油气初次运移的模拟模型

SIMULATION MODELS FOR PRIMARY HYDROCARBON MIGATION

提出了一种新的烃源岩排烃史模拟方法，把排烃过程划分为压实排烃和微裂缝排烃两个阶段，并分别建立了压实排烃模型、微裂缝排烃模型和扩散排烃模型。在压实排烃模型中，压实作用是油气初次运移的主要动力，除考虑烃源岩孔隙体积的压缩外，还考虑了烃源岩内由于粘土脱水、油气生成以及流体热膨胀造成的孔隙流体体积增大对压实排烃量的影响；在微裂缝排烃模型中，烃源岩内的异常高压是排烃的主要动力，造成异常高压的主要因素：压实作用、粘土脱水作用、油气生成以及扎隙流体的热膨胀等。这两个模型的特点是引入了热力学中的状态方程和流体相平衡准则，用以确定孔隙流体相态及饱和度的变化，并由此计算排烃量。利用这一方法可分别模拟出烃源岩的排油史和排气史。

This paper develops a new method to simulate hydrocarbon expulsion,In this method,hydrocarbon expulsion from source rock is divided into two main stages according to the fea-tures and the mechanism of hydrocarbon expuision under different burial conditions.The ex-pulsion of hydrocarbon in the first stage is mainly by means of compaction and diffusion,andin the second stage by means of microfracturing and diffusion,Therefore ,this paper sets upthree hydrocarbon expulsion models,namely compaction model,microfracture model and dif-fusion model.The compaction model in which the compaction of source rock is considered asthe main force for primary hydrocarbon migration. Taking into account not only the decreasein pore volume of source rock during compaction but the influence of the increase in pore flu-id volume resulted from clay diagenesis,hydrocarbon generation and the thermal expansion ofpore fluid as well.The microfracture model is based on the microfracturing mechanism of pri-mary hydrocarbon migration in which hydrocarbons are expelled from source rock by the ab-normally high pore fluid pressure through microfractures in a mixed phase of oil,gas and wa-ter. The main factors resulting in the abnormally highpressure compaction,clay diagenesis,hydrocarbon generation and the expansion of pore fluid are taken into account in the model.The expulsion amount of hydrocarbon through microfractures is calculated by the differenceof pore pressure and the fracture pressure of source rock.The important characteristics of theabove two models are that the equation of state and fluid phase equilibrium concept of ther-modynamics are used to determine the fluid phase behavior and saturation changes duringsource rock evolution,and hence to determine the amount of expulsion of hydrocarbons. Withthe above models,the oil expulsion history and the gas expulsion history can be simulated re-spectively.