Biopolymers present non-toxic and degradable fluids that have been used extensively in reservoir drill-in fluids (RDF) to drill through reservoir rocks in oil and gas wells. Their numerous advantages, such as viscosity enhancement, filtration control, flocculation prevention, friction pressure reduction during turbulent flow conditions and shale stabilization amongst others have made them indispensable in oilfield applications. At the same time, the inherent formation damage as a result of the polymer molecules settling or being adsorbed on or into the reservoir rock pore spaces has been an area of concern to the industry. On the other hand, surfactant based fluid (SBF) systems typically leave little residue or formation damage compared to biopolymer systems, thereby gaining acceptance as RDF’s. Low interfacial tension existing between SBF’s and the produced or injected fluids is one of the major criteria for this reduction in formation damage. However, SBF has much higher fluid leak-off at reservoir conditions than wall-building biopolymer fluids, which has significantly limited their use in the industry.

In this paper, several blends of a SBF or visco-elastic surfactant (VES) and a water soluble biopolymer, welan gum have been used to develop a SBF-biopolymer fluid system based upon compatibility, rheological and visco-elastic behavior. The study was performed by characterizing biopolymer-VES fluid systems for their ability to retain their rheological and visco-elastic properties at elevated temperatures. Data analysis showed that the blend captures the merits of the individual fluid systems, as well as reduction in overall cost as compared to using a SBF mud by itself. Blends consisting of higher concentrations of welan gum showed good thermal stability and retention of viscosity at elevated temperature. Hence, cost reduction is achieved in the amount of SBF utilized. Also, the results of surface tension measurements showed that the binary system exhibited values much lower than welan gum fluid, and about the same as the SBF. Filter press tests results showed the blends to have a lesser fluid loss. Other potential applications of this binary system are also discussed.

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