Analyzing well performance is an important step toward increasing profits by improving production techniques. The analysis is made by field tests and examination of well data. The acoustic liquid level instrument offers valuable information since downhole pressures can be determined from the depth to liquid measurement.
Fluid flow in a reservoir is caused by movement of fluid from a high-pressure area to a low-pressure area. Fluid flow into a wellbore occurs when fluids present in the wellbore are removed so that the pressure is decreased in the wellbore. Then, fluid from an area of higher pressure flows into the lower pressure wellbore (Fig. 1).
Fluid flow increases as the differential pressure increases. Vogel1 presents a curve for predicting flow rates based upon the ratio of the wellbore pressure to the reservoir pressure. This curve is shown on the Well Analysis Sheet. Note: approximately 70% of the maximum flow rate will occur when the wellbore pressure is one-half of the reservoir pressure. Also note, 90% of the maximum flow rate will occur when the wellbore pressure is 25% of the reservoir pressure.