Experimental Study on True Triaxial Hydraulic Fracturing Based on Distributed Fibre-Optical Monitoring

Abstract Fracturing stimulation is an essential means of developing unconventional oil and gas fields, and borehole monitoring technology is crucial to evaluate the result of reservoir stimulation. This paper introduces a distributed fibre-optical demodulator based on optical frequency domain reflectance (OFDR) in detail. Then, combined with large-scale true triaxial fracturing physical simulation equipment, the laboratory experiments of fracture monitoring of concrete samples were carried out with bare optical fibre. The experimental results show that OFDR optical fibre sensing technology can monitor the change of strain evolution with high spatial resolution and high accuracy in fracture initiation, propagation, and closure in the whole-time domain. When the pumping displacement is increased from 15mL/min to 50mL/min, the hydraulic fracture width generated after the fracturing of the concrete sample increases by about twice. Hydraulic fracture monitoring by distributed optical fibre sensors under true triaxial fracturing can provide reference and guidance for the oilfield stimulation and fracture monitoring technology. Introduction Cross-well monitoring technology represented by microseism is one of the most mature evaluation methods after decades of development and practice (Hou et al., 2022a; Zhang et al., 2021). However, microseismic monitoring technology has many disadvantages, such as difficult interpretation, poor timeliness, many noise points, and high cost (Hou et al., 2019a; Hou et al., 2019b). It cannot be monitored in the same well, which cannot meet the needs of industrial reservoir stimulation and evaluation. In-well monitoring technology based on optical fibre has entered the vision of oilfield engineers.