The Microseismic Monitoring of Hydraulic Fracturing of a CBM through Simultaneous Use of Downhole Monitoring Tools in the Stimulated and an Offset Well A Case Study – Sanga Sanga CBM, Mahakam Delta, East Kalimantan

Abstract

Abstract Microseismic hydraulic fracture monitoring uses state-of-the-art downhole seismic tools to record microseismicity from multi-staged hydraulic fracture stimulations in Coal Bed Methane (CBM) completions. This method uses an acoustic method to map in three dimensional space and time the geometry and propagation of fractures during a hydraulic fracture stimulation treatment. The technique has been used for some time in monitoring fracture stimulation in shales and other formations but has had limited use in coals for CBM production. Microseismic monitoring of hydraulic fracture stimulations in coal seams presents significant challenges as the ductility of coal produces low intensity individual microseismic events which can be difficult to record. Using an offset well to record the microseismic events may result in some uncertainty due to varying degree of attenuation by the coal seam. Additionally, successful recording of fracture stimulations in CBM wells typically requires the monitoring well to be relatively close to the well being stimulated and this often prevents downhole monitoring being applied to these wells. A microseismic monitoring tool that can be placed in the treatment well during the fracture stimulation provides additional information and potentially improves the data quality. Furthermore, two monitoring tools which simultaneously record microseismic events in the in-well and offset wells provide independent data for comparison and increase the quality and confidence of spatial location data. The Sanga-Sanga Block which is as a very large conventional gas producer in East Kalimantan is now growing as a potential CBM resource. The coal seams in Sanga-Sanga, East Kalimantan are contained in a complex formation of interbedded sandstone, siltstone, carbonaceous shale and coal and have been subject to initial attempts to stimulate the coals for CBM production by hydraulic fracturing. This paper examines the operational challenges of the simultaneous use of in-well and offset well microseismic monitoring tools in the Sanga-Sanga coal in Indonesia and compares the techniques and overall results and makes recommendations and suggestions for future microseismic coal monitoring.