A Multi-faceted Data Analysis of the Corrosivity of CO2 and H2O-Rich Phases in Well Production with H2S or Well Injection with O2 Ingress

Abstract In high-pressure reservoirs, well-construction materials are typically exposed to a formation brine (H2O-rich phase) and a dense CO2 phase with H2O solubility. The brine is often considered the most corrosive phase; however, (1) is it, and (2) does H2S from the reservoir or O2 from injection heavily influence the relative corrosivity of the brine vs. its co-existing CO2 phase? A better understanding of corrosion by different phases is highly relevant for selecting metallic materials for hydrocarbon production, EOR, and CCS. In this paper, the corrosivities of brines and dense phase CO2 are compared across temperatures, pH, H2S, and O2 contents, and are explained using autoclave test data and OLI(1) chemical simulations. The relative phase corrosivity was determined from the average corrosion rates of metallic samples of 9Cr-1Mo (UNS K90941), 13Cr (UNS S42000), S13Cr (UNS S41425), 17-4PH (UNS S17400), 925 (UNS N09925), and 718 (UNS N07718), among others. This study (1) establishes when one phase is more corrosive than the other, (2) identifies a correlation between the corrosion rate of the two phases, (3) confirms that O2 is an order of magnitude more corrosive than H2S, especially at low temperatures, (4) ranks the serviceability of the materials under each simulated test condition, and (5) provides valuable insight for downhole material selection.