EXPERIMENTAL STUDY OF MULTI-SCALE REACTION BETWEEN ACID AND ROCK IN ACID FRACTURING

Most of previous researches about acid/rock reaction are single scale and lack of multi-scale investigations.With orthogonal experiment method,nine acid erosion experiments of limestone particles,obtained from Changxing Formation of Permian in Sichuan Province,were designed and carried out.From the experiments result,it is discussed that the macroscopical reaction rate and mesoscopic reaction mechanism,which are influenced by four factors such as main acid concentration,temperature,reaction duration and acid type.The macroscopical reaction rate is most greatly affected by acid type,which is followed by main acid concentration.The rock mesoscopic structures observed by scanning electron microscope,such as pores,fractures and surfaces patterns,may be variously changed by acid erosion.In other words,there are various mesoscopic erosion mechanisms of carbonate rock."communicating fractures and expanding pore throat",summarized by previous researchers,is only a special case of mesoscopic erosion mechanism of limestone.When it comes to the relationship of different scale reaction properties,there is no obvious correlation between macroscopical reaction rate and mesoscopic reaction mechanism.