Study On Micro Characteristics Of The Low Permeability Reservoirs Of The Upper Mengyin Formation In Gaoqing Area

The low permeability reservoirs of the Upper Mengyin Formation are target exploration sequence of Gaoqing Area.At present,a lot of research work has been done in the Gaoqing Area in terms of tectonic,sedimentary,and reservoir-forming aspects.However,there are few systematic studies on microscopic features,which restricts the further exploration and development of the Mesozoic.With the guidance of theories such as subsurface geology of oil and gas fields,petroleum geology,petrophysics and reservoir geology,and based on the description of cores,and a lot of data of conventional thin section,casting thin section,cathodoluminescence,fluid inclusions,X-ray analysis,election microprobe and Hg injection,a systematic study of reservoir features of lithology and mineralogy,diagenesis features,pore structure characteristics,low permeability genesis,etc.was conducted,and reservoir classification and evaluation were performed.The results show that:(1)The reservoirs are mainly composed of feldspar quartz sandstone and lithic feldspar sandstone.The main diagenesis is manifested by strong compaction,carbonate mineral cementation,clay mineral cementation,siliceous cementation,calcite metasomatism,feldspar dissolution and quartz dissolution.The sandstones have entered a period of middle diagenetic stage A.(2)The main pore types were residual intergranular pores,intergranular dissolution pores,intragranular dissolutin pores,and cementation dissolution pores.Lamellar throat and curved throat are the main throat types.The pore throat has a large radius,but the pore throat is poor in sortability,and the connectivity of the pore and throat is well.(3)The deposits of reservoir are relatively fine size,controled by sedimentation.Compaction and cementation tightened the low permeability property.They are main causes of the low permeability reservoir of the Upper Mengyin Formation.(4)Based on the research,the reservoir is classified into three classes.The most widely distribution is type ?.It is also the best reservoir type of the Upper Mengyin Formation,distributed in braided channels and allubial plains.Type ? reservoir is relatively poor,distributed in braided channels and allubial plains.Type ? reservoir is the least and poorest reservoir,distributed in allubial plains.