| Author's Name: LIN Chengcheng1, LIU Hong1,2,3, LIU Ran4, XU Chang4, TAN Lei1,2,
WANG Dong1,2,ZHANG Kun1, |
| Abundant oil and gas discoveries have been made in the platform edge oolitic shoals of the Lower Triassic
Feixianguan Formation in Sichuan Basin. In order to further promote the research and exploration of the inner platform
oolitic shoal, based on drilling, logging, and three-dimension seismic data, the sequence characteristics, sequence
evolution and oolitic shoal distribution pattern of the Feixianguan Formation in Pengxi-Yanting area, northwestern
Sichuan Basin are studied. The results show that: (1) The Feixianguan Formation can be generally divided into three thirdorder sequences (SQ1, SQ2, SQ3), with typical rock electrical characteristics and seismic response of each sequence
boundary. SB1, SB2, and SB3 are all lithological discontinuity surfaces, corresponding to reflection peaks; SB4 is the
lithological conversion surface, corresponding to the reflection trough. The four interfaces exhibit abrupt changes in
logging responses such as natural gamma and interval transit time. (2) During the deposition period of SQ1 in the study
aera, the terrain slope was relatively steep, with a high-angle S-shaped progradational reflection structure. Mainly
controlled by the sea-level fluctuation cycle of high-frequency sequences, a high-frequency restricted oolitic shoal
sedimentary pattern was developed, in which the deposition scale of a single-stage shoal body was small, and the shoal
bodies migrated rapidly in the horizontal direction towards northwest. (3) During the deposition period of the SQ2, the
platform depression was basically filled, the overall terrain slope was relatively gentle, and the sequence had a low-angle
progradational reflection structure. Controlled by the sea-level fluctuation cycle of third-order sequences, a stable and
widely distributed oolitic shoal sedimentary pattern was developed, and the single-stage shoal body had a relatively large
thickness and a stable planar distribution. (4) The SQ3 sequence had a continuous parallel reflection structure, and
restricted-evaporative platform facies was developed, characterized by interbedded mudstone and dolomite gypsum with
uniform thickness. This study could provide a geological basis for the fine exploration and efficient development of oolitic
shoal reservoirs within the platform of the Feixianguan Formation in northwestern Sichuan Basin. |
