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摘要:
本文开展汶川地震断裂带科学钻探现场流体研究，探讨了泥浆添加剂产生的化学反应以及钻孔中岩性变化引起的流体异常特征，并在排除这些影响因素的情况下，讨论地震期间流体的异常。研究表明在WFSD-4S钻进期间发生的两次较大地震前均伴有Rn、Ar、N2和O2等气体异常现象，其中氡的日均值均超出背景值的2.5倍。根据岩心观察得到WFSD-4S钻井地区主断层约在1084 m，而在断层之上931 m处开始出现了大量气体的高值异常，该异常可能是由于地震孕育过程中地下气体的运移通道被打开造成气体向上迁移，使断层气体的响应特征提前发生。
Abstract:This paper deals with the in-site real-time fluid analysis in the drill hole WFSD-4S. The abnormal fluid during the earthquake was discussed after excluding the influence of chemical reaction affected by mud additives and anomaly characteristics caused by lithologic changes. The research shows that two strong earthquakes were accompanied by abnormal occurrence of Rn, Ar, N2 and O2 in WFSD-4S. What deserves attention is the daily average concentrations of radon were over 2.5 times higher than the background value. The mud gas yielded high concentrations above Principal Slip Zone (PSZ) in 931 m,which should appear in 1084m through the lithology investigation. It is inferred that the underground gas migration channel was opened and gas migrated upward because of the earthquake preparation process, which resulted in anticipating the response characteristics of fault gases.
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Keywords:
- Wenchuan Earthquake /
- Scientific Drilling /
- Fluid /
- geochemical features
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1. 研究目的（Objective）
尼玛盆地构造上位于班公湖—怒江缝合带中部，是发育在侏罗系—白垩系海相地层之上的古近系陆相裂谷盆地，北接羌塘地块，南邻冈底斯地块，近东西向展布，面积约3000 km2。本次研究目的是初步查明尼玛盆地东部冻土发育特征，调查盆地东部古近系地层层序，获取古近系烃源岩、储盖层等关键评价参数，进一步评价盆地油气资源潜力。
结合新获取的大地电磁测深、地表地质调查及藏尼地1井资料，通过对盆地东部石油地质条件的进一步论证，中国地质调查局油气资源调查中心在盆地东部赛布错坳陷部署实施了藏双地1井，该井的实施对于西藏高原陆相盆地的油气勘探具有重要意义。
2. 研究方法（Methods）
通过资料的收集和重新处理解释，建立了尼玛盆地基础资料数据库，结合之前在尼玛盆地东部发现的油气显示带及最新的大地电磁测深和藏尼地1井资料，优选井位。藏双地1井完钻井深1206.78 m，全井段进行了取心、录井和测井，共有岩心407箱，岩心总长1108.88 m，收获率95.9%。在古近系牛堡组选取烃源岩样品进行地球化学分析测试，通过分析有机质丰度、有机质类型、热演化成熟度来评价烃源岩生烃潜力；使用荧光分析仪对岩石进行荧光分析，主要进行干照和滴照实验，来检测岩石、岩屑中的沥青、烃类等有机物质。
3. 结果（Results）
藏双地1井从上到下钻遇地层依次为第四系+ 新近系—牛堡组三段—牛堡组二段（未穿），气测录井有3处气测异常段，总烃最高为0.159%，岩性为棕红色粉砂岩、灰色细砂岩。含气量解析取样井段527.90~1206.78 m，共取样54个，现场解析在标准大气压下最高含气量为0.213 m3/t；共做浸水试验20个，拍摄视频20个，其中井深744.40 m、752.08 m、767.30 m、774.66 m、797.20 m、832.43 m均有气泡冒出，以井深752.08 m最为明显。
荧光录井井段0~1206.78 m，对全井岩心按设计逐包进行荧光直照、拍照、氯仿浸泡，定级；全井共录取荧光资料421个点，其中井深1024.23~1026.23 m牛二段灰绿色泥岩断面处，可见黑色薄膜状干沥青，具荧光显示，干照下呈黄色、淡黄色，产状为星点状、带状，用氯仿滴照可呈片状；井深1077.46~1077.76 m牛二段见油迹；井深1078.16~1078.76 m牛二段见点状干沥青；井深1078.76~1079.16 m牛二段层理间见油斑；井深1079.16~1080.16 m牛二段顶部断面处见油迹，都具有荧光显示，呈黄色、淡黄色，产状为星点状、带状（图 1）。
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图 1 藏双地1井牛堡组二段录井柱状图及1079.16~1080.16 m油气显示Figure 1. Logging histogram and the oil and gas display in 1079.16-1080.16m of the second member of Niubao formation in Well Zangshuangdi 14. 结论（Conclusions）
（1）藏双地1井全井取心，获得了尼玛盆地东部古近系地层层序、烃源岩及储层等相关参数，分别在牛三段418.43~422.00 m、牛二段890.00~898.00 m及1068.16~1087.00 m发现3处气测异常段，总烃最高为0.159%，现场解析含气量值最大为0.213 m3/t，并在牛二段1077~1080 m处发现不同级别的油气显示，首次实现了尼玛盆地地下油气的重要发现，对盆地下一步的勘探部署具有重要意义。
（2）本井是继藏尼地1井后在西藏尼玛盆地部署实施的第2口地质调查井，通过对藏双地1井的钻井技术攻关，进一步总结出了适合高寒缺氧、地表及地下地质条件复杂的高原钻井施工工艺和设备参数，为下一步在该区钻井施工提供了重要的技术支撑。
尼玛盆地平均海拔近4800 m，由于其高海拔的特殊性，具有高寒缺氧、气候恶劣、生态脆弱等特征，在野外施工过程中与其他地区有着很大的不同，通过藏尼地1井、藏双地1井的钻探，克服了高寒条件下冻土发育钻井技术难题和高原缺氧条件下深井取心难题，基本形成了一套安全、环保、高效的作业技术体系，为高原地区的钻探施工工程积累了丰富的经验。
5. 致谢（Acknowledgement）
感谢李韬、李显亮等同志的交流和启发。
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图 3 WFSD-4S气体日均值变化
Figure 3. Time-variable curves of the daily average values of gases in drilling WFSD-4S
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图 4 WFSD-4S气体浓度-井深分布图
Figure 4. The real time drilling mud gas concentrations at different depths
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