Restimulation Design Considerations and Case Studies of Haynesville Shale

Abstract

This paper discusses a method for, and case histories of, using an environmentally acceptable, selfremoving particulate diverter that has proven to be successful in the refracturing efforts of horizontal unconventional reservoirs. This method is typically chosen for its low cost, self-assembly, self-removal, and ease of addition into treatment. An outline of the evolution of restimulation design, typical procedures, and candidate selection strategies is provided. The ability to add reservoir contact, restore conductivity, and remediate blockage makes this technique desirable. Different strategies can be applied when using this product and are typically customized to the particular candidate well selected for the refracturing treatment. The treatment design is also often customized to the particular candidate well; however, key components of the design are outlined. Candidate wells for refracturing typically fall into one or more categories:• Understimulation occurred in the original completion.• Production damaging mechanisms are present. • A low investment lease retention strategy is required. • A pressure-sink mitigation strategy is necessary for infill completions.A typical procedure will consist of casing inspection, wellbore cleanout, addition of perforations, and flowback considerations.In this study, different Haynesville shale refracturing treatments and results are compared. The evolution of treatment designs, such as carrier fluid, fluid volume, proppant volume, and diverting methodology, are explained. The results and the theory behind these changes are outlined, along with the economic viability of refracturing treatments. Pre/post-treatment estimated ultimate recovery (EUR) calculations are compared, along with treatment pressure trend analysis. The EUR uplift from the refracturing treatments is used to show the economic viability.Although performing secondary stimulation treatments is not uncommon, the industry's focus on improving production decline curves has led to a surging interest in refracturing horizontal unconventional reservoirs. Decline rates in unconventional reservoirs tend to be more rapid compared to conventional reservoirs because of their ultralow permeability, limited reservoir contact, and original completion strategy. Restimulation of these reservoirs enables the recovery of hydrocarbons trapped by these restrictions.

Prediction of Production Performance of Refractured Shale Gas Well considering Coupled Multiscale Gas Flow and Geomechanics

“…The earlier the refracturing time is, the higher the initial production and the cumulative production will be. However, the percentage difference of cumulative production increment after refracturing will become smaller as production time increases (8) The contribution of slip flow decreases, while the contributions of surface diffusion and Knudsen diffusion become more remarkable as the pore pressure declines, respectively. The decrease in permeability loss becomes smaller as the pore pressure decreases, because the apparent permeability will increase greatly owing to the significant enhancement of diffusion and slippage effects (9) The stress-sensitive effect is an important reason for the gas production loss, but slippage and diffusion effects can offset the production loss caused by matrix stress sensitivity to a certain extent.…”

“…A limited region of initial fracturing results in insufficient gas supply for propped hydraulic fractures, and fracture conductivity loss resulted from the geomechanical effect during the production process causes a rapid production decline [3][4][5][6][7]. To solve the problem of rapid production decline of shale gas wells, a large number of refracturing technologies and field experiments have been carried out in North America and achieved a well stimulation effect [8][9][10][11][12].…”