Computer-controlled model for determining internal friction angle, porosity, and fracture probability

摘要

An apparatus and method for determining three characteristics of strata cut by a borehole on a "real time" basis, namely, the internal friction angle φ , porosity Φ, and fracture probability pr(frac). To calculate the internal friction angle φ, the invention simulates apparent and theoretical model formulae of a chosen physical characteristic of a drill bit operating within a borehole. The apparent model formula is an accurate mathematical formula of the chosen physical characteristic, and the parameters of the formula are all known constant values or varying values measured by sensors. The theoretical model formula is a mathematical representation of the chosen physical characteristic, and it has one unknown parameter, the internal friction angle φ. The theoretical model formula is set equal to the apparent model formula, and the internal friction angle 0 is interatively determined. The internal friction angle φ is then used to calculate porosity from the relationship given byThe parameters A and K are calibration transform coefficients calibrated from values of "average" porosity as determined by several nearby wells. The facture probability of the formation is calculated from the relationship given bywhere CR is the cohesive rating and ΦR is the porosity rating.