Since the emergence of the shale gas multi-stage fracture stimulation era, many shale gas operators strive to contact as much reservoir volume from a single well as possible. In the process of optimizing production, completion practices tend to affect already producing wells. Altering the production of an existing well via the stimulation of an offset well, commonly referred to as a frac hit, has been a growing concern. The main driving force in producing any tight formation is the lumped parameter of fracture area and square root of reservoir permeability, Af√k. Often times during the producing life of a well, there is an apparent decrease or increase in the lumped parameter due to frac hits or refracs (a second fracturing or hydraulic stimulation at a later point in time of the same well), respectively. Previous work shows rate transient analysis as an option to evaluate the impact of frac hits or refracs on a well'sproductivity; however, a quantitative analysis will require a more detailed study that combines rate transient analysis with numerical modeling to tackle more complicated issues.

In this paper, we propose a performance based methodology to quantify the amount of area lost (frac hit) or gained (refrac) using analytical approaches that can subsequently be verified using numerical modeling to truly understand the change in stimulated area after the occurrence of a frac hit or a refrac. Several frac hit cases were examined in various shale gas plays such as the Haynesville and the Marcellus. The data from the field cases were used to quantify the impact of a frac hit. The stochastic modeling from rate transient analysis of future performance for the well was compared to the numerical solution. This approach is also valid for refracs to quantify the amount of area created based on well's performance and also pre-design stimulation techniques to study the area created during the refrac.

The approach will help operators to quickly compute the risk of performing refracs and selecting better spacing to control the occurrence of frac hits by quantifying the economical outcome. In addition, the approach might help to minimize the amount of time used in modeling, if required, by creating reasonable ranges for certain reservoir parameters. Lastly, the knowledge gained from this study will help to correlate the extent of potential fracture damage to reservoir properties (e.g. matrix permeability) and optimize future stimulation techniques prior to the stimulation job.

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