Multiphase Flow Pattern and Screen Selection: Two Overlooked Parameters Essential to Reservoir Control Valve Optimization

Abstract

The deployment of sophisticated Autonomous Inflow Control Valves (AICV) to manage reservoir uncertainty and water production in stand-alone completion is becoming increasingly popular, and the range of options available is constantly evolving. To date, much of the extensive testing performed with AICVs has assumed homogenous/dispersed flow (taking no direct account of production phase separation) and has ignored the potential role of varying screen geometries. Under a wide range of downhole conditions, stratified flow may be a more likely scenario and the full scale testing of AICV assembly under realistic downhole field conditions provides insights into the annular flow behavior and identifies critical interactions between the AICV and the screen, potentially leading to new means of enhancing AICV performance. A series of multiphase flow tests was performed on full size screen and housing assemblies to verify flow pattern under realistic conditions and assess the potential for screen geometry to have an impact on the AICV performance in stratified flow conditions. Various features of the screens, such as screen type (mesh screen, wire wrap), and screen/basepipe standoff height were investigated under various water fractions, flow rates and oil viscosities. The screen jacket was also partially blocked by a sleeve to simulate the partial burial of the screen in the wellbore. The multiphase flow patterns in the annular space around the screen and inside the valve housing were monitored through observation windows and high-speed camera, in conjunction with pressure drop across the screen and the entire assembly. Under normal flowrates, it is observed that the multiphase flow shows a stratified flow pattern around the screen, with the location of the water/oil interface highly sensitive to the oil viscosity. For high viscosity oil (100cp), the W/O interface is very low, resulting in a high water phase velocity high. This provides another reason why the onset of water production in heavy oil is often causing rapid screen plugging and high drawdown. Under these conditions, stratified flow is also prevalent in the valve housing, irrespective of the screen type. Under semi buried conditions, the screen type and standoff between the screen jacket and the basepipe played an outsize role in defining the flow pattern inside the housing. With a mesh screen and tall standoff, the flow pattern remains largely stratified while a wire wrap screen yields a bubbly/misty condition. As a result of these change in flow pattern, AICV performance is expected to be degraded when wire wrap screens are used in partially collapsed wellbore.