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Integrated Cleat Analysis and Coal Quality on CBM Exploration at Sangatta II PSC, Kutai Basin, Indonesia

Abstract

This study was undertaken to determine cleat orientation, the relationship between cleat spacing, aperture, and cleat height, interpretation for cleat density, cleat volume and permeability for Balikpapan Fm. Miocene age coals. The methods used in this study includes fieldwork, quantitative analysis, fracture modeling using a Hybrid Model and laboratory analysis including proximate, maceral and and Scanning Electron Microscope.were conducted. The cleat orientation of Balikpapan Formation measured at outcrop showing three main different domains cleat strike where the face cleat in Bengalon area has general E–W orientation, in North Pinang area has general NNW-SSE orientation and in the South Pinang area relative NE-SW. The largest variation of cleat direction between adjacent coalbed occurs where a large horizontal distance separates two sample location. Face cleat with a NNW-SSE orientation were interpreted as the result of superimposed endogenic process, the process associated with coalification. Face cleat with N-E and NE-SW orientation are mainly associated with local tectonic stress. Cleat formation is influenced by mechanical in response to tectonic and geochemical processes related to coal composition. Higher calorific value and low ash content corresponded to high cleat densities. Higher total sulphur corresponded to lower cleat density. Perhaps total sulfur content has been affected by local environmental factors. Quantitative analysis of cleat and fracture data from this study indicate that a power-law distribution exists between cumulative cleats with spacing and aperture, fractal dimension (c) ranges from 0.79 to 2.06 and r-square values greater than 0.90. Coal quality was affected cleat intensity and attributes. The cleat density for individual seams varies between 0.17 cm/cm2 – 0.51 cm/cm2, cleat density increases toward Pinang Dome, related to structural position. Based on SEM photos, outcrop sample cleat apertures range from 0.8 μm to 15 μm, increasing to 15 μm to 30 μm in the direction of maximum stress. Core samples apertures ranged from 0.1 μm to 6 μm and filling by pyrite. Characterisation of cleat attributes allows an indirect estimation of permeability which are critical parameters for commercial CBM development. Permeability was much higher in outcrops (200–5000 md) than in core samples from 260 m depth (0.1 – 19 md).