柴北缘冷湖七号地区碳酸盐胶结物特征及其意义

Characteristics and Significance of Carbonate Cement in the No. 7 Area of Lenghu, Northern Margin of Qaidam Basin

王晔桐 孙国强 杨永恒 秦彩虹 李艳明

WANGYetong SUNGuoqiang YANGYongheng QINCaihong LIYanming

中国科学院西北生态环境资源研究院, 甘肃 兰州 730000 中国科学院大学, 北京 石景山 100049 中国石油青海油田公司勘探开发研究院, 甘肃 敦煌 736202 中国石油集团东方地球物理勘探有限责任公司研究院地质研究中心, 河北 涿州 072751

Northwest Institute of Eco-environment and Resources, Chinese Academy of Sciences, Lanzhou, Gansu 730000, China University of Chinese Academy of Sciences, Shijingshan, Beijing 100049, China Research Institute of Exploration and Development, Qinghai Oilfield Company, PetroChina, Dunhuang, Gansu 736202, China Geological Research Center, Geophysical Research Institute, BGP, CNPC, Zhuozhou, Hebei 072751, China

碳酸盐胶结物是碎屑岩储层中最常见的胶结物类型，其形成环境、物质来源、反映的成岩温度对储层研究具有重要意义。通过对柴北缘冷湖七号下干柴沟组砂岩碳酸盐胶结物进行岩石学、矿物学和地球化学分析，研究区下干柴沟组砂岩碳酸盐胶结物包含方解石、含铁方解石、铁方解石和白云石等4种类型。碳同位素（δC）和氧同位素（δO）值分别为8.81‰~3.51‰和8.77‰~17.36‰，平均值分别为5.33‰及13.50‰；利用碳同位素和氧同位素计算出古盐度值和古温度值分别为113.61~102.85和63.03~123.06℃，平均值分别为109.66及94.47℃。反映出研究区下干柴沟组所处成岩阶段为早成岩阶段B期-中成岩阶段A期，形成过程受到有机质脱羧基作用影响，成岩环境偏酸性，成岩流体来自碎屑的析出水和大气淋滤淡水。储层物性除了受成岩环境和温度的影响外，与碳酸盐胶结物含量具有明显的负相关关系，随着碳酸盐胶结物含量的增加，储层的孔隙度和渗透率降低。

Carbonate cement is the most common type of cement in clastic reservoirs, and its formation environment, material source and diagenetic temperature are of great significance to the reservoir research. Through the analysis of petrology, mineralogy and geochemical of the sandstone carbonate cementation in the Xiaganchaigou Formation of Lenghu No.7 in the northern margin of Qaidam Basin, this paper shows that there are four types of sandstone carbonate cements in the Xiaganchaigou Formation in the study area which are calcite, iron-bearing calcite, iron calcite and dolomite respectively. The content of carbon isotopes (δC) and oxygen isotopes (δO) are 8.81‰~3.51‰ and 8.77‰~17.36‰ respectively, with averages value of 5.33‰ and 13.50‰, respectively. Paleosalinity and temperature are 113.61~102.85 and 63.03~123.06℃ according to carbon isotopes and oxygen isotopes calculation, the average value is 109.66 and 94.47℃, respectively. It reflects that the diagenetic stage of the Xiaganchaigou Formation is from early diagenetic stage B to middle diagenetic stage A, whose formation process is influenced by the decarboxylation of organic matter. The diagenetic environment is acidic, and the diagenetic fluids mainly come from the precipitated water of the clastic and the leaching fresh water in the atmosphere. Besides the influence of diagenetic environment and temperature, the physical property of reservoir has a significant negative correlation with the carbonate cement content. And with the increase of carbonate cement content, the porosity and permeability of the reservoir decrease.

10.11885/j.issn.1674-5086.2018.09.12.01