Genesis Of Zeolite And Its Reservoir Significance Of Lower Urhe Formation In Mahu Depression

The conglomerate reservoirs discovered recently in Mahu depression,Junggar Basin have been characterized by near-source,coarse-grained,deep-buried and low-permeability.The fan delta deposits dominated by volcanic source rocks are developed in the Lower Urhe Formation in Mahu Depression.Previous studies have shown that various zeolite cements developed in conglomerate reservoir in the Lower Urhe Formation in Mahu Depression,and the diagenesis process is complex.The reservoir quality is closely related to the precipitation and dissolution of zeolite minerals.However,studies on the origin of zeolite minerals,the symbiotic mechanism with other minerals,and the control factors of dissolution are weak.Based on the comprehensive analysis of seismic,well logging and drilling data,the experimental data of thin slice identification,scanning electron microscopy(SEM),electron probe,fluid inclusion and X-ray fluorescence spectroscopy of core samples are uesd to study the differences of the parent rock properties,the genesis of zeolitic minerals and the diagenetic evolution,which are studied to explore the genetic mechanism of the zeolite and the development of high-quality reservoirs in the background of volcanic parent rock.The results show that: 1)Five kinds of zeolites are developed in Wu 4 member in Mahu Depression,of which laumontite is the most common,followed by heulandite,and analcidite,clinoptilolite and stilbite are only developed in a few wells;2)the sedimentary facies control the spatial distribution of different zeolites,and the deposition process affects the content of laumontite.Among them,the laumontite is mostly developed in the thick coarse-grained conglomerate of the fan delta front,and the content is high;the heulandite is developed in the front of the fan delta plain,which is rich in tuff,and the content is low;3)the zeolite in the conglomerate reservoir are formed in two genetic models,in which the heulandite is formed in the transformation of the tuff,while the laumontite is formed in the cementation of the pores in the diagenesis;4)the high-quality conglomerate reservoir is affected by the properties of the parent rock,sedimentation,and paleostructure.The properties of the parent rock control the precipitation of chlorite and the diagenetic evolution sequence of the reservoir.The sedimentation affects the distribution and content of the different zeolites.The paleo-tectonic activities affect the dissolution degree of the zeolites in different diagenetic stages.The comprehensive analysis shows that the fan delta front,located in high paleo geomorphy,which is supplied with the acid volcanic parent rock,is most favorable for the formation of high-quality reservoirs.