Optimizing blast furnace slag cements

Abstract

A method and composition for cementing a well by combining water, blast furnace slag and sodium pyrophosphate to form a cement slurry, displacing the cement slurry into a well and allowing the cement slurry to set.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the optimization of methods and formulations for zonal isolation for vertical, deviated, and horizontal oil and gas wells using blast furnace slag cement.

2. Description of Prior Art

The general procedure of drilling an oil or gas well includes drilling a borehole using a drilling fluid. Subsequent to drilling the borehole, casing is run into the well and a cement slurry is placed in the annulus between the outside of the casing and the borehole wall. Typically, the cement slurry is placed in the annulus using a successive fluid displacement technique. In this technique, the cement is first pumped into the casing. Another fluid, often drilling fluid or water, is pumped behind the cement to space it out the bottom of the casing and up into the annulus between the casing and the borehole wall. The cement slurry is usually raised to a point above the uppermost section of the formations to be isolated and may be raised into the annulus between the casing string being cemented and a previously cemented casing.

Once placed, the purpose of the cement slurry is to harden in the annulus and provide an effective seal between the casing and the borehole. The hardened cement sheath prevents or inhibits communication of fluids between the various formations penetrated by the wellbore. Conditions providing zonal isolation of the cement is in contact with the casing and provides mechanical support and resistance to axial movement through the shear bond developed between the interfaces of cement and pipe and cement and formation.

Applicant's U.S. Pat. No. 5,058,679 dealt with an improvement in the bonding of the cement to the casing and borehole surfaces. This improvement was realized through the use of a cement comprising drilling fluid and blast furnace slag. This has proven to be an effective cementing technique and is rapidly gaining commercial acceptance. However, the formulation and design methodology for blast furnace slag cement and drilling fluid-blast furnace slag cements are presently not well defined. Requirements for slurry and hardened material properties are generally the same as Portland cement for a specific set of well conditions. The most effective way to formulate blast furnace slag cements or drilling fluid-blast furnace slag slurries and to obtain the desired properties is not completely understood by the art. Accordingly, the present invention is directed toward overcoming these and other problems in the art.

SUMMARY OF THE INVENTION

It is a primary purpose of the present invention to provide compositions and methods for optimizing the use of blast furnace slag cement and drilling fluid-blast furnace slag cements for cementing oil and gas wells.

A preferred embodiment of the invention comprises a composition and method for cementing a well by combining constituents comprising water and blast furnace slag having a particle size within the range of 2,000 cm.sup.2 /g to 15,000 cm.sup.2 /g, and an activator comprising sodium pyrophosphate to form a cement slurry; displacing the cement slurry into the well; and allowing the cement slurry to set.

Other purposes, distinctions over the art, advantages and features of the invention will be apparent to one skilled in the art upon review of the following.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the total impact of activator on set time of slag formulations, rate of early compressive strength development immediately after set time, and final or total compressive strength of the formulations.

FIG. 2 shows sodium carbonate as the preferred carbonate when the basic formulation is blast furnace slag plus 50% distilled water by weight of slag.

FIGS. 3-5 show the effects of the ratios of different components in the total activator on compressive strength, early compressive strength development rate and set time.

FIG. 6 shows data suggesting that sodium hydroxide has greater impact on set time of the formulation while sodium carbonate has greater impact on the compressive strength of the formulation.

FIG. 7 shows ratios of components controlling set time, compressive strength and early compressive strength development rate.

FIG. 8 shows similarity of benefits from sodium oxalate and sodium citrate.

FIGS. 9-10 are comparisons of the combination of citrate with phosphate and citrate, phosphate and sodium hydroxide.

FIGS. 11-12 show the effect of component ratios when other activators were used.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following preferred embodiments of the invention, together with the following Examples, explain the principles of the invention.

The present invention provides unique methods and formulations which are devised to provide optimum zonal isolation for vertical, deviated, and horizontal wells. The invention centers around the optimized solidification of oil or water-based muds in combination with blast furnace slag to compressive strengths well in excess of that required for casing support, zonal isolation, and borehole stability.

Water-based drilling fluids typically include water and several other additives such as viscosifiers, thinners, dissolved salts, solids from the drilled formations, solid weighting agents to increase the fluid density, formation stabilizers to inhibit deleterious interaction between the drilling fluid and geologic formations, and additives to improve the lubricity of the drilling fluid. The term "water-based" means that water is the continuous phase of the drilling fluid. The water for water-based drilling fluids can be fresh water, brackish water, brine, seawater or other water containing fluids.

Oil-based drilling fluids typically include oil, water, organophilic clay, primary and secondary emulsifiers and wetting agents. Oil may be diesel, mineral oil, vegetable oil, fish oil, synthetic oils (polyalphaolefins), and esters thereof.

Many different additives and dispersants have been utilized that provide the desired properties in drilling fluids. Exemplary of those additives are barium sulfate (barite), bentonite, low and medium yield clays, salt water clay, iron oxide, calcium carbonate, starch, carboxymethylcellulose, acrylonitrile, natural gum, molecularly dehydrated phosphate, tannin compounds, quebracho, mined lignins, lignosulfonate, mica, sugar cane fibers, and granular materials. Bentonite is an especially common additive which gives the drilling fluid a thixotropic or a gel structure. Bentonite is also a common additive which is added to the drilling fluids to control fluid loss; phosphate and lignosulfonate additives which deflocculate colloidal solids and thin the drilling fluids are also common.

Solidification of drilling fluid is accomplished by the addition of blast furnace slag along with additives for the control of setting time and rheological properties of the slag-treated fluid. The term "blast furnace slag" refers to the refuse from the melting of metals or reduction of ores in a furnace. Most notably, blast furnace slag is a by-product of the manufacture of steel in a blast furnace. In steel making, the blast furnace slag is discharged from the service as a molten stream at a temperature typically between 1400.degree. C. and 1600.degree. C. Rapid quenching of the slag results in its conversion into a material which has hydraulic properties. The rapid quenching of the slag converts it into a glassy state and it is generally recognized that the hydraulic quality of the slag depends upon the effectiveness of the process used to rapidly cool the slag and freeze it into the granulated, glassy state. The preferred blast furnace slag of the invention is a high glass content slag produced by quickly quenching the molten slag through intimate contact with large volumes of cool water. Slags produced by air quenching may be used in the invention provided they are determined to have cementitious properties. However, these are less desirable. The finest of the slag particles should be between about 2,000 cm.sup.2 /g and 15,000 cm.sup.2 /g, more preferably between 3,000 cm.sup.2 /g and 9,000 cm.sup.2 /g, most preferably between 4,000 cm.sup.2 /g and 6,500 cm.sup.2 /g. A commercially available blast furnace slag which fulfills the requirements of the invention is marketed under the trade name "NEWCEM" by the Blue Circle Atlantic Company. This slag is obtained from the Bethlehem Steel Corporation blast furnace at Sparrow's Point, Md.

