Ind. Eng. Chem. Res. 2005, 44, 5579-5584
5579
Class H Oil Well Cement Hydration at Elevated Temperatures in the Presence of Retarding Agents: An In Situ High-Energy X-ray Diffraction Study Andrew C. Jupe,† Angus P. Wilkinson,*,† Karen Luke,‡ and Gary P. Funkhouser‡ School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, and Duncan Technology Center, Halliburton, 2600 South 2nd Street, Duncan, Oklahoma 73536-0470
In situ powder X-ray diffraction was used to examine the hydration of API Class H cement slurries, with a water-to-cement ratio of 0.394, at 66, 93, 121, and 177 °C under autogenous pressure in the presence of varying amounts of the additives tartaric acid, modified lignosulfonate, and AMPS (2-acrylamido-2-methylpropanesulfonic acid) copolymer. All of these retarding agents inhibited the hydration of crystalline C3S (Ca3SiO5), but other modes of action were also apparent. The formation of ettringite was suppressed when tartaric acid was used by itself or in combination with other additives. Changes in the hydration of C3S vs time could not be correlated in a simple way with the observed pumping times for the cement slurries. The largest changes in pumping time as a function of temperature occurred in a temperature interval where ettringite/monosulfate decomposes and crystalline hydrogarnet starts to be formed. Introduction Portland cement is used in large quantities to “grout” oil wells. The cement is placed between a metal liner and the walls of the borehole to provide support for the liner and a seal to prevent the migration of gas, etc., along the outside of the liner.1 The cement has to perform under demanding conditions as high temperatures and pressures are encountered at depth, and chemically aggressive agents may also be present. It is very important that the cement slurry does not prematurely set while it is being pumped, as this can block the well. Additionally, the cement should set in a short time to help reduce costs due to delays. Long-term performance is also of great concern. If the cement does not provide a good seal, gas can migrate to the surface and lead to safety and environmental problems. Fully understanding the chemistry and materials engineering behind oil well cement setting and aging is a major economic issue and a very important issue for the health of our environment. The setting characteristics of oil well cements are in practice controlled by the addition of additives. Different additives or combinations of them are employed depending upon the temperature of the well. However, their effect on the cement hydration chemistry is in many cases not well established because tools for the in situ examination of hydration under realistic conditions are limited. Because all the cement clinker phases and some cement hydration products (aluminates and high-temperature silicate phases) are crystalline, time-resolved X-ray diffraction and neutron diffraction are potentially powerful tools. However, transmission measurements in sealed sample tubes are preferable to the flat plate reflection geometry that is commonly used in laboratory X-ray diffraction instruments as water loss and carbon* To whom correspondence should be addressed. Tel: (404) 894-4036. Fax: (404) 894-7452. E-mail: angus.wilkinson@ chemistry.gatech.edu. † Georgia Institute of Technology. ‡ Halliburton.
ation issues are avoided. The time resolution achievable using transmission geometry is limited by the attenuation of the beam passing through the sample. This is a particularly severe problem for the relatively long wavelength X-rays used in laboratory diffractometers. Kuzel2 tackled this problem by reducing the sample thickness to only ∼0.2 mm, but even then the X-ray transmission efficiency was probably only ∼10%, leading to long data acquisition times. Neutron beams are only weakly attenuated by most materials, but this approach suffers from the serious disadvantage that it is necessary to use D2O instead of H2O to avoid the strong incoherent scattering background and attenuation from the hydrogen. Deuteration for cement phase hydration studies is problematic, because it can alter the reaction kinetics very significantly.3,4 Even so, neutron diffraction was used by Christensen et al. to examine the hydration of various calcium aluminates with inorganic additives in D2O at elevated temperatures.5-7 The shortest data collection time in these studies was 5 min, a time scale well matched to cement hydration. Intense high-energy X-rays from synchrotron sources are now quite readily available, and offer significant advantages for in situ cement hydration studies. Sample penetration