Coupled Damage-Plasticity Modelling of Fractures related to Geological Folds

Abstract

Fractures induced by geological folds are pivotal in hydrocarbon exploration, ground water transport and harnessing of geothermal energy. This is because of the need to predict and understand fracture propagation in reservoirs which have folded rock formations. Despite its prominence, there is a lack of reliable numerical models for simulating fractures resulting from rock folding. This is partially due to the difficulty involved in fracture modelling. As a contribution to fold-fracture modelling, this work applies a coupled plasticity-damage model to rock fracturing and anticlinal folds with emphasis on Abu Dhabi hydrocarbon fields. The anisotropic continuum damage model which considers both tension and compression is formulated using the power damage evolution law. For ease in formulation, strain equivalence hypothesis is adopted whereby the strain is the same for both damaged and undamaged configurations. Lubliner plasticity yield criterion is adopted for plastic deformation. The model – applicable to quasi-brittle materials and coded in UMAT – is calibrated and validated using experimental data for Carrara marble. The model’s accuracy and robustness have been enhanced by curbing mesh-sensitivity based on a fracture energy approach and incorporating heterogeneity effects. Spatial variability of rock properties like Young’s modulus is captured using probabilistic methods. Additionally, parametric study is carried out to see how the degree of bending or folding affects the tensile stresses and fractures in rocks. Both sinusoidal and compressive forces are considered as drivers of folding. Over all, the model is able to simulate fold-induced fractures incorporating the effects of plasticity, damage, anisotropy and heterogeneity. It represents a flexible tool that could be readily tailored to any reservoir of interest given the pertinent field data.

Date of Award	May 2015
Original language	American English
Supervisor	Rita Sousa (Supervisor)