On Reservoir Fluid-Flow Control with Smart Completions

Abstract

SummaryPoor displacement efficiency in hydrocarbon formations is often caused by the natural variation in the mobility of fluids across the reservoir strata. Historically, completions with cemented casing, packers, conformance controlling fluids/gels, and selective perforations have been used to mitigate the disparities in water encroachment over the reservoir interval. Recently, completion technologies using downhole valves, which allow production and injection control over multiple zones, have become available. The central idea is that downhole control may be used to adjust flow distributions along the wellbore to correct undesired fluid-front movement.In this paper, we address several technical issues related to downhole controls. We consider a single system comprising the reservoir, the completion, the measurement, and the feedback algorithm that adjusts flow-control devices, with quantitative models for each of the components. Both pressure and flow-rate control systems are discussed. Downhole control is modeled for electrical, reversible hydraulic, and unidirectional hydraulic valves. The design methodology for different valve systems is described and the disadvantages of hydraulic systems are discussed. In particular, it is shown that in conjunction with an automated feedback control, hydraulic valves will oscillate. Computations also show that all other factors remaining equal, these oscillations occur most easily in low-permeability zones. For unidirectional hydraulic valves, we also illustrate novel anticipatory control algorithms that prevent overshooting.For communicating layered systems, a front movement equation is derived using perturbation techniques. This technique provides the zone of influence of wellbore flow-control devices, and illustrates the maximal benefit that may be obtained through down-hole control, thus providing a ready comparison with the cost of completion.