碳酸盐岩埋藏溶蚀的热力学分析及其地质意义

碳酸盐岩在地下的溶蚀作用本质上是在一定温度、压力条件下的水-岩反应。分析白云石和方解石溶解反应时的吉布斯自由能增量（ΔG）后指出,在25~200℃时,白云石和方解石溶解反应的ΔG随温度变化先减后增,溶解反应先易后难;115~140℃时,溶解最易发生;之后,可能由于沉淀反应加剧,溶解变难。压力的影响相对较小,特别是当压力大于15 MPa时,影响微弱。在相同埋深条件下,白云石较方解石更易溶解。随着埋深的增加,方解石和白云石溶解反应的ΔG同样先减后增,并在4 300~5 000 m达最小值,即埋藏溶蚀最易发生。这为寻找良好的储集层提供了理论依据。

Thermodynamic Analysis of Burial Dissolution of Carbonate Rocks and Its Geological ignificance

Carbonate burial dissolution in nature is water-rock interaction under certain of temperature and pressure.By analyzing the Gibbs free energy(ΔG) of calcite and dolomite dissolution reaction,this paper pointed out that ΔG initially decreased and then increased with temperature increasing gradually at 25～200℃.The dissolution mostly occurred as temperature equaling to 115～140℃.Then carbonate dissolving became difficult when temperature was more than 140℃ due to precipitation.But the impact of pressure on dissolution was relatively small.Especially,when the pressure was over 15 MPa,its impact could be neglected.At the same burial depth,dolomite is dissolved more easily than calcite.In addition,the ΔG also decreased firstly and then increased,followed by reaching to minimum at the depth of 4 300～5 000 m.That means the burial dissolution occurred most easily.It provides theoretical basis for looking for good reservoirs.