沙垒田地区奥陶系古岩溶储层热液流体改造的地球化学证据

Geochemical evidences of hydrothermal fluid alterations of Ordovician paleokarst reservoirs in Shaleitian area

刘超,马骄,萨如力草克提·沙拉克,刘志刚,徐小斐

西安石油大学地球科学与工程学院，陕西 西安 710065 西安石油大学陕西省油气成藏地质学重点实验室，陕西 西安 710065 中国石油新疆油田分公司采油二厂，新疆 克拉玛依 834009 中国石油华北油田分公司第五采油厂，河北 辛集 052360 中国石化胜利油田分公司勘探开发研究院，山东 东营 257015

School of Earth Sciences and Engineering, Xi′an Shiyou University, Xi′an 710065, China Shaanxi Key Laboratory of Petroleum Accumulation Geology, Xi′an Shiyou University, Xi′an 710065, China No.2 Oil Production Plant, Xinjiang Oilfield Company, PetroChina, Karamay 834009, China NO.5 Oil Production Plant, Huabei Oilfied Company, PetroChina, Xinji 052360, China Exploration and Development Research Institute, Shengli Oilfield Company, SINOPEC, Dongying 257015, China

利用普通薄片、染色薄片、阴极发光、荧光特征等信息，明确了沙垒田地区奥陶系古岩溶储层的岩石矿物学特征。在此基础上，对不同矿物进行锶、氧、碳同位素及锰、锶微量元素的综合分析。研究表明：古岩溶储层在地表风化淋滤作用后，重新埋藏时再次遭受其他流体改造，从而抹去了大气淡水成岩信息；填充于岩溶角砾岩中的自生晶粒方解石则是该流体作用的直接产物，该流体与辉绿岩侵入时携带的热液流体密切相关；尽管研究区碳酸盐岩普遍遭遇成岩改造，但少量泥—微晶石灰岩/白云岩由于致密而保留了原始海源特征（包括与同期海水一致的锶同位素值、低锰锶比值及无阴极发光特征）；热液流体对古岩溶储层孔隙具有双重影响，但整体上其改造作用增加了孔隙度，对储层发育具有积极影响。

The rock mineralogical features of Ordovician paleokarst reservoir in Shaleitian uplift were clarified through the information of regular thin-section, stained thin-section, cathode luminescence and fluorescence characteristics. On this basis, the strontium, carbon and oxygen isotopes, manganese and strontium trace elements different minarals were analyzed comprehensively. The study shows that, after subaerial weathering and leaching, the paleokarst reservoirs underwent other fluid-alterations during reburial process, thus erasing the record of meteoric-water diagenesis. Authigenic crystalline calcites filling in karst breccias were precipitated directly from this hydrothermal fluid. The combination of elements, isotopes and mineralogical characteristics indicated that the fluid was closely associated with magmatic hydrothermal fluid induced by diabase intrusion. Although diagenetic alterations were pervasive in the carbonates of the study area, a small proportion of micritic limestone/dolomites retained the characteristics of the originally marine-sourced fluid due to their tight permeability (mainly including 87Sr/86Sr isotopic values of the contemporaneous seawater, Mn/Sr ratio and non-cathodoluminescence feature). Hydrothermal fluid exerted double-influence on the physical property of paleokarst reservoirs. Nonetheless, this alteration increased porosity on the whole and had positive influence on reservoir development. 

10.6056/dkyqt202105008