In recent years, horizontal wells have played an increasing role as alternate production tools to vertical or slanted wells. Do they provide anything new to exploitation strategies for low permeability reservoirs ?

In this paper, we will contribute to answering this question by presenting results of analytical derivations pertaining to cases favorable to development with horizontal wells.

The effects of anisotropy related to shaly interbedding and natural fissuring will be discussed. The solutions and criteria are derived independently from the nature of the drive mechanisms because of their strong influence on the production profile of horizontal wells.

As some basic concepts usually applied in classical reservoir engineering to production with vertical wells have to be drastically re-evaluated when dealing with horizontal wells, the economic assessment of their spudding must be evaluated with new criteria. The new criteria, such as areal productivity and replacement ratio of vertical wells by horizontal wells, are introduced in order to help the decision-maker responsible for the exploitation of a low permeability reservoir.

The chief technical contributions of the paper are:

  • Criteria for comparing horizontal and vertical well productive efficiency.

  • Spatial depletion profiles around the horizontal well.

  • Areal productivity index and replacement ratio equations.

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