鄂尔多斯盆地西南部长砂岩致密时间再认识

Revisiting the Compaction Time of Chang 8 Sandstones in Southwestern Ordos Basin

周晓峰 李景 张建欣 李书恒 于均民

ZHOUXiaofeng LIJing ZHANGJianxin LIShuheng YUJunmin

中国石油大学(北京)石油工程教育部重点实验室, 北京 昌平 102249 油气资源与工程国家重点实验室, 北京 昌平 102249 中国石油玉门油田勘探开发研究院, 甘肃 酒泉 735019 西南石油大学地球科学与技术学院, 四川 成都 610500 中国石油长庆油田分公司勘探开发研究院, 陕西 西安 710018

MOE Key Laboratory of Petroleum Engineering, China University of Petroleum, Changping, Beijing 102249, China State Key Laboratory of Petroleum Resources and Engineering, Changping, Beijing 102249, China Exploration and Development Research Institute of Yumen Oilfield Company, PetroChina, Jiuquan, Gansu 735019, China School of Geoscience and Technology, Southwest Petroleum of University, Chengdu, Sichuan 610500, China Exploration and Development Research Institute of Changqing Oilfield Company, PetroChina, Xi'an, Shaanxi 710000, China

鄂尔多斯盆地延长组砂岩的致密时间目前尚无定论，这是由于对方解石胶结物的成因认识不一致造成的。通过铸体薄片和带有能谱仪的扫描电镜技术，对鄂尔多斯盆地西南部长砂岩中方解石胶结物的成因进行了研究。认为早成岩A期的泥岩压释水为方解石胶结提供物质来源，形成了浸染状均匀分布的I型方解石胶结物和斑块状或星点状散布的Ⅱ型方解石胶结物； I型方解石胶结的砂岩，流体难以进入而失去水岩反应能力，Ⅱ型方解石胶结物在中成岩A期经溶解沉淀反应转化为Ⅱ型方解石胶结物；碳氧同位素和流体包裹体资料不能作为研究方解石胶结物成因的主要依据，这些资料的解释必须服从于岩石显微结构特征。鉴于此，鄂尔多斯盆地西南部长砂岩致密时间为早成岩A期，其与成藏时期的配置关系为先致密后成藏。

Owing to disagreements in the understanding of calcite cement formation, the compaction time of sandstones of the Yanchang Formation in Ordos Basin has not yet been determined. Employing scanning electron microscopy (SEM) with energy spectrometry and casted rock thin sections, the origin of calcite cement in Chang 8 sandstones in southwestern Ordos Basin was investigated. The results show that water released from mudstone compaction during phase A of the early diagenetic stage induced calcite cementation, forming type I calcite cement with evenly distributed dissemination structures or type Ⅱ with patchy or scattered dissemination structures. Fluids cannot easily penetrate sandstones derived from type I calcite cementation, and thus water-rock reactions cannot take place. Type Ⅱ calcite cement is transformed into type Ⅱ via dissolution-precipitation during phase A of the mid-diagenetic stage. Carbon and oxygen isotopes and fluid inclusion data cannot be used as the main reference for studying calcite cement formation because their interpretation must follow rock microstructure characteristics. In view of the above, the compaction time of Chang 8 sandstones in southwestern Ordos Basin was determined to be phase A of the early diagenetic stage, and its relationship with reservoir formation is "compaction followed by accumulation."

10.11885/j.issn.1674-5086.2017.01.24.02