UGS wells help store natural gas and reduce the risk of interrupted delivery and service. Often these wells are in depleted gas reservoirs into which gas from other sites has been injected. They must tolerate high injection pressures, high production rates, and frequent changes in temperature and pressure—and still produce gas fast enough to meet peaks in demand.
Maximizing the efficiency of existing gas resources requires that the storage capacity in these reservoirs also be maximized, mainly through an increase in storage pressure. Putting more gas in existing storage areas causes the pressure to increase above customary levels. When these levels are exceeded, the pressure must be carefully monitored to ensure that no leaks or other damage to the storage system occurs.
In Italy, where constant downhole pressure monitoring of UGS wells is required by law, an operator needed to install a highly reliable pressure gauge system that could withstand the high pressures and that would not need to be replaced.
Because of its impressive track record with permanent downhole gauges, SLB was asked to provide a reliable monitoring system that would take continuous downhole temperature and pressure measurements while also providing metrology redundancy.
SLB used the WellWatcher Neon DTS, DAS, and PT gauge system, which combines a fiber-optic line and an electrical conductor in a single permanent downhole cable, along with multiple electrical gauges. The WellWatcher BriteBlue™ multimode DTS fiber provided continuous and intermittent distributed temperature measurements at approximately 3-ft [1-m] intervals along the entire length of the fiber. Simultaneous acquisition of the DTS data and the pressure and temperature data from WellWatcher Quartz™ premium high-temperature, high-resolution PT gauges provided rapid wellsite diagnostics.
By combining the different types of sensors, which had totally different modes of functionality yet similar metrology, the operator had greater confidence in its monitoring and control of the reservoir's pressure and analysis of reservoir behavior trends. As a result, the operator was confident that the gas storage facility was being run within its locally allowed pressure limits and knew that peak gas demand would be met. The operator ordered 11 additional WellWatcher Neon DTS, DAS, and PT gauge systems for its UGS wells.
