平面压降梯度计算原则及其应用

Calculation and application of plane pressure decrease gradient

超压作为油气运移的动力条件,其变化速率与油气运移方式存在一定的关系。为定量判识超压盆地中油气运移方式,建立了应用地层压降梯度分析的计算思路与方法,并以渤海湾盆地沾化凹陷渤南洼陷为例进行了应用和探讨。以实测压力与单井预测压力为基础,对油气主要运移层系进行了压力分布特征分析,结合超压成因机制分区、沉积相变以及断层发育特征,分别对压力均匀降低区、沉积相变非均匀降低区和断层分割非均匀降低区采用不同的压降梯度计算思路进行计算。渤南洼陷深洼带的压降梯度最高,其次为断阶带、陡坡带以及缓坡带,且垂向连通的断层附近压降梯度较高,定量地解释了在超压控制下油气运移方式的变化特征,从而有效判识油气优势富集的位置。

As a driving force for oil and gas migration,the overpressure change rate has a relationship with oil and gas migration mode.In order to quantitatively identify the hydrocarbon migration modes in overpressure basins,some calculation ideas and methods of the application of formation pressure decrease gradient were established,and were applied in the Bonan Subsag,Zhanhua Sag,Bohai Bay Basin.Based on measured pressure and single well predicted pressure,the pressure distribution characteristics of the main hydrocarbon migration layer were analyzed.According to the characteristics of overpressure genesis,sedimentary facies and faults,different pressure drop gradient calculation methods were applied to the uniform pressure attenuation zone,the inhomogeneous pressure decrease zone of sedimentary facies transformation and the inhomogeneous pressure decrease zone of the faulted zone.The results show that the pressure decrease gradient is the highest in the deep sag of Bonan Subsag,followed by the fault step,steep slope and gentle slope zones,and the pressure decrease gradient near the vertically connected faults is higher.The variation characteristics of oil and gas migration mode under overpressure control were quantitatively explained so that the location of hydrocarbon enrichment can be effectively judged.