Study On Organic Phosphonic Acid Adjust To The Acidizing Of Sandstone

Due to a variety of problems caused by mudacid acidizing,for example,the fast acid-rock reaction at process of mudacid acidizing,which is easy to cause secondary damage near wellbore and un-fully acidizing in far wellbore.Phosphonic acid system is proposed to solve these problems.Firstly,using dissolution experiments to evaluate the different acid systems,the results show that the dissolution rate of phosphonic acid system on the sandstone is slightly higher than mud acid system.But with time growth,the dissolution rate of the phosphonic acid system on the sandstone mud was significantly higher than the mudacid system,indicating that phosphonic acid has obvious retarder effect.The results of the the dissolution experiment of four kinds of clay minerals indicate that CH phosphonic acid has a better dissolution rate.At the 4h dissolution rate reached about 45%,only half the dissolution rate of mudacid system.And acid the dissolution curve system is significantly slower than mud acid system,indicating that CH acid clay mineral has good retarder effect.Wettability evaluation shows that the wetting contact angle of the two phosphonic acid system with sandstone were 21.2° and 27.5°,less than mud acid system wetting angle 36.2°,showed acid system in the rock surface has a better wettability.Through the evaluation for the chelating ability of acid to calcium ion and ferric ions showed that the chelating ability of CH phosphonic acid system to calcium ions was 145.6mg/m L,and the ability to chelate iron was 59.1mg/mL.The phosphonic acid system have a good chelating ability to prevent secondary sedimentation reservoir damage reduction.The dynamic dissolution rate experiments and scanning electron microscopy showed that the structure of the surface of montmorillonite internal pore throat covered with a layer of white protective film after the dissolution system by CH phosphonic acid,which to prevent the continued the dissolution of phosphonic acid montmorillonite.And it has some obstructions(which was the secondary sedimentation)in some large pore of montmorillonite after the dissolution of mudacid system,further evidence of the ability of phosphonic acid system having better inhibitory secondary precipitation.Through the core flow experiment,the results show that for high and low permeability sandstone reservoir of high clay content in sandstone and carbonate reservoirs,the acidizing effect by phosphonic acid system is significantly higher than the acidification by the mud acid system.Due to the retarder performance and chelating metal ion properties by phosphonic acid,not only can dissolve clay or carbonate of reservoirs,but also effectively inhibits the generation of precipitation.