Natural CO₂ reservoirs provide an opportunity to study long-term fluid-rock interactions, which are essential to reassure the safety of mineral storage of carbon-dioxide. The Mihályi-Répcelak field (Pannonian Basin, Central Europe) is one of the largest natural CO₂-bearing reservoirs in Europe (25 Mt). The CO₂ was trapped in Neogene sandstones, which contain various carbonate minerals (dolomite, ankerite, siderite, dawsonite). To reveal the origin of the parent fluid, from which these minerals precipitated, dawsonite and siderite were separated by a new physical method to minimise the uncertainties in the analysis of their stable isotope composition. The δ¹³C_Daw values range from +1.3‰ to +1.6‰ and the calculated δ¹³C_CO2 values in equilibrium with dawsonite (−4.8‰ - –2.0‰) overlap with the carbon isotope compositions of the local CO₂ and the European Subcontinental Lithospheric Mantle (−3.9‰ - –2.1‰). This indicates that the dawsonite-forming CO₂ had a magmatic origin. The siderite data indicates that some formed from the magmatic CO₂, possibly simultaneously with dawsonite (−6.0‰ - –3.9‰), whereas the rest (−8.4‰ - –6.1‰) formed either from a fractionated CO₂ with magmatic origin or before the CO₂ invasion. The hydrogen isotope composition of structural OH⁻ of dawsonite (−57‰ to −74‰) was determined and was used to estimate the origin of the interacting porewater. The calculated porewater data (δD: −69‰ - –103‰ and δ¹⁸O: −1.4‰ - +4.7‰) indicate that the parent fluid was meteoric water modified by water-rock interaction. Our data allows estimation of the total amount of CO₂ stored in the dawsonite-bearing sandstone reservoir to be 25 kg/m³, well in line with previous modelling works, which gives a total of 2.01 × 10⁶ t of CO₂, higher than previous estimates.

We suggest that individual mineral analysis complemented by hydrogen isotope analysis is to be employed to effectively trace in-reservoir fluid-rock interactions in CO₂ reservoirs and provide valuable input data for geochemical modelling for better predicting conditions for mineral storage of CO₂.

天然 CO ₂储层提供了研究长期流体-岩石相互作用的机会，这对于确保二氧化碳矿物储存的安全性至关重要。Mihályi-Répcelak 油田（中欧潘诺尼亚盆地）是欧洲最大的天然含 CO ₂油藏之一（25 Mt）。CO ₂被困在新近纪砂岩中，砂岩含有各种碳酸盐矿物（白云石、铁橄榄石、菱铁矿、片钠铝石）。为了揭示这些矿物沉淀的母体流体的来源，采用新的物理方法分离片钠铝石和菱铁矿，以最大限度地减少对其稳定同位素组成分析的不确定性。δ ¹³ C _Daw值范围从 +1.3‰ 到 +1.6‰ 并且计算的 δ ¹³ C _CO2值与片钠铝石平衡 (-4.8‰ - –2.0‰) 与当地 CO ₂和欧洲次大陆岩石圈地幔 (- 3.9‰ - –2.1‰）。这表明形成片钠铝石的CO ₂具有岩浆成因。菱铁矿数据表明，一些由岩浆 CO ₂形成，可能与片钠铝石同时形成 (-6.0‰ - –3.9‰)，而其余 (-8.4‰ - –6.1‰) 由岩浆成因的分馏 CO ₂或在 CO ₂入侵之前。结构 OH 的氢同位素组成^-片钠铝石 (-57‰ 至-74‰) 的含量被确定并用于估计相互作用孔隙水的来源。计算的孔隙水数据（δD：-69‰ - –103‰ 和 δ ¹⁸ O：-1.4‰ - +4.7‰）表明母液是水-岩相互作用改性的大气水。我们的数据允许估计含有片钠石的砂岩储层中储存的 CO ₂总量为25 kg/m ³，这与之前的建模工作完全一致，这给出了总共 2.01 × 10 ⁶  t CO ₂，更高比之前的估计。

我们建议采用单矿物分析并辅以氢同位素分析来有效追踪 CO ₂储层中的储层内流体-岩石相互作用，并为地球化学建模提供有价值的输入数据，以更好地预测 CO ₂矿物储存的条件。