Dealing with well integrity non-compliances with respect to the principle of two well barrier envelopes is a problem of paramount importance in well integrity governance during the life cycle of wells. Besides, during production phase, operators might experience several difficulties related to the feasibility and conclusiveness of well integrity assessments, this is especially true for subsea wells. On the other hand, those assessments are quite conclusive and easy to perform by the rig when a workover is in progress. Namely, because there is usually only one fluid phase (brine) during pressure test and the feasibility of performing those tests in the actual flow direction, the well barrier elements evaluations performed by the workover rig are, in general, conclusive when compared to the verifications done by the production platform during production phase.
Thus, it is common to find out some unforeseen well integrity non-compliances with respect to the principle of two well barrier envelopes during a workover. Therefore the operator must establish a process for making up a decision concerning whether the handover process after the intervention back to the production team or downhole plugging the well whenever it is necessary, depending upon the well integrity status. This decision is based upon a preemptive (preventive and anticipative) risk assessment.
The use of a preemptive risk assessment leads to very interesting results, namely: a) standardization of decision making process avoiding subjectivities about well integrity statuses evaluation; b) savings on applying highly skilled technical human resources; c) mitigating environmental and compliance problems; and d) guidance on workover designers with better intervention planning practices concerning well integrity uncertainties.
This paper describes how it can be done as well as the regulations aspects related to it. Furthermore, it is shown case studies to illustrate the whole process of making up the right decision of handing the well over or downhole plugging whenever it is needed.