川西地区中三叠统雷口坡组四段上亚段沉积特征

利用野外露头、钻井岩心、测井、岩石薄片以及碳氧同位素等资料，对川西地区中三叠统雷口坡组四段上亚段沉积特征与沉积模式进行系统分析，明确储层发育有利沉积相带。川西地区中三叠统雷口坡组四段上亚段沉积时期主要为局限—蒸发台地潮坪沉积环境，发育膏云坪、（藻）云坪、（藻）云灰坪、（藻）灰云坪、（藻）砂屑滩、（藻）灰坪、砂屑滩等沉积微相。通过沉积模式的建立，认为川西地区雷四段上亚段沉积时受滩/岛的阻隔及干旱气候条件等因素影响，海水补给受限，在强蒸发作用下海水逐渐咸化，形成高盐度的沉积环境，有利于大规模白云岩化；川西地区地势平坦、水体浅、能量低，多期频繁的暴露引起了大气水淋滤溶蚀作用；藻类广泛发育，藻类活动所形成的碳酸盐岩类型多样，主要有藻叠层白云岩、藻凝块白云岩、藻纹层白云岩和藻砂屑白云岩等。综合分析认为，川西大部分地区在该时期为潮间带（藻）云坪微相沉积，有利于准同生期暴露并接受大气水淋滤溶蚀，是孔隙型储层发育的有利区带。 

Sedimentary characteristics of the upper part of the fourth member of Leikoupo Formation of Middle Triassic in western Sichuan Basin

Based on the data of outcrop, drilling core, logging, rock thin section and carbon and oxygen isotope test, this paper carried out systematic analysis for characteristics and model of sedimentary of the upper part of the fourth member of Leikoupo Formation in western Sichuan Basin, favorable sedimentary facies for the development of reservoir were proposed. Results showed that in the sedimentary period of the upper part of the fourth member of the Middle Triassic Leikoupo Formation, the western Sichuan Basin was in the sedimentary environment of tidal flat within restricted and evaporative platform. The sedimentary microfacies were gypseous-dolomite flat, (algae)-dolomite flat, (algae)-dolomite-lime flat, (algae)-lime-dolomite flat, (algae) intraclast beach, (algae)-lime flat, intraclast beach etc. According to the establishment of the sedimentary model, due to the barrier of beach/island and the influence of arid climate conditions, the seawater supply was limited during the deposition of the upper submember of the fourth member of Leikoupo Formation in the western Sichuan Basin, which formed a high salinity sedimentary environment by strong evaporation and was good for large-scale dolomization. Flat terrain, shallow water, low energy, and the frequent exposure of multiple periods caused atmospheric water leaching and dissolution in the western Sichuan region. Algae were widely developed, which formed diverse carbonatite by algal activities, including algal stromatolite dolomite, algal clot dolomite, algal lamina dolomite and algal arene dolomite. By comprehensive analysis, for most part of the western Sichuan Basin, it was in the intertidal zone (algae)-dolomite flat sedimentary area, which was favorable for the penecontemporaneous exposure to atmospheric water leaching and dissolution, and was a favorable developing zone for porous-type reservoir.