Spacer fluid additive for cement system

Abstract

Well spacer materials containing a small amount of cement raw material are used to precede pumping cement precursors into a well. Use of cement raw material in the spacer material reduces hardening loss in the cement at the interface with the spacer material. The cement raw material can be a cement reactant or an activator.

Description

SPACER FLUID ADDITIVE FOR CEMENT SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority benefit of United States Provisional Patent Application Serial No. 63 / 600340 filed November 17, 2023, which is entirely incorporated herein by reference.FIELD

[0002] This patent application relates to compositions and methods for completing wells for hydrocarbon production. Specifically, compositions to be used with cementitious materials for cementing wells are described herein.BACKGROUND

[0003] Wells are drilled to access subterranean hydrocarbon deposits. During the drilling operation, a drilling fluid is used to facilitate drilling by lubricating the interface between the drill bit and the geologic structures being drilled. The drilling fluid is also circulated within the lengthening well to fluidize and remove solids generated by the drill bit. The drilling fluid, often called “mud” also contains weighting materials to create a pressure within the well to counteract pressure within the geologic structure that would tend to collapse the well walls and close the drilled well around the drill bit.

[0004] When drilling is complete, in many cases the well is prepared for completion by casing and cementing. The well is lined with a cementitious material to maintain integrity of the well against pressure within the geologic formations, and provides isolation of materials at different depths within the geologic formations. To form the lining, a hollow cylindrical member is typically lowered into the well, either during drilling or after drilling is complete. For example, when drilling is complete the drill bit can be removed from the well, which is left full of drilling fluid, and the hollow cylindrical member, often called a “casing,” is lowered into the well. The casing is typically somewhat smaller in diameter than the well itself to provide an annular space around the casing between the casing and the well wall. A cap or seal is emplaced at the surface to seal the well and to form a seal with the casing, resulting in a flowpathway in the interior of the casing and a flow pathway between the casing and the well wall. These flow pathways will be used to remove the drilling fluid from the well and to deploy a pumpable cement precursor.

[0005] Conventional cements such as Portland cement, and variants thereof, are often used as the cementitious material. To avoid mixing between the cement precursor and the drilling fluid, which can contaminate both the cement precursor and the drilling fluid, a spacer material is pumped into the well before pumping the cement precursor. The cement precursor is then pumped after the spacer material. During pumping, the spacer material can mix with the cement precursor at the interface between the two materials. The spacer material typically has water, various natural and / or synthetic polymers, and density selection materials to provide fluid properties that facilitate pumping the spacer material and displacing the drilling fluids already in the well.

[0006] When a cement precursor is pumped after a spacer, materials from the spacer can mix with the cement precursor and dilute the polymerizable materials of the cement precursor. When the cement precursor hardens, there is often a portion of the hardened material that has reduced strength due to dilution from the spacer materials. Because cements are often highly engineered for specific properties, effects of such dilution on cement precursor can mean significant portions of the hardened cement depart widely from the desired properties, particularly compressive strength. There is a need for methods and compositions that prevent such regression of compressive strength in cements placed following spacer compositions.SUMMARY

[0007] Embodiments described herein provide a method, comprising pumping a spacer material into a well, the spacer material comprising a cement raw material; and pumping a cement precursor into the well following the spacer material, and in contact with the spacer material.

[0008] Other embodiments described herein provide a method, comprising pumping a spacer material into a well, the spacer material comprising a cement rawmaterial; and pumping a cement precursor containing the cement raw material into the well following the spacer material, and in contact with the spacer material.

[0009] Other embodiments described herein provide a method, comprising pumping a spacer material into a well, the spacer material comprising a cement raw material, water, polymeric materials, and density materials, and one or more component selected from the group consisting of an antifoaming agent, a viscosifier, a surfactant, a mutual solvent, a cleaning agent, or a combination thereof; and pumping a cement precursor containing the cement raw material into the well following the spacer material, and in contact with the spacer material.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 is a graph illustrating the effect of adding a cement raw material to a spacer material to be pumped in contact with a cement precursor.

[0011] Fig. 2 is a graph illustrating the effect of adding a cement raw material, different from the cement raw material of Fig. 1 , to a spacer material to be pumped in contact with a cement precursor.DETAILED DESCRIPTION

[0012] Compositions and methods are described herein for spacer materials to be used with cement precursors in cementing wells. The spacer materials described herein generally contain a small amount of a cement raw material, such as a pozzolanic material or alkali activator, to counteract the effect of any mixing of material from the spacer with a cement precursor pumped into a well following the spacer. Including a small amount of a cement raw material that is reactive with the other cement raw materials in the cement precursor can counteract the dilution effect on hardening of the cement precursor at or near the interface with the spacer material.

