Research About Quantitative Risk Assessment Method Of Drilling Well Control On Formation Factor

Well blowout and its out of control is the top catastrophic accident in drilling engineering.The causes of blowout accident can fall into three categories: human factor,drilling condition factor and formation factor.The large quantity statistics data indicates that formation factor accounts for a large proportion,even reaches 50%,so the formation factor is the intrinsic and objective factor leading to drilling blowout.Therefore,research on risk assessment method of drilling well control on formation factors,in particular,quantitative risk assessment(QRA)method,will help to identify risk causes and take measures to reduce risk in advance to avoid the happening of the blowout.On the basis of investigation and statistics,this article I summarized the common six evaluation method for drilling risk,analyzed and compared the advantages,disadvantages and application of them.Then,this article I summarized the advantages of grey relational analysis and applied to well control risk evaluation.Against to the short of troditional grey relational analysis evaluation,this article proposed improved grey relational analysis evaluation process on the basis of the TOPSIS method.Determining the index weight is one of the key technologies in comprehensive risk assessment,its rationality impacts assessment's scientific directly.In this paper,through investigation and analysis for more than 450 risk assessment documents in the past 20 years.this article selected the most commonly used 5 methods from a dozen weighting methods.I analysed and contrasted these methods from the aspects of theory,scope and relative merits,then took instance data in well control risk quantitative evaluation of oil and gas drilling for example,worked out and sorted index weight with each method.The difference of the results is bigger since different methods have different emphasis,which indicates a single weighting method has certain defects.In order to give full play to the advantages of subjective and objective weighting methods,this article proposed a combination of subjective and objective weighting methods and the calculation steps to make index weight allocation more reasonable in risk assessment.Analysising the three internal conditions leading to well blowout,with the actual state this article established a formation factor hierarchical chart consisting of three levels and 12 indexes.Each index is divided into four risk levels with the corresponding grade standards.Based on the improved grey correlation evaluation method and the formation factor index system,this article built the quantitative risk assessment mode of drilling well control on formation factor.Applying this model to three typical wells,this artilcle determined their level of risk,find out the key incentives.A repeated comparison and assessment prove that the results are basically consistent with the well's risk-liability survey done by the experts,and the model we have proposed is rational and feasible so as to be taken as a valuable reference to high-pressure oil and gas well risk assessment.The research can provide guidance to identify well control risk and take scientific technology measures for on-site engineering and technical personnal.