江汉盆地潜江凹陷王场地区深层卤水水化学特征及成因研究

沉积盆地油田卤水中蕴藏着锂、铷、铯等战略性关键矿产资源, 其成因研究具有重要意义。本次研究采集了江汉盆地潜江凹陷王场地区地下卤水样品18件, 测试了其化学组成, 分析了卤水的水化学特征、元素相关性和特征系数, 探讨了该地区深层卤水成因。研究区卤水赋存于古近系潜江组砂岩中, 矿化度(TDS)平均值为260.04 g/L, 水化学类型为Cl-Na型, pH值在7.03~8.01之间。与往年相比, 潜江凹陷卤水矿化度呈逐年下降趋势, 可能与油田的开采注水有关。Na、Cl含量与TDS呈现了明显的正相关性, Li、K、B和Br含量随着TDS增加而升高, 而Ca含量随着TDS增加呈下降趋势, 可能揭示了原生沉积卤水蒸发浓缩的过程。高的钠氯系数(1.09~1.21)和氯溴系数(480~1547.60)以及低的钾氯系数(3.75~14.82)表明了来自石盐溶解的贡献, 波动的钙镁系数和脱硫系数反映了不均一的封闭性和变质程度, 从潜一段至潜四段封闭性变好、变质程度变高。研究区地下卤水为陆相盐湖原生蒸发沉积, 有明显石盐淋滤的物源补给, 储集空间整体封闭性较差, 变质程度较低。

Hydrochemical Characteristics and Genesis of Deep Brines in Wangchang Area, Qianjiang Depression, Jianghan Basin

There are strategic key mineral resources such as lithium, rubidium and cesium in oilfield brine of sedimentary basin. In this study, 18 underground brine samples from the Wangchang area in Qianjiang depression, Jianghan Basin were collected. Their chemical composition was tested, hydrochemical characteristics, element correlation, and characteristic coefficients were analyzed, and the genesis of deep brine in this area was discussed. The brine in the study area is found in the sandstone of the Paleogene Qianjiang Formation. The average total dissolved solid (TDS) concentration is 260.04 g/L, while the hydrochemistry type is Cl-Na, and the pH value is between 7.03 and 8.01. The TDS of brine in Qianjiang depression decreases yearly, which may be related to water injection. The contents of Na and Cl were positively correlated with TDS, and the contents of Li, K, B, and Br increased with an increase in TDS, while the content of Ca decreased with an increase in TDS, which may clarify the evaporation and concentration processes of the primary sedimentary brine. The high sodium-chloride coefficient (1.09~1.21) and chloro-bromine coefficient (480~1547.60), and the low potassium-chloride coefficient (3.75~14.82) indicate the contributions from the dissolution of stone salt. The fluctuating Ca/Mg coefficient and desulphurization coefficient reflect the uneven sealing and metamorphic degree, and the sealing and metamorphic degree increases from the first subduction to the fourth subduction. The underground brine in the study area is the primary evaporative deposit of the continental salt lake, which is supplemented by the obvious source of stone salt leaching. The overall sealing of the reservoir space is poor and the metamorphism degree is low.