is good at high energies, beam intensity is very high, somewhat compensating for absorption problems, H2O in samples presents no problems, and the published diffraction peak intensity values found in sources such as the powder diffraction files can guide phase identification. This last point is not trivial, as the peak intensities in neutron diffraction experiments are quite different from those measured with X-rays and they are typically not tabulated. Furthermore, the neutron intensities cannot always be calculated, as the crystal structures of some cement hydration products are not well-known. There have been two approaches to the use of synchrotron X-rays for cement hydration studies, energy-dispersive diffraction (EDXRD)8 and conventional monochromatic angle-dispersive methods. EDXRD employs a fixed-2θ geometry that is very convenient for sample cells that have limited X-ray
10.1021/ie049085t CCC: $30.25 © 2005 American Chemical Society Published on Web 06/11/2005
5580
Ind. Eng. Chem. Res., Vol. 44, No. 15, 2005
windows and typically uses highly penetrating X-rays in the 20-120 keV range (λ ) 0.6-0.1 Å). It has been used to study the early stages of portland cement hydration,9 the hydration of mine-packing calcium aluminate/calcium sulfate/lime cement,10 and the thermal stability of ettringite.11 Monochromatic angle-dispersive diffraction methods using synchrotron radiation have also been used recently. In a study of an expansive cement blend, Evju and Hansen12 used ∼1.5 Å synchrotron radiation and 0.7 mm glass capillary sample containers with a CCD area detector and were able to collect one diffraction pattern every 3 min. Christensen et al.13 also used 0.7 mm capillaries with an area detector and an X-ray wavelength of 0.9 Å, allowing them to collect data sets at intervals of less than 2 min. The need for small diameter samples and very thin capillary tubes in these experiments illustrates the disadvantage of longer wavelength radiation. The use of significantly shorter wavelength X-rays enables the use of thicker samples that are more representative of bulk cement slurry, in more substantial, and nonreactive, containers. It also pushes the diffraction peaks of interest to lower Bragg angles, removing the need for sample ovens with large X-ray windows. The cement used for oil well grouting closely resembles the ordinary portland cement used in construction, the main difference being a higher Fe/Al ratio.14 The main phases in unhydrated oil well (“Class G” or “Class H”)14 cement are tricalcium silicate, Ca3SiO5 (C3S), β-dicalcium silicate, Ca2SiO4 (β-C2S), calcium aluminoferrite, Ca2FeAlO5 (C4AF), and calcium sulfate, which is usually present as the dihydrate gypsum. The two calcium silicates and the ferrite phase are intimately mixed in the form of cement grains, with little or no pore space. The surfaces of these grains are partially coated with gypsum from the intergrinding process. At ambient temperature, the most important cement hydration process is the conversion of the silicate phases to an amorphous calcium silicate hydrate, referred to as “C-S-H”, and Ca(OH)2 (CH). At sufficiently high temperatures the crystalline calcium silicate hydrates R-C2SH (Ca2SiO3(OH)2) and C6S2H3 (Ca6(Si2O7)(OH)6), also known as jaffeite or tricalcium silicate hydrate, form, and the resulting cement matrix has lower mechanical strength and higher permeability, though this is not necessarily a serious drawback.15 Silica flour is typically added for downhole applications to prevent this strength degradation from occurring by forming lower calcium-to-silicate ratio crystalline calcium silicate hydrates.16 The most rapid reaction during the early hours of cement hydration at ambient temperature is the formation of ettringite, Ca6Al2(SO4)3(OH)12‚26H2O. Ettringite decomposes to give “14-water monosulfate” Ca4Al2O6(SO4)‚14H2O, which is itself unstable at higher temperatures and is converted to a stable, crystalline hydrogarnet phase. The rate of ettringite decomposition is dependent on both temperature and the relative amounts of sulfate and aluminate phases present. In the present work we examine the effect of three retarders, (A) a modified lignosulfate, (B) an AMPS (2acrylamido-2-methylpropanesulfonic acid) copolymer, and (C) tartaric acid on the hydration of a class H oil well cement at 66 °C (150 °F), 93 °C (200 °F), 121 °C (250 °F), and 177 °C (300 °F) using time-resolved highenergy monochromatic powder diffraction. Complementary consistency measurements were also made on some
Figure 1. Schematic of the sample container design used for the in situ X-ray diffraction studies.
