塔河油田奥陶系缝洞型储层小型缝洞及其充填物测井识别

Identification of small fracture-vugs and their fillings through log interpretation in fractured-vuggy Ordovician reservoirs in Tahe oilfield

塔河油田是以奥陶系碳酸盐岩古岩溶油藏为主的古生界海相大油田,洞穴和其周缘的裂缝是其主要储集空间。由于数量众多,小型缝洞成为缝洞型储层的重要储集空间和渗流通道。小型缝洞可以在露头、岩心和成像测井上识别,但在非取心和非成像测井段还不能有效识别,影响了油藏地质模型的建立。利用岩心和成像测井资料标定常规测井信息,优选出5个洞穴敏感参数和3个裂缝敏感参数,建立了塔河油田小型缝洞归一化加权识别函数,并利用DEN-Vsh和RLLD-Vsh交会图版识别出了洞穴充填物类型:碎屑充填物、垮塌角砾岩和化学充填物。识别效果与岩心及FMI成像对比,洞穴符合率超过81%,裂缝符合率超过82%,洞穴充填物识别成功率超过84%,基本满足了小型缝洞识别要求。利用此方法对塔河油田117口井进行了识别,结果显示该方法也适用于洞高在0.5 m以上的缝洞及充填物识别,并提高了识别精度,为精细研究古岩溶缝洞型储层提供了新方法。

Tahe oilfield is a famous marine Paleozoic giant oilfield dominated by paleokarstic reservoirs of the Ordovician carbonates.Caverns and fractures around them are the main pore space.Numerous small fracture-vugs act as important pore space and and flowpaths.Although the small fracture-vugs can be recognized on outcrops,cores and image logs,they are not readily recognizable in intervals without core and image logging data,seriously influencing the study of fractured-vuggy reservoirs and the establishment of accurate reservoir geological model.To tackle the problem,we calibrated the conventional logging data with cores and image logs and selected five vug-sensitive parameters and three fracture-sensitive parameters.These parameters were used to build a norma-lized and weighted function for identification of small fracture-vugs in Tahe oilfield.We used DEN-Vsh,RLLD-Vsh cross plot method to recognize the types of fillings,including clastics,breccias and chemical fillings.The results of recognition are fairly good compared with that from core observation and image log interpretation.The vug recognition rate is above 81%,fracture recognition rate is larger than 82%,and cave fills recognition rate is over 84%.The method can meet the basic requirements for identification of small vugs and fractures.The application of the method to 117 wells in Tahe oilfield proves to be quite encouraging and the results also show the potential of the method for identification of caverns and fractures with a height over 0.5 meters and their fillings.It provides a new approach for fine study of reservoir space of paleokarstic reservoirs.