Design of Intelligent Well Downhole Valves for Adjustable Flow Control

Abstract

Abstract This paper describes the considerations and integrated design process for specifying the Cv characteristics of an adjustable flow control valve for an intelligent well. The paper emphasizes the need to consider the complete well as a control system, including inflow, choke performance and well bore outflow performance. The paper describes a method for establishing the most suitable flow control design for the application. The method combines nodal analysis and choke performance modelling to model the behaviour of the entire well bore system. This analysis is extended to multiple layer or multiple zone intelligent well completions. An example of the analysis is presented. Introduction An intelligent well completion is a system capable of collecting, transmitting and analysing completion, production, and reservoir data, and taking action to better control well and production processes. The value of the intelligent well technologies comes from their capability to actively modify the well zonal completions and performance through downhole flow control, and to monitor the response and performance of the zones through real-time downhole data acquisition, thereby maximizing the value of the asset. Downhole flow control valves for intelligent wells must handle a number of performance criteria that are often conflicting. In particular, the desire for minimum pressure drop at full open conditions can be opposed to the desire for sensitive flow control in a variable or adjustable flow control valve design. In a reservoir/well bore system, the friction pressure drop through the permeable reservoir rock surrounding the well bore (inflow), and the friction pressure drop in the production tubing to surface (outflow) absorb a large percentage of the energy and controlling pressure drop, hence the design of the flow control trim must account for these factors. The purpose of the design process is to specify a choke trim design, described as a Cv profile, that gives good flow control sensitivity across the range of valve positions. Because positioning of the valve control components is typically linear, the objective of the design process is to achieve linear flow performance in relation to the linear position of the choke i.e. with 30% linear position of the choke, the flow rate of the choke is approximately 30% of the design maximum rate. In general, an equal percentage control trim is the most suitable for downhole flow control design. Intelligent Well Flow Control Intelligent wells can be used to restrict or exclude production of unwanted effluents (water and/or gas) from different zones in a production well. They can be used to control the distribution of water or gas injection in a well between layers, between compartments, or between reservoirs. As a result, the operator can manage where water is injected or oil is extracted to mobilize unswept reserves. These capabilities can significantly enhance the performance of secondary water floods or tertiary EOR projects, and are particularly important for wells with complex architecture - extended reach, long horizontal or multilateral wells - and for reservoirs characterised by high degrees of anisotropy, heterogeneity or compartmentalization. Downhole flow control valves may be binary (on-off), choking with limited discrete settings, or infinitely variable choking. Actuation methods may be hydraulic, electric, or the hybrid electro-hydraulic. For infinitely variable choking or multiple discrete choking, the control trim profile can be standardized (typically equal percentage or linear) or can be custom designed for the reservoir application. The selection of the right flow control design is critical, as it may have an impact on the number of zones/intervals that can be effectively controlled in one well. The ability to modulate flow in multi-zone intelligent completions has been shown to accelerate production and enhance the recovery efficiency of development projects1,2. Variable flow control allows the operator to optimize the production from the well when water or gas begin to encroach on oil production, and to balance production from individual zones to deplete reservoir layers at a rate proportional to the reserves in place. Multi-zone injection wells depend on variable flow control for the appropriate distribution of the injectant to ensure uniform pressure maintenance or balance voidage replacement.