ABSTRACT:

In a scenario where overburden rock coring in the petroleum industry seldom occurs, the fault reactivation analyses lack of real fault material retrieval for peak and residual strength characterization. The strength properties of a fault are commonly defined based on personal judgments of experienced rock mechanicists. This work attempts to deliver more realistic residual strength parameters for artificial slip planes produced in triaxial and direct shear tests performed on shale samples. These artificial planes do not account for rock heterogeneity, fault roughness or breached zones, but may produce a lower boundary of strength properties for robust fault reactivation risk analyses. The individual results matched the expected stress-strain behavior pattern for a frictional material under shear stresses and the final residual strength envelope was consistent. During slippage the specimens presented slickenside features natural to clay-rich rocks which might have affected the friction angle. This behavior is supported by literature experience on soils. As expected, the final strength values were lower than the usually adopted values in the numerical analyses.

1. INTRODUCTION

The trend of coupled hydro-geomechanic analysis in the reservoir and well drilling activities demand rock and fluid information over a much larger domain than the usual uncoupled analyses did. Reservoir rock and fluid data of good quality as well as over-, side- and often also underburden rock data build the dataset necessary for a successful geomechanical simulation. Moreover, this dataset must also include the geometry of the main (or mapped) faults and its mechanical behavior as well as the main boundary conditions for the problem under study. One may notice these coupled analyses require large data-gathering and computational efforts and thus should only be applied when populated with realistic data and using proper simulators. The unavailability of rock data and rock material for testing purposes is unfortunately usual.

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