Kechao Gao

Gravel sandstone reservoirs are characterized by low porosity, low permeability, and strong heterogeneity, presenting significant challenges for hydraulic fracturing. This study investigates the fracture propagation mechanisms in gravel sandstone formations using a combination of laboratory experiments, numerical simulations, and theoretical modeling. The findings reveal that gravel size, strength, and distribution significantly influence fracture morphology and propagation behavior. Under low stress differences, cracks tend to wind around gravel, while under high stress differences, cracks are more likely to penetrate gravel. Numerical simulations highlight the complex fracture network caused by high gravel content, leading to increased filtration loss, accelerated energy dissipation, and reduced fracture length. A quantitative model was developed to describe trans-gravel behavior, offering theoretical support for optimizing hydraulic fracturing designs in gravel sandstone reservoirs. This work provides valuable insights into the coupling mechanisms between gravel properties, stress conditions, and fracture propagation, contributing to more effective stimulation strategies for complex reservoirs.

The sand conglomerate has strong heterogeneity, great difference in rock mechanical properties, and serious filtration loss of fracturing fluid. In order to describe the effect of heterogeneous gravel distribution on the filtration loss of conglomerate reservoir, a dual media filtration model was established based on the equivalent flow principle, and the heterogeneous distribution relationship was characterized by Fuller gradation and solved by numerical method. The degree of non-uniformity, formation gravel characteristics and pressure process parameters were taken into account for simulation analysis and calculation. The results show that the average filtration rate of 60% gravel content is 54.2% lower than that of 20% gravel content. When the degree of non-uniformity is 6, the average filtration rate is 73% higher than that of uniformity. Injection rate and injection pressure have a great influence on the filtration loss of fracturing fluid. The research results can provide theoretical support for fracturing optimization design.