Abstract:

In the Tahe oilfield of the Tarim basin, the Middle-Lower Ordovician surface and subsurface karsts were diverse morphologically in the early Hercynian. There are abundant oil and gas resources in subsurface karst fracture-vug systems. Based on high-precision seismic data and drilling data, and by unifying the subsurface and surface water systems, the Middle-Lower Ordovician karst water system in the early Hercynian movement in the Tahe oilfield was constructed. The research results show that, in the early stage of the Hercynian movement in the Tahe oilfield, there developed four karst platforms in the Middle-Lower Ordovician, generally distributed in a step-like pattern with higher elevation in the east than in the west. The differential drainage and dissolution of karst water resulted in various hydromorphology, such as canyon, underground river, incised meandering river, and wide valley. The karst water system are mainly bounded by surface watershed, drainage baseline, stratigraphic lithology assemblage, fault, and weak dissolution zone. The karst water system in the Tahe oilfield can be divided into four relatively independent secondary karst water systems: plateau canyon water system, underground river canyon water system, incised meandering river water system, and wide valley water system. This classification of the hierarchical structure of the karst water system provides a geological basis for further understanding the karst fracture-vug system and karst fracture-vug unit in the Tahe oilfield.

Key words: Tarim basin, Tahe oilfield, early Hercynian movement, Ordovician, karst fracture-vug, karst water system, hydromorphological feature