Dating the Effective Fractures of Qinglong Formation Limestone in Southern Jiangsu Area
Duan Hongliang, Wang Hongwei Jiangsu Oilfield Branch Company,SINOPEC,Yangzhou,Jiangsu 225009,China
Based on the detailed observation and description of the macroscopic and microcosmic features,the development periods of the fractures,and formation time of effective fractures are studied in this paper by cathodeluminescence and carbon and oxygen isotope analyzing of fracture fillings. The results show that there are 6 stages of fracture development identified in Qinglong Formation,southern Jiangsu area. The fractures of first stage are stylolites,which developed during the early period of Qinglong Formation. The fractures of second stage developed during the early Indosinian-Yanshanian,which are filled by calcites and with weak oil show. The third stage fractures developed during early Yizheng movement,which are half-filled by calcite and with abundant oil show. The fourth stage fractures are stylolites,which developed during middle Yizheng movement. The fifth stage fractures developed during the early period of Sanduo movement,which were filled by calcites. The sixth stage fractures developed during Yancheng Period,which were unfilled. The third stage fractures are the most effective fractures with rich oil show and cavities. The tectonic stress field of early Yizheng movement should be an important factor in the predicition of effective fractures in Qinglong Formation.