Laboratory Evaluations and Field Testing of Silica-CMHEC-Cement Mixtures
- C.F. Rust (Mobil Oil Co. de Venezuela) | W.D. Wood (Mobil Oil Co. de Venezuela)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- November 1960
- Document Type
- Journal Paper
- 25 - 29
- 1960. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 4.2.3 Materials and Corrosion, 5.6.5 Tracers, 1.14 Casing and Cementing, 1.14.3 Cement Formulation (Chemistry, Properties), 2.4.3 Sand/Solids Control
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The discussion which follows represents a report on laboratory evaluations and field testing of silica-carboxymethyl hydroxyethyl cellulose (CMHEC)-cement mixtures. While the major part of the laboratory work reported, and all of the field tests, were carried out in Mobil Oil Co.'s operations in Venezuela, the work received its impetus at the Magnolia Petroleum Co. Field Research Laboratory (now Socony Mobil) in Dallas, a Mobil affiliate. Laboratories of other companies have been active in this area of cementation methods, although very little data are available in the literature.
Extensive laboratory tests, involving the use of a high-temperature consistometer in conjunction with high-temperature curing baths, have indicated that at temperatures exceeding 250°F oilwell cements of all types develop undesirable properties. These tests show that at elevated temperatures compressive strengths retrogress and become dangerously low near a temperature of 300°F. This fact is illustrated in the upper part of Fig. 1, which represents a plot of compressive strength vs time for an oilwell Class E cement at various temperatures. This figure shows that at 180°F compressive strengths build up and remain essentially constant with time. At 260°F, high strengths are realized early but pass through a maximum and then decline. At 320°F, the maximum compressive strength is reached in less than 24 hours and is much lower than at the lower temperatures.
This is not the only detrimental factor which affects the properties of a cement cured at high temperatures. Fig. 2 illustrates that corresponding increases in permeability accompany the strength retrogression. At 320°F, the permeability of this sample increased from 4 X 10(-6) to 2,780 X 10(-6) darcies.
Fortunately, these deficiencies can be corrected by the use of proper amounts of silica. The lower part of Fig. 1 shows the effect on compressive strength when 35 parts of silica are added to 100 parts of Class E cement. For a curing temperature of 180°F, maximum compressive strength is obtained more slowly but reaches the same order of magnitude as in the case of neat cement. For a temperature of 260°F, an increase in compressive strength is realized, with no evidence of subsequent retrogression apparent. At 320°F, an initial strength is observed which is not only satisfactory but which, for all practical purposes, remains constant. The effects on the water permeability of adding 22.5 parts of silica to 100 parts of Class E cement are shown in the lower right-hand portion of Fig. 2. The water permeability decreased with curing time and is much lower than in the case where no silica was used.
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