Abstract

Over the last several years, PDC bits have continued to encroach on traditional rollercone (RC) applications. The expanding PDC envelope has reduced rollercone usage to only the most demanding applications and hard/abrasive formations. Increasingly difficult wellbore requirements dictate that rollercone bits survive more on-bottom drilling/circulating hours with more footage drilled at higher RPM and weight-on-bit (WOB). Additionally, many applications require the use of directional drive systems that apply additional forces on the bit's cutting structure. Additional tool challenges include deep/hot holes, high mud weights, harsh mud chemistry, high temperatures and applications with less than desired solids control.

These hostile down-hole environments contribute to bit damage and can often lead to the failure of moving components, specifically rollercone bit bearings and seals. Failure of any component in the bearing package often results in a catastrophic failure of the entire system, ending the run with the potential of fishing for lost parts. Mud encroachment into the seal is often the reason for bearing failure.

To solve this problem, extensive analysis of field data and dulls was conducted to identify the conditions limiting seal/bearing life. The solution was identified and new bits were developed during field tests. Field testing included a large data set of 28 test runs against 61 control runs, all in the IADC 527-537 range and in the same application. The test results show and improvement in seal life of the test group of 26.9% over the offset data set. Since these results, testing has expanded to four different bit sizes and bit types. This paper will outline the significant time/cost savings to the operator in the test area.

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