Rheological properties of the slag treated drilling fluid can be modified through the use of many conventional chemical dispersants for water-based or oil-based drilling fluids. Examples of such compounds include lignosulfonates, naphthalene sulfonates, phenol sulfonates, phosphates, phosphonates, sulfonated styrene maleic anhydride, sulfonated toluene maleic anhydride, sulfonated styrene maleimide, polyacrylates, polymethacrylates, blends of polyacrylates and polymethacrylates, acrylamide-acrylic acid copolymers, or blends of any of these classes of materials provided they are chemically compatible to allow their mixing while retaining the ability to disperse particles in the drilling fluid.

Selecting General Types of Activators

Blast furnace slag is a latent hydraulic material. It must be activated to set in order to form a useful cement. Activation can be either thermal energy (heat) or chemical energy (chemical activation). If there is sufficient thermal energy (high temperature) no chemical activators may be required. However, at low temperatures, chemical activators are almost certainly required to optimize set time and compressive strength. In most cases, it is common and often desirable to use a combination of thermal and chemical activation to optimize the properties of the slag-containing cementitious mixture.

Alkali or bases, compounds which increase the pH of the liquid portion of a blast furnace slag/drilling fluid mixture or blast furnace slag cement slurry, are used as chemical activators. However, since thermal energy contributes to the total activation energy, the type of chemical activators and their amount can vary. Strong alkali are required at low temperatures where weak alkali can be used when the temperature is higher.

Components of the activator can be a mixture of alkali or alkali in combination of chelating, complexing or sequestering agents. It is desirable in cases where temperatures are low to use strong alkali-containing hydroxyl groups such as alkali earth metal hydroxides. These oxides include lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, as examples. The more soluble alkali earth metal hydroxides are, in general, better activators at low temperature. It is believed that their higher solubility in water at low temperatures is the primary reason they are better low temperature activators. The most commonly applied alkali earth metal hydroxides at low temperature are sodium hydroxide, potassium hydroxide, lithium hydroxide and barium hydroxide. These alkali earth metal hydroxides have a greater effect on the set time of the slag-containing cementitious mixture. Concentrations range between 0.01 to 20%wt of slag, more preferably 0.1 to 16%wt of slag, even more preferably between 0.25 to 14%wt of slag, and most preferably 0.5 to 10%wt of slag.

It is also common to use a weaker alkali as part of the activator component, in particular, weaker alkali containing a carbonate or phosphate group. The carbonate ion in particular has a beneficial effect on the compressive strength development and overall compressive strength of the slag-containing mixture. Few anion species can replace carbonate as a part of the activator which significantly affects compressive strength. Alkali earth metal carbonates which are most commonly applied as a component in the total activator include lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, barium carbonate, sodium potassium carbonate, etc., as examples. Again, as with the alkali-containing hydroxyl groups, greater solubility provides greater effects. The most commonly applied carbonate-containing compounds used include sodium carbonate, potassium carbonate and sodium potassium carbonate. Typical concentrations are 0.25 to 25%wt of slag, more preferably 0.5 to 20%wt of slag, even more preferably 1.0 to 15%wt of slag, and most preferably 2 to 12%wt of slag.

The phosphate anion is an anionic chemical species which can contribute to compressive strength like the carbonate ion. However, the phosphate ion-containing compounds tend to retard the slag hydration much more than the carbonate. Basic phosphates such as sodium pyrophosphate, sodium hexametaphosphate, tetrasodium polyphosphate, tetrasodium polyphosphate, etc., have application in formulations to control set time and contribute to compressive strength development. Of these, sodium pyrophosphate has shown the greatest potential. Typical concentrations are 0.001 to 15%wt of slag, more preferably 0.01 to 10%wt of slag, even more preferably 0.1 to 8%wt of slag, and most preferably 0.25 to 6%wt of slag.

The citrate ion also can contribute to compressive strength. Alkali earth metal salts of citric acid such as sodium citrate, calcium citrate, potassium citrate, etc., are examples. Of these, sodium or potassium citrate are most preferred.

Compounds containing phosphate and citrate have an advantage over carbonate or hydroxyl-containing compounds in rheological properties of the slurry. Phosphate or citrate-containing compounds are effective dispersants for slag and clays in drilling fluid formulations. Thus, less dilution may be required for drilling fluid-blast furnace slurries or better rheological properties may be obtained.

Other components of the activator include a chelating, complexing or sequestering agent. These types of compounds include the phosphate and citrate ion-containing compound previously described. Other compounds such as ethylenediamine tetraacetic acid and its salts, phosphonic acids and their salts, glutamic acid and its salts, gluconic acid and its salts, some amines, phosphinic acids and their salts, aminophosphinic acids and their salts, lactic acid and its salts, aspartic acid and its salts, tartaric acid and its salts, etc. It is most desirable to use salts since the acid forms counteract the alkali added for chemical activation. Highly soluble salts are preferred. Sodium and potassium salts are usually quite soluble. Many other types of chelating, complexing or sequestering agents are known and many are listed in the book Organic Sequestering Agents by Stanley Chaberek and Arthur E. Martell, published by John Wiley & Sons, New York. Concentrations typically range between 0.001 to 10%wt of slag, more preferably 0.01 to 8%wt of slag and most preferably 0.05 to 5%wt of slag.

Chemical compounds which are chelating, complexing, or sequestering agents for alkali earth metals and transition metals through iron in the Periodic Table of Elements have been found most suitable as components in the chemical activator mixture. Concentrations typically range between 0.001 to 10%wt of slag, more preferably 0.01 to 8%wt of slag and most preferably 0.05 to 5%wt of slag. Chelating, complexing or sequestering compounds with log (base 10) values for the equilibrium stability constants for complexed calcium between 2 and 5 have been most effective in improving strength and dispersing the slag with lowest effect on set time. A broad range for these log values is 0.5 to 11. The lower values tend to be stronger retarders while the higher values (above about 6) have less retarding effect but do not show an improvement in compressive strength development. In general, small amounts of these materials are used. Concentrations typically range from 0.001 to 8%wt of slag, preferably 0.01 to 6%wt of slag, and most preferably 0.05 to 5%wt of slag.

Selecting Total Activator Concentration

There is an optimum amount of activator which provides the maximum compressive strength for a given concentration of slag. The optimum total activator concentration is based upon the weight of slag used in the formulation. Therefore, the optimum weight ratio of total activator to slag is selected. This weight ratio varies with temperature because thermal energy (heat or temperature which is a measure of heat) is an activator for slag. The optimum weight ratio of total activator to slag decreases with temperature. For example, the optimum ratio is about 6 percent or 0.06 percent (activator weight/slag weight) at 125.degree. F. The optimum may be about 8 percent (0.08) at 100.degree. F., 12 percent (0.12) at 80.degree. F., 2.5 percent (0.025) at 175.degree. F. These optimum ratios also may vary with the compounds used as the activators. The ratios cited above are exemplary of mixtures of sodium hydroxide and sodium carbonate. Ranges for total activator concentrations are: 0.01 to 20%wt of slag, preferably 0.1 to 18%wt of slag, even more preferably 0.25 to 14%wt of slag, and most preferably 0.5 to 10%wt of slag.

