Increased efficiency in production operations requires that the formation and completion characteristics be well defined and analyzed before committing funds to stimulation and/or workover operations. Such information is generally obtained from analysis of pressure transient data measured with wireline recorders. Until recent times, these measurements have been seldom made in pumping wells, due to the time required to trip the rods and pump out of the tubing in order to run the wireline pressure recorders. This need spurred the development of techniques for calculation of transient bottomhole pressure from surface measurements.
This paper describes the design and application of a fully digital system for automatic calculation of bottomhole pressure from echometric surveys of the annular fluid level. This portable system integrates specially designed high resolution A/D conversion and conditioning with advanced signal processing and digital filtering techniques. This results in very accurate determination of the depth to the fluid level, even in the presence of background noise caused by gaseous liquid columns.
Automatic signal generation and recording is undertaken by the software at predetermined, operator selected frequency so as to maximize the quality of the pressure transient data. Surface pressure and temperature measurements are used in conjunction with gas gravity and gas acoustic velocity to determine the pressure at the gas/liquid interface and the pressure at the sandface.
Graphic displays allow the operator to monitor the progress of the transient test by plotting in real time the current status of the well, the acoustic signals and the calculated pressures. Data that has been acquired at that point can be plotted as standard transient analysis graphs ( Horner, MDH, Log-Log etc.) Data files can be exported to other analysis programs.