25th International Meeting on Organic Geochemistry IMOG 2011

P-378
East Texas-North Louisiana USA unconventional shale gas
resource systems
Daniel Jarvie 1 , Francoise Behar 2 , Yongchun Tang 4 , Rolando di Primio 3 , Brian Horsfield 3 ,
Wilhelm Dominik 1
1 Technische Universitat Berlin, Berlin, Germany, 2 Insitut Francais du Petrole, Rueil-Malmaison, France,
3 GFZ, Potsdam, Germany, 4 PEER Institute, Covina, United States of America (corresponding
author:danjarvie@wwgeochem.com)
Unconventional shale gas accounts for about
20% of the available gas resource in the USA with a
resource amounting to about 1000 tcf of gas-in-place
(GIP). There are over 50 shale resource plays active
in North America either for shale gas or shale oil. The
focus of this work is the shale gas systems present in
the East Texas-North Louisiana Salt Basin (ETNLSB)
consisting of gas with minor condensate from
Tithonianian Bossier and Kimmeridigian Haynesville
shales.
Petroleum system analysis of gas petroleum
systems is difficult when attempting to correlate to
high maturity gas source rocks. However, recovery of
gases and in some cases, condensates directly from
the source rock aids this assessment. In the case of
the principal source rocks in the ETNLSB, the
Tithonian Bossier and the Kimmeridgian Haynesville
shales are highly mature typically over 1.2%Roe.
Age-equivalent immature source rocks from the
deepwater Gulf of Mexico provide material for
evaluation of this resource by laboratory maturation
experiments optimized to field results.
The original source potential of the Tithonian
and Kimmeridigian systems can be subdivided into
multiple mappable organofacies based on hydrogen
indices (HI) and TOC. The Bossier Shale is
subdivided into three mappable organofacies with
variable hydrogen indices, whereas the Haynesville
Shale is divided into two mappable organofacies
based on TOC differences.
Not unexpectedly condensate analysis
shows oil cracking by loss of the labile
dimethylcyclopentanes consistent with MSSV oil
cracking experiments. Comparison of light
hydrocarbon data to diamondoid cracking parameters
shows good correlation. Interestingly, the C2 isotopic
rollover does not occur in certain parts of the basin
despite high thermal maturity (ca. 2.0%Ro), behaving
in a purely thermogenic realm following model
predictions (Jarvie et al., 2010) (Fig. 1). Other areas
of the basin at comparable thermal maturity show C2
carbon isotopic rollover with increasing gas dryness
Ethane Carbon Isotope (� 13 C 2)
0 5 10 15 20 25
-20
-25
-30
-35
-40
-45
-50
Thermogenic trend
Rollover
Gas Wetness (%C2+)
Shale 1
Shale 2
Haynesville
Figure 1. No rollover in high maturity ETNLSB gas.
(Figure 1) where C2 carbon isotopes become lighter at
high maturity (Ferworn et al., 2008). Tang and Xia
(2010) have observed a new reaction where water
can react with condensates to generate CO2 and
hydrogen. It is not clear under what condition the CO2
and hydrogen can generate methane, ethane and
propane with isotope reversal (like abiogenic gases
from geothermal fluid). Rollover and non-rollover
systems may be a function of Tithonian organofacies
differences.
Phase kinetics and gold tube pyrolysis on
age-equivalent immature Tithonian and Kimmeridgian
immature samples substantiated yields and
composition at various levels of maturation for these
source units. These results are applicable to
evaluation of petroleum generation in the ETNLSB as
well as the Deepwater Gulf of Mexico.
References
Jarvie, D., F. Behar, L. Mazeas, 2010,
Decomposition of organic matter and impact on shale
resource play assessments, AAPG New Orleans ACE
Ferworn, K., Zumberge, J., Reed, J. and
Brown, S., Gas Character Anomalies Found in Highly
Productive Shale Gas Wells, GeoMark Research
Technical Presentation, Houston, October 2008, 26 p.
Tang, Y. and X. Xia, 2010, Kinetics and
mechanism of shale gas formation: a quantitative
interpretation of gas isotope ―rollover‖ for shale gas
formation, AAPG Hedberg Research Conf., Austin,
Texas, December 5-10, 2010, abstract.
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