Analyzing Well Perform
Authors: McCoy James N. 
Published: December 2007

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Introduction

Analyzing well performance is an important step toward increasing profits by improving production techniques. Generally the analysis production techniques. Generally the analysis is made by field observations and examination of well data. The acoustic liquid level instrument offers valuable supplemental 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. 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 pressure flows into the low pressure wellbore (Fig. 1).

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

The importance of the static and producing wellbore pressures becomes obvious. Numerous techniques for determining wellbore pressures exist but the most common is the use of acoustic liquid level instruments which involve measuring the depth to liquid in a well. Using the depth to liquid the casing pressure and certain other data, an operator can determine the pressure at the wellbore. pressure at the wellbore. A minimum producing wellbore pressure is generally desired for maximum inflow.

NECESSARY DATA FOR WELL ANALYSIS

Four factors are extremely important in analyzing well performance:

static bottomhole pressure, producing bottom-hole pressure, well test and pump capacity.

pressure, (3) well test and (4) 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 2,300 psi and practically all of the production is being practically all of the production is being obtained. However, if the static reservoir pressure is 100 psi, only one-fourth of the pressure is 100 psi, only one-fourth of the production is being obtained. The well test production is being obtained. The well test must also be known. If the producing wellbore pressure is low compared to the static 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 production, excessive wear and a mechanical loss of efficiency are occurring if the pump capacity greatly exceeds the production rate.