鄂尔多斯盆地乌审旗隆起东北侧怀远运动不整合特征及其对岩溶储层形成的意义

Unconformity characteristics of Huaiyuan movement in the northeast of Wushenqi paleo-uplift in Ordos Basin and its implications for karst reservoir generation

张军涛 张玉银 谷宁 金晓辉 张涛 刘四洪 贾会冲 杨佳奇 刘玲 高晓鹏

Juntao ZHANG Yuyin ZHANG Ning GU Xiaohui JIN Tao ZHANG Sihong LIU Huichong JIA Jiaqi YANG Ling LIU Xiaopeng GAO

怀远运动（加里东期Ⅰ-Ⅱ幕）是鄂尔多斯盆地早古生代一次较大的构造活动，其影响仅次于加里东期（Ⅲ幕）—海西运动，存在长时间的沉积间断，在古隆起附近形成了较为有利的岩溶储层。怀远运动不整合面在乌审旗隆起东北侧表现为奥陶系马家沟组一段与寒武系三山子组之间的平行不整合接触。不整合面上、下均为碳酸盐岩地层，但在测井电性、岩石矿物、元素以及同位素分析上都存在很大的差异。三山子组为细晶白云岩，在测井响应上具有低伽马值、高电阻率的特征，发育不规则状溶蚀孔隙，是岩溶储层发育段。三山子组储层多属于相对高能的近隆浅滩、正常海水环境，白云化作用为浅埋藏期渗透回流白云岩化。马家沟组一段是怀远运动后的首套沉积地层，由于靠近乌审旗古陆，岩性复杂，呈现出膏-云-泥-砂混杂沉积的特征，沉积时虽然也属于海相环境，但其与三山子组沉积时相比已发生了较大变化，属于海侵早期靠近古陆的混积潮坪沉积环境，气候相对干旱，以海源碳酸盐沉积为主，又常有间歇性的陆源碎屑补给，白云岩则是准同生期萨布哈白云岩化作用的产物。三山子组储层受相对高能原始相带以及怀远运动相关白云岩化作用和岩溶作用共同控制，储层多为白云岩化作用和表生岩溶作用叠加形成，分布于乌审旗隆起、镇原隆起和吕梁隆起附近。

Huaiyuan movement during the first and second episodes of the Caledonian was a major tectonic activity in the Early Paleozoic Ordos Basin， featuring long-term sedimentary hiatus and forming a more effective karst reservoir near the paleo-uplift， with the impact second only to the Caledonian （the third episode） - Hercynian movement. To the east side of Wushenqi paleo-uplift， the first member of the Ordovician Majiagou Formation （Ma 1 Member） was in parallel， unconformable contact with the Cambrian Sanshanzi Formation as the result of Huaiyuan Movement， and on either side of the unconformity were carbonate strata with great differences in terms of electrical logging properties， mineral， elemental and isotopic compositions. The Sanshanzi Formation was of fine-crystalline dolomites with irregular dissolved pores and karst reservoirs. The well logging response shows low gamma value and high resistivity at the interval. The reservoirs of the formation were mostly deposited in relatively high-energy shoals near the paleo-uplift with normal seawater， and experienced reflux dolomitization at shallow burial stages. The Ma 1 Member is the first interval of sediments after the Huaiyuan movement， featuring complex lithology and mixed deposition of anhydrite， dolomite， mud and sand due to its proximity to the Wushenqi paleo-land. In terms of the depositional setting， the Ma 1 member was of marine type， that is， mixed tidal flat near the paleo-land in the early transgression period， though with great difference from the Sanshanzi Formation. The climate was relatively arid during its deposition， and the deposits were dominated by marine carbonates with intermittent terrigenous clastic supply. Its dolomite was a result of enecontemporaneous sabkha dolomitization. Controlled by both the primary facies belt with relatively high energy and the dolomitization as well as karstification related to the Huaiyuan movement， the reservoirs in the Sanshanzi Formation were mainly formed by a combination of dolomitization and epigenetic karstification and are widely seen in the vicinity of Wushenqi， Zhenyuan and Lyuliang paleo-uplifts.

10.11743/ogg20230108