Purpose And Use Of Cement Plug
Cement plugging in underground operations is one of the commonly used process technologies.
The purpose and use of cement plugs are mainly as follows:
(1) Sealing the test oil layer back to the new layer to test the oil, or sealing the non-target layer when performing the layering operation.
(2) closing the bottom water layer;
(3) Find a layer of a gap by finding a leak, finding a seal, and testing the upper casing.
(4) Blocking the abandoned wells and backfilling the depletion horizon.
(5) Closed horizons for safety purposes (eg closed high pressure layers, toxic and hazardous fluid layers).
(6) Blocking under special circumstances.
Cementing plug method and construction steps
1. Cement plug method
According to the position of the cement plug, there are two kinds of solid cement plugs and suspended cement plugs. In order to save cement and facilitate construction, in general, the method of hanging suspended cement plug is adopted.
According to the pressure in the well and the construction process, it is divided into four methods: cementing plug for pouring method, cement plug for circulating method, cement plug for injection method (including circulation + extrusion), and cable/rope ashing method.
2, cement plug construction steps
(1) Recirculating cement plug
This is currently the most widely used method in oil fields. The cement slurry is pumped into the well for replacement to a predetermined position, and then solidified to form a plug. The construction steps are as follows:
The cemented pipe string is lowered to the bottom of the expected cement plug, and the well is circulated and washed to the well.
After the cement slurry is prepared according to the design, the pre-separation liquid, the cement slurry, the rear separation liquid, the replacement liquid sequence and the design amount are injected into the well.
Replace the cement slurry to the design position. At this time, the inside and outside of the pipe should be in balance, and the pipe string should be raised to 1-3 m above the predetermined cement surface. Reverse circulation to wash the well and wash out excess cement slurry.
Start the column to a safe position, sit at the wellhead, fill the killing fluid, shut down the well.
After a certain period of time, check the cement surface position (depth).
Test the cement plug seal according to the standard pressure test. The pressure test method adopts the corresponding method according to different well conditions.
(2) Squeeze cement plug operation procedure
The cement plug is used to seal the high pressure layer. The construction steps are as follows:
Plug the string or packer/bridge down to the design location.
Fully wash the well back of the well or the seat sealer.
Squeeze the absorbency with clean water to calculate the pressure, time and amount of extrusion.
According to the test data parameters, squeeze the amount of cement slurry and the amount of replacement, and lift it up to the backwash position.
Backwashing or positive (reverse) squeezing into the killing fluid, shutting down the well.
After a certain period of time, check the cement surface position (depth). Test the cement plug seal according to the standard pressure test. The pressure test method adopts the corresponding method according to different well conditions.
