Deep Cambrian Surface-karst Dolomite Reservoir and Its Alteration by Later Fluid in Tarim Basin

详细信息   

• 责任者：Zhu Dongya (Laboratory of Structural and Sedimentological Reservoir Geology ; Petroleum Production and Research Institute of SINOPEC ; Beijing 100083 ; China) ; Meng Qingqiang
• 刊名：Geological Review
• 出版年：2012
• 卷期：58(4)
• 关键词：碳酸盐岩储集层 ; carbonate reservoirs ; 深层气 ; deep gas ; 塔里木盆地 ; Tarim Basin
• 页码：p.691-701
• 图表：illus., 1 table, 46 refs.
• 分类号：1003
• issnNo：ISSN0371-5736
• isbnNo：CN11-1952/P

摘要

Observation of cores from wells such as TS1 and others which have drilled into the Cambrian dolomite indicates that there are plenty of pores which are some millimeters to some centimeters in size and were were though to be developed in surface -karst environment. Some of the Cambrian dolomite was buried to a depth more than 8000m. Abrupt variations of log curves of the TS1 well reflect several boundaries in the Cambriandolomite, and the boundaries are related to deposition absence intervals or exposure to surface. However, seismic events within the Cambrian dolomite seismic profile near the TS1 well are well continuous indicating that there is not remarkable angular unconformity. Characteristics of well logs and seismics suggest that the karst dissolution of the Cambrian dolomite took place contemporaneously or penecontemporaneously during deposition due to exposure caused by fall of relative sea level and that there was not strong tectonic uplift. There are always some minerals such as dolomite and quartz filling in vugs of the Cambrian dolomites in the well TS1 and others. The filling dolomite shows curved crystal surface and wave extinction. The maximal frequency of the homogenization temperatures of the fluid inclusions in the filling dolomite is between 110 - 130℃and the homogenization temperatures do not increase linearly with depth. Compared with matrix dolomite, the filling dolomite has relatively low Na, K and Sr but relatively high Fe, Mn and Ba contents. In isotope compositions, the filling dolomite is relatively light in oxygen isotope but has relatively high n（⁸⁷Sr）/n（⁸⁶Sr） values. The δ¹⁸O_PDB values are between - 11.62‰ and -5.13‰ and are -8.00‰ in average, and the n（⁸⁷Sr）/n（⁸⁶Sr） between 0. 709 361 and 0. 709 978 and 0. 709 590 in average. The above characteristics indicate that the infillings of the dolomite and other minerals are related to activities of deep hydrothermal fluids. Limited by strength of hydrothermal, the previously existed dissolution pores in dolomite were not completely destroyed by mineral filling, however, there are still some portion of the dissolution pores preserved.