Characterization of karst paleo-geomorphology and the paleo-water system on the top of the 4th member of the Dengying formation in the Gaoshiti area, Sichuan basin

Karst pore-cave reservoirs of the Dengying formation developed well in the Weiyuan, Ziyang and Gaoshiti-Moxi areas in the Sichuan basin, which are heterogeneous, thus making reservoir prediction difficult. One of possible approaches to solve this problem is recover the karst paleo-geomorphology and paleo-water system from the karst geological theory, so as to reveal the development and distribution of the reservoirs to guide exploration. In this paper, the karst paleotopography in the Gaoshiti area is restored by the impression method. Combined with the modern karst and karst dynamics theory, paleogeomorphology （second-class）are divided unto three types of the third class：karst platform, karst gentle slope and karst basin. Based on the modern karst classification method, according to the micro-geomorphic combination form, the second-class paleogeomorphology is finely characterized, and six kinds of third-class paleogeomorphology units are divided. Finally, according to karst dynamics and karst hydrogeology, The three major water systems, i.e. the north, west and southeast are depicted in the Gaoshiti area. It is considered that different geomorphological locations have different hydrodynamic conditions, and there are differences in the developmental characteristics of different types of karst paleogeomorphology, runoffs in ancient water systems, excretion and reservoir development, and filling characteristics. The fine paleogeomorphology and the depiction of the ancient water system have great importance for advancing oil and gas exploration and development of the Dengying formation in the Gaoshiti area.