Distributed Fiber Optic Monitoring of Asymmetric Fracture Swarm Propagation in Laminated Continental Shale Oil Reservoirs

Complex and vertically overlapped lithologies exist for the high-quality shale oil reservoir of the Lianggaoshan formation in the Sichuan basin. Continental shale oil reservoirs grow bedding, lamina, and natural fractures, challenging fracture network morphology control and monitoring in horizontal well multistage fracturing technology. This study proposed a true triaxial monitoring method based on distributed fiber optic sensing for the outcrops with good emergence, occurrence, and clear lithology. The U-shaped plane layout style is adopted to monitor the initiation and propagation of hydraulic fracturing in the full-time domain. The study first found that the main vertical fracture perpendicular to the wellbore and lamina fracture had an asymmetric propagation pattern, and fracture initiation was instantaneous and had a characteristic of elastic recovery. The asymmetric propagation of multistage/multicluster fractures can be grouped into nine types combing with the relative angle and position variation. Simultaneously, there is a 2-s time difference when the vertical fracture reaches the boundary on two sides and an included angle between the vertical fracture and the maximum horizontal principal stress. Besides, the low-viscosity slick water will filtrate into the existing lamina plane after the initiation of vertical fracture under high-pressure pumping. It is helpful to open the lamina and form a complex fracture network of vertical fracture cross lamina fracture, usually in the form of a cross, I-shaped, and fishbone. This experimental study can effectively improve the calculation accuracy of stimulated reservoir volume (SRV) and shale oil production and guide the fracturing stimulation monitoring of adjacent wells.