High-resolution visualization of flow interference between frac clusters (Part 1): Model verification and basic cases

The reservoir drainage around horizontal wells is visualized at high-resolution using a newly developed analytical streamline simulator based on complex potentials. Drainage contours show the progressive oil recovery from the stimulated rock volume (SRV). The method plots streamlines, the time-of-flight for fluid to fracs, velocity contours and pressure distribution around fracked wells. Independent simulations with a commercial reservoir simulator confirm the visualizations with complex potentials are accurate, and that the latter method gives high-resolution images of the pressure and flow field around individual fracs. We show the depth of investigation reflected by pressure contour gradients is a poor indicator of drained reservoir volume. Drainage contours based on particle velocity tracking give a much clearer view of the actual region drained by a well via its fracs. First, matrix drainage by 2-frac and 3-frac clusters is studied in detail. Flow separation surfaces between 2 clustered fracs (with equal length and flux) are always straight, creating planes of symmetry between adjacent drainage regions. Clusters of 3 fracs develop curved flow separation surfaces, convex toward the inner frac. For frac spacing less than 4 times total frac length, drainage of the central region of the 3-frac clusters slows down due to flow interference, which confirms earlier findings that production gains become insignificant above certain frac length/spacing ratios. Next, the analysis shows the flow field, drainage contours, velocity contours and pressure distribution for a horizontal, synthetic well with 11 transversal, kinked fractures. The basic analysis in this paper (URTeC 2670073A, Part 1 of our study) is expanded in a companion paper (URTeC 2670073B, Part 2 of our study), which applies the methodology of flow visualization using drainage and velocity contours to a sample well from the Midland Basin, Texas.