Development Characteristics and Genetic Evolution of Carbonate Karst Ancient River: Example from the Middle-Lower Ordovician in Block-12 of Tahe Oilfield, Tarim Basin

In order to clarify the origin of the ancient river channel on the top of the Middle and Lower Ordovician in Block 12 of Tahe Oilfield, the Tarim basin, using techniques of seismic profile analysis and seismic attribute extraction, combined with drilling data, the development characteristics of the ancient landform and ancient water system are depicted, the meander characteristics of the ancient river channel are quantitatively describe, and the genetic evolution model of the ancient river channel is established.The results show that the ancient channel on the top of the Middle and Lower Ordovician is entrenched meander river, and the entrenched meander is characterized by a "V" shape of the valley, symmetrical slope banks on both sides of the valley, steep valley walls, and the development of the meander core and natural bridge formed by process of natural cutoff. The ancient channel on the top of the Middle-Lower Ordovician developed a "high curvature" meander shape. Statistical meander parameters indicate that the meander ratio C values are larger than 2.20, with an average value is 4.27, the C value of the whole North-South meander is 1.87, and the C value of the whole East-West meander is 2.38. The evolution of meandering superimposed Valley in block-12 has three stages: Silurian sedimentary period, free-meander and entrenched-meander, and its genesis is closely related to the early Hercynian movement.