Distributed fibre-optic temperature sensing technique (DTS) for surveying underground gas storage facilities

The temperature distribution inside a storage facility and its variation with time and depth are key parameters for assessing operating conditions. Determining these parameters requires a technique which allows measuring temperature vs. depth and time simultaneously for the full length of a production string with a high depth and temperature resolution and with a high logging rate (30 seconds or 1 minute) over periods of several hours or days. These kind of data cannot be obtained using standard well logging techniques. Fibre-optic temperature sensing meets these requirements and hence opens up new possibilities for detecting and monitoring processes in production wells of storage facilities and producing oil and gas fields. This paper describes the capabilities of the measuring technique, presenting typical results of measurements taken to determine and exact location of leaks in pipe strings and technical installations, assess processes in caverns and aquifers and monitor fluid levels and long-term temperature changes in the overburden of aquifer storage facilities. The experience gained from the investigations shows that these kind of measurements are possible without any redesigns or technical modifications at the well head or inside the string, and without extended disruptions to storage operation. Fibre-optic temperature sensing is a low-cost diagnostic tool and therefore of great benefit when operating and monitoring underground storage facilities.