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Optimization of Well Placement and Fracture Design for Multi-Well Pads in Unconventional Tight Reservoirs Chen, Nancy Shengnan

Description

Well pads with multiple horizontal wells are widely used to develop the unconventional tight and shale oil reservoirs, which is driven by both the economic and environmental considerations. Thus, determining the optimal well spacing, placement configuration, and stimulation design is critical to optimizing hydrocarbon production from multi-well pads in unconventional. Recent research efforts have been devoted to maximizing the oil/gas production or the NPV in unconventional reservoirs by utilizing analytical models and reservoir simulations. However, owing to the complexity and computationally expensive simulation of the field-scale problem, the optimization process is mostly restricted to the parametric-sensitivity analysis, where a single variable is varied while others are fixed as constant values. In this work, a new Generalized Differential Evolution (GDE) algorithm has been developed and successfully applied to optimize the well placement as well as fracture parameters of a multi-well pad under constraints. A new well completion economic model based on the field dataset is developed and incorporated into the optimization framework, allowing us to find a practical optimum scenario for the multi-well pad development. A field case in Cardium tight oil reservoir is finally used to demonstrate the successful application of the newly developed optimization framework. It is shown from optimum solutions that the well spacing between 230 and 280 m is considered to be the optimum range for the multi-well pad development in Cardium tight formation. The optimum fracture half-length ranges from 82 to 97 m, and the optimum value of fracture conductivity is between 220 and 240 md⸱m. Under an optimal design of well placements and fracture parameters, the proppant pumped per stage ranges from 15 to 20 tonnages and fracturing fluid injection volume is between 100 and 130 m3 per stage. In summary, the relationship between the overall NPV and total fracture volume is complicated and it is of practical importance to optimize the total fracture volume and strike a balance between the oil production and stimulation cost in order to achieve a higher NPV.

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