I herewith present some notes on the use of Portland cement to cement in thecasing, and for plugging, to exclude water from oil and gas, wells, and the methods employed. I have used my best efforts to make each step of theoperation of cementing wells perfectly clear. The information is the result of actual experience and observation. The illustrations are from original drawingsmade especially for this paper.
It is not necessary to discuss here the manufacture of cement. Anyestablished brand of the slower setting Portland cements may be purchased withthe confidence that it will harden, if properly used, and exclude water fromand plug wells efficiently.
Setting.- By the setting of cement is meant its initial change from a soft orplastic mortar to a friable solid. After the cement has become thoroughly set it is still very weak and can be readily pulverized in thefingers. Setting is thought to be effected by the crystallizing out of the silicate and the aluminate of lime, which are soluble in water in theiranhydrous form. After dissolving in the water they pass to the hydrated state, in which they are insoluble, and hence are precipitated in acrystal line form.
Ordinarily neat Portland cement mortar remains perfectly plastic for from 1 to 1 1/2 hr. after mixing with water at about 70 degrees F. A highertemperature accelerates and a lower retards setting.
Hardening.-This is due to a continual crystallization of salts fromsolution, and to further chemical and physical changes which develop slowly, but which continue for long periods of time.
Testing.-It is no more necessary for an operator to go into the scientifictesting of cement to be used in a well than to so test the pipe used. He must depend for the quality of each on the tests and reliabilityof the manufacturer. Cement or pipe may be damaged in shipment so as to be unfit for use and such damaged material can easily be avoided by proper inspection.
A practical test of cement can be made in advance of its use for thispurpose by filling a common galvanized-iron bucket one-third full of water and stirring in neat cement until the mixture is as stiff as it can bemade and still be fluid enough to pour or pump. Then fill several tin cans (oldfruit cans will do) with the mixture and at once immerse these samples inwater. Take out one sample in 24 hr. and examine for set and hardness, anotherin 48 hr., and so on daily for a week. Thus a fair idea of how a given cementwill act in use may be formed.