A program was conducted for the simulation of paraffin oil and acid gas flowline conditions in a laboratory using a variety of experimental methods. Laboratory experiments were selected and designed to produce the wall shear stress values calculated for field oil and gas flowlines on test electrodes. The second objective of the program was to study the corrosivity of steel under various flow conditions and to study the effectiveness of chemical inhibition and corrosion monitoring using various techniques. The experimental techniques utilized to study the corrosivity and chemical inhibition in the environments were conventional weight loss measurements and electrochemical linear polarization resistance (LPR).
In recent years there has been significant interest in the utilization of multiphase flowlines for of shore field development. This technique commingles gas, oil and water production and allows for the production of wet gas. Such operations, if successful, can result in major reductions in costs normally associated with separation at each well site or platform. However, the challenges associated with this innovative type of operation are related to the ability to quantify the severity of corrosion in the three phase operating environment and, if necessary, the ability to inhibit the system to maintain an acceptably low level of corrosion.
Laboratory Simulation
The essence of laboratory simulation of multiphase environments is the understanding of the relationship between the conditions utilized in the laboratory for evaluation versus actual service conditions.1 The basic considerations are the various chemical factors that must be reproduced such as acid gas partial pressures, aqueous phase composition and the nature of the oil phase. Second, but of equal importance, are the various parameters that characterize the kinetic effects of flow which produce shear stresses that can effect the formation and stability of both corrosion and inhibitor films.2In developing the basis for this study, a significant effort was utilized to first establish the field /laboratory link. This was accomplished via the use of flow modeling methodologies described herein. Additionally, three types of laboratory methodologies were utilized in the study: (1) flow loop tests employing CLI''s Multiphase Autoclave Pipeline Simulator (MAPSTM), (2) autoclave rotating cylinder electrode studies, (3) spinning autoclave coupon tests and (4) turbidity cell tests in laboratory glassware. This paper focuses on the results obtained in flow loop experiments which provided insight into the inherent corrosivity of specific acid gas and paraffin flow line environments, the efficacy of the selected candidate inhibitor formulations and relationship between electrochemical and mass loss corrosion measurements. These flow loop tests were utilized to characterize three conditions: (1) paraffin oil line at high temperature (near wellhead condition), (2) paraffin oil line at low temperature (sea bottom pipeline condition), and (3) acid \gas flow line at low temperature (sea bottom pipeline condition).
INITIAL INHIBITOR SCREENING
Initial inhibitor screening was conducted on candidate formulations utilizing several basic procedures which included turbidity cell tests3 The formulations were also pre-screened based on prior use experience, supplier data and availability.