从表生到深埋藏环境下有机酸对碳酸盐岩溶蚀的实验模拟

Experimental simulation of dissolution for carbonate rocks in organic acid under the conditions from epigenesis to deep burial environments

通过细粉晶白云岩、泥晶灰岩、泥灰岩和含生屑泥晶灰岩与2 ml/L乙酸溶液的溶解动力学实验，研究了从表生到深埋藏环境下有机酸对碳酸盐岩储层的改造作用机理。结果显示，四种类型碳酸盐岩的溶解速率在3.34＆#215;10-9~2.27＆#215;10-8 mol/（cm2＆#183;s）之间，并且溶解速率随埋藏深度（地层温度和地层压力）的增加而增大。从表生到中埋藏环境下，泥晶灰岩、泥灰岩和含生屑泥晶灰岩的溶解速率大于细粉晶白云岩；在深埋藏环境下，细粉晶白云岩的溶解速率逐渐与泥晶灰岩、泥灰岩和含生屑泥晶灰岩的一致，这揭示出在相对高温高压下，埋藏有机酸性流体对碳酸盐岩的溶蚀改造作用中，碳酸盐岩的溶蚀速率与其方解石和白云石含量的关系并不大。反应前后样品表面的扫描电子显微镜分析结果表明，细粉晶白云岩的晶间溶孔、晶内溶孔更加发育。细粉晶白云岩中白云石溶解成蜂窝状溶解孔，晶间缝溶蚀加大且相互连通，这种微观溶蚀特征更有利于油、气的储集及运移。结合岩石的溶蚀速率及其微观溶蚀演化特征，指出碳酸盐岩矿物成分和含量固然对其溶蚀作用具有控制影响，但是碳酸盐岩溶蚀形成的孔隙类型及其连通性能与碳酸盐岩有利储层形成的关系更为密切。

This contribution aim to study the control factors and mechanism of carbonate rocks dissolution in organic acid under the conditions from epigenesist to deep burial digenesis environments. The reactions of acetic acid （initial 2 ml/L） with finely crystalline dolostone, bicritic limestone, barlstone, and bioclasts packstone were investigated using continuous flow column reactor system. The results indicate that dissolution rates of carbonate rocks are between 3.34＆#215;10-9-2.27＆#215;10-8 mol/（cm2＆#183;s）, and dissolution rates increase as the burial depth increasing. In the conditions from epigenesist to middle burial digenesis environments, the dissolution rates of bicritic limestone, barlstone, and bioclasts packstone are larger than that of finely crystalline dolostone. In the condition of deep burial environments, the dissolution rates of bioclasts packstone, bicritic limestone, barlstone, and finely crystalline dolostone are basically the same. The dissolution rates of carbonate rocks indicate that the content of calcite and dolomite in the carbonate rocks is not the main control factor for burial dissolution of carbonate rocks in organic acid fluid. Scanning Electron Microscope images and EDX spectrum were used to analyse the carbonate rocks before and after experiment. The results indicate inter-crystal and intra-crystal dissolution pores of finely crystalline dolostone were more developed. The dolomites of finely crystalline dolostone were eroded into honeycomb-like pores on the rock surface. The inter-crystal fractures of dolomite were enlarged by dissolution and became interconnected. The micro-corrosion characteristics of finely crystalline dolostone are better for reservoir and permeability of oil and gas. The results of dissolution rates and micro-corrosion characteristics of finely crystalline dolostone, bicritic limestone, barlstone, and bioclasts packstone in acetic acid solution show that the mineral composition and content of carbonate rocks control the dissolution process. There is a close relationship between the type of dissolution pore and connectivity for carbonate rocks and carbonate reservoir formation.