Perforation Cavity Stability: Comprehensive Laboratory Experiments and Numerical Analysis

Abstract

SPE Members Abstract The paper describes comprehensive laboratory and numerical studies of perforation cavity stability and sand production from a perforation tunnel. Jacketed cores with a cavity simulating a perforation tunnel were loaded in a high-pressure vessel and fluid flow was applied. The cavity deformation and failure were monitored by a cantilever deformation gauge, while produced sand was monitored acoustically and volumetrically at the outlet of the cavity. A cavity stability analysis was conducted using a 3D non-linear finite element model. The numerical analysis shows that the onset of limited sand production matches the initiation of shear failure at the cavity wall. However, the perforation cavity is still relatively stable in the sense that it does not collapse. The sand production increases with the expansion of the post-failure zone, and the cavity finally collapses if excessive confining load is applied to the sample. The post-failure mechanisms are critical with respect to cavity collapse and sand production problems, which may explain the discrepancy between experimental and analytical results. Introduction Sand production prediction is currently considered as a major economical and technical issue by many operating companies. On the one hand, the systematic use of sand control completions to minimize potential sand production risk may lead to high skins [11, resulting in large productivity losses. On the other hand, completion without sand control device may lead to sand production problems with economical loss [2] and major safety risks - e.g. in an extreme case of unsuspected sand production from a high pressure gas reservoir, a leak can be created by sand blasting in a 20 000 psi wellhead in less than 1 hour. The ability to predict accurately where and when sand control will be necessary appears therefore crucial. Two recent conceptual papers [3–4] explored the issues raised by sand production modelling and showed that accurate modelling was still out of reach because sand production was responsible for dramatic geometry and parameter changes in the near wellbore area, where no existing model could simulate the step by step process of cavity evolution. Nonetheless, for engineering design, it is important to he able to predict the onset of sand production under given production practices even though the amount of produced sand cannot be fully quantified [1,2]. Such a prediction is made by modelling the onset of failure at the wall of perforation cavities in weak reservoir sandstones. In such models - e.g. [5] - the stresses at the cavity wall are computed by using 3D finite element codes, which must account for the complex 3D geometry of the perforated well [6], the non-linear rock rheology [7,8] and the fluid flow contribution [9], and then compared to the rock failure envelope. P. 339^