cement slurries to look for correlations between pumping time and cement hydration chemistry. Experimental Section Cement Slurries for X-ray Measurements. All additives were dry blended with the cement powder before the slurry was prepared. The slurries were prepared using 39.4 g of water per 100 g of Class H cement (batch oxide analysis 21.8% SiO2, 3.4% Al2O3, 5.6% Fe2O3, 63.6% CaO, 1.1% MgO, 2.8% SO3, 0.11% Na2O, 0.53% K2O, loss on ignition 0.53%, 0.08% insoluble residue). The phase composition was 54% C3S, 22% C2S, 0% C3A, and 17% C4AF, on the basis of the Bogue calculation.17 Mixing was carried out in a Waring blender immediately prior to the start of the X-ray experiments. Sample Environment. The cement slurries for X-ray investigation were placed in PEEK (poly(ether ether ketone)) polymer cups, with an internal diameter of ∼4.75 mm, which acted as disposable liners for an X-ray-transparent pressure vessel that consisted of a titanium rod drilled to hold the PEEK cup. The pressure vessel was sealed using 3/8 in. stainless steel “Swagelok” compression pipe fittings (Figure 1). The titanium was locally thinned (∼0.25 mm) to provide good transmission characteristics at the X-ray energies used for the experiments. Great care should be taken in using containers of this type to help prevent catastrophic failure; ours were hydraulically leak tested to 800 psi at room temperature prior to use. The titanium sample containers were heated in a custom-built small fan oven with X-ray-transparent windows made from 50 µm Kapton film. X-ray Diffraction Data Collection. All the diffraction data were collected using the 5BMD (5 Bending Magnet D) beam line, located in the DND CAT (DupontNorthwestern-Dow Collaborative Access Team) sector of the Advanced Photon Source, Argonne National Laboratory. An X-ray beam with a nominal energy of 65 keV was selected using a Si(111) double-crystal monochromator and collimated to a 1 × 1 mm cross section. The diffraction data were recorded using a MAR 165 CCD camera located ∼76 cm from the sample. The sample to detector distance was calibrated using a TiO2 sample. After the samples were placed in the fan oven, it was ramped to the final temperature over a period of 54 min and held there until the end of the experiment. The ramp rate was chosen to match that used in the
Ind. Eng. Chem. Res., Vol. 44, No. 15, 2005 5581 Table 1. Pumping Times (min) for Class H Cement Slurries (w/c ) 0.394) Examined by in Situ Time-Resolved X-ray Diffraction at Different Run Temperaturesa 66 °C 93 °C 121 °C 177 °C no retarder 0.3% AMPS 0.75% AMPS 0.3% AMPS + 0.3% tartaric acid 0.35% tartaric acid 0.3% lignosulfonate
74 229
181
73 215 651 199 177
61 59 171 166 92 76
80 134
a The amount of retarding additive is specified as a percentage of the dry cement weight.
pumping time measurements. Diffraction patterns were recorded every 5 min. X-ray Data Processing. The raw X-ray diffraction images were integrated using the program FIT2D.18 Zingers, spikes in the raw images due to radioactive decay or cosmic ray events, were eliminated from the data, and the scattering background was subtracted. Peaks from the individual phases of interest were identified and integrated to give intensity versus time plots for the various phases in the samples. The data were corrected for the decay in incident beam intensity using an ion chamber monitor located before the sample. Pumping Time Measurements. Pumping time measurements were carried out for the same cement slurry compositions as used in the time-resolved diffraction studies. These measurements employed a highpressure, high-temperature consistometer where the slurry was ramped to the final temperature and a pressure of 7800 psi over a 54 min period and then held there for the duration of the measurement. The time taken to reach a consistency of 70 Bc (Bearden units of consistency)19 was recorded as the pumping time of the slurry.19 The results of these measurements are presented in Table 1 for all of the slurries studied by in situ XRD. Results and Discussion Many of the phenomena observed in our time-resolved diffraction experiments can be seen in a single timeresolved diffraction data set for a slurry sample containing 0.3%, by weight of cement, AMPS copolymer that had been heated to 121 °C (Figure 2). These data show (1) the decomposition of the initially formed ettringite to 14-water monosulfate and ultimately the complete disappearance of all crystalline aluminosulfate phases as the sample is heated to 121 °C (first 54 min) and subsequently held there, (2) the gradual loss of crystalline C3S as it hydrates, (3) the slow loss of brownmillerite, C4AF, as it hydrates, (4) the loss of gypsum, (5) the appearance of portlandite, Ca(OH)2 (CH), (6) the appearance of a hydrogarnet, C3AH6, and (7) the appearance and disappearance of an intermediate with a Bragg peak at 3.52 Å d spacing, which is probably anhydrite (CaSO4). There is considerable scattering from the titanium sample container walls at higher Bragg angles that unfortunately obscures peaks from the β-C2S in the sample. The effect of the added retarders on calcium silicate hydration can be clearly seen in Figure 3, where we present plots of C3S relative concentration vs time for several different retarder types and concentrations at 93 and 121 °C. In general, these curves show an initial small loss of C3S followed by a plateau-like region, the induction period, and then the quite rapid loss of C3S
Figure 2. Time-resolved diffraction data for a cement slurry containing 0.3% AMPS copolymer retarder hydrating at a 121 °C final temperature.
