Abstract
With the introduction of O2 during oil and gas production, the erosion-corrosion rate of tubing steels increases; the objective of this report is to explore the reason for this. Erosion–corrosion experiments were performed in environments of CO2 and CO2–O2, respectively. Macrographs, microstructures, and the compositions of erosion-corrosion scales were investigated using a digital camera, scanning electron microscope (SEM), Kevex-SuperDry energy spectrometer (EDS) and X-ray diffraction (XRD). The results show that the erosion-corrosion products are composed of large FeCO3 particles and some amorphous product in the CO2 environment, while they are made up of FeCO3, Fe2O3, Fe3O4, and bits of amorphous product in the CO2–O2 environment. The interface between erosion-corrosion scales and the substrate of 3Cr steel is smooth, and Cr enrichment obviously exists in the erosion-corrosion products in the CO2 condition. However, the erosion-corrosion scale is loose and porous with little Cr enrichment in the CO2–O2 environment, which makes the protectiveness of the erosion–corrosion scale weak, and pitting corrosion occurs. The addition of O2 may destroy the protective FeCO3 scale and Cr enrichment in the erosion-corrosion scale, which may be the main reason for the decline in the level of protectiveness of the erosion-corrosion scale, making it weak in terms of preventing the corrosive medium from diffusing to the substrate.
Highlights
In the later stages of oilfield development, the addition of an oil displacement agent into the oil well is a common technology used to increase oil recovery [1]
There was a significant difference in the erosion-corrosion rate of 3Cr steel comparing the CO2 and the CO2 –O2 conditions
Compared with the change from 0 MPa to 0.2 MPa in the partial pressure of O2, the erosion-corrosion rate of 3Cr steel increased slowly when the O2 partial pressure increased from 0.2 MPa to 0.6 MPa
Summary
In the later stages of oilfield development, the addition of an oil displacement agent into the oil well is a common technology used to increase oil recovery [1]. Carbon dioxide (CO2 ) has been studied for many years as a widely-used oil displacement agent [2]. It can expand the volume and reduce the viscosity of crude oil [3]. Much equipment employed in the production of oil and gas is made up of steel, such as pipelines. There is formation water in oil and gas extraction, and this can significantly promote electrochemical corrosion in steel in humid or water-containing environments, leading to uniform and/or local corrosion [4]
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