Fracture propagation law of multi-well hydraulic fracturing in conglomerate reservoir: A laboratory study

Tight conglomerate reservoirs have become a strategic focus in unconventional resource development. Nevertheless, achieving cost-effective production remains challenging through single-well horizontal fracturing operations. Deploying multiple horizontal well fracturing systems emerges as a cost-effective strategy to overcome the production bottlenecks described earlier. Therefore, by configuring three horizontal wellbores, true triaxial fracturing experiments were conducted on large-scale specimens to investigate fracture propagation mechanisms in multi-well fracturing, and the effects of gravel size, horizontal stress contrast coefficient, injection rate, and viscosity were systematically analyzed. The results indicate that when hydraulic fractures encounter gravel, three types of behaviors can be observed: penetration, termination, and deflection. Two distinct deflection behaviors were further identified. An increased injection rate can enhance the capability of hydraulic fracturing (HF) fluids to penetrate gravel. Specifically, the upward propagation distance of the middle HF fluids shows an increase of about 70%. This is conducive to improving the reservoir transformation effect between the outer and inner HF. High viscosity will produce strong stress shadows, resulting in insufficient expansion of the middle HF height. The HFs are more likely to penetrate gravel of small particles. To balancing the transformation effect and construction safety, it is recommended to first use variable viscosity and variable injection rate fracturing fluid(high → low) in actual field fracturing to prevent frac hits. The injection rate can be appropriately increased in subsequent fracturing wells to obtain the optimal reservoir volume after transformation. This study has the capacity to offer theoretical guidance and suggestions for multi-well fracturing operations in the field.