Evaluating Proppant Performance and Fracture Conductivity Dynamics in Marine Hydrate Reservoirs

Abstract

Hydraulic fracturing, which creates propped fractures to establish conductive pathways near production wells, emerges as a promising technology for boosting gas production and energy efficiency in low-permeability natural gas hydrate (NGH) reservoirs. Yet, the sustainability of fracture conductivity during depressurization and hydrate decomposition remains uncertain. This study focuses on assessing the effectiveness of artificial fracture propping and monitoring the changes in fracture conductivity and proppant embedment depth during the processes of depressurization and hydrate decomposition post-hydraulic fracturing. It was found closure pressure significantly reduced fracture conductivity, 6.9 times more than hydrate decomposition. The main causes of this loss were proppant embedment and rearrangement, with rearrangement playing a larger role than sediment deformation or embedment itself. This effect became slightly more pronounced during hydrate decomposition, especially at around 35% saturation. Proppant embedment had a more significant impact in hydrate reservoirs compared to other unconventional reservoirs, and interestingly, larger proppant sizes didn’t correlate with higher conductivity; in fact, 40/70 mesh was more effective than 30/50 mesh. Furthermore, an increase in proppant concentration led to a reduction in embedment due to the rearrangement of proppant packing. Different mechanisms contributed to the reduction in conductivity across various proppant loading concentrations; single-layer concentrations experienced a rapid decline in conductivity due to proppant embedment, while multilayer concentrations saw major reductions from proppant compaction. Seawater flow further reduced conductivity by 20.68%, primarily due to the softening and expansion of sediment clay, exacerbating proppant embedment. This present study highlights the importance of closure pressure and proppant properties in maintaining fracture network permeability for long-term gas extraction in NGH clayey-silt reservoirs, offering key insights for optimizing offshore NGH production.

Keywords: Natural gas hydrates, Hydrate decomposition, Fracture conductivity, Proppant embedment, Closure pressure