An Experimental Study on Evaluation Methods for Fracturing Effect of Fractured-Vuggy Carbonate Reservoir

The lack of evaluation system for evaluating communication of fractures in vuggy carbonate reservoirs makes it impossible to quantitatively analyze post frac treatment. Therefore, it is necessary to establish an evaluation method for post frac according to the characteristics of abundant natural fractures and karst caves in carbonate reservoirs. A physical experiment simulated hydraulic fracturing on artificial fractured-vuggy carbonate cores was conducted, the evaluation criteria that meets the fracturing characteristics of fractured-vuggy carbonate reservoirs were proposed based on the experimental results, and the concept of fractured-vuggy communication coefficient was proposed. Then, the proposed coefficient was used to quantitatively analyze the influence of in-situ differential stress on vuggy carbonate fracturing effect. The experimental results show that the SRV coefficient used to evaluate fracturing effect cannot accurately evaluate the effect of fractured-vuggy carbonate fracturing, while the fractured-vuggy communication coefficient can make a more accurate evaluation. The influence of horizontal in-situ differential stress on fractured-vuggy carbonate fracturing effect was evaluated with the proposed coefficient. It is found that the coefficient decreases first then increases with the increase of in-situ differential stress. The results demonstrate that the influence of various factors on fracturing effect of fractured-vuggy carbonate reservoirs are different from that of conventional ones, and the proposed fractured-vuggy communication coefficient can be used to more precisely analyze the fracture propagation and communication conditions, and to more effectively evaluate such reservoirs.