New Visco-Elastic Surfactant Formulation with Excellent Carrying Properties in Multiple Brine Systems and Wide Temperature Ranges

Abstract

Abstract Visco-elastic surfactants (VES) are widely used in oil and gas-well drilling and completion operations, mainly due to their non-damaging characteristics and excellent sand and proppant carrying properties. A challenge of VES is to maintain visco-elasticity over a wide set of temperature and brine conditions. The scope of this study was to develop a VES system with a robust rheology stability in low density to high density monovalent and di-valent brines and in wide temperature ranges aiming for a versatile formulation applicable for many conditions. Rheology of VES formulations of zwitterionic and cationic surfactants were screened in a wide range of typical drilling and completion brines with densities ranging from 8.7 −16.5 PPG of different monovalent and divalent salts and in temperatures up to 350 °F. As a final test, the capacity to hold and disperse sand and gravels at different conditions were investigated for selected brine formulations. A specific long-chained zwitterionic surfactant exhibits excellent brine stability in many situations as a stand-alone surfactant and here are shown to show improved temperature and brine stability when formulated with various cationic quarternary ammonium-based surfactants. Further improvements in temperature and brine stability are seen both types of surfactants in the formulation had long tail-groups and in many cases if both had unsaturation. For these formulations, even when changing brine conditions from 8.7 ppg CaCl2/MgCl2 to 16.5 ppg CaCl2/ZnCl2/CaBr2, they show improved visco-elasticity and carrying properties compared to standalone surfactant formulations and in a wide temperature range from 75 °F to above 245 °F. The viscoelastic behavior over broad brine and temperature ranges also showed excellent carrying properties in gravel sedimentation tests. The proposed formulations are of advantage both in water-based drilling and completion fluids and are non-damaging to the formation.