Development and Field Evaluation of the Production Surveillance Monitor
Authors: Alford B.J. , Patterson M.M. , Womack F.A. 
Published: December 2007

The production surveillance monitor is an electronic oilwell surveillance tool that responds to the liquid flow rate in a single or two-phase flow stream. This paper describes the operation and the results of laboratory and field testing of the device, which now is ready for use in routine computer surveillance of oilwell performance.

Introduction

A simple device is needed to estimate or to measure flow in the production line of an oil well. Absolute accuracy is not a major requirement for production surveillance. Errors of +/- 10 percent can be tolerated if an indication of the flow is determined. Because most oilfield production is two-phase flow, the device should indicate the total liquid production of two-phase flow and possibly estimate the total amount of liquid in a single-phase flow. Also, this device must be reliable and rugged, so that it will not fail under oilfield conditions. A simple transducer was developed. Then, the necessary complex analysis was used to monitor the oil wells. Many types of flow meters and flow-measuring techniques were investigated in the laboratory. This paper reports a new flow-measuring plan that met oilfield needs. A dynamic pressure transducer was used to measure small pressure pressure transducer was used to measure small pressure fluctuations that relate directly to liquid flow rate.

Prototype Development Prototype Development The phenomena observed in the laboratory indicated a relationship between a crystal pressure transducer measuring dynamic pressure and the flow rate. Dynamic pressure (delta p) is defined in this study as the perturbations pressure (delta p) is defined in this study as the perturbations in the flowline pressure caused by turbulence, valued two to three orders of magnitude less than the static pressure (p) of the line. Fig. 1 shows the difference between dynamic pressure and the flowing line pressure. Eq. 1 relates the dynamic pressure measurement to the velocity in the flowing line:

(1)

Using Eq. 1, velocity can be determined with a single point measurement. The theory of the relation between point measurement. The theory of the relation between dynamic pressure and velocity is found in the Appendix.

A quartz crystal can measure dynamic pressure, but an electronic circuit must convert this measured pressure to the required velocity. The instantaneous variation of pressure shown in Fig. 1 fluctuates with time. Its root pressure shown in Fig. 1 fluctuates with time. Its root mean square (RMS) value also fluctuates widely with time. To reduce these fluctuations and to provide an output that is proportional to velocity, the square root of the RMS signal must be measured and the signal smoothed so that the recorder or computer can follow the flow rate. Fig. 2 contains a schematic of the instrumentalion setup used to measure the dynamic pressure in the laboratory and in limited field tests. The crystal is piezoelectric quartz. The coupler converts the piezoelectric quartz. The coupler converts the highimpedance signal from the quartz crystal to a lowimpedance signal that can be amplified so that its RMS value and square root can be measured. Quartz is suited ideally for this kind of measurement and because of its structure is not subject to distortion by temperature gradients or vibration and shock. In general, it has a linear output and because of its stability, gains in the order of 100,000 may be used.

The laboratory prototype tested successfully in more than 20 wells at Shell Oil Co. lead to the development of a model for field use.

JPT

P. 160