The Effect of Dissolved Cavern on the Fracture Propagation in Vuggy Carbonate Reservoir

Abstract

The acid-fracturing is applied wildly to simulate the formation in vuggy carbonate reservoirs. But it does not figure out clearly the mechanism of fracture propagation while fracture encountering dissolved cavern and there are few researches considering the influence of dissolved cavern on fracture propagation. In order to study fracture propagation regularity in vuggy carbonate reservoirs, numerical simulations are carried out by the seepage-stress-damage coupling equation based on the damage mechanics theory and the accuracy of the model is validated by comparison with experimental results. Some factors influencing the fracture propagation such as dissolved cavern, formation parameters and construction parameters are considered. The simulation results show that there are four fracture propagation forms after the fracture encountering dissolved cavern, namely block, crossing over directly, crossing over after deflection and deflection. The entire process of injecting the pressure curve can be divided into five stages: initial initiation zone, encountering dissolved cavern pressure released zone, the dissolved cavern inside builds the pressure zone, re-ruptured zone, fracture propagation zone. The horizontal principal stress difference of the formation controls the tendency of fracture propagation and the generation of branch fractures. It is easy to generate branch fractures under the condition of low horizontal principal stress. The increase of horizontal principal stress limits the deformation of fracture, making it more convenient for fracture to extend towards the maximum horizontal principal stress. The study results are significant for optimizing fracturing construction plans and improving the probability of connection between fracture and dissolved cavern.

The Enhanced Oil Recovery Effect of Nitrogen-Assisted Gravity Drainage in Karst Reservoirs with Different Genesis: A Case Study of the Tahe Oilfield

“…It is of great significance to explore and investigate the core action mechanism of the typical fracture propagation and to consider the effect of the karst cave on fracture propagation for optimizing the fracturing scheme and improving the probability of fracturecave connection in a carbonate reservoir. To deeply study the fracture development law of the carbonate reservoir, Guo et al [26] combined with the damage mechanics theory and carried out the numerical simulation through the seepage-stress-damage coupling equation; the accuracy of the numerical simulation was verified by the experimental results. The results show that there are four types of crack propagation, including block, direct span, cross after deflection, and deflection.…”

Effect of Vugs on Hydraulic Fracture Propagation with Phase Field Method

“…Liu et al [5] conducted experiments to investigate the effect of vugs on hydraulic fracture propagation by using true triaxial apparatus and identified three main interaction modes; that is, the hydraulic fracture may cross, bypass, or be arrested by the vug. Guo et al [6] carried out a numerical simulation to examine the effect of dissolved cavern on hydraulic fracture by using the seepage stress damage coupling model, and some influencing factors including cavern property, reservoir parameter, and treatment parameters were analyzed. Luo et al [7,8] presented numerical simulation to investigate the effect of caverns on hydraulic fracture propagation direction under triaxial stress condition based on the extended finite element method and concluded that fractures tend to deflect from the maximum horizontal principal stress direction due to caverns.…”