A comparative risk assessment was conducted to evaluate the risk associated with a Steam Assisted Gravity Drainage (SAGD) well blowout. The main comparison was between an isolated (double barrier) completion and an open (single barrier) completion used in conjunction with an effective blowout response plan. The target application was a SAGD pilot project in the Orinoco Belt in Venezuela.
The overall approach for the risk assessment included the investigation of the blowout flowing potential of the SAGD wells pair through reservoir modelling, the estimation of the probability of a blowout using fault-tree analysis, and the evaluation of the possible consequences (life safety, environmental and economic) of such blowout using various quantitative consequence models. Details of this approach are discussed in this paper, along with the results specific to the target application.
Results of this work can provide guidance for similar operations where decisions regarding completion options and blowout response plans are required. One key result was that, for this specific SAGD pilot project, a blowout response plan must be able to reduce the blowout duration substantially (from 3 days to 1 day for environmental risk, and from 3 days to 2 hours for economic risk) for the environmental and economical risks associated with a open completion to be comparable to those of an isolated completion.