Abstract

Modelling of rock masses is important to assess the geomechanical behaviour of oil & gas reservoirs, especially in fractured tight reservoirs. The presence of discontinuities will significantly influence the general behaviour of the rock masses. In order to achieve realistic simulation process a good knowledge of rock behaviour is required together with calibration or matching data of actual and controlled tests on rock. Artificial saw-cut joints on granitic rock specimens have been used to simulate a rock mass analogues at the laboratory scale with the aim of attempting to identify and quantify pre- and post-peak behaviour trends for different levels of confinement and jointing. The mechanical behaviour of intact and jointed rock samples are studied using an equivalent continuum modelling approach and a discrete approach. Advantages and limitations of each numerical approach are identified and give us an insight into the response of rock masses modelling at engineering scale.

1 Introduction

Rock mass comprises of discontinuities in the form of fractures, bedding planes, folds and faults. The presence of discontinuities makes rock masses heterogeneous and anisotropic materials. Because of this, the determination of the hydro-mechanical behaviour of jointed rock mass is one of the most challenging task in rock engineering. In the oil & gas industry, an accurate description of the discontinuities behaviour is a fundamental aspect during reservoir development and production.

Mechanical properties of rocks are usually determined from laboratory or in-situ tests. Since early rock mechanics developments, much effort was dedicated to study and model the elastic or prior-to-failure behaviour of rock masses and, thus, there are models that reasonably represent this actual pre-failure behaviour. However, the post-failure behaviour has been much less studied, due to its inherent difficulties and because the primary objective engineers was typically to avoid failure. Nevertheless, fracturing of the rock mass is a requirement for some applications and knowing how the rock mass in the plastic state ("broken") will behave can be a key design factor for particular studies, such as for instance the evolution of fractured reservoirs. Artificial saw-cut joints on Blanco Mera granite rock specimens have been used to simulate a rock mass analogues at the laboratory scale with the aim of attempting to identify and quantify pre- and post-peak behaviour trends for different levels of confinement and jointing (Arzúa & Alejano, 2013; Alejano et al., 2017).

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