Experimental research on fracture initiation and propagation behavior in argillaceous silt hydrate reservoirs

Abstract

Natural gas hydrates hold great promise as an environmentally friendly energy resource, yet the trial production capacity remains an order of magnitude below the threshold for commercial development. Scholars have verified the effectiveness and viability of applying hydraulic fracturing stimulation technology to hydrate reservoirs through laboratory experiments and numerical simulations. However, the unique low-temperature and high-pressure environment of hydrates complicates the initiation and propagation characteristics of hydraulic fractures in unconsolidated argillaceous sediments. Building on previous researches, we conducted true triaxial fracturing experiments using hydrate-bearing sediments (HBS) substitute in both vertical and radial wells. The results indicate that radial well fracturing provides enhanced stimulation effects compared to vertical well fracturing, increasing the stimulated volume and fracture complexity by 27% and 5%, respectively. Due to the weak physical properties of the hydrate reservoir, drilling multiple radial wells in the same horizontal layer causes reservoir degradation to form weak bedding planes, inducing fractures to initiate and propagate in the horizontal direction. Employing high injection rates and low-viscosity fracturing fluids can boost fracture complexity by approximately 10%, facilitating proppant placement and transport and thereby maintaining the efficient, long-term, and safe development of hydrates. Our study offers insights and theoretical frameworks to facilitate the implementation of hydraulic fracturing techniques in the exploitation of hydrate reservoirs.