A Tentative Specification for Oil-Well Cement

THE increasing use of cement in oil-wells has unfortunately not led to satisfactory standardization of the cement or cements in use. Various companies have different methods of 'test and some purchase cement solely on the standard specification for construction cements, although this specification is largely recognised as inadequate. The desirability of a uniform specification for oil-well cements is briefly discussed, and it is thought that some such standard or standards must be adopted. A tentative specification is put forward in the present paper. It is clearly to be understood that this specification, which is based on the experience and researches of the author, is incomplete, for reasons mentioned, and it is intended solely to provide an impetus for the production of a suitable specification. The need for research on a number of points is noted and the likely effects on the specification, arising from such research, is discussed. The experience and research which has led to the present tentative proposals is discussed at some length. It is considered that additional tests may have to be added, but a caveat is entered against the addition of too many tests, which will seriously limit the manufacturer's scope. It is often said that cement is "the cheapest thing put in an oil-well." Its use may have become almost a commonplace, but it is an important commonplace, for bad cementations may lose, perhaps do lose, many thousand barrels of potential production. It is, therefore, surprising to find that there is, at the moment, no universal standard specification for oil-well cement, nor even one meeting with a general acceptance. Some producers buy on the strength of the British Standard Specification for constructional cement. Others have devised, apparently, specifications on the empirical basis of their immediate needs, and preserve silence on the nature of such standards. As an illustration, Rumanian companies appear to prefer a test of bending strength; American companies use compression strength, or tensile strength; and at least one company, a combination of the latter two. The problem of a specification for oil-well cement faced the author in a recent investigation into an unusual series of cementation failures in a well-developed oilfield. There was no marked indication of the cement being at fault, but there was a decided possibility of its so being, and the absence of a definite specification made it almost impossible to eliminate cement from the list of possible causes of failure. As a result, an extremely tentative specification has been produced, based on the, as yet incomplete, laboratory and field research of the author and others.