Cement with reduced permeability

Abstract

A cementitious mixture to make structures with reduction of gas permeability was disclosed. The mixture includes, cementitious materials, and one or more divalent magnesium-iron silicate that in neutral or basic aqueous solutions have the capacity to be a latent hydraulic binder comprising 2% to 99% of divalent magnesium-iron silicate by weight of total hydraulic solid materials. This can be used to produce a cementitious structure for preventing gas transfer between a first region and a second region. A cement slurry was also disclosed.

Claims

1. A cementitious mixture for reduced gas permeability that comprises: a) an alkaline cement; b) one or more divalent magnesium-iron silicate from a natural earth-based system wherein more magnesium ions than iron ions are present that in neutral or basic aqueous solutions is a latent hydraulic binder comprising 2% to 99% of divalent magnesium-iron silicate by weight of total hydraulic solid materials.

2. The cementitious mixture of claim 1, wherein the magnesium-iron silicate is by weight of total hydraulic solid is between 10% and 98%.

3. The cementitious mixture of claim 1, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 15% and 99%.

4. The cementitious mixture of claim 1, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 10% and 55%.

5. The cementitious mixture of claim 1, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 20% and 50%.

6. The cementitious mixture of claim 1, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 20% and 80%.

7. The cementitious mixture of claim 1, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 15% and 25%.

8. The cementitious mixture of claim 1, wherein the magnesium-iron silicate comprises mineral group olivines, orthopyroxenes, amphiboles, serpentines, or a mixture thereof.

9. The cementitious mixture of claim 1, wherein the magnesium-iron silicate consists of mineral group olivines, orthopyroxenes, amphiboles, serpentines, or a mixture thereof.

10. The cementitious mixture of claim 1, wherein the magnesium-iron silicate is of mineral group orthopyroxenes.

11. A cementitious slurry for reduced gas permeability that comprises: a) an alkaline cement; b) water; and c) one or more divalent magnesium-iron silicate from a natural earth-based system wherein more magnesium ions than iron ions are present that in neutral or basic aqueous solutions is a latent hydraulic binder comprising 2% to 99% of divalent magnesium-iron silicate by weight of total hydraulic solid materials.

12. The cementitious slurry of claim 11, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 15% and 25%.

13. The cementitious slurry of claim 11, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 10% and 55%.

14. The cementitious slurry of claim 11, wherein the magnesium-iron silicate by weight of total hydraulic solid is between 20% and 80%.

15. The cementitious slurry of claim 11, wherein the magnesium-iron silicate comprises mineral group olivines, orthopyroxenes, amphiboles, serpentines, or a mixture thereof.

16. The cementitious slurry of claim 11, wherein the magnesium-iron silicate is of mineral group orthopyroxenes.

17. The cementitious slurry according to claim 11, wherein the water has a chloride concentration of between 0.4% to 14 by weight.

18. The cementitious mixture of claim 5, wherein the magnesium-iron silicate is of mineral group orthopyroxenes.

19. The cementitious mixture of claim 7, wherein the magnesium-iron silicate is of mineral group orthopyroxenes.

20. The cementitious slurry of claim 13, wherein the magnesium-iron silicate is of mineral group orthopyroxenes.

Description

DESCRIPTION OF THE FIGURES

(1) The above and further features of the invention are a set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description. Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein:

(2) FIG. 1A discloses results for a water saturated carbon dioxide with permeability experiment.

(3) FIG. 1B discloses results for a water saturated carbon dioxide with permeability experiment.

(4) FIG. 2 discloses results for a water saturated carbon dioxide with permeability experiment.

(5) FIG. 3 discloses experimental results for permeability of silicate added cement and the cement of the present invention to nitrogen.

(6) FIG. 4A discloses results for a nitrogen permeability experiment.

(7) FIG. 4B discloses results for a nitrogen permeability experiment.

(8) FIG. 5 discloses a test rig of measuring nitrogen permeability in nitrogen experiments 2 and 3.

(9) FIG. 6A discloses a structure inside a hollow container.

