四川盆地及邻区寒武纪古地理与构造-沉积环境演化

四川盆地寒武纪台地滩相储集体是一套重要的油气勘探目的层,准确预测其发育部位、储集性能与分布规律是其油气勘探的重要基础,其中,寒武纪不同地质历史时期古地理与构造-沉积环境的研究是储集体预测的关键。根据野外实测剖面、钻井和测井分析、地震资料,应用活动论构造-古地理思想,在沉积地质条件、区域连井地层剖面,地层厚度与沉积相等分析的基础上,综合编制了寒武纪各个时期的构造-沉积环境图件,反映了四川盆地寒武纪的古地理特征及盆地演化。四川盆地寒武纪整体呈现西高东低、北高南低的古地理格局,西部发育潮坪和滨岸等碎屑岩沉积相,中东部发育缓坡相、台地相及台地边缘浅滩相等。沉积相在时空上的响应为由早寒武世梅树村期局限台地→筇竹寺期碎屑岩台地和深水盆地→早寒武世沧浪铺期滨岸-混积台地→早寒武世龙王庙期碳酸盐岩缓坡→中寒武世陡坡寺期蒸发局限镶边台地→中晚寒武世洗象池期成熟镶边台地的演化过程。其中,筇竹寺期为巨厚的烃源岩生成期;龙王庙期和洗象池期,为碳酸盐岩储集层发育的有利时期;龙王庙期及陡坡寺期发育的蒸发岩可形成良好的盖层。

Palaeogeography and tectonic-depositional environment evolution of the Cambrian in Sichuan Basin and adjacent areas

The Cambrian platform bank or shore reservoir is an important petroleum exploration target in Sichuan Basin,so it is important for the oil and gas exploration to accurately predict the occurrence,reservoir performance and distribution patterns of the sedimentary facies. The study of Cambrian palaeogeography and tectonic-depositional environment is the key to reservoir prediction. Based on the field measurement of profiles,drilling and logging analysis and seismic data,with the thought of mobilistic tectonics-palaeogeography, the maps of the Cambrian tectonic-depositional environment,which can reflect the palaeogeography and basin evolution in Sichuan Basin, have been drawn by analyzing the sedimentary geology conditions,regional well profiles,stratigraphic thickness and sedimentary facies and so on. From the maps it can be seen that it was relatively higher in the west and north,lower in the east and south of Sichuan Basin during the Cambrian. The shore land and tidal flat facies were developed in the western basin; and inner gentle slope,platform and platform marginal shoal facies were developed in the middle and eastern of study area. The response of sedimentary facies evolution in space and time is: the restricted platform in the Meishucun Age of Early Cambrian→clastic platform and deep basin in the Qiongzhusi Age of Early Cambrian → shore-mixd platform in the Canglangpu Age of Early Cambrian→carbonate ramp in the Longwangmiao Age of the Early Cambrian → the evaporation and limited rimmed platform in the Douposi Age of the Middle Cambrian → the mature rimmed platform in the Xixiangchi Age of the Middle-Late Cambrian. Among the above,the Qiongzhusi Formation was a thick bed of source rocks;the Longwangmiao and Xixiangchi Formations were benefied to forming carbonate reservoirs;gypsum rocks formed in the Longwangmiao and the Douposi Formations were good caps.