Autonomous inflow control valves - Their modelling and "added value"

Wells equipped with inflow control devices (ICDs) are a proven method of improving sweep efficiency by passively controlling the influx of fluids into the well by the addition of a restriction to each completion joint. The application of ICDs is also essential to development of some oil fields previously found to be uneconomic. The ICD-completion design is a complex process requiring selection of the ICD restriction size, ICD type, and annular flow isolation (AFI). Several commercial ICD designs are now available, each of which react differently to the flowing fluid properties. This complicates the completion design process, which often requires the ICD completion to be specified against a poorly known reservoir and well performance prior to drilling the well. This adds a requirement for the ICD completion to improve oil recovery in a range of potential production scenarios. Unfortunately ICDs do not provide an optimal well design after breakthrough of the unwanted phases, despite their ability to balance the well inflow profile and achieve a uniform sweep towards a horizontal well in early years. Field experience has taught that ICD completions balance the well influx initially, but may not offer the optimal solution throughout the well's life due to the changes in the inflow conditions as the well matures. The recently introduced Autonomous Inflow Control Device (AICD) aims to restrict unwanted phases (gas and water), (partially) overcoming the results of reservoir uncertainty at the well completion design stage. Autonomous Inflow Control Valves (AICVs) are the next generation of flow control technology, being designed to virtually shut-off unwanted fluid inflows at completion joints. This paper describes the first AICV modelling workflow for integrated well/reservoir simulators. Its application allows reservoir and well engineers to quantify the value added by the optimal use of this new, down-hole completion technology. The workflow has been used to compare the performance of advanced well completion options (AICVs and ICDs) in a synthetic, oil-rim reservoir model mimicking a larger North Sea field where production is dominated by gas-coning problems. Down-hole flow control with AICVs significantly increased oil recovery compared to ICDs and conventional wells employing wellhead choke control. Unwanted fluid production was also reduced by up to 80%; a result that combines higher oil recovery with more efficient use of reservoir energy by the AICV completion.