Abstract
Early in 1998, three horizontal oil producers were drilled with short radius horizontal section of 1000 ft to 1600 ft. Those wells were shut in 2007 due to the evolution of watercut as a result of inverse water coning experienced in Zone-Y. Gas lift was selected as the preferable artificial lift technique for subject reservoir, accordingly, the three horizontal producers were planned to be worked-over during 2011 in order to install gas lift mandrel. The expected production rate with GL was estimated to be around 400 bopd with a high watercut of ±70% after the gas lift application.
An extensive review of actual wells’ performance in addition to the application of simulation model were performed in order to study the optimum scenario to reactivate and put the wells back on stream naturally taking the advantage of the workover job. Evaluation of multiple scenarios recommended to extend the horizontal section of subject wells to unswept area and also to consider water shut-off technique in the original hole to enable producing them naturally prior to Gas lift startup.
An innovative one step approach, with direct rig intervention, utilized LWD (Logging While Drilling) resistivity data to identify intervals swept by advancing waterfront instead of the conventional approach carried out in two steps; the first being the rigless coiled tubing intervention to identify water entry intervals (PLT-Production Logging Tool) and the consequent utilization of rig intervention to carry out the actual water shut-off plus horizontal section extension operation.
Using LWD data further improved the shut-off operation efficiency by deepening the depth of investigation while extending the horizontal section in the pay-zone, which was not possible with the rigless PLT operation. Another setback with rigless PLT operation is the requirement of minimum threshold flow condition which was not possible to achieve in the inactive producers.
During the Workover, the Openhole log (LWD) recorded while drilling for all the three wells showed that the area around the original hole is depleted to Sw of ~70% and the extended hole is totally located in oil bearing Zone-YL, thus confirming the model findings and the analytical analysis. Accordingly, it was decided to isolate the original hole with 4 ½" pipe and swell packers and complete each well as single producer. The production test results for the three wells, post the workover, showed that each well is currently producing dry oil of around 1500 bopd with nil watercut.
Results of accomplishment team recommendation revealed the following:
The three wells were able to flow naturally and became active with nil watercut.
A cost saving of around 15.0 MM$ was achieved as a result of the cancellation of drilling three infill horizontal wells that were originally planned in the same locations to sweep the unswept areas including new surface flowlines, equipments and cathodic protection.
Additional capacity of 4500 bopd has been added to Zone-YL sustainable production capacity.