from the slurries. This is expected from calorimetry and other work on cement hydration.20 As the strong C3S diffraction peak used to construct these graphs overlaps with a weak β-C2S peak, we see some tailing off in the apparent level of C3S at longer times at 121 °C that we believe is a consequence of the lower hydration rate for the β-C2S and not an inherent feature of C3S hydration. Various models for the presence of an induction period have been proposed, including the formation of a semipermeable layer around the cement grains that inhibits the ingress of water, and sulfate, but at some point this barrier fails due to internal pressure.20 We can use the time at which the induction period ends and the rapid hydration of C3S begins as a measure of the retarding ability of the additive(s) that were used. On the basis of the diffraction data for slurries containing 0.3% AMPS copolymer, 0.3% modified lignosulfate, and 0.35% tartaric acid, and this measure of retarder performance, we conclude that the order of effectiveness is AMPS copolymer > tartaric acid > modified lignosulfate > control. This order is consistent with the measured pumping times for these slurries at 93 °C (215, 199, 177, and 73 min), but not the pumping times measured at 121 °C (59, 92, 76, and 61 min). In general, there is not a clear correlation between slurry viscosity development as indicated by the pumping time and the onset time for the rapid hydration of C3S when data at different temperatures are considered; this is very obvious when C3S concentration is followed as a function of time at different temperatures with the same slurry composition (Figure 4). However, the diffraction data clearly indicate that one mode of action for all of the retarders included in this study is the inhibition of C3S hydration. All of the retarders examined increase the time period before the rapid hydration of C3S begins. This is consistent with two possible models for retarder action. The first is where the retarder interacts with and stabilizes a surface layer on the cement grains that inhibits the ingress of water. The second is where the retarder indirectly stabilizes the surface layer by poisoning the nucleation or growth of CH, preventing precipitation, and thereby maintaining supersaturation of the aqueous phase.21
5582
Ind. Eng. Chem. Res., Vol. 44, No. 15, 2005
Figure 4. Time dependence of the C3S concentration for cement slurries containing 0.3 wt % modified lignosulfonate hydrating at 66 °C (filled diamonds), 93 °C (filled circles), and 121 °C (open squares). The arrows indicate the measured pumping times for the slurries.
Figure 5. Time dependence of the crystalline gypsum content in several different cement slurries as they hydrate at 93 °C.
Figure 3. Time dependence of the C3S concentration for cement slurries containing a variety of additives at (a) 93 °C and (b) 121 °C.
