Experimental study on fracture propagation during in-fracture temporary plugging and diverting fracturing in carbonate rock

Karst caverns are the main storage space in the fractured-vuggy carbonate reservoirs in the Tahe oilfield, and many accumulations around wellbores are not located in the direction of the maximum horizontal principal stress. Therefore, the temporary plugging and diverting fracturing is demanded for stimuilation of reservoirs deviating from the maximum horizontal principal stress. The simulation experiments of in-fracture temporary plugging and diverting fracturing (ITPDF) were performed using 30 cm × 30 cm × 30 cm outcrop specimens of carbonate rock. The fracture morphology after conventional fracturing and ITPDF was observed via CT scanning to analyze the effects of the in-situ stress difference, natural fractures, and fracturing fluid viscosity on the fracture morphology, and the fracture initiation in ITPDF was theoretically investigated. The research shows that well-developed natural fractures or beddings in rock and sufficient temporary plugging pressure are essential for a successful ITPDF. ITPDF is workable under varied in-situ stress differences; the smaller the in-situ stress difference, the more complex the fracture morphology, and the larger the stimulated volume. Entry of temporary plugging agent into fractures is critical for diverting fracturing. A fracturing fluid with too low viscosity is less capable of sand carrying and may induce primary fractures with small aperture, hindering the smooth entry of temporary plugging agent. The research results provide a theoretical basis for the fracturing design of fractured-vuggy carbonate reservoirs in the Tahe oilfield.