Modeling the Effectiveness of Diverters for Matrix Acidizing Based on Filter Cake Characteristics

Abstract

During acidizing treatments in carbonate reservoirs, a degradable diversion system (DDS) is commonly applied to achieve a more uniform distribution of acid along the wellbore. The effectiveness of a DDS strongly depends on the permeability of the filter cake, which is formed by diverter materials that accumulate inside perforation tunnels or on the rock face. A new DDS with a lower filter cake permeability than a conventional DDS is presented, along with a study based on an acidizing model to show the effect of fiber cake permeability on acid diversion. An existing acidizing model was applied as a tool to evaluate the diversion effect of a DDS. The model was created by considering fluid flow in the wellbore, fluid distribution among reservoir zones, and predicted wormhole propagation inside the formation. The model also has the capability to simulate the formation of filter cake, either inside perforation tunnels or on the rock face, and redistribute the fluid flow accordingly. To fully understand the role of filter cake permeability on the effectiveness of a DDS, simulation cases were established for both a conventional DDS and the newly-introduced, low permeability DDS. The reservoir permeability contrasts among zones was also varied to understand the applicable range of a given DDS. The DDS effectiveness can be evaluated by comparing the simulated bottomhole pressure response and the acid injection rate into each zone. The simulation results indicate that the low permeability DDS is significantly more effective than the traditional DDS. In all cases, the use of the low permeability DDS predicts a larger pressure response resulting from the temporary blocking of high permeability zones as well as better acid injectivity in low permeability zones. Based on the flow rate distribution, the effect of filter cake permeability is clearly observed up to a permeability contrast of 50 between reservoir zones. By providing a better flow to low permeability reservoir zones, the new DDS demonstrates better diversion performance than the traditional DDS; this results in a more successful acidizing treatment, especially when the permeability contrast of the reservoir zones is high.