CAI Wenjie,born in 2001,is a master degree candidate. He is mainly engaged in research of carbonate sedimentology and reservoir geology. E-mail: CaiWenjie_01@163.com.
The Permian Taiyuan Formation in Hengshan area of the central and eastern Ordos Basin is characterized by mixed sedimentation of coal-bearing continental clastic rocks and carbonates,with significant hydrocarbon generation and reservoir formation potential. However,there are still disputes regarding the sequence-sedimentary filling process,which hinders an accurate understanding of the development laws and configuration relationships of source and reservoir. Based on the latest drilling core and well-logging data,this study systematically sorts out the characteristics of sequence boundaries at different levels and reveals the sedimentary filling laws and source-reservoir development mechanisms of the Taiyuan Formation through detailed sequence division and correlation. The results show that: (1)The Taiyuan Formation developed one second-order sequence,five third-order sequences(SQ1-SQ5),and multiple fourth-order sequences,all exhibiting a binary system tract structure with no lowstand system tract developed. Among them,the lower part of the second-order sequence is dominated by clastic rocks,while the middle and upper parts are dominated by carbonates. Coal seams are generally developed at the top of the third-order sequences. SQ2-SQ4 are the main intervals for the development of Taiyuan Formation limestones and grain shoals,and SQ5 has a relatively high degree of missing. The fourth-order sequence has a small thickness of strata. The maximum flooding surface is located within the Xiedao Section. (2)The stratigraphy of the Taiyuan Formation is characterized by the sedimentary filling process of “sedimentary center migration”,“filling in”and “top cutting”. The southern part of the study area is the limestone sedimentary center,and the northern part is the clastic rock sedimentary center. (3)The development of source and reservoir in the Taiyuan Formation is controlled by sequence-sedimentary evolution,which is manifested as “third-order sequences control the development of coal-bearing source rocks,and fourth-order sequences control the vertical superposition distribution of reservoirs”. Horizontally,grain shoals are concentrated in the slope area. The study suggests that the Maoergou Section and Xiedao Section sedimentary periods in the paleogeomorphic slope area are favorable areas for natural gas exploration.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |