四川盆地河坝地区下三叠统嘉陵江组气藏储集层沉积特征与成岩作用*

利用录井、测井和地震资料,运用岩心观察、薄片观察以及扫描电镜等方法,结合孔隙度、渗透率、微量元素和同位素分析测试结果,对四川盆地东北部河坝地区下三叠统嘉陵江组二段气藏主要储集层段进行地层对比、沉积特征、储集层特征及成岩作用研究。结果显示:(1)河坝地区嘉陵江组二段顶、底界面特征清楚,可进一步划分为3个亚段,储集层主要发育在嘉二中亚段的白云岩中,总体为局限台地沉积,发育台内滩、潮坪和潟湖等微相,台内滩是储集层发育的最有利沉积微相,主要位于河坝区块的中部;(2)储集岩岩性主要为残余(藻)砂屑白云岩、细粉晶白云岩,孔隙类型主要以晶间(溶)孔和粒内溶孔为主,总体以低孔、低渗的Ⅲ类储集层为主,储集层空间类型主要为裂缝—孔隙型;(3)储集岩的成岩作用类型有泥晶化、溶蚀、胶结、白云岩化、压实压溶和破裂等,储集层的形成主要与准同生期的大气水溶蚀作用、深埋条件下的埋藏溶蚀作用以及构造裂缝的发育有关;(4)准同生期的大气水溶蚀作用是嘉二段颗粒碳酸盐岩孔隙发育的基础,白云岩化、埋藏溶蚀等埋藏成岩作用有利于孔隙的改善,微古地貌高地发育区及断裂、裂缝相对发育区可能为储集层发育有利区。

Sedimentary characteristics and diagenesis of the gas reservoir in theLower Triassic Jialingjiang Formation in Heba area,Sichuan Basin

Based on well logging and seismic data,through observation of core and thin section and scanning electron microscopy,combined with test results of porosity,permeability,trace elements and isotopes,the stratigraphical correlation,sedimentary characteristics,reservoir characteristics and diagenesis of the gas reservoir in Member 2 of Lower Triassic Jialingjiang Formation in Heba area,northeastern Sichuan Basin were analyzed.The results showed that:(1)The Member 2 of Jialingjiang Formation can be divided into Upper,Middle,and Lower Sub-Members, and the main reservoir developed in the Middle Sub-Member dolostone of restricted platform which was dominated by intra-platform shoal,tidal flat and lagoon microfacies.The intra-platform shoal mainly located in the middle of Heba area and was the most favorable sedimentary microfacies for reservoir development.(2)Reservoir rocks mainly include residual (algae-) sand-sized introclast dolostone and fine silt-zized crystalline dolostone with intercrystal(dissolved)pores and intragranular dissolved pores.It was dominated by Ⅲ-type reservoir with low porosity and low permeability.The reservoir space type is fracture-porosity type.(3)Several types of diagenesis were developed,such as micritization,dissolution,cementation or filling,dolomitization,compaction-pressolution and fracturing.The reservoir was mainly controlled by penecontemporaneous meteoric dissolution,burial dissolution and tectonic fracture.(4)The penecontemporaneous meteoric dissolution was the key factor controlling the development of reservoir pores in granular carbonate rocks of the Member 2 of Jialingjiang Formation,and some burial diagenesis,such as dolomitization and burial dissolution,promoted the development of reservoir pores.Thus,the favorable exploration targets were distributed in microtopography uplands and areas where faults and fractures developed.