This paper presents a diagnostic-driven method of evaluating refracturing (refrac) techniques in unconventional wells. Detailed analysis across the lateral, using intervention based distributed fiber optic (DFO) measurements, allows for a comprehensive understanding of the refrac performance. While there are various approaches to refracing an unconventional well, there is a categorical division of two main strategies: iterations of limited interval re-stimulation or re-stimulate the entire lateral at once. Stage-by-stage refrac, via casing-in-casing or coil tubing with isolation-type packer tool, offers potential control over stimulation distribution but often incurs heavier cost compared to refracing the entire well simultaneously. The economically favorable simultaneous refrac of all stages (Bull head) can be executed at a lower price but at the cost of not knowing the extent of lateral distribution. With several possible approaches for refracing an entire lateral at once, further questions arise regarding which method provides the most laterally uniform re-stimulation and whether the resultant production improvement is from re-stimulated existing or newly created fractures. A major hurdle in both executing and evaluating the success of an all stage simultaneous refrac is the uncertainty of creating new fracture initiation points; furthermore, with complex heterogenic rock, different fracture designs, and different well completions, it is difficult to develop a comprehensive understanding of how well the refrac design worked. Diagnostic validation of the success of a refrac operation, as well as iterative improvements based on those learnings, is fundamental to determining a cost-effective strategy. A strong data set takes the guesswork out of refrac and is the best method for understanding how effective the refrac designs performed.

Implementation of video production logging in conjunction with the use of high molecular weight polymer gels, has led to successful water isolation operations in the Fayetteville shale. The dry natural gas field, located in northern Arkansas, is a horizontal play with the wells cased, cemented, and completed with multi-stage slickwater fracture stimulations using perforation and plug technology (Harpel, 2012).Accurate detection of extraneous water entry points along the wellbore is vital for precise water isolation treatment, while still protecting the hydrocarbon producing intervals. Conventional production logging tools have been utilized in the past but proved to be expensive, due to the wellbore configuration, and imprecise because of the horizontal trajectory and debris encountered in the wellbore, with the debris generally rendering the spinner tool inoperable. Video logging tools, deployed in combination with high frequency temperature and pressure gauges, have considerably improved identification of water entries along the wellbore. In addition, the use of a smaller logging assembly has also drastically reduced workover costs by permitting logging through the existing 2-3/8" OD production tubing whereas conventional production logging required the removal of the production tubing due to size limitations. By maintaining this wellbore configuration the flowing conditions remain undisturbed and increase the accuracy of the production log.Based on video production log results the proper water isolation operation is subsequently selected. While cement squeezes and mechanical isolation tools have been applied successfully in horizontal wells to isolate inflow from water producing perforations, they are limited in their applications due to the wellbore configuration and operational costs. Recently, treatment of water producing perforations with chrome (III) carboxylate acrylamide polymer (CC/AP) gel technology has allowed selective treatment in additional sections of the wellbore. These gel treatments have yielded strong results by isolating water production and increasing gas production by reducing the flowing bottomhole pressure. Evaluation and selection of the appropriate polymer gel is discussed along with design considerations and implementation.

The Barnett Shale continues to offer vast opportunities for refracturing operations. This study covers diagnostic data and case histories of refracturing in the Barnett Shale. Job design and completion techniques are evaluated throughout the project. Candidate selection planys an important role in the overall success of a refracturing program. Wells are grouped by area and original completion design. Completion diagnostics are utilized to test and optimize a variety of refracturing techniques. These techniques include bullhead treatment with and without diverter, various types of diversion, and mechanical isolation. The evaluation of the refracturing program will be broken up into two parts. Bullhead refracturing techniques will be evaluated for new and existing perforation coverage as well as overall lateral coverage. The second part of the paper will evaluate mechanical isolation techniques. These techniques include the installation of a liner with and without isolation on the annulus. A plug and perf treatment is then performed through the newly installed liner. In addition to the optimization through the use of completion diagnostics, the wells are evaluated based on production analysis. This study will compare the overall economics to the method deployed. Twenty-nine horizontal wells are included in this study with some form of diagnostics utilized during the frac. Accessing new rock shows a correlation with incremental reserves as expected. Diversion is evaluated with economic projects on bullhead operations. However, the diversion is not always effective at opening up new perforations and stimulating the well effectively. This study provides data that is utilized to develop best practices for refracturing in the Barnett Shale that can be applied directly to additional basins. In addition to the direct applicability of this work, the methodology utilized to test and optimize diversion can be applied not only to refracturing operations, but also to new well completions.

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