鄂尔多斯盆地庆阳古隆起下古生界储层发育主控因素及成因模式

Main controlling factors and genesis models of reservoir development in Lower Paleozoic of Qingyang paleo-uplift, Ordos Basin

  • 摘要: 近年来鄂尔多斯盆地西南部庆阳古隆起下古生界深层天然气勘探取得了一定进展,但储层整体致密,优质储层形成机理复杂,对深层天然气“甜点”预测造成一定困难。基于钻井、测井、地震资料以及实验测试数据,对庆阳古隆起寒武系张夏组和三山子组、奥陶系马家沟组二段(马二段)和马家沟组四段(马四段)等含气层的储层发育类型、主控因素进行分析,建立了庆阳古隆起下古生界的储层成因模式。庆阳古隆起下古生界共发育4类储层,分别为白云岩储层、颗粒滩储层、岩溶型储层(表生岩溶型和断溶体型)和构造微裂隙储层,其中三山子组、马二段和马四段以白云岩储层为主,张夏组以颗粒滩储层为主,岩溶型储层及构造微裂隙储层在各层均有发育。沉积相带、风化壳、断裂对庆阳古隆起下古生界储层发育的控制作用明显,其中沉积相带控制着颗粒滩粒间(溶)孔和白云岩晶间(溶)孔的发育;两期风化壳控制着表生岩溶型储层的发育,以奥陶系顶部风化壳对表生岩溶控制最为明显,岩溶残丘控制了平面强溶蚀区的分布,纵向溶蚀强度、含气性则与距风化壳顶部距离关系密切;断裂控制着断溶体储层的分布,其伴生的微裂缝能有效改善储层物性。在此基础上,建立了颗粒滩—断裂型、残丘—断裂型、白云岩—岩溶型及白云岩—断裂型等4种储层成因模式,为庆阳古隆起下古生界天然气的勘探提供了思路。

     

    Abstract: In recent years, significant progress has been made in exploring the Lower Paleozoic deep natural gas of the Qingyang paleo-uplift in the southwestern Ordos Basin. However, the reservoirs in this region are generally tight, and the formation mechanisms of high-quality reservoirs are complex, making sweet spot prediction difficult. Based on drilling, logging, and seismic data, as well as experimental test data, this study analyzed the reservoir development types and main controlling factors of the gas-bearing layers, including the Cambrian Zhangxia Formation and Sanshanzi Formation, and the second and fourth members of the Ordovician Majiagou Formation (Ma 2 and Ma 4). A genesis model of the Lower Paleozoic reservoirs in the Qingyang paleo-uplift was established. Four types of reservoirs were developed in the region: dolomite reservoirs, shoal reservoirs, karst reservoirs (supergene karst and fault-karst reservoirs), and structural micro-fracture reservoirs. Among them, the Sanshanzi Formation as well as the Ma 2 and Ma 4 members mainly featured dolomite reservoirs, while shoal reservoirs dominated the Zhangxia Formation. Karst reservoirs and structural micro-fracture reservoirs were developed across all layers. The controlling effect of sedimentary facies belts, weathered crusts, and faults on the development of Lower Paleozoic reservoirs in the Qingyang paleo-uplift was significant. Sedimentary facies belts controlled the development of intergranular (dissolution) pores in shoals and intercrystalline (dissolution) pores in dolomite. Two phases of weathered crusts controlled the development of supergene karst reservoirs, with the weathered crusts at the top of the Ordovician being the most influential. Karst residual hills controlled the planar distribution of strong dissolution areas. The vertical dissolution intensity and gas content of reservoirs were closely related to their distance from the top of the weathered crust. Faults controlled the distribution of fault-karst reservoirs, and their associated micro-fractures effectively improved the reservoir properties. Based on these findings, four reservoir genesis models, including shoal-fault type, residual hill-fault type, dolomite-karst type, and dolomite-fault type, were established, providing insights into the exploration of the Lower Paleozoic natural gas in the Qingyang paleo-uplift.

     

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