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As the demand for energy increases, more and more low-permeability reservoirs are being developed with the help of advancements in hydraulic fracturing and horizontal drilling technologies. Integrated reservoir modeling studies become increasingly important to understand and improve reservoir management of such reservoirs for optimum depletion planning. This paper presents the approach used for applying an integrated reservoir modeling workflow to the tight gas sands of the Cotton Valley reservoir. The main objective of the study is to understand well performance for horizontal infill wells with multiple hydraulic fractures. In order to accurately simulate gas flow in hydraulically fractured wells (HFW) in full-field or regional models of unconventional gas reservoirs with many HFW, it is critical to appropriately represent these wells in the simulation models. Various methods have been used in the industry to numerically simulate hydraulic fractures in large reservoir models. In this paper, we will also review these methods and show that almost all the methods require calibration with fine grid models in which the hydraulic fracture is explicitly gridded. For homogeneous models calibration is relatively easy, but it is almost impossible for heterogeneous models. Therefore, we used local grid refinement (LGR) as the solution for modeling hydraulically fractured wells in coarse grid simulation. Our approach is different than other LGR approaches presented in the literature in that we only refine the coarse gridblocks that contain the fractures and wells. Finally, since it is very time consuming to generate LGRs manually for models with many wells a software tool was developed to generate LGR gridding automatically for HFW for commercial simulators. |
