This paper discusses the application of DAS for flow monitoring. While previous publications (Van der Horst et al (2013, 2014)) focused on vertical and horizontal tight gas wells in North America, the focus here is on liquid producers and injectors in Brunei. Specifically, it was found that DAS has potential for zonal production and injection allocation across ICVs, monitoring interzonal inflow from the reservoir, monitoring artificial lift, tracking fluid transport through the well bore, detecting leaks, and monitoring wax build up or other types of deposition in the well.
Distributed Acoustic Sensing is an emerging technology in the oil and gas industry, coming from the defence industry, which has the potential to revolutionize the way we secure our transport pipelines, acquire (micro-) seismic data, and monitor and optimize our wells and fields in the future. Following the successful introduction for pipeline integrity monitoring several years ago (Williams (2012)), Shell and OptaSense started a collaboration to develop DAS also for downhole applications (Koelman (2011), Koelman et al (2012, 2012)). This has led to major developments in the area of in-well monitoring (Boone et al (2014), Johanessen et al (2012), Molenaar et al (2011, 2011), Ugueto et al (2014), Van der Horst et al (2013, 2014)) and geophysical imaging and surveillance (Mateeva et al (2012), Mestayer et al (2012), Webster et al (2013, 2014)). The focus of this paper will be on the application of DAS for in-well flow monitoring.
DAS offers many advantages over traditional surveillance methods such as production logging tools, gauges, or geophones. A standard telecom fiber can be used for time lapse or continuously for both in-well and seismic applications throughout the life of the well and can also be shared with other fiber-optic technologies such as Distributed Temperature Sensing (DTS). The full length of a well can be interrogated simultaneously providing data at a spatial resolution as low as 1 m and at sample rates as high as 20 kHz. As a result DAS is a robust and potentially a cost-effective and powerful technology for permanent real-time monitoring of well operations. It also does not require well interventions, thereby reducing deferment and HSSE exposure.
The main drivers for pursuing fiber-optic technologies such as DAS and DTS are the increasingly complicated recovery mechanisms that we are going into, such as improved or enhanced oil recovery and unconventional oil or gas, the requirements to reduce the operational costs and HSSE exposure, and the need to increase production and reservoir recovery. In these types of environments there is a need for frequent and high-quality data that conventional logging methods often cannot offer. The reason is that they are either expensive, cause production deferment, increase HSSE risks, or because surveillance cannot be done frequent enough or over all depths of interest. Especially offshore, subsea, or in horizontal wells the costs and complex logistics of traditional surveillance often cannot be overcome.