[0013] Cements are typically made using a mixture of silicate and aluminosilicate raw materials, much of which is calcium silicate and calcium aluminosilicate. Portland cement, for example, ranges from about 45% calcium silicates to about 95% calcium silicates (dicalcium silicate and tricalcium silicate). Aluminosilicate source materials such as fly ash, volcanic ash, boiler ash, bioashes such as rice husk ash, other ashes,metakaolin, blast furnace slag (ground granulated blastfurnace slag, GGBS), other slags having substantial amounts of calcium, and silica fume are commonly used. Adding water and an alkali activator causes reaction of the silicon, aluminum, calcium, and oxygen to form a polymer network as the cement hardens. The alkali activators can be alkali metal and alkaline earth metal hydroxides such as sodium hydroxide, potassium hydroxide, and calcium hydroxide. Sources of such materials, such as limes, potashes, and the like can be used to activate cements. Other sources of silicate and some sulfates can also commonly be found in cements.

[0014] The cement raw materials are generally contacted in aqueous solution, for example by adding the alkali activator to water to form an activator solution and then adding the activator solution to the other solid cement raw materials, or by adding the alkali activator to the other solid raw materials and then adding water to the resulting mixture.

[0015] Mixtures of alkali metal hydroxides, alkaline earth metal hydroxides, and mixtures of both alkali metal and alkaline earth metal hydroxides can be used as activators. The metal hydroxide may be in the form of a solid or an aqueous mixture. Also, the activator in another embodiment can be encapsulated. The activator when in solid and / or liquid state can be trapped in a capsule that will break when subjected to, for example, mechanical stress on the capsule, or coating degradation owing to temperature, chemical exposure or radiation exposure. Also, the activator when in solid and / or liquid state can be trapped in a capsule that will naturally degrade if made from a biodegradable or self-destructive material. Furthermore, the alkali activator when in liquid state may be adsorbed into a porous material and may be released after a certain time or due to a predefined event. The alkali activator may be present in the cement precursor composition at a concentration between about 0.1 moles / L (M) to 10M or between 3M and 6M.

[0016] As noted above, the cement precursor made by contacting cement reactant with alkali activator in an aqueous medium is pumped into a well following a spacer material to separate the cement precursor from drilling fluids displaced by pumping the spacer and the cement precursor into the well. The spacer prevents mixing of material from the drilling fluid with the cement precursor. The spacermaterial typically includes water, polymeric materials, and density materials such as barite and / or calcium carbonate to provide a bulk density for the spacer material that will result in the spacer material moving downward in the well against the drilling fluid and displacing the drilling fluid into the annular space between the casing and the well wall and flowing the drilling fluid upward, in the annular space, to the surface. Spacer materials can also contain antifoaming agents, viscosifiers, surfactants, mutual solvents, and cleaning agents such as fibers.

[0017] Herein, the spacer material also contains a cement raw material, such as those described above. A small amount of a cement raw material, such as a pozzolan or alkali activator, that can participate in, or facilitate, chemical reaction with materials of the cement precursor, is included in the spacer material prior to deploying the spacer material into the well. Any of the cement raw materials mentioned above can be used, or any mixture thereof. In some cases, the cement raw material in the spacer material can be the same material used to activate the cement reactants. In other cases, a different activating material can be included in the spacer material from the activating material used for the cement precursor. In general, the cement precursor used in the spacer material can be a material that is also used in the cement precursor, or the cement precursor can be free of the cement raw material used in the spacer material. In some cases, the cement precursor comprises a plurality of cement raw materials, each of which is different from the cement raw material used in the spacer material. In other cases, the cement precursor comprises a plurality of cement raw materials, the plurality including the cement raw material used in the spacer material. In other cases, the spacer material contains a first plurality of cement raw materials and the cement precursor contains a second plurality of cement raw materials free of any of the cement raw materials in the first plurality. In still other cases, the spacer material contains a first plurality of cement raw materials and the cement precursor contains a second plurality of cement raw materials different from the first plurality, wherein the second plurality of cement raw materials contains a first cement raw material and the second plurality of cement raw materials also contains the first cement raw material, so that at least one cement raw material in the first plurality is also in the second plurality. The quantity of cement raw material in the spacer material is typically about 10 percent by weight, or less, but can be up to 20%.In many cases, a concentration of cement raw material in the spacer material of 5 percent by weight can be used, for example 3 percent or 4 percent by weight.

[0018] In some cases a cement precursor accentuated in one or more raw materials can be used in the spacer material. For example, a mixture of pozzolanic material and alkali activator that has an excess amount of pozzolanic material can be used as the cement raw material in the spacer material. A low activation cement precursor can be prepared that has activator concentration of less than 3M or less than 1 M, and the precursor can then be added to a spacer precursor, which can be a conventional spacer material, such that the spacer material contains up to about 10 wt% of the low activation cement precursor.

[0019] In some cases, two spacer materials can be used to separate a cement precursor from drilling fluids. A first spacer material, free of any cement raw material, can be pumped, and then a second spacer material, containing a cement raw material, can be pumped. In this way, use of cement raw material in the spacer material can be minimized.

[0020] Inclusion of a cement raw material, such as an activator material or a pozzolan, in the spacer material reduces or precludes regression of hardening in the cement precursor due to mixing with spacer material components. Since a small amount of a cement raw material like rice husk ash can be used, overall properties of the spacer fluid important to its function, such as rheology, pumpability, or ability to displace fluids and clean the well are not affected by including such materials.

