Cementitious slurry compositions, cement compositions, and methods for using such compositions for downhole applications

Abstract

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Description

This application is a divisional of PCT international application PCT / CA2025 / 050070, filed 17 January 2025 and published as WO2025 / 151966, which claims priority from US patent application 63 / 622,882, filed 19 January 2024. This application also claims priority from US patent application 63 / 849,420, filed 23 July 2025. The entire content of each of these applications is incorporated herein by reference. FIELD

[0001] The present disclosure relates to cementing composition for use in downhole environments. BACKGROUND

[0002] Cementing compositions are useful downhole to facilitate production of reservoir fluid from a subterranean formation. In some cases, and amongst other things, the cementing composition, upon curing downhole, creates a barrier within a subterranean formation for selectively interfering with flow communication between the subterranean formation and a wellbore. In some cases, and amongst other things, the cementing composition, upon curing downhole, reinforces the structural integrity of the subterranean formation and, therefore, the wellbore. In some cases, and amongst other things, the cementing composition, upon curing downhole, supports the wellbore casing.

[0003] Cementing compositions are not only useful for well completion, but are also useful for wellbore remediation. For example, cement (resulting from the curing of the cementing composition) is emplaced within an annular space between a pre-existing perforated wellbore string (such as, for example, a casing string, a liner string, or a combination of a casing string and a liner string). In some cases, such remediation is necessitated by a determination that the structural integrity of the subterranean formation is being compromised by flow of formation water, into the wellbore, which has been induced by hydrocarbon material production operations. In some cases, such flow of formation water causes solid particulate 2026208007   22 Jul 2026 material, from regions within the subterranean formation containing unconsolidated fines, to become displaced from the subterranean formation, and carried with the formation water flow to the wellbore. Upon becoming emplaced within the wellbore, such solid particulate material interferes with hydrocarbon material production from the wellbore. In some cases, and amongst other things, the solid particulate material causes erosion of production equipment. In some cases, and amongst other things, the solid particulate material accumulates within an annular space between a wellbore string that is disposed within a wellbore that extends into a subterranean formation, thereby interfering with flow communication between the wellbore and rich sources of hydrocarbon material within the subterranean formation, and thereby interfering with production of such hydrocarbon material from the subterranean formation.

[0004] For example, these phenomena have been reported in relation to the production of natural gas from coal seams within subterranean formations in Australia and Southeast Asia. The geology in these regions often has multiple layers of coal seams layered between interburden layers of clay. Unlike coal seams found in other regions of the world, the interburden layers in these regions are often unconsolidated, which means that the microscopic structure of the fines within the interburden is not cemented together. When this interburden layer is dry, it is very hard and appears to be cemented together, however when exposed to relatively low salinity water, this interburden layer quickly reacts with the water (or uptakes water) and disintegrates into an unconsolidated mound of sand or clay. This material may sink to the bottom of the well where it builds up, or it may get pumped out of the well where it builds up in surface handling equipment.

[0005] It has become common practice in these regions not to cement the pre-perforated casing in place throughout the coal seam / interburden zones. This was adopted because many coal seams are so permeable that they would accept the unset cement slurry directly, which would seal off the coals from subsequent production. It was thus decided to simply hang pre-perforated casing across these subterranean formations and only cement that casing which is placed across non- 2026208007   22 Jul 2026 productive subterranean zones which are typically closer to the surface. The result of this strategy is that coal seam water reacts with the unconsolidated interburden clays, and this causes the unconsolidated interburden clays to break down and slough off to the bottom of the well. Over time, these fines build up and cause problems, as described above. This is exacerbated in those instances where an extensive dewatering period is required prior to producing hydrocarbon material (e.g. natural gas) from the subterranean formation. SUMMARY

[0006] In one aspect, there is provided a cementitious slurry, for use in downhole cementing of a wellbore string within a wellbore, comprising: a hydraulic binder and a solid density modifying agent. The solid density modifying agent is characterized by a water absorption that is less than 30%, determined in accordance with the reference methods specified in European Standard EN 10976:2022, produced by the European Community for Standardization, and having the title: “Tests for mechanical and physical properties of aggregates - Part 6: Determination of particle density and water absorption.”

[0007] In another aspect, there is provided a method of cementing a wellbore string within a wellbore, comprising: producing a cementitious slurry characterized by a density of less than, or equal to, 1.05 kilograms per litre, wherein the producing is effected in the absence of foaming; and injecting the cementitious slurry into the wellbore, with effect that a downhole barrier-forming composition becomes emplaced within a space disposed between the wellbore string and a subterranean formation.

[0008] In another aspect, there is provided a cementitious slurry, for use in downhole cementing of a wellbore string within a wellbore, comprising: a hydraulic binder, and expanded glass. 2026208007   22 Jul 2026

[0009] In another aspect, there is provided a cementitious barrier, emplaced within a space disposed between a wellbore string and a subterranean formation, and characterized by a compressive strength of less than, or equal to, 250 psi.

[0010] In another aspect, there is provided a slurry base configured for combining with a solid density modifying agent for producing a cementitious slurry for use in downhole cementing of a wellbore string within a wellbore, comprising: a hydraulic binder, and an aqueous liquid (e.g. water), wherein the slurry base is characterized by a viscosity of greater than 25 centipoise, as measured by a FANNTM Viscometer Model 35 (manufactured by Fann Instrument Company of Houston, Texas, U.S.A.) at standard temperature and pressure conditions and using the B1 Bob at a rotation rate of 300 rpm which generates approximately 511s-1 of shear force to the fluid. In a related aspect, there is provided a cementitious slurry obtained from combining the slurry base and a solid density modifying agent.

[0011] In another aspect, there is provided a cementitious slurry, for use in downhole cementing of a wellbore string within a wellbore, comprising a hydraulic binder and a solid density modifying agent. The cementitious slurry has a density of less than, or equal to, 1.05 kilograms per litre. At least five (5) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from plus 16 mesh (Tyler Standard Sieve) to minus three (3) mesh (Tyler Standard Sieve).

[0012] In another aspect, there is provided a cementitious slurry, for use in downhole cementing of a wellbore string within a wellbore, comprising: a hydraulic binder, and a solid density modifying agent. The cementitious slurry has a density of less than, or equal to, 1.05 kilograms per litre. At least five (5) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from one (1) millimetre to six (6) millimetres. 2026208007   22 Jul 2026

[0013] In another aspect, there is provided a method of cementing a wellbore string within a wellbore, comprising: producing a cementitious slurry including a hydraulic binder and a solid density modifying agent, and injecting the cementitious slurry into the wellbore, with effect that a downhole barrier-forming composition becomes emplaced within a space disposed between the wellbore string and a subterranean formation. At least five (5) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from plus 16 mesh (Tyler Standard Sieve) to minus three (3) mesh (Tyler Standard Sieve).

