Refracturing Success Study in Medium Permeability Conventional Reservoirs

Abstract Hydraulic fracturing operation is often the most efficient method to develop low-to-mid permeability reservoirs. However, not every reservoir and not every fracturing operation have the same longevity of the positive impact. Re-fracturing operations have proven to be a success on many occasions, however industry still lacks a consistent guideline of when, how and where to perform re-fracturing treatments. This study provides in-depth research of refracturing methods for mid-permeability conventional oil reservoirs. Study represents an integrated approach covering all aspects of brown field development via re-stimulation that included candidate selection; verification of remaining oil-in-place; estimating the current skin-factor of the well through sophisticated workflow of production history match and initial fracturing geometry match through pressure behavior; assessing the risk of water breakthrough from underlying layers or waterfront from offset injector wells. The methodology to optimize refracturing operation was formulated through design-execution-evaluation cycle with detailed workflows across each phase. Mathematical normalization methods were used to compare different wells under common grounds for efficiency identification. Statistical analyses were based on refracturing operations in more than 30 wells from 9 oil fields and multiple reservoirs. The study revealed that even under-designed initial fracturing treatments could result in a skin-factor of -3.5 to -4.0 and throughout the period of 2-10 years’ time more than half of the wells could maintain the negative skin factor of an average of -1.8 at the time of refracturing operation. However, the refracturing operation could still gain significant benefit and improve the final skin factor up to -5.1 when a careful candidate recognition process was followed. Four case studies with different scenarios are given to showcase the process to decide of refracturing and succeed through the design-execution-evaluation cycle with the detailed workflow. As shown in the paper, the integrated approach helped engineering team to enhance the incremental oil production from refracturing operations by 43% when compared to conventional refracturing approach; and respectively increased economics success ratio from 34% to 79% based on normalized cash flow after 270 days of post-refracturing cumulative oil production. Study represents one of the few documented cases of massive refracturing operations in medium permeability reservoirs. Mathematical methods used to visualize and normalize the production history for the representative comparison and workflow optimization. Comprehensive decision trees and refracturing flow charts will be valuable for a wide audience of engineers involved in mid-permeability formations development through hydraulic fracturing methods. This discipline is expected to gain momentum in the Middle East soon.