STRESS CORROSION CRACKING OF A COLD WORKED 22Cr DUPLEX STAINLESS STEEL PRODUCTION TUBING IN A HIGH DENSITY CLEAR BRINE CaCl_2 PACKER FLUID--Results of the Failure Analysis at Deep Alex and Associated Laboratory Experiments

摘要

The Deep Alex well was a gas well in the Gulf of Mexico with a bottom hole temperature of 370 deg F (188 deg C) and pressure of 16,800 psi (116 MPa). The gas contained H_2S at a maximum partial pressure of 0.25 psi (1.7 kPa) and CO_2 partial pressure of 672 psi (463 kPa), i.e., at bottomhole. The well was completed with a 22Cr duplex stainless steel (UNS S31803) that had been cold drawn to a minimum yield of 125 ksi (862 MPa). The production environment was within the environmental limits established in-house for this 22Cr duplex stainless steel. The use of the tubing and its properties also complied with NACE MR0175. The annular completion fluid was 11.0 ppg CaCl_2 that contained an oxygen scavenger and high temperature inorganic corrosion inhibitor; the contents of additives at the time of well completion were not stated. After one month of production of gas from the Deep Alex well in late 1999, the production tubing failed, forcing the well to be shut-in. No one was injured and no harm to the environment occurred because of the failure or subsequent operations to control the well. A failure analysis and subsequent laboratory program demonstrated that the cause of the failure was environmentally assisted cracking of the 22Cr duplex, a direct result of the production of H_2S by the decomposition of the sodium thiocyanate corrosion inhibitor in the CaCl_2 completion fluid in the annulus.