Abstract: 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.

Key words: permeability, activation energy, compositional kinetics, reaction kinetics, in-situ heating, pyrolysis of organic matter, low maturity, shale oil