[0014] In another aspect, there is provided a method of cementing a wellbore string within a wellbore, comprising: producing a cementitious slurry including a hydraulic binder and a solid density modifying agent, and injecting the cementitious slurry into the wellbore, with effect that a downhole barrier-forming composition becomes emplaced within a space disposed between the wellbore string and a subterranean formation. At least five (5) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from one (1) millimetre to six (6) millimetres. BRIEF DESCRIPTION OF DRAWINGS

[0015] The preferred embodiments will now be described with the following accompanying drawings, in which:

[0016] Figure 1 is a schematic illustration of an embodiment of a system in which is practised an embodiment of the process of the present disclosure;

[0017] Figure 2 is a schematic illustration of an embodiment of a system for producing reservoir fluid from a subterranean formation via a wellbore string within which is disposed a wellbore string including an uncemented portion, prior to any producing; 2026208007   22 Jul 2026

[0018] Figure 3 is a schematic illustration of an embodiment of the system illustrated in Figure 2, after production having been suspended due to accumulation of solid particulate material within the wellbore; and’

[0019] Figure 4 is a schematic illustration of an embodiment of the system illustrated in Figure 2, after remediation of the system following the suspension, the remediation including cementing of the uncemented wellbore string portion by an embodiment of a cementitious slurry of the present disclosure. DETAILED DESCRIPTION

[0020] There is provided a cementitious slurry for use downhole to facilitate production of reservoir fluid from a subterranean formation.

[0021] In some embodiments, for example, the cementitious slurry includes a hydraulic binder and a solid density modifying agent. The liquid component of the slurry includes water.

[0022] In some embodiments, for example, the hydraulic binder includes a calcium-based binder, such as, for example, a Class A cement, a Class B cement, a Class C cement, a Class D cement, a Class G cement, a Class H cement, or a Class J cement. In some embodiments, for example, the hydraulic binder includes a magnesia-based binder, such as, for example, a Sorel cement. These cement formulations may include additive salts containing counterions such as chloride, sulfate, phosphate, or carbonate ions.

[0023] In some embodiments, for example, the hydraulic binder is present in an amount that is within a range, and the range is from ten (10) weight %, based on the total weight of the slurry, to 60 weight %, based on the total weight of the slurry. In some of these embodiments, for example, the hydraulic binder is present in an amount that is within a range, and the range is from 20 weight %, based on the total weight of the slurry, to 50 weight %, based on the total weight of the slurry. In some of these embodiments, for example, the hydraulic binder is present 2026208007   22 Jul 2026 in an amount that is within a range, and the range is from 20 weight %, based on the total weight of the slurry, to 30 weight %, based on the total weight of the slurry. By limiting the quantity of the hydraulic binder that is present within the cementitious slurry, in some embodiments, for example, the cementitious slurry can be designed with a desired density.

[0024] In some embodiments, for example, the solid density modifying agent is particulate material.

[0025] In some embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 950 kg / m3. In some of these embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 900 kg / m3. In some of these embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 800 kg / m3. In some of these embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 700 kg / m3. In some of these embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 600 kg / m3. In some of these embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 500 kg / m3. In some of these embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 400 kg / m3.

[0026] In some embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying 2026208007   22 Jul 2026 agent, is characterized by a particle density of less than 950 kg / m3. In some of these embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 900 kg / m3. In some of these embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 800 kg / m3. In some of these embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 700 kg / m3. In some of these embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 600 kg / m3. In some of these embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 500 kg / m3. In some of these embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 400 kg / m3.

[0027] In some embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 950 kg / m3. In some of these embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 900 kg / m3. In some of these embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 800 kg / m3. In some of these embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 700 kg / m3. In some of these 2026208007   22 Jul 2026 embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 600 kg / m3. In some of these embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 500 kg / m3. In some of these embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 400 kg / m3.

[0028] In some embodiments, for example, the solid density modifying agent has a particle density of less than 950 kg / m3, only, such as, for example, less than 900 kg / m3, only, such as, for example, less than 800 kg / m3, only, such as, for example, less than 700 kg / m3, only, such as, for example, less than 600 kg / m3, only, such as, for example, less than 500 kg / m3, only, such as, for example, less than 400 kg / m3, only.

[0029] In some embodiments, for example, no more than 75 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density that is at least 1150 kg / m3.

[0030] In some embodiments, for example, no more than 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density that is less than 100 kg / m3. In some embodiments, for example, no more than 25 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density that is less than 100 kg / m3.

[0031] In some embodiments, for example, at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density that is within a range, and the range is from 300 kg / m3 to 500 kg / m3. In some embodiments, for example, at least 75 weight% of the solid density modifying agent, based on the total weight of the solid 2026208007   22 Jul 2026 density modifying agent, is characterized by a particle density that is within a range, and the range is from 300 kg / m3 to 500 kg / m3. In some embodiments, for example, at least 90 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density that is within a range, and the range is from 300 kg / m3 to 500 kg / m3.

[0032] In some embodiments, for example, the solid density modifying agent is, or includes, a lightweight aggregate. In some embodiments, for example, the solid density modifying agent is, or includes, expanded glass, such as PORAVERTM expanded glass granules produced by Denner Poraver GmbH of Postbauer-Heng, Germany.

[0033] In some embodiments, for example, the solid density modifying agent is characterized by a water absorption that is less than 30% (such as, for example, less than 20%), determined in accordance with the reference methods specified in European Standard EN 1097-6:2022, produced by the European Community for Standardization, and having the title: “Tests for mechanical and physical properties of aggregates - Part 6: Determination of particle density and water absorption.” By providing a solid density modifying agent characterized by relatively lower water absorption characteristics, in some embodiments, for example, production of a cementitious slurry, having a reduced density, is facilitated.

[0034] In some embodiments, for example, the solid density modifying agent is present in an amount that is within a range, and the range is from five (5) weight %, based on the total weight of the slurry, to 45 weight %, based on the total weight of the slurry. In some of these embodiments, for example, the solid density modifying agent is present in an amount that is within a range, and the range is from ten (10) weight %, based on the total weight of the slurry, to 40 weight %, based on the total weight of the slurry. In some of these embodiments, for example, the solid density modifying agent is present in an amount that is within a range, and the range is from 15 weight %, based on the total weight of the slurry, to 30 weight %, based on the total weight of the slurry. 2026208007   22 Jul 2026

[0035] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least 0.5 millimetres. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least 0.5 millimetres. In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least 0.5 millimetres. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least 0.5 millimetres. In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least 0.5 millimetres. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least 0.5 millimetres.

