25th International Meeting on Organic Geochemistry IMOG 2011

P-324
Occurrence of organic matter effect hydrocarbon generation and
expulsion in South China
Jianzhong Qin 1,2 , Baojian Shen 1,2 , Xiaodong Fu 1,2
1 Sinopec Research Institute of Petroleum Exploration and Production, Beijing, China, 2 Wuxi Institute of
Petroleum Geology, Sinopec Research Institute of Petroleum Exploration and Production, Wuxi, China
(corresponding author:qinjz@mail.wuxisuo.com)
Eight samples were collected from the hydrocarbon
reservoirs of the Sichuan Basin, which is located in
the Northwest of China. The samples are from
Paleozoic marine source rocks, including the Lower
Cambrian, Silirian, the Lower and the Upper Permian.
The geochemical characteristics of the samples with
high-over mature marine source rocks are as follows:
1) the TOC is mainly range of 3.93~14.95% and
kerogen Type belongs to II; 2) the minerals are
composition of quartz, calcite, dolomite and clay
minerals. An accurate assessment of oil generation
potential and expulsion efficiency of source rocks,
amongst other important features of a petroleum
All the source rock samples were simulated in the
same semi-closed generation–expulsion system. The
results of our simulated experiments shows petroleum
(oil and gas) generating were strongly dependent on
lithology in the same experiment condition. the marine
siliceous or carbonate rock has relatively higher
accelerating effect on hydrocarbon generation from
kerogen in comparison with marine mudstone and
shale during early stage, and siliceous or carbonate
rock easy generated heavy oil, clay rock generated
normal oil and gas, so siliceous or carbonate rock has
lowers the temperature of peaks of total oil
generation, and easily forms immature-low mature
heavy oil, and enlarging yields of total gas, CO2, H2,
total oil, oil carried by gas, residual oil, hydrocarbon
gas and total hydrocarbons with the temperature
increasing. This is because certain proportions of the
petroleum generated remains in the pore system of
the source rock, or adsorbed by kerogen and
minerals, there more oil was absorbed in clay rock
relative siliceous or carbonate rock. The results show
that minerals such as quartz, calcite has a positive
correlation with the quartz content but a negative
correlation with clay minerals content. And the marine
excellent source rock mainly consists of siliceous or
calcareous. It was mainly generated heavy oil in the
stage of early-middle maturation.
system, is essential. The purpose of this paper is � The marine siliceous or carbonate rock has the higher
using simulated experiments to distinguish oil expulsion efficiency than clay rock during the early-
occurrence of organic matter effecting hydrocarbon
middle maturation stage, but they have the same oil
generation and evaluate their oil expulsion efficiency.
expulsion efficiency which is about 60% in the late
Organic matters in these source rocks have three maturation stage. So in the early-middle stage organic
main occurrences by scanning electron microscope matter associated with siliceous or calcareous is more
and energy spectrum: 1) organic matter associated easy expulsive heavy oil, thus the clay rock hardly
with siliceous or calcareous matter. It is the main expulsive heavy oil. There distributed much bitumen
occurrence in the quality marine source rock in South
in the reservoir which came from the early generation
China; 2) organic matter associated with calcareous
matter. It is the main occurrence in some quality
of heavy oil in Sichuan basin, and the early expulsive
calcareous source rock in the Permian; 3) organic heavy oil would be cracked into gas with the buried
matter associated with clay, or coated by flaky clay depth. This cracking gas of heavy oil is the main
particles and associated with siliceous and calcareous source of gas pools in Sichuan basin.
biofacies.
Based on the experimental results and the discussion
above, it can be concluded that: Super thin siliceous
or calcareous layers rich in organic maters are easy
to expel early generated heavy oil, and thus a giant
heavy oil pool may be formed. On the contrast,
organic matters coated by flaky clay particles are hard
to expel early-generated heavy oil, and thus a light oil
pool may be formed. The natural gas of Sichuan
basin is come from heavy oil cracking.
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