Corrosion Behavior of 13Cr Casing in Cement Synthetic Pore Solution

Abstract

A test procedure was designed and employed for exposure and degradation testing of well cements in a simulated downhole environment of offshore deep drilling. A Class H cement sample was crushed to coarse grains and was exposed to 5 % mass NaCl(aq) solution in contact with CO2 at 100 °C and 10 MPa for 200 hours. Key ionic species were identified from the aqueous phase from the testing to develop the cement synthetic pore solution (CSPS) recipe. The CSPS was then used for corrosion characterization of high chromium well casing steel at the same conditions of the cement exposure for 60 hours. The corrosion potential in the measurements ranged between -0.4 and -0.5 V vs. SHE. The average corrosion rate of the steel samples was on the order of 0.1 mm/year, representing a worst-case scenario for degradation of the cement material, but significant for critical steel components like a well casing.

Effects of H2S and CO2 on Cement/Casing Interface Corrosion Integrity for Cold Climate Oil and Gas Well Applications

“…These conditions were well above the critical point of CO 2 at 31 °C and 7.39 MPa, meaning the non-aqueous phase was in a supercritical state. The test conditions were selected to allow comparison to a previous study using a similar cement sample but with a different extraction procedure (10).…”

Corrosion Behavior of 13Cr Casing Steel in Cement-Synthetic Pore Solution Exposed to High Pressure CO2 and H2S

“…(11) It has been reported in literature that in deep wells the ratio of CO 2 :H 2 S can be expected to be on the order of 1000, and this ratio was selected for the tests reported here. (14) A mole ratio of 0.05 for CO 2 :H 2 O was selected, as this allowed an adequate volume of solution to ensure coverage of the electrodes and weight loss samples at both 85 and 200 °C. The solution pH was calculated using OLI Analyzer software taking account of temperature, system volume, and solution composition.…”

“…(11)(12)(13) In previous tests, the cement pore solution composition was determined after exposure of Class H cement to acid gas CO 2 and formation brines, and the corrosion of casing steel L-80 was investigated in the cement synthetic pore solution (CSPS) in contact with 10 MPa CO 2 . (14) Therefore, in this work, the corrosion behavior of casting steel L-80 was further investigated in the CSPS in contact with a CO 2 and H 2 S mixture at 85 °C and 200 °C, respectively. In-situ electrochemical measurements, ex-situ surface analyses, and mass loss sample measurements were performed to study of H 2 S and temperature effects.…”