Features of Middle-Lower Ordovician paleo-karst caves in western slope area, Tahe Oil Field, Tarim Basin

Abstract

Seismic and drilling data were obtained to study the paleo-karst development conditions and cave developmental characteristics of the Middle-Lower Ordovician in the incised meandering canyon area on the western slope of Tahe Oilfield, Tarim Basin. Using layer leveling, tectonic trend surface, amplitude anomaly and other methods, the paleo-hydrogeographic conditions and paleo-karst fluid system were restored, the types of karst caves in the incised meandering canyon area were divided, and the development model of karst caves under the background of incised meandering canyons was re-constructed. Results showed that: (1) Early Hercynian paleo-karst was developed in the study area. The paleo-geomorphology was generally high in the east and low in the west. The karst geomorphic units were mainly valleys, karst hills and depressions. The incised meandering of the main surface water system was the lowest karst water discharge benchmark in the study area, and the underground and surface branch water systems converged from the southern and northern platforms to the central main body. (2) The underground river caves in the incised meandering canyon area were identified as subterranean river type, swallet stream type, perforated type, phreatic type along river valley and vadose type of sink hole, which were mainly distributed 0-90 m below unconformity surface. The perforated type and phreatic type along river valley were easy to be filled by mud. (3) Incised meandering canyon, karst residual hill and fault controlled the development of ancient karst caves, forming a central confluence karst cave model in the Early Hercynian incised meandering canyon area of the Tahe karst basin.

Keywords

• incised meandering
• canyon
• early hercynian
• paleokarst
• karst cave
• tahe oil field