An evaluation of methods for permanent downhole temperature monitoring for the Valhall Field
Downhole monitoring is valuable to the oil and gas industry due to the advantages knowledge brings when it comes to well optimisation. The more information available about an individual well strengthens the understanding of the total field dynamics, making it possible to maximise a field's productivity. An evaluation of applying one of two types of temperature monitoring systems, Distributed Temperature Sensing (DTS) and Wellwatcher Flux to the Valhall field has beenconducted. The two systems have been evaluated on the basis of the following criteria:Instillation complexity, operational reliability after instillation, cost of instillation including rig time, contingency plan, experience and the different features the system provides. DTS consists of either a prefabricated ber optic cable or a hollow steel cable that is clamped to the outside of the liner, where an optical ber is pumped in place after the completion string is installed. Due to the well design on Valhall, only the pumpable system is applicable for implementing to the Valhall eld. The fiber itself serves as the temperature sensors, enabling a continuous thermal prole of the well to be measured.The upper and lower completions are mated by a control line wet mate (CLWM), which allows for the fiber to be pumped from the upper to the lower completions. With the pumpable DTS system, it is currently not possible to incorporate pressure sensors. BP has relatively good experience with DTS in Azerbaijan, where improvements have been made to the system. It has continuous sensors, is more cost effective and is also able to monitor the effect of gas lift valves. However, the system has a slightly higher risk of failure during installation due to the CLWM. Once installed however, DTS has abetter contingency plan in the case of failure. Well watcher Flux is an electric cable that has up to 50 temperature point sensors attached.Pressure sensors are most likely available in 2014 and can be spliced directlyon to the cable. The upper and lower completions are connected through an inductive coupler, which allows communication between the two completions. Wellwatcher Flux is relatively new on the market. The system has only had 6 trialruns in India. The Wellwatcher Flux system has a maximum amount of sensors, is more expensive than DTS, and appears to be slightly less complicated to install due to the simplicity and reliability of the inductive coupler connecting the upper and lower completions. Based on the evaluation of the set criteria for the two systems, Wellwatcher Flux is determined to be a better candidate for implementing permanent temperature monitoring on Valhall.