A Analysis Of Reservoir Characteristics And Main Controlling Factors In Paleogene Huagang Formation Of A Structure,Xihu Sag

In recent years,many pivotal researches have been carried out on the reservoir of Huagang Formation in Xihu Sag of the East China Sea,and great progress has been made in oil and gas exploration on the A Formation Huagang Formation reservoir.However,in the A Formation,the Huagang Formation sandstone reservoir show low-porosity and low-permeability reservoirs,the control factors for reservoir development need to be further studied,the geological background and conditions of reservoir development,diagenetic evolution mechanism,and pore evolution process are not yet fully understood.On the basis of the literature investigation in the study area,this paper carries out various research methods such as thin section observation,high-pressure mercury injection analysis,cathodoluminescence observation,clay mineral analysis,and inclusion temperature measurement to analyze the petrological characteristics,physical characteristics,and pore characteristics of the reservoir sandstones in the Huagang Formation,and the diagenetic evolution history and pore evolution history of reservoirs are restored,the main controlling factors of the reservoirs in the study area are comprehensively analyzed to promote the exploration and development of the A Formation Huagang Formation in the Xihu sag of the East China Sea.The main understanding is as follows:(1)Based on the analysis of core observations and thin sections of the Huagang Formation in the study area,it is considered that feldspar lithic quartz sandstone is main lithology of the A Formation Huagang Formation,and there are also some feldspathic lithic sandstones and lithologies sandstone.The content of quartz in this area is relatively high,and its grain size is mainly fine-medium sand,followed by coarse-medium sand,preference for sorting,roundness of secondary edge-secondary round,low content of miscellaneous materials and cement in interstitial,it can be seen that this area is clean sandstone and the physical property classification in this area is mainly for special geotechnical low permeability reservoirs.(2)Through the identification of cast thin slices and high-pressure mercury injection experimental data analysis,pore type and pore structure in the study area are known.The developed pores are primary pores,secondary pores,partial microfractures,and the total average porosity is 8.57%,secondary pores composed of intergranular dissolved pores,intragranular pores,and mold pores contribute greatly to reservoir porosity.According to the analysis,the changes in physical properties of reservoirs are negatively correlated with changes in expulsion pressure and median pressure,and are positively correlated with changes in median pore throat radius and average pore throat radius.(3)By using the cathodoluminescence analysis,casting thin section observation,scanning electron microscopy analysis and other technical methods,it is believed that the study area undergoes compaction,cementation and dissolution,and based on this,the diagenetic evolution sequence of the Huagang Formation in the A Formation was established and the pore evolution process was restored.The effect of compaction throughout the evolution of diagenesis has made more than 80% of the original pores disappear;precipitation of early carbonate minerals,deposition of quartz at the late edges,and deposition of authigenic quartz result in decreasing porosity;in the early atmosphere freshwater dissolution and later organic acid media reacted to feldspar and rock debris to form a large number of secondary pores,which have evolved to a porosity of approximately 7.65%.(4)According to the comprehensive analysis,rock and mineral associations,sedimentation,abnormal high pressure,and diagenetic differences jointly control the development of the Huagang Formation reservoir in the study area.The content of quartz in the rock particles is high,the content of the heterobasic is low,the sandstone has better sorting and rounding,the particle composition is diverse,and the quality of the reservoir is relatively good;sedimentary microfacies develop extensively on the puddle and riverbed deposits,favoring pre-existing pores and developing relatively good reservoir performance;the abnormal high pressure in the lower section of the Huagang Formation is very resistant to the compaction effect of the reduction hole and protects the pores;different diageneses have changed the process of pore development,and most of the pores have disappeared due to compaction and cementation,the early atmospheric freshwater and late organic acid fluids dissolved feldspar and other minerals in the rock,resulting in a large number of secondary pores and the development of relatively high-quality reservoirs.