四川盆地侏罗系大安寨段湖相含云质储层成因研究

Research on the origin of lacustrine dolomitic reservoir in Jurassic Da'anzhai Formation of Sichuan Basin

四川盆地侏罗系大安寨段是典型的致密油发育层段,勘探开发成果揭示,大安寨储层岩性主要为介壳灰岩致密储层。侏罗系大安寨段致密油勘探开发成效引人关注,特别是近期川中南部侏罗系大安寨段滨浅湖相的GSTMX地区,大安寨段显示频繁,部署的GQ1H在大安寨段获得高产工业油流。根据对最新钻探的GQ1H井解剖表明,含云质岩具有更好的储集条件和含油气性,是储层"甜点"有利分布岩性。通过老井复查、岩心、岩屑、薄片、测井等综合分析表明,含云质储层岩性包括云质灰岩、灰质云岩和泥-粉晶云岩,储集空间主要为粒间、粒间溶孔和微裂缝,储层储集条件好,成像显示溶蚀孔洞发育,川中南部云化程度高于北部。根据碳氧同位素、X衍射、地层水特征以及古地形综合分析初步认为,四川盆地大安寨沉积时期虽然为淡水湖泊,但在古地形、古气候、沉积环境以及湖平面变化共同控制下,局部地区仍然发育一定规模的含云质储层,该认识为川中侏罗系大安寨段相对优质储层深化认识奠定了坚实的地质基础。

The Jurassic Da'anzhai Formation in the Sichuan Basin is a typical layer characterized by the development of tight oil.Exploration results reveal that the Daanzhai reservoir is mainly lacustrine limestone reservoir in lithology.The tight oil exploration results of Jurassic Daanzhai Formation has aroused much interest;especially during the recent exploration of Duan shore shallow lake facies in the GST-MX area of southern Sichuan,Da'anzhai Formation was frequently seen,and the deployment of GQ1H led to the obtaining of high-yield industrial oil flow in Da'anzhai Formation.The newly drilled well GQ1H indicates that dolomitic rocks have favorable reservoir condition and oil potential,and is also the lithology of“sweet spot”distribution.Comprehensive analysis of old-wells’reinvestigation data,cores,cuttings,rock chips and well logging shows that the lithology of dolomitic reservoir includes dolomitic limestone,limy dolomite and micrite-crystal powder dolomite,the reservoir space is mainly composed of intergranular pores,interparticle dissolution pores and microfractures,and the dolomitic reservoir has the good reservoir condition.The imaging logging displays the development of solution pores,and the degree of dolomitization in the southern part of central Sichuan basin is higher than that in the northern part.According to the comprehensive analysis of carbon and oxygen isotopes,X-ray diffraction,characteristics of formation water and the ancient landform,the authors preliminarily hold that,although Da'anzhai Formation in the Sichuan basin was a freshwater lake during the deposition of Da'anzhai Formation,there still existed some dolomitic reservoirs locally under the control of ancient landform,ancient climate,sedimentary environment and change of lake-level.The understanding obtained by the authors has laid a solid foundation for deepening the understanding of the relatively high quality Jurassic reservoir in central Sichuan Province.