MATHEMATICAL MODEL OF MATRIX ACIDIZING FOR PERFORATED WELL IN SANDSTONE AND ITS APPLICATIONS

Wellbore is linked to formation by perforation tunnels in perforated well. The flowing pattern, pressure distribution and the flowing front of acid fluid in perforated well are different that in openhole well. But the acidizing is always designed on the basls of openhole well in China at the moment. In order to obtain more reasonable acidizing design, the pressure differential equation and acid equilibrium equation for matrix acidizing of perforated well in sandstone are esiablished in elliptic coordinate system. Moreover, the minerals in sandstone are dIvlded into two kinds of pseudo-mineral with different dissolution velocity taking silicate and quartz as representative respectively. The pressure distribution, acid concentratlon distribution, sillcate or quartz concentration distribution, porosity and permeabllity distributlon, effective operating radius and production increment multiple can be calculated and predicted by solving the basic equation group in elliptic coordinate system.