[0036] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least one (1) millimetre. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least one (1) millimetre. In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least one (1) millimetre. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least one (1) millimetre. In some of these 2026208007   22 Jul 2026 embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least one (1) millimetre. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least one (1) millimetre.

[0037] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least two (2) millimetres. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least two (2) millimetres. In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least two (2) millimetres. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least two (2) millimetres. In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least two (2) millimetres. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least two (2) millimetres.

[0038] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least three (3) millimetres. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least three (3) millimetres. In some 2026208007   22 Jul 2026 of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least three (3) millimetres. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least three (3) millimetres. In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least three (3) millimetres. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least three (3) millimetres.

[0039] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least four (4) millimetres. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least four (4) millimetres. In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least four (4) millimetres. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least four (4) millimetres. In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least four (4) millimetres. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least four (4) millimetres. 2026208007   22 Jul 2026

[0040] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least five (5) millimetres. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least five (5) millimetres. In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least five (5) millimetres. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least five (5) millimetres. In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least five (5) millimetres. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least five (5) millimetres.

[0041] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least six (6) millimetres. In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least six (6) millimetres. In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least six (6) millimetres. In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least six (6) millimetres. In some of these embodiments, for example, at least 50 weight % of the solid density modifying 2026208007   22 Jul 2026 agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least six (6) millimetres. In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least six (6) millimetres.

[0042] In some embodiments, for example, at least five (5) weight % (such as, for example, at least ten (10) weight %, such as, for example, at least 15 weight %, such as, for example, at least 20 weight%) of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from one (1) millimetre to six (6) millimetres. In some embodiments, for example, at least five (5) weight % (such as, for example, at least ten (10) weight %, such as, for example, at least 15 weight %, such as, for example, at least 20 weight%) of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from two (2) millimetres to four (4) millimetres. Referring to Figures 1 and 2, by employing a solid density modifying agent, which is characterized by the above-described particle sizes, within the cementitious slurry in the weight percentages specified, in some embodiments, for example, the solid densifying modifying agent is effective in sufficiently occluding passages, extending into the subterranean formation 100 from an interface that is defined between the subterranean formation 100 and an annular space 104 disposed between the wellbore string 200 and the subterranean formation 100, such that invasion of the cementitious slurry, into the subterranean formation 100, is sufficiently mitigated (or prevented), such that interference to hydrocarbon production, from the subterranean formation 100, by the cementitious slurry, is sufficiently mitigated.

[0043] In some embodiments, for example, no more than one (1) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of at least ten (10) millimetres. 2026208007   22 Jul 2026

[0044] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 32 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 32 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 32 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 32 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 32 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 32 mesh (Tyler Standard Sieve).

[0045] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 16 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 16 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 16 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 16 mesh (Tyler Standard 2026208007   22 Jul 2026 Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 16 mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 16 mesh (Tyler Standard Sieve).

[0046] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus nine (9) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus nine (9) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus nine (9) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus nine (9) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus nine (9) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus nine (9) mesh (Tyler Standard Sieve).

[0047] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus eight (8) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % 2026208007   22 Jul 2026 of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus eight (8) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus eight (8) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus eight (8) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus eight (8) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus eight (8) mesh (Tyler Standard Sieve).

[0048] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus seven (7) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus seven (7) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus seven (7) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus seven (7) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus seven (7) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 2026208007   22 Jul 2026 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus seven (7) mesh (Tyler Standard Sieve).

[0049] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus six (6) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus six (6) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus six (6) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus six (6) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus six (6) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus six (6) mesh (Tyler Standard Sieve).

[0050] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus five (5) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus five (5) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid 2026208007   22 Jul 2026 density modifying agent, is characterized by a particle size of plus five (5) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus five (5) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus five (5) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus five (5) mesh (Tyler Standard Sieve).

[0051] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus four (4) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus four (4) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus four (4) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus four (4) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus four (4) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus four (4) mesh (Tyler Standard Sieve). 2026208007   22 Jul 2026

[0052] In some embodiments, for example, at least ten (10) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus three (3) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 20 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus three (3) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 30 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus three (3) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 40 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus three (3) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 50 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus three (3) mesh (Tyler Standard Sieve). In some of these embodiments, for example, at least 60 weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus three (3) mesh (Tyler Standard Sieve).

[0053] In some embodiments, for example, at least five (5) weight % (such as, for example, at least ten (10) weight %, such as, for example, at least 15 weight %, such as, for example, at least 20 weight%, such as, for example, at least 30 weight%, such as, for example, at least 40 weight %, such as, for example, at least 50 weight %, such as, for example, at least 60 weight %) of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from plus 16 mesh (Tyler Standard Sieve) to minus three (3) mesh (Tyler Standard Sieve). In some embodiments, for example, at least five (5) weight % (such as, for example, at least ten (10) weight %, such as, for example, at least 15 weight %, such as, for example, at least 20 weight% such as, for example, at least 30 weight%, such as, for example, at least 40 weight %, such as, for example, at least 50 weight %, 2026208007   22 Jul 2026 such as, for example, at least 60 weight %) of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from plus nine (9) mesh to minus five (5) mesh. Referring to Figures 1 and 2, by employing a solid density modifying agent, which is characterized by the above-described particle sizes, within the cementitious slurry in the weight percentages specified , in some embodiments, for example, the solid densifying modifying agent is effective in sufficiently occluding passages, extending into the subterranean formation 100 from an interface that is defined between the subterranean formation 100 and an annular space 104 disposed between the wellbore string 200 and the subterranean formation 100, such that invasion of the cementitious slurry, into the subterranean formation 100, is sufficiently mitigated (or prevented), such that interference to hydrocarbon production, from the subterranean formation 100, by the cementitious slurry, is sufficiently mitigated.

[0054] In some embodiments, for example, no more than one (1) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size of plus 2-1 / 2 mesh.

[0055] In some embodiments, for example, the ratio of the weight of the solid density modifying agent to the weight of the hydraulic binder is within a range, and the range is from 0.3 to 1. In some of these embodiments, for example, the ratio of the weight of the solid density modifying agent to the weight of the hydraulic binder is within a range, and the range is from 0.7 to 1. In some of these embodiments, for example, the ratio of the weight of the solid density modifying agent to the weight of the hydraulic binder is within a range, and the range is from 1.5 to 1.

[0056] In some embodiments, for example, the cementitious slurry includes from 20 weight % water, based on the total weight of the cementitious slurry, to 70 weight % water, based on the total weight of the cementitious slurry. In some of these embodiments, for example, the cementitious slurry includes from 35 weight 2026208007   22 Jul 2026 % water, based on the total weight of the cementitious slurry, to 55 weight % water, based on the total weight of the cementitious slurry. In some of these embodiments, for example, the cementitious slurry includes from 40 weight % water, based on the total weight of the cementitious slurry, to 50 weight % water, based on the total weight of the cementitious slurry.

