Efficient Simulation of Well Production with Multi-Scale Complex Natural Fractures

Abstract

ABSTRACT In general, natural fractures are favorable for hydrocarbon-producing enterprises in low-permeability unconventional reservoirs. In conventional reservoirs with higher permeabilities on the other hand, such natural fractures could be counterproductive since it can be used by water to bypass oil. This study is concerned with natural fractures in a conventional gas reservoir with porosity and permeability of 20% and 10 md, respectively. Natural fractures with different scales are incorporated into the numerical reservoir model in order to investigate the effects of various natural fracture scales to the recovery. Here, the Embedded Discrete Fracture Model (EDFM) is used to insert a couple natural fractures sets to the numerical reservoir models. With EDFM, the natural fractures in the model can be slanted, randomly placed across the reservoir volume, and varied in dimensions which are more likely the traits of natural fractures found subsurface. Seemingly, the larger the natural fracture scale is, the higher its gas estimated ultimate recovery (EUR). This is probably due to the larger scale natural fractures having greater total fracture area and vice versa. Furthermore, the small-scale natural fractures contribution to the EUR in 20 years of primary production seems rather minimal. Omitting natural fractures of such scale in the reservoir model used in this study that translates to about 20% reduction in total fracture area, reduces the EUR of about 3% which means the omission might be acceptable to some extent. The connectivity of the fractures does not seem to play a significant role for the EUR. In summary, it does not really matter which fractures scale is used, as long as the total area is significant, those fractures should be included in the reservoir model. However, this is true for the model used in this study where the reservoir has relatively high permeability and natural fractures have a relatively low conductivity.