鄂尔多斯盆地南部奥陶系碳酸盐储层的胶结作用
摘要: 鄂尔多斯盆地南部奥陶系马家沟组主要由原始沉积的碳酸盐岩和岩溶角砾岩组成。储集空间以次生孔隙为主。中奥陶世沉积作用之后不久，即发生了溶解作用、白云石沉淀、干化脱水作用、机械压实作用、岩溶作用和胶结作用。胶结作用很普遍，主要发生在中石炭世之后的埋藏条件下，是对储层重要的破坏作用。充填于硬石膏结核溶模孔和非组构选择性溶蚀孔、洞、缝的方解石和白云石是最常见的胶结物。这些方解石和白云石胶结物具泥晶、嵌晶状或粒状晶粒结构。泥晶白云石基质的δ18O值-10.98‰~-0.8‰，平均-5.54‰；δ13C值-4.76‰~5.77‰，平均1.51‰。充填于溶蚀孔、缝中的白云石的δ18O值-12.54‰~-2.67‰，平均-7.34‰；δ13C值-5.56‰~3.48‰，平均0.28‰。充填于溶蚀孔、缝方解石的δ18O值-15.42‰~-6.02‰，平均-9.51‰；δ13C值-12.44‰~1.33‰，平均-3.20‰。总的来说，白云石和方解石胶结物的δ18O和δ13C值低于泥晶白云石基质的，原因是形成晚，受淡水淋滤、埋藏作用和有机质影响较大。泥晶白云石基质的Na含量0~350 μg/g，平均59 μg/g； Sr含量0~380 μg/g，平均10 μg/g；Fe含量0~14 570 μg/g，平均1 040 μg/g；Mn含量0~4 670 μg/g，平均183 μg/g。充填于次生孔隙中的胶结物的Na、Sr、Mn含量与泥晶白云石基质的差别不大，因这些元素含量均低。充填于次生孔隙的碳酸盐胶结物较泥晶白云石基质有明显高的Fe含量。胶结物包裹体的均一温度在90℃~140℃范围内。胶结物沉淀于埋藏较深，温度较高的还原条件下。流体包裹体的气相成分以CH4最为普遍，液相成分以H2O占绝大多数。早期胶结物形成于天然气形成前，晚期胶结物形成于天然气形成之后。岩溶洼地是胶结作用最发育的地带。
Cementation of the Ordovician Carbonate Reservoirs in the South Ordos Basin, China
Abstract: The Ordovician Majiagou Formation mainly consists of carbonate rocks originally deposited and karst bareccia. The reservoir space is mainly secondary pores. After deposition dissolution, dolomitization, desiccation, physical compaction, karstification and cementation soon began. Cementation, which mainly occurred under the burial conditions after the middle Carboniferous, is common and important destructional dianenesis for reservoirs. The micritic, equant sparry and poikilotopic calcite and dolomite, infilling moldic pores of anhydrite concretion, and nonfabric selective dissolution pores and fractures, are common cements. The δ18O and δ13C values of micritic dolomite range from 10.98‰ to 0.8‰, averaging 5.54‰; and from 4.76‰ to 5.77‰, averaging 1.51‰, respectively. The δ18O and δ13C values of dolomite cements infilling dissolution pores range from 12.54‰ to 2.67‰, averaging 7.34‰; and from 5.56‰ to 3.48‰, averaging 0.28‰ respectively. The δ18O and δ13C values of calcite cements infilling dissolution pores range from 15.42‰ to 6.02‰, averaging 9.51‰; and from 12.44‰ to 1.33‰, averaging 3.20‰, respectively. The δ18O and δ13C values of dolomite and calcite cements are generally lower than of micritic dolomite, because of late formation, fresh water leaching, burial diagenesis and influence of organic materials. The Na, Sr, Fe and Mn content of micritic dolomite, dolomite cements and calcite cements ranges from 0 to 350 μg/g, averaging 59 μg/g; from 0 to 380 μg/g，averaging 10 μg/g; from 0 to 14 570 μg/g, averaging 1 040μg/g; and from 0 to 4 670 μg/g, averaging 183 μg/g, respectively. The Na, Sr, and Mn content of dolomite and calcite cements is similar with that of micritic dolomite, because all trace elements content is low. Fe content of dolomite and calcite cements is higher than that of micritic dolomite. The homogenization temperatures of fluid inclusions in the cements range 90~140℃. All indicates that the cements formed under reduced conditions with high temperature in the deep burial environments. The most gaseous phase of the fluid inclusions consists of CH4, while the most liquid phase is H2O. The early and late cements formed before and later formation of the natural gas respectively. The cementation developed extensively in the kart depressions.
鄂尔多斯盆地南部奥陶系碳酸盐储层的胶结作用[J]. 沉积学报, 2013, 31(3): 527-535.
| 引用本文: |
鄂尔多斯盆地南部奥陶系碳酸盐储层的胶结作用[J]. 沉积学报, 2013, 31(3): 527-535.
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Cementation of the Ordovician Carbonate Reservoirs in the South Ordos Basin, China[J]. Acta Sedimentologica Sinica, 2013, 31(3): 527-535.
| Citation: |
Cementation of the Ordovician Carbonate Reservoirs in the South Ordos Basin, China[J]. Acta Sedimentologica Sinica, 2013, 31(3): 527-535.
|
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