基于半封闭体系热模拟实验页岩全岩与粉末样品的排烃效率与孔隙演化差异对比

Comparison of expulsion efficiency and pore evolution between shale whole rock and powder samples in semi-closed thermal simulation experiments

与传统基于粉末样品的模拟实验相比,基于页岩全岩样品的模拟实验能更好地保存岩石微观结构及孔隙特征,结果更接近地质实际,但有关全岩与粉末样品的排烃效率与微观孔隙差异尚无系统的研究。本文利用半封闭体系热模拟实验获取延长组7段页岩全岩圆柱与粉末样品的排烃效率,并利用低压气体吸附实验表征孔隙特征。当Ro从0.61%升至1.68%时,粉末样品和圆柱样品的排烃效率差值最高达32.47%,随后降至3.98%,粉末样品孔隙分形维数从2.46增加至2.53,而圆柱样品分形维数总体稳定。圆柱样品宏孔体积比例整体随着温度的升高而上升,而中孔体积比例则逐渐下降。与粉末样品相比,页岩全岩样品保留了岩石结构,能反映烃类运移排出过程,孔隙演化更具规律性。本研究最终建立了页岩圆柱、粉末样品生-排烃过程与孔隙演化模型,为研究地质情况下页岩排烃效率与孔隙演化提供了新的思路。

Compared with the traditional powder sample-based simulation,the simulation results based on the whole rock sample are closer to geological conditions because it well preserves the micro-structure and pores of the rock.However,the difference in expulsion efficiency and pores evolution between whole rock and powder samples have not been systematically studied.In this study,we used thermal simulation experiments of semi-closed high-pressure system to obtain the expulsion efficiency,and used low-pressure N2/CO2 adsorption experiments to characterize the pore properties of whole rock columns and powder samples of the Chang7 shale.The results showed that when Ro increased from 0.61%to 1.68%,the difference in expulsion efficiency between powder samples and whole rock column samples reached a maximum of 32.47%and then decreased to 3.98%,and the fractal dimension of powder samples increased from 2.46 to 2.53,while the whole rock column samples were generally stable.With the increase of temperature,the total volume ratio of macro-pores in the whole rock column increased,while the volume ratio of meso-pores gradually decreased.Compared with powder samples,shale whole rock samples preserve rock structure,which can reflect the hydrocarbon migration/expulsion process and have more regular pore evolution.Finally,this study established a model of hydrocarbon generation/expulsion process and pore evolution of shale whole rock columns and powder samples,which provides new ideas for understanding the evolution of expulsion efficiency and pores of shale under geological conditions.