Hydraulic Fracturing in Unconventional Gas Reservoirs: simulation using discrete element methods
Dalma Arrieta1; Sergio Fontoura1; Guilherme Righetto2
1 Pontificia Universidade Católica do Rio de Janeiro, PUC- Rio; 2 Pontificia Universidade Católica do Rio de Janeiro
Resumo
The development and deployment of shale gas formations around the world are relatively recent, starting in the United Stated in the late 1990. From the results obtained with the application of hydraulic fracturing as a method of stimulation, the study and evaluation of other prospects of shale gas in others places in the world was encouraged. However, the analysis, study and characterization of this type of reservoirs are difficult, because it must be taken into account several factors such as geology, mineralogy, petrophysics, geochemistry among others. Hydraulic fracturing is a complicated hydromechanical coupled process, with high difficulty degree especially in shale gas reservoir, where natural fractures exist. A numerical study is conducted to investigate the hydromechanical behavior of a natural fracture during fluid injection. UDEC (Universal Distinct Element Code) software based on discrete elements method was employed to numerical modeling development. UDEC has the ability to model the hydro-mechanical behavior of a fracture including phenomena like fracture enlargement, closure, slippage, and dilation under contact or separation condition. In this numerical investigation, numerical reservoir models, with random natural fractures through a distribution voronoi were created aiming to represent the network complexity of natural fractures present in shale gas formations. The numerical study results show that the hydromechanical system behavior is strongly dependent on the parameters variation such as in situ stress, fluid fracturing viscosity and fluid injection rate. Differences in in situ stress result in fluid flow and pore pressure diffusion on principal maximum stress direction. For higher stress ratio major fracture aperture are developed once fractures are located at principal maximum stress direction. In addition, higher-pressure injections are developed for isotropic stress acting over mass rock. Besides, higher injection rates result in major blocks rotation and consequently higher fractures ap
Palavras-chave: Naturally fractured formations; Shale gas; Hydromechanical behavior; Hydraulic fracturing