DOE:10.2516/ogst:1999011 DOE:10.2516/ogst:2001008 DOE:10.2516/ogst:2001011 DOE:10.2516/ogst:2002028 DOE:10.2516/ogst:2002040 DOE:10.2516/ogst/2010021 DOE:10.2516/ogst/2013107 DOE:10.2516/ogst/2015024