鄂尔多斯盆地苏里格地区奥陶系古岩溶储层成岩作用

DIAGENESIS OF ORDOVICIAN PALEO-KARST RESERVOIR IN THE SULIGE AREA, THE ORDOS BASIN

王宝清 章贵松

Wang Baoqing Zhang Guisong

西安石油大学, 油气资源学院, 西安, 710065 2. 中国石油天然气股份有限公司, 长庆油田分公司, 勘探开发研究院, 西安, 710021

School of Petroleum Resources, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China 2. Research Institute of Exploration and Development, Changqing Oil Field, PetroChina, Xi'an, Shaanxi 710021, China

鄂尔多斯盆地苏里格地区奥陶纪主要沉积环境为水下凸起—隆间洼地和(内)陆棚盆地。奥陶系由原始沉积的碳酸盐岩和岩溶角砾岩组成。溶蚀孔是最主要的孔隙类型,裂缝是重要的储集空间;孔隙度为0.02%～16.70%,平均为2.19%;渗透率为(0.0014～706.35)×10-3μm2,平均为 1.90×10-3μm2。奥陶系碳酸盐沉积物(岩)经历的成岩作用有压实、白云石化、胶结、交代、溶蚀和去白云石化作用。全岩白云石样品较低的δ18O值和较高的Mn,Fe含量以及明显低的Sr含量说明白云石受到淡水淋滤和埋藏作用的影响,不低的δ13C值说明碳来自原始沉积物中的CaCO3。白云石胶结物较全岩白云石具有较低的δ18O和δ13C值,说明白云石胶结物形成于裸露期的风化壳岩溶作用阶段。岩石经历了早期成岩作用、表生成岩作用和晚期成岩作用。低孔、低渗是该储层的特点,原因是岩溶作用强度不够和埋藏较深。

The Sulige area is located to the northeast of the ancient central uplift in the Ordos Basin.The main sedimentary environments during Ordovician in the area include under-water uplift and inter-uplift depression as well as inner shelf basin.The Ordovician mainly consists of host carbonate rocks and karst breccias.Dissolution pores are the most important pores,and fractures are important reservoir spaces.Porosity ranges from 0.02% to 16.70%,averaging 2.19%.Permeability ranges from 0.0014×10-3 to 706.35×10-3μm2,averaging 1.90×10-3μm2.Diagenesis,which the Ordovician carbonate sediments(rocks) have experienced,includes compaction,dolomitization,cementation,replacement,dissolution and dedolomitization.The slightly lower δ18O values,higher concentration of Mn and Fe,and obviously lower concentration of Sr for dolomite of whole rocks indicate that the dolomite is influenced by meteoric leaching and burial diagenesis.The δ13C values are not low since carbon comes from CaCO3 of original sediments.The δ18O and δ13C values of dolomite cements are generally lower than those of dolomite of whole rocks,suggesting that the dolomite cement is formed during karstification at epidiagenetic expose phase.The rocks have experienced early diagenesis,epidiagenesis and late diagenesis.Reservoir rocks are characterized with low porosity and permeability,due to weak karstification and deep burial.

https://doi.org/10.11781/sysydz200606518