Corrosion of Rubber Materials of Packer for different CO2 Phase Behavior in Actual HTHP Gas Wells

摘要

The oil and gas wells face much harsh environment due to high temperature, high pressure (HTHP) and high content of gases (CO_2 H_2S) in the reservoir. Packer is a widely used tool in HTHP gas wells, which can prevent the corrosive medium from channeling into the annulus between tubing and production casing. The sealing ability of packer mainly depends not only on the mechanical properties of rubber materials but also on the actual downhole conditions. Therefore, it makes great sense to study the performances of rubber materials under real gas well environments. During experimental setup, the sealing element of packer was usually situated in a compressive stress state, and the corrosive medium CO_2 was in a supercritical state under HTHP corrosive conditions. Three kinds of rubber materials as packer were developed for CO_2 environment. Furthermore, a method was proposed and relevant devices were developed to investigate their corrosion behaviors in gaseous CO_2, liquid CO_2 and supercritical CO_2 environments under a free state and a tensile load, which could simulate the true surrounding conditions of the coupon of the packer rubber and full scale packer rubber respectively. The dissimilarity of attack for packer rubber coupon and full scale packer rubber was compared in three exposure conditions i.e. gaseous CO_2, liquid CO_2 and supercritical phase under different compressive stress by mechanical properties testing and morphology analysis. Experimental comparisons showed that rubber samples exposed to liquid CO_2 exhibited greater reactivity as compared to gaseous CO_2, and the existence of compressive stress would aggravate the corrosion of CO_2 to rubber materials.