[0021] Fig. 1 is a graph illustrating the effect of adding a cement raw material to a spacer material to be pumped in contact with a cement precursor. The graph includes data for five cases. For each case, an 18 pound per gallon (“ppg”) cement precursor is used. At 102, the cement precursor alone is allowed to harden as a control case. In all the other cases, 20 wt% of a 14.7 ppg spacer material is added to the cement precursor before hardening. The spacer material in each case is identical, except that different amounts of rice husk ash are added to the spacer material before the space material is added to the cement precursor. At 104, the spacer material has 1 wt% rice husk ash. At 106, the spacer material has 2 wt% rice husk ash. At 108, the spacer material has 4 wt% rice husk ash. At 110, a comparative case is shown where1 wt% rice husk ash is added to the cement precursor before adding 20 wt% of a conventional spacer material, which is free of rice husk ash for the comparative case. All wt% figures are based on the total weight of the cement precursor that is allowed to harden.

[0022] As shown in Fig. 1 , boosting the amount of pozzolanic material in the cement precursor prior to dilution with a conventional spacer material does not recover the cement hardening performance of the control case. Performance of the rice husk ash as an ingredient of the spacer material is more conducive to cement hardening than as an additive to the cement precursor before mixing with a conventional spacer material, shown by the higher rate of compression strength development in case 104 than in case 110. Higher amounts of rice husk ash in the spacer material, cases 106 and 108, boost compression strength more. Fig. 1 indicates that use of cement raw materials, such as rice husk ash, in a spacer material that is used in contact with a cement precursor in a well cementing activity, would be expected to preserve cement compression strength performance at the interface between the cement precursor and the spacer material in the well.

[0023] Fig. 2 is a graph showing data similar to Fig. 1 , but using metakaolin as the spacer additive material. The same cement precursor and spacer material is used, in the same proportions, as for the cases of Fig. 1 , but with metakaolin as the spacer additive instead of rice husk ash. As in Fig. 1 , a control case is at 202. At 204, the spacer material has 1 wt% metakaolin, at 206 2 wt%, and at 2084 wt%. At 210, the same comparative example is presented as in Fig. 1 , but using metakaolin.

[0024] Although the metakaolin has a different activity profile than the rice husk ash, the data in Fig. 2 are consistent with the data in Fig. 1 , showing a positive effect of using small amounts of metakaolin in the spacer material used in contact with a cement precursor in a well. The data of Figs. 1 and 2 show that the methods herein can preserve compression strength of cements that harden in contact with spacer materials in subterranean wells.

[0025] The preceding description has been presented with reference to present embodiments. Persons skilled in the art and technology to which this disclosure pertains will appreciate that alterations and changes in the described structures andmethods of operation can be practiced without meaningfully departing from the principle, and scope of this present disclosure. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

Claims

Claims1 . A method, comprising: pumping a spacer material into a well, the spacer material comprising a cement raw material; and pumping a cement precursor into the well following the spacer material, and in contact with the spacer material.

2. A method, comprising: pumping a spacer material into a well, the spacer material comprising a cement raw material; and pumping a cement precursor containing the cement raw material into the well following the spacer material, and in contact with the spacer material.

3. A method, comprising: pumping a spacer material into a well, the spacer material comprising a cement raw material, water, polymeric materials, and density materials, and one or more component selected from the group consisting of an antifoaming agent, a viscosifier, a surfactant, a mutual solvent, a cleaning agent, or a combination thereof; and pumping a cement precursor containing the cement raw material into the well following the spacer material, and in contact with the spacer material.

4. The method of any of claims 1 to 3, wherein the cement raw material is a pozzolanic material.

5. The method of any of claims 1 to 3, wherein the cement raw material is an alkali material.

6. The method of any of claims 1 to 3, wherein the cement raw material is rice husk ash, metakaolin, or a combination thereof.

7. The method of any of claims 1 to 6, wherein the spacer material is a first spacer material, and further comprising, prior to pumping the first spacer materialinto the well, pumping a second spacer material into the well, the second spacer material being free of cement raw materials.

8. The method of any of claims 1 to 7, wherein an amount of the cement raw material in the spacer material is up to 20% by total weight of the spacer material.

9. The method of any of claims 1 to 8, wherein the cement precursor is a first cement precursor, and the spacer material is prepared by adding a second cement precursor to a conventional spacer material.

10. The method of claim 9, wherein the second cement precursor is a low activation cement precursor.11 . The method of claim 10, wherein the low activation cement precursor has an activator concentration less than 3M.

12. The method of any of claims 1 to 11 , wherein the cement raw material is also present in the cement precursor.

13. The method of any of claims 1 to 12, wherein the cement precursor is free of the cement raw material.

14. The method of any of claims 1 to 13, wherein the cement precursor comprises a plurality of cement raw materials that are different from the cement raw material in the spacer material.

15. The method of any of claims 1 to 14, wherein the spacer material comprises a first plurality of cement raw materials, the cement precursor contains a second plurality of cement raw materials, and at least one cement raw material in the first plurality is also in the second plurality.

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