基于油气输导门限与组合控藏作用定量预测有利勘探区带的新方法——以珠一坳陷珠江组下段为例

A new method based on hydrocarbon migration threshold and combined reservoircontrolling function for quantitatively predicting favorable hydrocarbon exploration zone:a case study of the lower Member of Zhujiang Formation in Zhu Ⅰ depression

以南海珠江口盆地珠一坳陷为研究对象,对其油气输导条件进行综合分析,探讨油气输导主控因素与模式,预测油气有利勘探区带。研究结果表明:断裂、连续性砂体、构造脊以及不整合面是油气输导的4大主控因素,各主控因素表现出门限控藏特征;珠一坳陷已发现油气藏全部分布在以断裂为中心12km、地层含砂率介于25%~75%和距离构造脊顶点相对距离为1的范围内;烃源岩排烃边界与基底构造脊之间的不整合区域可供油气发生侧向运移。通源断裂、连续性砂体、构造脊3个地质要素输导门限的叠加复合控制了源内垂向输导模式有利运聚区;不整合面、非通源断裂、连续性砂体、构造脊4个地质要素输导门限的叠加复合控制了侧向阶梯状输导模式有利运聚区。应用上述研究成果,对珠一坳陷珠江组下段有利勘探区带进行了预测,认为恩平中半地堑、西江北—西江南半地堑、惠州凹陷、陆西半地堑是油气运聚有利区;用已发现油气田对预测结果进行检验,结果显示84.8%的油气储量和92.1%的油藏都分布在上述预测有利区带内,验证了该方法的有效性和可靠性。

Taking Zhu I depression at Pearl River Mouth Basin of South China Sea as the research subject,this study performs comprehensive analysis on hydrocarbon transport conditions,explores key controlling factors and mode of hydrocarbon migration,and predicts favorable exploration zones.The results indicate that fault,continuous sandbody,structure ridge and unconformity surface are four key controlling factors for hydrocarbon migration,and each of them is characterized by the threshold controlling reservoirs.In Zhu I depression,it is found that all hydrocarbon reservoirs are distributed within range of 12 km from fault center,with 25%-75% sand content and relative distance of 1 to the structure ridge.The uncomformity area between hydrocarbon expulsion boundary of source rock and structure ridge of basement enables lateral hydrocarbon migration.The migration threshold of three geological factors,i.e.,connected-source rock fault,continuous sandbody and structure ridge,are superimposed and compounded to control favorable migration and accumulation area under the mode of vertical migration in source rocks.The migration threshold of four geological factors,i.e.,uncomformity surface,unconnected-source rock fault,continuous sandbody and structure ridge,are superimposed and compounded to control favorable migration and accumulation area under the mode of lateral ladder-like migration.The above research results are applied to predict favorable exploration area in the lower Member of Zhujiang Formation,suggesting thatsemigrabens in central Enping sag,in the north and south of Xijiang and in the west of Lufeng sag,as well as Huizhou sag are the favorable zones of hydrocarbon accumulation and migration.The discovered oil and gas fields are used to verify the predicted results.The results show that 84.8% of hydrocarbon reserves and 92.1% of hydrocarbon reservoirs are distributed within the above predicted zones,which proves the effectiveness and reliability of this method.