[0057] In some embodiments, for example, the cementitious slurry has a density of less than, or equal to, 1.05 kilograms per litre, such as, for example, less than, or equal to, 1.0 kilograms per litre, such as, for example, less than, or equal to, 0.95 kilograms per litre, such as, for example, less than, or equal to, 0.94 kilograms per litre, such as, for example, less than, or equal to, 0.92 kilograms per litre, such as, for example, less than, or equal to, 0.90 kilograms per litre, such as, for example, less than, or equal to, 0.88 kilograms per litre, such as, for example, less than, or equal to, 0.86 kilograms per litre, such as, for example, less than, or equal to, 0.84 kilograms per litre, such as, for example, less than, or equal to, 0.82 kilograms per litre, such as, for example, less than, or equal to, 0.80 kilograms per litre, such as, for example, less than, or equal to, 0.78 kilograms per litre, such as, for example, less than, or equal to, 0.76 kilograms per litre. By providing a cementitious slurry with a reduced density, in some embodiments, for example, invasion of the subterranean formation, by the cementitious slurry is mitigated, thereby mitigating interference by the cementitious slurry to the production of hydrocarbon material from the subterranean formation. In some embodiments, for example, the cementitious slurry has a density that is greater than 0.5 kilograms per litre.

[0058] In some embodiments, for example, there is provided a slurry base. The slurry base is configured for co-operating with solid density modifying agent such that, in response to a combining of the slurry base and the solid density modifying agent, the cementitious slurry is produced. In some embodiments, for example, the slurry base is a cementitious slurry precursor, and the combining includes an admixing of the cementitious slurry precursor with the solid density modifying agent. The slurry base includes the hydraulic binder and an aqueous 2026208007   22 Jul 2026 liquid (e.g. water) and is characterized by a viscosity of at least 25 centipoise, such as, for example, at least 30 centipoise, such as, for example, at least 35 centipoise, such as, for example, at least 40 centipoise, such as, for example, at least 45 centipoise, such as, for example, at least 50 centipoise. In some of these embodiments, for example, the slurry base has a viscosity of less than 500 centipoise, such as, for example, less than 400 centipoise, such as, for example, less than 300 centipoise, such as, for example, less than 200 centipoise, such as, for example, less than 100 centipoise. In some of these embodiments, for example, the viscosity of the slurry base is within a range, and the range is from 25 centipoise to 500 centipoise, such as, for example, from 30 centipoise to 400 centipoise, such as, for example, from 35 centipoise to 300 centipoise, such as, for example, from 40 centipoise to 200 centipoise, such as, for example, from 45 centipoise to 200 centipoise. All of the specified values for viscosity of the slurry base, herein, are based on measurements by a FANNTM Viscometer Model 35 (manufactured by Fann Instrument Company of Houston, Texas, U.S.A.) at standard temperature and pressure conditions and using the B1 Bob at a rotation rate of 300 rpm which generates approximately 511s-1 of shear force. In some embodiments, for example, by providing the slurry base, characterized by the above-described viscosity, the co-operation of the slurry base with the solid density modifying agent, for which the slurry base is configured, is such that, in response to the combining of the slurry base and the solid density modifying agent, a cementitious slurry is produced such that suspension of the solid density modifying agent, within the cementitious slurry (while in a static state, without agitation) is encouraged, during the curing time within which the cementitious slurry transitions to the cementitious barrier, such that separation of the solid density modifying agent, from the cementitious slurry, due to gravity settling or floatation, is retarded. In this respect, in some embodiments, for example, configuring the slurry base, to obtain the above-described viscosity, retards the above-described separation of the solid density modifying agent, from the cementitious slurry, due to gravity settling or floatation, for cementitious slurries that comprise of a solid density modifying agent that includes lightweight solid particulate matter, such as, for example, a cementitious slurry obtained in response to the combining of the 2026208007   22 Jul 2026 slurry base and the solid density modifying agent that is characterized in that at least one (1) weight % (such as, for example, at least five (5) weight %, such as, for example, at least ten (10) weight %, such as, for example, at least 15 weight%) of the solid density modifying agent, based on the total weight of the solid density modifying agent, has a particle density that is within a range, and the range is from 300 kg / m3 to 500 kg / m3. In some of these embodiments, for example, additionally, by providing the slurry base, characterized by the abovedescribed viscosity, in response to the combining of the slurry base and the solid density modifying agent, a cementitious slurry is produced such that suspension of the hydraulic binder within the cementitious slurry (in a static state, without agitation), is also encouraged, during the curing time within which the cementitious slurry transitions to the cementitious barrier, such that separation of the hydraulic binder, from the cementitious slurry, due to gravity settling, is also retarded. In some embodiments, for example, the slurry base further includes a viscosifying agent. Suitable viscosifying agents include viscosifying agents that are based on: (i) xanthan gum, or its derivatives, (ii) guar gum, or its derivatives, (iii) cellulose, or its derivatives, (iv) polyacrylamide derivatives, (v) polyacrylate derivatives, or (vi) bentonite.

[0059] In some embodiments, for example, a cementitious slurry is provided, and the cementitious slurry is obtained in response to combining the abovedescribed slurry base with a solid density modifying agent, wherein at least one (1) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density that is within a range, and the range is from 300 kg / m3 to 500 kg / m3.

[0060] In some embodiments, for example, the cementitious slurry further includes one or more of a cement salt, a hardener, and a setting time retarder. In some embodiments, for example, suitable cement salts include calcium chloride, magnesium chloride, calcium sulfate, magnesium sulfate, calcium carbonate, and magnesium carbonate. In some embodiments, for example, suitable setting time retarders include boric acid, citric acid, lignosulfate derivatives, cellulosic polymer 2026208007   22 Jul 2026 derivatives, sugars, such as, for example, glucose and sucrose, phosphates, and tartaric acid.

[0061] In some embodiments, for example, there is provided a method of producing a cementitious slurry characterized by a density of less than, or equal to, 1.05 kilograms per litre, wherein the producing is effected in the absence of foaming. In this respect, in some embodiments, for example, the producing of the cementitious slurry includes admixing of at least the hydraulic binder, the solid density modifying agent, and an aqueous liquid (e.g. water) to produce an admixture, and the absence of foaming includes an absence of foaming of the admixture. In some embodiments, for example, the admixing includes admixing of other components, such as, for example, one or more of the cement salt, the hardener, and the setting time retarder.

