DIAGENETIC CHARACTERISTICS AND CONTROLLING FACTORS OF THE PERMIAN TIGHT SANDSTONE RESERVOIRS IN ZHONGGUAI AREA

The Jiamuhe Formation of the Permian in the Zhongguai area of the Junggar basin is a sort of tight sandstone reservoirs with a large amount of volcanic detritus, which were believed to be formed in a fan delta environment. Comprehensive studies of core observation, thin section identification and core geophysical property test, the deep research of diagenetic characteristics and controlling factors of tight sandstone reservoirs has been conducted. It shows that the intense compaction and cementation of the reservoirs in Jiamuhe Formation may lead to the densification of reservoirs, and that laumontite, heulandite and analcite occur as the main cements of the sandstones. Because of the unconformity above the Jiamuhe Formation and the thermal maturation of the source rock, there occur weak acidic meteoric water dissolution and organic acid dissolution in the reservoirs of the Jiamuhe Formation, which lead to the dissolution of zeolite cement. As the result, the plane porosity averages 0.74%. Petrology, zeolites cementation and thrust fault activity controlled the mechanical compaction of Jiamuhe reservoirs. Volcanic detritus were the material basis of zeolite cement precipitation, and sedimentary facies and lithology resulted in the differentiation of zeolite cement in different regions. Weak acidic meteoric water was the main factor that leads to the dissolution of Jiamuhe reservoirs.