Lost circulation is a widespread problem in many formations in the United Arab Emirates, including Shallow Unconsolidated, Shallow Vuguler and Limestone. To minimize losses during drilling and cementing, several types of lost circulation solutions such as bridging agents and surface-mixed and downhole-mixed solutions have been used. Still, operators lose huge volumes of mud and cement slurry and expensive rig time. Consequently, many wells also require remedial operations, which can compromise well integrity.
Loss-zone diagnosis and characterization helped to tailor the loss-circulation control solution for different requirements. Losses can occur due to unconsolidated formation (surface holes) or induced and natural fractures. Typical loss rates can vary between 150 to over 700 bbl/hr, particularly while drilling the 16-in. and 12 1/4-in. openhole sections. Thus, total losses in shallow vuguler formation require a different treatment than induced losses in shallow unconsolidated or limestone formation. Induced losses in limestone while drilling prevented increase in mud weights required to drill deeper reactive shale formation. A composite fiber-based system based on a novel four-step methodology was designed using advanced software analysis. Prior to the field trial a complete lab-scale and yard-scale testing was done to confirm superior effectiveness.
In one of the pilot wells, multiple leakoff tests (LOTs) were performed in the Limestone formation to verify the minimum stress (1.40 SG), which did not change with subsequent LOTs. The formation was then treated with the reinforced composite mat based system, and the following formation LOT showed integrity buildup to 1.51 SG. It proved to be an easy to apply solution that can be mixed and pumped through a qualified bottomhole assembly (BHA).
Zone and mechanism specific lost circulation control solutions are most effective in reducing nonproductive time (NPT). It was also demonstrated that fiber-based solutions work well for controlling losses and formation strengthening. The engineered composite fiber-blend system exhibits improved performance and robustness in terms of curing losses and even improves formation integrity.