Enabling Well and Reservoir Surveillance in Dual Water Injectors Through Distributed Fiber-Optic Sensing

Abstract

Abstract Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) are novel surveillance technologies which are increasingly being used for in-well surveillance, including in injector wells. Some of the applications include injection profiling, acid-stimulation optimization, well-integrity monitoring, and fracturing diagnostics. Our goal here is to demonstrate how this can be applied to a particular type of water injectors that use dual injection lines to improve conformance by decomingling the injection between shallow and deeper reservoir targets. Specifically, annulus injection will be used to target the shallow reservoirs and tubing injection to target the deeper reservoirs. Several case studies will be presented from water injectors located in the South of the Sultanate of Oman. This required integrated evaluation combining data from surface meters, downhole gauges, open-hole formation evaluation, as well as DAS and DTS. It will be shown how the data was analyzed to assess the efficiency of the waterflood, to optimize the water injection operating envelope, to identify fracture initiation or plugging, but also to analyze the effectiveness of the well and completion design. Through its high sample rate and narrow spatial resolution, DAS is particularly effective at monitoring changes to injectivity in real-time. This is especially helpful for identifying the onset of fracture initiation and monitoring the growth in fracture height, which is difficult to achieve with other technologies. DTS warm-back analysis was also performed to complement the DAS interpretation and monitor changes in conformance with a deeper depth of investigation than DAS. The unique value of the fiber-optic sensing technology is that it enables the implementation of the dual annulus-tubing injection completion design without limiting surveillance capabilities, as conventional surveillance in this well design is either impractical, not feasible, or too costly.