Refracturing of existing producing wells is an economical option for increasing production when compared to new drills (Urban et al., 2016; French et al., 2014). However, stage isolation during refracturing of horizontal wells can be a challenge, especially in open-hole horizontal wells. Segmentation with common mechanical tools is of high risk and costly, even ineffective sometimes. This paper presents a new tool-free refracturing technology for open-hole horizontal wells in tight oil reservoir employing chemical diverting agents and real time microseismic monitoring technology.
The implementation procedures are as follows: First, reservoir characteristics, surplus oil distribution and brittleness index are evaluated to identify the best perforation candidates for creating new fractures. Second, through the classification of predicted breakdown pressures, number of temporary plugging and diverting fracturing stages are determined. The dosage of granular and powdery plugging agents is designed. Finally, refracturing treatment are performed with an injection procedure of ‘granular plugging agents+ fracturing fluid + proppants+ powdery plugging agents + fracturing fluid’, and microseismic monitoring technology is used to help judge the effect of refracturing and adjust the refracturing operations in real time.
The refracturing treatment was performed in Well X located at Junggar Basin in western China using the method presented in this paper. The microseismic monitoring results show that multi-stage new fractures perpendicular to the horizontal well were created and a more complex fracture network was generated by refracturing in the reservoir, which verifies the validity of the tool-free refracturing of open-hole horizontal wells with chemical diversion agents. After refracturing operation, daily oil production of Well X remarkably increased from 5.1 t/d to 25.1 t/d (one year after refracturing) in the field test.
This study provides an effective tool-free refracturing technology for open-hole horizontal wells, and it was firstly applied in China. It also provides guidelines to the working engineers with respect to refracturing stimulation design and commercial viability. In addition, this technology is not only suitable for open-hole horizontal wells, but also for casing-completion horizontal wells.