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Technical Paper: Conical Diamond Element Enables PDC Bit Efficiently Drill Chert Interval at High ROP Replacing Turbine/Impregnated BHA

Society: SPE
Paper Number: 178765
Presentation Date: 2016
 Download: Conical Diamond Element Enables PDC Bit Efficiently Drill Chert Interval at High ROP Replacing Turbine/Impregnated BHA (3.49 MB PDF) Login | Register

 

Abstract

Developing reserves in Kazakhstan's Chinarevskoe field frequently requires the operator to drill an 8.5-in. vertical hole section through extremely hard carbonates which contain high concentrations of problematic chert inclusions. The first significant chert layer is encountered at 3050-3110m, which has 10-50% chert content. Penetrating the chert interval with PDC bits has been challenging and in many cases impossible due to the cutters' inability to withstand high impact forces, which resulted in catastrophic cutter damage. The application of impregnated bits on high-speed turbines (1300-1400 RPM) led to significant improvement in run lengths and this BHA became the standard approach.1 One impregnated bit could drill approximately 55m at 3/4m/hr. The hole section typically requires 3 bits to reach TD.

However, the impregnated bit generated very small cuttings and high frictional heat altered chip appearance hampering lithology characterization and efforts to identify formation properties. Additionally, the centrifuge was unable to separate the extremely small cuttings from the drilling fluid, resulting in a gradual increase in mud weight over the interval creating the need for constant mud replacement.

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