“Casing in Casing” Mechanical Isolation Refracturing Technology in Fuling Shale Gas Wells

The application of temporary plugging and diverting refracturing in Fuling Shale Gas Field brought on technical difficulties accompanied by poor production increase. To solve this problem, this paper analyzed principles and characteristics of technologies used in shale gas wells abroad. They included temporary plugging and diverting refracturing, and mechanical isolation refracturing. What was found was that that mechanical isolation could completely block the perforations and precisely control fracture initiation of hydraulic refracturing. From that, the “casing in casing” mechanical isolation refracturing technology took shape. In Fuling Shale Gas Field, this technology was tested with a casing (outer diameter of 88.9 mm) inserted into the other one (inner diameter of 115.0 mm) where in a new and closed well casing was formed. In addition, refracturing technologies targeted for different residual oil distribution in the reservoir were developed through studies. In the original well casing, attention should be paid to exploring the residual oil among fractures in the stimulated well section. At the same time,emphasis should target the poorly stimulated sections, to see how to recover the flow conductivity of the fractures. After implementing that technology in Well JYAHF, the recoverable reserve for a single well increased by 0.36×10⁸ m³, and the recovery efficiency increased by 4.8%. The study shows that the “casing in casing” mechanical isolation refracturing technology can significantly improve the result of stimulation and provide technical support for long-term and efficient shale gas field development in China.