塔里木盆地卡塔克隆起中下奥陶统鹰山组白云岩储集层特征及主控因素

摘要

Dolostones of the Middle-Lower Ordovician Yingshan Formation in Katak Uplift of Tarim Basin are hydrocarbon reservoir rocks of vital importance. Based on detailed petrographic and geochemical investigations, the characteristics and origin of the reservoir have been figured out. Silt-sized limy dolostone and silt-sized dolostone are the two main types of reservoir rocks. Intercrystal pores, intercrystal dissolved pores and acicular pores occupied more than 85% of the reservoir space. Intracrystal dissolved pores, dissolved vug and other pores are minors. Geological and geochemical analyses suggested that dolostone reservoir was controlled by several factors. Dolomitization produced massive intercrystal pores and provided later dissolution with potential spaces. A large number of intercrystal dissolved pores are formed during the epigenic karstification, the 87Sr/ 86Sr value of the dolostone was modified during this process and the value decreased with growing depth, at the same time the trace elements concentration of Fe and Mn decreased, the luminescent was getting weak. The epigenic karstification was also indicated by logging responses and dedolomitization. Bitumen impregnation was suggested by the bitumen alongside sytlolites, moderate bright to moderate dark fluorescence can be seen in some intercrystal pores. Burial dissolution was less fabric selective and caused most of the acicular pores, so occurrence of the pores was less relative to the fabric. Some acicular pores were filled by calcite, among which the Fe content was 18. 1×10-4 in average, and Mn was 16. 5×10-4 in average. Both of the content was less than that of matrix dolomile apparently, which was 617. 4×10-4 and 166. 8×10-4, and the fluorescence was also darker than matrix dolomite.%塔里木盆地卡塔克隆起中下奥陶统鹰山组白云岩储集层主要由灰质粉晶—细晶白云岩和粉晶—细晶白云岩构成,储集空间以晶间孔、晶间溶孔和针状溶孔为主,所占比例大于85％.地质、地球化学综合分析表明,鹰山组白云岩储集层受多种因素控制.去白云石化形成大量晶间孔并为后期溶蚀流体提供了运移通道.表生岩溶过程中形成大量晶间溶孔,并使白云岩的87Sr/86Sr值随深度增加而降低,同时其Fe、Mn含量下降、阴极发光变弱,并使局部发生去白云石化,在测井曲线上表现为“三高二低”.沥青充注作用表现为缝合线中充填沥青,同时部分样品晶间孔中也有荧光显示.埋藏溶蚀作用的非选择性强,形成大量针状溶孔,其产状与岩石组构无明显相关关系,部分针状溶孔被方解石充填.