The Lower Cambrain Marine Shale Porosity Evolution Of Qiongzhusi Formation In JingYan -Qianwei Area

The shale gas resource what contains in Qiongzhusi formation of the lower Cambrian shale reservoir of Southern Sichuan basin is very rich.but because of shale reservoirs is very dense,is low porosity low permeability as even ultra low permeability reservoir,conventional technology is difficult to produce industrial air flow.Southern Sichuan region,however,Characteristics of the Marine shale of Qiongzhusi formation of the lower Cambrian is about tectonic deformation is weak,moderate buried,rich organic shale large thickness,high abundance of organic carbon,high evolution degree,brittle shale mineral is rich,the nanoscale pore and microfracture development of kinds of types.shale gas position well section of The Qiongzhusi formation has hole perforating and sand fracturing tests,a gas production 2.88 x 10~4 m~3/d,the shale gas exploration breakthrough,shale gas reservoir of Qiongzhusi formation of exploration area has a good exploration potential.as shale gas reservoir space,the research of porosity evolution have guiding significance for finding high quality reservoir and reservoir reconstruction after completion provides.Before the research of shale reservoir pore evolution,must first clear the influencing factors of shale pore characteristics,although many scholars have made a lot of analysis and study for the influencing factors of marine shale reservoir pore characteristics of Southern sichuan basin,there are few research work about Qiongzhusi formation and the less research work of shale porosity evolution.To make up the blank in the research of predecessors in this field,this paper using the scanning electron microscopy(sem),the log data,core analysis data,nitrogen adsorption experiments et al to research characteristics of porosity of Qiongzhusiz formation in the study area.found that the Qiongzhusi formation shale reservoir pore is divided into organic pore,inorganic qualitative pore and fracture,organic pore can be divided into pyrite intergranular pore and pore between the layers of clay minerals;Inorganic mass pore include clay minerals intergranular pore,brittleness mineral intergranular pore,intragranular dissolution pore,and pyrite intergranular pore.And then using the data of geological data,drilling core experimental analysis,whole rock X-ray diffraction and clay X-ray diffraction experiment analysis,comparative analysis of how to control characteristics of porosity of Qiongzhusi formation about diagenesis,clay minerals content,organic carbon content,organic matter maturity.Found that diagenesis are the main factors affect the pore space in early,the organic carbon content and organic matter maturity it mainly controls the formation and development of organic pore.Transformation of clay minerals mainly by influencing the pore structure to influence the size of the porosity.At last,through the above analysis,in combination with the sedimentary characteristics,burial history and other information to divide diagenetic evolutionary stages,establish a model of diagenetic evolution,combined with the mode of the organic matter evolution of shale reservoirs,clarify the pore evolution,set up the model of pore evolution.Study found that shale pore of Qiongzhusi formation experienced a process of rapid decrease-Slightly higher-down again.Stage of rapid decrease correspondence to early diagenetic stage,give priority to compaction,a small amount of dissolution and cementation,organic matter evolution immature,pore types is given priority to with primary pore,a small amount of secondary pore development,clay minerals content is given priority to with montmorillonite,kaolinite,a small amount of illite and smectite mixed layer.Stage of slightly higher correspondence to mid-diagenetic stage,diagenesis is given priority to with dissolution and cementation,transformation of clay minerals,organic matter in the mature and high mature stage,pore types is given priority to with secondary porosity,primary pore.Clay minerals is given priority to with illite and smectite mixed layer,illite,chlorite,montmorillonite,kaolinite in small quantities.Stage of again to reduce correspondence to late diagenetic stage,weak diagenesis,give priority to with cementation,organic matter in a mature stage,primary pores almost disappear,give priority to with secondary pore and fracture,clay minerals should give priority to with illite and chlorite,kaolinite,montmorillonite,illite and smectite mixed layer disappeared,but due to mid-diagenetic stage,in the cause of K~+in short supply in shale reservoir,lead to ransformation of clay minerals is not completely.result in the late diagenetic illite and smectite mixed layer content remains high,also contains a certain amount of kaolinite in reservoir.