There are several different types of reservoirs that have a high degree of natural fracturing. In these reservoirs, the fluid loss mechanisms are more complicated than those found in more coherent formations. The loss of fluid to intersecting fractures is especially important in the fracturing of coalbeds, Devonian type shales, limestones and naturally fractured sandstones. In many cases, the reservoir permeability is often such that the fluid loss to these fractures is the primary fluid-loss mechanism. Little is known about how to handle this type of fluid loss in fracture simulation calculations, or the effects of this fluid-loss mechanism on pressure drop in the fracture. While the loss of fluid to intersecting fractures is not the only fluid-loss mechanism in naturally fractured sandstone reservoirs, it can dominate the fluid loss to the reservoir under some conditions. Examination of the problem from both a computer based modeling and laboratory standpoint is clearly warranted.

Flow of fluid down a fracture in a sandstone reservoir is modified by the continual loss of fluid to the reservoir through the permeability of the rock. In a naturally fractured reservoir, fluid loss occurs mainly at points where the fracture intersects an existing fracture in the rock. This not only changes the nature of fluid loss in the fracture, but it also creates serious flow disturbances that can change the pressure drop in the fracture. It has been shown that flow into orifices placed perpendicular to the major axis of flow results in a highly extensional flow situation. Extensional flows have been shown to increase pressure drop in porous media using non-Newtonian fluids. In addition, it has been shown that two-phase fluids will separate to some extent when a branching of the flow path occurs. These factors have important implications in the flow of fracturing fluids in fracturing treatments in naturally fractured reservoirs.

To study the flow effects, a computer model of a small section of a fracture with one intersecting fracture was setup. A commercial finite element analysis program (FIDAP) is used for the fluid flow calculations. This program is optimized for power law type fluids. Computations for several different values of the power law parameters coupled with different intersecting fracture widths and fracture width ratios will be presented. Conclusions about the nature of the fluid loss in naturally fractured reservoirs will also be made.

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