Seismic characteristics and hydrocarbon significance of saucer-shaped intrusions in Qiongdongnan Basin
Wu Xiaochuan1,2, Zhang Gongcheng3, Pu Renhai1,2
1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an, Shaanxi 710069, China; 2. Department of Geology, Northwest University, Xi'an, Shaanxi 710069, China; 3. CNOOC Research Institute, Beijing 100027, China
Abstract：There are two types of saucer-shaped intrusions:sandstone intrusion and magmatic intrusion.Both of them have similar seismic response characteristics.Abnormal reflection bodies in Qiongdongnan Basin show obviously saucer-shaped high amplitude;the lower disordered columnar reflection from the crystalline basement of the basin is regarded as the vent of magma upwelling;and the upper strata was forced to become fold and form overlap unconformity.The forced fold width is larger than the saucer-shaped intrusion,and the earliest time of intrusion indicated by the overlap unconformity is 10.5Ma.Based on VSP data from periphery wells and reflection strength of intrusions,wave impedance could be calculated,and its value 1.1×107kg·m-2·s-1 much bigger than drilling statistics of the maximum value of sand wave impedance 5.3×106kg·m-2·s1-.In addition,the adjacent layers of intrusions do not display over-pressure or material conditions which would lead sand liquefaction.Therefore,the saucer-shaped intrusions are igneous sills.According to the damaged degree of the low penetrative chilled selvage at the sill margin,the sill traps can be divided into covered trap,cap rock trap,lenticular trap,and secondary trap in country rocks,which are potentials in the oil and gas exploration.
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