Numerical Simulation Of Oil Shale In-Situ Upgrading By Steam Injection

Oil shale is a combustible solid sedimentary rock with high ash content that mainly for the kerogen and a small amount of asphaltene.There is a lot of oil shale which converted into shale oil is about 2.5 times the global conventional crude oil reserves in the world.Currently,the main oil shale mining way is the ground dry distillation technology,however,which will bring polluting gases,high content of acid water and a large number of abandoned slag to the environment.Taking into account the issue of environmental pollution,oil shale in-situ upgrading technology has been the trend of large-scale commercialization in the future.The injection of steam with high temperature is an effective method for oil shale in-situ upgrading.Compared with the traditional ground dry distillation technology,the new technology have many benefits,such as environmentally friendly,high heating efficiency,good economic,and without damaging the shale reservoir.At present,oil shale in-situ upgrading by steam injection and its numerical simulation both are new research topics.In this paper,firstly,the characteristics of oil shale in the injecting high temperature steam process were discussed.As temperature rose,the main oil shale pyrolysis process was divided into three stages: drying and dehydration stage,kerogen pyrolysis stage and high temperature inorganic mineral decomposition stage.The experimental data on the relationship between oil generation rate,porosity,permeability and temperature of oil shale in three regions were studied.The curve fitting was carried out by using the cftool toolbox of MATLAB software to obtain the fitting relation of the oil shale that prepare basic data for numerical simulation.Secondly,CMG numerical simulation software was used to simulate oil pyrolysis experiment.In the process of establishing the numerical model,considered the change characteristic of the oil shale,the model was designed as a double porosity seepage geological model.The kerogen decomposition chemical reaction was explained by the alternating reaction mechanism that was simplified the decomposition process into three chemical reaction equations.The results show that the initial kerogen concentration,specific heat capacity,thermal conductivity,medium type,kerogen conversion oil and gas conditions,and transformation rules of Fushun oil shale could be sure by the experimental results.Thirdly,with reference to an oil shale in-situ electric heating project,the numerical model was established that the electric heating well was changed to steam injection well and the decomposition of kerogen was considered.The effects of these two main factors,injection of steam rate and heating range,on oil shale in-situ upgrading by steam injection were discussed.Finally,a five-point method was proposed for the actual demand of Fushun oil shale.The results show that: the oil generation rate,porosity,permeability and temperature change of the oil shale are similar to the statistical results,and the variation trend is consistent and the fitting error is small;In the process of simulating oil shale pyrolysis oil production,the numerical simulation results are compared by the experimental results.The numerical simulation results are in good agreement with the actual situation.So the oil shale steam injection pyrolysis numerical model has higher reliability.Compared with the in-situ electric heating,when steam injection in-situ heating oil shale,the temperature of oil shale layers is higher and the decomposition of kerogen is faster.The peak time of oil production also comes earlier.With the injection rate increases and the heating range decreases,the reaction rate of kerogen pyrolysis becomes faster and the shale oil production ends earlier.Fushun oil shale is designed for five-point well pattern mining.It begins to produce oil at the sixth month and the output is increasing.The output reaches the peak at the sixty months and the maximum peak yield is 3.14 t/day.Then,the output begins to decrease to zero which the final mining of the cumulative oil production is 6938.10 t.So this way has a better application potential.The results of this study will provide technical parameters and theoretical basis for field application of oil shale in-situ upgrading.