Capsule corrosion inhibitor loaded with hyperbranched chitosan: Carbon dioxide corrosion protection for downhole pipelines in oil fields

In the process of crude oil exploitation, carbon dioxide (CO2) and salt (especially NaCl) cause substantial serious corrosion to the pipelines. In this research, a novel, environmentally friendly corrosion inhibitor (HCTS) was synthesized by modifying chitosan. It effectively inhibited CO2-NaCl corrosion pipeline. In addition, the bentonite/acrylamide capsule-loaded with the corrosion inhibitor (HCTS) was prepared in accordance with the downhole corrosion environment of oil wells. Compared with the traditional method of inhibiting corrosion by adding a liquid corrosion inhibitor to oil wells, capsules that contained HCTS corrosion inhibitors delivered to the bottom of the oil well. The strength of the capsules was changed by adjusting the content of acrylamide, bentonite and cross-linking agent. The capsules ruptured at various depths downhole to the released corrosion inhibitors. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction results indicate that capsule corrosion inhibitor (loaded with HCTS) significantly inhibited the corrosion at a downhole of 500 m (5 MPa, 27.5 ℃), 1000 m (10 MPa, 45 ℃), and 1500 m (15 MPa, 62.5 ℃). This research is the first time to synthesis a capsule corrosion inhibitor for the severe corrosion environment of downhole pipelines. It successfully prevented the CO2-NaCl corrosion of downhole pipelines under high temperatures and pressures.