Analyzing Well Performance VII
Authors: McCoy James N. 
Published: December 2007

Introduction

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 (GENERALIZED)

Fluid flow in a reservoir is caused by a higher pressure pushing fluid into an area of lower pressure. pressure pushing fluid into an area of lower pressure. 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 high pressure flows into the low pressure wellbore (Fig, 1).

FIG 1 - FLUID FLOW INTO A WELL

------------------- -- -- -- -- ----------------------- ------&gt;= = &lt;-------- HIGH FLUID FLUID PRESSURE FLOW = LOW = FLOW PRESSURE FLOW = LOW = FLOW ------------------- PRESSURE ------------------------ -------------- FIG. 1 - FLUID FLOW INTO A WELL

Fluid flow into a wellbore is approximately proportional to the drawdown pressure which is the proportional to the drawdown pressure which is the difference in pressure between the higher pressure reservoir and the lower pressure wellbore, The greater the difference, the greater the fluid flow. Figure 2 represents some ideal cases of fluid flow in a reservoir.

The lower the wellbore pressure the greater the inflow rate. Generally, in the past, the inflow rate has been assumed to be proportional to the drawdown pressure. This procedure is still used in wells which pressure. This procedure is still used in wells which produce liquid without gas. Vogel presents a curve produce liquid without gas. Vogel presents a curve for predicting flow rates in 2 phase flow (liquid and gas). This curve is shown on the Well Analysis sheet and should be used when predicting flow behavior in wells making liquid and gas.

NECESSARY DATA FOR WELL ANALYSIS

Four factors are extremely important in analyzing well performance:static bottom hole pressure,producing bottom hole pressure,well test andproducing bottom hole pressure,well test andpump capacity.

pump capacity. For maximum withdrawal, the producing bottom hole pressure must be low compared to the static bottom hole pressure, A producing bottom hole pressure of 75 psi is low compared to a static reservoir pressure of 75 psi is low compared to a static reservoir pressure of 2300 psi and practically all of the pressure of 2300 psi and practically all of the production is being obtained. However, if the static production is being obtained. However, if the static reservoir pressure is 100 psi, approximately one-fourth of the production is being obtained. The well test must also be known. If the producing wellbore pressure is low compared to the static reservoir pressure, maximum inflow is occurring. But, if the maximum inflow is less than commercial production, action must be taken. Last, the pump capacity must be known. If the pump capacity is not matched suitably to the well's production, excessive wear and a mechanical loss of efficiency are occurring if the pump capacity greatly exceeds the production rate.

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