Abstract:

According to the principle of thermodynamics, thermodynamic phase diagrams are calculated and drawn, the possibility, direction and physicochemical conditions of the two chemical reaction processes of TSR reaction and dissolution of carbonate rocks by H₂S are determined, and the direct reduction of CaSO₄ (or SO₄²⁻) to H₂S at different temperatures is obtained. It shows that when CaCO₃ is at the boundary between precipitation and dissolution in geological system, a small amount of acidic fluid will make the precipitated CaCO₃ dissolved, and when the concentration of Ca²⁺ and CO₃²⁻ increases, a new equilibrium of precipitation and dissolution will be achieved. When the depth of dissolution of CaCO₃ is about 1000 m, H₂S achieves the best effect. Only long-term and repeated TSR reactions can produce sufficient acidic fluid (H₂S), which is the necessary condition for dissolution modification of carbonate reservoirs to achieve obvious results.

Key words: TSR reaction, H₂S, carbonate reservoir, thermodynamic phase diagram

摘要：

从化学热力学的角度, 通过热力学计算和绘制热力学相图, 针对硫酸盐热化学还原反应(TSR反应)和H₂S对碳酸盐岩的溶蚀两个化学反应过程, 判别其发生的可能性、方向和物理化学条件, 求取不同温度下CaSO₄ (或SO₄²⁻)被直接还原为H₂S的离子浓度、pH和氧化还原条件; 指出在地质体系中, 当CaCO₃处于沉淀–溶解的边界时, 少量酸性流体的加入就会使沉淀转为溶解, 而当Ca²⁺和CO₃²⁻浓度升高时, 又达到新的沉淀–溶解平衡。H₂S对CaCO₃的溶蚀在深度约为1000 m时达到最佳效果, 长期、多次的TSR反应才能产生充足的酸性流体(即H₂S), 这是溶蚀改造碳酸盐岩储层达到明显效果的必要条件。

关键词: TSR反应, H₂S, 碳酸盐岩储层, 热力学相图