四川盆地东北部三叠系飞三段沉积特征及油气地质意义

Sedimentary characteristics and petroleum geological significance of the third member of Triassic Feixianguan Formation in northeastern Sichuan Basin

近年来,四川盆地东北部三叠系飞三段天然气勘探持续获得新发现。通过钻井岩心观察、测井解释、相标志鉴定和颗粒岩优势相分析,系统研究了四川盆地东北部三叠系飞三段沉积特征及油气地质意义。研究结果表明:(1)研究区飞三段主要发育开阔台地和局限—蒸发台地,可进一步识别出台内滩、滩间海、潮坪和瀉湖等4种沉积亚相。(2)台内滩以颗粒岩沉积为主,可进一步分为鲕滩微相和生屑滩微相,鲕滩形成于开阔台地或局限—蒸发台地内部微地貌高地,生屑滩形成于开阔台地,两者沉积水体能量高,均具有向上变粗的逆粒序特征。(3)滩间海和瀉湖主要发育于台地内部较低洼地区,沉积环境能量低,可进一步划分为灰质滩间海(灰质瀉湖)、云质瀉湖微相,属于半局限—局限滩间海(瀉湖)范畴。潮坪发育于台地内部平均海平面附近,发育于多级次海平面下降晚期,是沉积水体变浅和水动力变弱的沉积响应,可进一步划分为膏坪微相和云坪微相。(4)P6—L1—L5井区东北部颗粒岩厚度大于15 m,膏岩厚度为15~20 m,为研究区飞三段天然气藏勘探的重点区域。

In recent years,new discoveries have been made in natural gas exploration of the third member of Triassic Feixianguan Formation(T;f;)in northeastern Sichuan Basin. The sedimentary characteristics and petroleum geological significance of T;f;in northeastern Sichuan Basin were studied through drilling core observation,logging interpretation,facies marker identification and analysis of dominant facies of granular rock. The results show that:(1)The T;f;in the study area is dominated by open platforms and restricted-evaporate platforms,and four sedimentary subfacies can be identified,including intra-platform shoal,interbank sea,tidal flat and lagoon.(2)The intra-platform shoals are mainly composed of granular rock deposits,which can be further divided into oolitic shoal microfacies and bioclastic shoal microfacies. Oolitic shoals formed in micro-topographic highlands of open platforms or restricted-evaporate platforms,and bioclastic shoals formed in open platforms,both of which had high energy sedimentary water,with upward coarsening reverse grain sequence.(3)The interbank seas and lagoons were mainly developed in the low-lying areas inside the platform,with low depositional environment energy.They can be further divided into calcite interbank seas(calcite lagoons)and dolomitic lagoon microfacies,which belong to semi-restricted to restricted interbank seas(lagoons). The tidal flats were developed near the mean sea level inside the platform in the late stage of multi-level sea level decline,corresponding to the sedimentary response of sedimentary water shallowing and hydrodynamic weakening,and they can be further divided into gypsum flat microfacies and dolomitic flat microfacies.(4)The thickness of granular rocks is greater than15 m and the thickness of gypsum rocks is 15-20 m in the northeastern P6-L1-L5 well areas in the study area,and this area can be a key area for exploration of natural gas reservoirs of T;f;.