Laboratory Development of a Novel High-Shear Corrosion Inhibitor and Field Implementation in the Permian Basin

Objective / Scope As fluid production from unconventional, horizontal wells continues to increase in Permian Basin, corrosion rate due to CO2 on carbon steel surfaces has been observed to increase. During initial flowback periods, upwards of 35,000 barrels of fluids per day had been observed in the Permian. High fluid rates create a high wall shear-stress on the tubular wall. Due to increased mass transfer rate of corrosive species from the bulk fluid to the metal surface as well as the inability of corrosion inhibitor to form tenacious film, flow-accelerated CO2 corrosion has been observed (Figure 1). Corrosion model (e.g. MultiCorp (1)) was employed to calculate general corrosion rate (CR). Average CR calculated based on average fluid properties and initial flow conditions appears to agree with the average tubing life for those that have shown damages. New combination chemistries have been formulated to provide corrosion and scale inhibition on downhole tubulars. They were trialed and applied during initial production phase in the field. A new methodology is developed to monitor performance of the inhibitor chemistries and is discussed here. Methods, Procedures, Process Given wellbore dimensions and peak production rates with corresponding pressure and temperature as well as fluid properties, OLGA (2), a multiphase flow simulator, was employed to calculate shear stress on the pipe wall. Wall shear stress as high as 200 Pa was determined. Previous laboratory studies (3) showed that by increasing rotational speed (and hence shear stress on coupon surfaces) in Rotating Cage Autoclave (RCA), blank corrosion rates were found to increase. Sherwood number calculations have been established by different experiments in literature to determine relationship between CR and shear stress due to mass transfer of corrosive species. Rotating Cage Autoclave was employed here to evaluate performance of the new chemistries by matching shear stress closely to field conditions by using methods described in ASTM G170 (4). Several newly developed high-shear corrosion inhibitor / scale inhibitor combination (combo) chemistries were first screened in the laboratory by using RCA at specified conditions to simulate high shear field conditions. These conditions include CO2 partial pressure, temperature, and shear stress, etc. Emulsion tendency and compatibility tests as discussed ASTM G170 (4) were performed next with actual field fluids (i.e. produced water and oil). Periodic water sampling was performed to analyze for dissolved Iron (Fe) and Manganese (Mn) before and after commencement of combo chemistry. A new method is devised here to account for the contribution of Fe and Mn from the horizontal section which is not expected to be protected by the high-shear corrosion inhibitor.