Study On Pore Structure Characteristics Based On Constant-rate Mercury Injection

The pore structure of reservoir is about the geometry, size, distribution and connection of pore and throat, which is a major research object of petroleum geology, petroleum exploration and development. As the petroleum industry develops, reservoir research becomes more and more important, not only deciding reservoir sizes but also directly controlling eventual recovery and production of oil and gas wells. Pore structure character is the core of reservoir research. Mostly general core analyses method is used to study reservoir pore structure which can provide porosity, permeability and saturation data before constant-rate mercury injection method appears. Special core analyses method can provide capillary pressure curve, wettability and relative permeability data. Constant-rate mercury injection method enhance the cognition on reservoir by not only providing pore distribution and separating pore with throat, but also acquiring pore and throat quantity and providing three kinds of capillary pressure curve shapes. Special surface area represents the rate of divergence of rock particles, i.e. the total surface area of all rock particles of per unit volume. The more fine particles in the rock, the bigger specific surface area it has, vise verse. The specific surface area of rock has effect on flow of liquid in the reservoir, surface phenomenon and filtration resistance when the liquid flows in the rock, permeability and liquid adsorption to rock surface. It was considered that specific surface area of the rock was the function of permeability and porosity. Now specific surface research is far away perfect, it is usually measured by adsorption test which needs some hypothesis conditions and limitations exist. This paper contains two parts, one of them aims to study pore structure of three permeability classes’cores (mid high permeability, low permeability and ultra-low permeability), analyzing pore, throat and pore throat ratio distribution characters and exploring their effect on porosity and permeability, which shows that there is an inverse correlation between permeability and pore throat ratio. The other part tries to calculate specific surface area of rock from constant-rate mercury injection test data, comparing the results with adsorption test and exploring the effect of specific area on permeability, end saturation and eventual recovery, which shows that the specific area calculated from constant-rate mercury injection test is reliable and specific area has an inverse correlation with rock permeability, as well as recovery, but a proportional correlation with end saturation.