[0062] In some embodiments, for example, upon curing, the cementitious slurry is converted to a cement barrier, and, in some of these embodiments, for example, the cement has a compressive strength that is less than, or equal to, 500 psi, such as, for example, less than, or equal to, 450 psi, such as, for example, less than, or equal to, 400 psi, such as, for example, less than, or equal to, 350 psi, such as, for example, less than, or equal to, 300 psi, such as, for example, less than, or equal to, 250 psi, such as, for example, less than, or equal to, 200 psi. In some embodiments, for example, the cement has a compressive strength that is no less than 100 psi.

[0063] In some embodiments, for example, there is provided a cementitious barrier, emplaced within a space disposed between a wellbore string and a subterranean formation, and characterized by a compressive strength that is less than, or equal to, 500 psi, such as, for example, less than, or equal to, 450 psi, such as, for example, less than, or equal to, 400 psi, such as, for example, less than, or equal to, 350 psi, such as, for example, less than, or equal to, 300 psi, such as, for example, less than, or equal to, 250 psi. In some embodiments, for example, the cementitious barrier has a compressive strength that is no less than 100 psi. 2026208007   22 Jul 2026

[0064] By providing a cement with a lower compressive strength, flow communication (such as, for example, by perforation) between the subterranean formation and the wellbore, may be established via a jetting operation or a low-pressure hydraulic fracturing operation, versus more elaborate and costly procedures which may required specialized equipment, as explained above.

[0065] Referring to Figure 1, in some embodiments, for example, a method is provided for cementing a wellbore string 200, disposed within a wellbore 102 that extends into a subterranean formation 100, to the subterranean formation 100. In some embodiments, for example, the wellbore string 200 is in the form of a casing string. In some embodiments, for example, the casing string is defined by jointed segments of pipe. The jointed segments of pipe typically have threaded connections. Typically, a wellbore 102 contains multiple intervals of concentric casing strings, successively deployed within the previously run casing. Casing strings typically run back up to the surface 10. In some embodiments, for example, the casing string is set short of total depth. Hanging off from the bottom of the casing string, with a liner hanger or packer, is a liner string. The liner string can be made from the same material as the casing string, but, unlike the casing string, the liner string may not extend back to the wellhead.

[0066] In some embodiments, for example, a cementitious barrier 202 is emplaced within an annular region 104 disposed between the wellbore string 200 and the subterranean formation 100, such that the cementitious barrier 202 is disposed within the annular region 104. The cementitious barrier 202 and the wellbore string 200 co-operate to define a wellbore barrier configuration 204. In some embodiments, for example, the cementitious barrier 202 defines a passage configuration, and such passage configuration is defined by at least one passage (in the illustrated embodiment, for example, six (6) passages 106A-F are shown), and each one of the at least one passage, independently, extends through the cementitious barrier 202, and the wellbore string 200, and the wellbore string 200 also defines a passage configuration, and such passage configuration is defined by 2026208007   22 Jul 2026 at least one passage (in the illustrated embodiment, for example, six (6) passages 108A-F are shown), and each one of the at least one passage, independently, extends through the wellbore string 200. The passage configuration, of the cementitious barrier, co-operates with the passage configuration, of the wellbore string 200, for defining a passage configuration of the wellbore barrier configuration 204. In this respect, in the illustrated embodiment, for example, the passage configuration, of the wellbore barrier configuration 204, is defined by six (6) passages 110A-F.

[0067] The wellbore 102 is disposed in flow communication, via the passage configuration of the wellbore barrier configuration 204, or is selectively emplaceable into flow communication via the passage configuration of the wellbore barrier configuration 204, with the subterranean formation 100. In some embodiments, for example, when disposed in flow communication with the subterranean formation 100, the wellbore 102 is disposed for receiving reservoir fluid flow from the subterranean formation 100 for producing the reservoir fluid. In some embodiments, for example, when disposed in flow communication with the subterranean formation 100, the wellbore is disposed for injecting fluid into the subterranean formation 100 (e.g. during a hydraulic fracturing operation).

[0068] In some embodiments, for example, the passage configuration (e.g. passages 106A-F), of the cementitious barrier 202, is obtained by perforating the cementitious barrier 202, in-situ within the wellbore 102. In some embodiments, for example, the passage configuration is effected by jetting through the cementitious barrier 202. In some embodiments, for example, the passage configuration is effected by hydraulic fracturing. In some embodiments, for example, the passage configuration is effected by jetting with an acid solution.

[0069] In some embodiments, for example, the method of emplacing the cementitious barrier 202 includes injecting the cementitious slurry into the annulus 104 disposed between the wellbore string 200 and the subterranean formation 100, with effect that, upon curing of the cementitious slurry, the cementitious barrier 202 (e.g. cement) becomes emplaced within the annular space 104 disposed 2026208007   22 Jul 2026 between the wellbore string 200 and the subterranean formation 100. In some embodiments, for example, prior to the injecting, the cementitious slurry is produced, and the producing includes admixing of at least the hydraulic binder, the solid density modifying agent, and an aqueous liquid (e.g. water) to produce an admixture. In some embodiments, for example, the producing of the cementitious slurry is effected in the absence of foaming of the admixture. In some embodiments, for example, after the curing of the cementitious slurry, the passage configuration, of the cementitious barrier 202, is established, such as, for example, via the perforating. In some embodiments, for example, the passage configuration (e.g. passages 106A-F), of the cementitious barrier 202, exists as a characteristic of the cementitious barrier itself.

[0070] In some embodiments, for example, the passage configuration, of the wellbore string 200, is established prior to installation of the wellbore string 200.

[0071] In those embodiments where the passage configuration, of the wellbore string 200, is established prior to installation of the wellbore string 200 within the wellbore 102, in some embodiments, for example, the wellbore string 200, with a pre-existing passage configuration is deployed within the wellbore 102, cemented, with effect that the cementitious barrier 202 is established. After the cementitious barrier 202 is established, the cementitious barrier 202 is then perforated (as described above), with effect that the passage configuration of the cementitious barrier 202 is established, and with additional effect that the passage configuration of the wellbore barrier configuration 204 is also established. The perforating includes perforating via the pre-existing passage configuration of the wellbore string 200, wherein such perforating is effected via the passage configuration of the wellbore string 200. In some embodiments, for example, the perforating also includes perforating of both of the wellbore string 200 and the cementitious barrier 202, such that new perforations are established and extend through the wellbore string 200, such that the passage configuration, of the wellbore barrier configuration, includes a passage configuration established by the perforating of both of the wellbore string 200 and the cementitious barrier 202. In 2026208007   22 Jul 2026 some of these embodiments, for example, the wellbore string 200, which is deployed within the wellbore 102, is a pre-perforated wellbore string.

