VES: An Alternative to Biopolymers in Reservoir Drill-In Fluids

Abstract A novel reservoir drill-in fluid (RDF) has been developed that utilizes viscoelastic surfactants (VES) as the primary viscosifier and as a consequence, eliminates the need to use biopolymers for viscosity. Biopolymers have been the standard RDF viscosifier for a long time. They provide stable rheological properties required for drilling and completing the reservoir section, but they have been difficult to remove as very few chemical breakers can effectively destroy the polymer chain. The VES-based viscosifier can be easily removed by a variety of non-aqueous materials, including produced hydrocarbons making this new RDF a viable alternative for a variety of openhole completion projects, particularly low-temperature and injector applications. This new VES-based RDF system not only suspends soluble bridging material, but supplies the rheological properties necessary to transport cuttings out from the wellbore. Fluid-loss control is achieved with a novel polysaccharide starch that is compatible with the surfactant used in the system. With the addition of this particular starch, the VES-based RDF exhibits similar characteristics to a biopolymer-based RDF which also utilizes polysaccharides and soluble bridging agents, and is stable enough to withstand conventional water-based RDF contaminants. This paper will detail the laboratory phase involved in the development of this new system. The testing confirmed that the properties normally associated with conventional biopolymer-based RDF systems are also achieved with this innovative VES RDF system. Additional testing revealed solids contamination effects and the effect that the addition of lubricants had on this unique system. Further investigation will also show the effect of a water-based filter cake breaker system currently being used in completion operations. Results of return permeability testing will also be discussed in this paper. The development of this new RDF system showed that VES technology currently being applied in other aspects in oil and gas completion operations can now be applied in drilling the reservoir, and that this unique system can achieve the same functionality as conventional water-based RDF without the use of biopolymers.