Deep, overpressured wells account for a disproportionately large share, about 27 percent, of all U.S. drilling costs. Poor bit performance in deep formations is a major contributor to these costs. The cause of this poor performance has been uncertain because it could not be identified or observed directly in the field. The focus of this study was to identify the characteristic symptoms of the problem in the field for subsequent comparison to the symptoms resulting from different possible causes in laboratory tests. Additional analysis was performed to determine the effect of lithology and operating parameters on field bit performance.
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