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Type: Journal article
Title: Drilling data of deep coal seams of the Cooper Basin: analysis and lessons learned
Author: Salmachi, A.
Dunlop, E.
Rajabi, M.
Citation: Australian Petroleum Production and Exploration Association (APPEA) Journal, 2018; 58(1):381-394
Publisher: CSIRO Publishing
Issue Date: 2018
ISSN: 1326-4966
Statement of
Alireza Salmachi, Erik Dunlop and Mojtaba Rajabi
Abstract: Deep (>4920 ft; >1500 m) coal seams of the Cooper Basin accommodate large amounts of natural gas; however, permeability of this unconventional resource is low and reservoir stimulation in prospective coal intervals is essential to achieve commercial production. This paper aims to analyse drilling data of deep coal seams of the Cooper Basin in South Australia. Drilling data obtained from mud logs are utilised to construct a drillability index (DI), in which rate of penetration is normalised by drilling factors, making DI more sensitive to coal rock strength. Analysis of DI and gas show information provides a preliminary screening tool for studying prospective deep coal seams, before performing in-depth reservoir characterisation and production tests. The decline in DI with depth is attributed to a compaction effect that makes deeper coal seams more difficult to drill through compared with shallow seams. The existence of a fracture network can reduce coal rock strength and consequently DI may increase. The increase in DI may be indirectly related to fluid flow characteristics of the coal seam helping in identifying prospective coal intervals. The DI is also affected by other factors and, hence, should be used in combination with reservoir information to yield conclusive indications. Gas show information and DI results were utilised to indicate the effectiveness of dewatering operation and hydraulic fracture confinement in the wells drilled in the Klebb area located in the Weena Trough.
Keywords: Drillability index; gas show; mud logging; permeability; Weena Trough
Rights: Journal compilation © APPEA 2018
DOI: 10.1071/AJ17055
Published version:
Appears in Collections:Aurora harvest 4
Australian School of Petroleum publications

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