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ROP verses Sample Quality with PDC Bits
The introduction and prolific use of Polycrystalline Diamond Cutter Bits (or as commonly known as PDC Bits) over the past decade or so, has created a growing challenge for Wellsite Geologists to properly interpret drill cutting samples. PDC Bits were the Oil Company Drilling Department’s answer to increase ROP (Rate of Penetration) and lower operational costs while drilling Oil & Gas Wells, but created a new set of interpretational problems for Wellsite Geologists. Improper evaluations of these drill cutting samples can and have been a costly failure for Oil Companies to evaluate the Well Data with any type of accuracy.
The development and advancements of PDC Bit designs have greatly improved since their conception; with Bit Suppliers claiming to have models that perform well in most every rock type. PDC Bits are designed to be rotated at relatively high RPM causing drilling characteristics that include tearing and pulverizing all or part of the rock fabric to produce bit flour, clay, or sand; depending on the rock types being drilled. This produces bit-generated pseudo-sample textures that differ substantially from those of the actual in-situ formational rocks. This process can be further complicated by the introduction of drilling fluid contamination especially when using oil base (Invert) drilling mud.
With the introduction of all of these problems, the modern Wellsite Geologist must have the necessary skills to properly interpret these bit-generated textures. Geologists can then begin to accurately correlate these bit-generated pseudo-sample textures into a valid strip log interpretation utilizing near realistic Lithology, porosity and structure types.
In conclusion, Polycrystalline Diamond Cutter Bits are not going to disappear anytime soon, therefore it will be up to the Wellsite Geologists in the future to familiarize themselves with the skills to properly recognize these mechanically produced cutting textures.
