【摘要】 方解石在沉积岩成岩环境中的溶解度与地下水化学特征、温度等有着极为密切的关系。地下水碳酸体系中各碳酸组分的比例是溶液pH值的函数,可溶性CO2、HCO3-和CO32-分别在pH≤pK1的酸性介质、pK1≤pH≤pK2的弱酸至中性介质和pH≥pK2的碱性介质中具有绝对数量。而地下水体系中碳酸总量及各组分的变化受到pH值、气相CO2分压PCO2及固相方解石的溶解-沉淀效应的控制。通过限定溶液中离子的电价平衡和质量守恒约束条件可以确定各种温压环境中的地下水组成及方解石的溶解度特征。溶液pH值和温度是方解石溶解度的最直接的控制因素,且方解石的溶解随pH值不同分别在强酸、弱酸和碱性介质中表现出不同的反应方式。基于质量守恒条件,溶液中初始[ΣCO2]-[Ca2+]值对中性至碱性介质中的方解石溶解度带来很大的影响,当[ΣCO2]0<[Ca2+]0有利于方解石的溶解,当[ΣCO2]0>[Ca2+]0时有利于方解石的沉淀。如果CO2—H2O—CaCO3体系同时受到电价平衡和质量守恒条件的约束,则方解石只在酸性介质中溶解,碱性介质中沉淀。新疆塔里木盆地库车坳陷克拉2气田及相关储层中方解石分布特征表明,该区碎屑岩储层中方解石的大量沉淀发生于重碳酸钠型地下水环境中,而孔隙度极好、次生孔隙发育的储集段则出现于氯化型的地下水环境,从而验证了成岩作用中地下水类型对方解石溶解—沉淀的控制机制。更多还原

【Abstract】 The solubility of calcite in the diagenesis is closely related to the chemistry of groundwater and the temperature.The percentage of components of carbonic acid in groundwater is dependent on the pH value.Soluble CO₂,HCO^-₃ and CO^2-₃ are the predominant components in the acidic medium with pH≤pK₁,the neutral one with pK₁≤pH≤pK₂ and the alkaline one with pH≥pK₂,respectively.The total carbonic acid and the component concentrations in groundwater are controlled by the pH value,the partial pressure of gas CO₂ and the solution-deposit effect of solid calcite.The pH value and the temperature of solution is the main factors to control the solubility of calcite.Based on the mass conservation condition,the initial [ΣCO₂]-[Ca²⁺] value deeply influences the solubility of calcite in neutral and alkaline media.The condition with [ΣCO₂]₀<[Ca²⁺]₀ in the solution is favorite to dissolution of calcite and that with [ΣCO₂]₀>[Ca²⁺]₀ is favorite to deposit of calcite.It is shown from the distribution of calcite cements in sandstone reservoirs from Kela 2 gas field,Tarim basin,that the deposit of calcite cement occurs in the sandstone reservoirs with the groundwater of NaHCO₃ patterns and the dissolution takes place in those with groundwater of CaCl₂ patterns.It gives us an example to discuss the mechanism of dissolution and deposit of calcite cement controlled by groundwater patterns.更多还原