Selecting the Ratio of Components in the Total Activator

Within the total activator concentration, there is a ratio of the individual components which provide optimum set time or optimum compressive strength or optimum early compressive strength development rate or optimum rheological properties for the cementing operation. There is also a combination of activators which will produce optimum properties for all these variables for a specific cementing operation.

The total activator concentration may be made up of different concentrations of different chemical components.

Selecting the Retarder

Once the total amount of activator and ratio of activator components has been selected which will optimize compressive strength and compressive strength development, a retarder is usually required to provide adequate fluidity time (sufficiently long set time) in order to place the cement in the well. Retarders are often added in a concentration of 0.001% to 12% by weight of slag, preferably 0.01 to 8%, and more preferably 0.05% to 5%wt of slag.

Retarders are of two types: complexing agents and salts of transition metals with atomic numbers above iron or nickel in the periodic chart. In particular, copper, zinc and aluminum salts can be effective retarders for slag hydration.

Complexing agents such as lignosulfonates and sulfonated lignins, and sulfonated Kraft lignins, lignin amines, etc., can be effective retarders. These are common retarders for Portland cements.

The most desirable retarders are low molecular weight complexing agents because they also contribute to improved compressive strength and early compressive strength development rate. Sodium glucoheptonate, sodium gluconate, sodium citrate, etc. can improve strength in combination with the activators in the formulation.

There is a ratio of activator to retarder which provides the greatest early compressive strength development and final strength for a given slag concentration. This ratio depends upon the strength of the retarders and activators used. In general, a combination of activators and retarders which will produce a set time less than about 10 hours, more preferably less than about 8 hours, and most preferably between 3 and 6 hours at the static temperature of the well will provide a high rate of early compressive strength development after setting and high final strength for the selected slag concentration.

Dispersion

Given two formulations with optimized ratios of slag and activators, activator components and activator-retarder ratio, the formulation which is more dispersed will generally have better compressive strength development after setting. Many of the complexing, sequestering or chelating agents mentioned earlier in this text are good dispersants for slag and drilling fluids containing clays.

Control of Sulfide Odors

Blast furnace slags contain some sulfur as residue from the iron or steel making process. This sulfur may be in forms which can produce sulfide species. Hydrogen sulfide may form although this is not expected at the alkaline pH of most activated slag cements.

However, sulfide scavenging compounds may be included as part of the activator or retarder on the slag-containing cementitious material. Additives such as zinc oxide, zinc carbonate are known scavengers for sulfide. Inclusion of one or more of these scavengers may prevent formation of hydrogen sulfide if a set slag-containing cement is drilled out or otherwise comes into contact with a low pH fluid which would favor formation of hydrogen sulfide.

EXAMPLES

The data presented in FIG. 1 is based on the following: Test Temperature: 125.degree. F. (52.degree. C.); Base Formulation: "NEWCEM".RTM. blast furnace slag+50% distilled water (by wt of slag)--(a) total activator concentration is percent by weight of slag; (b) the weight ratio of sodium hydroxide to sodium carbonate is 1:3 for all total activator concentrations; hence, 1% total activator=0.25% sodium hydroxide+0.75% sodium carbonate (by wt of slag); 2% total activator=0.5% sodium hydroxide+1.5% sodium carbonate (by wt of slag); 4% total activator=1% sodium hydroxide+3% sodium carbonate (by wt of slag).

FIG. 1 shows the impact of total activator on the:

a) set time of slag formulations,

b) rate of early compressive strength development immediately after set time, and

c) final or total compressive strength of the formulations.

A decrease in set time is seen along the X-axis as the lines showing compressive strength begin to move upward off of the O compressive strength line which is represented as the horizontal line of the X-axis. No activator produced a set time of about 2.5 hours. Increasing the activator concentration to 4% or 6% by weight of slag reduced the set time to less than 1 hour.

The rate of early compressive strength development is directly impacted by the activator concentration. The slope of the line from the set time until the strength reaches a plateau, wherein the rate of strength change with time has decreased to a near steady-state rate, is affected by the activator concentration. The slope is gradual without activator and becomes near vertical at 4% to 6% total activator at this temperature. It is desirable to have rapid early compressive strength development in many cementing operations. Slopes as compared in Table 1 labeled Example A-2.

The final compressive strength of each formulation increases with the total activator concentration. It is important to remember that the only thing changed is the total activator concentration. The amount of slag in each formulation is constant.

Also, there is an upper limit to the total activator concentration. This limit is the dilution effect limit and solubility limit of the activators.

Base Formulation: "NEWCEM" Blast Furnace Slag+50% Distilled Water (by weight of slag) Test temperature: 125.degree. F. (52.degree. C.)

a) Total Activator concentration is percent by weight of Slag.

b) The weight ratio of sodium hydroxide to sodium carbonate is 1:3 for all total activator concentrations, hence:

1% total activator=0.25% sodium hydroxide+0.75% sodium carbonate (by weight of slag) 2% total activator=0.5% sodium hydroxide+1.5% sodium carbonate (by weight of slag) 4% total activator=1% sodium hydroxide+3% sodium carbonate (by weight of slag). TABLE 1__________________________________________________________________________Set Time and Compressive Strength Data Equation for Compressive Total Test Line Between Strength FinalAdditives and Activator Duration Set Time 50 psi and 500 psi 14 hrs after StrengthConcentration % bwos Hours Hours Slope Intercept Set Time psi__________________________________________________________________________None 0 18 2.72 78.44 -128.72 723 740None 1 18 1.68 507.51 -844.57 1039 1068None 2 18 1.4 741.96 -1046.07 1611 1677None 4 18 0.6 1024.55 -647.00 2836 2966None 6 18 0.5 794.33 -417.14 3824 3924__________________________________________________________________________ Base Formulation: "NEWCEM" Blast Furnace Slag + 50% Distilled Water (by w of slag) Test Temperature: 125.degree. F. (52.degree. C.)

FIG. 2 shows sodium carbonate as the preferred carbonate. The basic formulation is: "NEWCEM" blast furnace slag+50% distilled water (by weight of slag)+4% total activator (by weight of slag). Test temperature: 125.degree. F. (52.degree. C.).

FIGS. 3-6 and Tables 2 and 3 show the effects of the ratios of different components in the total activator on:

1) 24 hour compressive strength (FIG. 3)

2) early compressive strength development rate (FIG. 4)

3) set time (FIG. 5)

Each formulation contained 4% total activator. This total activator could be composed entirely of sodium hydroxide or entirely sodium carbonate or any weight ratio in between of these two components. The X-axis of these plots shows the amount of sodium carbonate present in the total activator. Hence, at 0 on the X-axis there is no sodium carbonate in the total activator; the total activator is 4% sodium hydroxide. At 4 on the X-axis only sodium carbonate is used as the total component of the activator; no sodium hydroxide is present in the total activator. At 2 on the X-axis, the total activator concentration of 4% (by weight of slag) is made up of 2% sodium hydroxide and 2% sodium carbonate.

