论碎屑岩储层成岩过程中有机酸的溶蚀增孔能力

Porosity enhancement potential through mineral dissolution by organic acids in the diagenetic process of clastic reservoir

碎屑岩储层成岩过程中，烃源岩中有机质热演化能够释放大量有机酸并强烈溶蚀铝硅酸盐和碳酸盐矿物，进而形成规模性次生孔隙的观点为石油地质学家所普遍接受。笔者以国内外有机质热解生成有机酸的实验为依据，系统计算了单位质量干酪根的生酸潜力。以东营凹陷北部陡坡带为例，在计算古近系沙河街组沉积地层泥砂比、主力烃源岩有机质丰度及主力烃源岩最大生一排酸潜力的基础上，分别计算了有机酸溶蚀铝硅酸盐和溶蚀碳酸盐矿物对储层的最大增孔能力。然后以全球范围油气储层地层水有机酸浓度为参考，结合室内有机酸溶蚀碳酸盐矿物的实验，探讨了碳酸盐矿物的规模性溶蚀作用与地层酸性流体供给能力的匹配关系。结果表明：在缺少断层和不整合等优势运移通道时，有机质热演化过程中释放的有机酸溶蚀铝硅酸盐矿物能够产生的最大次生孔隙度约4．49％～7．48％，这一数据在一定程度上与现有认识一致；而有机酸溶蚀碳酸盐矿物能够产生的最大次生孔隙度约1．54％～2．56％，这一数据要大大低于多数学者的主观认识。在缺少足够的碳酸盐溶蚀证据的情况下，将中深层异常高孔隙度储层中大量的粒间孔隙界定为早期碳酸盐胶结物完全溶蚀形成的次生孔隙的观点值得商榷。

In the diagenetic process of clastic reservoirs, organic matters in source rock can release large amounts of organic acids during the thermal evolution process. The hypothesis that these organic acids can strongly corrode aluminum silicate minerals and carbonate minerals to create secondary pores of certain scale is prevalent in petroleum geologists. On the basis of worldwide experimental data of pyrolysis of organic matter, the author calculated the organic acid production potential of unit mass of kerogen. Taking the northern steep slope of Dongying Sag as an example, shale/sand ratio, abundance of organic matter and organic acid production-expulsion potential of main source rock were calculated. With these parameters, porosity enhancement potential for reservoirs through dissolution of aluminum silicate minerals and carbonate minerals by organic acids expulsed from source rock was calculated. Then, with the concentration of organic acids in worldwide oil and gas reservoir formation water as reference, combining with the water-rock reaction experiment, matching relationship between mass dissolution of carbonate minerals and supply capacity of acid formation fluid was analyzed. The result shows that without faults and unconformity as dominant migration pathway, secondary porosity created by dissolution of aluminum silicate minerals by organic acids released through thermal evolution of organic matters can reach as much as 4. 49%- 7. 48%, which is in consistent with existing cognition in some extent. However, secondary porosity created by dissolution of carbonate minerals is at most 1. 54%- 2. 56%, which is much less than the subjective perception of most scholars. Without convincing evidence, the idea that large amounts of intergranular porosity in mid-deep buried anomalously high porosity reservoir should be the secondary porosity produced by the dissolution of the early carbonate cement is fairly questionable.