某砂岩型铀矿钻孔中镭氡平衡系数的数值模拟

砂岩型铀矿勘查及开采过程中,钻孔在揭穿地层后,原有封闭地层被破坏,镭氡平衡发生位移,由于砂岩比较松散,孔隙度较大,连通性较好,透水性好,有效岩心采取率不高等原因,用传统矿段分析的结果与伽马测井解释结果对比确定Ra-Rn平衡系数的方法,其结果误差较大。通过利用放射性地球物理测井长期观测资料,钻孔岩心样品数据等,用数值模拟的方法模拟氡从矿层运移到围岩及钻孔的瞬态过程,研究矿体及围岩放射性场的分布规律和特点,综合分析由于氡迁移导致Ra-Rn不平衡的原因,以气态氡为研究对象,利用氡浓度计算从镭氡平衡被破坏到重新达到平衡后的镭氡平衡修正系数,研究总结钻孔中Ra-Rn平衡变化的规律,用数值模拟计算得到的平衡系数对比传统方法计算得出镭氡平衡系数,确定有效的镭氡平衡系数计算方法,在误差允许范围内,可先用数值模拟计算得到的平衡系数进行校正,定量解释矿层铀含量,对野外测井中镭氡平衡修正具有参考意义。

Numerical simulation of Ra-Rn equilibrium coefficient in a sandstone type uranium deposit

During the drilling in the exploration and mining of sandstone type uranium deposits,the radon in original bed will dispersed due to the pressure unbalance caused by the penetration of the borehole through the closed stratum and result in the shift of radium-radon balance.Because the ore hosting sandstone is usually loose,porous and good in water permeability,but unsatisfied in effective core collection rate,traditional Ra-Rn balance coefficient determined by comparing the result of ore segment analysis to gamma logging interpretation often produce significant error.The numerical simulation method was used to simulate the transient process of radon migration from the ore layer to the host and boreholes based on the long-term observation data of radioactive logging,geological data etc.so as to study the distribution and pattern of radioactive fields around the ore bodies and hosting rocks.With the modulated pattern,radium-radon balance correction coefficient is calculated and set up re-equilibrium.The balance coefficient calculated by numerical simulation is compared with the radium-radon balance calculated by traditional methods,and the err is found within the allowable range.The balance coefficients calculated by numerical simulation can be used to correct the uranium content of the ore layer quantitatively,which is of well significance to guide the radium-radon balance correction in field logging.