This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Denver, Colorado, USA, 22-24 July 2019. The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper by anyone other than the author without the written consent of URTeC is prohibited. Abstract Unconventional reservoirs with prolific production may contain a significant number of complex natural fracture networks. Partially conductive or partially mineralized natural fracture networks could further open due to the stress induced during hydraulic fracturing, and then provide additional pathways for the flow of reservoir fluids in the matrix near the wellbore and its hydraulic fractures. This study investigates the still insufficiently understood complex interaction of natural fracture networks with hydraulic fractures, which impacts the estimation of the drained rock volume (DRV), and fracture spacing for optimal production. Flow in natural fractures is modeled at high resolution using recently developed algorithms, which enable fast, grid-less, Eulerian particle tracking based on Complex Analysis Methods (CAM). Publicly available production data from the Permian Basin was used to visualize the DRV with time-of-flight contours and particle paths, initially assuming a homogeneous reservoir without any natural fractures. Next, the distortion of the DRV, by including natural fractures with different conductivity in the proximity of the hydraulic fractures, is visualized and compared to the homogeneous reservoir without any natural fractures. The shape and location of the DRV in shale wells will be profoundly impacted by the overall location, density, and hydraulic conductivity (strength) of the natural fractures. High-resolution contour plots of (1) drained rock volume, (2) pressure depletion, and (3) spatial velocity variations are presented to compare the fluid migration paths near hydraulically fractured wells with and without natural fractures. Detailed case studies of several wells completed in Wolfcamp landing zones from the Permian Basin (i.e.