Paleogeomorphological reconstruction and geological implications of the weathered-crust karst on the top of the Middle Triassic Leikoupo Formation in the Longgang area, Sichuan Basin, China

Abstract

Weathered-crust karst carbonate is developed in the third submember of the fourth member of the Middle Triassic Leikoupo Formation (Lei 4 3 submember) in the Longgang area of Sichuan Basin, China, and acts as an important oil and gas reservoir. To reconstruct the paleogeomorphology of the weathered-crust karst, we analyzed the seismic thickness of the interval from the erosional unconformity surface on the top of the Leikoupo Formation to the karst at the bottom of the third member of the Xujiahe Formation (Xu 3 member), based on existing three-dimensional seismic and drilling data, and the sedimentary characteristics of the Leikoupo and Xujiahe formations. There are three secondary types of geomorphological unit, namely the karst highlands, the karst transitional zone, and the karst basin, and these have distinct karst water development patterns and hydrological conditions that determine the intensity of karstification and reservoir quality. Among them, the karst highlands have a poor reservoir capacity due to their long-term exposure above the water table, which resulted in severe denudation. The karst transitional zone features the superimposition of multiple periods of strong karstification, and this has resulted in high-quality reservoir conditions in the karst monadnocks but poor reservoir conditions in the

Special Issue: Advances of petroleum exploration and geology research in West China's petroliferous basins

“…The pressure evolution during the middle Permian is divided into three stages: (1) a brief overpressure stage (T 2 -T 3 ); (2) an overpressure stage (J 1 -K 2 ); and (3) an overpressure reduction stage (K 2 -present). Liu et al (2018a) reconstruct the Middle Triassic 3D paleogeomorphology of weathered karst in the Longgang area, Sichuan Basin. They identify three geomorphological units above the Leikoupo Formation, referred to as the karst highlands, karst transitional zone, and karst basin.…”

Calculating the Eroded Thickness Corresponding to a Short-Term Tectonic Uplift with Milankovitch Theory: A Case Study of the Middle Permian Maokou Formation in Southeastern Sichuan Basin, Southwest China

“…The development of numerous karst reservoirs is usually based on long-term tectonic uplift and strong denudation. − In contrast, the Dongwu movement was a short-term tectonic uplift, with a duration of about 0.5–2.5 Ma . Several studies revealed that the residual thickness of the Maokou Formation in the Sichuan Basin varies from 180 to 360 m, and the maximum eroded thickness does not exceed 200 m .…”