The Real Story of Cement Expansion

American Institute of Mining, Metallurgical and Petroleum Engineers Inc. This paper was prepared for the Rocky Mountain Regional Meeting of the Society of Petroleum Engineers of AIME, to be held in Billings, Mont., June 2–4, 1971. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. One of the most serious problems encountered when cementing casing in a well is the failure of the cement casing and cement formation bond. The failure of the cement bonding is a major problem from the standpoint of allowing problem from the standpoint of allowing migration of fluids from one zone to another. Also, poor bonding can result in large losses of reservoir fluids, premature reservoir depletion, and unsatisfactory stimulation operations. With these factors in mind, it has long been recognized that superior cementing operations could be achieved if expansion could be induced in oil well cements. Expansion currently is induced in oil well cements by two methods, addition of salts (salt cements), or addition of an expanding component (chemically compensated cement). The purpose of this paper is to compare the expansion characteristics of these types of cements. Additional characteristics such as pumping time, compressive strength, and bonding pumping time, compressive strength, and bonding are also compared. Introduction Good bonding of the cement to pipe and cement to formation is essential for effective zone isolation. This problem is evident in oil, gas, and gas storage wells. Secondly, poor bonding may limit the desired production and stimulation techniques of the well in question. The introduction of expansion in a well cementing system has long been recognized as a possible means of improving the primary cement job. At present, these are four basic methods that may be used to accomplish better bonding. These are as follows:Completely replace the wellbore fluid with cement.Treat the casing or pipe (sand coat, prestress, etc.).Use expanding cement.Increase the chemical bonding ability of the cement. We will limit our discussion to the effects of method 3. There is evidence that expanding cement has much higher bonding strengths than conventional cements under oil well conditions. The improved bonding is caused by mechanical resistance or tightening of the cement against the pipe. Even if mud is left on the casing or formation surface, good bonding can be obtained. This is probably due to the absorption of water in the mud by the expanding cement. Actual chemical bonding is not present. present.