Drilling long laterals at depths deeper than 17,000 ftTVD in Oklahoma offers numerous challenges due to high-pressure gradients in combination with narrow pressure windows of sometimes less than 0.5 ppg. This necessitates Managed Pressure Drilling techniques allowing use of a hydrostatically underbalanced drilling mud.

Due to geological factors, bit runs are short and trips frequent. However, the pore pressure, narrow window, and the volume of mud in the vertical section hinders the use of the standard trip method of laying out a series of mud caps making conventional trips slow and cumbersome. As a result, over a series of consecutive bit trips, a method of balancing the well with a combination of a heavy slug and fixed volume backfill while stripping to surface was implemented and optimized and then further applied over successive bit trips and on a subsequent well. Once the bit was at surface, the well was hydrostatically balanced. Trips performed this way were significantly faster, saving time when compared to offsetting wells.

This paper details this slug and backfill trip method as a concept along with a series of three increasingly complex models for slugging and backfilling with MPD. The key depths model is succeeded by a constrained lightweight analytical model followed by a more elaborate, full numerical model for this type of well. The full numerical model can accommodate all slugging and backfilling scenarios and has wider applications.

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