Abstract
A novel drilling fluid containing specially designed micro-bubbles -- "aphrons" – was recently introduced and has now been employed successfully in various parts of the world to drill through formations which previously had experienced uncontrollable losses and high incidence of differential sticking. The aphron-laden fluid appears to be particularly well suited for drilling through depleted zones. Wellbore stabilization is accomplished by (a) greatly reducing the invasion rate of the base fluid with additives that minimize the thixotropy of the fluid and enhance its shear-thinning character, and (b) reversibly plugging pores and fractures by the aphrons.
A recent innovation has permitted modification of the original fluid design to permit incorporation of selected clays in the fluid for rheology control and stabilization of the aphrons. In addition, the chemistry of the aphron membrane has been altered using a polymer/surfactant package so that the longevity and resistance to pressurization of the bubbles are greatly improved.
The authors will discuss the design and properties of the new Alternative aphron-based drilling fluid and how these characteristics can be used to advantage in a drilling operation.
