油气初次运移理论新探

应用渗流力学的基本原理,研究油气初次运移的机制问题。研究认为,油气的初次运移是以连续相、而不是以溶液相和扩散相的形式进行的;油气初次运移的动力是浮力,因而初次运移的方向是向上的;油气初次运移所需的时间与源岩的渗透能力有关,与油气的粘度有关,还与源岩的厚度有关;油气藏的异常高压是一种暂时的压力状态,气藏的异常高压多于油藏,新生油气藏多于古油气藏;油气初次运移的通道就是源岩的粒间孔隙,源岩的非均质性和微裂缝对油气初次运移十分不利,因形成微油气藏而降低油气运移效率;源岩的厚度越大,越有利于油气聚集;“倒灌”现象是不存在的,缺少基本的动力驱动,基岩油气藏的形成是二次运移过程中侧向运移的结果。初次运移与二次运移具有相同的动力机制、运移相态和运移方向,因而两者是完全统一的。

New viewpoints of the primary migration of oil and gas

The present paper deals with the driving mechanism of primary migration of oil and gas based on the fundamentals of flow mechanics in porous media. The main conclusions are as follows. Oil and gas flow out of source rocks as a continuous phase of oil and gas, but not as a water solution of oil and gas or as diffusion. Buoyancy is the main driving force for the primary migration, and the direction of flow is upward. The time necessary for primary migration to occur is related to the permeability of source rocks, the viscosity of oil (gas) and the thickness of source rocks. The abnormally high pressure of reservoirs is temporary. Gas reservoirs can tolerate abnormal pressures better than oil reservoirs, whereas younger reservoirs can tolerate abnormal in pressure better than older reservoirs. Channels of migration are the intergranular pore spaces of source rocks. The heterogeneity and micro-fissures in source rocks will retain the oil and gas in-situ forming micro-reservoirs, and for this reason are unfavorable to primary migration. The large thickness of source rocks is conducive to the accumulation of oil and gas. Down-flow in primary migration is impractical and cannot occur, owing to the lack of a suitable driving force. The basement rock reservoirs are the result of lateral flow of oil and gas during secondary migration. The driving mechanism, the phase and migration direction are identical both in primary and secondary migrations, so that they can be unified.