塔里木盆地西克尔露头区鹰山组古岩溶特征及其储层意义

摘要

鹰山组上段因主要发育岩溶型储层而成为塔里木盆地奥陶系的重要含油气层，但因钻井资料的局限储层特征难以精确揭示。塔里木盆地西缘西克尔地区经历了多期构造运动，发育了多期不整合之下的表生岩溶作用，出露的鹰山组发育丰富的古岩溶现象，为研究鹰山组岩溶储层特征和揭示岩溶储层成因规律提供了良好的条件。通过野外剖面和室内薄片观察和描述，识别出了大型溶洞及其充填物、小型溶孔以及构造裂缝和溶蚀缝等。强烈的表生岩溶作用形成的溶洞和角砾岩可直接形成溶洞型储层；小型溶孔广泛发育，常与溶蚀缝伴生形成孔洞型或缝洞型储层；多期构造裂缝叠加在岩溶储层之上，能显著提升储层的渗透性。结合岩相分析表明，颗粒灰岩中溶孔的发育密度要明显高于泥晶灰岩；同时溶蚀缝和构造裂缝也更易发生在颗粒含量高的灰岩中，从而形成裂缝型和孔洞缝复合型有利储层。%The Yingshan Formation is one of the most important oil and gas reservoirs for Tarim Basin due to the karstification developed in upper part of the formation.However,the detailed characteristics of reservoir can not be precisely unraveled on the basis of limited well data.The Xiker outcrop area,located in the west of Ta-rim Basin,has undergone multiple tectonic movements since Ordovician.Karstification developed at these tec-tonic unconformities.Therefore,the exposed Yingshan Formation shows varied paleokarst characteristics.By field and thin-section observation and description,diverse karst-characteristics have been identified,including large caves,cave breccias,vugs,fractures and dissolution channels.Caves and breccias,produced by intense dissolution and collapse,can directly form reservoir.Dissolution vugs are widely developed and usually genera-ted with dissolution channels and fractures.Multiple tectonic fractures can significantly increase the permeability of the karst reservoir.Combining with the lithofacies of the Yingshan Formation,the grain-dominated limestones have greater density of dissolution vugs than lime mud dominated limestones have.In addition,dissolution channels and tectonic fractures are more likely to be generated in limestones with higher grains ratio.As a result,the high-quality fracture reservoir and compound reservoir with vug,cave and fracture are produced.