Predicting and Managing Sand Production: A New Strategy

Abstract

Abstract Sand prediction at BP has been developed by dividing it into three parts:onset,transient sanding,steady-state sanding. For example, as drawdown is increased in a well in a sand-prone formation, significant sanding begins at some point (the onset), and this is followed by a transient sand burst, which may last hours or days or months. The sanding eventually declines to a background level (steady-state), in the range 1–100 pptb. We have made recent step-changes in (2) and (3), and we now have a tool that can predict sanding onset, and volumes during any stage of a well's production history, or even injection history. The onset of sanding is predicted using a stress-based model. This model is conservative, based on a benchmarking study of field applications. One application predicts sanding in water injectors during shut-in, and recommends not using sand control. Another application explains delayed sanding in an HPHT gas reservoir, in terms of restraining forces due to capillary cohesion (i.e., the damp sand effect at the beach). The transient sanding model is a fully-coupled finite element (FE) model. The model has successfully predicted sand volumes in laboratory and field tests. With this model, we can judge whether we can manage the produced sand, from both production and injection wells. Finally, we have applied this to predict whether a well will kill itself after a blowout, due to sand in the wellbore increasing the hydrostatic pressure. The steady-state model is an empirical model that is based upon extensive tests of sanding from cores in the laboratory. The model has been applied to predict sanding in an offshore field, and this has led to the conclusion that sand rates can be managed at surface, without sand control: a huge economic advantage. Finally, we present a case history where we use all three models to make an integrated prediction of onset, transient, and steady-state sanding, and find quite good agreement with field observations. In summary, the new three- fold strategy of sand prediction at BP has significantly increased our capability to predict sanding in production or injection wells. This quantum leap is invaluable to help decide if we can manage the sand at surface (or if downhole sand control is required); to decide if we can defer sand control until a later date (possibly increasing production as well as saving completion costs); to decide how much sand will be produced if we increase the drawdown in a sand-prone well; and even decide if we need sand control in water injectors. Introduction Sand prediction at BP has progressed in three stages:onset,transient sanding,steady-state sanding. As drawdown is increased in a well in a sand-prone formation, significant sanding begins at some point (the onset). Alternatively, the trigger may be an increase in depletion. This is followed by a transient sand burst, which may last hours or days or months. The sanding eventually declines to a background level (steady-state), in the range 1–100 pptb. Figure 1 is a summary of the three stages.