DTS Transient Analysis: A New Tool To Assess Well-Flow Dynamics

Abstract

Abstract Distributed temperature sensing (DTS) is a valuable tool used to understand the dynamics of oil and gas production and injection rates. This is achieved by monitoring the temperature variations caused by flow or injection rates at the reservoir entry points. Although most documentation to date has been limited to the discussions resulting from the examination of steady-state temperature profile behavior, significantly more knowledge and better assessment of "what's happening" in wells can be gained when sequences of complete wellbore temperature profiles are analyzed during rate-related or other induced thermal transient events, such as seen in pressure transient analysis. DTS technology allows complete wellbore temperature profiles to be obtained in a short period of time without the need for wire line. Discrete temperature measurement information can be obtained along the entire wellbore using optical fiber and a laser source/detector to repeatedly pulse light down the fiber and detect the back-scattered light from every depth. The back-scattered light is the result of the interaction of each laser pulse with the fiber molecules and is proportional to the temperature of the glass at a given depth. Intensity responses of repeated light pulses are averaged to obtain acceptable temperature resolution and can be improved by increasing acquisition time. This paper discusses the value added from transient temperature analysis of DTS profiles for oil and gas wells under production, injection, and treatment conditions. Data taken with DTS technology and thermal simulators from several actual field cases will be provided to demonstrate how these techniques can improve analytical capabilities and how a temperature change has a direct relationship to production/injection layer contributions, reservoir flow properties, tubular leaks, and steam breakthrough locations. The field cases also will demonstrate how a DTS-acquired transient temperature profile analysis can be applied. In addition to the improved data acquisition capabilities, the paper will also provide the cost and safety advantages gained by using DTS transient analysis techniques.