白云岩地球化学特征及成因——以鄂尔多斯盆地靖西马五段中组合为例  

Geochemical characteristics and origin of dolomite: A case study from the middle assemblage of Majiagou Formation Member 5 of the west of Jingbian Gas Field, Ordos Basin, North China

作　　者：贺训云[1,2,3,4] 寿建峰[3,4] 沈安江[3,4] 吴兴宁[3,4] 王永生[3,4] 胡圆圆[3,4] 朱吟 韦东晓[3,4] 

机构地区：[1]中国科学院地质与地球物理研究所 [2]中国科学院大学 [3]中国石油杭州地质研究院 [4]中国石油天然气集团公司碳酸盐岩储层重点实验室

出　　处：《石油勘探与开发》2014年第3期375-384,共10页Petroleum Exploration and Development

基　　金：国家科技重大专项"海相碳酸盐岩沉积与有效储层大型化发育机理与分布研究"(2011ZX05004-002)

摘　　要：通过主微量元素、稀土元素及碳、氧、锶同位素特征分析,系统研究鄂尔多斯盆地靖边气田西侧奥陶系马家沟组马五段中组合白云岩地球化学特征及成因。样品分析结果表明:中组合白云岩MgO和CaO含量呈负相关性,Mg/Ca值总体较高;总体具有高Fe、较高Mn和低Sr、Na含量特征,部分白云岩Fe、Mn含量相对较低,Na含量相对较高;稀土元素含量总体很低,且具相似稀土元素配分模式,轻稀土元素富集,重稀土元素亏损,具明显Eu负异常和弱Ce负异常;δ13C值与同期海水值一致,多数白云岩δ18O值较同期海水值偏负;少数87Sr/86Sr值与同期海水值接近,多数显著偏正。结合区域地质背景及上述特征,认为马五段中组合白云岩很可能主要为渗透回流白云石化成因,同时在后期广泛叠加了埋藏白云石化作用。靖西东部地区为有利储集层发育区且可向东大范围拓展。The trace elements, rare earth elements （REE）, carbon and oxygen isotopic compositions and strontium isotopes were analyzed to study systematically the geochemical characteristics and origin of the middle assemblage dolomites from the Ordovician Majiagou Formation Member 5 in the Jingxi area （the west of Jingbian Gas Field）. The analytical results of samples demonstrate that the MgO and CaO contents of the middle assemblage dolomite are negatively correlated, and the Mg/Ca values are high;the dolomites are characterized by high Fe content, relatively high Mn content and low Sr and Na content, while part dolomites have low Fe and Mn content but high Na content; the dolomites have very low REE content and similar REE distribution patterns, which are generally characterized by enrichment of light REE, losses of heavy REE, obviously negative anomaly of Eu and weak negative anomaly of Ce;The δ13C values of dolomites are consistent with those of the coeval seawater, while most of the δ18O values of dolomites are more negative than those of the coeval seawater; most of the 87Sr/86Sr values of dolomites are significantly higher than those of the coeval seawater while only a few are close to those of the coeval seawater. Combined with the geological setting and geochemical characteristics of the middle assemblage dolomites, the middle assemblage dolomites of the Majiagou Member 5 are probably the origin of seepage reflux dolomitization, and were superimposed by burial dolomitization during the burial period. The eastern part of the Jingxi area is favorable reservoir development area, the favorable area can extend eastward.

关 键 词：白云岩成因 地球化学特征 马家沟组中组合 鄂尔多斯盆地 锶同位素 氧同位素 稀土元素 

分 类 号：TE122.1[石油与天然气工程—油气勘探]