Abstract
Determination of Fluid Level in Oil Wells by the Pressure-wave Echo Method.
Introduction
In its essence, an Acoustic Fluid Level Survey determines the depth to the Fluid Level by generating an Acoustic Pressure Pulse (or Wave) that travels down the well, reflects off the Fluid Level, and then
returns back to the surface where it is recorded by a sensitive internal microphone inside the Fluid Level Gun. The longer it takes for the wave to reflect the surface, the deeper the fluid level. The microphone also records other “disturbances” and reflections of the Acoustic Wave that result from the wave encountering tubing collars, a TAC, perforations, or other changes to the cross-sectional area of the annulus. The plot of the acoustic reflections recorded by the microphone is known as the Acoustic Trace. The shot is generated on the left side, the kicks of decreasing amplitude along the trace are the tubing collars, and the fluid level "kick" is on the right side.
Meta-analysis
Echo Test:
Echo test is an integrated artificial lift data acquisition and diagnostic system that allows an operator to maximize oil and gas production and minimize operating expenses. It is a computerized instrument for acquiring liquid level data, acoustic pressure transient data. Well, productivity, reservoir pressure, overall efficiency and well performance have derived from the combination of measurements of surface pressure, acoustic liquid level and pressure transient response.
Echometer:
an apparatus for measuring depths of objects in water or underground by
timing the echoes of sound reflected from them.
Remote fire gas gun:
The Remote Fire Gas Gun offers the convenience of not having to manually open the gas valve on the gun to generate the pressure wave. A solenoid the valve is triggered automatically from the Well Analyzer system or the Model M recorder that opens the internal gas valve and releases compressed gas from the volume chamber into the well.
The gun's microphone records the reflected pressure waves in relation to their polarity (UP or DOWN-kicks) and this is of great significance. When the acoustic wave encounters a restriction in cross-sectional area (like a TAC, salt ring, liner top, the fluid level, etc.) a positive pressure reflection reverberates back to the microphone and is plotted on the Acoustic Trace as a " dow kick". Conversely, when the acoustic wave encounters an opening in cross-sectional area (like perforations, a down-tapering from 2-7/8" to 2-3/8" tubing, etc.) a " Rarefaction Wave" (a negative polarity, or reduced-density pressure disturbance) is generated and this disturbance equally transmits through the gas medium back to the surface microphone—and is plotted as an "up-kick & quote.
Results
We can determine the fluid level in oil wells to confirm that Sucker rod pump or ESP Pump work efficiently.
Discussion
Note to reader: the terms LIQUID LEVEL and FLUID LEVEL are used interchangeably here. As my fellow engineers out there will attest, technically speaking the term Liquid Level should only be used when talking about determining the depth to the oil/water. However, the historical industry terminology used for the gun depicted above was a Fluid Level Gun. It is an unfortunate terminology blunder that has taken root and we even find it difficult to not instinctively say Fluid Level at every chance. The key difference to keep in mind is that oil, water, and gas are all fluids but only oil & water is liquids. Since gas flows up the casing to surface, the equipment described herein is obviously not determining the depth to just any fluid rather it is measuring the depth to the Liquids. Maybe someday even these old dogs here at Downhole The diagnostic will conform to the proper scientific terminology, but until we do (and the industry does as well) we are stuck in limbo as both terms are commonly used.
References
1. Prof. DR. Adel Salem. “Production Engineering”. Suez University, Faculty of Petroleum &
Mining Engineering.
2. Downhole Diagnostic.
3. Intern at Qarun Petroleum Company
Submitted By:-
Mahmoud Rayan
Faculty of Petroleum & Mining Engineering, Suez University, Petroleum Exploration and Production
Engineering Program, Suez, P.O.Box 43512, Egypt
mahmoud.saddik2013@gmail.com