四川盆地湖相泥页岩沉积模式及岩石相类型

Sedimentary models and lithofacies types of lacustrine mud shale in the Sichuan Basin

四川盆地湖相页岩气勘探已在建南、涪陵、元坝地区中下侏罗统获得了显示和工业气流,展示了良好的勘探前景。通过对该盆地中下侏罗统不同层段湖相泥页岩中石灰岩和砂岩夹层比例的统计,将中下侏罗统湖相泥页岩划分为最大湖进期碳酸盐岩湖泊和局限湖进期陆源碎屑湖泊2种沉积模式,前者主要分布于川东北地区下侏罗统自流井组大安寨段和东岳庙段,后者主要分布于川东—川东北地区中侏罗统千佛崖组(凉高山组)和川东北地区自流井组东岳庙段。在此基础上,按照页岩气地质、开发、工程一体化的思路,根据岩性及岩性组合、有机碳含量、脆性矿物类型3大关键参数,建立了该区湖相泥页岩岩石相划分方案,将其划分为6种岩石相类型。最后通过有机地球化学、压汞—吸附联合测定、脉冲渗透率、纳米CT、X射线衍射矿物组分、含气性测试等技术方法,对不同岩石相类型的页岩气形成基础条件进行了综合对比评价。结论认为:以碳酸盐岩占主导沉积的湖坡风暴滩与湖坡泥交替沉积的中—高碳低硅中钙页岩与介屑灰岩互层相,具有良好生烃、储集、渗透和可压裂的配置条件,有利于页岩气的形成和改造,为湖相泥页岩最有利的岩石相类型。

In the Sichuan Basin, lacustrine shale gas exploration presents good prospects, with gas show and commercial gas flow dis- covered in the Middle-Lower Jurassic strata in the areas of Jiannan, Fuling and Yuanba. Based on the statistics of interbedded limestone- sandstone ratio, the lacustrine mud shale of Middle-Lower Jurassic in the Sichuan Basin was divided into two sedimentary models, i.e., the carbonate lake deposited during the maximum transgression and the terrigenous clastic lake deposited during the restricted transgres- sion. The former is mainly located in Da＇anzhai and Dongyuemiao Members of Lower Jurassic in the NE Sichuan Basin, and the latter is mainly distributed in the Middle Jurassic Qianfoya （Lianggaoshan） Fm in the E-NE Sichuan Basin and the Lower Jurassic Dongyue- miao Member in the northeastern Sichuan Basin. Then, according to the concept of integrated geology, development and engineering, the lithofacies classification scheme of lacustrine mud shale in this area was worked out by using three key parameters （i.e., lithological and lithological combination, TOC and fragile mineral type）. Based on this scheme, it was divided into 6 lithofacies types. Finally, the basic forming conditions of shale gas in different types of lithofacies were evaluated and comprehensively compared by using a series of tech- nologies, such as organic geochemistry, combined mercury injection-adsorption measurement, pulse-decay permeability, nanometer CT, X-diffraction mineral composition and gas-bearing property test. It is concluded that the alternative facies of middle-high carbon, low silicon and middle calcium shale and shell limestone where lake slope storm beach and lake slope mud are deposited alternatively with carbonate rocks as the dominant sediments is good in hydrocarbon generation, reservoir, permeability and fracturing conditions, so they are favorable for the formation and stimulation of shale gas reservoirs and the most favorable lithofacies type of lacustrine mud shale.