On Reservoir Fluid-ow Control with Smart Completions

Abstract

AbstractPoor displacement efficiency in hydrocarbon formations is often due to the natural variation in the mobility of fluids across the reservoir strata. Historically, completions with cemented casing, packers, and selective perforations have been used to mitigate the disparities in water encroachment over the reservoir interval. Recently, completion technologies using downhole valves allowing production and injection control over multiple zones have become available. The central idea is that the 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 the completion, the reservoir, the measurement, and the feedback algorithm that adjusts flow-control devices as a single system 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. System design requires a quantitative description of both the orifices in the control valves, and the feedback control algorithm. 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. We also illustrate novel anticipatory control algorithms that prevent overshooting with unidirectional hydraulic valves.For layered systems that communicate, 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 downhole control, and hence provides a ready comparison of the benefit with completion costs.