Remote Real-Time Well Monitoring and Model Updating Help Optimize Drilling Performance and Reduce Casing Strings

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Summary Remote real-time pore pressure monitoring using a combination of Logging-While-Drilling (LWD) services coupled with a predrill pore-pressure model reduces risk and cost by providing significant insight into wellbore stability and allowing for casing seat optimization. This paper presents the results of a shelf job in the Gulf of Mexico (GoM) that allowed an operator to drill successfully in a very tight hydraulic envelope and even eliminate a string of casing. The uncertainty in the pore-pressure prediction ahead of the bit can be significantly reduced by model updating. The LWD measurements allow the predrill velocity-to-pore-pressure transforms to be updated while drilling using the velocities from the sonic tool and pressures from the LWD formation pressure tool. This calibrated transform is then applied to revise the predrill pore-pressure model while drilling, and thus provide an estimate ahead of the bit. In this case study, the predrill model used interval velocities extracted from a 3D mechanical earth model of the northern GoM based on velocities derived from checkshots and sonic logs. These velocity data were kriged to give a 3D velocity model over the entire northern GoM with uncertainty estimates. Using state of the art LWD technologies, a new methodology was used to optimize drilling performance on a well in Vermillion Block 338. Continuously updated LWD annular pressure measurements effectively gauge wellbore pressures and help the driller rapidly intervene in pressure and/or geomechanical wellbore stability issues. A complete understanding of the hydraulic forces acting on a borehole can increase the rate of penetration, provide greater safety, minimize casing strings, reduce or eliminate kicks and formation fracturing, and allow faster and less expensive completions. The techniques described in this paper using real-time measurements allowed the operator to extend both the 9 5/8-in. intermediate casing and 7 in. liner to TD. As a result, a critical casing string was pushed 1,287 ft deeper than planned and a pre-planned 5 in. liner eliminated. This saved casing expense, as well as slimhole drilling and completion costs.