CALIBRATION OF ROCK STRENGTH AND YIELDING BY USING HOLLOW CYLINDER EXPERIMENTAL DATA

摘要

Understanding borehole collapse mechanisms during underbalanced drilling (UBD) in shale is becoming increasingly important for the petroleum industry, due in particular to the implementation of the UBD technique in operational practices. However, it is challenging to determine the proper constitutive material model to describe the UBD borehole environment sufficiently and accurately. Moreover, it is difficult to define how and where "borehole failure" occurs during simulation or even in laboratory conditions. In an attempt to minimize borehole instability problems, detailed and careful analysis of the excavation process is often performed during the planning stage. However, the accuracy of these analyses is highly dependent on the constitutive model adopted for the shale. Three important features of the constitutive model for shale are the dissipation of the pore pressure, the strength and the plasticity after yielding. This paper presents rock strength and borehole deformation results from a hollow cylinder (HC) testing program on Pierre-1 shale. Furthermore, a calibration was performed on a virtual borehole model [1] against HC laboratory data. The HC tests at underbalanced conditions were performed on samples drilled parallel and perpendicular to the bedding to properly quantify the effects of anisotropy and to determine possible scaling/geometry effects. Laboratory observations of material failure were compared with numerical outcome and showed promising similarities.