ANALYSING CLEAT ANGLES IN COAL SEAMS USING IMAGE ANALYSIS TECHNIQUES ON ARTIFICIAL DRILLING CUTTINGS AND PREPARED COAL BLOCKS
Delft University of Technology, Department of Applied Earth Sciences, Dietz Laboratory, Mijnbouwstraat 120, 2628 RX Delft, the Netherlands. E-mail: k.h.a.a.wolf@ta.tudelft.nl
Institut Francais du Petrole, 1- 4 Avenue de Bois-Preau, BP 311 – 92506 Rueil-Malmaison, Cedex – France. E-mail : Dan.Bossie-Codreanu@ifp.fr
Delft University of Technology, Department of Applied Earth Sciences, Dietz Laboratory, Mijnbouwstraat 120, 2628 RX Delft, the Netherlands.
Delft University of Technology, Department of Applied Earth Sciences, Dietz Laboratory, Mijnbouwstraat 120, 2628 RX Delft, the Netherlands.
Abstract
For coal seams, considered as gas reservoirs, the orientation of the major cleat directions are dominating the flow direction and control the Darcy permeability. Information on the intra-cleat angles is obtained from coal fragments, which simulate drill cuttings. The methodology here below describes the use of image analysis techniques to determine from cuttings the intra-cleat angle and the angles between the cleats and bedding. The analysis is based on the phenomenon that cleats and bedding planes form the weakest bounds in a coal bed. Up to two thousand fragments, of three French coal samples, are analysed to characterize a cleat angle distribution for each coal. After the extraction of the (sub-) spherical fragments, shape factors are calculated for the fragments left behind. These shape factors act as a second filter, which remove grains with no rectangular or parallel like shape. The relationships between measured spatial properties are summarized into frequency histograms, which give a picture of the most abundant face angles in the accepted fragments. The resulting histograms are compared with 3D cleat angle reconstructions of the same coal samples, obtained from CT-scans. These scans are analyzed on their fracture patterns in three orthogonal directions. Here the results are from macro-cleat spacings with a larger cleat distance than obtained from the fragments.