Abstract

The operator must reduce deviation tendencies in the 8-1/2" vertical hole section drilling the difficult J2x formation to efficiently develop gas reserves in Turfan basin, China. The challenge is to maintain near perfect perpendicular hole trajectory from 2400-3500m while drilling interbedded sandy claystone and coal layers. In the worst case scenario, the operator is forced to make several costly correction runs before starting the horizontal production hole. To solve the problems, engineers experimented with pendulum and steerable motor BHAs to maintain wellbore vertically with limited success.

Most recently, Kekeya wells Ke28 and Ke33 required 6-5 bits/trips respectively to complete the 8-1/2" hole section at unacceptably low average ROPs of 1.6 m/hr and 2.4 m/hr. The operator required a PDC/deviation control tool to maintain verticality and increase ROP. To accomplish the objective, the drilling team utilized a rock strength program and a bit/BHA modeling system to investigate several different cutting structures to determine the best blade count and cutter placement configuration. Based on the study, a six-bladed 8-1/2" PDC bit was identified as the best candidate to accomplish the objectives. To mitigate deviation tendencies, a reliable automatic vertical drilling system (VDS) was selected. The reliable VDS tool does not require a MWD logging sub and can be deployed during normal drilling operations including backreaming and shoe drillout.

The new-style 8-1/2" PDC bit was run in combination with VDS on new well Ke282 with outstanding results. The bit/VDS bottom hole assembly drilled the entire 740m section at 7.1 m/hr through the difficult J2x formation in a single run setting a new field benchmark. The optimized PDC bit increased ROP by 250% while reducing trips/bit consumption by 82%. The performance improvement saved the operator more than 14 days of rig time for a total cost savings of $93,000 USD.

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