Fault Permeability

Publication Overview

The present review adds to an earlier report (IEAGHG, 2015a) by using the published literature to examine how fault permeability is modified by fault zone and host rock properties and in situ stresses of anthropogenic or geological origins. The primary goal of the report is to use publically available literature to examine when, where and how faults may negatively or positively impact the storage and migration of injected CO₂. In particular, four key tasks have been undertaken and are outlined below. TASK 1 – Provide a brief summary of the key parameters that influence the mechanical and hydraulic properties of fault zones including a summary of CO₂ flow data along faults at natural seeps. TASK 2 – Review current oil industry practices that are used to assess and control the unwanted migration of hydrocarbons along faults. Use the experience of different industry/academic teams to assess and model fault leakage from potential CO₂ storage sites. TASK 3 – Review the approaches used by other industries (e.g. waste disposal, hydrocarbons, civil engineering) to assess the properties, permeabilities, and leakage thresholds of faults and examine how these approaches might be useful for CO₂ storage sites. TASK 4 – Identify the knowledge gaps in current understanding of fluid migration along faults. Identify the challenges in modelling fault permeability, and monitoring fluid migration (including CO₂), along and across faults. Recommend the direction of future research and development that is directly related to a better understanding of fault permeability. The principal objective of this report is to provide a review and synthesis of international research and current understanding of fault permeability, with emphasis on how it could influence (positively or negatively) CO₂ storage. To address this principal aim and the four key tasks outlined above, the report contains 10 main sections. These main sections are summarized below.

Publication Summary

The CO₂ storage industry is reliant on numerical flow simulation and geomechanical models for establishing migration scenarios along and across faults (e.g. Tsang et al., 2007; Rutqvist, 2012; Tillner et al., 2013; Jeanne et al., 2014; Rinaldi et al., 2014). The use of such models to examine the role of faults on CO₂ migration is consistent with best practice across a range of industries including, petroleum, waste water and geothermal. The outputs from these models constrain CO₂ migration and, with the increase in computing power over the last 20 years, permit sensitivity testing of the results by modification of the fault and stratigraphic input parameters. However, as is the case with all modelling, interpretation of the results requires an understanding of the input parameter uncertainties and the ability of these parameters to describe the processes arising from CO₂ injection. The recommendations outlined below fall into three main categories; i) improved definition and quantification of fault hydraulic properties, ii) developing and sensitivity testing flow simulator models and geomechanical flow predictions, and iii) testing and validating these models using empirical fluid flow observations from fault zones.