The Microcosmic Characteristics Of Bin-425 Extra-low Permeability Reservoir

The Bin-425 reservoir is a typical extra-low permeability reservoir.It is necessary to study the reservoir's microstructure to further understand the microscopic characteristics of the reservoir and provide basis for the formulation of technical policies for oilfield developme nt and adjustment.In this paper,starting from the core test of the target reservoir,the porosity and permeability of cores were determined by the gas permeability.On the basis,high-press ure mercury injection and nuclear magnetic resonance methods were used to measure and explain the core pore structure.Three kinds of boundary layer thickness test experiment schemes were set up and experiments were conducted to obtain the boundary layer thickness parameters.Based on the above results,the interrelationships between pore structure,permeability,porosity,and boundary layer thickness were comprehensively analyzed.In this paper,the permeability and porosity of 43 cores were measured by gas permeabilit y test and porosity measurement experiment.The experimental results showed that the gas permeability and porosity of the core in the same position are basically the same;the gas permeability in the core is relatively low,and the distribution difference is large.In the semi-logarithmic coordinate system,the permeability and porosity have good correlation,and based on the experimental results,the empirical relationship between permeability and porosity was fitted.Next,constant pressure mercury injection and nuclear magnetic resonance experiments were carried out.The surface relaxation rates of 30 cores were obtained by interpolation method.The core pore throat characteristics were explained,and the curves of median radius,average throat radius and permeability or porosity are derived,and an empirical formula is derived.The results showed that with the increase of median radius and average throat throat radius,the permeability and porosity increase obviously;the mercury removal efficiency increases with the increasing of the homogenization coefficient;the threshold pressure increases with the decrease of permeability.Especially when the permeability is less than 2×10^-3?m²,the threshold pressure rapidly increases.Based on the correlation between pore structure parameters,permeability,and porosity,it is initially proposed that the median pore radius is greater than 0.5?m,the porosity is greater than 9%,and the permeability is greater than 2×10^-3?m² as the judgement basis of effective reservoir in this reservoir.Finally,three experimental methods,speed difference method,mass difference method and centrifugal displacement method,were set up,and boundary layer thickness measurement was carried out.The results showed that the thickness of the boundary layer is related to the pore throat radius,displacement pressure gradient and displacement medium.When the pressure gradient is smal,the thickness of the boundary layer increases with the increase of the pore throat radius,and the thickness of the boundary layer increases firstly and then decreases with the increase of the pore throat radius when the pressure gradient is larger,.and the thickness of the boundary layer decreases with the increase of displacement pressure gradient,and the empirical relationship of the thickness of the boundary layer and displacement pressure gradient is regressed according to the experimental data.