Abstract:
Lost circulation is a typical condition during drilling in naturally-fractured, induced-fractured, and high-permeability formations, which could result in a kick and/or blowout. In this research, lost circulation materials (LCM) in combination with other fluid loss control (FLC) additives with a small amount of barite nanoparticles in a weighted water based drilling fluid were used to investigate the plugging capabilities of the mixtures. A high pressure LCM testing apparatus was used to evaluate the performance of three different water-based drilling fluids in sealing a slotted/tapered disc. For this testing, barite nano-micro particles were prepared chemically and mechanically, and substituted API barite replacing 3% by total sample weight in the base case. Ground nutshells were used in the formulated water based drilling fluid systems to increase the sealing capability. Based on the results, the combination of both 142 gr/lit (50-ppb) nutshells and barite nano-micro particles resulted in higher sealing pressure than other LCM treated drilling fluids. Using nano-micro particles in conjunction with the nutshells improved the sealing pressure more than 205 % using the mechanically generated nanoparticles as compared to the base case. The paper discusses the potential reasoning behind the large increase in the sealing pressure.
Introduction
Lost circulation is one of the most challenging situations during drilling fractured and highly permeable formations. The related consequences include an increase in well construction cost, wellbore instability due to losing hydrostatic pressure, kick and blowout in severe lost circulation conditions. Improving wellbore stability and reducing non-productive time caused by lost circulation can be controlled by mitigating drilling fluid losses into permeable or fractured zones. Primary attempts to control lost circulation include reducing the mud weight, treating the mud with: granular bridging materials, fibrous, flaky materials, or a combination. Selecting the appropriate material depends on the type of lost circulation zone and the severity of the losses. Traditionally, lost circulation materials (LCM) such as mica, sized graphite, nutshells, cottonseed hulls, cellulose fibers and plastic chips are used to seal (and bridge) seepages in fractured zones and pore throats in permeable formations. Previous studies focused on improving both chemical and mechanical ways to control lost circulation, and developing a standard test method which simulate actual conditions.
Vidick et al., 1968. suggested using a solid-free silicate system to cure lost circulation. They evaluated the performance of their system based on gelation time, plugging capability and long-term stability. The reported results showed a successful application of their silicate system for cores with different permeabilities. Burton et al., 2001. used cross-linked polymers in combination with fibrous LCM to control drilling fluid loss into cavernous formations. It was found that drilling fluid losses were successfully stopped after the injection of chemically activated cross-linked pills (CACP). Whitfill et al., 2007. studied the use of resilient graphite carbon and ground marble with different particle size distribution to produce deformable-viscous-cohesive systems, which successfully controlled lost circulation in depleted sand formations in a well in Gulf of Mexico.
