In the Upper and Lower Bakken shales, laminated shale structures exhibit variable mechanical properties depending on orientation relative to bedding planes, which can increase the likelihood of cement left-in-pipe events (CLIPs). CLIPs occur when cement fluids are not completely displaced from the casing during placement. These incidents can be costly both in terms of well costs and non-productive time, with rates of approximately 2% of total wells drilled in the Williston basin at a USD 750,000 estimated costs to the operator per incident. Experts in geomechanics, drilling fluids, and well integrity have collaborated to focus on the geomechanical factors associated with drilling the curved section through the Upper and Lower Bakken shales.

A 3-year study of CLIPs and successfully completed offset wells was conducted to assess the roles of numerous contributing factors. Basin geomechanics, drilling practices, cuttings removal, and well cementing practices were evaluated for each of the cases and it has been determined that in-situ shale stresses have the greatest impact on wellbore stability and CLIP occurrence. Construction of Mechanical Earth (MEM) and wellbore stability (WBS) models for a typical Williston well suggests that several geomechanical factors contribute to successful cement placement.

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