Field Application of Glass Bubbles as a Density-Reducing Agent

Abstract

Abstract This communication describes preliminary results and observations of a successful application in a field environment that incorporated hollow glass spheres, also known as glass bubbles, as a density reducing agent in a drilling fluid. In this field application, a proprietary oil-in-water emulsion fluid developed by PDVSA-INTEVEP which contained hollow glass bubbles (3M) was used during the drilling of a producing interval. The oil-in-water emulsion provided a suitable fluid base, whereas the glass bubbles, by virtue of their low density, imparted a lower finished density than that of the corresponding base fluid. The density lowering capacity of the glass bubbles is proportional to the concentration of bubbles incorporated in the fluid. The field trial substantiated that the fluid-glass bubble pair is stable, homogenous, and compatible through conventional mud motors, bits, surface cleaning equipment, and of such rheological and filtrate properties, as to lend itself to be used in low pressure reservoirs and in producing zones of high permeability. During this field application, we were able to lower and maintain the density of the base fluid at 7.1 PPG. Additional oil production increase was observed relative to a vicinal well (vs. GF-134D) drilled with oil based fluids at an excessive overbalanced. This observation may suggest that damage to the producing zone has been avoided. This technology is an alternative to the use of aerated fluids, with potential economic and technical advantages due to the elimination of surface compressing and air injection controller equipment, and to the simplification of operations required to avoid excessive overbalance during pipe trips. Other potential benefits of using this low density fluid includes torque reduction as a result of higher lubricity, reduction in casing wear, higher penetration rates, decreased formation damage, lost control mitigation, and the use of mud pulse MWD tools. Glass bubbles are also a viable alternative to reduce the density of water based drilling fluids, oil and polymer-based fluids, and brines. Laboratory tests were also carried out with conventional fluid systems to include water-based, 100% mineral oil and oil-in-water emulsions, with different concentrations of LITEDEN™ in order to evaluate the potential field use of such formulations as 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 filtrate control or rheological properties. Fluid densities as low as 5.5 and 6.0 ppg were obtained for corresponding 100% oil and O/W emulsions based fluids. Introduction In the last few years there has been an increasing necessity to drill deposits which have entered a partially depleted stage because of extended years of production. Excessive levels of overbalance pressure can increase fluid invasion. Differential sticking is a costly common problem associated with fluid invasion. In principle, loss of fluid allows the deposition of drilling fluid solids as a filter cake on the well bore. With further filter cake growth, the drill string and drill collars continued to be pulled against the side of the well bore. With time, mud filtrate flows further, building and accumulating solids around the tubulars, and preventing the pipe from moving. The drilling of the above mentioned depleted deposits requires the use of lower density fluids with specific gravity less than 1 (8.33 ppg), such as mist, foam, and aerated or nitrified muds (Figure 1B). These fluids, in principle, would permit maximum extraction while minimizing damage to the producing formation from filtrate or solid invasion. However, there are limitations in the available fluids aimed to operate in a depleted reservoir.