Invert emulsion fluids (IEF) typically consist of an aqueous brine internal phase emulsified into an oil external phase. Conventionally, an aqueous solution of calcium chloride is used as the internal phase to balance osmotic pressures while drilling through shales. The use of traditional chloride salts, however, can cause disposal issues and environmental concerns while drilling onshore wells. To address these concerns and to provide an eco-friendly green invert emulsion fluid with improved technical performance, two types of salt-free IEFs have been developed: clay-based and clay-free.
The salt-free IEFs comprise a biodegradable and non-toxic internal phase to mitigate the potential negative effects of a brine-based IEF. The internal phase of the new fluid achieves 70% biodegradation in 28 days in accordance with OECD (Organisation for Economic Co-operation and Development) method.
The 12.0-ppg and 16.0-ppg salt-free IEFs, both clay-based and clay-free, were stable at temperatures greater than 300°F. The salt-free clay free IEFs were formulated in the presence of a novel organic secondary emulsifier. These salt-free fluids exhibited comparable rheological and fluid loss properties and offered improved shale inhibition as compared to conventional IEFs. The salt-free IEFs showed good tolerance to contaminants and static ageing. Shale erosion and shale swelling performance of the 12.0-ppg and 16.0-ppg salt-free IEFs were comparable with the CaCl2 based conventional IEFs. This paper presents experimental data corroborating the technical and environment performance of salt-free IEFs.
Salt-free drilling fluids formulated with this biodegradable and non-toxic calcium chloride alternative provide a solution to environmental concerns. The novel salt-free clay free fluids also eliminate the use of organophilic clay, thereby resulting in an IEF with low solids content, better equivalent circulating density (ECD) control and faster rates of penetration (ROP).