Evaluation Of Micro-Pore Throat And The Percolation Characteristics Of Gao-3 Reservoir Group In Qijia Area

The micro-pore throat distribution of Gao-3 reservoir group in Qijia area is wide,the pore throat structure is complex,the fluid seepage resistance is large,and the micro-scale seepage mechanism is complex.In this paper,the development of pore throat was evaluated on multi-scale by means of high pressure mercury injection,environmental scanning electron microscopy and casting thin section,and the characteristics of micro-scale seepage were discussed.The Gao-3 reservoir group in the study area is mostly lithic feldspar sandstone and feldspar lithic sandstone.The main minerals are quartz,feldspar and lithic debris,with relatively low porosity and permeability.According to the shape of mercury injection curve,displacement pressure and other related parameters,combined with the relative permeability,the reservoirs of Gao-3 reservoir group can be divided into conventional reservoir,low permeability reservoir,tight reservoir type I and tight reservoir type II,in which the conventional reservoir is mainly located in the northwest of the study area.According to the inflection point position of mercury injection curve of various reservoirs,combined with the microscopic characteristics of scanning electron microscopy and the relative permeability,the pore throats of various reservoirs are divided into three grades: macropore,transition pore and small pore.Based on mercury injection to simulate the filling process of oil and gas,according to the volume increment of mercury injection and the corresponding capillary pressure,combined with the definition of expectation and variance in mathematics,the "grading parameters" are introduced to evaluate the pore throats at all levels.Based on the existing pore-throat connection model and established a new pore-throat connection model.The permeability formula is derived by combining the relevant mathematical and physical formula theorems.According to formula,the concept of "seepage control factor" is introduced and the identification chart of the lower limit of flowable pore throat is established.The lower limit of seepage is determined according to the intersection point of curve and abscissa,and the seepage characteristics of fluid in it are discussed.