Permanent downhole pressure and temperature gauges have been installed in many intelligent wells worldwide. They provide surveillance data about performances of the wells and the reservoirs in a fashion of high resolution and precision. Compared to the pressure data, the temperature data have been underutilized in petroleum industry.
In this paper, we first examine the measured downhole temperature variation caused by the Joule-Thomson effect and infer the true reservoir temperature and productivity index (PI) history from the temperature data. An analytical relationship between the temperature data and the PI will be presented. Using this relationship, many useful surveillance studies, such as monitoring the skin change of the well and the impact of reservoir compaction during the depletion can be conducted. Examples of such studies will be provided and discussed using some deepwater field data.
Furthermore, the downhole temperature can also be used to detect whether water breakthrough occurs via matrix or fracture. By deriving the mathematical model to quantify the distance between the water front and the thermal front, we find the breakthrough via fracture usually leads to a small front distance, while the breakthrough via matrix causes a significant front distance. Coupling with the production data which includes water cut changes in producers, the temperature history reveals the real water breakthrough scenario. Observation from this analysis is of practical interest for subsea well development because of prohibitive costs and high risks of the production logging.