25th International Meeting on Organic Geochemistry IMOG 2011

P-083
Thermal maturity assessment of potential source rocks and
reservoired condensates in kish gas field, Persian Gulf Basin
Bahram Alizadeh 1 , Seyed Hossein Hosseini 1 , Mehdi Khaleghi 2
1 Department of Geology, Faculty of Earth Sciences, S. Chamran University of Ahvaz, Ahvaz, Iran, Islamic
Republic of, 2 National IranianOil Company, Tehran, Iran, Islamic Republic of (corresponding
author:alizadeh@scu.ac.ir)
Persian Gulf is the location of phenomenal
hydrocarbon reserves and is an area of the world
where the oil industry is engaged in intense
hydrocarbon exploration and production. Kish gas
field is a giant gas field which was discovered in 2006
and holds 59 Tcf of gas in place of which 45 Tcf is
recoverable. The field also holds 946 Million barrels of
condensate of which 331 million barrels are
recoverable.
Thermal maturity of Kish gas field has been studied
using preliminary and complementary analyses such
as Rock Eval Pyrolysis, Vitrinite Reflectance (VRo)
and maturity related biomarkers. For this a total of 31
well cutting samples from potential source rocks (e.g.
Pabdeh, Gadvan, Surmeh, Dashtak, Dalan and
Faraghun Formations) and 2 condensate oils from
Dehram Group Reservoirs (Permian - Triassic) in Kish
gas field were selected.
The amounts of Tmax parameter for potential source
rocks ranges between 429 - 443 °C, and increased by
depth gradually from Pabdeh (Tertiary) to Faraghun
Formation (Permian). Based on Tmax parameter,
Faraghun unit is the only Formation that enters the oil
window (Tmax > 435 °C). Conclusions on thermal
maturity based on Tmax was supported by other
geochemical measurements such as VRo, and
biomarkers (Peters et al., 2005).
For vitrinite reflectance five polished samples with
highest TOC have been prepared from potential
source rocks. Measured VRo values are 0.48, 0.5,
0.65, 0.68 and 0.7% for Pabdeh, Kazhdomi, Gadvan,
Surmeh and Faraghun Formations respectively.
The C32–homohopane results were used to calculate
the 22S/((22S+22R) ratio rising from 0 to 0.6 during
maturation. This ratio for Pabdeh and Gadvan
Formations (0.37 and 0.52) indicate that both the
units are immature. These results for other potential
source rocks, as well as two condensate oils from the
Dalan Formation range between 0.59 - 0.62 and
suggest that the condensate oils have been
generated at the peak of oil window and even beyond
the zone of petroleum generation. The
moretanes/hopanes ratio for studied samples
indicates that Pabdeh Formation has the highest
value of the ratio (0.24) and for other potential source
rocks as well as condensate samples this ratio ranges
between 0.08 – 0.14. These values determine the
lowest maturity for Pabdeh Formation and also
suggest that in other samples the VRo should be
greater than 0.6 (Catagenesis Stage). There is a
systematic increase in the relative abundance of Ts
and a decrease in C27 17β-trisnorhopane compared
with Tm with depth (0.2 – 0.6). As it is predictable,
among the studied samples condensate oils have the
highest values of this ratio. Diasteranes/(Dia +
Regular) C27 steranes versus Ts/(Ts+Tm). The Plot
clearly indicates increasing maturity with depth in
studied samples (Fig. 1). Ts/hopanes ratio, C29 Ts/(C29
hopane + C29 Ts) ratio as well as metylphenanthrenes
index (MPI-I) to MPI-II all authenticate that maturity of
potential source rocks in Kish gas field increase with
depth while the source for condensates must be at
gas window and deeper than studied source rocks.
Fig.1: Plot of Ts/(Ts+Tm) vs. C27 Dia /(Dia+Reg)
Steranes demonstrating the increase in maturity of
source rocks with depth.
Reference:
Peters, K. E., Walters, C. C., Moldowan, J. M. (2005).
The Biomarker Guide: Biomarkers in Petroleum
System and Earth History. Vol.2. Second Edition.
Cambridge University Press.United Kingdom.
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