Low-Permeability Reservoirs Development Using Horizontal Wells

Abstract

Abstract 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. Introduction Horizontal wells have become a subject of renewed interest over the last ten years. More than thirty horizontal wells have now been drilled. The increase in productivity comes up to expectations based on theoretical calculations. Excellent results have also been obtained in restricting the inflow of undesirable fluids when producing reservoirs involving a gas cap or an aquifer. Theoretical tools have been proposed to explain this favorable behavior. Since low permeability reservoirs contain large reserves of oil that are difficult to extract, it is worth examining whether horizontal wells can contribute to increasing the recovery rate in an economical manner. OBJECTIVES This paper aims firstly at providing a basis for estimating horizontal well production in low permeability reservoirs. Steady state flow to a horizontal well is described first in a homogeneous environment then in a fractured or anisotropic environment. The influence of the eccentricity of the well is analyzed. P. 173^