A new model to calculate the hydraulic fractures propagation which adds the influence of vugs in carbonate reservoir

ABSTRACT: The fractured-vuggy carbonate reservoirs are widely distributed in North American and west of China. According to statistics, there have more than 70 fractured-vuggy reservoirs in the world. The logging data shows that the diameters of vugs are between 0.15-15 meters, several times bigger than fractures. That means the vugs may hugely influence the geomechanical characteristics nearby, then impact the direction and the length of hydraulic fractures. Besides that, the internal fluid pressure of the vugs may attract or repel the fractures. Therefore, we establish a fracture propagation calculation model by solid-fluid method for fractured-vuggy carbonate reservoirs which considers the vugs influence. Through this model, we calculate the stress field around the vugs when hydraulic fractures approach, analyze the data of stress variation. Then, establish a fracture expansion criterion under near-vug circumstances use to judge whether the hydraulic fractures can through into the vugs. Overall, we found that there is a stress inversion zone around the filling carbonate vugs. The strike of the hydraulic fracture is mainly determined by the relative position and approach angle of the fractures to the vugs.