The data in FIG. 3 is based on the following: Base Formulation: "NEWCEM".RTM. blast furnace slag+50% distilled water (by wt of slag)+4% total activator (by wt of slag).

The data in FIG. 3 is based on the following: Base Formulation: "NEWCEM".RTM. blast furnace slag+50% distilled water (by wt of slag)+4% total activator (by wt of slag).

This data (FIG. 3) shows that higher compressive strengths are obtained (slag concentration is constant for all tests) when the sodium carbonate concentration is slightly in excess of the sodium hydroxide concentration in the total amount of activator.

A small amount of sodium carbonate (FIG. 4) in the total activator concentration is beneficial for improving the early compressive strength development rate.

A small amount of sodium hydroxide (FIG. 5) in the total activator concentration is beneficial for reducing the set time of the slag cement mixture.

This data suggests that sodium hydroxide has greater impact on the set time of the formulation while sodium carbonate has greater impact on the compressive strength of the formulation. This is more clear in FIG. 6.

TABLE 2__________________________________________________________________________Effects of Ratios of Different Components in Total Activatoron Compressive Strength Development Rate and Set Time Elapsed Weight Molar Time in Ratio of Ratio of Minutes Sodium Sodium Elapsed Time BetweenSodium Sodium Hydroxide Hydroxide in Minutes.sup.1 50 psi Compressive Strength, psi, after indicatedHydroxide Carbonate to Sodium to Sodium to Reach and 500 elapsed time% bwos* % bwos* Carbonate Carbonate 50 psi 500 psi psi.sup.2 2 hrs 4 hrs 8 hrs 12 hrs 24__________________________________________________________________________ hrs4 0 4 to 0 13 118 .sup. 105.sup.5 516 907 1272 1379 15363.27 0.73 4.5 to 1 11.87 to 1 17 52 35 885 1068 1236 1339 15293.2 0.8 4 to 1 10.6 to 1 19 51 32 882 1038 1204 1306 15143.12 0.88 3.5 to 1 9.4 to 1 17 52 35 856 994 1136 1247 14453 1 3 to 1 7.95 to 1 17 48 32 823 919 1038 1126 13242.85 1.15 2.5 to 1 6.57 to 1 18 50 32 961 1128 1271 1376 15942.66 1.34 2 to 1 5.26 to 1 18 49 31 966 1148 1310 1419 16422.4 1.6 1.5 to 1 3.97 to 1 17 46 29 967 1136 1298 1407 16092 2 1 to 1 2.65 to 1 16 42 26 1082 1269 1469 1592 18202 2 1 to 1 15 36 21 997 1138 1315 1424 16261.6 2.4 0.67 to 1 1.77 to 1 20 49 29 1374.sup.4 .sup. 1657.sup.4 .sup. 1921.sup.4 .sup. 2084.sup.4 .sup. 2356.sup.41.34 2.66 0.5 to 1 1.33 to 1 25 56 31 1645 2011 2366 2534 28301.15 2.85 0.4 to 1 1.07 to 1 37 75 38 1341 1792 2132 2344 26511 3 .33 to 1 0.88 to 1 42 74 32 1466 1861 2216 2438 27580.88 3.12 .28 to 1 0.75 to 1 43 64 21 1534 1870 2195 2381 26560.8 3.2 .25 to 1 0.66 to 1 .sup. 79.sup.3 102 23 1121 1806 2180 2399 27520.73 3.27 .22 to 1 0.59 to 1 .sup. 83.sup.3 107 24 995 1830 2241 2465 27970 4 0 to 4 0.00 134.sup.3 170 36 33 1566 2011 2237 2631__________________________________________________________________________ *By weight of slag Total Activator concentration was 4% by weight of slag for all tests. Sample Formulation: "NEWCEM" Blast Furnace Slag + 50% fresh water (bwos) 4% Total Activator (bwos) Test Temperature: 125.degree. F. .sup.1 This is set time. .sup.2 Early compressive strength development rate .sup.3 Sodium hydroxide in small quantity helped reduce this set time .sup.4 Higher strength when carbonate in excess of hydroxide .sup.5 Early compressive strength development rate increased due to carbonate TABLE 3__________________________________________________________________________Effects of Ratios of Different Components in Total Activatoron Compressive Strength Elapsed Weight Molar Time in Ratio of Ratio of Minutes Sodium Sodium Elapsed Time BetweenSodium Sodium Hydroxide Hydroxide in Minutes.sup.1 50 psi Compressive Strength, psi, after indicatedHydroxide Carbonate to Sodium to Sodium to Reach and 500 elapsed time% bwos* % bwos* Carbonate Carbonate 50 psi 500 psi psi.sup.2 2 hrs 4 hrs 8 hrs 12 hrs 24__________________________________________________________________________ hrs4 0 4 to 0 12 51 39 998 1097 1190 1255 13793.27 0.73 4.5 to 1 11.87 to 1 12 30 18 1027 1178 1348 1463 16993.2 0.8 4 to 1 10.6 to 1 9 27 18 991 1122 1287 1397 16233.12 0.88 3.5 to 1 9.4 to 1 10 28 18 846 955 1092 1200 13893 1 3 to 1 7.95 to 1 12 32 20 911 1027 1174 1288 15112.85 1.15 2.5 to 1 6.57 to 1 11 29 18 1049 1152 1317 1427 16762.66 1.34 2 to 1 5.26 to 1 10 25 15 1067 1173 1342 1454 17332.4 1.6 1.5 to 1 3.97 to 1 9 25 16 1042 1130 11275 1382 16032 2 1 to 1 2.65 to 1 10 22 12 1078 1182 1331 1422 16451.6 2.4 0.67 to 1 1.77 to 1 12 25 13 .sup. 1657.sup.4 .sup. 1870.sup.4 .sup. 2055.sup.4 .sup. 2200.sup.4 .sup. 2455.sup.41.34 2.66 0.5 to 1 1.33 to 1 16 32 16 1953 2237 2495 2637 29071.15 2.85 0.4 to 1 1.07 to 1 19 34 15 1993 2280 2543 2686 29201 3 .33 to 1 0.88 to 1 21 32 11 1864 2131 2343 2441 26500.88 3.12 .28 to 1 0.75 to 1 21 28 9 1937 2186 2405 2505 26830.8 3.2 .25 to 1 0.66 to 1 .sup. 26.sup.3 35 9 2065 2399 2641 2792 29510.73 3.27 .22 to 1 0.59 to 1 .sup. 31.sup.3 40 9 1980 2298 2565 2673 29070 4 0 to 4 0.00 .sup. 44.sup.3 58 14 1593 1888 2127 2274 2465__________________________________________________________________________ *By weight of slag Total Activator concentration was 4% by weight of slag for all tests. Sample Formulation: "NEWCEM" Blast Furnace Slag + 50% fresh water (bwos) 4% Total Activator (bwos) Test Temperature: 175.degree. F.

