Corrosivity studies of Well Completion Fluids Comprising ZnCl2/CaCl2 on N-80 Steel

摘要

The corrosion behavior of mixed ZnCl2 and CaCl2 well completion fluids was studied. These brines areused in oil and gas high pressure production and exploration operations. This study investigates thepitting type corrosion issue which the use of these solutions can cause to tubular goods.This study identified CaCl2 and ZnCl2 mixture solutions with acceptable corrosivity that also satisfies theprimary requirements for balancing well pressure and avoiding other application issues such ascrystallization.The corrosion behavior of API 5CT grade N80 was investigated in these solutions, by means of weightloss coupons, DC polarization and AC-Impedance Electrochemical techniques.Surface observations and analysis were conducted by means of a Scanning Electron Microscope(SEM) to determine the pitting morphology on API N-80 steel surfaces.A tri-phase diagram based on ZnCl2, CaCl2 and water at 21 ℃ was developed to determine the correctfluid density with different concentrations of each component. In addition, pH-related diagrams weredeveloped based on different compositions of each component and their mixtures with different fluiddensities. The corrosivity of fluid compositions with densities ranging from 1.20 kg/m3 (10 ppg(1)) to 1.80kg/m3 (15 ppg) at temperatures of 25, 60, 90 and120 ℃, were investigated.