| 鄂西宜昌下寒武统水井沱组页岩气聚集条件与含气特征 |
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| 引用本文： | 罗胜元,陈孝红,李海,刘安,王传尚.鄂西宜昌下寒武统水井沱组页岩气聚集条件与含气特征[J].地球科学,2019,44(11):3598-3615. |
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| 作者姓名： | 罗胜元 陈孝红 李海 刘安 王传尚 |
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| 作者单位： | 中国地质调查局武汉地质调查中心, 湖北武汉 430205 |
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| 基金项目： | 国家科技重大专项2016ZX05034001-002中国地质调查局项目DD20179615 |
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| 摘 要： | 鄂西宜昌下寒武统水井沱组页岩具有良好的气体显示，页岩气成藏条件研究薄弱.利用最新钻探的井下资料、周边露头地质调查资料及大量样品的分析测试结果，从富有机质页岩区域展布、地球化学特征、岩石储集特征、含气性、保存条件等方面研究鄂西宜昌地区下寒武统水井沱组页岩气聚集条件.研究区水井沱组形成于陆棚-斜坡相带，厚度为50~140 m.有机碳含量高（TOC值为0.43%~10.45%，平均值达2.65%），TOC大于2%的优质页岩有效厚度为28~41 m，有机质热成熟度为2.4%~3.2%，处于高演化阶段.页岩脆性矿物含量高，石英含量平均值为29.33%，碳酸盐含量平均值为25.94%，黏土矿物含量平均值为35.06%，且以伊/蒙间层为主.水井沱组富有机质页岩孔隙度为0.96%~3.32%，平均值为2.08%，页岩渗透率为0.01×10-3~3.05×10-3 μm2.氩离子抛光电镜与吸附测试表明，页岩孔隙发育具有成因类型多、孔径尺度小的特点，有机孔孔径主要集中在10~50 nm范围内.水井沱组页岩气层顶、底板条件良好，区域构造稳定、断裂不发育，页岩气保存条件优越.钻井过程中水井沱组气显频繁，解析含气量为0.31~5.48 m3/t，连续含气量大于2 m3/t的累计厚度达44.05 m.水井沱组水平井压裂获工业气流，页岩气组分中CH4含量为87.17%~92.75%，C2H6为0.83%~0.94%，N2为5.86%~9.37%，CO2为0.05%~2.25%.总体上宜昌地区下寒武统水井沱组页岩气成藏条件较好，是四川盆地外页岩气新的勘探区.
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| 关 键 词： | 宜昌地区 下寒武统 水井沱组 页岩气 页岩储层 成藏条件 油气地质 |
| 收稿时间： | 2019-07-16 |
Shale Gas Accumulation Conditions and Target Optimization of Lower Cambrian Shuijingtuo Formation in Yichang Area,West Hubei |
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| Abstract: | Good gas shows in the Cambrian Shuijingtuo Formation indicate the resources potential in Middle Yangtze region. The weakness of basic research on the shale gas accumulation constrains gas exploration and development in this area. In this paper,it focuses on the geological characteristics of Shuijingtuo shale gas in Yichang area by integrating geological and geochemical data from latest exploration well and outcrop. The gas potential is discussed based on preliminary evaluation of lithofacies,geochemical characteristics,reservoir features,and shale gas content. These organic-rich intervals are concentrated along and between continental shelf and slope. Thermally mature strata of the Shuijingtuo shale attain thickness between 28 and 41 m,with a total organic carbon (TOC) exceeding 2%. Organic matter within Shuijingtuo shale is high,which contains an average of 2.65% TOC,with present-day thermal maturity between 2.4% and 3.2% equivalent vitrinite reflectance (Ro),which is in the high mature of dry thermogenic gases dominated stage. The Shuijingtuo shale is noted for having generally high silica content. Mineral composition of shale consists of 29.33% quartz,25.94% carbonatite calcite/dolomite,35.06% clay minerals. Illite smectite mixed layer is the major clay mineral. The gas shale reservoir has an extremely low porosity and permeability. Porosity ranges from 0.96% to 3.22%,with an average value of 2.08% at the bottom of Shuijingtuo Formation. The effective permeability in gas shale is (0.01-3.05)×10-3 μm2. Through scanning electron microscope observation and isothermal adsorption,pores in shale also show multiple genetic types and small size of multi-pore diameter. Fractal dimensions of the organic pores vary from 10 to 50 nm. Overlying formations and underlying strata are favorable for shale gas preserved. The tectonic stress field is regionally very stable and short of fault activity,which all indicates favorable preservation conditions for Shuijingtuo shale gas in gentle slope of Yichang area. Measurement of total hydrocarbon and methane through mud logging indicates anomaly. The measured gas content of the Shuijingtuo shale in Well Yiye-1 ranges between 0.31 to 5.48 m3/t. Thermally mature strata of the Shuijingtuo Formation attain thickness of 44.05 m,with a continuous gas content exceeding 2 m3/t. Well Yiye-1 tested an industrial gas flow after horizontal well fractured. Methane is the main constituent of gas sample and varies in concentration from 81.17% to 92.75%. Ethane ranges from 0.83% to 0.94%,nitrogen in non-hydrocarbon gas ranges from 5.86% to 9.37%,and carbon dioxide ranges from 0.05% to 2.25%. It is concluded that it could be the favorable area for shale gas accumulation in the Middle Yangtze region,and it's a new area for shale gas exploration outside Sichuan basin. |
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