珠一坳陷文昌组锆石定年物源示踪及其对储层的影响

Provenance tracing of zircon dating from Wenchang Formation in ZhuⅠDepression and its influence on reservoir

为示踪珠一坳陷文昌组砂岩物源,对研究区20口井22个砂岩岩屑样品进行了碎屑锆石U-Pb定年分析。结果表明:陆丰凹陷中部及其东部,年龄复杂,年龄谱呈现多峰特征;陆丰凹陷西部及惠州凹陷东部,年龄相对集中,年龄谱主峰值为中生代,另出现了少量古生代、元古代和太古代年龄;惠州凹陷中部及以西所有凹陷,年龄集中,呈现出中生代单峰的特征。对比沉积区与潜在物源区的锆石年龄谱系,推测珠一坳陷文昌组物源东西有差异,东部以中生代沉积岩为主,西部以中生代花岗岩为主,2种母岩混合区在陆丰凹陷西部和惠州凹陷东部。不同母岩类型成岩演化路径的差异,形成物性迥异的储层,中生代沉积岩提供物源,较易形成原生孔发育的低孔中渗或中孔中高渗优质储层;中生代花岗岩提供物源,较易形成混合孔隙发育的低孔特低渗、中孔低渗特低渗储层;2种母岩混合区形成的储层介于上述两者之间。这些认识揭示了珠一坳陷文昌组储层差异的根本原因,同时也为珠一坳陷文昌组优质储层预测提供新的指导方向。

In order to trace the provenance of the Wenchang Formation sandstone in the ZhuⅠDepression,22 sandstone debris samples from 20 wells in the study area were analyzed by detrital zirzon U-Pb geochronology.The results show that the middle and eastern parts of Lufeng Sag have complex ages and multi-peak characteristics;the western part of Lufeng Sag and the eastern part of Huizhou Sag have relatively concentrated ages,the main peak of the age spectrum is the Mesozoic,and a small number of Paleozoic,Proterozoic and Archean Age;in the middle of Huizhou Sag and all sags in the west of it are concentrated in age,showing the characteristics of a Mesozoic single peak.Comparing the zircon age spectrum between the sedimentary area and the potential provenance area,it is speculated that the provenance of the Wenchang Formation in ZhuⅠDepression is different from east to west.The east is dominated by Mesozoic sedimentary rocks,the west is dominated by Mesozoic granites,and the mixed zone of the two parent rocks is in the west of Lufeng Sag and the east of Huizhou sag.Different parent rock types have different diagenetic evolution paths,forming reservoirs with very different physical properties.In the area where the Mesozoic sedimentary rocks provide provenance,it is easier to form low porosity&medium permeability or medium porosity&medium-high permeability high-quality reservoirs with primary pores.In the area where Mesozoic granite provides provenance,it is easier to form low porosity&low-super permeability,medium porosity&low or low-super permeability reservoirs with mixed pores.The reservoir formed in the mixed area of the two parent rocks is between the above two.These understandings reveal the root cause for the reservoir differences of Wenchang Formation in the ZhuⅠDepression,and also provide a new direction for the prediction of high-quality reservoirs from the Wenchang Formation in the ZhuⅠDepression.