Reliability analysis of permanent downhole monitoring systems

Permanent downhole gauge (PDG) systems have been installed in many oil and gas wells. These systems improve reservoir management and production optimi zation. Currently, more complex down-hole monitoring and control systems ar e being installed in what are often called "Intelligent Wells." Reliability is a critical aspect for all these systems. We evaluated the performance of 952 pressure- and temperature-monitoring sy stems installed since 1987. The 5-year survival probability of these system s improved from 40% for systems installed in the period 1987-88 to 75% for the period 1991-92. No further improvements have been observed from 1992, r esulting in a 5-year survival probability of 69% for the period 1993-98. Failure modes have been evaluated and could be attributed primarily to the downhole gauge and to the cable. Based on these findings, recommendations h ave been made to achieve reliability improvements.