25th International Meeting on Organic Geochemistry IMOG 2011

P-344
Can mud gas tell us a bigger story?
Daniel McKinney, Heidi Albrecht
Shell <strong>International</strong> E&P, Inc., Houston, United States of America (corresponding
author:daniel.mckinney@shell.com)
Traditionally, mud gas analysis has consisted of
qualitative mud gas extraction coupled to a slow, low
resolution GC-FID gas analyzer. These mud gas
logging techniques look at only a small portion of the
entire reservoir fluid, typically methane through
pentane, with only qualitative assessment of some
isomers of C6 in advanced systems (e.g., benzene, n-
C6, and cyclohexane). In contrast, open hole
samples permit the chemistry and petroleum system
analysis of the gasoline range hydrocarbons, mainly
isomers of C6 and C7, as well as full biomarker
studies. Past efforts have developed these methods
to yield fundamental understanding about an oil or
condensate's geochemical history such as
biodegradation, water washing, source rock origin,
thermal maturity, etc. (See Mango, 1997 and
references within). But what if you do not have an oil
sample? Can you get the same type of C6 or C7
isomer analysis from a mud gas sample?
In this study, we investigate the potential of C6 and
C7 isomer analysis from isotube® samples of
entrained mud gas collected from Geoservices' FLAIR
system (Breviere et al., 2007). The FLAIR system
was essential for this study as it assesses the
extraction efficiency of C1-C5 in the drilling mud. An
extraction efficiency coefficient (EEC) is calculated for
each unique well and drilling mud combination and
applied to each C6 and C7 isomer as a function of
boiling point. Figure 1 shows the C7 ternary ring
preference diagram for 3 separate prospects using 3
different mud systems: A) water based mud (WBM),
B) Saraline 185V OBM, and C) Accolade OBM. EEC
corrected isotube data, for the majority of the samples
analyzed, mimicked the standard C6/C7 analysis
approach, within reasonable expectation, when
compared to oil samples collected from the same
intervals. A few notable exceptions were documented
which were mainly tied to contamination from drilling
mud. For example, Saraline 185V base oil, is a broad
molecular weight aliphatic mixture, and it
contaminated the isotube sample (Isotube B in Figure
1) with additional n-heptane. Isotube samples
collected from WBM yielded the best match to the
reservoir fluid, and the isotube sample collected from
the Accolade drilling mud was only slightly impacted
by contamination; most likely from recycling issues.
Thus, this methodology allows the geochemist to
gather additional information, relative to the standard
mud gas and show analysis reports, to further
fingerprint reservoir hydrocarbons.
Figure 1. C7 ring preference comparison between FLAIR
isotube and oil obtained from the same reservoir interval: A =
WBM, B = Saraline 185V OBM, and C = Accolade OBM.
References
[1] Mango, F.D. (1997) The light hydrocarbons in
petroleum: a critical review. Org. Geochem. 26, 417-440.
[2] Breviere J., Lessi, J., Jaulneau, P. and Shell‘s
FEAST Team (2007) Abstract. 23 rd <strong>International</strong> <strong>Meeting</strong> on
Organic Geochemistry, Torquay, United Kingdom.
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