Abstract
Several theories exist for estimating permissible well drawdowns based on mechanical properties of the formation. These models are well developed and extensively used for the initiation of sand failure. However, models for predicting sand volumes and the sanding behavior post failure are plagued by difficulties in characterizing the mechanical properties of the failed/plastified area, the complicated interplay of erosion and production of sand on stress distribution in the near wellbore and from assumptions of idealized geometries. This work describes a method for determining optimum bean-up strategies that limit mobilization of material such as fines or sand from failed perforations/sand-face. The method nicely circumvents issues that can limit the applicability of theoretical models when optimizing well bean-up by simply ensuring that any transient pressure gradients that develop are lower than the pressure gradients that exist in near wellbore for the normal operating state of the well. The assumption is that the asset is operating the wells at flow rates/drawdown that are acceptable to them in terms of sanding/solids production. Such an approach can be used to minimize sand production during regular bean-ups for wells that are produced at ASR (Acceptable Sand Rates) and for wells where fines mobilization is suspected in causing time dependent skin effects and plugging. Different strategies are given to estimate the maximum step change increases in drawdown, the number of discrete steps and the total bean-up time. Furthermore, a method is presented showing how the pressure profile observed following a shut-in can be used to determine the optimum bean-up rate for any well - without knowing the exact details of the well and flow geometry or the different diffusivity coefficients and properties of the various producing layers. This is a new insight and can be a very powerful tool.
