Throughout the development of major shale plays, a better understanding of stimulation influence on reservoir productivity has led to significant changes in industry completion practices. The relatively fast development of fields combined with the evolution of completion design suggests the completions performed on the earlier completed wells are understimulated and inadequate for optimum recovery. In the Eagle Ford and Haynesville shales, refracturing treatments were first performed using degradable particulate diversion, but yielded inconsistent results. However, a new method using the installation of a new casing string has been applied to these two separate plays to help reduce risk and maximize asset production.
Precise placement of the restimulation treatment using degradable particulate diversion is complex because of a lack of treatment isolation. The fluid used in restimulation must overcome friction pressure differentials, the presence of several existing perforations, and reservoir depletion. Advancements in cement slurries and wellbore design have made it possible to install a new, smaller casing string into the existing wellbore and restore treatment isolation. Despite the tight annular clearances, a specialized slurry has been designed to maintain circulation and to provide good mechanical properties for proper zonal isolation.
The reconstruction of the wellbore with the smaller casing string enables the refracturing treatment to be performed like new-drill completions by means of plug-and-perforate methodology. Although the treatment injection rate might be limited in comparison, many of the complications in diversion refracturing treatments are eliminated. This process has confirmed greater repeatability and more consistent production results across two separate plays.
The successful implementation of 75 casing-in-casing refracturing treatments in the Haynesville resulted in an average estimated ultimate recovery (EUR) increase of approximately 150%. This technique has been implemented in the Eagle Ford and, although the number of wells in the dataset is fewer, the EUR of some wells observed have experienced an average increase of 140%. This method is becoming increasingly popular, with multiple operators successfully applying this technique throughout different portions of the Haynesville and Eagle Ford Shale.