FIG. 7 and Table 4 show sodium citrate as a viable replacement for sodium hydroxide. Combinations of sodium citrate, sodium carbonate and sodium hydroxide can be made with improved properties.

The data in FIG. 7 is based on the following: Base Formulation: "NEWCEM".RTM. blast furnace slag+50% distilled water (by wt of slag)+4% total activator (by wt of slag).

FIG. 7 shows ratios of components are still important to controlling set time, compressive strength and early compressive strength development rate.

Replacing sodium hydroxide with sodium citrate improved total compressive strength while maintaining a high early compressive strength development rate.

Table 4 shows incorporation of sodium hydroxide to change the set time and early compressive strength development rate.

TABLE 4______________________________________Incorporation of Sodium Hydroxide to ChangeSet Time and Early Compressive Strength Development Rate 0.5% Sodium 0.5% Sodium 1% Sodium Hydroxide Hydroxide Hydroxide 1% Sodium 0.5% Sodium 1% Sodium 1% Sodium Citrate Citrate Citrate CitrateTime 3% Sodium 3% Sodium 2.5% Sodium 2% SodiumHours Carbonate Carbonate Carbonate Carbonate______________________________________0 0 0 0 00.8 18 18 15 .sup. 90.sup.41.07 18 18 17 .sup. 263.sup.41.33 16 28 .sup. 46.sup.3 .sup. 502.sup.41.6 18 .sup. 92.sup.2 .sup. 206.sup.3 7182.04 .sup. 50.sup.1 .sup. 620.sup.2 791 9882.4 .sup. 188.sup.1 1116 1170 11723.2 934 1584 1621 14664 1468 1782 1849 16964.8 1762 1930 2003 18365.6 1933 2035 2113 19376.4 2038 2146 2199 20177.2 2149 2234 2290 21008 2207 2326 2353 215812 2526 2628 2660 237216 2704 2816 2811 250520 2857 2935 2970 264724 2978 3059 3054 2721______________________________________ .sup.1,2,3 Show fast early compressive strength development .sup.4 Shows slower early compressive strength development. TABLE 5__________________________________________________________________________Evaluation of Phosphates to Replace Sodium Hydroxide in Total Activator 1% Sodium 1% Calcium 1% Trisodium 1% Sodium 1% Sodium 1% Sodium 1% Tetrasodium Hydroxide Phosphate Phosphate Pyrophosphate Tripolyphosphate Hexametaphosphate PyrrophosphateTime 3% Sodium 3% Sodium 3% Sodium 3% Sodium 3% Sodium 3% Sodium 3% SodiumHours Carbonate.sup.1) Carbonate.sup.2) Carbonate.sup.3) Carbonate.sup.4) Carbonate.sup.5) Carbonate.sup.7) Carbonate.sup.8)__________________________________________________________________________ 0 0 0 0 0 0 0 0 0.5333333 13 22 20 22 18 11 18 1.066667 355 25 23 20 20 13 16 1.6 1207 25 23 22 20 15 16 2.133333 1488 60 25 22 18 17 16 2.666667 1633 440 0 22 16 17 15 3.2 1721 1024 0 22 18 19 16 3.733333 1815 1288 0 22 18 19 15 4.266667 1889 1409 25 22 18 21 15 4.8 1940 1502 531 22 18 21 15 6.4 2103 1644 1577 26 18 21 16 8 2219 1754 1906 26 20 23 16 9.6 2311 1848 2069 26 20 23 1611.2 2408 1922 2216 30 20 25 1612.8 2474 1999 2341 172 18 25 1314.4 2508 2053 2407 786 16 23 1116 2578 2107 2544 1373 34 21 5817.6 2613 2136 2616 1626 155 31 35919.2 2650 2194 2690 1806 506 103 96820.8 2686 2222 2690 1955 931 393 130324 2761 2283 2805 2176 1563 1368 171432 2880 3010 2234 2418 229540 2960 3141 .sup.6) 2593.sup. 2849 259348 3044 323356 3088 332564 3131 3374__________________________________________________________________________ .sup.1) "Control"- .sup.2) Lower compressive strength than .sup.3) Set time delayed. Slightly higher comp. strength than "Control". .sup.4) Set time delayed. Lower comp. strength than "Control" at 24 hrs .sup.5) Set time delayed. Lower comp. strength than "control" at 24 hrs .sup.6) Strength increasing, approaching .sup.7) Set time delayed. Lower comp. strength than "control" at 24 hrs .sup.8) Set time delayed. Lower comp. strength than "control" at 24 hrs TABLE 6__________________________________________________________________________Evaluation of Phosphates to Replace Sodium Carbonate in Total Activator 1% Sodium 1% Sodium Hydroxide 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium Hydroxide 3% Hydroxide Hydroxide Hydroxide Hydroxide HydroxideTime 3% Sodium Calcium 3% Trisodium 3% Sodium 3% Sodium 3% Sodium 3% TetrasodiumHours Carbonate.sup.1) Phosphate.sup.2) Phosphate.sup.3) Pyrrophosphate.sup.4) Tripolyphosphate.sup.5) Hexametaphosphate.sup.6) Pyrrophosphate.sup.7 )__________________________________________________________________________1 0 0 0 0 0 0 00.5 13 40 9 19 13 14 171.07 355 208 11 21 19 12 1111.6 1207 330 16 42 24 17 4672.13 1488 407 17 323 30 26 6812.67 1633 463 67 551 38 33 8663.2 1721 499 113 751 42 37 10203.73 1815 538 452 943 46 41 11434.27 1889 566 921 1097 49 43 12024.8 1940 587 1331 1199 51 45 12656.4 2103 617 1899 1344 263 51 13828 2219 673 2128 1451 1450 53 14739.6 2311 716 2297 1527 1934 55 153011.2 2408 742 2419 1608 2180 59 159012.8 2474 780 2516 1650 2362 64 165314.4 2508 809 2616 1715 2493 117 169616 2578 829 2721 1760 2632 574 174117.6 2613 849 2794 1806 2705 1303 176319.2 2650 870 2869 1830 2820 1823 180920.8 2686 892 2832 1878 2858 2079 183324 2761 925 2947 1928 3021 2375 190632 2880 3152 2059 3239 2792 200840 2960 3239 2170 3378 .sup.8) 3076 211648 3044 3375 2258 3526 217356 3088 3420 2319 362664 3131 3467 2382 3733__________________________________________________________________________ .sup.1) "Control"- .sup.2) Lower comp. strength than .sup.3) Higher comp. strength than control, but longer set time. .sup.4) Lower comp. strength than control .sup.5),6),7) Larger set time, higher comp. strength .sup.8) Higher strength than control @ 40 hrs TABLE 7__________________________________________________________________________Combination of Phosphate (Sodium Tripolyphosphate),Sodium Carbonate and Sodium Hydroxide to Vary Set Time and Strength(Total and Early Compressive