The concentrations of the sulfate-bearing phases in the slurries are a complex function of time, additive, and temperature. The data from our 93 °C experiments appear to indicate that the loss of gypsum from the slurries mirrors the hydration of C3S (Figure 5). There seems to be, in general, an initial loss of gypsum followed by a plateau and finally a period in which the remaining gypsum is rapidly consumed, which is consistent with solution studies.22 This again is consistent with a model where a layer on the surface of the cement grains initially prevents the ingress of water, and hence dissolved sulfate, to the unhydrated silicates and ferrite in the cement grains. The concentration of gypsum versus time in the slurries heated to 121 °C does not follow the same pattern as that seen for the 93 °C samples, as some of the gypsum is directly converted to anhydrite under these conditions (see later). The time-resolved XRD measurements at low temperature (66 and 93 °C) generally showed the presence of some ettringite at the start of the experiment all the way out to the end of the measurements (typically 300400 min). However, in the case of 0.35% tartaric acid
at 93 °C, the ettringite was not observed to form until nearly 300 min into the measurements. This suggests multiple modes of action for some or all of the retarders, and it is consistent with both the known effect of other additives on ettringite growth/morphology23-25 and previous reports that, in the presence of tartaric acid, the formation of aluminum tartarate complexes may be important.26 The use of 0.3% modified lignosulfate in a 93 °C slurry led to the complete disappearance of the initially present ettringite from the slurry by about 300 min. Ettringite has limited thermal stability, decomposing at ∼120 °C when in contact with pure water under autogenous pressure,11,27 but it has been reported to decompose at lower temperatures.11,28 Ettringite has been reported to decompose to give monosulfate and bassanite on heating in water,11 and monosulfate has also been reported to thermally decompose.13 Decomposition processes of this type are apparent in our data from the experiments at 121 °C, although we observe that anhydrite is formed rather than bassanite or γ-anhydrite, but the slurry composition affects the details of what is observed. Slurries with no additive and 0.3% and 0.75% AMPS copolymer show the initial formation of ettringite followed by its decomposition, giving monosulfate, which itself decomposes at longer times. Similar behavior was observed for a slurry containing 0.3% modified lignosulfonate, but there was much less ettringite present at short times.
Ind. Eng. Chem. Res., Vol. 44, No. 15, 2005 5583
decomposition of ettringite/monosulfate, and the formation of crystalline hydrogarnet at the higher temperature. These chemical changes are probably in part responsible for the observed rheological changes. Conclusions
Figure 6. Time dependence of the sulfate-containing phases in a cement slurry containing 0.3% AMPS copolymer hydrating at 121 °C. All the curves have been normalized to give a maximum of 1.0. The apparent residual gypsum seen at long times is an artifact from an imperfect background subtraction as there is a scattering feature from the sample container at the same position as the gypsum Bragg peak.
However, when 0.35% tartaric acid was used, no ettringite appeared at short times and a small amount of monosulfate appeared and disappeared at around 80 min into the run. These decomposition reactions are coupled to changes in the crystalline calcium sulfate content of the slurries as shown in Figure 6 for a sample containing 0.3% AMPS copolymer. In this sample the decomposition of the ettringite takes place at about the same time as the loss of gypsum. It seems that, as these processes take place, anhydrite is formed along with monosulfate. The monosulfate that was formed then decomposes, leading to the formation of more anhydrite. The anhydrite is then consumed, leaving no crystalline sulfate bearing phases, indicating that all the sulfate has been incorporated into the C-S-H gel matrix.29,30 The production of anhydrite is thermodynamically reasonable because it is more stable than gypsum in the CaSO4-H2O system at ambient pressure above ∼60 °C.31,32 In our experiments at 66 and 93 °C, there was no evidence