Minimizing Over-Flush Volumes at the End of Fracture-Stimulation Stages - An Eagle Ford Case Study

Abstract

With the growing popularity of multi-stage hydraulic fracturing treatments in horizontal wellbores, various completion systems have been utilized for mechanical isolation and staging of individual fracture treatments. One of the more popular fracture staging techniques is the plug-and-perf technique in cemented casing, which requires the lateral section of the wellbore to be free of debris and proppant so that the plug and perforation tool string can be pumped down to the desired setting depth. Proppant that has settled in the lateral can result in plugs getting stuck and prematurely setting at the wrong depth, requiring costly intervention work and delaying the progress of completing the well. The industry standard practice to prepare a clean wellbore has been to over-flush each fracture treatment by 50 to 100 barrels in excess of the volume to the perforations. This practice has raised concerns about disturbing near-wellbore proppant conductivity and potentially harming fracture continuity with the wellbore, and thus productivity. Since operators have achieved satisfactory economics in many shale plays, this practice continues despite its controversy. These concerns have led to experiments in minimizing excess flush volumes in wells located in the liquids-bearing window of the Eagle Ford Shale. This paper proposes a process involving the use of real-time treatment data displayed within a wellbore model simulation to adjust the flush volume of each stage based on the reduction in proppant concentration at the perforations. Over 200 stages were successfully placed with this method with no incidences of plugs sticking in the lateral. This paper contains a selection of treatment charts and wellbore diagrams from actual applications of this method. Simulated fracture profiles of different over-flush scenarios are also compared and discussed. This paper will be useful for engineers and managers involved in well completions and stimulation, and presents detailed methodology for successfully applying this strategy in their fields. By applying these procedures, continuity between the proppant pack in the fractures and the wellbore should be improved, and fresh water usage will be reduced.

An Evaluation of Completion Effectiveness in Hydraulically Fractured Wells and the Assessment of Refracturing Scenarios

“…• ЉLiquidsЉ dropout-in rich gas reservoirs, condensate will drop out once reservoir pressure is below dew point; this can create a condensate bank in the greater depleted region surrounding the wellbore altering the effective permeability. • Overdisplacement during treatment-Standard industry practice is to over-flush the wellbore by approximately 50 to 100 bbl more than the volume of the wellbore to the top perf of the treatment (Al-Tailji et al 2014). This process tends to displace the proppant in the NWB region and can reduce the connectivity of the fracture to the wellbore.…”

“…This practice of overflushing can have a measurable impact on NWB conductivity at even 20 bbl greater than the volume to the top of the perforation (Al-Tailji et al 2014). This paper demonstrates that this NWB conductivity damage can severely impact productivity and EUR.…”