| Horizontal well performance is typically estimated using a steady-state productivity index equation similar to Joshi's productivity index, which assumes constant wellbore pressure. The wellbore pressure in a horizontal well is not constant, and the pressure drop in the horizontal section can approach the reservoir drawdown. Other authors have looked at the effects friction and influx have on the wellbore pressure by developing apparent friction factors. However, there has not been a method presented that incorporates the wellbore hydraulic effects in the productivity estimate.; This research reviews the equations used to determine horizontal well productivity, the models used for wellbore pressure, and develops a new method to estimate horizontal well productivity incorporating the effects of friction, acceleration, gravity, and fluid influx. The method is implemented in a program that is simple and quick to use. The new method calculates the wellbore pressure behavior and the apparent productivity, and compares the calculated productivity to three horizontal well productivity estimates. The proposed method reproduces the experimental results of two authors. Sensitivity analysis of the model shows the horizontal wellbore pressure has a characteristic shape on a dimensionless pressure-length graph and that fluid and well properties have significant effects on the estimate of friction factor. |
