利津洼陷北部砂砾岩储层异常高孔渗带形成机制

Formation mechanism of anomalously high porosity and high permeability zone of sandy conglomerate reservoirs in northern Lijin Sag, Jiyang Depression

济阳坳陷利津洼陷北部利563块沙四上段发育厚层砂砾岩储层。基于岩心、测录井数据和储层微观观察等,明确了储层异常高孔渗带的存在及其形成机制。研究表明:2500~2900 m深度范围内异常高孔渗带特征显著;异常高孔渗带成因机制有石油早期侵入、异常高压作用、溶蚀孔隙和压裂缝的发育等。储层粒间及压裂缝中沥青质的残余说明石油早期侵入;泥岩声波时差曲线的异常高值说明异常高压的存在。岩心和薄片观察揭示研究区砾石中压裂缝广泛存在,并显著提升了储层渗透率。储层溶蚀面孔率整体为2%左右,压裂缝发育基础上的溶蚀扩缝作用可有效提高储层孔隙度。

Thick layers of sandy conglomerate reservoirs are distributed in the upper part of the Fourth Member of Shahejie Formation in Li-563 area,the northern Lijin Sag of Jiyang Depression.Based on the data of cores,logging,rock microscopic feature and physical property,the paper reveals the existence of anomalous porosity-permeability zone and its formation mechanism.The study finds that it is remarkable for the feature of anomalous porosity-permeability zone among the interal of 2,500-2,900 m.The formation mechanism of the anomalous porosity-permeability zone includes the petroleum emplacement in early time,anomalously higher pressure,dissolution pores and mechanical compaction fissures.The remaining bitumen among intergranular spaces and fissures indicates early petroleum emplacement.Anomalously higher values of interval transit time logging indicate the strata′s anomalously higher pressure.The observation of cores and thin sections reveals that the extensive existence of mechanical compaction fissures improves reservoirs′permeability remarkably.Surface porosity of dissolution pores is around 2%,and fissures′enlargement promoted by dissolution improves the reservoir porosity effectively.