Stochastic modeling of in-situ sandstone-type uranium leaching in response to uncertain and heterogeneous hydraulic conductivity
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摘要:
砂岩型铀矿矿层渗透系数普遍具有空间非均匀性,但受试验和分析手段制约,非均匀渗透系数难以准确刻画,导致地浸采铀过程预测出现偏差,限制了地浸采铀过程精细化管控。针对该问题提出一种矿层非均匀参数分布随机表征方法,在此基础上,开展水盐耦合数值随机模拟,揭示不同渗透系数空间分布条件下,群井抽注所引起的溶浸剂储层内部迁移过程和影响范围。在内蒙古某铀矿床应用结果显示:沿区域地下水流方向渗透系数增加,有利于注入溶浸剂疏散;相反,溶浸剂易出现聚集效应。利用水位监测数据对模型边界条件进行识别与验证后,在均质假设条件下溶浸剂扩散速率为210 m2/d,20 a 开采周期波及范围为1.53 km2;考虑矿层非均质性和参数不确定性,预测溶浸剂扩散速率为191~228 m2/d,波及范围为1.47~1.74 km2。相比于均质假设,溶浸剂扩散速率和波及范围不确定性显著,分别为17.62%和17.65%。考虑渗透系数非均质性和不确定性,使得溶浸剂迁移转化行为预测结果更具代表性,可为合理制定地浸采铀方案提供更加可靠的依据。
Abstract:Hydraulic conductivity in sandstone-type uranium-bearing formations is of high heterogeneity. However, restricted by the means of test and analysis, it is difficult to accurately describe the heterogeneous coefficient of permeability, which results in the deviation in the prediction of in-situ leaching uranium mining process and limits the fine control of in-situ leaching uranium mining process. To solve this problem, a random characterization method of heterogeneous parameter distribution of an ore bed is proposed in this paper. On this basis, water salt coupling numerical random simulation is carried out to reveal the internal migration process and influence range of leaching agent reservoir caused by pumping and injection of multiple wells under the conditions of different spatial distribution of coefficient of permeability. The application results in a uranium deposit in Inner Mongolia show that the coefficient of permeability increases along the direction of regional groundwater flow, which is conducive to the evacuation of the injected leaching agent. On the contrary, the leaching agent is prone to the aggregation effect. After identifying and verifying the boundary conditions of the model with groundwater level monitoring data, the diffusion rate of the solution is 210 m2/d under the assumption of homogeneity, and the diffusion area of the 20-year mining cycle is 1.53 km2. Considering the heterogeneity of the ore bed and the uncertainty of parameters, the expansion rate of the leaching agent area is predicted to be 191−228 m2/d, and the diffusion area of the leaching agent is 1.47−1.74 km2. Compared with the assumption of homogenization, the uncertainty of the diffusion rate and diffusion area of the leaching agent is 17.62% and 17.65%. Considering the heterogeneity and uncertainty of coefficient of permeability, the prediction results of leaching agent migration and transformation behavior are more representative, which provides a more reliable reference for the design of in-situ leaching uranium mining scheme and the development of sandstone type uranium resources.
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表 1 采区监测数据与参数计算结果
Table 1. Data measurements and hydraulic conductivities estimated at the exploited zone
井号 降深
/m注采强度
/(m3·d−1)渗透系数
/(m·d−1)井号 降深
/m注采强度
/(m3·d−1)渗透系数
/(m·d−1)#01 30.80 207.68 0.26 #11 37.32 221.85 0.30 #02 45.24 183.28 0.07 #12 48.93 190.65 0.06 #03 32.56 212.15 1.08 #13 31.16 119.41 0.53 #04 24.37 211.77 0.70 #14 25.46 199.72 3.02 #05 35.23 207.02 0.24 #15 45.00 207.48 0.11 #06 30.10 199.25 0.64 #16 34.00 129.30 0.09 #07 33.43 211.21 0.72 #17 27.79 215.37 0.23 #08 30.18 186.52 0.17 #18 25.60 216.75 1.31 #09 29.45 190.88 0.87 #19 26.72 214.09 3.91 #10 29.64 215.18 0.78 #20 35.27 208.55 0.16 -
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