A Simplified Pseudo 3D Model To Evaluate Sand Production Risk in Deviated Cased Holes

Abstract

Abstract When comparing various wells on a given field in terms of sand production, it often happens that they display quite different behaviours: for example, deviated wells will produce sand whilst vertical ones won't. A major reason behind such an apparent paradox is the orientation of the well and its perforations in the in-situ stress field. Such a problem is usually studied by using complex non linear 3D Finite Element Models. In an attempt to make such an approach more flexible, this paper presents a simplified, semi quantitative analytical model able to evaluate sand production risks in cased holes with various deviations. This pseudo 3D model, based on linear elasticity, confirms that sand production risk for a given perforation strongly depends on well deviation and on the orientation of the perforation in the plane orthogonal to the wellbore. A field case illustrates how the model can hence provide an understanding for observations which could have otherwise remained unexplained. Finally, by introducing special failure criteria calibrated on hollow cylinder and cavity failure tests, an extension of the model is compared favourably to some 3D non linear numerical simulations in the case of a second field case. Because of its analytical nature, such an extension can easily be used in conjunction with logs in order to give a rather precise idea of the sand production risk on a newly drilled well. Introduction From an industrial point of view, accurate sand production prediction is an essential issue: a recent internal survey within Elf revealed that for 70 % of all wells drilled, the question of sand production is posed in one way or another before deciding upon the completion method. The Productivity Index (PI) of wells being itself very strongly affected by the completion method e.g., one can understand why such an issue has been considered as essential by the industry for more than two decades. In practice, the question of sand production is essentially raised when the development of a reservoir is planned. At this stage, it is usually decided whether the development wells for a given field will be equipped with sand control or if natural completion will be adopted. However, in many dubious cases, the available experience from exploration and appraisal wells - e.g. observations from tests - is not sufficient to allow for a complete assessment of the sand production risk and a conservative attitude is generally adopted - i.e. all wells will be equipped with sand control. P. 323^