Abstract

Acoustic instruments have been used routinely for many years as an aid in analyzing well performance of normal-pressure oil producers.

Recent developments in equipment and techniques now permit more accurate calculations of acoustic static bottomhole pressures at surface pressures up to 15,000 psi in corrosive (CO2 and H2S) environments. pressures up to 15,000 psi in corrosive (CO2 and H2S) environments. Equations and charts are presented herein for determining static bottomhole pressures from acoustic and well data. Also, a special technique is pressures from acoustic and well data. Also, a special technique is recommended for shutting-in a well which in most cases will yield more-accurate results.

This method has been programmed for an inexpensive, portable notebook-size computer which can be used in the field to easily perform these calculations.

Introduction

The liquid level in a well may be determined acoustically by generating a pressure pulse at the surface and recording the echos from collars, obstructions, and liquid level.

A blank cartridge was the conventional source of pressure pulse until development of the modern gas gun. On wells having less than 100 psi, the gas gun volume chamber is pressurized to approximately 100 psi in excess of well pressure. The gas is then rapidly released into the well to create the pressure pulse. On wells having pressures in excess of 100 psi, the volume pressure pulse. On wells having pressures in excess of 100 psi, the volume chamber in the gas gun is bled to a pressure less than the well pressure. Then, a valve is rapidly opened to permit wellhead pressure to expand into the volume chamber and create a rarefraction pressure wave.

A microphone converts the pressure pulses reflected by collars, liquid, and other obstructions (or changes in area) into electrical signals which are amplified, filtered, and recorded on a strip chart (Fig. 1). The liquid level depth can be determined by counting the number of tubing collars to the liquid-level reflection.

Changes in cross-sectional area are also recorded. When these changes are known, they can be used as depth references to determine liquid-level depth. Also, the distance to the liquid level can be calculated by travel time from the acoustic chart and acoustic-velocity data. Acoustic measurements were generally obtained by "shooting" down the casing/tubing annulus in packerless completions (Fig. 1).

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