Tomography, scanning electron microscopy techniques and image analysis of coal for natural gas recovery

Abstract

Flow paths including porosity and fracture networks in reservoirs are essential for oil and gas recovery. Core analysis cannot reliably reflect reservoir quality if the pore network is highly heterogeneous. In coal cores, the matrix can be so fractured, heterogeneous or complex that experiments may require the support of modelling, which itself requires detailed 3D images and computational analysis of the pore space. One prime example is coal bed methane, which is becoming increasingly important to Eastern Australia’s energy security. Other Western markets already have producing coal and shale wells, although quite often the recovery rates are poor and difficult to understand or predict. This thesis describes novel sample preparation, imaging and image analysis techniques that can be used to better quantify carbon rich reservoirs, and in particular coal. A 3D imaging and computational analysis technique was used to visualise and quantify the location of coal fractures and cleats, minerals and microporous regions that are important for gas storage in coal reservoirs. 2D techniques are used to provide higher resolution information and classification of detrital and diagenetic minerals within sectional planes of the coal samples. Furthermore, this 2D information was spatially aligned with its corresponding slice within the 3D tomogram of the coal sample. The study examined the effectiveness of combining the methods above in order to use the results obtained from 2D analysis techniques can be used to improve the interpretation and quantification of mineral and pore features throughout the 3D tomogram. The thesis includes the analysis of three coal samples from the Sydney Basin in Eastern Australia, each with a significantly different distribution of minerals and porosity. 3D computer tomography imaging is already well established for sandstones and dolomite rich carbonates, but less so or reservoirs where a majority of the features exist at a size that is below a few micrometres. Results will include a comparison of conventional laboratory techniques and 3D imaging at the micron resolution scale. Techniques developed in this thesis can also be applied to microporous reservoirs such as carbonates and shales. Show more