Sand control completions are an increasingly more significant part of the overall well cost as hydrocarbon developments are pushed into ever more challenging reservoirs. Successful project economics and performance hinges on reducing the risk and consequences of failure to a practical minimum. Erosion is often identified as the failure mode when investigating sand screen failures - even though the true root cause is often procedural or operational in nature. Determining the cause of such failures is nearly always problematical when the equipment cannot be retrieved to surface. Erosion is therefore perceived to be a major risk in cased hole sand control completions and even in high rate open-hole and water injection wells. The key to controlling this risk is an understanding of the erosion rate and how it affects the sand retention properties of the selected screen.
The results of a comprehensive set of erosion tests have been used to develop a erosion model which predicts probable time to screen failure based on fluid type, flux rate, solids loading and size distribution. The model has been verified against a number of actual screen failures and also to predict failure times based on specific completion designs.
The model described in this paper has been developed based on the particular characteristics of a slotted expandable sand screen. Expandable sand screens (ESSÒ) differ from conventional screens in that they are expanded mechanically or hydraulically to contact either the sand-face in open-hole or the inside of the casing/liner in cased-hole. Some expandable screens are expanded compliantly to form an intimate contact with the borehole wall and some are expanded to a fixed OD (i.e. non-compliantly) and can leave a small annulus. Hence, in a cased hole environment, the particles and fluid entering the borehole impact the screen immediately with little or no dispersion. Because expandable screens can offer significant practical advantages in other areas in such cased hole completions, it was necessary to develop a more in-depth understanding of the erosion mechanisms affecting potential applications. A fluid velocity (flux) based screen erosion model was developed in 2003 and can be used to validate stand-alone screen applications.
Operators also use drawdown and flux based guidelines to determine production limits for erosion sensitive completions. These methods do not predict service life at a given rate and are not directly applicable to expandable screens.