砂岩夹层储层分级评价及展布特征——以松辽盆地长岭凹陷大情字井地区青山口组一段为例

Classification evaluation and distribution characteristics of sandstone interlayer reservoirs:A case study of the first member of Qingshankou Formation in Daqingzijing area,Changling Sag,Songliao Basin

松辽盆地南部青山口组一段夹层型页岩油具有良好的勘探潜力,其夹层品质对含油性及产能影响大。然而,夹层物性呈现较强的非均质性,急需对夹层储层进行表征与描述,建立一套适合夹层储层的分级方案。通过场发射扫描电镜、高压压汞、核磁共振等实验对储层进行表征,基于压汞分形理论,建立适用于砂岩夹层的储层物性分级标准,结合测井资料对储层物性参数进行预测,进而刻画夹层优质储层平面展布。研究表明:根据源岩成熟度的差异,松辽盆地南部大情字井青一段可分为低熟区(R_(o)<1.0%,R_(o)为镜质体反射率)和中高熟源岩区(R_(o)>1.0%),夹层物性随烃源岩成熟度增大而变差。根据储层物性差异特征,分区块建立了夹层物性分级标准,将砂岩夹层分为Ⅰ—Ⅲ类和无效储层;由Ⅰ类储层到无效储层的大孔含量和中孔含量依次变少,储集空间由粒间孔、粒间溶蚀孔过渡至粒内溶蚀孔和晶间孔;压汞形态由弱平台型、缓直线型过渡至上凸状,储层含油性逐渐变差。优质夹层“甜点”主要沿着河口坝主体、水下分流河道等沉积微相分布,厚度自西南向东北方向减薄。研究成果为该区青山口组一段夹层型页岩油“甜点”优选提供重要支撑。

The intercalated shale oil within the first member of the Qingshankou Formation in the southern Songliao Basin exhibits significant exploration potential,primarily influenced by the quality of its intercalations,which impacts both oil content and productivity.The physical properties of these interlayers are notably heterogeneous,highlighting the necessity to characterize and describe interlayer reservoirs comprehensively and establish a suitable classification scheme.This study utilized advanced techniques such as field emission scanning electron microscopy,high-pressure mercury injection,and nuclear magnetic resonance to characterize the reservoir.Employing the fractal theory associated with mercury injection,a physical property classification standard tailored for sandstone interlayers was developed.This standard was combined with logging data to predict the physical property parameters of the reservoirs,facilitating the identification and mapping of high-quality interlayer reservoirs.The results delineate the first member of the Qingshankou Formation in the Daqingzijing area into regions of varying source rock maturity:low maturity areas with a vitrinite reflectance(R_(o))of less than 1.0%and areas with middle to high maturity source rocks(R_(o) greater than 1.0%).It was found that interlayer physical properties deteriorate as the maturity of the source rock increases.A grading standard for interlayer physical properties was established,categorizing the sandstone interlayers into ClassⅠtoⅢ,and deeming some as invalid reservoirs.From ClassⅠto invalid reservoirs,there is a sequential decrease in the content of large and medium pores,with reservoir space transitioning from intergranular pores and intergranular solution pores to intragranular solution pores and intergranular pores.The mercury injection profiles evolve from weak platforms and slow straight lines to convex shapes,indicating a gradual degradation in oil content.High-quality interlayer reservoirs are predominantly situated along the main body of the estuary bar and the underwater distributary channels,with the thickness decreasing from southwest to northeast.The findings of this research provide crucial insights for targeting interbedded shale oil prospects within the first member of the Qingshankou Formation in the southern Songliao Basin,assisting in the strategic selection of exploration and development sites.