(10) FIG. 6B discloses a structure surrounding a gas source.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(11) Reference will now be made in detail to the present embodiments of the inventions, examples of which are illustrated in the accompanying drawings. Alternative embodiments will also be presented. The drawings are intended to be read in conjunction with both the summary, the detailed description, and an any preferred and/or particular embodiments, specifically discussed or otherwise disclosed. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided by way of illustration only. Several further embodiments, or combinations of the presented embodiments, will be within the scope of one skilled in the art.

(12) Direction terms such as up, down, left, right, above, below, etc. are being used in reference to the orientation of the elements in the figures. In no way is this intended as limiting.

(13) This invention is an extension of previous work with a cementitious material that seal off liquids and gasses. However, we have found that the materials are significantly better at sealing off gaseous materials than previously predicted or expected. While liquids and supercritical fluids are in the reservoirs of petroleum systems at crustal pressures and temperatures, the phase transformation from liquid to fluid can bring on a major pressure release. This e.g. can occur when liquids in the reservoir zone under pressure flows toward and into the well with less pressure. This invention works well for saltwater or fresh water used in mixing the slurry.

(14) At formation pressures and temperatures a gas may be transformed to a supercritical fluid. An example is CO.sub.2 gas, which becomes supercritical at temperatures above 31° C. at a pressure of 73.8 bar. Supercritical fluids have a viscosity similar to a gas but a density similar to the corresponding liquid.

(15) Permeability is dependent on the viscosity of the gas or fluid that is flowing through the matrix. Therefore, the properties of the supercritical fluids are similar to the properties of the corresponding gas in this invention. The supercritical fluid of a gas molecule (e.g. CO.sub.2, H.sub.2S, N.sub.2, CH.sub.4) will behave roughly same as a non-supercritical fluid of a gas molecule with regards to the reduced permeability properties of the invention.

(16) The inventors observed that very low concentrations of magnesium-iron silicate may have properties that are significant for operations that need blends very close to ordinary blends, while exploiting gas proofing. Likewise, blends that are nearly all magnesium-iron silicates with a small concentration of cementitious materials will potentially need longer to set but will have a much lower permeability once set. As mentioned previously, the inventors observed that magnesium-iron silicates provided self-healing characteristics. However, the reduction in permeability was incredibly surprising even in the face of the potential self-healing properties.

(17) FIGS. 6A and 6B disclose schematically how a structure made from the inventive mixture can be used in different circumstances for creating a gas proof structure. In both figures, the arrows represent a gas pressing against the cementitious structure 100. In FIG. 6A, a hollow container 200 (e.g. pipe or production casing) has a cementitious structure 100 (e.g. plug) bonded to the inside of it. This creates a first region 300A and a second region 300B where gas does not transfer (or move) from one region to the other 300A/300B. This is a common method that could be used in the case of needing to plug a hydrocarbon well during plugging and abandonment (or carbon capture and storage). FIG. 6B discloses an example where the cementitious structure 100 is not inside of a pipe. Instead, it is shown as surrounding a gas source. This prevents the gas inside of the structure 100 from moving from the first region 300A to the second region 300B.

(18) Though FIGS. 6A and 6B indicate that there is gas pressure on a single side of the cementitious structure 100, this is by way of example only. The invention could be used to keep two or more sources of gas separate if desired.

(19) The invention is well suited for use in making plugs and other cement structures to prevent gas from moving or flowing into areas where it is not wanted.

(20) The term “gas proof” refers to a structure having a low enough gas permeability that, ideally, a gas cannot cross from one region to another. However, depending upon the application, a gas permeability lower than an accepted threshold will be considered sufficiently “gas proof”.

CARBON DIOXIDE EXPERIMENTS

(21) Numerous experiments were performed to measure the permeability of a cement structure (e.g. plug) to water saturated with carbon dioxide. Note that usually a cement plug will be about 100 times more permeable to gas than it is to a liquid.

Carbon Dioxide Experiment 1

(22) Previous work in U.S. Ser. No. 10/774,001 has shown that a mixture including olivine has properties related to self-healing in the presence of water or carbon dioxide. This includes a disclosure of reduction of permeability after a multiple day exposure to water saturated with CO2. This was thought to be due to water or saltwater being carried into the pores and voids and triggering the “self-healing” reactions that result in matter being precipitated there.

