Scale Removal Operations in High Pressure High Temperature Tight Carbonate Reservoir and Sour Environment - Challenges and Guidelines

Abstract

Currently, Kuwait Oil Company (KOC) is successfully producing from high pressure and high temperature formations. The reservoirs are deep with True Vertical Depth (TVD) approximating 15,000 feet, and pressures and temperatures of 11,000 psi and 275 o F respectively. The formations are composed of carbonates both tight and porous. The produced hydrocarbons are of high H2S and CO2 content, up to 10% and 12%, respectively.The aforementioned sour environment in addition to water cut occurrence during the production phase have led to scale creation. In addition, corrosion, erosion and pitting also occur, requiring well intervention to sustain production. Furthermore, well monitoring is essential and planning for workover and well interventions is becoming unconventional with higher associated risk.The recent scale removal activities proved to be very challenging with weight loss seen from the coiled tubing (CT) of approximately 7,000 Ib and CT leakage while operating at the hole condition. The CT pressure control equipment failed due to sudden increased in H2S concentration, which was attributed to the chemical reaction between the cleaning fluid (15% HCl) and the well fluids/scale mixture. This paper explains the well history, objectives of operation, execution history, procedures and causes of these challenges. Hence, lessons learned, observations and knowledge gained by the Kuwait Oil Company (KOC) are evolving, advancing, and being employed at an accelerated rate despite high cost.