珠江口盆地新近纪相对海平面变化精细表征及其对三角洲沉积演化的反映——以恩平凹陷恩平A油田韩江组—珠江组为例

Detailed Characterization of Neogene Relative Sea Level Change in Pearl River Mouth Basin and Its Control over Delta Sedimentary Evolution:Taking Hanjiang Formation and Zhujiang Formation of Oilfield A in Enping Sag as an Example

恩平凹陷恩平A油田在新近纪位于古珠江三角洲前缘,一方面由于砂体普遍偏薄,使得储层预测难度大,另一方面由于三角洲前缘河流作用和海洋作用的往复交替,也使得三角洲沉积微相变化复杂,影响后期的增储上产。针对上述问题,本文在钻井小层精细对比的基础上,充分利用测井解释成果,依据古三角洲地势平坦、地层厚度变化小的特点,采用砂层组平均砂岩体积分数表征相对海平面的变化;并进一步利用岩心和地震沉积学方法,确定主力砂层组的平面沉积相展布。研究表明:研究区珠江组、韩江组的砂层组平均砂岩体积分数能够较好地表征古海平面的相对变化,可以实现对五级相对海平面变化的精细刻画。通过对砂层组级别砂体的沉积微相分析,表明相对海平面变化与三角洲的沉积微相演化具有良好的对应关系,验证了基于砂层组平均砂岩体积分数来表征相对海平面变化的方法具有可行性,可以用来预测三角洲的演化和砂体的叠加关系。

Oilfield A in Enping sag was located in the ancient Pearl River delta front in the Neogene period.The sand bodies were generally thin,which made it difficult to predict the reservoir.The alternating of fluvial and oceanic processes also complicated the sedimentary microfacies transformation.These factors affect the increase of reserves and production in the future.Concerning the above problems,based on fine layer correlation and logging interpretation results,the average sandstone volume fraction in sand sets is used to characterize the relative sea level changes according to the characteristics of flat terrain and fewer changes in stratum thickness of ancient delta.Research shows that the average sandstone volume fraction of Zhujiang Formation and Hanjiang Formation in the study area can better represent the relative sea level changes and accurately describe the fifth order relative sea level change.By analyzing the sedimentary microfacies of sand sets,it revealed a good correspondence between relative sea level changes and the sedimentary microfacies evolution of deltas.The feasibility of characterizing relative sea level changes based on the average sandstone volume fraction of sand layers was verified,which can be used to predict the evolution of deltas and the superposition relationship of sand bodies.