Engineered Polymeric Solution for Lost Circulation Treatment in Fractured Limestone and Sandstone Formation: Case Studies
Authors: Ahmad Syed Hamza , Anwar Rameez , Yousaf Arif , Khokhar Saad Yousaf , Elmoneim Hossam A. , Asad Abdul 
Published: February 2024

Lost circulation is a major concern during drilling and workover operations, particularly in aging fields and depleted reservoir, resulting in significant financial and time losses. In addition to the loss of expensive drilling fluids, it also leads to wellbore instability and drill string sticking, necessitating additional resources and time for safe operation. Despite significant research and engineering efforts, the use of traditional lost circulation materials (LCMs) remains limited due to operational and technical constraints. These materials are often solid-laden, limiting their use with advanced BHAs containing directional drilling and MWD tools. Similar challenges exist during rig less well intervention operations that use coiled tubing (CT) for well intervention solutions.

To address these challenges, a temperature-activated anionic polymer combined with a carboxylate complex cross-linking agent is formulated to produce a rubber-like ringing gel structure that reduces the formation permeability to milli darcy immediately once cross linking starts and improves wellbore stability by strengthening the formation, rather than just plugging the sand face. In addition to being solids-free, the product is non-biodegradable and insoluble in acid enhancing the product's robustness and effectiveness in workover operations. This paper presents two case studies that demonstrate the successful implementation of the engineered LCM solution in drilling and workover operations. In first case, the product was deployed thru the drill bit to seal off naturally fractured limestone that had caused the drill string to become stuck due to total losses in the underlying thief zone and unstable shale above it. The polymeric LCM for formulated to initiate immediate cross-linking to effectively seal off the fractures. To increase structure sturdiness, it was reinforced with a silicious-based bond enhancer. It immediately shuts off the thief zone and allows to establish returns and stabilize shale to release the stuck string. In a different scenario, the product was formulated and applied using Coiled Tubing (CT) to seal off a low-pressure (BHP ~600psi) depleted sandstone formation with extremely high bottom hole temperature (&gt;300degF). This enabled safe perforation of the deeper zone and the addition of reserves without requiring rig workover.

The polymer gel is solids-free, non-biodegradable, and acid-insoluble, enhancing its effectiveness. Two case studies demonstrate the successful use of this engineered LCM solution. In one case, it sealed off fractured limestone to cure complete loss and release stuck drill string, while in another, it sealed a low-pressure depleted sandstone formation via coiled tubing, enabling safe perforation and reserve addition. This innovative approach overcomes traditional LCM limitations for improved well isolation. This approach highlights the limitations of traditional LCMs and offers a new opportunity to design ringing polymer gels to achieve desired isolation objectives within existing operational constraints.