Selective matrix acidizing of horizontal wells

The productivity index of a horizontal well in an anisotropic medium is calculated before and after 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 (UTACID) that calculates the permeability distribution around the wellbore, and a reservoir simulator (UTCHEM) that calculates the productivity index of the well. By applying some mathematical transformations, it was possible to reduce the two-dimensional problem to a simpler one-dimensional problem so that the radial acidizing simulator UTACID could be used. A newer and more accurate model for sandstone acidizing, the four-parameter model, is described and implemented in the UTACID simulator. The UTCHEM simulator was tested and shown to be applicable for partially open horizontal wells, with and without a damaged zone. Also, a modification was introduced to allow the calculation of the productivity index of the well.;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 with and without anisotropy. Simulation results indicate that it is possible to reduce the total amount of acid required to achieve a given productivity increase by applying partial acidization. In most cases, the optimal injection rate is the maximum rate that does not fracture the formation. More experimental work is required to extend the validation of the four-parameter model to sandstones that are less permeable and have higher clay contents than Berea sandstone, whose data was used in this research.