(23) The results of such an experiment are shown in FIG. 1A. This experiment was performed using 20% of olivine by weight. The sleeve volume was pressurized with 50 bar of nitrogen, and the core outlet was connected to a burette for collection of gas. Leakage of gas through the sleeve was monitored for a period of 24 hours. Finally, nitrogen was displaced with a viscous paraffin at a constant pressure of 50 bars. The paraffin was injected from the bottom and nitrogen was bleed off from the top via back pressure valve.

(24) Prior to injection, the core sample was heated to a stable temperature of 60° C. and pressurized to a confining pressure of 110 bar, where both parameters, where kept constant throughout the experiment. Seawater (saturated with CO.sub.2) was subsequently injected into the core with a high pressure Quizix piston pump. Flow rate was set at low as 360 microliters/hour, and back pressure was set to 10 bars. Differential pressure was measured at steady state conditions at each rate, and permeability calculated according to Darcy's Law.

(25) An additional, a long-term seawater test was conducted, and the permeability calculated. The initial permeability was 0.26 μDarcy. After nearly 11 days of brine flooding and 45 ml of seawater injected, the permeability reduced to 0.129 μDarcy, as shown in FIG. 1A. The line with filled circles represents the permeability and the smooth line represent for the injection pressure.

Carbon Dioxide Experiment 2

(26) An experiment was performed where sea water saturated with carbon dioxide was forced through the sample as it cured. The results are shown in FIG. 1B, where “Volume SSW Injected” stands for the volume of saturated seawater was injected into the test rig. Of interest in both FIG. 1A and FIG. 1B is the behavior of the solid line that represents the injection pressure. As can be seen, in FIG. 1A, at around 8.5 days, the injection pressure begins to vary in an erratic manner. This behavior is also observed in FIG. 1B around 35 of SSW injected. This is due to the cement having cured to a point where the gas cannot pass through the sample in a controlled manner. This is very apparent when looking at the variation in the injection pressure of days 10-11. The gas simply cannot pass through the sample in an appreciable manner. At this point, the sample is so impermeable that it makes the pressure build up and release in busters. This was causing the test rig to start jumping. These show that the permeability is being reduced to a surprisingly low degree.

Carbon Dioxide Experiment 3

(27) Another experiment was performed that studied the results of permeability to brine that was saturated in CO2. Batch CO.sub.2 exposure was performed for seven days in an autoclave at 90° C. and 280 bar. The cores were submerged in 1.0 wt % NaCl-brine and dry CO.sub.2 was pumped in from the inlet at the top of the autoclave, forming a gas cap and ensuring that the brine was saturated with CO.sub.2. No brine was added or replaced during the exposure.

(28) Porosity before and after CO.sub.2 exposure for batches with different percentages of the magnesium-iron silicate (olivine in this case) as shown in Table 1 below:

(29) TABLE-US-00001 TABLE 1 Initial and final porosity after CO.sub.2 exposure as estimated from CT results. % Core Initial Final % Olivine Number Porosity Porosity Reduced 20% 4 0.5 0.1 80% 5 1.2 0.4 67% 6 0.75 0.3 60% 35% 5 0.8 0.2 75% 6 0.4 0.05 88% 50% 4 0.6 0.1 83%

(30) This again shows the ability of the present invention to greatly reduce the permeability of cement to CO.sub.2 across the percentage ranges of the magnesium-iron silicate. It would be expected that the results would extend over a wider range.

Carbon Dioxide Experiment 4

(31) Reference is now made to FIG. 2. Experiments were run to measure the permeability of cured cement to carbon dioxide. A blend of cementitious materials containing 19.6 wt % out of total solids of olivine, and water added as required, was blended by the normal API 10A Standard methods. The materials were cemented into a sleeve, cured under pressure for one week at 60° C. Water was then flooded through the sample. After about 100 hours, CO2 was added to the water, resulting in a steady decline of the permeability of the sample. The measurements of the flow through the cement was made in ml/min resulting in very small numbers with a lot of variability in the measurements. Opening chambers for operational procedures also resulted in spikes and troughs in the measurements. This noise and variability is omitted for clarity. The final permeability of the same was below 0.05 μDarcy.

