cement bond integrity

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cement bond integrity

Probe provides a variety of tools that are used to determine cement bond integrity. These tools actually evaluate the bonding of the cement job to the well casing and, in turn, to the rock formation. When these bonding interfaces are of good integrity, you are assured of a good hydrostatic seal which prevents communication between the producing formation and other formations, such as a fresh water aquifer.

Probe’s tool uses piezoelectric transducers which, when compared with magneto-strictive transducers, provide better performance with less maintenance and greater electrical efficiency. The peizo crystal is a more precise acoustic device with better mechanical tolerances which result in a very consistent measurement from tool to tool. The defacto standard for transmitter frequency within the industry is 20Khz. The reason for this is a compromise. The signal must be in the low ultrasonic range to provide sufficient energy coupling to the wellbore environment from a physically compact transducer. At the same time, the signal should not be at too high of a frequency because the higher frequencies are too easily attenuated by anything touching the outside of the well casing, which would result in an optimistic indication of bonding where, in fact, none exists.

Probe’s acoustic transmitters operate at the highest radiated power of any equivalent tool in the industry. The electronics creates a crystal controlled 20Khz signal with an amplitude of 1200 Volts peak to peak which is applied to the transducer crystal through a specially designed impedance matching network, resulting in extremely high electrical to mechanical conversion efficiency. The amplifiers, which condition the signals from the two receivers, operate at very low gain. This results in a transducer system that is very low noise with a very wide dynamic range. Since the receivers do not require a great deal of amplification, the tool is very insensitive to mechanical noise resulting from movement in the well bore. This allows the operator to record a bond log at higher than normal logging speeds. Since this reduces the time required to run the service and since time is money….enough said.

Probe manufactures two diameter tools, 2-1/8” and 1-11/16”. The smaller tool is for thru-tubing work. In the larger tool, both transmitter and receiver are working at 20Khz which happens to be the mechanical resonance of the transducers. The 1-11/16” tool operates at 20Khz as well. This is not trivial. Most of our competitors’ small tools operate at between 40 and 60Khz. This is because that is the resonant frequency of the smaller transducers. Our patented transducers in our 1 11/16” tool to operate at 20Khz so that it runs the equivalent log of the larger tool.

Probe also provides radial bond tools which provide cement integrity information from 8 separate radial sectors at any given depth. Wells with more tortuous well paths, or passing through multiple zones where cross flow and flow behind casing may occur are likely candidates for the radial bond tool. The decision to go with either the 1 11/16” tool or the 2 3/4” tool is dependent on the size of casing through which the cement bond will be measured. The 1 11/16” tool is appropriate for casing sizes up to 7” (177.8 mm), while the 2 3/4” tool is appropriate for all casing sizes up to 13 5/8” (346.1 mm).