Workover operations in shallow low pressure heavy oil unconsolidated sandstone reservoir in Kuwait presents a major challenge due to significant killing fluid loss which causes wellbore plugging, incremental operational costs due to more rig days, excess brine volumes, and more importantly the impact of deferred production due to formation damage. This paper presents an innovative fluid-loss control pill added to killing fluids, which has resulted in significant cost savings and well productivity improvements.
The subject heavy oil reservoir have formation pressure equivalent to 6.3 PPG versus 9.3 PPG Potassium Chloride brine used as killing fluid. This overbalance condition is a requirement as safety barrier but conversely it leads to hundreds of barrels of killing fluid losses with the consequently invasion and formation damage. Kuwait Oil Company recently added a new customized fluid loss control pill of high purity vacuumed dried evaporated salt to the well killing procedure. Using this fluid loss control pill both drilling and reservoir engineers achieved their aim in terms of safety operation and no formation damage.
To test this new pill, two shallow wells with 220 psi reservoir pressure and perforation set at 630 ft were selected to record the losses. The first well had undergone workover including recordings from caliper, cement, and ultrasonic logs, which measured the positive impact of the new control pill on logs quality by excluding fluid pumping while logging and having constant fluid level at surface, which saved cable head from unnecessary tensions. In a second well, there was hanged standalone screen on a packer against the perforation and there is no direct access to the perforation. The control pill was customized to be pumped into the screen, which sealed the screen itself perfectly. The control pill flowed back easily in both wells and same loss rate was observed after removing the pill, which confirmed no negative impact on reservoir permeability.
KOC confirmed that the two jobs were successful and the pill to be approved for full field implement in other operations. The achieved success criteria summarized as follows:
Hydrostatic column is a safety barrier that assuring fluid level at surface during workover is safety requirement especially in high Gas oil ratio wells.
Full circulation enhances sand cleanup operation.
Fluid level at surface results in accurate logging by eliminating invasion into reservoir and support improved operations.