This study presents a workflow for identifying and evaluating well interference, and investigating how interference affects fracture cleanup in a multi-well pad.
We analyze flowback pressure and tracer data from a 10-well pad completed in three shale members of the Horn River Basin. Three key steps are used in this study: First, we analyze the tracer concentration profiles to investigate well interference in the pad before flowback. Second, we compare the casing pressure of the wells during selective shut-in and re-opening to investigate well interference during flowback and post-flowback periods. Third, we construct diagnostic plots of gas-water ratio (GWR) to see how well interference affects fracture cleanup during flowback.
We observe that well interference in the pad occurs in three stages – before flowback, during flowback and during post-flowback. Before flowback, concentration profiles from some wells show early breakthrough of tracers injected into neighboring wells in the pad. Analysis of the tracer data suggests that fracturing operations create connecting pathways among the wells in the pad. During flowback and post-flowback, we observe that the shut-in and re-opening of some wells in the pad disturb the recorded pressure in the remaining wells. The log-log plots of GWR versus cumulative gas production for late-opened wells show an approximate half-slope, suggesting fracture cleanup. However, this trend of fracture cleanup is not observed for the early-opened wells. This shows that the early-opened wells drain fracturing water from the late-opened wells through connected fractures, when the wells in a pad are opened for flowback in a sequence. Combined analysis of flowback and tracer data helps to understand how fracturing water migrates between wells, and to optimize well placement in a pad.
"Frac-hit" is a common phenomenon when multi-fractured horizontal wells are tightly spaced in an unconventional reservoir. Frac-hit is a rapid pressure increase in wells that are shut-in during the fracturing treatment of offset wells. Well interference during fracturing operations has been identified and evaluated using the pressure increase during frac-hit (Sardinha et al. 2014; Lehmann et al. 2016). However, it is not clear if the well interference caused by frac-hit is sustained after fracturing treatment, and how it affects hydrocarbon production.
