5.3. Ascribing meaning to the formation and exploration of oil
and gas
Combined with the actual geological evolutionary conditions, they were
not a definitive form of thermal evolution. Using the corresponding
pyrolysis experiments, we identified the evolutionary model of different
thermal evolutional stages, which helped us analyze the formation
mechanisms of oil and gas in the Pinghu Formation in actual geology. The
variation of methane carbon isotopes in shale gas ranged from -39.7‰ to
-30.0‰ in our experiments. Cao et al. (2015) studied the composition,
light hydrocarbons, and carbon isotopes of natural gases from the Xihu
Sag and found that the gases were a mixture of coal type, accounting for
the major proportion and oil-type gases with high maturities. In
addition, they also found that the
δ13C1 Xihu Sag had delta values
between -47.74‰ and -28.2‰. As a result, the values of methane carbon
isotopes in the process of artificial simulation fell in the range of
methane carbon isotopes during the actual geological evolution process
in the Xihu Depression. Thus, it can be inferred that there is great
potential for coal-oil-type gases. In addition, the natural gas carbon
was seen as a performance for the series of carbon isotope changes and
presented the order of δ13C1< δ13C2 <
δ13C1. There was no carbon isotope
reversal, which also proved the larger evolutional space. Therefore, the
carbon isotope in this area can indicate the maturity of oil-gas and
provide a theoretical basis and guidance for production evaluation.
Combined with the analysis of geochemical characteristics of the Pinghu
Formation coal-oil-type gas in actual strata, it can be considered that
this area also has development potential.