This paper shows the results of a successful application of the addition of hollow glass spheres, also known as glass bubbles, as a density reducing agent in a drilling fluid. In this field application, glass bubbles were used in combination with an oil based drilling fluid (Core-Drill-N). It was corroborated that the fluid-glass bubble mix is stable, homogeneous, and is compatible with conventional mud motors, bits and surface cleaning equipment.. The system has good rheological and filtration control properties and is suitable for drilling low pressure reservoirs, low permeability and pay zones.
During this field application in the well MOT-25B in Venezuela, the density of the base fluid was maintained between 7.1-7.3 ppg (near balance condition) with calcium carbonate as bridging agent.
This technology is an alternative to the use of aerated fluids where the reservoir requires a fluid density between 6.0-7.5 ppg, offering some economical and technical advantages due to the elimination of surface compressing and air injection facilities, and to the simplification of operations required to avoid excessive overbalance during drillpipe trips. Additional potential benefits of this low-density fluid include torque reduction as a result of higher lubricity, higher penetration rates and decreased formation damage due to lower invasion of drilling fluid. Glass bubbles are also an alternative to decrease the density of water based drilling fluids, polymer-based fluids, emulsion systems and brines.
Laboratory tests were also carried out with different concentrations of glass bubbles in order to evaluate potential field substitutes for aerated fluids in wells which might require lower density fluids. Several formulations for the systems mentioned above were developed with the purpose of achieving maximum density reduction without affecting some mud properties. Fluid density as low as 6.0 ppg was obtained from a 100% oil base mud.