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.