PDC Bit Performance Under Simulated Borehole Conditions

Abstract

SPE Members Abstract Laboratory drilling tests were used to investigate the effects of differential pressure on Polycrystalline Diamond Compact (PDC) drill bit performance. Catoosa shale core samples were drilled with PDC and roller cone bits at differential pressures up to 1750 psi. All testing was conducted in a controlled environment using a full-scale laboratory drilling system. Results from these tests indicate that under similar operating conditions differential pressure reduces PDC bit performance as much as, or more than conventional rock bit performance. Specific energy calculations indicate that rock strengthening, chip hold down, and bit balling may have caused the reductions. Recognizing that differential pressure does significantly reduce PDC bit performance will help researchers to better interpret test results and improve bit designs, and help drilling engineers to run PDC bits more effectively in the field. Introduction Since PDC bits were first introduced in the mid - 1970s, they have been utilized in an ever widening array of drilling situations. Both research efforts and field experience have helped operators learn how to correctly utilize PDC bits, and how to save significant time and money in the process. To date, PDC bit research has focused primarily on bit design and bit hydraulics. These efforts have resulted in improved cutter and matrix materials and inventive fluid jet/cutter combinations. Innovative operating techniques have also been instrumental in expanding the utilization of PDC bits to previously unimagined applications. Even with all the improvements and successes, PDC bits are far from being successful on every bit run, and there are still many areas of PDC bit technology that need to be examined. One area that has not been investigated is the effects of differential pressure on PDC bit performance. Differential pressure effects were first documented by industry research during the late 1950s when a number of studies were conducted using roller cone bits. These research efforts concluded that differential pressure detrimentally affects rock bit performance, and that overbalanced drilling conditions should be limited as much as is safely possible. PDC bits utilize a shearing action to break rock that is very different from the indenting action used by conventional roller cone bits. P. 77^