Carbon Dioxide Experiment 5

(32) In an experiment, solid cementitious mineral admixture products were fabricated based on a mixture of 80% Portland cement, and 20% olivine (which is a divalent magnesium-iron solid solution silicate) by weight, and water having an ordinary W/C number (W/C=water to cement ratio). The fraction of olivine was 0.2 with denatured water added. A solid cementitious mineral admixture cylinder was prepared and flooded by a seawater analog brine for a period of eleven days. The changes of permeability was measured throughout the experiment and the porosity was evaluated before and after the experiment by using a CT scanner.

(33) The measurements showed that porosity of the product, when applying the inventive cementitious mineral admixture was reduced by as much as 55%, and permeability went down by 70% after said just eleven days exposed to brine. The experiments show that the gas permeability of the resulting cement decreased.

NITROGEN EXPERIMENTS

(34) We will now discuss a series of different permeability experiments using nitrogen gas. For these experiments, the gas will not be dissolved in water. This is a different type of experiment than has been performed previously.

(35) As discussed previously under Carbon Dioxide Experiment 1, when water or saltwater is forced into the body of the solidified cement plug, the self-healing reactions cause the pores to fill with new material. However, in experiments that do not have an appreciable amount of water, this cannot be the case.

(36) Any reduction in permeability of the cement to a gas which is not dissolved in water, is not expected in light of previous work with this inventive mixture for self-healing. Note that the amount of water vapor that can be dissolved in nitrogen is very low and will not significantly contribute reducing permeability through self-healing.

Nitrogen Experiment 1

(37) Reference is made to FIG. 3. These are the test results as described in SPE/IADC-194158-MS, where the Neat cement and the Silicate added cement shows high flow at low differential pressures, while the present invention over displays a significantly lower flow rate over the same differential pressures (Test A and Test B). Test A is represented by open circles and a solid line, Test B is represented by closed circles with a solid line, neat cement is represented by an open triangle, and silicate added cement by a closed|triangle. The vertical axis is the flow rate in ml/min and the horizontal axis is differential pressure and is in units of bars.

(38) A study published in SPE/IADC-194158-MS, shows how neat cement cured at 66 degrees C. and silicate added cement cured at 120 degree C. inside a smooth casing tube under pressure, the cement was cured for four days and then N.sub.2 was allowed to be pushed through the cement-casing apparatus. The study indicated that neat and silicate added cement had fairly significant leaks through the experiment and was not a good seal against flow of N2 at even low differential pressures. The authors of the paper indicated that “Both cement systems, neat cement and silica cement, cured at their optimum temperature are not sufficient to produce a tight seal plug. Leak path development at the interface is consistent with shrinkage mechanism during hydration.”

(39) The inventors replicated this experiment using 66 degree Centigrade and 20% of the finely crushed olivine with 80% Portland cement in the mixture. The results are shown FIG. 3. Test A and Test B indicate far superior sealing capacity of the material, even without adding expanding materials or other pozzolans. This shows that adding magnesium-iron silicates, in particular olivine, will cause a continued hydraulic pressure towards the surrounding material providing a superior gas sealant for as long as the mixture has magnesium-iron silicates present.

(40) It can be shown that the permeability of a sample is inversely proportional to the square of the differential pressure. FIG. 3 shows that the best differential pressure achieved in by a sample of neat cement or a silicate cement is about 4 bar. Test A achieved a differential pressure of about 15 bar and Test B of about 30.5 bar. These indicate that the permeability of the cement of Test A was about 7% and Test B about 1% that of the neat/silicate cement.

Nitrogen Experiment 2

(41) An experiment was conducted over a range of pressures in order to establish the difference between the present invention and Portland G cement. Each were made using a standard process and a standard water to solid ratio.

(42) The setup consists of a custom-built test cell 10 containing the cement plug placed inside a heating cabinet for temperature control, and a process board located outside the heating cabinet with the process tubing, valves, flow meters, pressure indicators, an automated pressure regulator and an automated logging system. A technical drawing of the test cell 10 is shown in FIG. 4. The major components of the test cell are: Bottom cap 2 with two Swagelok ⅛″ connection ports 21 and a built-in movable teflon piston 23 used for retaining 22 the cement slurry during curing. Expandable steel pipe 1 with inner diameter of 50 mm, wall thickness of 13 mm and a length allowing a maximum of 460 mm of cement to be placed inside the pipe. Top cap 3 with two Swagelok ⅛″ connection ports 31.

