Casing and cementation

Casing

Casings are used both to maintain the stability of the borehole and to separate individual rock formations. A borehole is cased by several casing sections similar to a telescope towards the bottom of the hole.

Dimensions

The required diameter of a well depends on the maximum expected production rate. Final diameters at RAG normally are 4 1/2" and 7". Smaller tubings are inserted in them for production purposes.

Setting depths

Setting depths of individual sections vary. They are dictated by the ground water horizons, the expected gas and oil reservoirs, geological faults and expected pressures.

Liners

Liners are casing strings ranging from the bottom hole to the lower mast end of the previous string but not to the surface and landed in a liner hanger.

Cementation

After having run the casings or liners the annulus between the borehole wall and the pipe is filled with cement to seal rock formations containing liquids or gases.

Stage cementation

Friction pressures may increase to a point when cementation can be carried out only by stages. So-called stage cementers are placed in the casing string in order to cement the lower section and finally, after opening the stage cementer – the upper section of the hole.

Stage tool for cementation (from left: post plug 2. stage free falling bomb to open the stage tool stage tool (sliding side door) post plug 1. stage baffle-plate for post plug whiper plug 1. stage)