滇东北DD1井五峰-龙马溪组页岩气地质特征及其勘探启示

Geological characteristics of shale gas of the Wufeng Fm-Longmaxi Fm in DD1 well in Northeast Yunnan and their exploration significances

关键词:  五峰-龙马溪组  页岩气  有利相带  保存条件  滇东北

Key words:  the Wufeng Formation-Longmaxi Formation  shale gas  favorable facies zone  preservation conditions  Northeastern Yunnan

摘要:

四川盆地南缘五峰-龙马溪组页岩气勘探难度大。以滇东北彝良县DD1井页岩气调查井为例，利用钻测井、岩心分析测试等资料评价其页岩气地质条件。滇东北彝良县DD1井的五峰-龙马溪组富有机质页岩厚度较小、有机质丰度低、热演化程度高、含气性差、N₂含量高，其主要评价指标与盆地内JY1、N203等盆内页岩气高产井差异明显。在页岩气核心评价参数对比基础之上，对DD1井五峰-龙马溪组页岩气勘探失利的地质因素进行深入分析，认为其原因主要在于3个方面：1）五峰-龙马溪期距离黔中古隆起较近，五峰-龙马溪组下段为浅水潮坪相沉积，缺乏黑色富有机质页岩的物质基础；2）五峰-龙马溪组页岩热演化程度高，导致页岩孔隙度变差；3）五峰-龙马溪组埋深较浅，多种尺度裂缝发育，页岩气逸散严重，页岩气构造保存条件差。对滇东北彝良县DD1井页岩气钻探失利的分析，为盆外五峰-龙马溪组页岩气勘探提供了启示意义。

Abstract:

Shale gas exploration of the Wufeng Fm-Longmaxi Fm outside Sichuan Basin is much more difficult than that within Sichuan Basin. In this paper, taking the DD1 well in Yiliang County, northeastern Yunnan as an example, we discussed geological characteristics of shale gas of the Wufeng Fm-Longmaxi Fm in DD1 well in Northeast Yunnan and their exploration significances. The geological conditions of shale gas of DD1 well are evaluated by drilling data, logging, core analysis and testing. The results show, comparing to wells in Sichuan Basin, the organic shale of the Wufeng Fm-Longmaxi Fm in DD1 well is with a thinner thickness, a lower organic matter abundance, a higher thermal evolution level, and poor gas-bearing and N₂ bearing leavels. The main evaluation indicators in DD1 well are obviously different from those of high-yield shale gas wells such as JY1 Well and N203 Well in Sichuan Basin. By comparing main evaluation parameters of shale gas of wells in Sichuan Basin to those out Sichuan Basin, we think there are three reasons which led to the failure of shale gas exploration in DD1 Well. First, the DD1 Well is close to the Central Guizhou paleo-uplift, and the Wufeng Fm-Longmaxi Fm in DD1 Well is shallow tidal flat deposit, lacking the material basis of black organic shale. Second, The high Ro of the Wufeng Fm- Longmaxi Fm shale in DD1 Well resulted in poor porosity. Third, the burial depth of the Wufeng Fm-Longmaxi Fm in DD1 Well is shallow, and multiple scale fractures are developed, and shale gas escaped seriously. DD1 Well has a very poor shale gas preservation condition. The failure of shale gas exploration in DD1 well provides a reference for shale gas exploration outside Sichuan Basin.