(43) A pressure test at 100 bar and 22° C. was performed on the test cell showing no signs of deformation on pipe diameter or damage to the pipe threads.

(44) The test setup is also equipped with a temperature probe for control of the experimental conditions. The output data from the tests is the differential pressure needed to observe breakthrough of gas through the cement plug, and the relationship between the measured flow rate and differential pressure across the cement plug. Possible manipulated variables for the test setup can be the cement type and casing surface properties.

(45) Before every new experiment, a pressure test was performed on every new test cell. This was done by fully mounting the test setup with no cement inside the cell. The setup would then be pressured up to the working pressure (20 bar) and the main valve to the pressure bottle would be closed. By monitoring the decrease in pressure over a period of 1-2 hours, the level of gas leakage from the entire setup was monitored. In an ideal situation there would be zero leakage; in a case of losing more the ˜1 bar over 1 hour an attempt to localize the leakage would be performed. If the pressure test was assessed to be successful, the gas in the setup would be evacuated and the top cap to the test cell would be unscrewed.

(46) The cement placement was performed by moving the teflon piston in its top-position and by pouring the designated cement volume into the test cell. All valves would be opened, and the automated pressure regulator would be set to maintain a minimum pressure of 20 bar. The top cap would be screwed in place tightly and the cell would be carefully pressurized to 20 bars. The cement plug would be left to cure at 20 bar and 66° C. for 5 days.

(47) The cement plug integrity test started by moving the teflon piston down, leading to an open volume above and below the cement plug. By closing a valve, the two chambers would be isolated from each other and the only connection between them could be through the cement plug. By using the automated pressure-regulator a controlled differential pressure across the cement plug was generated. When the differential pressure was large enough for enabling flow through the cement plug, the pressure regulator connected to the bottom chamber would detect a decrease in pressure, and the regulator would try to maintain the set pressure. This flow of gas from the gas bottle through the process line would be detected by the flow meters. A sequential increase in the differential pressure would be applied to the cement plug. Thus, each experiment gives the pressure differential to which there is gas breakthrough the cement plug, and the relationship between the applied differential pressure and the flow rate through the cement plug. Figure (The one with the data) shows the raw data of flow rate and differential pressure plotted versus time for one of the experiments. For the data analysis and presentation of data stable values of the flow rate and differential pressure would be extracted and plotted against each other.

(48) Test samples were made using 0%, 20%, and 80% of olivine by weight of total cementitious solids. The results of this are shown in the table below:

(49) TABLE-US-00002 TABLE 2 Permeability of Sample/Permeability of net Portland Cement % of Permeability Magnesium- Relative % Iron Pressure to Portland Silicate (bar) Cement 20% 1.014 4.0% 20% 1.073 4.6% 20% 1.084 3.4% 20% 1.084 1.9% 80% 1.620 1.7% 80% 1.223 1.5% 80% 1.590 1.0%

(50) This clearly shows the improvement of the present invention when compared to Portland G for permeability to nitrogen over a wide range of pressures.

Nitrogen Experiment 3

(51) Reference is now made to FIGS. 4A and 4B. Experiments were run to measure the permeability of cured cement to nitrogen. One set of experiments were made with repeated runs of 20% magnesium-iron silicate and 80% Portland G cement, measured by weight of dry materials. The other set was made with repeated runs of 80% magnesium-iron silicate and 20% Portland G measured by weight of dry materials. In both sets of experiments, the solids were mixed neat with water (in a water-to-solids ratio of 0.44) and the slurry was poured into a test chamber where the materials were cured.

(52) The setup for a cement plug test consists of a custom-built test cell containing the cement plug placed inside a heating cabinet for temperature control, and a process board located outside the heating cabinet with the process tubing, valves, flow meters, pressure indicators, an automated pressure regulator and an automated logging system.

(53) The results of the 20% magnesium-iron silicate tests are shown in FIG. 4A. The lines on the left most side of the figure are from samples of regular Portland G (marked with a filled triangle). These show that it does not take a high differential pressure to get a high flow rate through (or around) the sample.

