Published: 01/01/2009
Published: 01/01/2009
An operator was redeveloping the Bokor field offshore Malaysia. The multizone, mostly sandstone reservoirs were relatively shallow and poorly consolidated. Several zones were stacked, with some distinctly separated from the others by shale columns. Reservoir predictions indicated that the reservoir layers varied in pressure, permeability, and oil and gas characteristics.
An initial well had been drilled to explore the deeper layers of the reservoir. Schlumberger had installed a WellWatcher Neon DTS, DAS, and PT gauge system to gather pressure, distributed temperature, and derived flow data. However, during a pressure integrity check, the pressure did not hold. The operator asked Schlumberger to help determine the pressure leak's location and reason.
If the WellWatcher Neon system had not already been installed, the operator would have had to find the leak by traditional trial-and-error testing of each seal. That process requires that slickline tools be run separately to each gas lift mandrel if any one of the gas lift valves is suspected of leaking. The valve then must be reset to determine whether it is positioned properly in the side pocket mandrel and is making the seal. The pressure has to be retested, and if the seal fails, the gas lift valve or the plug at the end of the string must be removed and run again to test the seal—and the pressure test repeated once more. This repetitive process is time-consuming and costly. An alternative technique to identify a leak source involves production logging, or pipe integrity logging. It requires an intervention and costs even more.
Because the well had been designed with the WellWatcher Neon DTS, DAS, and PT gauge system, the operator was able to monitor temperature measurements throughout the well in real time without intervention. The data obtained by the WellWatcher Neon system indicated that the temperature dropped by 1.5 degC at the fourth gas lift valve in the longer tubing, identifying the tubular with the leak and the improperly seated valve that was the source of the leak in that tubular.
The problem was resolved within a few hours instead of the extended time that the repetitive and time-consuming trial-and-error search would have taken. The operator was extremely satisfied that the WellWatcher Neon system was able to quickly identify the location of the leak, thereby reducing intervention-related risks and saving an estimated USD 1 million in intervention costs.
Challenge: Identify source of pressure leak during tubing pressure integrity test in initial exploration well.
Solution: Use WellWatcher Neon DTS, distributed acoustic sensing (DAS), and PT gauge system to detect the source of the leak.
Results: Identified an improperly seated gas lift valve as the leak and quickly reset it via slickline, saving the operator an estimated USD 1 million in intervention costs.
