Substantial heterogeneity in lacustrine shale brings
significant
challenges to oil exploration. Therefore, a clear and effective resource
evaluation standard can significantly reduce the exploration risk
and cost, thus further guiding the prediction in productive areas.
However, due to the lack of consideration of the thermal maturity
and kerogen type, the present evaluation standards may result in the
misjudgment of the resource quality of shale oil reservoirs. In this
study, a method based on mass balance involving a hydrocarbon generation
statistical model was proposed to calculate oil movable threshold
(OMT) values. The OMT values for different types of kerogens are determined
from simple and easily obtained pyrolysis parameters. Based on the
OMT values, a three-dimensional resource quality evaluation model
is constructed and applied to the source rocks in Member (Mbr) 1 of
the Shahejie Formation (Fm) Nanpu Sag, Bohai Bay Basin, eastern China.
The results show that the Mbr 1 of Shahejie Fm shale is a set of high-quality
source rocks with high total organic matter (TOC) and S
1c
(calibrated free hydrocarbons) content. Meanwhile, the hydrocarbon
generation potential of the studied lacustrine shales are in the order
of type I > type II
1
> type II
2
> type
III,
whereas the OMT values show a similar order. From type I to type III,
the hydrocarbon expulsion threshold (HET) values for the four types
of shales correspond to pyrolysis peak temperatures (
T
max
) at 438, 426, 428, and 432 °C with the maximum
OMT values being 143, 128, 127, and 122 mg HC/g TOC, respectively.
The movable and favorable shale oil accumulations are mainly associated
with type II
1
and II
2
shales. Our work provides
a novel method for distinguishing the resource quality and locating
a favorable exploration target for lacustrine shale, improving efficiency
and reducing exploration risks.