(54) Compare those to the two other lines on FIG. 4A. Each of these represent a different test run (test run A with solid circles and test run B with open circles). It was surprising that one of the 20% samples can tolerate over 12.5 times as much differential pressure to reach a 30 mL/min of flow rate. The second sample performed even better. Even at a differential pressure of 45, the flow rate is half of the other samples. Notice that the result shows that the cement is almost impermeable to nitrogen, even under a large pressure differential. In fact, the test ring was not able to supply enough pressure in order to achieve the same flow rate as the other samples. A simple regression of the data estimates that it would take a differential pressure of over 110 bar/m to cause the same flow rate through the sample (tolerating over 36.5 times as much differential pressure than the reference samples).

(55) Reference is made to FIG. 4B. FIG. 4B shows the results of the tests of FIG. 4A using samples with 80% magnesium-iron silicates. Both of these tests (test A with a closed circle and test b with an asterisk) show an improved behavior when compared to the Portland G to differential pressure.

(56) It can be shown that the permeability of a sample is inversely proportional to the square of the differential pressure. FIGS. 4A and 4B demonstrate that the present invention makes cured cement with a surprisingly lower permeability to nitrogen when compared to Portland G cement.

Nitrogen Experiment 5

(57) The permeability of a solidified test sample from the present invention was measured using an apparatus as disclosed in Appendix B-4.11 (“Permeability”) of “Well Cementing”, second edition, edited by Erik B. Nelson and Dominique Guillot. This type of test apparatus and setup is well known in the industry where cement permeability to gas needs to be measured.

(58) The samples had a measured permeability of between 0.03 μD and 0.006 μD to nitrogen gas.

(59) As nitrogen gas has a very small diameter, it is expected that molecules of approximately the same size (e.g. methane) or larger molecules (e.g. carbon dioxide) will also behave similarly.

(60) It is a very surprising for such a large reduction of gas permeability. The present invention should be able to achieve solid structures with a gas permeability of at most 1 μD, preferably 0.5 μD, more preferably 0.1 μD, even more preferably 0.05 μD, and most preferably 0.005 μD.

(61) Something that must be kept in mind is that gases have, in general, viscosities (compared to liquids) that indicate that if a low viscosity gas is not passing through, then the higher viscosity gas will not pass through (per Darcy's law). In other words, if nitrogen gas does not have the possibility to pass through the pores of the cement it will not be possible for gas types (e.g. CO2, CH4, and H2S being some of the most important) to pass through the pore pathway (e.g. permeability) of the cement.

(62) Additionally, this behavior will be the same if the cement is in saltwater or freshwater. Nitrogen does not dissolve appreciable in water, and salt would not change this situation, so it is readily apparent that the results of the nitrogen experiments can be extended to saltwater. It is well known that saltwater will degrade the structure of regular cement. Using freshwater causes less of this degradation. While it is surprising how well the present invention performs in saltwater, there is no reason to assume that it will not perform as well or better in fresh water. It is expected that water has a chloride concentration of between 0.4% to 14% by weight of water would not appreciably affect the previously presented permeability results. The most common saltwater that are found has a chloride concentration of between 0.7% and 10% by weight of water. Freshwater sources will normally have a chloride concentration of less than 250 mg/L.

(63) For guidance of one skilled in the art, the table below gives the percentage of magnesium-iron silicates in the solid mixture that are highly suited to different applications:

(64) TABLE-US-00003 TABLE 3 Effect of percentage of magnesium-iron silicates on different desired characteristics on the final cement structure Ideal % of Magnesium- Iron Silicate Characteristic Low High High Strength of Solid 2 35 Expansion to Compensate Shrinking 10 98 Sealing of Pores and Channels 15 99 Sealing of Pore Necks 2 99

(65) The table above is not a definitive statement of where the present invention has no effect. It is intended to give one skilled in the art an understanding of ranges to choose if one than one effect is important. For example, the range of 15% to 35% shows the best balance of characteristics for numerous applications. However, tests that have been performed of strength at 10% and 55% magnesium-iron silicate have demonstrated that the present invention is a significant improvement over Portland G.

(66) In the current state of the cement industry, 10-55% is the easiest range for a company to add to their current production line. With a change in the process, however, the other ranges of use described in the table above, will be achieved. As shown above, the gas permeability characteristics of the present invention are very desirable over a large range of percentages.