Abstract: In sandstone reservoir acidizing,there are problems of conventional mud acid system that it reacts with minerals too quickly,secondary precipitation happens easily and the effective distance of acid liquid is short.The existing retarded acid system can not overcome the huge contrast of the reaction speed between clay and quartz interfaces,new deep acidizing technique can increase the penetration distance of acide liquid in a certain degree though,the technique is complicated and it can not solve the problems of precipitation and block-out.The multi-hydrogen acid system,compared with existing HF system,reacts more slowly,is more capable of dissolution and anti-scaling and dispersivity property,it can constrain formation damage nearby well bore and effectively control secondary precipitation.The acidity characteristics,dissolving property,wettability,stastic corrosion property,dispersivity and anti-scaling property of multi-hydrogen acid are tested in-door,the aciding effectiveness test of mud acid,fluoboric acid and multi-hydrogen acid is evaluated.Case study indicates the multi-hydrogen acid is excellent in property and acidizing effectiveness can be enhanced considerably.

Key words: multi- hydrogen acid, mud acid, acidizing, secondary precipitation, field application