泥质岩封盖油气门限的确定

泥质岩盖层孔隙直径随埋深而减小,只有当其减小到等于或小于油、气分子直径时,泥岩盖层方能对任何相态的油气构成完全封闭,达到封盖油和气的临界点。根据油气分子直径和泥岩盖层孔隙直径随埋深呈函数变化的关系,可分别求出泥岩封盖油和气的门限深度,再根据地层厚度与沉积速率求出对应的门限时期。据Φ_m=54.74exp(-0.0009354z),K=0.136(Φ_e)^4.4/(S_WB)²和r=√8K/Φ的关系,求出松辽盆地三肇地区泥质岩盖层的封油门限深度为2500～3000m,封气门限深度为5000～5200m.这里所强调的是临界门限,并不排斥在未达到封盖门限深度的情况下,仍能依靠毛管压力、异常孔隙流体压力、烃浓度对油气的有效封盖。

DETERMINATION OF THRESHOLD OF ARGILLACEOUS ROCK SEALED HYDROCARBON

The pore diameters of argillaceous caprock decreases as its buried depth increased.Only when the pore diameters are as small as or even smaller than the diameters of oil and gas moleculars,the argillaceous caprock could seal completely every states of hydrocarbon,and reach the sealing critical point.According to this rule,the sealing threshold depths of argillaceous caprock for both oil and gas could be calculated.Then the corresponding threshold time value could be calculated based on bed thickness and the rate of deposition.According to Φ