Abstract This study reviews 87Sr/86Sr depth profiles of formation waters sampled by Sr residual salt analysis (Sr RSA) from >100 oil/gas wells and research sites, including reservoirs with clastic and carbonate host rocks and with gas, oil and water as the continuous fluid phase. Globally, the water data form a smooth trend between low seawater-like 87Sr/86Sr ratios (~0.706) at shallow depths and high (~0.724) ratios in deeply buried rocks, where water-rock interaction dominates. We test the hypothesis that 87Sr/86Sr depth profiles in individual wells could be influenced by diffusional mixing processes by developing 1D diffusion mixing equations to simulate compositional patterns through time and comparing them with observed profiles. Different combinations of boundary and initial conditions generate various patterns characteristic of diffusion, including non-steady-state curves relating to incomplete mixing and steady-state patterns (such as vertical or inclined straight lines) where initial heterogeneities have fully mixed. The dataset yielded 193 occurrences of these patterns. Steady-state patterns are more common and longer in water zones, while non-steady-state patterns are more common and longer in oil and gas zones. The detection of diffusional mixing patterns in hydrocarbon-saturated rocks suggests that diffusion is active, although on average a factor of ~13–18 slower, than in comparable water-saturated rocks. Pattern generation and equilibration times were modelled for each non-steady-state pattern and compared with the time since reservoir filling with oil/gas, revealing that 90% of them could have been generated since filling, but 60% of them would already have mixed to steady state had the initial compositional heterogeneities arisen during or before reservoir filling. This is critical evidence that at least some of the initial heterogeneities must have arisen, and subsequently partially mixed, after filling ; these patterns tend to be short ( The evidence for post-fill water-rock interaction and diffusive transport has important implications for porosity/permeability prediction, indicating that key diagenetic processes like quartz cementation may be inhibited by hydrocarbon filling but not stopped altogether. Compositional differences of water within oil/gas zones reveal the folly of using one aquifer water sample as the basis for interpreting water saturations from well resistivity logs for in-place resource estimation. Sr RSA studies may thus be useful in designing water sampling strategies.

中文翻译：

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石油、天然气和水饱和岩石中水 87Sr/86Sr 变化的模式：对流体连通过程、距离和时间尺度的影响

摘要 本研究回顾了通过 Sr 残盐分析 (Sr RSA) 从超过 100 口油/气井和研究地点采样的地层水的 87Sr/86Sr 深度剖面，包括具有碎屑和碳酸盐围岩的储层以及以天然气、石油和水为主要来源的储层。连续流体相。在全球范围内，水数据在浅层的低海水样 87Sr/86Sr 比率（~0.706）和深埋岩石中的高（~0.724）比率之间形成平滑趋势，其中水-岩相互作用占主导地位。我们通过开发一维扩散混合方程来模拟随时间变化的成分模式并将它们与观察到的剖面进行比较，来检验单个井中 87Sr/86Sr 深度剖面可能受扩散混合过程影响的假设。边界和初始条件的不同组合产生了不同的扩散模式特征，包括与不完全混合和稳态模式（例如垂直或倾斜直线）相关的非稳态曲线，其中初始异质性已完全混合。数据集产生了 193 次这些模式。稳态模式在水区更常见、时间更长，而非稳态模式在油气区更常见、时间更长。对碳氢化合物饱和岩石中扩散混合模式的检测表明，扩散是活跃的，尽管平均比类似的水饱和岩石慢约 13-18 倍。为每个非稳态模式模拟了模式生成和平衡时间，并与油/气储层充填后的时间进行了比较，表明其中 90% 可能是自充填后产生的，但是，如果在储层填充期间或之前出现初始成分异质性，其中 60% 将已经混合到稳定状态。这是重要的证据，表明至少某些初始异质性必须在填充后出现，随后部分混合；这些模式往往很短（填充后水-岩相互作用和扩散输运的证据对孔隙度/渗透率预测具有重要意义，表明像石英胶结这样的关键成岩过程可能会被碳氢化合物填充抑制但不会完全停止。成分差异油/气区中的水揭示了使用一个含水层水样作为基础来解释来自井电阻率测井的水饱和度以进行就地资源估计的愚蠢行为。