Maximizing Reservoir Production Using New Technologies for Permanent Continuous Downhole Sensors
Authors: Flecker Michael J. , Thompson Stephen J. , McKay Colin S. , Buchwalter James L. 
Published: October 2008

Abstract
The applications of new technology for permanent continuous downhole sensors are creating exciting new opportunities for enhanced reservoir management, optimization and development. Greater reliability, higher temperature ratings, lower costs and a wider range of sensor types together with new, efficient data management and analysis software allows operators to exploit the technology and extract more value from their production data. New downhole sensors under development such as scale and sand detection as well as recent advances in fiber optic technology promise to further expand availability of the 'real time' knowledge of dynamic reservoir conditions. The economic value of permanent downhole sensors is significantly increased with the advent of PC based software tools specifically designed to manage and analyze the volumes of data from these systems.

Introduction
Permanent continuous downhole reservoir monitoring systems have only been applied to a small number of the world's oil and gas wells. Cost, reliability, risk, environmental limitations, arduous data evaluation processes and the lack of awareness have limited the widespread use of these technologies. New technologies for deployment, data management and interpretation have lowered the cost of the entire well monitoring process. The most significant improvements have been made in extracting the value from the acquired data as well as improving reliability and reducing environmental limitations. Some improvements to the entire system process are shown in figure 1.

Sensor Technologies
The primary sensors being used today are for measuring downhole pressure and temperature. Additional new sensors have been developed or are under development that measure other physical parameters of the downhole environment.
These downhole sensors are either electronic or nonelectronic as described in the following sections. Numerous advances in both areas over the past several years have yielded more reliable systems, higher temperature and pressure ratings, lower cost and smaller size.

Electronic Systems.
The vast majority of downhole pressure and temperature systems installed today are electronic systems. The early electronic systems utilized strain gauge technology for pressure measurement; this technology had limited resolution and suffered from inherent drift problems over time at pressure and temperature. A number of other sensor technologies were tried and tested including quartz capacitance sensors. Today resonating quartz, which utilizes the inverse piezoelectric effect to induce the resonator to vibrate at its mechanical resonant frequency, has been the primary sensor technology utilized in downhole pressure measurement. This technology provides the highest accuracy and resolution of pressure measurement.
In recent years improvements in the manufacturing process have improved both the reliability and ruggedness of the sensors. In addition, market demands have resulted in reduced diameter and higher pressure and temperature rated sensors.
The ability to communicate with multiple sensors on a single downhole cable has enabled the measurement of flow using the venturi principle. This is becoming a common measurement in high profile subsea tieback wells. In addition the running of dual pressure sensors has the benefit of increased reliability over time.