Formation Evaluation Using in Situ Penetration Testing and Simulation Data

Abstract

ABSTRACT Values of uniaxial compressive strength (UCS) and tensile strength (TS) are two key rock properties which determine the mechanical response of rock under penetration loading. Penetration testing is a popular means for obtaining values of UCS and TS of rock. A novel method has been developed for rock formation parameter identification with in situ penetration testing data obtained in the in situ, intact state. The workflow includes two parts: 1) developing a set of numerical models for simulating the rock penetration process within the in-situ environment. These models include the penetration cone and the rock to be penetrated. Continuum Damage Mechanics (CDM) is used for simulating the fracturing process of rock during penetration. Frictional contact is assigned to the cone-rock interaction. 2) developing a regularized least squares method for parameter identification with the measured data from the in-situ penetration test. A sensitivity matrix is derived for identification of values of UCS and TS of the rock being penetrated. Methodology validation was completed through parameter identification of UCS and TS of a concrete barrel. The values of UCS and TS of the concrete were obtained with a set of lab tests which are conventional processes for UCS and TS measurement. With a given displacement loading of the penetration cone, the 3D numerical model simulated the penetration process. By using the least squares method, a numerical solution of parameter identification for UCS and TS is obtained with a given accuracy tolerance. Contours of damage variables during penetration are presented along with the curves of penetration force vs time. These numerical resultant values of UCS and TS are consistent with the values of UCS and TS obtained with conventional tests. In conclusion, the method was proven to be practical and reliable in identifying the values of UCS and TS with data obtained by the in-situ penetration test