Slickline With Fiber-Optic Distributed Temperature Monitoring for Water-Injection and Gas Lift Systems Optimization in Mexico

Abstract

Abstract Sensa tube with fiber optic distributed temperature sensing (DTS) has provided useful real time information for Pemex in various wells through thermal analysis of distributed temperature data. Four case studies are presented in this paper: the first case corresponds to a water injection profile survey at a Northern project. The other cases are related to gas lift optimization in the Northern and Southern Mexican regions. As a part of the Pemex operated secondary recovery project in a Northern field, Fiber Optic Distributed Temperature Sensing technology has been used to monitor the water injection and warm-back temperature profiles across two perforated and fractured intervals, revealing the preferential flow into a one interval. The DTS thermal analysis provided important information to Pemex, which used the results as a guideline to take corrective action to increase the efficiency of their secondary oil recovery project. Pressure transient data was also collected to aid in the interpretation of the system using memory pressure gauges run on the fiber optic Sensa tube. The remaining case studies will demonstrate DTS gas lift systems optimization projects. One of these cases shows an example of an efficient gas lift system, meaning no need of post work-over well intervention. The other two case studies reveal issues with the gas lift system design, which compromised the lift efficiency and consequently the well productivity. Data acquisition using a portable fiber-optic Sensa tube unit has provided important information in a cost effective way. The DTS measurement provides a real-time and continuous temperature profile of the entire well, enabling the operator to monitor simultaneously all the gas lift valves, which is not possible to achieve with the usual time-consuming PLT surveys. Ultimately, the DTS monitoring has proven to be an efficient and reliable tool, saving the operator well intervention time and allowing immediate rectification of the issues observed. Introduction Temperature logs have been used to monitor producing wells since the early 1930's (Ref 1) and a considerable number of papers have been dedicated to the measurement and its analysis over the years. The data they generate has been used to calculate the flow contribution in both oil and gas wells and also to evaluate water injection profiles, the effectiveness of fracture jobs, identify cement tops, cross-flow between zones, flow outside the casing and other flow and well bore related events. Normally analysis of the temperature log is viewed as secondary to that of the spinner flow meter that gives flow velocity directly, and temperature is conventionally used only as an indicator of gas influx with the Production Logging Tool (PLT). The main challenge of the PLT temperature log is that only one thermal profile is obtained at the time the PLT is run, and this makes analysis difficult on a stand-alone basis. However Sensa's fiber optic Distributed Temperature System (DTS) can generate many temperature logs (from every 7 seconds upwards) over the life of the well because it is pre-installed with the completion and this allows well productivity to be evaluated without the need for other log data. In addition, the system identifies the source of a change in the wells performance when it occurs, rather than having to wait for a production log to be run.