25th International Meeting on Organic Geochemistry IMOG 2011

P-265
Analysis of dissolved gases from drilling mud samples for
geochemical and isotope mud gas logging
Philipp Weniger 1 , Stefan Schlömer 2 , Bernhard M. Krooss 1
1 Institute of Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Aachen,
Germany, 2 Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Germany
(corresponding author:weniger@lek.rwth-aachen.de)
The chemical and isotopic composition of gas
dissolved in drilling mud provides information on the
penetrated rocks as well as the origin of fluids in
these rock formations. Mud gas isotopic analysis is
frequently applied during petroleum exploration.
Especially in shale gas exploration, the identification
of isotopic anomalies e.g. ethane ‗rollover‘ could
improve the identification of productive zones.
Commercial mud gas logging equipment extracts gas
mechanically from the drilling mud by a mud trap
(mud gas separator), which is then analyzed online or
transferred to sample vessels for analysis in a
laboratory. In many instances, mud gas logging is not
performed in order to reduce drilling costs.
The purpose of the present study was to investigate
the feasibility of gas extraction from drilling mud
samples without an installed mud gas separator.
Drilling mud samples were collected at the well-site at
regular depth intervals during coal bed methane
(CBM) and mine gas drilling operations. The
dissolved gas was extracted using helium as host
gas. The chemical and stable carbon isotopic
composition of the extracted gas was analyzed by gas
chromatography (GC), and isotope ratio mass
spectrometry (GC-IRMS). Carbon isotope analyses
on hydrocarbons (C1 – C4) and CO2 were
successfully performed at concentration levels down
to