Analytical Development of Seastate Limits Associated to the Abandonment Operations of a Structurally Compromised Subsea Well

摘要

When drilling a subsea well, a loss of structural integrity of the conductor can lead to a substantialreduction in the well’s ability to resist the axial and lateral loads imposed by the drilling riser and BOP.This can then lead to hazardous conditions and increased risks to the asset performing the drilling as wellas the personnel onboard. This may leave the operator with no choice but to abandon the well. In thissituation, the hazards associated with the loss of integrity must also be considered when planning theabandonment operation itself. This paper presents a case study that details the analysis methods used todevelop seastate limits for the abandonment of a subsea well with compromised structural integrity.The well’s high pressure and low pressure housings were observed by ROV inspection to have becomeun-latched during drilling. The inspection also revealed substantial conductor subsidence which suggesteda failure of the 30on conductor and 20on surface casing cement jobs. Initial investigations indicated the welllacked the required levels of structural integrity to resist the loads involved with drilling to total depth. Asa result, the decision was taken by the operator to suspend and then permanently abandon the well.This paper discusses the technical approach used to develop the seastate limits imposed during theabandonment operation. The methodology utilized advanced non-linear finite element analysis techniquesin conjunction with a novel statistical treatment of previously recorded in-situ BOP motion data.