压汞法和气体吸附法研究富有机质页岩孔隙特征

Determination of organic-rich shale pore features by mercury injection and gas adsorption methods

页岩储层孔隙由宏观裂缝到微观纳米级孔隙构成,具有较低的孔隙度。为了对页岩孔隙进行有效分析,将页岩中的孔隙分为3类并分别运用相应的方法对其进行测定:①页岩中的微孔(<2nm)应用CO2低温吸附法(D-R方法)测定;②介孔(2～50nm)应用N2低温吸附法(BET理论)测定;③宏孔(>50nm)应用高压压汞法测定,进而对孔隙分布进行全面分析。利用以上方法对中国典型海相和湖相页岩孔隙进行测定并分析孔隙发育控制因素后发现:①四川盆地海相页岩孔隙发育,其中牛蹄塘组、五峰组较好;②页岩中宏孔主要与矿物相关,微孔、介孔主要与有机质相关;③随着热演化程度升高,页岩中有机孔隙逐渐增大。

The porosity of gas shale is comparatively low,commonly in a macropore to nano-scale range.In order to effectively assay pores of gas shale,mercury injection and gas adsorption methods were applied,respectively,to determining different porosity of organic-rich shale.The gas adsorption of carbon dioxide at 0℃（D-R）,capable of the access to the porosity as fine as 0.35 nm,was chosen to determine micropores（〈2 nm）.Mesopores（2~50 nnm） were determined using the nitrogen adsorption（at-196℃） method（BET theory） while macropores（〉50 nm） measured with the high-pressure mercury injection method.Therefore,a combination of mercury-injection data with low-pressure nitrogen and carbon dioxide adsorption analyses can provide a more comprehensive assessment of different pore-size distributions.Characteristics of different pores in typical marine and lacustrine shales in China and their influencing factors were recognized by means of the above-mentioned approach as follows： ①pores are well developed in marine shales of the Sichuan Basin and the highest porosity is found in the Niutitang and Wufeng Formation shale;②macropores in shales develop mostly related to minerals,while micro and mesopores develop mainly related to organic matter;③with the increase of thermal maturity,organic pores in shales becomes gradually larger.