Unique ROP Predictor Using Bit-specific Coefficient of Sliding Friction and Mechanical Efficiency as a Function of Confined Compressive Strength Impacts Drilling Performance

Abstract

Abstract It has become standard practice to plan wells and analyze bit performance by using log-based rock strength analysis and/or the specific energy theory. The most widely used characterization of rock strength is unconfined compressive strength (UCS), but this is somewhat problematic because the apparent strength of the rock to the bit is typically different than UCS. Those who understand bit performance are aware of this problem, but to date there is not an industry standard or widely used methodology to address it. The specific energy theory has been used for bit performance assessment for years. One of the challenges of application of the specific energy theory, however, is uncertainty or lack of consistency in reasonable values for the input variables. Globally applicable solutions and methods to address these problems have been developed and implemented by ChevronTexaco. A new method to calculate rock confined compressive strength (CCS), based on both conventional and somewhat innovative rock mechanics principles, has been developed. A new method to determine input variables for bit performance prediction based on the specific energy theory and CCS has been developed. These have been integrated to provide new capability for rapid and accurate log-based determination of the expected or achievable rate of penetration and operating parameters for all bit types. The new models have proved valuable, improving drilling performance and reducing well cost by improving bit performance prediction, bit selection, and the determination of optimum drilling parameters. The methods are robust, based on fundamental and/or first principles, and require little or no calibration. Any required calibration is intuitive and simple. This document presents background, theory, research results, new methodolo gies, and field and lab data that validate and illustrate the methods.