LAUSR

Several factors affect the performance and stimulation design of hydraulically fractured wells. Moreover, the dominant factors vary for different quantities of interest, and vary based on the spatial location and with the time of interest. Thus, it will be beneficial if there is a systematic procedure to identify the dominant factors affecting the quantities of interest. To this end, 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 two main reasons for choosing the Sobol method are that it can capture the individual and interaction effects of input variables on the variance of outputs (which is not the case with local sensitivity analysis techniques). It also furnishes a systematic procedure with strong mathematical underpinning to generate ROMs for various quantities of interests for a given mathematical model and for a given set of input variables. The main findings of this research are as follows: (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 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.