Research Of Surfactant Micellar Drill-in Fluid System

Viscoelastic surfactant(VES) molecules are gathered to form spherical micelles and worm-like micelles or rod-like micelles under the action of countra-ion and co-surfactant; its high viscosity structure are quickly decomposed to very low viscosity after contacting with formation water or crude oil or synthetic gel breaker. So less residue exist in the formation pore and high fluid flowback rate as well as permeability recovery degree are formed, which leads to effectively reservoir protection. Rheological properties of cationic viscoelastic surfactant CTAB were studied as well as the properties temperature resistance, fluid loss and gel breaking performance of matched breaker. Experimental results shows that systemviscosityincreases to 160mPa·s when CTAB and additives(Sodium Salicylate) are used cooperatively; filter loss drops greatly at the existence of fluid loss agent LA(0.5%) and system viscosity is significantly reduced to 3mPa·s when new gel breaker is added. A new drilling fluid system with cationic viscoelastic surfactant CTAB as the main agent of surfactant micellar drilling fluid DIF-a, which brings low flow friction and filter loss, are studied. The results show that reservoir damage, generated by external fluid, is greatly reduced, which ensures that reservoir permeability retention rate can reach to 91.41%. Due to poor heat-resistant properties of cationic viscoelastic surfactant CTAB, synthesis of a new type heat-resistance and salt tolerance of viscoelastic surfactant stearic acid amide propyl ammonium oxidation OA-a is studied by orthogonal method including amidation reaction and quaternary amination reaction. Analysis and evaluation of the OA-a viscosity change with different temperature/pH/Ca2+ concentration. Experimental results shows that the stearic acid amide propyl ammonium oxidation OA-a heat-resistant performance is greatly improved whose viscosity reaches to 113mPa·s at 150℃ as well as excellent salt tolerance, which meets the demand of the drilling fluids as to the minimum viscosity to carry cuttings.