for the formation of simple crystalline hydrates of either calcium aluminates or calcium silicates. However, the formation of crystalline hydrogarnet, C3AH6, was the norm at temperatures of 121 °C and above, and in our two experiments at 177 °C crystalline silicate hydrates were observed. Interestingly, in one of the 177 °C runs (0.75% AMPS copolymer) only R-C2SH was formed, but in the other (mixed 0.3% AMPS copolymer and 0.3% tartaric acid) a mixture of jaffeite and R-C2SH was formed. This result suggests that the additives used can to some extent control which crystalline hydrates are formed. This possibility is of interest as the formation of crystalline silicate hydrates at high temperatures leads to differences in the cement’s physical properties. The appearance of hydrogarnet, C3AH6, in the slurries seemed to be correlated with a steplike decrease in C4AF concentration. The pumping times that were measured for the various cement slurry compositions decrease as the slurry temperature is raised, as is expected. However, most slurry compositions examined showed a marked decrease in pumping time on going from 93 to 121 °C (Table 1). Over this temperature interval there are significant changes in the cement chemistry for most of the slurry compositions examined, including the
In situ X-ray diffraction is a powerful method for following cement hydration because it allows the quantification of crystalline phases at elevated temperatures and pressures. The slurry compositions examined exhibited quite complex behavior. All of the retarders inhibited the hydration of crystalline C3S, but other modes of action were also apparent. The formation of ettringite was suppressed when tartaric acid was used by itself or in combination with other additives. Changes in the hydration of C3S versus time could not be correlated in a simple way with the observed cement slurry rheology. The largest changes in cement pumping time as a function of temperature occurred in a temperature interval where ettringite/monosulfate decomposes and crystalline hydrogarnet starts to be formed. Acknowledgment This work was performed at the DuPont-NorthwesternDow Collaborative Access Team (DND-CAT) Synchrotron Research Center located at Sector 5 of the Advanced Photon Source. DND-CAT is supported by E.I. DuPont de Nemours & Co., The Dow Chemical Co., the U.S. National Science Foundation through Grant DMR9304725, and the State of Illinois through Department of Commerce and Board of Higher Education Grant IBHE HECA NWU 96. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Energy Research, under Contract No. W-31-102-Eng-38. Literature Cited (1) Nelson, E. B. Well Cementing; Elsevier: Amsterdam, 1990; Vol. 28. (2) Kuzel, H.-J. Initial Hydration Reactions and Mechanisms of Delayed Ettringite Formation in Portland Cements. Cem. Concr. Compos. 1996, 18 (3), 195-203. (3) Ogura, T.; Goto, S. Hydration of cement with heavy water. Semento Konkuriito Ronbunshu 1992, 46, 116-121. (4) Clark, S. M.; Barnes, P. A Comparison of Laboratory, Synchrotron and Neutron Diffraction for the Real Time Study of Cement Hydration. Cem. Concr. Res. 1995, 25, 639-646. (5) Christensen, A. N.; Lehman, M. S. Rate of Reactions Between D2O and CaxAlyOz. J. Solid State Chem. 1984, 51, 196204. (6) Christensen, A. N.; Fjellvag, H.; Lehman, M. S. The Effect of Additives on the Reactions of Portland and Alumina Cement Components with WatersTime Resolved Powder Neutron-Diffraction Investigations. Acta Chem. Scand. 1986, A40, 126-141. (7) Christensen, A. N.; Fjellvag, H.; Lehman, M. S. A TimeResolved Neutron and x-ray-powder diffraction investigation of reactions between Ca12Al14O33, CaCl2, CaBr2 and water. Acta Chem. Scand. 1988, A42, 117-123. (8) Giessen, B. C.; Gordon, G. E. X-ray Diffraction: New HighSpeed Technique Based on X-ray Spectrography. Science 1968, 159, 973-975. (9) Barnes, P.; Clark, S. M.; Hausermann, D.; Henderson, E.; Fentiman, C. H.; Muhamad, M. N.; Rashid, S. Time-resolved Studies of the Early Hydration of Cements using Synchrotron Energy-Dispersive Diffraction. Phase Trans. 1992, 39, 117-128. (10) Muhamad, M. N.; Barnes, P.; Fentiman, C. H.; Hausermann, D.; Pollman, H.; Rashid, S. A Time-Resolved Synchrotron Energy Dispersive Study of the Dynamic Aspects of the Synthesis of Ettringite During Minepacking. Cem. Concr. Res. 1993, 23, 267272.
