Selective matrix acidizing of horizontal wells

The productivity index of a horizontal well in an anisotropic medium is calculated during a process of partial acidization in which damage removal occurs only over a fraction of the length of the well. Two numerical simulators are used in this work: an acidizing simulator which calculates the permeability distribution around the wellbore and a reservoir simulator which calculates the productivity index of the well. By applying mathematical transformations, it was possible to reduce the acidizing model from a two-dimensional (2D) problem to a one-dimensional (1D) one. By comparing treatment results, it is possible to select the optimal volume of acid, injection rate, and fraction of the length to be acidized for each particular well. The same procedure may also be applied for vertical wells both with and without anisotropy. Simulations results indicate that the application of a partial acidizing strategy reduces the total amount of acid required for a significant improvement in well productivity. This may substantially reduce the financial, operational, and environmental risks involved in the treatment of a horizontal well. In most cases, the optimal injection rate for sandstone acidizing is the maximum rate which does not fracture the formation.