Diagenesis of zeolite minerals and its significance for hydrocarbon accumulation in the second member of Jiamuhe formation of Zhongguai area, Junggar Basin

Key words:  zeolite minerals  volcanic materials  transforming sequence  laumontite dissolution  secondary pore

Abstract:

Diagenesis of zeolite minerals and its significance in hydrocarbon accumulation in the second member of Jiamuhe formation of Zhongguai area were studied using data from the core, casting thin section observation,electron probe and inclusions. The results show that there are three kinds of zeolites, which include laumontite,heulandite and analcite in the second member of Jiamuhe formation of Zhongguai area, Junggar Basin. Zeolite cementation is the main type of cementation. The cementation of early zeolite reserved some of the original pores, which formed a foundation for the dissolution of laumontite and analcite at the later stages. The zeolites whose formation is closely related to volcanic material are mainly distributed in the glutenite of fan delta river in the formation. The formation of zeolite types is determined by the chemical properties of surrounding water:the pH value, the properties of the ions and their ratios between each other, and the temperature and pressure. The transforming sequence of zeolite is from analcite, to heulandites, and then laumontite downwards. Additionally, albitization of plagioclase can also form some part of laumontite. Enriched reservoirs, in which the secondary pores are favorable for oil and gas accumulation, can be determined by the content of laumontite and the degree of dissolution.