Application of Autonomous Outflow Control Devices to Optimise Three Simultaneous Operations in Monobore Wells, Case Study of Offshore China

Abstract

Abstract In a recent intervention campaign, improved field recovery was targeted by CNOOC through redesign of completions of several wells at Offshore China. This was to maximise the production and injection capacity of each platform with limited available wells per platform. Therefore, a new completion design was suggested that could accommodate performing three operations using one single completion wellbore simultaneously. The new completion comprises a system that allows oil production from the deepest reservoir (operation 1) while the string is used to produce water from the shallowest reservoir (operation 2) and re-inject the water down to the deeper reservoirs without bringing water up to the surface (operation 3). However, the control of fluid influx and outflux for each section of the wells was key to the success of the campaign especially since the reservoir management plan requires maintaining prescribed injection profiles. Focusing on injection operation and considering the risks associated with reservoir uncertainty and the likelihood of development of thief zones, it was recognised that the challenges could be mitigated by deploying autonomous outflow control devices (AOCDs). The device allows the flow of a certain amount of fluid toward the reservoir while autonomously closing after reaching a designed flowrate. As mentioned above, the wells usually pass through a water-bearing zone vertically where the water would be produced and pumped down to be injected into a middle reservoir. This middle reservoir section normally comprises a few separate sub-layers. This section of the wells was then divided into several completion zones separated by swellpackers with an appropriate number of AOCD installed on the screens in each zone. An integrated workflow was followed to deliver successfully the AOCD application for these complex wellbores. The workflow comprised performance evaluation of the basecase completions and sensitivity analyses to determine the best AOCD completions for the wells. The performance of one of the wells equipped with AOCD completion shows the devices have managed to achieve the prescribed outflow injection profile to these sub-layers supporting the nearby wells based on the reservoir management plan. This study demonstrates the possibility of maximizing the net value of each well drilled using new technologies. The AOCD completion enabled the operator to implement an optimum reservoir drainage strategy that uses downhole control which autonomously control the flow based on well dynamic conditions.