高温地热系统中粘土矿物形成对Na-K和 K-Mg地球化学温标准确性的影响
Impact of Clay Mineral Formation in High-Temperature Geothermal System on Accuracy of Na-K and K-Mg Geothermometers

传统地球化学温标在估算高温地热系统内浅层热储温度(一般为100～200℃)时存在局限性，其中应用广泛的Na-K温标和K-Mg温标出现误差的原因仍不清楚.在收集了全球代表性热田内采自地热井的201个流体样品的水文地球化学数据后，利用软件WATCH将井口流体地球化学数据还原为热储条件下的对应值；在此基础上，对Na-K温标和K-Mg温标进行了评价，发现钾长石和常见富钾双八面体粘土矿物均可能对浅层热储内地热流体中的钾含量产生影响，富镁双八面体粘土矿物也可达到与地热流体的平衡，而地热流体中钠含量则受水-岩相互作用的影响很小.因此，浅层地热流体的Na-K比值与热储温度不具有对应关系，而K-Mg温标在计算浅层热储温度时虽然具有一定指示意义，但仍无法得到足够准确的结果.
Traditional geochemical geothermometers have limitations when used to estimate the temperature of shallow reservoirs(100-200℃)in high-temperature geothermal systems, and it remains unclear about the cause of the error due to the widely used geothermometers of Na-K and K-Mg. In this study, the hydrogeochemical data of 201 water samples from geothermal wells in the typical hydrothermal areas across the world were collected, based on which the corresponding geochemical compositions of reservoir fluids are calculated using the code WATCH. An evaluation of Na-K and K-Mg geothermometers was further made. The results show that K-feldspar and common dioctahedral potassium-rich clay minerals are likely to control the content of potassium in geothermal fluid from shallow reservoirs and dioctahedral magnesium-rich clay minerals can be equilibrated with geothermal fluid as well, whereas the content of sodium in geothermal fluid is little affected by water-rock interactions. Hence, the Na-K ratio of shallow geothermal fluid doesn't match well with reservoir temperature. K-Mg geothermometer is capable of indicating shallow reservoir temperature to some degree, but still not accurate enough