Multi-stage acid fracturing of horizontal wells is a necessary and effective technology in developing tight carbonates. In open-hole horizontal wells in high-temperature, naturally fractured deep formations, segmentation with tools is of high risk and costly, even ineffective sometimes, so segmentation with diversion agents is alternative to tools and was pilot tested in some fields. The stimulation results were satisfactory, and pressure response feature was in accord with expectation. However, this technique has not been studied experimentally or numerically extensively yet.
In this study, we investigated tool-free multi-stage fracturing experimentally in open-hole horizontal wells with diversion agents. Firstly, we designed a multi-stage tri-axial fracturing system and experimental procedures to satisfy the requirements of diverted fracturing in horizontal wells. Next we conducted a series of experiments to investigate feasibility of multi-stage fracturing with diversion agents using natural carbonate outcrop cubic blocks with the size of 300*300*300mm. CT scanning was used to obtained detailed fracture geometry after experiment. Finally we analyzed the effect of diversion agent type, concentration, and injection procedure on diversion.
The experimental results show that multi-stage fractures perpendicular to the open-hole horizontal wells was created, which verifies the validity of the tool-free multi-stage fracturing of open-hole horizontal wells with diversion agents. Proper agents or combinations can effectively plug the fracture generated previously and generate pressure high enough to initiate another fracture. The breaking pressure or propagation pressure of second fracture was monitored higher than the one of the first fracture. Under experiment conditions, 1-3mm fiber or combination of fiber and particle (0.8-1.2mm) can effectively plug fractures and realize segmentation. Concentration of diversion agents tested ranges 0.4-1.6wt%. Injection procedure for two-stage fracturing was fracturing fluid + diversion fluid + fracturing fluid. The amount of diverter and open-hole length are the vital factor for the success of experiments.
This study newly designed a multi-stage tri-axial fracturing system and experimental procedures for the diverted fracturing. The finding verified the validity of the tool-free multi-stage fracturing of open-hole horizontal wells with diversion agents and provides fundamental for field treatment design.