[0072] In those embodiments where the passage configuration, of the wellbore string 200, is established prior to installation of the wellbore string 200, in some embodiments, for example, the wellbore string 200 includes a plurality of downhole valves (e.g. sliding sleeves). In such embodiments, for example, the wellbore string 200 is deployed within the wellbore 102, and cemented, with effect that a cementitious barrier 202 is established. To effect the perforating of the cementitious barrier 202, the downhole valves are opened, thereby revealing, for each one of the valves, independently, a respective port configuration (defined by at least one port), which, collectively, define the passage configuration of the wellbore string. For each one of the downhole valves, independently, after opening of the valve, the perforating of the cementitious barrier is effected through the port configuration of the valve, with effect that the passage configuration of the cementitious barrier 202 is established, and with additional effect that the passage configuration of the wellbore barrier configuration 204 is established. In this respect, the wellbore barrier configuration is selectively emplaceable, via the passage configuration of the wellbore barrier configuration 204, into flow communication with the subterranean formation 100 in response to the opening of one or more of the downhole valves.

[0073] In some embodiments, for example, the cementitious slurry is injected into a wellbore 102 with an uncemented, perforated wellbore string 200, through which production of reservoir fluid (such as, for example, reservoir fluid including hydrocarbon material, defined by at least one hydrocarbon compound) has been ongoing, but which has now been suspended due to unacceptable production rate or unacceptable production quality.

[0074] Referring to Figure 2, in some embodiments, for example, uncemented wellbore strings 200 are employed within a system 5 for producing hydrocarbon material from formations with relatively permeable hydrocarbon-rich seams (such as, for example, coal seams), so as to avoid invasion of the hydrocarbon-rich 2026208007   22 Jul 2026 seams by a cementitious slurry during wellbore string cementing operations, which would at least interfere with flow communication between the reservoir fluid producing subterranean formation 100 and the wellbore 102. In the illustrated embodiment, for example, three such hydrocarbon-rich seams 105A, 105B, and 105C are shown. In some embodiments, for example, a portion 200A of the wellbore string 200, disposed closer to the surface 10 (e.g. surface casing), extends across non-productive zones of the subterranean formation 100, and is, typically, cemented to establish a pre-existing cementitious barrier 201, while a portion 200B of the wellbore string 200 (e.g. a pre-perforated wellbore string portion), extending across productive zone of the subterranean formation 100, is hung from the portion 200A and is uncemented. Referring to Figure 3, in such cases of uncemented completion, while the subterranean formation 100 is producing reservoir fluid from the formation 100 via the system 5, formation water migrates into the annular region between the formation and the wellbore string, and interacts (e.g reacts) with subterranean interburden layers disposed between the hydrocarbon-rich seams 105A-C, with effect that the interburden layer disintegrates into solid particulate matter 114 (e.g. fines) which accumulates at least within the bottom of the wellbore 102. In some embodiments, for example, the accumulated solid particulate matter interferes with operation of downhole production equipment (e.g. rotating equipment). In some embodiments, for example, the solid particulate matter may reach the surface and interfere with the operation of surface reservoir fluid handling equipment. In some embodiments, for example, the accumulated solid particulate matter at least partially occludes other hydrocarbon-rich seams within the wellbore. In such cases, remedial efforts are required before resuming production, and, in some embodiments, for example, such remedial efforts include emplacing the cementitious barrier 202 within the annulus 104 between the perforated wellbore string portion 200B and the subterranean formation 100 to mitigate contact of formation water with reactive subterranean interburden formations 112A, 112B, while avoiding invasion of the cementitious slurry into the hydrocarbon-rich seams 104 within the wellbore. In this respect, in some embodiments, for example, a method is provided for producing the reservoir fluid from a subterranean formation 100 which defines a formation interface surface 101 2026208007   22 Jul 2026 at an interface between the subterranean formation 100 and the annular region 104 between the subterranean formation 100 and the wellbore string 200. In some embodiments, for example, the formation interface 101 defines at least one permeable formation interface-defining surface portion which effects flow communication between the hydrocarbon-rich seams 104 within the subterranean formation 100 and the annulus 104. Each one of the at least one permeable formation interface-defining surface portion, independently, is characterized by a permeability of at least 0.01 Darcies. In some embodiments, for example, each one of at least one permeable formation interface-defining surface portion, independently, is a hydrocarbon-rich seam. In those embodiments where the subterranean formation is a coal seam gas formation, in such embodiments, for example, each one of at least one permeable formation interface-defining surface portion, independently, is defined by a coal seam. The method includes producing reservoir fluid via a wellbore 102, within which is disposed an uncemented, perforated wellbore string 200, such that the producing includes: producing reservoir fluid from the subterranean formation 100, via the uncemented, perforated wellbore string 200 and into the wellbore, and from the wellbore 102 to the surface 10; suspending the producing; and injecting the cementitious slurry into the annulus disposed between the uncemented perforated wellbore string 200 and the subterranean formation 100, with effect that a downhole cementitious barrier 202 (e.g. cement) becomes emplaced within the annulus upon curing of the cementitious slurry.

[0075] In some embodiments, for example, the method further includes, after the suspending, and prior to the injecting of the cementitious slurry, cleaning out accumulated solid particulate material 114 from the wellbore 102 (including the annulus 104). Such procedures may include preparing a salt solution, such as, for example, a salt solution of potassium chloride, sodium chloride, tetramethyl ammonium chloride, choline chloride, and / or other chemical additives, that prevents water uptake into clays. This solution will be pumped at a high flowrate 2026208007   22 Jul 2026 from the bottom of the well where it will lift the deposited clays up and out of the well.

[0076] In some embodiments, for example, the method further includes, after the emplacement of the cementitious barrier 102 within the annulus 104, the jetting of at least the emplaced cementitious barrier 202 with effect that the passage configuration, of the cementitious barrier 202, and with additional effect that the passage configuration of the wellbore barrier configuration 204 is established, such that flow communication is established between the wellbore 102 and the subterranean formation 100 via the passage configuration of the wellbore barrier configuration 204.

[0077] In some embodiments, for example, at least some of the jetting is of the cementitious barrier 202 only, in which case, the established passage configuration, of the wellbore barrier configuration 204, includes one or more passages, wherein each one of the one or more passages, independently, includes a combination of the passage configuration, of the cementitious barrier, obtained by the perforating, and a pre-existing passage configuration (defined by perforations) of the perforated wellbore string portion 200B.

