准噶尔盆地玛湖凹陷二叠系风城组碱湖盐岩储层特征及成因

Characteristics and Genesis of Alkali Lake Salt Reservoirs in the Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin

通过薄片偏光显微镜、扫描电镜、全岩X射线衍射、微区原位碳氧同位素、包裹体测温等测试分析,对准噶尔盆地玛湖凹陷二叠系风城组碱湖盐岩储层的特征与成因进行了系统研究。玛湖凹陷风城组碱湖盐岩主要分布在半深湖、深湖中,与泥岩呈高频互层分布,盐岩储层储集空间以盐类矿物溶孔为主,其次是裂缝。玛湖凹陷风城组碱湖烃源岩热演化提供了丰富的酸,且在多期裂缝沟通下,对盐类矿物进行溶蚀,形成了发育的溶孔,是玛湖凹陷风城组盐岩储层形成的关键。烃源岩早期充注形成的异常高压,是孔隙得以保存的重要原因,早成岩期普遍的白云石化以及大量盐类矿物析出,抵抗了部分压实,既有效保护了粒间体积,也为后期溶蚀增孔提供了物质条件。The characteristics and genesis of the alkali lake salt reservoirs of the Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin were systematically studied by testing and analysis such as thin-section polarizing microscopy, scanning electron microscopy, X-ray diffraction of whole rock, micro-in-situ carbon and oxygen isotopes, and inclusion temperature measurement. The alkali lake salt rocks of the Fengcheng Formation in Mahu Sag are mainly distributed in semi-deep lakes and deep lakes, and are distributed with mudstones at high frequency interbedded, and the reservoir space of salt reservoirs is dominated by salt mineral dissolution pores, followed by fractures. The thermal evolution of the alkali lake source rocks of the Fengcheng Formation in the Mahu Sag provides abundant acids, and the salt minerals are dissolved under the communication of multi-stage fractures, forming developed dissolution pores, which is the key to the formation of the salt reservoir of the Fengcheng Formation in the Mahu Sag. The abnormal high pressure formed by the early filling of the source rocks is an important reason for the preservation of the pores, and the common dolomitization and the precipitation of a large number of salt minerals in the early diagenetic period resisted partial compaction, which not only effectively protected the intergranular volume, but also provided material conditions for the later dissolution and pore increase.