164 / 2019-06-03 23:09:58

Karst Palaeogeomorphology Restoration and Petroleum Geological Significance of the Top of the Middle Triassic Leikoupo Formation in the Northwest of Central Sichuan Basin

orthwestern of central Sichua basin,Middle Triassic, Leikoupo Formation,Lei43 submember,paleogeomorphology

The weathered-crust karst reservoir is an important type of carbonate reservoir. Its reservoir prediction is a hotspot research at home and abroad. The karst paleogeomorphology can reflect the intensity, extent and depth of the surface karst in the reservoir, which is of great significance for the prediction of weathering crust reservoirs. Based on the data of drilling and testing in the north and west of Central Sichuan Basin, the denudation line and thickness distribution of the third submember of the fourth member ofthe Middle Triassic Leikoupo Formation in the study area are determined. Using the 2D and 3D seismic data, Establishment of isochronal framework of strata at the top of Leikoupo Formation and the bottom of Xujiahe Formation in the study area. Based on the regional sedimentary filling and tectonic evolution background, two stratigraphic interfaces with stable distribution and seismic reflection characteristics are selected: the bottom of the third member of the Xujiahe Formation and the second submember of the fourth member of the Middle Triassic Leikoupo Formation
as benchmarks for restoration of karst paleogeomorphology by impression and residual thickness methods and discuss the results of the two methods of recovery. It is pointed out that the study area is a “stepped” paleo-geomorphic pattern with high east and west low. It can be divided into three secondary karst paleogeomorphic units from east to west: karst highlands, karst slopes and karst depressions. The karst slope zone is divided into sub-level geomorphic units such as karst residual hills and karst valleys. The karst highlands are developed in the Yingshan and Nanchong areas; the karst slopes are developed in most areas of Longgang; the karst depressions are distributed in the Xichong and Gongshanmiao areas. Combined with the actual oil and gas production, it is pointed out that paleo-geomorphology controls the development degree of reservoirs, and then controls the reserves and distribution of natural gas. The karst residual hill on the karst slope is a favorable area for the exploration of weathered-crust karst reservoirs; the inheritance paleogeomorphology control The overburden Xujiahe Formation deposits, which affects the distribution of the early reservoirs of the Xujiahe Formation. The erosion tanks in the karst depressions are more likely to enrich the channel sands, which is a favorable area for the exploration of the early sandstone reservoirs of the Xujiahe Formation.