川南盆地长宁页岩气田五峰组⁃龙马溪组成藏动力学过程及其意义

Based on on the low⁃temperature thermochrological data，burial history analyis，inclusion analysis and balaced section etc.，this study investigates on the hydrocarbon generation and shale⁃gas accumulation in the Wufeng⁃Longmaxi formations in the Changning shale⁃gas field at the southern Sichuan basin. It suggests that the homogenization temperatures of the inclusions in the Wufeng⁃Longmaxi formations are characterized with two episodes dominated with 120~140 ℃ and pressures of 36~39 MPa，and with 160~180 ℃ and pressures of 45~47 MPa，respectively. Apatite fission track data and related thermal history suggest regional exhumation is about 2.0~2.5 km in Cenozoic time. Furthermore，burial history of N201 well indicates four⁃stage thermal evolution of the Wufeng⁃Longmaxi formations in the Changning shale⁃gas field as follows: Early mature in the Middle Silurian to Middle Permian，Middle mature in the Late Permian to Late Triassic，Late Mature in the Early Jurassic to Early Cretaceous，and the Over mature since Middle Cretaceous. It suggests that the Wufeng⁃Longmaxi formations are dominated with a normal hydrostatic pressure index in Palaeozoic times，however，the gas generation and pressure index are substantially increased since Late Jurassic，in particular in the Early to Middle Cretaceous with a maximum of pressure index about 2.0. Due to a widespread uplift and exhumation occurred in Cenozoic across the Changning shale⁃gas field and its periphery，the pressure index of the Wufeng⁃Longmaxi formation decreased into 1.9，indicating of a positive condition for reservation. Thus，we suggest that the Changning shale⁃gas field is characterized with a limited accumulation in early stage and a subsequent high⁃pressure accumulation of shale⁃gas.

Keywords： Shale⁃gas accumulation ; Wufeng⁃Longmaxi formations ; Changning shale⁃gas filed ; Sichuan Basin