Permanent Downhole Monitoring For Extreme Temperature and Pressure Environments

Abstract

Abstract This paper directly addresses a field proven reliable solution for permanent monitoring in high temperature and high-pressure (HT/HP) oil and gas well environments. The petroleum industry has struggled with a solution for monitoring in these environments for years and is continually held back by the limitations of electronics at elevated temperatures. The development of cutting edge surface electronics has enabled a remote sensor to be queried and the output frequency signal to be interpreted from several miles away. What makes this unique is that electronics are not required downhole. Low-level frequency signals are extracted directly from the sensor via a cable and are directly related to measured parameters. Modern digital signal processing techniques are used to eliminate noise and measure the frequencies to a very high degree of accuracy and resolution. The millivolt level signals, which were once unidentifiable, can now produce pressure and temperature measurements with resolutions suitable for reservoir analysis. The elimination of the downhole electronics has resulted in the ability to operate many years at temperatures well above the current limitations of electronics. In addition to high temperature operation the elimination of downhole electronics has improved the reliability of permanent monitoring substantially. This increase in reliability is demonstrated from PDVSA’s use of the technology in the Cueta Field located in the southern region of Venezuela’s, Lake Maracaibo. One hundred percent (100%) of the sensors are operational, some of which were installed over four years ago. These results are quite favorable when compared with industry published reliability statistics of less than 55% for electronic technologies at much lower temperatures. This paper will focus on PDVSA’s experiences in their HT/HP field in South Lake Maracaibo, compared with two recent studies performed on electronic based permanent downhole monitoring (PDM) systems.