Light-Density Hollow-Glass-Beads Drilling Fluid Achieves High Solids-Control Efficiency

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212470, “Full-Scale Solids-Control Testing of a Light-Density Hollow-Glass-Beads Drilling Fluid,” by Nikolay Kostov, ExxonMobil; Glenn Penny, SPE, Contractor for ExxonMobil; and James White, NOV, et al. The paper has not been peer reviewed. _ Light-density drilling fluids with hollow glass beads (HGBs) are being used increasingly in applications for drilling depleted formations with minimal losses and increasing rates of penetration. Studies about how best to use typical solids-control equipment are lacking, however, because current practices and procedures based on barite-weighted muds are inefficient. In the complete paper, the authors report a systematic full-scale test program to study and optimize solids-control efficiency with such fluids using centrifuges, hydrocyclones, and shale shakers. HGB Fluid Formulation The fluid formulation developed for the field test had a target design density of 7.2 lbm/gal. Significant effort was put into developing an HGB fluid that matched or exceeded all design requirements for the existing drilling fluid used to drill a production hole interval in a depleted field. The HGB drilling fluid showed excellent fluid loss and rheology. An overview of the composition and some of the fluid properties is provided in the complete paper. HGB 19K46 is a product with a nominal hydrostatic collapse pressure rating of 19,000 psi and a density of 0.46 g/cm3 (approximately 3.8 lbm/gal). The HGBs are almost perfectly round spheres made up of a thin shell of borosilicate glass a few micrometers thick. The glass density is approximately 2.50–2.55 SG. The hardness is approximately 5 on the Mohs scale, in between barite (3.5) and quartz (7.0). HGB Large-Batch Mixing Based on the testing time to reach steady conditions and the tanks available at the test facility, it was determined that a volume of approximately 40 bbl was required for the field-scale solids-control testing. A mixing plant was used, and the fluid was mixed over a period of 3 days. Good agitation is crucial to mix the additives and HGBs effectively into the base oil. With the exception of the process used to add HGBs, however, no special equipment or modified procedures are needed to mix the HGB fluid. For adding the HGBs, a hopper was used and an efficient additive process developed while dust was eliminated. A 100-bbl mixing tank unit mounted on a trailer was used to generate the HGB fluid for testing (Fig. 1). The unit consists of a multicompartment 100-bbl tank, a diesel-engine-driven centrifugal pump, a hopper, and a series of control valves for directing the fluid flow. One specific modification to the tank was the installation of large eductors at the ends of the feeding pipe. This ensured good circulation of the fluid in the tank, promoted good mixing, and eliminated any dead zones where fluid could become stagnant. The large-scale mixing resulted in approximately 43 bbl of HGB drilling fluid. Samples were collected, and properties were measured. All properties were within the specification window, confirming a successful operation.