SOURCE ROCK POTENTIAL OF EOCENE, PALEOCENE AND JURASSIC DEPOSITS IN THE
SUBSURFACE OF THE POTWAR BASIN,
T. Fazeelat*1, M. I. Jalees1 and T.
1 Chemistry Department, University
of Engineering and Technology, Lahore 54890,
2 Department of Oceanography, Texas A
& M University, 3146 TAMU, College Station, Texas 77843-3146, USA.
* Corresponding author, email@example.com
The hydrocarbon source rock potential of five formations in the Potwar
Basin of northern Pakistan – the Sakesar
Formation (Eocene); the Patala, Lockhart and Dhak-Pass
Formations (Paleocene); and the Datta Formation (Jurassic)
– was investigated using Rock-Eval pyrolysis and total
organic carbon (TOC) measurement. Samples were obtained from three producing
wells referred to as A, B and C. In well A, the upper ca. 100 m of the Eocene
Sakesar Formation contained abundant Type III gas-prone
organic matter (OM) and the interval appeared to be within the hydrocarbon
generation window. The underlying part of the Sakesar
Formation contained mostly weathered and immature OM
with little hydrocarbon potential. The Sakesar Formation
passes down into the Paleocene Patala Formation. Tmax was variable
because of facies variations which were also reflected in variations in hydrogen
index (HI), TOC and S2/S3 values. In well A, the middle
portion of the Patala Formation had sufficient maturity (Tmax 430
to 444°C) and organic richness to act as a minor source for gas. The underlying
Lockhart Formation in general contained little OM,
although basal sediments showed a major contribution of Type II/III OM and were
sufficiently mature for hydrocarbon generation.
In Well B, rocks in the upper 120 m of the Paleocene Patala
Formation contained little OM. However, some
Type II/III OM was present at the base of the formation, although these sediments
were not sufficiently mature for oil generation. The Dhak Pass Formation was in general thermally immature and
contained minor amounts of gas-prone OM.
In Well C, the Jurassic Datta Formation
contained oil-prone OM. Tmax data indicated that the formation was marginally
mature despite sample depths of > 5000 m. The lack of increase in Tmax with
depth was attributed to low heat flows during burial. However, burial to depths
of more than 5000 m resulted in the generation of moderate quantities of oil
from this formation.
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