The Forming Mechanism Of High Quality Reservoirs Of Huagang Formation In N Structure,Xihu Depression

The exploration of the East China Sea showed that the basin is widespread of oil and gas reservoir with low porosity and low permeability.The amount of natural gas trap resource is expected to more than 400 billion cubic meters,and it's very rich in resources.Researches of the reservoir diagenetic evolution for Xihu Depression has carried out,it is still not clear what are the formation of high quality reservoir,distribution and controlling factors,and it has seriously hampered the exploration and development of the high quality reservoirs in Xihu Depression.Huagang Formation of N structure in Xihu Depression is the main target Formation in this paper,and the the main target segments are H3,H4,H5,H6.Based on a lot of research about the sedimentary characteristics of Xihu Depression and a large number of relevant documents,using sedimentary petrology,reservoir geology theory and diagenesis theory as a guide,according to lots of slice analysis,combining with X-ray diffraction analysis,vitrinite reflectance,carbon and oxygen isotope,fluid inclusion,cathodoluminescence,scanning electron,core properties,reservoir pressure and other geochemical data.This paper studied H3,H4,H5,H6 characteristics of reservoir rock,pore structure and diagenesis,discussed the main types,characteristics and effects on reservoir properties.Establish reservoir formation and evolution models on this basis,and analyze the factors affecting the reservoir control.This paper mainly obtains the following main understanding and achievement:The main rock type of Huagang Formation in N structure is medium fine feldspar detritus quartz sandstone,accounted for more than 90%,and a small amount of feldspar lithic sandstone and lithic sandstone.The compositional maturity of sandstone is moderate,high maturity,well sorted,low matrix contents,and low content of cement.H3 and H4 reservoir types are mainly in the medium and low permeability and low porosity and extra low permeability reservoirs.H5 and H6 small layers are mainly low porosity and low permeability and low porosity and low permeability reservoirs.the secondary dissolution pore is the main pore type in the reservoirs,followed by primary pore,the pore throas are medium-thick,only fine in litharenite.According to the analysis of the fluid inclusions and the X-diffraction,Huagang Formation in this aera experienced early diagenetic stage A,B and diagenetic stage A and B,and also experienced weak alkaline-weak acid-strong acid-acid transfer tape-strong alkaline-weak alkaline stages.Three oil and gas filling occured,the strength of the former two is small,but the filled acidic fluid play a positive role in reservoir reconstruction.The third oil and gas Although the third phase of oil and gas filling strength is large,but a large number of cements produced with the organic acid being neutralized by alkaline fluid.So it has not much effect.Based on a large number of core properties measured date and the classification standard of East China sea basin,Xihu Depression reservoirs can be divided into I,II,III1,III2 and IV.The analysis results show that H3 and H4 are mainly I types of reservoirs,with a small amount of II and III2,and H5 and H6 are mainly of IV type.High quality reservoir can be divided into two types: conventional high quality reservoir and "dessert".Conventional high-quality reservoirs are mainly distributed in the H3 and H4 layer.The main controlling factor of reservoirs is compaction,followed by rock types and the source of the material.In low porosity and permeability reservoirs,the "desserts" are mainly distributed in the H5,H6 layer with mixed sand conglomerate,or a better medium coarse sandstone reservoir,which is poor in sorting,and has strong compressive strength in the buried process.