Boundary-layer behaviour in a hydraulic theory of horizontal oil wells

In many cases, modern oil production occurs by means of long, more or less horizontally drilled cavities in an oil reservoir, so-called horizontal wells. Oil production by means of these horizontal wells is usually advantageous because the contact area between the well and the reservoir can be increased significantly, in particular for oil reservoirs with large aspects ratios. However, it turns out that the production profile along the length of a horizontal well may have boundary-layer-like characteristics with the consequence that a large fraction of the production comes from a small section of the well. In this paper the boundary-layer characteristics of the production profile are analysed. It is shown that different boundary layers with different characteristics can occur simultaneously. In particular it is shown that there may be a thin 'annulus-induced' boundary layer and a thick, reservoir-induced' boundary-layer.