Invert-Fluid Flocculation: A Method for Recycling Drilling Fluid

Abstract

A new technology is now in use to increase the efficiency of traditional solids-control equipment in removing colloidal fines and water from invert drilling fluids. This method makes it possible to extend fluid lifespan and recover and reuse valuable components. Colloidal fines—particles measuring less than 2 µm equivalent spherical diameter—are typically difficult to remove through the exclusive use of mechanical devices relying on screening or gravity. Through the application of chemistry and equipment packages, these colloidal solids now can be removed from systems with a hydrocarbon-continuous phase through a process of flocculation, which aggregates these fines to facilitate their removal. The use of this process results in a high-performance fluid with lower density, increased oil content, and no colloidal solids. The benefits go beyond those associated with traditional treatment methods and include the alternative provided to the disposal of unusable stock. The invert-fluid flocculation technology, called Reclaim, was introduced recently by M-I Swaco. Invert drilling fluids are water-in-oil emulsions containing a hydrocarbon-continuous phase with an emulsified internal aqueous "brine" phase in addition to clays, weighting agents, and other additives (Darley and Gray 1988). These fluids serve many functions during drilling, one of which is to remove excavated rock, or "drill cuttings," from the borehole. These solids are incorporated continuously into the mud, with solids-control equipment employed at the rigsite to remove them and return the drilling fluid to the active system in a usable condition. Typical equipment, such as shakers and centrifuges, remove solids greater than 5 to 7 µm (ASME 2005). However, as drilling fluids are used to drill multiple holes, fine particles can build up and ultimately create problems for efficient drilling. Typically, the drilling fluid is diluted and reformulated to reduce the concentration of these fine solids and return the fluid to acceptable physical properties. This is often costly and also increases the volume of drilling fluid, leading to problems of storage, transport, and disposal. In severe cases, in which dilution is uneconomic, the drilling fluid will be disposed of as waste and fresh fluid mixed. This involves significant cost and environmental impact. The new technology uses polymeric inverse emulsions and surfactants coupled with defined-shear and mixing systems to flocculate fine solids in invert drilling fluids, enabling them to be removed by use of standard oilfield centrifuges. The result is the reclamation of the hydrocarbon component with no fine-contaminant solids, and this reclaimed hydrocarbon stream can be used as base fluid for new drilling formulations. This significantly benefits the processes of fluids recycling and inventory control, reduces disposal volume, and improves drilling performance.