Engineered Reinforced Composite Mat Pills to Effectively Combat Losses While Drilling in Qatar

Abstract

Drilling into fractures and fissures in carbonate reservoirs with lateral pore pressure variations is a major challenge. Accurately predicting and managing fracture initiation and fracture closure pressure is not practically feasible in naturally fractured carbonate rocks. Local fracture closure pressure (FCP, minimum in situ stress) around fractures are much lower than the mean value of FCP for the area, as observed in the Al Shaheen field. Drilling operators are experiencing massive lost circulation resulting in potential formation damage; and cost overruns. To address these lost circulation instances, modern lost circulation pills must be implemented. Drilling through the natural fractures within parts of the Shuaiba limestone reservoir usually results in significant drilling fluid losses, up to 50 m3/h. Lateral pore pressure variation causes dynamic inflow conditions within the wellbore, which make plugging fractures difficult. In addressing these lost circulation challenges, various approaches were previously used, notably reducing the hydrostatic pressure of fluids column, utilizing lighter weight drilling fluids, reducing the penetration of fluids into fractures with the use of various lost circulation materials, and the use of thixotropic cement slurries and lightweight high-solids-content cement slurries. Conventional lost circulation treatments provided very limited success under these conditions. An engineered composite fiber-based lost circulation pill with an innovative blend of fibers and sized solids to bridge and plug thief zones has been developed to address these lost circulation challenges. This pill was designed to be pumped through either a dummy bottomhole assembly (BHA) or through bypass circulation ports above the BHA with total flow area of 1.571 in2. These pills have been successfully used to mitigate losses while drilling as well as to achieve an incremental equivalent static density up to 144 kg/m3 to drill and cement the section. An impermeable grid created by this system was able to withstand the additional pressures. As a result, all the wells treated with these pills in the field were successfully drilled and cemented. After establishing the field specific guidelines over 2 years, continuous success was replicated in other wells for all the operator's rigs in Qatar.