Noble gases record fluid interactions in multiphase subsurface environments through fractionation processes during fluid equilibration. Water in the presence of hydrocarbons at the subsurface acquires a distinct elemental signature due to the difference in solubility between these two fluids. We find the atmospheric noble gas signature in produced water is partially preserved after hydrocarbons production and water disposal to unlined ponds at the surface. This signature is distinct from meteoric water and can be used to trace oil-field water seepage into groundwater aquifers. We analyse groundwater (n = 30) and fluid disposal pond (n = 2) samples from areas overlying or adjacent to the Fruitvale, Lost Hills, and South Belridge Oil Fields in the San Joaquin Basin, California, USA. Methane (2.8 × 10⁻⁷ to 3 × 10⁻² cm³ STP/cm³) was detected in 27 of 30 groundwater samples. Using atmospheric noble gas signatures, the presence of oil-field water was identified in 3 samples, which had equilibrated with thermogenic hydrocarbons in the reservoir. Two (of the three) samples also had a shallow microbial methane component, acquired when produced water was deposited in a disposal pond at the surface. An additional 6 samples contained benzene and toluene, indicative of interaction with oil-field water; however, the noble gas signatures of these samples are not anomalous. Based on low tritium and ¹⁴C contents (≤ 0.3 TU and 0.87–6.9 pcm, respectively), the source of oil-field water is likely deep, which could include both anthropogenic and natural processes. Incorporating noble gas analytical techniques into the groundwater monitoring programme allows us to 1) differentiate between thermogenic and microbial hydrocarbon gas sources in instances when methane isotope data are unavailable, 2) identify the carrier phase of oil-field constituents in the aquifer (gas, oil-field water, or a combination), and 3) differentiate between leakage from a surface source (disposal ponds) and from the hydrocarbon reservoir (either along natural or anthropogenic pathways such as faulty wells).

稀有气体通过流体平衡期间的分馏过程记录多相地下环境中的流体相互作用。由于这两种流体之间的溶解度不同，地下存在烃类的水会获得明显的元素特征。我们发现采出水中的大气惰性气体特征在碳氢化合物生产和将水排放到地表无衬里的池塘后部分保留。这种特征与大气水不同，可用于追踪油田水渗入地下水含水层的情况。我们分析地下水 ( n  = 30) 和液体处理池 ( n = 2) 来自美国加利福尼亚州圣华金盆地 Fruitvale、Lost Hills 和 South Belridge 油田上覆或邻近区域的样品。甲烷（2.8 × 10 ^-7至 3 × 10 ^-2  cm ³ STP/cm ³) 在 30 个地下水样本中的 27 个中检测到。使用大气惰性气体特征，在 3 个样品中确定了油田水的存在，这些样品已与储层中的热成因碳氢化合物平衡。两个（三个）样本也含有浅层微生物甲烷成分，这是在采出水沉积在地表的处理池中时获得的。另外 6 个样品含有苯和甲苯，表明与油田水相互作用；然而，这些样品的惰性气体特征并不异常。基于低氚和¹⁴C 含量（分别≤ 0.3 TU 和 0.87-6.9 pcm），油田水的来源可能很深，可能包括人为和自然过程。将惰性气体分析技术纳入地下水监测计划使我们能够 1) 在甲烷同位素数据不可用的情况下区分产热和微生物碳氢化合物气源，2) 识别含水层中油田成分的载体相（天然气、石油） - 现场水，或组合），以及 3) 区分来自地表源（处理池）的泄漏和来自碳氢化合物储层的泄漏（沿着自然或人为途径，如故障井）。