碳酸盐胶结物对深层优质碎屑岩储层影响研究

The influence of carbonate cement on deep high-quality clastic rock reservoir

古近系沙河街组是渤海湾盆地的重要含油层系,但在渤海海域的渤中凹陷北部,沙河街组由于埋深大、成岩演化复杂,储层物性一般较差。为寻找深部优质储层,以辽西凸起南段LD25-AE构造油气的新钻探井为研究对象,针对沙一二段中孔中渗储层,基于多种实验手段,明确了碳酸盐胶结物对深层碎屑岩储层的影响。结果表明,储层内发育成分、成因和产状存在明显差异,分别为同生期生屑型、早期基底式胶结型和晚期交代富铁型3类碳酸盐胶结物;储层中方解石发生了同生期蒸发泵白云石化和晚期热液白云石化两期作用。同生期强烈的波浪淘洗导致粒间孔隙较为干净,利于胶结物发育;早期碳酸盐呈基底式胶结,保存了原生孔隙空间;有机酸溶蚀了早期碳酸盐矿物和长石颗粒,形成了大量次生孔隙。辽西凸起南段沙一二段富生屑碳酸盐混积型储层的发现进一步揭示了渤海海域3 500 m以深的勘探潜力,为海上少井区寻找古近系深部优质储层提供依据。

The Paleogene Shahejie Formation is a significant oil-bearing series in Bohai Bay Basin.However,in the northern part of Bozhong Depression in the Bohai Sea,the Shahejie Formation exhibits poor reservoir properties due to deep burial and complex diagenetic evolution.In order to explore deep high-quality reservoir,this paper focuses on the newly drilled LD25-AE structure well in the southern segment of the Liaoxi Uplift,which has shown promising oil and gas indications.The research,utilizing various experimental techniques,elucidates the impact of carbonate cements on deep clastic rock reservoirs within the medium-porosity and medium-permeability reservoir within the 1st and 2nd members of Shahejie Formation.The results indicate the presence of three distinct stages of carbonate cements in reservoirs,characterized by different compositions,origin and occurrence:syngenetic bioclastic carbonate,early basement cemented carbonate and late metasomatic iron-rich carbonate.Additionally,the calcite in the reservoir underwent two stages of dolomitization which are evaporative pump dolomitization and late hydrothermal dolomitization.The intense wave washing during the syngenetic period resulted in relatively clean intergranular pores,favorable for cement development.The early carbonates were cemented in a basal manner,preserving the primary pore space.Organic acids dissolved early carbonate minerals and feldspar particles,forming a large number of seconday pores.The discovery of this type of reservoir further reveals the exploration potential below 3 500 m depth in the Bohai Sea,providing a basis for identifying high-quality deep Paleogene reservoirs in offshore areas with limited wells.