长石溶解-沉淀的热力学和动力学特征及其对储层物性的影响——以渤海湾盆地渤南洼陷沙三段为例

The impact of thermodynamics and kinetics of feldspar dissolution-precipitation on reservoir quality: A case study from the E, Bonan Sag, Bohai Bay Basin

沈臻欢 于炳松 白辰阳 韩舒筠 杨志辉 费志斌

Zhenhuan Shen Bingsong Yu Chenyang Bai Shujun Han Zhihui Yang Zhibin Fei

长石溶解及其次生孔隙的形成对砂岩储层质量具有重要影响。为了研究渤海湾盆地渤南洼陷有利孔隙发育带，利用长石溶解-沉淀的热力学和动力学计算，结合薄片分析、孔隙度和渗透率资料，开展了对沙三段长石次生孔隙发育的研究。结果显示，现今的地层水多有利于长石沉淀，部分区域发生长石溶解。结合孔隙度平面分布图和镜下薄片分析可知：孔隙度发育较好的区域主要是钾长石发生溶解，钙长石Δ < -15 kJ/mol溶解速率较快和钠长石Δ < 15 kJ/mol沉淀速率较慢的区域。此外，粘土矿物（高岭石等）在长石溶解形成的次生孔隙中的沉淀，降低了储层的渗透率；且在埋深超过3 000 m的区域，地层水中的SiO（aq）沉淀速率的显著加快降低了储层孔隙度。综上：埋藏环境中，长石的溶解对于次生孔隙的贡献十分重要，但是如果其副产物未发生迁移则对次生孔隙的贡献较小，并且较高的粘土矿物含量会降低储层的渗透率。本文对于利用热力学和动力学模型预测储层发育提供了新的方法。

Feldspar dissolution along with the formation of secondary pores has a great impact on sandstone reservoir qua-lity.In order to study belts favorable for pore development in the Bonan sag, Bohai Bay Basin, we mainly focused on the research of secondary pores of feldspar in the E, by means of thermodynamics and kinetics calculation of feldspar dissolution-precipitation, combined with petrologic characteristics such as thin section observation, porosity and permeability data.The results show that formation water nowadays is favorable for the precipitation of feldspars, with feldspars in some areas having dissolved.According to the horizontal distribution of porosity and the thin section observation under microscope, we may conclude that the areas of better porosity are characterized by K-feldspar dissolution, fast dissolution of anorthite (Δ < -15 kJ/mol) and slow precipitation of albite (Δ < 15 kJ/mol).In addition, the reservoir permeability decreases as clay minerals (including kaolinite) precipitate in those secondary pores with feldspar dissolution.Meanwhile the reservoir porosity decrease accelerates significantly when SiO (aq) precipitation in the formation water in areas is triggered at a burial depth of over 3 000 m.In all, the feldspar dissolution has a great contribution to the formation of secondary pores in burial.However, the contribution may be compromised if by-products from feldspar dissolution are not removed, and higher clay content also tends to undermine the reservoir permeability.The study is a positive demonstration of a new way to predict reservoir quality by thermodynamics and kinetics models.

10.11743/ogg20200204