Simulation of wellbore erosion and sand transport in long horizontal wells producing gas at high velocities

Abstract

Horizontal wells play a crucial role in improving the recovery of hydrocarbons from thin reservoirs. In weakly consolidated formations, these wells may encounter sand production and this may lead to several problems including wellbore instability, production time loss, corrosion and plugging of downhole and surface facilities. Sand production in wellbores can be linked to two physical phenomena. The first is stress concentration along the wellbore causing mechanical instability and localized failure of the rock. The second is related to hydro-mechanical forces that cause internal and surface erosion, triggering the release of particles from rock surface, by the action of drag forces of produced matter. In open hole completions, high-velocity gas flow can trigger the release of particles from rock surface.We present a reservoir-wellbore flow model to simulate high-velocity gas flow in porous media and in open-hole horizontal wells. Since gas wells are associated with high-velocity flows, this study is focused on dry gas production from long open-hole wells, where large sections of wellbore wall are exposed to the stresses caused by the flowing stream of gas. The Forchheimer equation is coupled with conservation of mass to solve for gas flow in the porous media while the Bernoulli's equation is coupled with mass conservation to solve for gas flow in the horizontal wellbore. Computed wellbore velocities are then used to calculate sand erosion using the Water Erosion Prediction Project (WEPP) model. Subsequently, an advection equation is used to model the transport of the eroded sand particles in the wellbore. An example is presented to study how wellbore erosion affects the flow of gas and pressure drop in the horizontal well. The results indicate that the erosion due to high-velocity gas flow in open-hole horizontal wells affects the gas production rate as well as the well flowing pressure.