Chevron U.s.a. Inc.

William Malcolm Calhoun

Russell Thomas Ewy

Hector Ulpiano Caicedo

A method for predicting the rate of penetration (ROP) of a drill bit drilling a well bore through intervals of rock of a subterranean formation is provided based on determined relationships between a bit-specific coefficient of sliding friction &#x3bc; and mechanical efficiency EFFand confined compressive strength CCS over a range of confined compressive strengths CCS. Confined compressive strength CCS is estimated for intervals of rock through which the drill bit is to be used to drill a well bore. The rate of penetration ROP is then calculated utilizing the estimates of confined compressive strength CCS and those determined relationships.

Method for predicting rate of penetration using bit-specific coefficients of sliding friction and mechanical efficiency as a function of confined compressive strength

A method for estimating the CCS for a rock in the depth of cut zone of a subterranean formation which is to be drilled using a drilling fluid is disclosed. An UCS is determined for a rock in the depth of cut zone. A change in the strength of the rock due to applied stresses imposed on the rock during drilling is calculated which includes estimating the &#x394;PP. The CCS for the rock in the depth of cut zone is calculated by adding the estimated change in strength to the UCS. The present invention calculates the &#x394;PP in accordance with Skempton theory where impermeable rock or soil has a change in pore volume due to applied loads or stresses while fluid flow into and out of the rock or soil is substantially non-existent. CCS may be calculated for deviated wellbores and to account for factors such as wellbore profile, stress raisers, bore diameter, and mud weight utilizing correction factors derived using computer modeling and using a baseline formula for determining an uncorrected value for CCS.

Method for estimating confined compressive strength for rock formations utilizing skempton theory

A method for predicting the rate of penetration (ROP) of a drill bit drilling a well bore through intervals of rock of a subterranean formation is provided. The method uses an equation based upon specific energy principles. A relationship is determined between a bit-specific coefficient of sliding friction &#x3bc; and confined compressive strength CCS over a range of confined compressive strengths CCS. Similarly, another relationship for the drill bit is determined between mechanical efficiency EFFand confined compressive strength CCS over a range of confined compressive strengths CCS. Confined compressive strength CCS is estimated for intervals of rock through which the drill bit is to be used to drill a well bore. The rate of penetration ROP is then calculated utilizing the estimates of confined compressive strength CCS of the intervals of rock to be drilled and those determined relationships between the bit-specific coefficient of sliding friction &#x3bc; and the mechanical efficiency EFFand the confined compressive strengths CCS, as well as using estimated drill bit speeds N (RPM) and weights on bit (WOB).

Method for predicting rate of penetration using bit-specific coefficient of sliding friction and mechanical efficiency as a function of confined compressive strength

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The Woodlands, TX, United States of America

William Malcolm Calhoun