Strength Development Rate 0.5% Sodium Tripolyphosphate 1% Sodium 0.5% Sodium Tripolyphosphate 3% SodiumTime Hydroxide 1% Sodium Hydroxide Tripolyphosphate 1% Sodium Tripolyphosphate 1% Sodium HydroxideHours 3% Sodium Carbonate 2% Sodium Carbonate 1% Sodium Hydroxide 3% Sodium Carbonate 3% Sodium__________________________________________________________________________ Carbonate0 0 0 0 0 00.53 18 16 13 18 131.07 19 20 19 20 3551.6 19 22 24 20 12072.13 19 24 30 18 14882.67 21 24 38 16 16333.2 21 26 42 18 17213.73 21 26 46 18 18154.27 21 28 49 18 18894.8 21 28 51 18 19406.4 23 30 263 18 21038 23 65 1450 20 22199.6 23 884 1934 20 231111.2 23 1465 2180 20 240812.8 61 1830 2362 18 247414.4 352 2035 2493 16 250816 875 2204 2632 34 257824 1984 2701 3021 1563 2761__________________________________________________________________________ TABLE 8 Effect of Cation of Sulfate Salts on Set Time and Compressive Strength of Blast Furnace Slag Cement Compressive Strength, psi, of Formulations Containing the Indicated Activators 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium 1% Sodium Elasped Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Hydroxide Time 3% Sodium 3% Sodium 3% Magnesium 3% Calcium 3% Ferrous 3% Ferric 3% Cobalt 3% Nickel 3% Cupric 3% Zinc 3% Aluminum 3% Ammonium Hours Carbonate Sulfate Sulfate Sulfate Sulfate Sulfate Sulfate Sulfate Sulfate Sulfate Sulfate Sulfate 0 0 0 0 0 0 0 0 0 0 0 0 0 1.07 281 150 20 34 13 13 30 121 12 19 17 13 2.13 1505 374 28 109 193 11 332 473 10 17 16 13 4.09 1886 576 275 457 8 2216 703 948 1002 742 419 696 899 10 17 19 95 12.1 2438 770 1294 1053 16 2575 821 1506 1093 968 1510 872 1100 9 13 17 1141 17.6 2610 843 1564 1093 980 1589 894 1129 9 11 17 1261 19.2 2647 854 1604 1106 1018 1695 928 1157 9 11 17 1342 20.8 2683 876 1667 1120 1044 1762 952 1187 8 11 17 1430 22.4 2721 888 1710 1134 1071 1832 976 1217 8 14 17 1504 24 2758 899 1744 1134 1084 1880 964 1202 8 20 17 1562 25.6 911 1800 1098 1930 1001 1233 8 29 17 1602 27.2 935 1823 1127 1981 1026 1249 8 40 17 1665 28.8 947 1871 1141 2034 1039 1265 8 54 17 1708 30.4 959 1895 1155 2061 1052 1265 8 67 17 1730 32 959 1920 1170 2088 1066 1280 8 82 17 1775 33.6 972 1945 1185 2144 1079 1297 8 99 17 1821 35.2 984 1971 1200 2172 1092 1313 8 114 17 1845 36.8 997 1996 1215 2202 1106 1330 8 129 17 1869 38.4 1010 2022 1231 2202 1106 1347 8 141 17 1893 40 1010 2022 1247 2230 1120 1347 8 152 17 1918 41.6 1023 2049 1247 2260 1135 1364 8 163 17 1943 43.2 1263 2291 1149 1364 8 171 17 1969 44.8 1278 2291 1149 1382 8 177 17 1994 46.4 1278 2321 1163 1382 9 186 17 1994 48 1295 2352 1178 1400 10 189 17 2020 56 1345 2416 1208 1435 323 207 17 2101 64 1380 2482 1255 1473 1084 217 17 2157 72 1286 1511 1541 29 80 1319 1530 1820 16 88 1353 1570 1993 16 Base Formulation: NEWCEM Blast Furnace Slag mixed with 50% Distilled Wate (by weight of the slag) plus indicated activator mixtures Test Temperature: 125 F. (52 C.) Curing Pressure: 3000 psi Calcium Sulfate = CaSo.sub.4.2H.sub.2 O Ferrous Sulfate = FeSo4.7H.sub.20 Ferric Sulfate = Fe.sub.2 (So.sub.4).sub.3.H.sub.2 O Cobalt Sulfate = CoSo.sub.4.7H.sub.2 O Nickel Sulfate = NiSo.sub.4.6H.sub.2 O Zinc Sulfate = ZnSo.sub.4.7H.sub.2 O Aluminum Sulfate = Al.sub.2 (SO.sub.4).sub.3.16H.sub.2 O TABLE 9__________________________________________________________________________Set Time and Compressive Strength DataComparisons of Activator:Retarder Ratio with Different Retarder Types andStrengths Equation for Total Test Line Between Activator Duration Set time 50 psi and 500 psi Compressive Strength Final StrengthAdditives and Concentration % bwos hours hours Slope Intercept 14 hours after Set psie__________________________________________________________________________None 0 18 2.72 78.44 -128.72 723 740None 1 18 1.68 507.51 -844.57 1039 1068None 2 18 1.4 741.96 -1046.07 1611 1677None 4 18 0.6 1024.55 -647.00 2836 2966None 6 18 0.5 794.33 -417.14 3824 39240.1% "REAX" 100M 0 18 3.78 113.04 -470.89 867 8690.1% "REAX" 100M 1 18 1.93 574.26 -1109.86 1153 11630.1% "REAX" 100M 2 18 1.48 877.10 -1311.57 1707 17780.1% "REAX" 100M 4 18 0.65 1316.57 -931.80 2941 30830.1% "REAX" 100M.sup.1) 6 18 .sup.3) 60:1 0.52 976.47 -519.82 3498 35480.2% "REAX" 100M 0 22.5 6.15 130.57 -768.22 996 10600.33% "REAX" 100M 0 18 14.63 135.26 -1971.55 795 5680.33% "REAX" 100M 1 18 2.97 527.32 -1561.04 1278 12940.33% "REAX" 100M 2 18 2.12 732.72 -1558.23 1655 17140.33% "REAX" 100M 4 18 .sup.3) 12.1:1 0.75 1652.63 -1304.50 3032 31130.33% "REAX" 100M 6 18 .sup.3) 18.2:1 0.6 1455.75 -768.60 3504 35540.1% "SEQLENE 540" 0 66 34.2 78.68 -1674.31 939 13650.1% "SEQLENE 540" 1 66 5.78 434.89 -2502.49 1248 16440.1% "SEQLENE 540" 2 66 3.62 862.37 -3138.26 1849 24820.1% "SEQLENE 540" 4 66 1.4 1680.75 -2407.00 3166 39900.1% "SEQLENE 540".sup.2) 6 68 .sup.3) 60:1 0.77 1708.88 -1369.30 3670 45220.1% Sodium Gluconate 0 90 57.72 55.19 -3173.07 808 14780.1% Sodium Gluconate 1 90 6.88 460.20 -3172.23 1435 20080.1% Sodium Gluconate 2 90 3.77 792.32 -3018.93 1873 26550.1% Sodium Gluconate 4 90 1.95 1239.75 -2429.60 2993 39360.1% Sodium Gluconate 6 90 .sup.3) 60:1 1.23 1618.88 -2000.70 3607 45650.33% Sodium Gluconate 0 43 -- -- -- -- --0.33% Sodium Gluconate 1 43 24.5 147.93 -3633.58 2540 28050.33% Sodium Gluconate 2 43 17.23 197.88 -3398.37 2919 34830.33% Sodium Gluconate 4 43 .sup.3) 12.1 8.9 344.25 -3079.35 3858 45470.33% Sodium Gluconate 6 43 .sup.3) 18.2 6.05 633.48 -3844.71 4050 47100.33% Sodium Gluconate 8 43 .sup.3) 24.2 3.73 1468.02 -5457.53 3412 4148__________________________________________________________________________ .sup.1) "REAX" is sulfonated Kraft lignin .sup.2) "SEQLENE 540" is sodium glucohepatonate .sup.3) Activator:Retarder ratio

