SELECTIVE MATRIX ACIDIZING OF HORIZONTAL WELLS

The productivity index of a horizontal well in an anisotropic medium i s calculated during a process of partial acidization in which damage r emoval occurs only over a fraction of the length of the well. Two nume rical simulators are used in this work: an acidizing simulator which c alculates the permeability distribution around the wellbore and a rese rvoir simulator which calculates the productivity index of the well. B y applying mathematical transformations, it was possible to reduce the acidizing model from a two-dimensional (2D) problem to a one-dimensio nal (1D) one. By comparing treatment results, it is possible to select the optimal volume of acid, injection rate, and fraction of the lengt h to be acidized for each particular well. The same procedure may also be applied for vertical wells both with and without anisotropy. Simul ations results indicate that the application of a partial acidizing st rategy reduces the total amount of acid required for a significant imp rovement in well productivity. This may substantially reduce the finan cial, operational, and environmental risks involved in the treatment o f a horizontal well. In most cases, the optimal injection rate for san dstone acidizing is the maximum rate which does not fracture the forma tion.