A new rod source model for pressure transient analysis of horizontal wells with positive/negative skin in triple-porosity reservoirs

Although the concept of triple-porosity system has been introduced to describe naturally-fractured reservoirs, few models have been reported for horizontal wells in triple-porosity reservoirs; meanwhile, horizontal well is usually considered as a line source in conventional methods for the purpose of pressure transient analysis, but theoretically it is more like a rod source rather than a line source considering the radius of horizontal well. In this paper, the pressure transient behavior is obtained for horizontal wells with non-negligible well radius in triple-porosity reservoirs, which is achieved by utilizing source function method, substituting rod source for line source and sphere-surface source for point source. The concept of effective radius of horizontal wells is introduced after the similarity has been identified by comparing the early-stage flow characteristics of horizontal wells with vertical wells. Based on the concept, a new method is developed to calculate the pressure transient behavior and to plot the type curves for horizontal wells with negative skin factors. This method finally solves the problem of calculating pressure transient behavior of horizontal wells with negative skin factors which cannot be solved by conventional methods in the past 30 years. At last, the comparison of calculated results from both conventional and proposed method is presented in this paper, which indicates that the method proposed in this paper is correct and more applicable than conventional methods.