Abstract
Bedding corridors are sub-horizontal tabular bodies of bedding plane weak zones formed as shear swarms, which vertically divide the entire reservoir thickness and extend laterally as their layers. Bedding corridors are genetically related to shearing along the bedding planes and they contribute to the conductive systems in few Abu Dhabi reservoirs. They can be best identified from horizontal borehole image logs, and as spikes in open-hole logs. Natural bedding corridors can be considered as indicators of the reservoir stress history, where they form extraordinary clusters of a huge number of quasi-parallel shear fractures in a transpressional regime.
In many oil and gas reservoirs, natural bedding corridors networks help drain hydrocarbons and other fluids. The role of bedding corridors is particularly important in reservoirs having a tight matrix. In carbonate formations, for example, it is quite common to observe a permeability contrast of 1000mD or more between the rock matrix and surrounding bedding corridors. In this paper we differentiate between image-log porosity and density-neutron porosity, which is regarded as secondary porosity attributable to fractures. We also introduce here a working hypothesis about their effect on hydrofraccing being part of geomechanical assessment.
Results indicate that the horizontal stress anisotropy (Shmin/SHmax ratio) is the key parameter to predict bedding corridors behavior under different stress regimes. Swapping stresses with depth is common in Abu Dhabi fields, where a strike-slip regime can open and dilate the shear along the bedding planes. It is recommended to opt for horizontal wells hydrofraccing to maximize the intersection of those bedding corridors compared to vertical wells.
The significance of this approach is that once a diagnostic signature can be recognized in open-hole logs, in combination with lost circulation data, it can be used to locate bedding corridors in other vertical wells with no image logs. Geomechanically, these corridors can be used efficiently to increase production particularly in tight and unconventional reservoirs.
