潍北凹陷孔店组异常低压分布特征及成因机制

Distribution characteristics and contributing factor mechanism of the abnormal low pressure zones of the Ek in Weibei Sag

潍北凹陷孔店组异常低压主要分布在北部洼陷带孔二段地层中。应用流体包裹体方法和盆地模拟方法恢复了古压力,发现油气充注时(孔店组末期—沙河街组早期)古压力系数为1.12-1.66,表现为超压状态。潍北凹陷孔店组压力场演化经历了"压力积累—压力释放—压力分异"3个阶段,古压力演化可分为3种模式:北部洼陷带发育"超压—低压—弱超压"压力演化模式;瓦城断阶带和灶户断鼻带发育"超压—低压—低压"压力演化模式;南部斜坡带发育"常压—低压—常压"压力演化模式。分析认为,构造抬升作用和地温降低的共同作用是潍北凹陷发育低压的基础条件,地下流体供排不平衡和浓差作用促进异常低压发育。

The abnormal low pressure developed in the Ek in Weibei Sag mainly distributed in Ek2 in the north of the Sag, The palaeopressure are restored by the fluid inclusions and basin modeling, the results show that the palaeopressure coefficients were 1.12-1.66 while the hydrocarbon filled in from the last stage of Ek to the early stage of Es, it showed super pressure. The evolution of the pressure field of Ek had experienced three stages （pressure buildup-pressure release-pressure differentiation）. The evolution of the palaeopressure could be divided into three patterns, they were the overpressure-low pressure-weak overpressure in the north of the Sag, overpressure-low pressure-low pressure in fracture zone of Wacheng and fault nose zone of Zaohu and normal pressure-low pressure-normal pressure in the slope of the south of the Sag. Analyzed results show that the combined action of the tectonic uplift and formation temperature decrease is the basic condition to develop the low pressure in Weibei Sag, the supply-discharge imbalance and concentration effect of the subsurface fluid promoted the development of abnormal low pressure.