页岩气井场区域土壤重金属含量特征及生态风险评价

Characteristics of Heavy Metal Content and Ecological Risk Assessment of Soil in Shale Gas Field Area

【目的】为了探究页岩气开采对井场区域土壤重金属含量的影响。【方法】以完井正产气井场S1、含油基处理站井场S2、正钻井井场S3和集气中心站S4,4个不同功能页岩气井场周围土壤中Cr、Ni、Cu、Zn、As、Cd、Pb等重金属含量特征为研究对象。采用单因子污染指数法、内梅罗综合污染指数法及潜在生态风险评价等方法对井场周围土壤重金属含量特征进行评价。【结果】各井场周围土壤重金属平均含量均低于对照参比值;各井场区域土壤各重金属元素单因子指数平均值均小于1,无重金属污染。各井场单一重金属元素潜在风险指数平均值均小于40,属轻度风险;S1、S2、S3、S4井场区域土壤重金属内梅罗综合污染指数分别为0.88、1.12、0.89、0.77,其中S1、S3、S4井场土壤无重金属污染,S2井场存在轻度污染。各井场综合潜在生态风险指数均小于150,属轻度风险水平。【结论】页岩气开采对井场周围土壤重金属含量无明显影响,但由于该地区Cd背景值较高,使得井场周围土壤存在一定程度的重金属污染,需要注意采取一定的防控措施降低土壤重金属的移动性,以保证粮食生产的安全。

【Objective】To investigate the pollution of heavy metals in soil after shale gas exploitation.【Method】The heavy metals Cr,Ni,Cu,Zn,As,Cd,Pb in soils around 4 different function shale gas wells, including well-produced gas well field (S1),oil-bearing base treatment station (S2),drilling well field (S3) and gas gathering center station (S4) were determined. The single factor pollution index method,Nemerow comprehensive pollution index and potential ecological risk assessment were employed to analyze the effects of different shale gas wells exploitation on the concentrations of heavy metals in the soil.【Result】The average content of heavy metals in soil around each well field was lower than the control parameter ratio. The single factor index of soil heavy metal elements in each well field area were less than 1,and there was no pollution. The potential risk index of single heavy metal elements in each well field was less than 40,which was a mild risk. The Nemerow Comprehensive Pollution index in S1,S2,S3 and S4 was 0.88,1.12,0.89,0.77,respectively,with a light heavy metal pollution level of S2 and a no pollution level of S1,S3,S4. The comprehensive potential ecological risk index in all well fields was less than 150T indicating a light risk level.【Conclusion】 In conclusion,the exploitation of shale gas mining had no obvi- ous influence on the concentrations of heavy metals in the soil around the well field, while the wells pose po-tential heavy metal pollution because of the high content of Cd in the soil before exploitation. Therefore, it is necessary to take some measures to reduce the mobility of heavy metals in soil for the food security production.