The relative importance of wellbore pressure drop and formation damage in horizontal wells
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Numerous studies have examined the roles of wellbore pressure drop and near-wellbore formation damage on the production performance of horizontal wells. These studies identified particular conditions for which these effects are important, but no quantitative general guidelines have been developed. In this paper, we present simple, analytical expressions that can be used to determine the relative effects of wellbore pressure drop and formation damage on horizontal well inflow. The equations developed are used to show how horizontal wells or laterals can be designed so that neither of these effects causes significant flow restrictions. The relative importance of the pressure drop in a horizontal wellbore is shown to be a simple function of two dimensionless numbers: the Reynold's Number for the flow in the wellbore and a new dimensionless number called the Horizontal Well Number. With this relationship, we illustrate how the wellbore diameter and length can be designed to ensure that the wellbore pressure drop is not restricting production. In this paper, we also illustrate a technique for identifying the most critical part of the well flow system (far-field reservoir flow, near-well convergent flow, or flow through the completion) from the relative sizes of different terms in the inflow equations. This analysis method shows that the importance of formation damage and the efficiency of well stimulation depend on formation thickness, well length, and reservoir extent in the horizontal plane. Guidelines are presented to show how much damage can be tolerated while still maintaining productivity within a prescribed fraction of the undamaged productivity. Copyright 2008 Society of Petroleum Engineers.