FIG. 8 shows sodium oxalate as giving similar benefits as sodium citrate.

FIGS. 9 and 10 show comparison of the combination of citrate with phosphate and citrate, phosphate and sodium hydroxide. (Sodium hydroxide can reduce set time.)

Other activators were tried and the effect of component ratios is clearly distinguishable in FIGS. 11 and 12.

Tables 9 through 12 show that ratio for set time, early compressive strength development rate and final strength varies with retarder strength, temperature and activator strength.

TABLE 10__________________________________________________________________________Base Slurry: "NEWCEM" Blast Furnace Slag + 0.1% Sodium Gluconate (bwos*)+ 50% Distilled Water (bwos)Test Temperature: 125.degree. F.__________________________________________________________________________ No 0.10% 0.20% 0.40% 0.80% 1% 1.20% 1.40% 1.60% 1.80% Activator Activator Activator Activator Activator Activator Activator Activator Activator Activator__________________________________________________________________________Time to 33.93 18.1 16 12 11.55 9.72 73750 psiTime to 43.97 20.63 17.9 13.55 12.93 10.9 8.43500 psiTime from 10.04 2.53 1.9 1.55 1.38 1.18 1.0650 psi to500 psiActivator:Retarder 4:1 8:1 10:1 12:1 14:1 16:1 18:1Ratio__________________________________________________________________________ 2% 2.20% 2.40% 2.60% 2.80% 3% 4% 5% 6% 7% Activator Activator Activator Activator Activator Activator Activator Activator Activator Activator__________________________________________________________________________Time to 6.08 5.38 5.27 5.2 5.17 4.43 3.1 0.93 1.78 1.1550 psiTime to 6.82 6.03 5.97 5.87 5.8 5 3.58 1.28 2.1 1.4500 psiTime from 0.74 0.65 0.7 0.67 0.63 0.57 0.48 0.35 0.32 0.2550 psi to500 psiActivator:Retarder 20:1 22:1 24:1 26:1 28:1 30:1 40:1 50:1 60:1 70:1Ratio__________________________________________________________________________ *bwos = by weight of slag TABLE 11__________________________________________________________________________Base Slurry: "NEWCEM" Blast Furnace Slag + 0.1% Sodium Gluconate (bwos*)+ 50% Distilled Water (bwos)Test Temperature: 150.degree. F.__________________________________________________________________________ No 0.10% 0.20% 0.40% 0.80% 1% 1.20% 1.40% 1.60% 1.80% Activator Activator Activator Activator Activator Activator Activator Activator Activator Activator__________________________________________________________________________Time to 43.15 22.52 15.7 9.68 4.98 4.53 4.2 4 2.95 2.2750 psiTime to 53.37 28.9 20.35 12.62 6 5.58 5.28 4.83 3.57 2.63500 psiTime from 10.22 6.38 4.65 2.94 1.02 1.05 1.08 0.83 0.62 0.3650 psi to500 psiActivator:Retarder 0 1:1 2:1 4:1 8:1 10:1 12:1 14:1 16:1 18:1Ratio__________________________________________________________________________ 2% 2.20% 2.40% 2.60% 2.80% 3% 4% 5% 6% 7% Activator Activator Activator Activator Activator Activator Activator Activator Activator Activator__________________________________________________________________________Time to 2.23 2 2.1 1.82 1.43 1.5 1.2 1.02 1 0.9750 psiTime to 2.68 2.38 2.45 2.2 1.62 1.75 1.45 1.15 1.15 1.12500 psiTime from 0.45 0.38 0.35 0.38 0.19 0.25 0.25 0.13 0.15 0.1550 psi to500 psiActivator:Retarder 20:1 22:1 24:1 26:1 28:1 30:1 40:1 50:1 60:1 70:1Ratio__________________________________________________________________________ *bwos = by weight of slag TABLE 12__________________________________________________________________________Base Slurry: "NEWCEM" Blast Furnace Slag + 0.1% Sodium Gluconate (bwos*)+ 50% Distilled Water (bwos)Test Temperature: 175.degree. F.__________________________________________________________________________ No 0.10% 0.20% 0.40% 0.80% 1% 1.20% 1.40% 1.60% 1.80% Activator Activator Activator Activator Activator Activator Activator Activator Activator Activator__________________________________________________________________________Time to 17.95 10.3 7.37 4.17 2.58 2.1 1.87 1.38 1.48 1.450 psiTime to 22.27 15.12 9.57 5.68 3.45 2.72 2.38 1.68 1.78 1.73500 psiTime from 4.32 4.82 2.2 1.51 0.87 0.62 0.51 0.3 0.3 0.3350 psi to500 psiActivator:Retarder 0 1:1 2:1 4:1 8:1 10:1 12:1 14:1 16:1 18:1Ratio__________________________________________________________________________ 2% 2.20% 2.40% 2.60% 2.80% 3% 4% 5% 6% 7% Activator Activator Activator Activator Activator Activator Activator Activator Activator Activator__________________________________________________________________________Time to 1.05 1.17 1.03 1.15 1.22 0.73 0.6 0.62 0.62 0.7250 psiTime to 1.22 1.37 1.27 1.33 1.4 0.83 0.73 0.75 0.7 0.83500 psiTime from 0.17 0.2 0.24 0.18 0.18 0.1 0.13 0.13 0.08 0.1150 psi to500 psiActivator:Retarder 20:1 22:1 24:1 26:1 28:1 30:1 40:1 50:1 60:1 70:1Ratio__________________________________________________________________________ *bwos = by weight of slag

Claims

1. A method for cementing a well, comprising:

combining constituents comprising water, blast furnace slag having a particle size within the range of 2,000 to 15,000 cm.sup.2 /g, and an activator comprising sodium pyrophosphate to form a cement slurry;

displacing the cement slurry into the well; and

allowing the cement slurry to set.

2. The method of claim 1 wherein the activator includes an oxalate ion-containing compound.

3. The method of claim 1 wherein the activator includes a citrate ion-containing compound.

4. The method of claim 3 wherein the citrate ion-containing compound is selected from the group consisting of sodium citrate, calcium citrate and potassium citrate.

