Empirical and Numerical Geomechanical Approaches to Unconventional Resources

Abstract

A geomechanical model is a fundamental requirement for considering any unconventional related geomechanical application such as fracture permeability, hydraulic fracture placement or wellbore stability. These models are the cumulative understanding of the distribution of physical rock properties, pore pressure and stress magnitudes. Each of these three elements is interdependent and a change in any one impacts on the other two. Therefore, robust assessment is required across multiple disciplines to ensure a valid predictive model. Geomechanical models can be 1D, 3D or 4D representations and can be derived from empirical observations or calculated numerically. The available dataset or project objectives can impact on the approach taken to assemble a geomechanical model and substitutions can be made utilising data sources with differing resolutions such as seismic data for log data. In some cases a combination of empirical and numerical elements may be appropriate. This presentation summarises a range of workflows that can be implemented to create a geomechanical model based on typical unconventional datasets and objectives. An unconventional borehole-centric dataset is used to demonstrate these concepts in conjunction with 1D numerical models to illustrate the impact of high and low lateral stresses on stress distribution within a stratigraphy characterised by varying rock properties. An empirical 1D geomechanical model is presented for Cow Lagoon-1 located within the McArthur Basin, Northern Territory, Australia which was drilled by Armour Energy in 2012 to assess the unconventional prospectivity of the Batten Trough. This model is used in conjunction with image log data to determine fracture orientations and formation properties conducive to permeable fracture networks. Contemporary stress magnitudes vary considerably ranging between strike-slip and extension between formations with differing elastic properties. Fracture density and permeability also varies between formations and is related to the geomechanical model. Target horizons in the Batten Trough are characterised by low Young's Modulus, low differential and low effective stresses.

AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014