相对盖层厚度封闭效应及其应用

提出了相对盖层厚度封闭效应的概念,并从理论、实验、实际应用3个方面论证了相对盖层的厚度封闭效应.理论上根据非达西流的渗流公式,油气的驱动压力梯度只有达到盖层启动压力梯度时才能穿过盖层发生渗漏.地层和流体性质确定时,启动压力梯度不变.随盖层厚度增加,盖层封闭油气不渗漏所能承受的油气的驱动压力增加,能封住的油气柱高度增加.实验中将盖层岩心进行拼接后测得的突破压力随岩心拼接长度增加而增加,且与拼接前测得的各段岩心突破压力之和成正相关的关系.相对盖层厚度封闭效应作为封盖机理之一,可以很好地解释柴达木盆地第四系生物气藏高孔渗、低突破压力的盖层条件下形成工业气藏的原因.

Thickness sealing effect of relative caprock and its application

The concept of the thickness sealing effect of relative caprock is put forward,and the thickness sealing effect of relative caprock is proven according to theory,experiments and practical application.Theoretically,it is known from the seeping formula of non-Darcy flow that petroleum can leak through caprock only when the driving pressure gradient is greater than the starting pressure gradient of the caprock;the starting pressure gradient is determined when the properties of stratum and the fluid are given,so with the increase of the caprock thickness,the caprock can afford the greater driving pressure of petroleum and the sealed petroleum column is higher.According to experiments,the breakthrough pressure of the connected caprock core increases with the increase of the length of the connected core and it is direct proportion to the sum of the breakthrough pressures of the connected cores.Practically,it is well interpreted using the thickness sealing effect of relative caprock why commercial biogenic gas pool can be formed in the Quaternary of Qaidam Basin under the caprock condition of high-porosity,high-permeability and low breakthrough pressure.