Characteristics and characterization of karst paleo-geomorphology and paleo-water system on the top of the Maokou formation in the Z area in southern Sichuan basin

The limestone karst reservoir of Maokou formation in southern Sichuan is relatively developed， and it is one of the important producing strata in southern Sichuan. However， the reservoirs has strong heterogeneity and high degree of fracture-cavity filling， which makes it difficult to predict reservoirs. The recovery of karst paleo-geomorphology and paleo-water system can help us to master the development and distribution of karst reservoir， which is of great significance for the oil and gas exploration of the Maokou formation in the southern Sichuan basin. In this paper， the karst paleotopography in the Z area in southern Sichuan basin is restored by the impression-trend surface method with referring sediment thickness form the top of Maokou formation to the top of Changxing formation. According to the micro-geomorphic combination form， four kinds of three-level paleogeomorphology are divided， and the north-south paleo-water system is depicted according to the theory of karst hydrogeology. The analysis shows that the hydrodynamic circumstance is quite different in different geomorphologic locations. The both sides of the fluvial are located in the runoff area， with the strongest hydrodynamic conditions and the most developed dissolution pores and fractures， which is the next reservoir exploration direction.