computer modeling.
In this study, the mechanism of sand production problem in an oil reservoir producing medium oil (30° API) from a weak sandstone formation was investigated. An analytical model is elaborated based on linear-poroelastic solution of stress state around circular openings as well as Mohr-Coulomb failure criterion and Darcy's equations for fluid flow through porous media in vertical and horizontal wellbores.
In this study, a new important factor necessary for the estimation of the mount of free sand generated between sheared planes caused by the fluid drawdown was introduced. This factor is called sand production capability factor. Sand capability factor was evaluated experimentally for the studied reservoir.
Observations of sand production in the studied oil reservoir were utilized to tune and verify the model used in this study. For open-hole completion, it was found that; free sand ready to move into the wellbore is inversely proportional to radial distance. Furthermore, free sand ready for production from the yielded zone around vertical wells is higher than that in the case of horizontal wells. The predicted free sand in all studied cases is in accordance with field observations.
Selection of borehole and perforation orientation (in case of perforated casing completion) with respect to the maximum horizontal principal in-situ stress has a great effect in reducing the potential free sand amounts ready to move into the wellbore along with the producing reservoir fluids. Horizontal wellbores oriented at 45° produce minimum sand compared with other horizontal orientations for the studied reservoir. Similar effect is found for perforations phased at zero angular position.
