Quantifying Increased Corrosion Risks in Chemical Injection Lines and Gas Lift Systems Due to Partial Evaporation Effects

Abstract

Abstract The application of production chemicals downhole via dedicated injection lines or by means of gas lift systems, whilst not new, is becoming more commonplace in the oil and gas industry. The corrosion characteristics of injected chemical formulations in such systems can be complex and require detailed testing to understand the behaviour and assess the potential corrosion risk of chemical formulations under the extreme conditions of temperature and pressure that exist within either of these injection systems. In the presence of a fast flowing stream of hot gas, the more volatile components can be stripped from the formulated product, resulting in separate condensed vapours and chemical residues. Similarly, low-pressure vapour pockets formed within downhole chemical injection systems due to hydrostatic pressure fluctuations may cause some components of the injected chemical to be evaporated. Materials compatibility tests are commonly conducted using samples of "as supplied" production chemicals However, there is also a risk that different material compatibility/corrosivity characteristics can be induced by the condensed vapours or stripped residues of the production chemicals when compared to the originally applied chemical formulation. Laboratory testing is not commonly conducted to assess this behaviour. Samples have been prepared and corrosion tests conducted on collected vapours and residues from production chemicals. Distillations were conducted on the neat chemicals to obtain vapours and residues, and corrosion rates were measured on a range of different metallic specimens by conventional electrochemical or coupon weight loss methods. The results of these separated phase corrosion tests were then compared with the corrosion measurements on the original formulations. The test programme demonstrated that for some of the formulations tested, significantly higher corrosion rates were measured for either the condensed vapours or the distillation residues when compared to the original formulation. This work highlights the need to carefully consider the possible range of temperature/pressure conditions and gas/liquid phase interactions that will be experienced by injected chemicals within the chemical delivery system. Specifically, there is a need to assess the implications of solvent stripping/evaporation of volatile components. Chemicals that form more corrosive condensed vapours or residues may need to be avoided to prevent equipment failure or a loss of integrity. It is not adequate to simply test the ‘stability’ of a chemical at elevated temperatures, ambient pressure and static conditions; the separation effects within the gas/liquid system must also be considered.