Study on influencing factors of matrix acidzing residual flow back in sandstone gas pools

Formation fracturing and acidizing are the important stimulation treatments for low permeability gas formation. Many physical phenomenons happen in the process of residual fluid flow back after acidzing such as gas-liquid two-phase flow, gas channeling, water locking and gas driving water, so the residual returning efficiency is affected by such many factors. The experiments stimulating the single factor and multi-factors affect on return efficiency during matrix acidzing were conducted. The research results indicated that lower permeability has lower return efficiency under the same experimental conditions. Return efficiency is decreasing with the increasing of viscosity and surface intension, but the change is smooth while viscosity increase to a certain degree; in a certain range of surface tension, the effect of surface tension on flow back efficiency is very tiny, which means that the increase of tension causes small decline of flowback. In addition, the effect of parameters k /(??) on the return efficiency is similar to the viscosity according to experimental results. The results also indicate that the smaller the acidzing radius, the easy to get to the limit of flow back efficiency and the resulting efficiency is relative higher. The value of the final efficiency changes little while the radius reaches to a certain value, and the experiment illustrates the final efficiency different form various acidzing radius which is related to formation properties.