A Novel Model for Fracture Acidizing with Important Thermal Effects

Fracture acidizing is a well stimulation technique used to improve the productivity of low-permeability reservoirs, and to bypass deep formation damage. The reaction of injected acid with the rock matrix forms etched channels (that depend on injection rate, mass transport properties, formation mineralogy, reaction chemistry of the acid, and temperature) through which oil and gas can then flow upon production.

The use of a model that can effectively describe fracture acidizing is an essential step in designing an efficient and economical treatment. Several studies have been conducted on modeling fracture acidizing, however, most of these studies have not accounted for the effect of variation in acid temperature (by heat exchange with the formation and the heat generated by acid reaction with the rock) on reaction rate and mass transfer of acid inside the fracture.

In this study, a new fracture acidizing model is presented that uses the lattice Boltzmann method for fluid transport and takes into account these temperature effects. The lattice Boltzmann method incorporates both accurate hydrodynamics and reaction kinetics at the solid-liquid interface. This method is also well known for its capability to handle re- active transport in complex geometries. This enables the method to model realistic fracture shapes, on a pore-scale level, and predict the shape of the fracture after acidizing. Results of carbonate fracture dissolution with and without the thermal effects are presented. It is found that including thermal effects alters the predicted shape of the fracture after acidizing.