Effective Stress Factor Analysis of Proppant for Multi-stage Fracturing in Horizontal Wells

In order to determine the effective stress factor of proppants during the multi-stage hydraulic fracturing operation in horizontal wells and select the appropriate proppant type, the analysis of the effective stress characteristics of proppants is carried out. This analysis considers the geomechanics and long-term production characteristics of multi-stage fractured horizontal wells in reservoirs like Xinjiang Mahu shale oil and Southwest China shale gas. The analysis of influencing factors is also carried out. The results show that, during the multi-stage hydraulic fracturing operation in horizontal wells, the stress on proppants is not only related to geological factors such as reservoir closure stress, but also closely related to total injection volume, cluster spacing, liquid type, injection displacement and post fracture management. First, increasing injection intensity, reducing fracture spacing, using low viscosity fracturing fluid, adopting high injection displacement and utilizing reasonable flowback system can effectively supplement reservoir energy, postpone the effective stress peak of proppants, and increase the effective conductivity of proppants. Second, the production performance analysis results of nearly 300 horizontal wells (from Xinjiang oil field, Erdos tight oil reservoir, Sichuan shale gas reservoir, etc.) shows that: the effective stress of proppants in horizontal wells is only 50-60% of that in vertical wells, which results in a different proppant selection criterion in the volume stimulation of horizontal wells and provides the geomechanics basis of replacing ceramsite proppant with quartz sand to reduce cost and increase efficiency. Based on the above conclusions, the field test of replacing ceramsite proppant with quartz sand was carried out. The proportion of quartz sand increased from less than 30% in 2014 to 69% in 2019. Without any impact on production, the annual investment cost was decreased by more than 1 billion yuan, which set a great example for the promoted low-cost development of unconventional oil and gas reservoirs under low oil price background.

Automated summary

This study analyzes the effective stress characteristics of proppants during multi-stage hydraulic fracturing in horizontal wells and considers the geomechanics and long-term production characteristics of reservoirs. The results show that the stress on proppants is influenced by geological factors as well as injection volume, spacing, fluid type, displacement, and post-fracture management. Increasing injection intensity, reducing fracture spacing, using low-viscosity fracturing fluid, and implementing a reasonable flowback system can enhance the effective conductivity of proppants. Furthermore, the analysis of nearly 300 horizontal wells reveals that the effective stress of proppants in horizontal wells is only 50-60% of that in vertical wells, indicating a different proppant selection criterion and the potential to replace ceramsite proppant with quartz sand to reduce costs and increase efficiency.