  We present a systematic global sensitivity analysis using the Sobol method
which can be utilized to rank the variables that affect two quantity of
interests -- pore pressure depletion and stress change -- around a
hydraulically-fractured horizontal well based on their degree of importance.
These variables include rock properties and stimulation design variables. A
fully-coupled poroelastic hydraulic fracture model is used to account for pore
pressure and stress changes due to production. To ease the computational cost
of a simulator, we also provide reduced order models (ROMs), which can be used
to replace the complex numerical model with a rather simple analytical model,
for calculating the pore pressure and stresses at different locations around
hydraulic fractures. The main findings of this research are: (i) mobility,
production pressure, and fracture half-length are the main contributors to the
changes in the quantities of interest. The percentage of the contribution of
each parameter depends on the location with respect to pre-existing hydraulic
fractures and the quantity of interest. (ii) As the time progresses, the effect
of mobility decreases and the effect of production pressure increases. (iii)
These two variables are also dominant for horizontal stresses at large
distances from hydraulic fractures. (iv) At zones close to hydraulic fracture
tips or inside the spacing area, other parameters such as fracture spacing and
half-length are the dominant factors that affect the minimum horizontal stress.
The results of this study will provide useful guidelines for the stimulation
design of legacy wells and secondary operations such as refracturing and infill
drilling.
