深层优质砂砾岩储层特征及主控因素:以准噶尔盆地四棵树凹陷高泉构造带白垩系清水河组为例

Characteristics and Controlling Factors of High Quality Deep Conglomerate Reservoir:A Case from Lower Cretaceous Qingshuihe Formation of Gaoquan Structure Zone in Sikeshu Sag,Junggar Basin

准噶尔盆地南缘四棵树凹陷高探1井在白垩系清水河组底部砂砾岩储集层获得高产油气流,证实该套砂砾岩为优质储集层.利用岩心、岩石薄片等资料和储集物性分析、X射线衍射全岩矿物分析等测试手段,系统讨论了四棵树凹陷高泉构造带清水河组砂砾岩岩石矿物、储集物性、孔隙结构、成岩作用及其演化模式,并分析了优质砂砾岩储层的主控因素.清水河组砂砾岩的砾石成分主要为凝灰质,砂级碎屑颗粒含量普遍少于50%,根据砾石接触关系和砂级碎屑含量可将清水河组砂砾岩划分为颗粒支撑砾岩和基质(砂级颗粒)支撑砾岩两类.砂砾岩储层的主要储集空间为剩余粒间孔,孔隙均一性差;储集空间发育受多种成岩作用影响,其中,压实作用是主要的减孔因素.砂砾岩储层经历了早期长期浅埋和后期快速深埋的埋藏过程,目前处于中成岩阶段A期.清水河组砂砾岩优质储层的形成受多方面因素控制,其中,扇三角洲前缘水下分流河道砂砾岩是优质储集层形成的基础,较低的地温梯度及长期浅埋、短期深埋的埋藏方式是优质储集层形成的关键因素,先碱性、后酸性的成岩环境和异常高压是优质储集层形成的重要因素.

High-production oil flow was obtained from Lower Cretaceous Qingshuihe Formation in Well Gaotan-1,which is located in the southern margin of Junggar Basin.The result proves that high-quality conglomerate reservoirs are developed in Qingshuihe Formation.In this paper it analyzes the rock minerals,physical properties,pore structure and diagenesis of the conglomerate of Qingshuihe Formation in Gaoquan structure zone,Sikeshu sag,by using cores and thin section data,porositypermeability analysis and X-ray diffraction whole rock mineral analysis.The main controlling factors of high-quality conglomerate reseroirs were analyzed based on the result.The studies show that the tuffaceous gravels are the major content of the reservoir.The content of sandy grains is typically less than 50%.Based on the contact relationship of the gravels and the content of sandy grains,the conglomerate can be divided into grain supported conglomerate and matrix supported conglomerate.The reservoir space is strong in heterogeneity,which is dominated by primary pores.The development of reservoir space is affected by a variety of diagenesis,among which physical compaction is the major contributor to the porosity loss.The conglomerate reservoir has undergone the burial process of early long-term shallow burial and late rapid deep burial,and is currently in the mesogenesis stage A.The forming of high-quality conglomerate reservoir derives from the following controlling factors.Conglomerate from underwater distributary channels in fan-delta front is the foundation to form high-quality reservoir.Low geothermal gradient and the the burial process of early long-term shallow burial and late rapid deep burial are key contributors to the formation of the reservoir.The alkaline diagenetic environment in the early stage of diagenesis and later acid diagenetic environment,as well as the overpressure are also important to the formation of the reservoir.