Karst-controlled diagenesis and reservoir development: Example from the Ordovician main-reservoir carbonate rocks on the eastern margin of the Ordos basin, China
Karst-controlled diagenesis and reservoir development: Example from the Ordovician main-reservoir carbonate rocks on the eastern margin of the Ordos basin, China
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DOI：
10.1306/61eedd28-173e-11d7-8645000102c1865d
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发表时间：
2002-09
期刊：
影响因子：
3.5
通讯作者：
Baoqing Wang;I. Al-Aasm
中科院分区：
文献类型：
--
作者：
Baoqing Wang;I. Al-Aasm
鄂尔多斯盆地奥陶系马家沟组是鄂尔多斯中央气田的主要储层。5段顶部的产层由在晚奥陶世至中石炭世的长期陆上暴露和岩溶作用中改造的碳酸盐岩组成。在鄂尔多斯盆地东缘，该单元出露碳酸盐岩的孔隙度为0.5 ~ 15.1%，渗透率为8%，渗透率<0.1 ~ 5 md。储层孔隙主要为溶孔孔隙，与白云岩伴生。碳酸盐岩表现出很大的不均匀性，反映了岩溶作用在形成和改变孔隙度方面的不同影响。对这些碳酸盐岩中各种组分的岩相学和地球化学分析为沉积和成岩过程提供了证据。储层碳酸盐岩沉积于浅部局限性高盐环境，后期又受到岩溶作用和埋藏成岩作用的改造。白云石化似乎是海洋和大气沃茨混合的结果，可能发生在浅埋和深埋环境中。在不同的水动力条件下，方解石的胶结作用也发生在浅部和深部环境中。沉积环境和成岩作用（如大气降水淋滤、古岩溶作用、碳酸盐化作用和胶结作用）控制着储层的发育。露头和地下样品显示出相似的岩相学特征、孔隙类型和地球化学特征，但地层的暴露部分显示出更多的大气降水蚀变的证据。
The Ordovician Majiagou Formation contains the main reservoir of the Ordos Central gas field in the Ordos basin. The producing zone at the top of member 5 consists of carbonate rocks modified during a long period of subaerial exposure and karstification from the Late Ordovician to the middle Carboniferous. On the eastern margin of the Ordos basin, the porosity of the exposed carbonate rocks of this unit ranges from 0.5 to 15.1%, and permeability ranges from 8%, and permeability ranges from <0.1 to 5 md. The main reservoir porosity is a dissolution-enhanced vuggy porosity, associated with dolomite. The carbonate rocks show great heterogeneity, reflecting the varying effects of karstification in creating and modifying porosity. Petrographic and geochemical analyses of various components in these carbonates provided evidence for depositional and diagenetic processes. The reservoir carbonates were deposited in shallow and restricted hypersaline environments and were later modified by karstification and burial diagenesis. Dolomitization appears to have resulted from mixing of marine and meteoric waters and probably occurred in both shallow and deep burial settings. Cementation by calcite also occurred in both shallow and deep environments, under different hydrodynamic conditions. Both depositional settings and diagenetic processes, such as leaching by meteoric water, paleokarstification, dolomitization, and cementation, controlled reservoir development. The outcrop and subsurface samples show similar petrographic features, porosity types, and geochemical characteristics, but the exposed section of the formation shows evidence of more alteration by meteoric water.