四川盆地昭通地区太阳区块页岩气压裂返排液地球化学特征——以Y105井区为例  

Geochemical characteristics of shale gas hydraulic fracturing flowback water in Taiyang block,Zhaotong area,Sichuan Basin,China:A case study of Well Y105

作　　者：李林芝 倪云燕 姚立邈 王飞 隋建立[5] 张津川 王圆 董国梁 王力 赵桐 陈建平[3] 董大忠[3] LI Linzhi;NI Yunyan;YAO Limiao;WANG Fei;SUI Jianli;ZHANG Jinchuan;WANG Yuan;DONG Guoliang;WANG Li;ZHAO Tong;CHEN Jianping;DONG Dazhong(College of Environmental Sciences,Sichuan Agricultural University,Chengdu 611130,China;China University of Petroleum(Beijing)National Key Laboratory of Petroleum Resources and Engineering,Beijing 102249,China;PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China;PetroChina Zhejiang Oilfield Company,Hangzhou 311100,China;Institution of Geology,China Earthquake Administration,Beijing 100029,China)

机构地区：[1]四川农业大学环境学院,四川成都611130 [2]中国石油大学(北京)油气资源与工程全国重点实验室,北京102249 [3]中国石油勘探开发研究院,北京100083 [4]中国石油浙江油田,浙江杭州311100 [5]中国地震局地质研究所,北京100029

出　　处：《天然气地球科学》2024年第9期1699-1711,共13页Natural Gas Geoscience

基　　金：国家重点研发计划课题(编号:2019YFC1805505);黔科合战略找矿项目(编号:[2022]ZD005);中国石油科学研究与技术开发项目(编号:2021DJ5302,2021DJ0502)联合资助。

摘　　要：近年来中国在四川盆地昭通示范区针对埋深700~2 000 m的中浅层页岩气开展了卓有成效的勘探与开发,但页岩气开发采用的水平井技术和大型水力压裂技术存在水环境污染风险,尤其是在中国南方碳酸盐岩分布区,地质条件复杂、生态环境脆弱,开展水环境污染风险研究尤为重要。对四川盆地昭通地区太阳区块Y105井区垂深小于2 500 m的页岩气井的压裂返排液进行了微量元素、阴阳离子、锶同位素等组成的地球化学分析,并与威远、长宁和涪陵地区的页岩气压裂返排液进行了比较。研究结果表明,太阳区块浅层Y105井区页岩气压裂返排液具有以下3个特征:(1)返排液高含各种盐类、重金属等,K、Na、Ca、Mg等含量均值分别为153 mg/L、7 473 mg/L、162 mg/L、34 mg/L,Cl和Br含量均值分别为10 912 mg/L和52 mg/L,Li、B、Sr、Ba、Rb等含量均值分别为21.9 mg/L、14.3 mg/L、27.8 mg/L、37.4 mg/L、0.25 mg/L,不能直接排放。Br/Cl均值为0.002 1,与蒸发相海水相比具有相对富Ca贫Mg的特点,Sr、Ba、Rb等含量与Cl含量呈正相关关系,说明返排液为压裂注入液与地层束缚的卤水混合的产物,其高盐端具有蒸发相海水的特征,但又经历了水岩反应。(2)87Sr/86Sr值变化范围为0.716 5~0.717 2(均值为0.716 7),说明压裂注入液与具有高锶同位素比值的页岩地层之间有着强烈的水岩作用。与威远、长宁和涪陵页岩气田返排液相比,太阳区块返排液的87Sr/86Sr值较低,但又远高于地表水、杀菌剂等,是很好的鉴别指标。(3)返排液元素组成与页岩垂直埋深有着一定的相关性,如,Y105H3平台,当垂深从2 245.16 m增加至2 406.16 m,阴阳离子、微量元素等成分含量都有着不同程度的变化,并表现出一定的变化规律,这可能反映了温度、压力等因素的影响。In recent years,China has carried out fruitful exploration and development of medium and shallow shale gas with a burial depth of 700-2000 m in Zhaotong Shale Gas Demonstration Zone of Sichuan Basin.However,horizontal well technology and large-scale hydraulic fracturing technology adopted in shale gas development have the risk of water environment pollution,especially in the carbonate rock distribution area in southern China,which has complex geological conditions and fragile ecological environment.The study of water environmental pollution risk is particularly important.In this study,the composition of trace elements,anions,cations,and strontium isotopes in the flowback water of Y105 well area with vertical depth<2500 m in the Taiyang block,Zhaotong area,Sichuan Basin was analyzed and compared with that of Weiyuan,Changning and Fuling shale gas fields.It is pointed out that shale gas fracturing flowback water in Y105 well area of Taiyang shallow layer has the following three characteristics:(1)The flowback water is high in salts and heavy metals.The average contents of K,Na,Ca and Mg were 153 mg/L,7473 mg/L,162 mg/L,34 mg/L,respectively,and the average contents of Cl and Br were 10912 mg/L and 52 mg/L,respectively.The average contents of Li,B,Sr,Ba and Rb were 21.9 mg/L,14.3 mg/L,27.8 mg/L,37.4 mg/L and 0.25 mg/L respectively,which could not be directly discharged.The average Br/Cl ratio is 0.0021,it is relatively rich in Ca and poor in Mg compared with evaporative seawater,the content of Sr,Ba and Rb is positively correlated with the content of Cl.All of them indicate that the flowback water is the mixture product of the fracturing injected fluid and entrapped brine of the host shale formation.The high salt end of the flowback water has the characteristics of evaporative seawater,but it also experiences water-rock reaction.(2)The 87Sr/86Sr ratio ranges from 0.7165 to 0.7172(with an average value of 0.7167),indicating that there is a strong water-rock interaction between fracturing injected fluid and shale forma

关 键 词：四川盆地返排液 页岩气 昭通地区 太阳区块 地球化学 锶同位素 

分 类 号：TE122.113[石油与天然气工程—油气勘探]