Igbokoyi, A: Well Analysis in Naturally Fractured Reservoir

Naturally fractured reservoirs are anisotropic systems whose flow characteristics depend on the fractures network. Their permeability variation is not only stratigraphic in nature, but is also caused by the fractures‘ distribution, orientation and permeability impairment within the fractures caused by pressure solution or mineralization. The reservoir becomes more complex when both the matrix and fracture exhibit anisotropy and have the capability to flow into the wellbore as in the double permeability case. Well test analysis in these reservoirs has been based on the radial flow model, even when it is widely believed that such reservoirs are anisotropic. The radial flow model is however only applicable to purely homogeneous system. It cannot provide a complete formation analysis in anisotropic system. This study therefore presents a new method of estimating permeability anisotropy in naturally fractured reservoirs. The maximum permeability is attributed to the large scale fractures while the minimum permeability may be due to the small scale fractures orthogonal to the large scale fractures or the matrix.