Patent ID: 7412331

Claim:
A method for predicting the rate of drilling of a well bore in a subterranean formation, the method comprising the steps of: A) determining the rate of penetration (ROP) of a drill bit drilling a well bore through intervals of rock of a subterranean formation by: a) determining for at least one type of drill bit a relationship between a bit-specific coefficient of sliding friction μ and confined compressive strength CCS over a range of confined compressive strengths CCS; b) determining for the at least one type of drill bit a relationship between mechanical efficiency EFF M and confined compressive strength CCS over a range of confined compressive strengths CCS; c) determining the confined compressive strength for intervals of rock through which the at least one type of drill bit is to be drilled to form a well bore; and d) calculating the rate of penetration ROP for the at least one type of drill bit drilling along the intervals of rock to create a well bore, the calculations utilizing the confined compressive strength of the intervals of rock being drilled and the relationships between the bit-specific coefficient of sliding friction μ and the mechanical efficiency EFF M and the confined compressive strengths CCS; and B) selecting a drill bit for drilling the well bore through the intervals of rock of the subterranean formation based on the calculated rate of penetration ROP; wherein the confined compressive strength (CCS) of an interval of rock is determined at least in part based upon the unconfined compressive strength (UCS) of the interval of rock, the equivalent circulating density (ECD) of a drilling fluid being used to drill the interval of rock, the overburden stress (OB) removed from the interval of rock being drilled, the in situ pore pressure (PP) of pore fluids proximate the interval of rock being drilled, and the permeability of the interval of rock being drilled.