鄂尔多斯盆地奥陶系马家沟组白云岩储层特征及成因机制

鄂尔多斯盆地奥陶系白云岩是重要的天然气储集层，对其白云岩成因和储层发育规律的研究对于碳酸盐岩深层勘探理论的发展具有重要意义。文章基于大量岩心、薄片的观察，并结合稳定碳氧同位素、稀土元素、白云岩有序度、地层水、包裹体特征等地球化学分析，对盆地奥陶系存在的两种典型白云岩储层的发育特征和形成机理进行了详细研究。分析表明，含硬石膏结核或柱状晶的泥粉晶白云岩主要为潮坪蒸发环境的萨布哈成因，其规模储层的发育主要受到长时不整合的控制，不整合面以下发育大量硬石膏结核和柱状晶溶模孔；颗粒滩白云岩主要为回流渗透成因，其储层孔隙的发育主要受到海平面高频升降的影响，发育多旋回的粒（晶）间孔隙型储层。虽然两种白云岩的白云石化流体都为浓缩海水，但由于白云石化的机制和速率不同，二者的原始孔隙类型和特征迥异。两种白云岩孔隙在后期的成岩改造和演变过程中，既有相同之处，又有明显的区别。这一认识也将对深层的白云岩储层勘探提供指导作用。

Characteristics and Genesis Mechanism of the Dolomite Reservoir in theOrdovician Majiagou Formation in the Ordos Basin

The Ordovician dolomite in Ordos basin is an important natural gas reservoir. Studying the genesis of dolomite and reservoir development is of great significance to the development of the deep carbonate exploration theory. Based on observations of a large number of cores and thin sections, combined with geochemical analysis of stable carbon and oxygen isotopes, rare earth elements, order degree of dolomite, formation water and inclusions, the developmental characteristics and formation mechanism of two Ordovician type dolomite reservoirs in the basin were studied in detail. The analyses reveal that the dolomicrite containing anhydrite nodules or columnar crystals is mainly sabkha genesis in an evaporitic environment of tidal flat. The development of its large-scale reservoir was mainly controlled by the long-term unconformity surface, below which plenty of dissolved mold holes of the anhydrite nodules and columnar crystals were developed. The granular beach dolomite is mainly genesis result of seepage reflux and the development of its reservoir pores is primarily affected by the high-frequency fluctuations of the sea level, generating multi-cycle intergranular (intercrystalline) porous reservoirs. Although the dolomitization fluids of both types of dolomite were concentrated seawater, the original pore types and characteristics of the two dolomites are different due to their different mechanisms and rates of dolomitization. In the subsequent diagenetic transformation and evolution, the two types of dolomite pores show both similarities and obvious differences. This finding will provide useful guidance for the exploration of deep dolomite reservoirs.