Last-Shot Detection System

Ideally, shot detection equipment should detect not only the firing of the gun string, but also the high-order detonation of the entire gun string. The surface shot detection system provides a reliable but only qualitative indication of gun firing. Addition of the last-shot detection hardware can confirm that the complete gun string shot on high order.

Compatible with all firing heads

All firing heads are positioned on top of the gun string and spacer for safety reasons. The last shot detection hardware is positioned at the bottom of the gun string. The equipment is an implosion chamber, actuated only if a high-order detonation arrives at the bottom of the last gun.

The high-order detonation initiates a pyrotechnic delay that sets off the bullet propellant after 25 to 45 sec. The exact delay time, which is a function of temperature, may be predicted from a chart. The propellant shoots a steel bullet into the rupture plate of an air-filled implosion chamber. Two signals are recorded by the surface shot detection equipment, gun string firing and last-shot detection chamber implosion, indicating total gun firing.

Other last-shot detection methods

Radioactive marker pip tags may be installed in the top and bottom charges of the gun string. When the guns are fired, a radioactive streak (1 mCi) is sent into the formation. The streak is detected by a gamma ray tool after the guns are dropped or pulled out.

On the short string of dual string completions, pip tags may be placed in the bottom gun (usually 2 shots, 4 ft apart). When a gamma ray tool is logged from the long string before and after firing, the attenuation of gamma ray activity after firing confirms the high-order firing.