Abstract Accurate prediction of CO2 partial pressure (pCO2) in sedimentary basins is important for reducing risk in natural gas exploration, predicting non-hydrocarbon gas in geological formations, improving reservoir quality prediction, optimizing production and reservoir management operations, and understanding geological storage of CO2. It has been proposed for some time now that pCO2 in sedimentary basins is buffered by water-mineral-gas interactions and is primarily related to the temperature. However, the pCO2 values predicted from thermodynamic calculations do not always match field observations. Here, we developed a new and general geochemical model to predict pCO2 in sedimentary basins. By treating each component of the geochemical model of CO2-water-rock reactions rigorously, our model is able to match observed pCO2 in a number of sedimentary basins around the world. The thermodynamic treatments introduced in the model include: (a) a gas mixture including CH4(g), CO2(g), H2S(g), and H2O(g) rather than a single gas in previous models; (b) the Peng-Robinson Equation of State to calculate the fugacity coefficients in the gas mixture rather than assuming ideal gas; (c) taking into account of the hydrostatic pressure of the system and make pressure corrections on equilibrium constants of gas, aqueous species, and minerals reactions. For sedimentary basins with complicated uplift and subsidence history, we introduced reaction path modeling to account for the P-T history. The geochemical model allows the input of basin-specific conditions and serves as a tool to identify the key processes that control pCO2 in sedimentary basins.

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作为沉积盆地温度函数的 pCO2 矿泉水-气相互作用模型

摘要 沉积盆地 CO2 分压 (pCO2) 的准确预测对于降低天然气勘探风险、预测地质地层中的非烃气、提高储层质量预测、优化生产和储层管理操作以及了解 CO2 的地质储存具有重要意义。 . 一段时间以来，有人提出沉积盆地中的 pCO2 受到水-矿物-气相互作用的缓冲，并且主要与温度有关。然而，从热力学计算中预测的 pCO2 值并不总是与现场观测相符。在这里，我们开发了一种新的通用地球化学模型来预测沉积盆地中的 pCO2。通过严格处理 CO2-水-岩反应地球化学模型的每个组成部分，我们的模型能够与世界各地许多沉积盆地中观测到的 pCO2 相匹配。模型中引入的热力学处理包括： (a) 包含 CH4(g)、CO2(g)、H2S(g) 和 H2O(g) 的气体混合物，而不是以前模型中的单一气体；(b) Peng-Robinson 状态方程计算气体混合物中的逸度系数，而不是假设理想气体；(c) 考虑系统的静水压力并对气体、水相和矿物反应的平衡常数进行压力修正。对于具有复杂隆起和沉降历史的沉积盆地，我们引入了反应路径模型来解释 PT 历史。