The technology of hydraulic fracturing in horizontal wells has been widely applied to successfully developing unconventional reservoirs. However, observations show that that there are occasions that lead to irregular performances resulting in poor recoveries. This paper examines one of the causes for such poor recovery performnces.
We studied the nonuniformity of stimulated volume size among staged fractures and the impact of such nonuniformity on well production and the ultimate recovery. The inspiration comes from studying microseismic fracture mappings from several wells in three shale plays. These images point to the existence of nonuniform stimulated volumes. The maps of various microseismic events show that stimulated reservoir volumes (SRVs) vary from stage to stage because of rock lithology, treatment volumes or other factors. We conducted model studies to simulate the impact of fractures with different SRVs on horizontal well production. We observed the presence of crossflow using the log-log plot of inverse rate versus Time. The results of the simulation show that the presence of crossflow can have a negative effect on well production and recovery factors. We examined the nature of crossflow as a function of fracture conductivities and stimulated volumes.
This paper for the first time shows the importance of prior detecting of unequal SRVs as seen on the microseismic data for potentially refracturing intervals with poor SRVs before a well is placed on production.