Risk assessment for Liwan relief well in South China Sea

Drilling engineering has a great amount of uncertainty and always involves huge investments and high risks. The term “relief well” refers to a well drilled from a secure area that intersects with an accident well. It is a key method to effectively deal with a blowout or fire hazard by using a well kill operation. Due to drilling uncertainty, a relief well assumes significant responsibility to cope with potential accidents during onshore and offshore drilling. Thus failure of the relief well leads to more serious consequences than caused by original accident. It is essential to analyze and assess the relief well risk before the drilling operation in order to prevent complex accident, improve drill efficiency and guarantee the rescued project will work smoothly. Based on Analytic Hierarchy Process (AHP) method and fuzzy set theory, this paper proposes a comprehensive risk assessment model of relief well, then applies the model to evaluate the drilling risk of LW21-1-1 relief well project in South China Sea. The assessment results demonstrate that the success rate of drilling this relief well is estimated at 48.7%, providing needed informational base to take decisions about controlling existing risks and therefore to drastically decrease wasted time, further accidents and direct financial losses.

► We establish multi-factor risk assessment model for relief well.
► We evaluate relief well risk using AHP and fuzzy Comprehensive Evaluation.
► Obtain each risk factor’s weight and final comprehensive risk value.
► Assessment result provides important information for drilling decision-making.