应用地震低速异常带特征研究轮南地区奥陶系古岩溶
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摘要
孔隙型储集层地震波速度越低，代表其孔隙越发育。但碳酸盐岩岩溶发育段却与此不同，地震波穿越这类岩溶段的速度与其缝、洞发育规模及缝、洞内的充填物质、充填程度有关，速度降低的程度与有效储集空间也有复杂的关系。利用塔里木盆地轮南地区合成声波测井剖面岩溶带低速异常特征，结合钻探获取的实际古岩溶及储集层特征信息，研究了该地区奥陶系古岩溶与低速异常的关系，进而研究古岩溶的横向分布特征。根据研究结果认为：岩溶发育段与致密碳酸盐岩段相比，速度要降低；Ⅰ类低速异常体速度（小于５ｋｍ／ｓ）降低较明显，主要反映被碎屑岩充填的大规模洞穴体，代表洞穴充填岩溶相带，对储油不利；Ⅱ类低速异常体（速度为５．０～５．３ｋｍ／ｓ）主要反映中、小型洞穴和裂缝发育段，被充填或部分充填；Ⅲ类低速异常体速度（５．３～５．７ｋｍ／ｓ）降低相对不明显，主要反映垂直渗流岩溶相带中未充填或半充填中、小规模裂缝发育段，这类裂缝发育段是轮南地区奥陶系油气聚集的主要场所。图４参１（邹冬平摘
With a lower seismic velocity the clastic reservoirs will have a higher porosity. While the paleo karst intervals of carbonates are quite different from this. The velocity in such intervals is related closely to the development of fractures and caves, the filling materiel in such spaces and the filling degree as well. The degree of decreasing in velocity is also bound up with the effective space of reservoirs. Based on the low velocity abnormal zones of paleo karst showing in the curves of synthetic sonic logging, and the drilling data of subsurface paleo karsts and reservoirs, the authors explored the relationship between the low velocity abnormalities and the paleo karst in Ordovician, and analyzed the lateral development of the paleo karst. A conclusion is finally got that the paleo karst intervals have a lower velocity compared to that of the tight carbonates. The type [WT6BZ〗Ⅰlower velocity abnormality (LVA) with its velocity lower than 5km/s reflects predominantly the big caves filled with clastics, characterizing the filled intervals of paleo karst caves, which is unfavorable for oil accumulation. The type ⅡLVA with a velocity ranging from 5.0 to 5.3km/s shows the intervals of medium to small caves and fractures, which are filled or partly filled. The type ⅢLVA has decreased its velocity not significantly, with a velocity ranging from 5.3 to 5.7km/s, which characterizes the fracture intervals of medium to small size in the vertical leaky zones of paleo karst. Such fracture intervals not or partly filled are the important reservoirs for hydrocarbon in Ordovician of Lunnan area.
With a lower seismic velocity the clastic reservoirs will have a higher porosity. While the paleo karst intervals of carbonates are quite different from this. The velocity in such intervals is related closely to the development of fractures and caves, the filling materiel in such spaces and the filling degree as well. The degree of decreasing in velocity is also bound up with the effective space of reservoirs. Based on the low velocity abnormal zones of paleo karst showing in the curves of synthetic sonic logging, and the drilling data of subsurface paleo karsts and reservoirs, the authors explored the relationship between the low velocity abnormalities and the paleo karst in Ordovician, and analyzed the lateral development of the paleo karst. A conclusion is finally got that the paleo karst intervals have a lower velocity compared to that of the tight carbonates. The type [WT6BZ〗Ⅰlower velocity abnormality (LVA) with its velocity lower than 5km/s reflects predominantly the big caves filled with clastics, characterizing the filled intervals of paleo karst caves, which is unfavorable for oil accumulation. The type ⅡLVA with a velocity ranging from 5.0 to 5.3km/s shows the intervals of medium to small caves and fractures, which are filled or partly filled. The type ⅢLVA has decreased its velocity not significantly, with a velocity ranging from 5.3 to 5.7km/s, which characterizes the fracture intervals of medium to small size in the vertical leaky zones of paleo karst. Such fracture intervals not or partly filled are the important reservoirs for hydrocarbon in Ordovician of Lunnan area.
引文
1白玉雷周路：塔里木盆地寒武、奥陶系岩溶型储层特征及发育模式；见：塔里木盆地油气勘探论文集，新疆科技卫生出版社（乌鲁木齐），1991。
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