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Abstract

Kuwait Oil Company embarked on an ambitious project to look for gaseous Hydrocarbons in a hitherto un-proven formation in the North Kuwait Field. As the target formation was extremely depleted and usually was drilled through under-total-loss conditions, these wells were designed to be Under-Balanced-Drilling (UBD) wells. The design conditions for an Under-balance or drawdown of 10% below formation pressure of the target zone called for Nitrified water as the fluid medium. Design simulations showed a normal Nitrogen pumping rate of around 1100 scfm for maintaining the UB conditions. Further testing of the target formation called for a huge drawdown of a maximum of 30%. This led to extreme conditions of pumping Nitrogen at the rate of 2000 scfm. The normal operating conditions with membrane NPU resulted in 5% Oxygen being pumped in with Nitrogen. This resulted in a highly corrosive environment under Bottom-hole conditions, especially when we started producing highly saline formation water. The above conditions led to very severe corrosion of our Drill string and UBD Coring equipment, creating a potential hazard of losing our whole string. Conventional corrosion inhibition completely failed to arrest the corrosion of the string. This led to intensive study and debates within the team to find a solution to the problem and quickly too. A multi-pronged solution comprising of controlling pH, usage of Phospate Ester Inhibitor formulation, filming amine and monitoring through usage of Corrosion coupon rings in the drill string led to a dramatic improvement of the corrosion damage. Corrosion hazards in UBD wells are a reality and a heady-mix of ideal conditions for corrosions could mean disaster. Conventional Corrosion programs usually fall short of dealing with the severe corrosion existing down-hole. Special operations such as Underbalanced Coring could fail dramatically before achieving objectives. A multi-pronged approach needs to be designed and the severity of the problem understood before embarking on such ambitious projects. The authors are going to present a strategy for putting the best foot forward when dealing with such issues. Being forewarned will always mean being forearmed.

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/content/papers/10.3997/2214-4609-pdb.395.IPTC-17598-MS
2014-01-19
2024-03-28
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.395.IPTC-17598-MS
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