A Comprehensive Model for Real Gas Transport in Shale Formations with Complex Non-planar Fracture Networks

Abstract

A complex fracture network is generally generated during the hydraulic fracturing treatment in shale gas reservoirs. Numerous efforts have been made to model the flow behavior of such fracture networks. However, it is still challenging to predict the impacts of various gas transport mechanisms on well performance with arbitrary fracture geometry in a computationally efficient manner. We develop a robust and comprehensive model for real gas transport in shales with complex non-planar fracture network. Contributions of gas transport mechanisms and fracture complexity to well productivity and rate transient behavior are systematically analyzed. The major findings are: simple planar fracture can overestimate gas production than non-planar fracture due to less fracture interference. A “hump” that occurs in the transition period and formation linear flow with a slope less than 1/2 can infer the appearance of natural fractures. The sharpness of the “hump” can indicate the complexity and irregularity of the fracture networks. Gas flow mechanisms can extend the transition flow period. The gas desorption could make the “hump” more profound. The Knudsen diffusion and slippage effect play a dominant role in the later production time. Maximizing the fracture complexity through generating large connected networks is an effective way to increase shale gas production.

A Theoretical Analysis of Pore Size Distribution Effects on Shale Apparent Permeability

“…Unconventional gas production has been the topic of much research, but its accurate prediction is still a challenge [2][3][4][5][6], especially for shale gas. The simulation of shale gas extraction requires information about the apparent permeability of shale, which deviates its intrinsic permeability due to the complex fluid dynamics in tight porous media.…”

Fracture Detection and Numerical Modeling for Fractured Reservoirs

“…Efficient simulation methods of modeling fractured reservoirs include analytical methods, semianalytical methods [6,8,27], and numerical methods [31,32]. The dual-porosity/dual-permeability approach is also often applied to model complex fractures and simulate the effect of fracture networks.…”

“…Fracture quantification and fracture modeling are very important in many disciplines of earth sciences, such as geophysics, petroleum and rock mechanics. Different combinations of fracture properties and rock matrix properties will generate different flow storage and transport mechanisms in the fractured reservoirs [3][4][5][6][7][8]. For example, in the case of high matrix porosity and low matrix permeability, the majority of hydrocarbon will be stored in the matrix, but fractures will act as the transport channel for producing wells.…”

Flow and Transport in Tight and Shale Formations: A Review

“…The modeling of shale-gas reservoir is divided into two different main models. The first one is the dual-continua model (e.g., [80,81,91]) and the second one is the discrete fracture model (e.g., [92,93]). …”

“…The fractures may be planar or nonplanar, natural or hydraulic. Some examples of different complex planar/nonplanar hydraulic/natural fracture networks are shown in Figure 11 [92]. The hydraulic fractures are connected with natural fractures and wellbores are connected in different schemes.…”