摘要： 应用高分辨率电成像测井资料,首次在川南大安地区下志留统龙马溪组泥页岩中发现了大型滑塌体。滑塌体分布在龙一₂亚段—龙二段内,岩性主要为灰黑色泥页岩,在常规测井曲线和岩心上与正常页岩特征一致、难以区分,但在电成像图像上可见滑塌构造和滑动构造,与正常页岩呈现的水平层理特征迥异、界面截然。大安地区1000 km²范围内的6口钻井中均发现有多层滑塌体,滑塌体层之间为正常的页岩,不同井中滑塌体的层数、厚度明显不同,在横向上缺乏对比性,总体表现为北厚南薄、北强南弱的趋势。单井中最多发育有35层滑塌体,最少为9层;单层滑塌体厚度最大为32.4 m,最小为0.5 m;单井滑塌体层累计厚度最大为194.5 m,最小为41 m。分析认为滑塌体分布范围广、发育层数多、单层厚度大,具有地震成因的特点,其分布受乐山—龙女寺古隆起东南斜坡控制,是近距离搬运、快速堆积沉积作用的产物,不同井区对同一地震事件的沉积响应不同,单层滑塌体可能是对1次地震事件的响应,也可能是多次地震事件叠加的结果。滑塌体的发现为川南龙马溪组的地层对比提供了新的沉积学信息,同时滑塌体厚度大、裂缝发育程度高、具有良好的储盖条件,可成为下一步页岩气勘探的备用层系。

关键词: 龙马溪组, 滑塌体, 高分辨率电成像测井资料, 页岩气

Abstract: Large landslide bodies are discovered for the first time in the Longmaxi Formation from the Da'an area,southern Sichuan basin,based on high-resolution borehole image well logs. Landslide bodies are distributed in the Long1₂ Sub-member and Long2 Member. They are both composed of black shales,and thus display similar features to background shale deposits on conventional logs. On borehole image logs,however,the landslide bodies can be identified by slide and slump structures,which have sharp contrasts with normal shale. Multi-layered landslide bodies are found in 6 drilling wells distributed in the Da'an area(~1000 km²). The landslide bodies are layered and separated by normal shales. The number of layers and thickness of landslide bodies in different wells are markedly different,making it challenging to correlate between wells. The landslide bodies are overall thick in the north and thin in the south. A single landslide body varies in thickness from 0.5 to 32.4 m,while composite landslide bodies in a single well can reach a thickness of 41 to 194.5 m. It is believed that landslide bodies are widely distributed,occur at multiple stratigraphic levels with large bed thickness,and have the characteristics of earthquake origin. They were the product of short distance transportation and rapid deposition,which was controlled by the southeast slope of the Leshan-Longnvsi palaeo-uplift. Different areas have different sedimentary responses to the same earthquake event. A single landslide body may be a response to one earthquake event,or it may be the result of the superposition of multiple earthquake events. The discovery of the landslide bodies provides a new perspective on stratigraphic correlation of the Longmaxi Formation in the southern Sichuan Basin. At the same time,the landslide bodies are thick with well-developed fracture networks,and feature favorable reservoir and seal conditions. These landslide bodies may thus represent potentially important prospects for the future shale gas exploration.

Key words: Longmaxi Formation, landslide body, borehole image logs, shale gas

中图分类号: 

• P512.32