Producing Petroleum

WELL COMPLETION

The next step, after setting casings and liners, is the completion phase of a well. Completion simply means making the well ready to produce oil and gas under controlled pressures and flow rates. Figure 7 shows the four common completion techniques. In all four, the casing prevents the formations above the producing zone from collapsing into the wellbore. If the producing formation is strong enough, as in the case of limestone, a length of casing can be cemented immediately above it, leaving the producing formation unsupported. This is called an open hole completion. If the reservoir rock needs support, other methods can be used:

Perforated casing or liner. In this method, casing or liner is run all the way through the producing zone and cemented in place. Then, holes are shot (by explosive charge) through the casing and cement, into the formation. These perforations are created with a perforating gun that is lowered into the hole on a wireline. The gun is then fired electrically, and powerful, shaped charges perforate the pipe and the zone at predetermined intervals. Once the perforations have been made, oil and/or gas can flow into the casing.

Perforated or slotted liner. In the second method, a pre-perforated or slotted liner (with holes or slots that are level with the producing zone) is hung from the bottom of the last string of casing. If the producing formation is weak or poorly consolidated, sand and other solids will be carried into the well as the oil or gas is produced. To prevent this “sand production,” the slotted or perforated liner may contain a wire-wrapped or a prepacked- gravel protective layer to keep the sand from entering the wellbore.

Gravel packing. Another approach that is helpful if the producing formation is weak (such as loose sand), and must be supported or held back, is the conventional gravel pack. A gravel packing operation consists of circulating and placing carefully sized gravel into the annular space between the liner and the wellbore wall. The pack forms a permeable layer to exclude any formation particles from the wellbore that become loose during production.

Literature.

1. “Drilling fluids Engineering Manual”. - Magcobar Division Oilfield Products Group Dresser Industries, INC. Houston, Texas, 2001.

Date: 2015-02-28; view: 2123