Development Methodology for Ultra-Lightweight Drilling Fluids Using Hollow Glass Beads

Abstract Lightweight drilling fluids are needed to drill depleted formations and can also be used to maximize drilling rates of penetration. This paper presents a methodology developed to design and test ultra-lightweight drilling fluids utilizing a high concentration of hollow glass beads (densities <5.5 lbm/gal). These fluids can be used as a simpler alternative to foam or air drilling in applications requiring densities in the 4-6.5 lbm/gal range. As a starting point the field application requirements were developed which then were used to define a set of functional requirements for the hollow glass beads (HGB) fluid; tests and procedures for evaluating the performance against functional requirements were then developed. These included survival of the beads at downhole pressures and temperatures, survival of the beads under mechanical impact, formulation stability against hollow glass bead floatation, and rheological stability in addition to normal drilling fluid design requirements (e.g. compatibility & contamination testing). Selection of bead type and base oil were part of the development process. Several new lab tests were developed and conducted which allowed for assessing the performance and making adjustments until the functional requirements were met. Several HGB drilling fluid formulations were successfully developed meeting all the functional requirements. Fluid densities as low as 4.6 lbm/gal were successfully tested; this is the lowest density hollow glass beads drilling fluid that we are aware of. Hollow glass bead survival at increased pressure and temperature was above 90% for pressures around 4000psi. In addition, the formulations show excellent stability with minimal glass bead floatation even at elevated temperatures. The mechanical survival of the glass beads was also studied in the lab and estimated to be over 90% in a typical well application. Rheological properties showed good stability with both pressure and temperature. Standard drilling fluid hydraulics software can be used for modeling the wellbore pressures. The methodology described presents a systematic approach to developing ultra-lightweight HGB drilling fluids (below 5.5lbm/gal); these can be used in drilling applications where significantly lower densities below base oil densities are needed, especially as a simpler alternative to foamed fluids used in drilling depleted reservoirs (e.g. conventional depleted wells, drilling with MPD, mud cap drilling). The methodology also allows for determining the lower limit of densities that can be designed for a particular application, and can also be utilized for developing ultra-lightweight fluids for non-drilling applications.