Numerical study of the cycling dynamics of valves subject to calcium carbonate scaling

Abstract

It is customary for the oil industry to manage inorganic scale with inhibitors and squeezing. However, pumping downhole chemicals is not always an option in modern and smart completion systems with multiple production zones because of the inaccessibility in cableless smart completion systems. In fact, smart completion usually employs interval control valves (ICV) for production management, flowing the production through tiny flow ports. The valve itself has a complex geometry with a robust mechanical system installed for actuation, whose power input may be mechanical, hydraulic or electric. If downhole conditions are scale-prone (in terms of chemical composition, temperature, and pressure), ICV valves might be vulnerable for scaling turning itself into a precipitation spot that triggers the formation of crystals that eventually deposit elsewhere downstream. Associated problems with deposition are an increase in pressure drop because of available flow area reduction and risk of damaging key features for equipment actuation, permanently letting the valve stuck. Well operators frequently cycle ICV’s (closing the valve departing from the fully opened position and then opening it again) to wipe out deposits by mechanical action and reduce the pressure loss imposed by accumulated mass. Although cycling has advantages, it also has setbacks with the imminent risk of getting the valve stuck, requiring expensive and laborious workover maneuvers. The main objective of the present work is to propose a methodology for simulating calcium carbonate deposition and valve cycling in the presence of scaling. Alongside, it is possible to determine the ideal cycling frequency in terms of the accumulated mass of calcium carbonate. First, the inorganic scale formation is modeled considering the precipitated crystals as dispersed particles in a turbulent flow. Particles agglomerate because of adhesive force and eventually reach the walls by the action of flow dynamics, remaining adhered. The use of a hybrid Lagrangian-Eulerian approach allows simulating the scale formation in a ICV by the means of coupled methods CFD-DEM, monitoring the pressure increase, the accumulated mass as well scaling hot spots. Flow dynamic parameters derive from field production information and adhesive parameters are drawn from a calibration procedure, also proposed in the present work, based on tribology scratching tests of calciumcarbonate. Following the understanding of scale formation mechanisms, a Lagrangian approach is applied for the modeling of valve cycling with deposited calcium carbonate. The Discrete Element Method simulates the cycling operation applying to the ICV movable part an actuation force. The simulation monitors the position of the movable part that constantly interacts with particles, observing whether it reaches the fully closed position and, subsequently, opens again reaching the fully open position. The present work proposes a modeling and simulation procedure that is groundbreaking for the oil industry outlooking opportunities to better evaluate the scale risk of completion tools, qualify downhole parts in call for bids, and planning workovers interventions focusing in increasing production reliability and cost-cutting. The methods may also work as an inorganic scale mitigation tool, allowing well designers engineers to specify valves that are less prone vulnerable to scale.