Chemical and Physical Characterization of Aphron-Based Drilling Fluids

The depleted reservoirs in many of the world’s mature fields contain hidden problems that can make further development unprofitable. Some zones are typified by water-wet sands that frequently trigger costly seepage losses and differential sticking. Others are characterized by laminated sand and shale sequences, which create the conditions for slow, dangerous and unduly expensive drilling when conventional rig equipment is used. If operators turn to underbalanced drilling as an alternative, the extra time and equipment required for safe operation can seriously degrade project economics in some applications. Aphron-based systems are engineered drilling-fluids that aid in well construction by controlling losses in depleted, high-permeability sands while stabilizing pressured shales. One of the more attractive features of an aphron-based system is that it does not require any of the extra equipment used in air or foam drilling. There are no compressors, high-pressure hoses or connections to add costs and safety concerns. The system uses conventional fluid-mixing equipment to form tough, flexible micro-bubbles. Once formed, these micro-bubbles, or “aphrons,” differ from the bubbles produced in air or foam drilling in two significant ways. First, aphrons resist coalescence into larger bubbles. The aphrons are attracted to lower-pressure regions in the formation but remain discreet from each other, forming a strong network of individual micro-bubbles. Second, aphrons are tough and stable. They are comprised of a core of air surrounded by layers of a proprietary polymer and a tensoactive additive. The authors will detail the chemical and physical characteristics of aphron-based drilling fluids that make them uniquely qualified to solve some operational problems.