Lost circulation (LC) is an expensive and time-consuming problem. It's desirable to minimize losses before cement job to ensure good cement coverage and maximize well integrity. But quite commonly, wells experience induced losses just before cementing, during casing running and circulation. In such a scenario, the options to control losses have been few, with limited results. The paper demonstrates a viable solution that can be successfully applied to reduce or eliminate such induced losses during the cement job.
To effectively solve lost circulation with the correct technique, it is necessary to know the severity of the losses and the type of lost circulation zone. In UAE fields, the loss rates range from 150 bbl/h to more than 700 bbl/h in the 17 1/2- and 12 1/4-in open hole sections. During cementing operations, lost circulation causes reduced top of cement, poor zonal isolation, and risks to drill ahead. To solve this problem, a composite fiber-based spacer system based on a novel four-step methodology was designed using advanced software. Before a field trial, rigorous lab-scale and yard-scale testing was conducted to optimize the application.
Initially, no losses were witnessed while drilling the 12 1/4-in section. But during casing running and circulation, severe losses of 150 bbl/hr were induced. To counter these losses, the specially designed fiber-based lost circulation spacer system was pumped ahead of the cement slurry using standard surface equipment. At the beginning of the displacement—while cement and spacer were still in the casing string—the loss rate increased to 700 bbl/hr (total losses). This high loss rate in the crucial intermediate section would normally have resulted in costly remedial operations, loss of mud and cement, and expensive rig time. It was observed that the loss rate remained at 700 bbl/hr until the lost circulation spacer arrived at the loss zone. Subsequently, the loss rate kept on declining finally resulting in full returns during remaining displacement. The designed excess of cement was received as returns, thereby ensuring the desired top of cement at surface. This proved that the fiber-based spacer was effective in curing the losses. An advanced cement bond log showed complete cement coverage over the entire section. This further proved the spacer's effectiveness in achieving all well integrity objectives.
The successful application of the engineered fiber-based lost circulation control spacer during primary cementing demonstrates a reliable solution to the challenge posed by losses induced immediately before a cement job. The system is easy to deliver and design and can plug the fracture network in the formation during the cement job. Globally, this engineered composite fiber-blend spacer has proved to improve performance during cementing operations by healing losses to maximize well integrity.