低成熟度页岩油加热改质热解动力学及地层渗透性

低成熟度页岩油加热改质是采用加热井对地层进行加热,将地层中滞留的重质烃转化为轻质烃,同时将尚未转化的固体有机质热解生成油气后采出。热解油气生成量预测及地层孔渗变化是页岩油改质开采研究的难点和挑战之一。利用页岩井下取心样品,采用黄金管实验装置,研究了页岩加热过程中的有机质热解规律及组分动力学,获得了烃类气体、轻质油及重质油的生成动力学参数。结果表明,在温度为280～500℃范围内,油的生成量先增后减,而气体量持续增加;低速升温条件下的转化率随温度变化曲线左移,热解温度变低。重质油、轻质油和气态烃的活化能分别为39～49,57～74和56～59 kcal/mol;动力学模型可预测任意时间的烃类生成量。应用三轴高温渗透率测试装置,获得了页岩从室温到高温(550℃)条件下的氮气测试渗透率动态变化规律。结果显示,页岩加热过程中的渗透性变化分为下降段、上升段和稳定段,在温度达到有机质热解温度后,基质及裂缝渗透率均出现明显改善,比初始渗透率提高1～2个数量级。热解油气生成量及渗透率变化可为低成熟度页岩油加热改质开采的产量预测提供依据。

Organic matter pyrolysis kinetics and formation permeability variation during upgrading process of low-maturity shale oil

Shale oil upgrading entails heating of formation through boreholes to convert heavy hydrocarbons in pore space into light ones,and it also stimulate the generation of oil and gas from kerogen through pyrolysis.Prediction of hydrocarbon yield through pyrolysis and changes of formation porosity and permeability are the challenges for shale oil upgrading and recovery.Organic matter pyrolysis and composition transformation in sample cores from shale wells during heating process using gold tube testing device were observed,and the formative kinetic parameters of hydrocarbon gases,light and heavy oil were calculated.The results show that oil generation increases first and then decreases through the temperature range of 280℃-500℃ while gas generation increases constantly.Under lower heating rate,the conversion curve shifts to the left and the pyrolysis temperature decreases.The kinetic parameters of pyrolysis of heavy oil,light oil and hydrocarbon gases were obtained,and the kinetic model can predict hydrocarbon generation amount at any time.The activation energy of heavy and light oil as well as gaseous hydrocarbons is 39-49 kcal/mol,57-74 kcal/mol and 56-59 kcal/mol respectively.In addition,shale permeability variation during the heating process (from ambient temperature to 550℃) were measured through nitrogen tests under triaxial stresses and high temperature.The results show that the permeability curve during the heating process can be divided into three stages,namely descending,ascending and stabilizing stages.Both the matrix permeability and fracture permeability improve remarkably by 1-2 orders of magnitude when reaching pyrolysis temperature.In short,generation of pyrolysis hydrocarbons and permeability variation may serve as a basis for production prediction of oil upgrading and recovery in low-maturity shales.