[0078] Referring to Figure 4, in some embodiments, for example, at least some of the perforating includes perforating of both of the cementitious barrier 202 and the perforated wellbore string portion 200B, such that, in some embodiments, for example, at least some of the perforating is of both of the cementitious barrier 202 and the perforated wellbore string portion 200B, such that the perforating establishes the passage configuration of the cementitious barrier 202, and such that the perforating also establishes new perforations within the perforated wellbore string portion 202B, such that the passage configuration, of the wellbore string 200, includes pre-existing perforation and new perforations. In the illustrated embodiment, for example, the passage configuration, of the cementitious barrier 102, includes ten (10) perforated passages 106A-J, and the passage configuration, of the wellbore string 200, includes six (6) pre-existing perforated passage 108A-F, and also includes four new perforated passage 108G-J. The passage configuration, 2026208007   22 Jul 2026 of the cementitious barrier 202, co-operates with the passage configuration, of the wellbore string 200, to establish the passage configuration, of the wellbore barrier configuration 204, for establishing the flow communication, between the wellbore 102 and the subterranean formation 100. In this respect, in the illustrated embodiment, for example, the passage configuration, of the wellbore barrier configuration 204, is defined by ten (10) passages 110A-J.

[0079] In some embodiments, for example, the method further includes, after the perforating, resuming the production of the reservoir fluid.

[0080] Further embodiments will now be described in further detail with reference to the following non-limitative examples. Examples 1 to 16

[0081] For all blends, the viscosifying agent (in this case, the xanthan gum) was first hydrated in 500mL of water for at least three minutes and mixed at approximately 700 rotations per minute. The cement retarder (boric acid in this case) was then added and mixed for 3 minutes. The magnesium sulfate or chloride salt was then added and blended for three minutes. The hydraulic binder (magnesium oxide) was then added and blended for another three minutes. Finally the lightweight aggregate was added with continuous mixing until blended. The slurry density was measured by weighing a known volume of slurry. Plugs were allowed to set at the desired temperature then demolded and remeasured for diameter, height, and mass before crush testing. Table 1: Examples of magnesium based cement formulations with low densities and employing different amounts of light weight expanded glass aggregate. All mass percentages are based on the total mass of slurry. ("Example % Water % Xanthan gum % Boric acid % Magnesium salt % Mg oxide % Expanded glass (0.51 mm) % Expanded glass (1-2 mm) % Expanded glass (2-4 mm) Approx. setting time (hrs.); (temp.) Plug density (kg / L) Crush strength (psi) 1 41.47 0.15 0.41 15.18 (MgSO4^7H O) 24.88 - 8.96 8.96 6.0 (20°C) 0.943 245 O 2 00 41.30 0.14 0.83 15.11 (MgSO4^7H2 O) 24.78 - 8.92 8.92 9.0 (20°C) 0.928 244 S 3 41.30 0.14 0.83 15.11(MgSO4 •7H2O) 24.78 - 8.92 8.92 3.0 (30°C) 0.928 290 v© O 4 41.30 0.14 0.83 15.11 (MgSO4^7H2 O) 24.78 - 8.92 8.92 1.5 (40°C) 0.928 247 5 41.30 0.14 0.83 15.10 (MgSO4^7H2 O) 24.76 - 8.91 8.91 0.75 (50°C) 0.943 231 6 41.30 0.14 0.83 15.11 (MgCl2• 6H2O ) 24.78 - 8.92 8.92 11 (20°C) 0.928 320 7 41.30 0.14 0.83 15.11 (MgCl2-6H2O ) 24.78 - 8.92 8.92 5 (30°C) 0.928 333 8 46.78 - 0.78 12.16 (MgCO3) 23.42 - 8.92 8.92 5 (30°C) 0.881 462 9 42.38 0.15 - 15.51 (MgSO4^7H2 O) 25.43 - 12.04 4.49 - 0.955 580 10 43.33 0.13 - 13.22 (MgSO4^7H2 O) 21.66 - 10.83 10.83 - 0.814 211 11 39.72 0.14 - 14.24 (MgSO4^7H2 O) 23.35 - - 19.46 - 0.836 182 12 32.15 0.11 - 18.14 (MgSO4^7H2 O) 30.18 12.07 - 9.05 - 0.973 838 13 41.30 - - 12.39 (MgCO3) + 15.11 (MgSO4^7H2 O) 12.39 - 8.92 8.92 2 (40°C) 0.90 54 14 39.98 0.14 4.0 14.63 (MgSO4^7H2 O) 23.99 - 8.63 8.63 0.5 (90°C) 0.93 56 15 39.98 0.14 4.0 14.63 (MgSO4^7H2 O) 23.99 - 8.63 8.63 >12 (20°C) 0.93 271 16 43.33 0.13 - 13.22 (MgSO4^7H2 O) 21.66 - 10.83 10.83 - 0.814 208 2026208007   22 Jul 2026 Examples 17 to 24

[0082] For all blends, the viscosifying agent (xanthan gum in this case) was first dissolved in 500mL of water for at least three minutes and mixed at approximately 700 rotations per minute. The hydraulic binder (Class G cement) was then added and blended for three minutes. Finally the expanded glass lightweight aggregate was added to the blend with continuous mixing until blended. The slurry density was measured by weighing a known volume of slurry. Plugs were allowed to set at the desired temperature then demolded and remeasured for diameter, height, and mass before crush testing. Table 2: Examples of calcium based cement formulations employing Class G cement and different amounts of lightweight expanded glass aggregate. All mass percentages are based on the total mass of slurry. Example % Water % Xanthan gum % Class G cement % Expanded glass (0.250.5 mm) % Expanded glass (0.5-1 mm) % Expanded glass (1-2 mm) % Expanded glass (2-4 mm) Plug density (kg / L) Crush strength (psi) 17 49.10 0.17 29.50 3.53 3.53 3.53 10.61 0.94 361 18 49.93 0.15 20.80 - 8.32 8.32 12.48 0.735 32 19 41.47 0.12 34.56 ^- 6.91 10.02 6.91 0.867 175 20 28.15 - 51.18 - 18.03 - 2.56 1.07 805 21 38.86 0.14 38.86 3.89 3.89 3.89 9.71 1.03 291 22 38.86 0.14 38.86 - 3.89 7.77 9.71 0.92 385 23 38.86 0.14 38.86 - 7.77 3.89 9.71 0.98 378 24 38.86 0.14 38.86 - - 7.77 13.60 0.86 404 Examples 25 to 29