5. The method of claim 1 wherein the weight ratio of activator to slag is adjusted to achieve optimum compressive strength of the cement.

6. The method of claim 5 wherein the weight ratio of activator to slag is further adjusted in accordance with well temperature to achieve optimum compressive strength of the cement.

7. The method of claim 3 wherein the ratio of activator components is adjusted to provide at least one of the following: (a) optimum set time of the cement slurry, (b) optimum compressive strength of the cement, (c) optimum early compressive strength development rate of the cement slurry, and (d) optimum rheological properties for the cement slurry.

8. The method of claim 3 wherein the weight ratio of activator to slag is adjusted to achieve optimum compressive strength of the cement.

9. The method of claim 8 wherein the weight ratio of activator to slag is further adjusted in accordance with well temperature to achieve optimum compressive strength of the cement.

10. The method of claim 5 wherein the activator includes multiple components and wherein the ratio of activator components is adjusted to provide at least one of the following: (a) optimum set time of the cement slurry, (b) optimum compressive strength of the cement, (c) optimum early compressive strength development rate of the cement slurry, and (d) optimum rheological properties for the cement slurry.

11. The method of claim 6 the activator includes multiple components and wherein the ratio of activator components is adjusted to provide at least one of the following: (a) optimum set time of the cement slurry, (b) optimum compressive strength of the cement, (c) optimum early compressive strength development rate of the cement slurry, and (d) optimum rheological properties for the cement slurry.

12. The method of claim 1 including adding a retarder to provide adequate fluidity time of the cement slurry in order to place the cement in the well.

13. The method of claim 12 wherein the retarder is a salt of a transition metal with an atomic number above iron in the periodic chart.

14. The method of claim 13 wherein the retarder is a copper, zinc or aluminum salt.

15. The method of claim 12 wherein the retarder is a complexing agent.

16. The method of claim 15 wherein the retarder is a lignosulfonate, sulfonated lignin, or lignin amine.

17. The method of claim 15 wherein the retarder is sodium glucoheptonate, sodium gluconate or sodium citrate.

18. The method of claim 12 wherein a ratio of weight of activator to weight of retarder is selected to provide the greatest early compressive strength development and the greatest final strength for a given slag concentration.

19. The method of claim 18 wherein the activator/retarder weight ratio is selected at the static temperature of the well to provide substantially the greatest early compressive strength development and substantially the greatest final strength for a given slag concentration.

20. The method of claim 18 wherein the activator/retarder ratio is selected for a set time of less than about ten hours.

21. The method of claim 18 wherein the activator/retarder ratio is selected for a set time of less than about eight hours.

22. The method of claim 18 wherein the activator/retarder ratio is selected for a set time of between three and six hours.

23. The method of claim 3 including adding a retarder to provide adequate fluidity time of the cement slurry in order to place the cement in the well.

24. The method of claim 23 wherein the retarder is a salt of a transition metal with an atomic number above iron in the periodic chart.

25. The method of claim 24 wherein the retarder is a copper, zinc or aluminum salt.

26. The method of claim 23 wherein the retarder is a complexing agent.

27. The method of claim 26 wherein the retarder is a lignosulfonate, sulfonated lignin, or lignin amine.

28. The method of claim 26 wherein the retarder is sodium glucoheptonate, sodium gluconate or sodium citrate.

29. The method of claim 23 wherein a ratio of weight of activator to weight of retarder is selected to provide the greatest early compressive strength development and the greatest final strength for a given slag concentration.

30. The method of claim 29 wherein the activator/retarder weight ratio is selected at the static temperature of the well to provide substantially the greatest early compressive strength development and substantially the greatest final strength for a given slag concentration.

31. The method of claim 29 wherein the activator/retarder ratio is selected for a set time of less than about ten hours.

32. The method of claim 29 wherein the activator/retarder ratio is selected for a set time of less than about eight hours.

33. The method of claim 29 wherein the activator/retarder ratio is selected for a set time of between three and six hours.

34. The method of claim 1 including adding a drilling fluid to the cement slurry.

35. The method of claim 5 including adding a retarder to provide adequate fluidity time of the cement slurry in order to place the cement in the well.

36. The method of claim 35 wherein the retarder is a salt of a transition metal with an atomic number above iron in the periodic chart.

37. The method of claim 36 wherein the retarder is a copper, zinc or aluminum salt.

38. The method of claim 35 wherein the retarder is a complexing agent.

39. The method of claim 38 wherein the retarder is a lignosulfonate, sulfonated lignin, or lignin amine.

40. The method of claim 38 wherein the retarder is sodium glucoheptonate, sodium gluconate or sodium citrate.

41. The method of claim 35 wherein a ratio of weight of activator to weight of retarder is selected to provide the greatest early compressive strength development and the greatest final strength for a given slag concentration.

42. The method of claim 41 wherein the activator/retarder weight ratio is selected at the static temperature of the well to provide substantially the greatest early compressive strength development and substantially the greatest final strength for a given slag concentration.

43. The method of claim 41 wherein the activator/retarder ratio is selected for a set time of less than about ten hours.

44. The method of claim 41 wherein the activator/retarder ratio is selected for a set time of less than about eight hours.

45. The method of claim 41 wherein the activator/retarder ratio is selected for a set time of between three and six hours.

46. The method of claim 41 including adding a drilling fluid to the slurry.

47. The method of claim 7 including adding a retarder to provide adequate fluidity time of the cement slurry in order to place the cement in the well.

48. The method of claim 47 wherein the retarder is a salt of a transition metal with an atomic number above iron in the periodic chart.

49. The method of claim 48 wherein the retarder is a copper, zinc or aluminum salt.

50. The method of claim 47 wherein the retarder is a complexing agent.

51. The method of claim 50 wherein the retarder is a lignosulfonate, sulfonated lignin, or lignin amine.

52. The method of claim 51 wherein the retarder is sodium glucoheptonate, sodium gluconate or sodium citrate.

53. The method of claim 47 wherein a ratio of weight of activator to weight of retarder is selected to provide the greatest early compressive strength development and the greatest final strength for a given slag concentration.

54. The method of claim 53 wherein the activator/retarder weight ratio is selected at the static temperature of the well to provide substantially the greatest early compressive strength development and substantially the greatest final strength for a given slag concentration.

55. The method of claim 53 wherein the activator/retarder ratio is selected for a set time of less than about ten hours.

56. The method of claim 53 wherein the activator/retarder ratio is selected for a set time of less than about eight hours.

57. The method of claim 53 wherein the activator/retarder ratio is selected for a set time of between three and six hours.

58. The method of claim 53 including adding a drilling fluid to the slurry.

59. The method of claim 1 including selecting an activator which also functions as a good dispersing agent, whereby dispersion will favor better compressive strength development after setting of the cement slurry.

60. The method of claim 1 including adding a sulfide scavenging compound to the cement slurry, said scavenging compound being selected from the group consisting of zinc oxide and zinc carbonate.