Drilling data of deep coal seams of the Cooper Basin: analysis and lessons learned
Alireza Salmachi A B , Erik Dunlop A and Mojtaba Rajabi AA Australian School of Petroleum, University of Adelaide, Adelaide, SA 5005, Australia.
B Corresponding author. Email: alireza.salmachi@adelaide.edu.au
The APPEA Journal 58(1) 381-394 https://doi.org/10.1071/AJ17055
Submitted: 1 December 2017 Accepted: 30 January 2018 Published: 28 May 2018
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.
Alireza Salmachi holds a PhD in petroleum engineering and is an Assistant Professor at the Australian School of Petroleum, University of Adelaide. His main research area is gas production from unconventional resources including coalbed methane reservoirs (CBM). His particular research focus is on production data and rate transient analysis in CBM reservoirs, well testing and drilling data analytics. |
Erik C. Dunlop is an Exploration Geoscientist with 30 years of experience in the upstream oil and gas industry. After graduating from the University of Adelaide in 1986, a stint of fieldwork in the Timor Sea and Cooper Basin led to employment at Santos Limited in 1988. Here he remained until 2015. The first 16 years were spent exploring for conventional hydrocarbon accumulations, mainly in the Cooper and Eromanga Basins of Central Australia. The next 11 years were spent in the unconventional realm, having transferred to the newly-formed Unconventional Reservoirs Group in 2004. In this role, he initiated a variety of Cooper Basin shale, deep coal and tight sandstone pathfinder projects and internationally-patented a process for accurately quantifying the total gas content of these and other unconventional reservoirs such as gas hydrates. Other highlights include Australia’s first shale and deep coal proof-of-concept gas flows at Moomba 175 and Moomba 77 respectively, the resultant resource bookings, the introduction of wireline and pressure-coring to the Cooper Basin, a microseismically monitored shear dilation fracture stimulation trial at Big Lake 54 and the milestone of achieving commercial production from the Moomba 191 shale gas well. In 2013, he transferred to the McArthur Basin shale gas project of the Northern Territory, responsible mainly for design and execution of the Tanumbirini 1 shale-specific geological evaluation program. In 2015 he commenced PhD studies at the Australian School of Petroleum, University of Adelaide, investigating controls on the dynamic gas production behaviour of Cooper Basin deep coal seams. Erik is a member of AAPG and PESA. |
Mojtaba Rajabi is a research associate at the Australian School of Petroleum, University of Adelaide. He is currently the Deputy Head of the World Stress Map project. His research interests are petroleum geomechanics, petrophysics and tectonic evolution of sedimentary basins. Mojtaba graduated with a PhD in Petroleum Geoscience from the Australian School of Petroleum in 2016. He has worked on the Australian Stress Map and the World Stress Map projects in Australia and Germany since 2012. Member: AAPG, ASEG, EAGE, EGU, IAMG, PESA, SEG, SPE and SPWLA. |
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