[0083] Five slot test caps, for slot flow tests, were fabricated by cutting slots of varying widths—0.5 mm, 1.5 mm, 2.5 mm, 3.5 mm, and 4.5 mm—into the base of standard 2” steel pipe caps. Each slot measured approximately 1” in length. These caps were individually threaded onto one end of a 6” long, 2” diameter pipe with NPT threads on both ends. The opposite end of the pipe was sealed with a pressure cap containing a ¼” NPT fitting connected via safety equipment to a 2026208007   22 Jul 2026 nitrogen cylinder equipped with a pressure regulator. For each test, the pipe assembly was filled with 195 grams of a cementitious slurry containing solid density modifying agents. The slurry was poured in with the selected slotted cap attached at the bottom, then sealed with the pressure cap. Nitrogen pressure was applied at 300 psi for five minutes. Slurry that escaped through the slot was collected and weighed, allowing calculation of percentage loss relative to the total mass initially added. Each slot width was tested independently. The slurry used in this evaluation corresponds to Example 5, with a solid plug density of 0.943 kg / L and an approximate crush strength of 231 psi. It comprised equal parts (by mass) of two solid density modifying agents: 50% in the 1-2 mm size range and 50% in the 2-4 mm range. The results, of the slot tests, are summarized below in Table 3. Table 3: Examples showing how the solid density modifying agent prevents the cementitious slurry from passing through the slots. All examples used the formulation described in example 5 from above. Example Width of slots in test caps Mass loss through the slot Percent slurry loss through the slot 25 0.5 mm 2 g 1.0 % 26 1.5 mm 3 g 1.5 % 27 2.5 mm 7 g 3.6 % 28 3.5 mm 13 g 6.7 % 29 4.5 mm 147 g 75.4   %

[0084] The preceding discussion provides many example embodiments. Although each embodiment represents a single combination of inventive elements, other examples may include all suitable combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, other remaining combinations of A, B, C, or D, may also be used. 2026208007   22 Jul 2026

[0085] Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations could be made herein.

[0086] Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

[0087] As can be understood, the examples described above and illustrated are intended to be examples only. The invention is defined by the appended claims.

[0088] The term “comprising” as used in this specification and claims means “consisting at least in part of”. When interpreting statements in this specification and claims which include the term “comprising”, other features besides the features prefaced by this term in each statement can also be present. Related terms such as “comprise”, “comprises”, and “comprised” are to be interpreted in a similar manner.

[0089] In this specification where reference has been made to other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents, or such sources of information, is not to be construed as an admission that such documents, or such 2026208007   22 Jul 2026 sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

Claims

1. A cementitious slurry, for use in downhole cementing of a wellbore string within a wellbore, comprising:a hydraulic binder; anda solid density modifying agent characterized by a water absorption that is less than 30%, determined in accordance with the reference methods specified in European Standard EN 1097-6:2022, produced by the European Community for Standardization, and having the title: “Tests for mechanical and physical properties of aggregates - Part 6: Determination of particle density and water absorption.”2. The cementitious slurry as claimed in claim 1;wherein:the hydraulic binder is present in an amount that is within a range, and the range is from ten (10) weight %, based on the total weight of the slurry, to 60 weight %, based on the total weight of the slurry; andthe solid density modifying agent is present in an amount that is within a range, and the range is from five (5) weight %, based on the total weight of the slurry, to 45 weight %, based on the total weight of the slurry.

3. The cementitious slurry as claimed in claim 1 or 2;wherein:the ratio of the weight of the solid density modifying agent to the weight of the hydraulic binder is within a range, and the range is from 0.3 to 1.

4. The cementitious slurry as claimed in any one of claims 1 to 3;wherein:the solid density modifying agent is expanded glass.

5. The cementitious slurry as claimed in any one of claims 1 to 4;wherein:at least 50 weight% of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle density of less than 950 kg / m3.

6. The cementitious slurry as claimed in any one of claims 1 to 5;wherein:the cementitious slurry has a density of less than, or equal to, 1.05 kilograms per litre.

7. The cementitious slurry as claimed in claim 6;wherein:at least five (5) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, is characterized by a particle size that is within a range, and the range is from one (1) millimetre to six (6) millimetres.

8. The cementitious slurry as claimed in any one of claims 1 to 7further comprising:a viscosifying agent.

9. The cementitious slurry as claimed in any one of claims 1 to 8;wherein:the hydraulic binder is a magnesia-based binder.

10. A method of cementing a wellbore string within a wellbore, comprising:injecting the cementitious slurry, as claimed in any one of claims 1 to 9, into the wellbore, with effect that a downhole barrier-forming composition, derived from the cementitious slurry, becomes emplaced within a space disposed between the wellbore string and a subterranean formation.

11. A slurry base configured for combining with a solid density modifying agent for producing a cementitious slurry for use in downhole cementing of a wellbore string within a wellbore, comprising:a hydraulic binder; andan aqueous liquid;wherein:the slurry base is characterized by a viscosity of greater than 25 centipoise, as measured by a FANNTM Viscometer Model 35 (manufactured by Fann Instrument Company of Houston, Texas, U.S.A.) at standard temperature and pressure conditions and using the B1 Bob at a rotation rate of 300 rpm which generates approximately 511s-1 of shear force to the fluid.

12. The slurry base as claimed in claim 11;wherein:the slurry base is configured for co-operating with solid density modifying agent such that, in response to a combining of the slurry base and the solid density modifying agent, the cementitious slurry is produced.

13. The slurry base as claimed in claim 12;wherein:the co-operation of the slurry base with the solid density modifying agent, for which the slurry base is configured, is such that, in response to the combining of the slurry base and the solid density modifying agent, a cementitious slurry is produced such that suspension of the solid density modifying agent, within the cementitious slurry is encouraged, during the curing time within which the cementitious slurry transitions to the cementitious barrier, such that separation of the solid density modifying agent, from the cementitious slurry, due to gravity settling or floatation, is retarded.

14. The slurry base as claimed in claim 13;wherein:the solid density modifying agent, for which the suspension is encouraged, is a solid density modifying agent that is characterized in that at least one (1) weight % of the solid density modifying agent, based on the total weight of the solid density modifying agent, has a particle density that is within a range, and the range is from 300 kg / m3 to 500 kg / m3.

15. The slurry base as claimed in any one of claims 11 to 14;further comprising:a viscosifying agent.

16. A cementitious barrier, emplaced within a space disposed between a wellbore string and a subterranean formation, and characterized by a compressive strength of less than, or equal to, 250 psi.

17. The cementitious barrier as claimed in claim 16;wherein:the cementitious barrier is derived from a cementitious slurry that has a density of less than, or equal to, 1.05 kilograms per litre.

18. The cementitious barrier as claimed in claim 16;wherein:the cementitious barrier is derived from a cementitious slurry; andthe cementitious slurry includes a hydraulic binder and a solid density modifying agent.

19. The cementitious barrier as claimed in claim 17 or 18;wherein:the hydraulic binder is present in an amount that is within a range, and the range is from ten (10) weight %, based on the total weight of the slurry, to 60 weight %, based on the total weight of the slurry; andthe solid density modifying agent is present in an amount that is within a range, and the range is from five (5) weight %, based on the total weight of the slurry, to 45 weight %, based on the total weight of the slurry.

20. The cementitious barrier as claimed in claim 18 or 19;wherein:the ratio of the weight of the solid density modifying agent to the weight of the hydraulic binder is within a range, and the range is from 0.3 to 1.

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