Three hydraulic fracturing have been performed in the Torunos field of southwest Venezuela. One was executed in the Gobernador "A/B" formation in which the fracture reached a water zone located nearby. The other two treatments were performed in the Escandalosa "O" formation. Placing the proppant into this formation was problematic owing to propagation of multiple hydraulic fractures and excessive leak-off. Today, several wells are inactive because of low productivity. Such wells could be potential candidates for reactivation by hydraulic fracturing if the problems encountered in previous treatments can be avoided. Therefore, the purpose of this study is to optimize the design of hydraulic fracturing treatments in the formations under consideration while avoiding the problems encountered in the previous attempts. Experimental design and response surface methods were used to perform sensitivity analyses and to evaluate uncertainty to optimize the design of hydraulic fracturing treatments. Experimental design was used to generate a reduced number of cases with simultaneous combinations of uncertain variables. Simulation of the cases generated was then performed, assisted by a commercial simulator. Response surface method was used to develop surrogate equation models that fit the simulation responses. Monte Carlos analysis was performed to estimate the probability distribution function of the propped fracture length, propped fracture height, depth to the fracture bottom, and net present value (NPV) to select the optimum designs based on technical, economical, and risk analyses. The results show that the optimum hydraulic fracturing treatment design for the Gobernador "A/B" formation should involve small slurry volume (around 300 bbl), a low injection rate (between 6 bbl/min and 8 bbl/min), and low viscosity crosslinked fluid (20 cp). This will control the fracture height and avoid fracturing the water zone. Moreover, reducing the perforated interval to around 20 ft and using low density shot (1 SPF) will help to minimize the propagation of multiple hydraulic fractures in the Escandalosa "O" formation. Finally, the optimum injection rate and slurry volume in this formation are 20 bbl/min and 800 bbl respectively.

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