The use of horizontal wells and multistage fracturing that is currently common in unconventional reservoirs first became popular during the early 2000s. Since then, the effectiveness and efficiency of horizontal wells has continued to be recognized. Because of the large number of these horizontal wells, significant opportunities for refracturing exist. Restimulation of these wells can allow the operator to increase production, as well as recoverable reserves, generally more economically than by installing new laterals or by infill drilling. An important challenge in refracturing these wells is to understand the rock system in which the well and the hydraulic fracture system are placed.
The major hurdle for net returns on any restimulation is effective candidate selection. This process involves not only choosing the right well, but also choosing the best zones within that well. Often, either a well (or zone) has not produced adequately or has been prolific and is in decline. However, there is no model that can predict production as accurately from unconventional reservoirs as from conventional ones. There are, however, measurable parameters that, when analyzed together, can indicate the relative potential of one zone to another. Therefore, to perform this analysis, any available data on the reservoir should be gathered. Then, well diagnostics are run to fill in the inevitable gaps in these data.
This paper discusses using a novel combination of cased-hole logging tools to gather these data. Using this combination to log the well after the first hydraulic fracturing treatment, the optimum restimulation candidate(s) can be determined. Then, whether to use existing perforation locations or to perforate new areas to cover non-stimulated rock can be decided; thus, optimizing the refracturing process. This selectivity of both candidates and zones during the refracture design can save time, costs, and resources, increasing the economic efficiency of the operation.