吸附水膜厚度确定致密油储层物性下限新方法——以辽河油田大民屯凹陷为例

伴随着致密油开采工艺技术的提高，其储层的可采物性下限也正逐渐降低，开采极限越来越接近致密油的成藏物性下限。引用水膜厚度理论，采用实验分析和理论计算相结合的方法，确定了辽河油田大民屯凹陷致密油储层物性下限。研究表明：大民屯凹陷沙河街组四段致密储层以油页岩为主，在相同地质条件下颗粒表面吸附的一层水膜（由强结合水和弱结合水组成）与储层喉道同处纳米级别。当喉道半径小于水膜厚度，相应孔喉及其所控制的微小孔隙则被束缚水所饱和；当喉道半径大于水膜厚度，喉道才能成为致密油有效的充注通道。通过对水膜厚度的受力分析，根据力平衡关系，可建立不同地层压力下水膜厚度与喉道半径的关系，进而求取致密油充注的临界喉道半径。通过借鉴土壤学中水膜厚度与孔隙度、比表面积及束缚水饱和度关系，又可把临界喉道半径下限值转化为适用范围更广的孔隙度下限值。该方法不仅理论依据强，又有实验数据支撑，具有一定的推广性。

A new method to determine porosity and permeability cutoffs of tight oil reservoirs by using thickness of adsorption water film: A case study from the Damintun Sag,Liaohe oifield

With the advancement of exploitation technologies of tight oil,the porosity and permeability cutoffs of tight oil exploitation have been greatly reduced,and are approaching to that of tight oil accumulation.In combination with experimental analysis and theatrical computation,this paper introduced the water film theory to determine the porosity and permeability cutoffs of the Damintun Sag.The results show that tight reservoirs mainly consist of oil shale in the 4^th Member of the Shahejie Formation in the Damintun Sag.Under the same geological conditions,there are water films (composed of strong bound water and weak bond water) adsorbed on the surface of tight sand particles.The minimum throat radius is equal to the thickness of water film which is so small that they can only be measured with nanometers.When the throat radius is smaller than water film thickness,the pore is filled with bound water.Only throats whose radius are larger than the film thickness can be valid oil charging pathways.Based on equilibrium of forces,relationship between water film thickness and throat radius is established,and the minimum throat radius valid for oil charging is calculated.The relationship of water film thickness with porosity,specific area and bound water saturation can be used to turn the critical value of throat radius into the critical porosity.This method not only has strong theoretical basis,but also the support of experimental data.