Combined Engineered Lost Circulation Approaches for a Complex Fractured Carbonate Horizontal Formation: Middle East Case History

Abstract Lost circulation is a major challenge when drilling a well with depth reaching 8000 m in the horizontal section and a fractured carbonate reservoir as the target. High mud losses range from 34 m3/hr (210 bbl/hr) up to 120 m3/hr (750 bbl/hr). These losses reduce the rate of penetration and increase material costs, resulting in an increased overall well cost. In a worst-case scenario, immediate drilling problems can result, which include well control issues, formation pack off, and stuck pipe. Based on earlier drilling experience in one of middle east location, no single solution resulted in a high success rate, reducing losses, and regaining returns. The solutions involve decreasing the density, controlling the viscosity, and adding lost circulation materials (LCM) to the drilling fluid. These LCMs help to control the drilling parameters while offering mediocre aid with drilling plug placement. To address this severe lost circulation problem, a decision flow chart was constructed and combined with an engineered lost circulation approach to combat losses and strengthen the wellbore across these natural fractures. This approach was designed to more efficiently drill a new well in this field. Firstly, combined engineered wellbore strengthening approaches to cure losses included a high-strength, high-solid lost circulation system with a goal to control the losses. This system initially appeared efficient and was later combined with particulate material to improve strengthening and plugging capabilities. Due to fracture size uncertainty, an engineered fiber-based design loss circulation control pill was implemented to increase the sealing efficiency of the uncertain fractured zones. This pill was based on a resilient engineered fiber portion that used a particle size distribution principle. The concept of combining fibers and optimized solids was to form an impermeable grid to strengthen the wellbore integrity. A laboratory test was performed to confirm the system's ability to bridge the loss zone. These solutions were pumped through circulation ports above the drilling bottomhole assembly a total flow area (TFA) of 1.571 in.2. Once these solutions were incorporated, they helped to successfully regain fluid returns across the naturally fractured zones while permanently sealing the losses. Deploying the combined engineered pill and resilient engineered fiber pill at a different depth proved their applicability under different conditions and a standard engineering approach for improving wellbore integrity was developed for future drilling in this field. The aggregated solid grid formed by this combined approach ensured additional force and pressure created by drilling more deeply into the section and making it possible to successfully drill to the section TD without additional nonproductive time and risk of well control loss.