Geochemical characteristics,genesis,geological and development significance of trace elements in water produced from coalbed methane wells:A case study of Zhijin Block in western Guizhou Province

GUO Chen; GAO Junzhe; QIN Yong; YI Tongsheng; CHEN Zhenlong; YUAN Hang; WANG Guoling; LU Lingling; LI Ruiteng; CHENG Xi

doi:10.13225/j.cnki.jccs.DM25.0160

Abstract：In order to deepen the formation mechanism of coal measure fluid geochemistry and the mechanism of coalbed methane(CBM)enrichment and high yield,and to facilitate CBM efficient development,based on the collection of water samples produced from CBM wells in the Zhijin block of western Guizhou and trace element geochemical testing,the composition characteristics,differential distribution and genesis mechanism of trace elements in the produced water were revealed,and their geological significance and indicative significance for CBM enrichment and high yield were explored.The results show that the high concentration of trace elements in the produced water from CBM wells in Zhijin block is the result of the interaction between water and inorganic minerals in coals,which is mainly due to the inorganic occur-rence of trace elements in coals in western Guizhou.The dissolution and precipitation of trace elements are two mechan-isms of water-coal interaction.Under retention conditions,easily soluble elements dissolve in large quantities,leading to an increase in the concentration of trace elements in coal seam water,represented by five characteristic trace elements:Li,Ga,Rb,Sr,and Ba.The main source of dissolution is clay minerals.When the concentration of trace elements in water is high,alkaline water environment will promote the precipitation of soluble elements and feedback the changes in trace ele-ments in coal.The concentration of trace elements in the produced water varies significantly between different coal-bear-ing synclines,due to differences in hydrodynamic conditions between synclines.The concentration of Li element in the produced water is positively correlated with the average daily gas production,while the spider web area of characteristic trace element concentration is negatively correlated with the average daily water production,which can indicate the coal measure hydrodynamic conditions and CBM production potential.The coal measure hydrodynamic conditions of the Zhuzang syncline are weak,and the concentration of trace elements in the produced water is high.In addition,the tectonic reconstruction is weak,and the coal body structure is relatively complete,which jointly create the best conditions for CBM enrichment and high yield in the Zhucang syncline.The Agong syncline also has high CBM production potential while en-suring drainage capacity,typically represented by the gently inclined SE oriented limb.The research results provide new ideas for understanding the regional controlling mechanism for the CBM enrichment and high yield in the Zhijin block from the perspective of the geochemical differences and genesis mechanisms of trace elements in the produced water from CBM wells,and provide direction for the future CBM development.