| In order to study the distribution pattern of oil and gas above the oil source fault-regional mudstone caprock
configuration (fault-caprock configuration) in petroliferous basins, a set of prediction methods for the distribution of
leakage periods was established based on qualitative analysis of the leakage mechanism. Firstly, determine the location of
oil and gas leakage in the fault-caprock configuration, that is, where the joint thickness of caprock between upper and
lower walls of fault (Hf) is less than the minimum required for the fracture segment connection (Hf-l). Secondly, determine
the beginning time of sealing failure, that is, according to a study spot in the fault, when its Hf is firstly less than the Hf-l.
Then, determine the starting time of fault rock sealing, that is, when the displacement pressure of fault rock is firstly
greater than that of the underlying reservoir rock. Finally, the combination of the three can determine the spatiotemporal
distribution of oil and gas leakage in the fault-caprock configuration. The leakage period is between the beginning time of
sealing failure and the beginning time of fault rock sealing. The application results of the example show that for the faultcaprock
configuration of the Nandagang fault and the mudstone caprock in the middle section of the Shahejie Member 1 in
the Qikou Sag, Huanghua Depression, Bohai Bay Basin, the oil and gas leakage to the overlying Dongying Member 3 is
mainly distributed in the central and eastern parts, from the middle period of Guantao Formation to the early Quaternary
with a relatively long duration. This is very favorable for the hydrocarbon’s accumulation in Dongying Member 3
generated by the source rocks of underlying Shahejie Member 3. The analysis results are consistent with the current oil
and gas display in Dongying Member 3 at the Nandagang fault, proving that this method is feasible for predicting the
distribution of leakage periods in fault-caprock configuration. |
