浊沸石溶解过程的热力学计算及地质意义

Thermodynamic calculation of laumontite dissolution and its geologic significance

通过热力学计算,探讨了浊沸石在不同成岩流体中溶解的热力学性质。结果表明:①浊沸石溶解反应的吉布斯自由能增量(ΔG)在埋藏成岩条件下都小于0,因此浊沸石溶解反应在埋藏成岩的温度和压力条件下可以自行发生;②浊沸石溶解反应的吉布斯自由能增量(ΔG)与埋藏深度呈正相关,深埋藏条件下的浊沸石溶解反应趋势弱于浅埋藏或地表条件;③在较高的PCO2条件、酸性环境、流体中Ca2+被移走、存在大量K+的情况下,浊沸石容易溶解形成次生孔隙;④浊沸石溶解反应具有减体积效应,其中在K+存在的流体中,Lm-Ill反应的体积减少最多,同时该反应消耗了K+,克服了钾长石溶解的动力学障碍,使得更多的钾长石溶解形成次生孔隙。因此,浊沸石溶解生成伊利石和石英有利于储层的形成。

Based on thermodynamic calculation, the thermodynamic features of laumontite dissolution in different fluid are disscussed. The result indicates that： （1）Gibbs free energy increment （A G） of the reactions involved laumontite dissolution is minus, so laumontite dissolution are all spontaneous reactions in diagenesis environment; （2）Gibbs free energy increment （ A G） of the reactions involved laumontite dissolution is plus relativity with burial depth, and the trend of laumontite dissolution in deeper burial depth is less than that in lower burial or the earth＇ s surface; （3）Laumontite dissolves easily and forms secondary pore in diagenesis environment of higher PCO2, lower pH, decrease of Ca2＋ and increase of K＋; （4）The reactions involved laumontite dissolution are accompanied by the decrease in the volume of the solids, the decrease in the volume of the solids in the reaction Lm-Ill is the most, and it consumes K＋ and conquers dynamics balk of K-feldspar dissolution and makes more K-feldspar dissolution to form secondary pore. So the way which laumontite dissolve to form illite and quartz is most profitable to form reservoir.