Chemical Remediation of Fracture Damage in Unconventional Well Completions

Abstract In unconventional reservoir wells completed with multi-stage hydraulic fracturing, the massive fracture network created is connected to the wellbore through a relatively small number of perforations and the propped fractures emanating from those perforations. Because all production must converge through a very small flow cross-section near the well, any permeability damage to the near-well propped fractures can drastically reduce well productivity. This paper describes the common sources of such near-well fracture permeability damage, the diagnostic procedures used to properly identify the damage source, and appropriate chemical remediation methods. Damage mechanisms that have been documented in fractured unconventional wells include capillary phase trapping, reduced hydrocarbon relative permeability, polymer gel damage from friction reducers, paraffin or asphaltene deposition, scale deposition, and biofilm deposition. A variety of chemical treatments are being applied to remediate these types of damage including acids, chelating agents, organic solvents, surfactants, oxidants, and combinations of these chemicals. The key to successful chemical remediation is correct diagnosis of the dominant impairment so that the proper chemical system is selected. Diagnosing near-well fracture damage relies on production history analysis, produced water chemistry, artificial lift performance, and detection of solids or scale deposition in tubulars or surface equipment. Changes in decline trends or flowing water/oil or gas/oil ratios, particularly when correlated with events such as offset-well stimulation, can indicate the onset of damage. Polymer gel damage caused by polyacrylamide friction reducers is one of the most common and severe contributors to near-well impairment in slickwater-stimulated unconventional formations. This paper uses this mechanism to illustrate the diagnostic workflow and treatment design to remove the damage. Case histories demonstrate that crosslinked polymer residue can be identified through abnormal decline behavior, frac-hit-induced performance degradation, or direct observation of solids during flowback, and that chemical remediation using acid and metal-complexing agents can successfully restore fracture conductivity and well performance.