PRESSURE-DROP IN HORIZONTAL WELLS AND ITS EFFECT ON PRODUCTION PERFORMANCE

Fluid flow in horizontal pipes becomes turbulent at Reynolds number larger than 2,000. In practical situations, turbulent flow in horizontal wells may occur at rates of thousands of cubic feet per day (for a 24.4-cm [95/8-in.] cased well). Wells flowing in a turbulent regime experience a flow resistance many orders of magnitude higher than that for laminar flow. Therefore, along-hole well-pressure gradients generally cannot be neglected, and a proper description of horizontal well flow needs to be included in the design of these wells (and in reservoir simulators). This is particularly imperative in situations of very low drawdowns (to avoid gas or water cresting). This paper presents a simple analytical method that links single-phase turbulent well flow to stabilized reservoir flow. The resulting second-order differential equation is solved numerically for the appropriate boundary conditions. Results are presented in dimensionless form for general applicability. A practical example is presented for a horizontal well in a highly permeable oil rim underlain by water. Drawdown is limited to about 100 kPa[1 bar] to produce at subcritical it is observed that for an 11.4-cm [4 1/2 -in.] well of 300 m [985 ft], little additional production results from extending the horizontal section.