Annular Phase Separation with AICD Completions – The Impact on Well Flow Performance and Control of Unwanted Effluents

Abstract The design and method of operation of Autonomous Inflow Control Devices are reviewed, including single-phase and multi-phase flow performance. Next, the multi-phase flow of fluids in the annular space between circular conduits is examined based on published information and flow pattern maps. This information is brought together in a thought experiment describing how AICDs and well performance will react to the segregation of fluids upstream of the flow control device, and the potential impact that the degree of restrictiveness on unwanted effluents can affect the flow performance of the reservoir and well. Finally, the impact on well flow performance is quantified by computer modelling of the reservoir inflow performance, annular flow performance, and AICD performance. The sensitivity of well productivity is assessed for multiple flow scenarios adjusting several model parameters, including type and number of AICDs per zone, GOR, water cut, flow rate, and well completion size. Although the concept of an AICD that completely shuts off gas and/or water production sounds appealing to those wishing to eliminate the production of unwanted effluents, a full understanding of the dynamics of inflow from the reservoir and phase segregation in the wellbore is necessary to evaluate the impact of highly restrictive AICDs on well productivity. With annular separation, even small water cuts or limited amounts of free gas flowing into the wellbore can cause most of the highly restrictive AICDs in a multiple device zone to shut, greatly impacting the oil productivity of the zone and the well. Using AICDs that are not as restrictive of the unwanted effluents allows the operator to continue to produce oil at significant rates when associated with low water cuts or reduced free-gas GORs. A workflow for determining the optimum degree of restrictiveness is proposed and demonstrated.