Watch your timing

Watch your timing

On small well work this is seldom a factor.

Conversely, you may want to decrease the initial setting time, which can be accomplished by adding two percent by volume of calcium chloride (CaCl2) to your mixture.

Not only will it reduce setting time, but the compressive strength (hardness) after 24 hours will be approximately equal to cement grout without calcium chloride at 48 hours.

The use of "hi-early" cement can make possible further reduction in the setting time.

4.) Shrinkage of the grout envelope upon hardening is another problem.

The accepted offset to this shrinkage is to use an additive of two to six percent finely-ground bentonite mixed with the slurry.

Not only will it control shrinkage, but it will make the solution more fluid, thereby reducing pumping pressure.

Bentonite is also a good loss circulation control material.

5.) Centering guides are often mentioned as being desirable when installing a liner in a drilled hole that is to be cemented.

In the author's opinion, guides should not be used.

It is rather naive to think that wells are drilled so straight that you end up with a concentric annular space between well bores and liners.

It would take an infinite number of centralizers to hold a pipe concentrically in a normal bore.

The fact that the casing may touch the well bore at one or more points will not result in any less an effective cement job.

If you install a liner with a well bore below the bottom of a liner to be cemented in place, there is reason to align the liner and the well bore with a centralizer to eliminate an offset of the finished well.

6.) If you are cementing through a drillable cement shoe, do not crowd the tools, either with rotary or cable tools, when drilling up the shoe.

If you are running threaded and coupled pipe, and particularly if you are drilling with a rotary machine, be sure to tack-weld the shoe and the couplings on the bottom two or three joints of pipe.

It is possible to unscrew a shoe or possibly a joint of pipe when drilling out a shoe.

You can also knock a shoe off with cable tools.

There's nothing worse than having a loose shoe in the bottom of the hole with the liner cemented in place.

Finally, there is no substitute for experience when it comes to improving the technique of cementing of wells.

I have observed the operation and the equipment of many well drillers, and I know that you cannot under-estimate the ingenuity of the individual who decides he is going to equip himself to do first class pressure cementing.

By repetition and refinement he will make better wells.

This is the goal of all of us in the field of well work.