致密砂岩气成藏研究进展及值得关注的几个问题

Progress of research on hydrocarbon accumulation of tight sand gas and several issues for concerns

连续型致密砂岩气藏是一种非常重要的非常规天然气。为了解该类气藏成藏地质研究进展,总结了其储层划分标准、分类、地质特征、成藏要素及封闭机制等方面的研究成果。分析认为,现有致密储层的划分标准不具有成藏内涵,连续型致密砂岩气的临界条件是随成藏条件而变化的。连续型致密砂岩气的成藏要素包括烃源岩、与源邻接的致密储层以及稳定的构造环境。需要注意的是,储层致密的本质是储层具有纳微观尺度的孔喉,且喉道与孔隙比例非常接近;异常压力属性不是致密砂岩气藏和常规气藏的区别点。文中提出了连续型致密砂岩气成藏机理值得深入研究的问题:一是致密砂岩气藏封闭的动力学机理研究,气、水倒置界面处存在动力(气体压力)与阻力(毛细管力、粘滞力及地层水压力)的力平衡关系,如何定量表征和模拟各种力的演化过程显得尤为重要;二是致密砂岩气藏的调整改造机理和过程及原型致密砂岩气藏恢复的研究,原型气藏的恢复可以通过气、水界面处的力平衡关系实现,后期不同的调整改造作用都是通过改变气、水倒置的临界条件而实现的;三是致密砂岩储层中"相对高孔渗体"的控藏作用研究,"相对高孔渗体"的存在改变了连续型致密砂岩气成藏条件,使得其成藏过程更为复杂。

Continuous tight sand gas is a significant unconventional resource for natural gas. To understand the progress of geological research on this kind of gas reservoir, this paper summarized the criteria for identification of tight sand reser- voirs, their classification, geological characteristics, elements of hydrocarbon accumulation, and trapping mechanisms. The current criteria for identivation of continuous tight sand gas reservoirs does not take accumulation conditions into conside- ration. The real critical conditions of tight sand gas change along with hydrocarbon accumulation conditions. The key ele- ments of hydrocarbon accumulation in tight gas reservoir involve hydrocarbon source rock, tight sandstone close to source rock and stable tectonic environment. It should be noted that the nature of tight sandstone is nano-micro scale pore throat and the percentage of pore throats is about the same as that of pores, and that abnormal pressure is not an essential differ- ence between tight sand gas reservoir and conventional gas reservoir. Several key issues concerning continuous tight sand gas accumulation are presented. The first is study on dynamic trapping mechanism for tight sand gas reservoir, i. e. the force balance between driving force （gas pressure）and resistance （capillary force, viscous force and formation water pres- sure） at the interface of gas water inversion. The quantitative description and simulation of evolution of these forces are particularly important. The second is the research on the mechanism and process of adjustment of tight sand gas reservoir as well as restoration of the original tight sand gas reservoir. The restoration of the original reservoir can be realized by means of force balance relation at the interface of gas water inversion. All of the late adjustment and modification were realized through changing the critical conditions of gas water inversion. The third is study of the control of sandbodies with relatively high porosity and permeability on gas accumulation in tight sandstone. The existence of these sandbodies chan- ges the accumulation conditions and complicates the accumulation process.