An Evaluation of Completion Effectiveness in Hydraulically Fractured Wells and the Assessment of Refracturing Scenarios
Authors: Dahl Jeff , Dhuldhoya Karan , Vaidya Ravimadhav , Tucker James , Samaripa James , Johnson Bill , Dusterhoft Ronald 
Published: January 2016

Abstract
For refracturing candidate selection, good reservoir understanding and a thorough evaluation of completion effectiveness is necessary to help minimize risk. However, this task can be difficult because of various uncertainties in terms of reservoir characterization and completion evaluation procedures.
Failure to identify damage mechanisms when evaluating potential refracturing candidates can cause varying success rates and often minimal incremental recovery or marginal economics. Stimulation effectiveness is often modeled, but current fracture models often do not accurately describe realistic fracture flow capacity and complex geometry. Detailed reservoir characterization, simulation, and production history matching in conjunction with pressure tests and diagnostics can be a much better indicator of completion effectiveness to assess the impact of refracturing design. This paper presents a case study of a well in the Eagle Ford Shale in which a holistic reservoir evaluation was performed using reservoir analysis and simulation.
The case study helped determine key reservoir and fracture attributes and allowed subsequent investigation into the effectiveness of various refracturing scenarios. Various information sources and tools were used, including a regional earth model, diagnostic fracture injection test (DFIT), and rate transient analysis (RTA) for the analyses. The study evaluated multiple models for the reservoir and fractures (fracture geometry length, height, and width) and cluster efficiency (number of fractures) and calibrated them to production history through the adjustment of various parameters (e.g., matrix permeability, relative permeability, gamma factor in both matrix and fractures, etc.). Comparison between the data derived from the DFIT and RTA to the calibrated reservoir models was performed to determine the most representative model. The refracturing study involved advanced reservoir analysis for these wells that identified the contribution of the various damage mechanisms and suggested the presence of significant near-wellbore (NWB) damage/skin. A comparison of the effectiveness of damage removal was performed for various refracturing scenarios (i.e., addressing only the NWB damage, new rock stimulation, and the combination of both). Simulation results indicated that, by addressing only the NWB damage, incremental recovery over a 10-year forecast yielded nearly identical or higher cumulative production than stimulating new rock (i.e., creating new fractures). These results suggest further investigation of the associated damage mechanisms and the refracturing methods to remediate them is necessary.
Refracturing economics have great potential for optimization; the need for optimization is especially prevalent during times of reduced drilling activity. Removal of NWB damage could likely be achieved at a lower cost in comparison to large scale refracturing treatments. Similar or greater simulated production provides strong support for the economic benefits of applying the methodologies presented. If proper identification of the damage mechanisms can be attained, then the tailoring of the refracturing design to address those damage mechanisms would result in higher efficiency and return on investment (ROI).