Model M Manual : Appendix

 

 

Acoustic Responses from Downhole Anomalies

 

Following are examples of the responses obtained from restrictions such as the liquid level and from enlargements such as perforations. The initial pulse generated by the gun is a compression (explosion) pulse; that is, the pressure in the gas gun volume chamber is in excess of well pressure. If the initial pulse were a rarefaction (implosion) pulse, the responses would be reversed.

 

COMPRESSION RESPONSE (Downward kick)

 

The liquid level, liners, gas mandrels and other anomalies causing a reduction in casing annulus area will cause a reflected signal back to the surface that will be of the same type as the initial pulse, which was a compression wave. The direction of the initial pulse is downward when the top of the chart is to the operator’s left.

 

RAREFRACTION RESPONSE (Upward kick)

 

Perforations, “shot” holes, a reduction in tubing size and other anomalies causing an increase in casing annulus area will cause a reflected signal back to the surface that will be of the opposite polarity as the initial pulse. Thus, the response from these anomalies will be upward when the top of the chart is to the operator’s left.