Chemical and Structural Degradation of Fluoroelastomers in Ultra-High H2 S Environments: A Comparative Analytical Study

Abstract The presence of H2S and CO2 in reservoirs is a persistent challenge, requiring seals that can withstand high concentrations and temperatures in the presence of workover chemicals. Downhole exposure to high H2S levels (above 30% H2S) at high temperature and pressures require understanding the chemical impact to those damaged sealing structures. Elastomers were exposed to this harsh environment and were evaluated using Micro XRF to assess their resilience and elemental modifications. The combined chemical environment consisted of a 75% by volume sour gas (40/10/50% H2S/CO2/CH4) and 25% liquid phase with H2S control chemicals. Pressurized to 5000 psi at 300°F for 7 days, the system was then depressurized and degassed. Exposed and unexposed samples were analyzed for hardness, tensile strength, volume change, and chemical structure using analytical techniques such as optical microscopy, laser-induced breakdown spectroscopy (LIBS), and Fourier-transform infrared spectroscopy (FTIR) and X-ray fluorescence (XRF). One type of fluoroelastomer categories was studied: FKM was chosen for their proven performance in low and medium H2S concentrations. Treated and untreated fluoroelastomers were examined for modifications in their chemical composition. The elastomers were chosen because of their physical response to exposure at high pressure and temperature in the presence of high concentrations of H2S and CO2 with workover chemicals. The results demonstrate significant changes in chemical composition, including variations in elemental ratios and trace elements, after exposure to the workover chemicals and the high H2S and CO2 at high pressure and temperature. Examination on a broader set of elastomers is currently underway with the hope of establishing some fundamental assessments of how the chemical changes modify the physical characteristics observed. An extensive study of the impact of acid gases at high temperatures and pressures has been done incorporating both the standard physical testing as well as unique chemical analyses for better understanding of how these gases degrade the sealing capabilities of these elastomers. At this point no detailed study of this type has been done especially at these high concentration of acid gases or pressures and temperatures.