5584
Ind. Eng. Chem. Res., Vol. 44, No. 15, 2005
(11) Hall, C.; Barnes, P.; Billimore, A. D.; Jupe, A. C.; Turrillas, X. Thermal decomposition of ettringite Ca6[Al(OH)6]2(SO4)3‚26H2O. J. Chem. Soc., Faraday Trans. 1996, 92, 2125-2129. (12) Evju, C.; Hansen, S. Expansive properties of ettringite in a mixture of calcium aluminate cement, Portland cement and β-calcium sulfate hemihydrate. Cem. Concr. Res. 2001, 31, 257261. (13) Christensen, A. N.; Jensen, T. R.; Hanson, J. C. Formation of ettringite, Ca6Al2(SO4)3(OH)12‚26H2O, AFt, and monosulfate, Ca4Al2O6(SO4)‚14H2O, AFm-14, in hydrothermal hydration of Portland cement and of calcium aluminum oxide-calcium sulfate dihydrate mixtures studied by in situ synchrotron X-ray powder diffraction. J. Solid State Chem. 2004, 177, 1944-1951. (14) Michaux, M.; Nelson, E. B.; Vidick, B., Chemistry and Characterization of Portland Cement. In Well Cementing; Nelson, E. B., Eds.; Elsevier: New York, 1990; Vol. 28, pp 2-01 to 2-12. (15) Bensted, J., Developments with oilwell cements. In Structure and Performance of Cements; Bensted, J.; Barnes, P., Eds.; Spon Press: London, 2002; pp 237-252. (16) Eilers, L. H.; Nelson, E. B.; Moran, L. K. High-temperature cement compositionssPectolite, Scawtite, Truscotite, or Xonotlites which do you want? J. Petrol. Technol. 1983, 35 (8), 1373-1377. (17) C150-99a: Standard Specification for Portland Cement, ASTM. (18) Hammersley, A. P.; Svensson, S. O.; Hanfland, M.; Fitch, A. N.; Hausermann, D. Two-dimensional detector software: From real detector to idealised image or two-theta scan. High-Pressure Res. 1996, 14, 235-248. (19) Well simulation thickening time tests. In Recommended Practice for Testing Well Cements, API Recommended Practice 10B; American Petroleum Institute: Washington, DC, 1997; pp 1821. (20) Double, D. D. New developments in understanding the chemistry of cement hydration. Philos. Trans. R. Soc. London 1983, A310, 53-66. (21) Meredith, P.; Donald, A. M.; Luke, K. Preinduction and induction hydration of tricalcium silicatesAn environment scanning electron microscopy study. J. Mater. Sci. 1995, 30, 1921. (22) Luke, K.; Glasser, F. P. Chemical changes occurring during the early hydration of PFA-OPC mixtures. Mater. Res. Soc. Symp. Proc. 1986, 65, 173-180.
(23) Coveney, P. V.; Davey, R. J.; Griffin, J. L. W.; Whitting, A. Molecular design and testing of organophosphonates for inhibition of crystallisation of ettringite and cement hydration. Chem. Commun. 1998, 1467-1468. (24) Luke, K.; Luke, G. Effect of sucrose on retardation of Portland cement. Adv. Cem. Res. 2000, 12 (1), 9. (25) Griffin, J. L. W.; Coveney, P. V.; Whiting, A.; Davey, R. J. Design and synthesis of macrocyclic ligands for specific interaction with crystalline ettringite and demonstration of a viable mechanism for the setting of cement. J. Chem. Soc., Perkin Trans. 2 1999, 1973-1981. (26) Rai, S.; Chaturvedi, S.; Singh, N. B. Examination of Portland cement paste hydrated in the presence of malic acid. Cem. Concr. Res. 2004, 34, 455-462. (27) Zhou, Q.; Glasser, F. P. Thermal stability and decomposition mechanisms of ettringite at < 120 °C. Cem. Concr. Res. 2001, 31, 1333-1339. (28) Grusczscinski, E.; Brown, P. W.; Bothe Jr., J. V. The formation of ettringite at elevated temperature. Cem. Concr. Res. 1993, 23, 981. (29) Luke, K.; Glasser, F. P. Time- and temperature-dependent changes in the internal constitution of blended cements. Cemento 1988, 85 (3), 179-192. (30) Fu, Y.; Gu, P.; Xie, P.; Beaudoin, J. J. A kinetic study of delayed ettringite formation in hydrated portland cement paste. Cem. Concr. Res. 1995, 25, 63-70. (31) Yamamoto, H.; Kennedy, G. C. Stability Relations in the System CaSO4-H2O at High Temperatures and Pressures. Am. J. Sci. 1969, 267A, 550-557. (32) Hardie, L. A. The Gypsum-Anhydrite Equilibrium at One Atmosphere Pressure. Am. Mineral. 1967, 52, 171-200.
Received for review September 17, 2004 Revised manuscript received May 2, 2005 Accepted May 7, 2005 IE049085T
