.jpg)
perforating charge
perforating charge
Mar 24, 2009 4:22:38 PM
.jpg)
.jpg)
Perforating
Since the pay zone is sealed off by the production string and cement, perforations must be made in order for the oil or gas to flow into the wellbore. Perforations are simply holes that are made through the casing and cement and extend some distance into the formation. The most common method of perforating incorporates shaped-charge explosives (similar to those used in armor-piercing shells).
Since the pay zone is sealed off by the production string and cement, perforations must be made in order for the oil or gas to flow into the wellbore. Perforations are simply holes that are made through the casing and cement and extend some distance into the formation. The most common method of perforating incorporates shaped-charge explosives (similar to those used in armor-piercing shells).
Shaped charges accomplish penetration by creating a jet of high-pressure, high-velocity gas. The charges are arranged in a tool called a gun that is lowered into the well opposite the producing zone. Usually the gun is lowered in on wireline. When the gun is in position, the charges are fired by electronic means from the surface. After the perforations are made, the tool is retrieved. Perforating is usually performed by a service company that specializes in this technique.
Look at the picture to the left. Usually, steel pipe is run all the way to the bottom of the hole and cemented in place. This stops oil, gas, and salt water from coming into the hole from formations above the pay zone.
Then a device called a "perforating gun" (A) is lowered into the hole at the depth where the oil or gas formation is found. This may be anywhere from several hundred feet down to tens of thousands of feet.
After the gun is lined up properly, powerful explosive charges are fired (B) from the control panel in the truck...up at ground level. These explosives blast a hole in the steel casing and cement, up to several feet out into the rock. Finally, the oil and gas fluids flow into the holes and up the well to the surface (C).
