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Toward improved coal density estimation from geophysical logs

2008; Taylor & Francis; Volume: 39; Issue: 2 Linguagem: Inglês

10.1071/eg08011

1834-7533

Binzhong Zhou, Joan Esterle,

Hydrocarbon exploration and reservoir analysis

AbstractDensity plays an important role in coal resource estimation and reconciliation, as well as in defining coal quality. Current practice employs direct density measurements on widely spaced core samples, rather than utilising abundant geophysical logging data. This is mostly due to the perception that the precision and accuracy of density estimation from geophysical logs is unsatisfactory. This paper demonstrates that the density wireline log, supported by other geophysical logs, provides a reliable direct measurement of in-situ coal density. We have produced a consistent and reliable correlation of geophysical log density with a laboratory-derived density to within an accuracy of ±3%. This is achieved through careful constraints such as compensating for lost pore spaces and moisture to bring the laboratory relative density closer to in-situ environmental conditions, matching the laboratory sample depths with geophysical logs, excluding thin, boundary, and stone-band samples from the dataset, and calibrating the geophysical density with laboratory testing data and other geophysical logs by linear regression or Radial Basis Function and Self-Organised Mapping techniques. In addition, we also illustrate that the improved geophysical log density can be used for coal quality estimation.Key words:: coal density, coal quality, geophysical logs. AcknowledgmentsThis work was funded by Australian Coal Association Research Program (ACARP), and supported by Rio Tinto Coal Australia Pty Ltd, Anglo Coal Australia Pty Ltd, and BHP Billiton Mitsubishi Alliance (BMA). We thank the following people: Ken Preston (Rio Tinto), Paul Sullivan (Rio Tinto), Mark Biggs (Anglo Coal), Andy Willson (Anglo Coal), Wes Nichols (Anglo Coal), Carrie Moffitt (BMA), Roland Turner (Borehole Logging Consultancy services), Peter Hatherly (University of Sydney) and Denis Mylrea (Weatherford International Ltd) for their various discussions, suggestions and supports during this study. Steve Fraser (CSIRO) is thanked for running the SOM algorithms on the data presented in this paper. Thanks also go to Gary Fallon and Bruce Dickson for their constructive review of the manuscript.Notes*Paper presented at the 19th ASEG Geophysical Conference & Exhibition, Perth, November 2007.1Vertical Enhancement by Combination and Transformation of Associated Responses (CitationElkington et al., 1990). This technique is also called alpha processing in the oil industry, which combines a measurement that has a high accuracy but low precision with another measurement of the same quantity that has a high precision but low accuracy in order to produce a result that is better than either alone.