Initial Souring Monitoring and Souring-Mitigation Testing Using an Online Souring-Mitigation Cabinet (SMC) Prior to Live Produced Water Reinjection (PWRI) and Nitrate-Based Souring-Mitigation Treatment on Norske Shell's Draugen Platform

摘要

The risk of reservoir souring is understood as one of the most serious effects of produced water reinjection (PWRI). Costly well backflows are traditionally used to monitor these effects. On Draugen (produced water 60 deg C, lean in carbon), a PWRI pilot is currently implementing nitrate to mitigate souring. Well backflows were not possible and another monitoring method for souring parameters was required. A souring mitigation cabinet (SMC) (two 1.4m columns with a 12 cm diameter, using a reservoir simulated sandstone medium), was designed. A side-stream of produced water was routed through the SMC over 3 months to allow typical reservoir biofilm development. Varying doses of nitrate (100, 80 and 50 mg per L) and nitrite (100mg per L) were then tested over a period of 15 days. Stoichiometric inhibition of SRB souring by nitrate (80 mg per L) and removal of background sulphide (100 mg per L) was exhibited. Nitrite (100 mg per L) exhibited short term stoichiometric mitigation. Control sulphide varied between 5 and 9 mg per L. 80 to 85% utilisation of nitrate and nitrite was shown. Dissolved organic carbon consumption was 28 and 29%, indicating no exacerbated carbon consumption in the test column. A two log10 difference in mesophilic SRB (30 deg C) and thermophilic SRB (60 deg C) was exhibited between the columns. NRB did not vary. The application of nitrate and nitrite stoichiometrically mitigated souring in the Draugen system and reduced the SRB population in the test column. This demonstrates the use of a SMC with a biofilm of the same properties as that developing in the near well area during PWRI. Such studies may reduce the requirement of backflows and give the opportunity to repeat trials of different mitigation strategies during operation and independent of PWRI. The SMC is being maintained on Draugen and is currently used to control mitigation effects on bulk produced water during PWRI.