To better understand the damage endured by mechanisms during downhole simulation testing (rapid gas decompression testing, or RGD testing), three downhole formulations (FKM, HNBR and NBR) were evaluated.
The downhole simulation test method was based on NACE TMO-192 (100 percent CO2, 5.2 MPa). The damage mechanisms were elucidated with involved various characterization tests. The characterization methods included dynamic mechanical analysis (DMA) by strain sweep, tensile properties, machine groove trouser tear (MGT), time-domain NMR (TD-NMR), modulus profiler and Mini-DeMattia crack growth. The property changes as a function of exposure time were measured.
Furthermore, the RGD method was combined with compression stress relaxation (CSR). The CSR jig was placed in the RGD vessel (high pressure CO2 vessel). The effect of the RGD test on compression stress was determined. For mechanistic understanding, the results (from DMA, tensile, MGT, TD-NMR, modulus profiler, Mini-DeMattia and CSR) were compared to the CO2 solubilities of the various polymer types.