Patterns of Hydraulically Conductive Fractures' Positions and Spatial Orientations Near Large Faults

Abstract

In the study the main tendencies in fracture development in rock masses are investigated. The question of natural shear fractures' fluid conductivity is particularly analyzed as this question is important for development of hydrocarbon fields. The localization of the majority of hydraulically conductive fractures in the reservoir and their preferable spatial orientations are analyzed based on the hypothesis of an existing relationship between current stress state of the rock mass and the fractures' hydraulic conductivity. A mathematical algorithm for solving the forward problem of finding all possible spatial orientations of hydraulically conductive fractures for an arbitrary stress tensor is proposed. Stereonets are used as a tool for interpreting the spatial orientations of fractures. The proposed algorithm is used to find the main tendencies in hydraulically conductive fractures' spatial orientations for the following cases: gradual increase of the considered object's depth; gradual change of one of the principal stresses; case of approaching a large fault. A relationship between typical behavior of the fractures and stress regime in the region is found out alongside with typical changes in spatial orientations of hydraulically conductive fractures while approaching faults of different types. The obtained results may be directly used for planning the development of oil fields, characterized by a considerable contribution of fractures to permeability. The results are particularly important for development of fractured zones in vicinities of large faults. Moreover, the proposed algorithm of finding the geometrical properties of hydraulically conductive fractures may be applied based on results of three- and four-dimensional geomechanical modeling carried out for particular fields providing an opportunity to both determine the zones being perspective for development, and predict the changes of these zones' properties during reservoir development.