WO2025216971A1

WO2025216971A1 - Solid surfactant package for spacer fluids

Info

Publication number: WO2025216971A1
Application number: PCT/US2025/022966
Authority: WO
Inventors: Allen Kelley; Jorge Fernandez; Cornell STANCIU
Original assignee: Sasol Chemie & Co Kg GmbH; Sasol USA Corp
Current assignee: Sasol Chemie & Co Kg GmbH; Sasol USA Corp
Priority date: 2024-04-12
Filing date: 2025-04-03
Publication date: 2025-10-16
Anticipated expiration: 2026-10-12

Abstract

The invention discloses a solid surfactant composition comprising one or more surfactants having a narrow range ethoxylate distribution and of the formula R - (C₂H₄O)x- (C₃H₆O)y - H; wherein hydrocarbon group R has 6-30 carbons; - (C₂H₄O) - is an ethoxylate group with x from 1 to 30, and greater than 80% of ethoxylates in the surfactant fall in a distribution range from x-5 to x+5; - (C₃H₆O) - is a propoxylate group with y from 0 to 30; at least one surfactant is a liquid at room temperature; and a soluble solid polymer matrix immobilizing the one or more surfactants. The invention further discloses use of the solid surfactant composition in a spacer fluid, a solid surfactant package comprising the solid surfactant composition, and a spacer fluid comprising the solid surfactant package.

Description

SOLID SURFACTANT PACKAGE FOR SPACER FLUIDS

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to US Application 63/633,132 filed on April 12, 2024, the disclosure of which is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The invention provides a solid surfactant package comprising liquid surfactants and/or liquid and solid surfactants entrained on a soluble organic matrix for use in oil and gas applications as a component of a spacer fluid to displace drilling fluids and provide surface treatment for improved cement adhesion in wellbores.

BACKGROUND TO THE INVENTION

A surfactant package comprises a blend of one or more surfactants dispersed and supported within a carrier for use in various applications. W02020/231606, for example, discloses a solid surfactant package for use in solid cleaning products, the package comprising polyethylene glycol as the carrier and supporting a liquid surfactant and a solid surfactant. US2025/0051688 discloses a surfactant package comprising a liquid surfactant and a carrier, which may be a polyethylene glycol carrier, for use in cleaning products, however, the surfactant package is solidified and dried by using a drying device and it is not disclosed that the surfactant is entrained by the carrier.

Surfactant packages are also used in the production of spacer fluids, where they are typically in liquid form which requires specialized equipment. A spacer fluid functions by displacing drilling fluid and oil from a wellbore, cleaning the wellbore surfaces and rendering them water-wet in order to improve cementing bonding and formation. The market interest for surfactant packages in spacer fluids is in “dry-on-the-fly” products, which provide increased ease of use and significantly reduced costs.

The dry-on-the-fly surfactant packages that are currently available present shortcomings in that they fail in at least one of the four requirements requested by industry, namely tunable hydrophilic lipophilic balance, low foamability, fast rate of dissolution in cold tap water and a melting point above 48.9 °C (120 °F). For example, WQ2020/023227 discloses a solid surfactant composite for a spacer fluid, wherein the composite comprises a liquid surfactant and a solid carrier, which is not disclosed as being a soluble carrier, thus limiting the ease of use of the product in a spacer fluid. Similarly, WO2017/074301 discloses a solid surfactant composite for use in a spacer fluid that comprises a surfactant and a solid carrier selected from solid materials such as diatomaceous earth, amorphous silica and clay, wherein the surfactant is intended to dissolve when added to a base fluid of a spacer fluid. The solubility of the present invention is enhanced in that the carrier dissolves and releases the surfactants.

Conventional dry-on-the-fly surfactant packages comprise commercially available solid surfactants that utilize large hydrophobes with large amounts of ethylene oxide (EO), thus greatly restricting their usability as every spacer fluid requires a unique blend of surfactants depending on the substrate and application.

With the large amount of EO present on the surfactant, such conventional solid surfactant packages present foaming issues and a low rate of dissolution, making field blending difficult. Solid surfactant packages can use up to 10 vol% alcohol, which in commercial solid surfactant packages must be added separately, negating the cost reductions generated by dry-on-the-fly designs. The melting point of the surfactant must be above 48.9 °C (120 °F) which is generally the maximum temperature observed in an unairconditioned warehouse.

All prior art documents identified in this section are incorporated herein by reference for all purposes.

Solution

The present invention provides a solid surfactant composition packaged for use in oil well management as a component of spacer fluids. One or more, and preferably two or more, surfactants, of which at least one is a liquid surfactant at ambient temperature (25 °C), are selected from non-ionic surfactants, anionic surfactants or blends of non-ionic and anionic surfactants and immobilized on a solid soluble organic polymer matrix to form the solid surfactant composition which, amongst its benefits, advantageously allows for convenient packaging and efficient transport to a field site. The solid surfactant composition forms an essential component of a spacer fluid, which is formed on site by adding a carrier fluid, such as water, to the composition and other desirable components as required for the particular application, such as a suitable weighting agent to manipulate the density of spacer fluid. All of the solid components will be preblended and packaged with the solid surfactant at the bulk plant.

The solid surfactant composition comprises a tunable mixture of one or more, and preferably two or more, linear or branched surfactants with carbon chains typically between C6 and C30, containing between 1 and 30 units of EO and/or propylene oxide (PO), and preferably includes narrow range ethoxylate (NRE) surfactants. NRE surfactants are NOVEL ethoxylates produced using the proprietary catalyst from Sasol (USA) Corporation as disclosed in US5627121A, incorporated herein by reference for all purposes, that display advantages over conventional broad range surfactants. NRE surfactants have a narrow distribution range of EO with a narrow distribution of lower molecular weight ethoxylates at one end of the distribution curve and higher molecular weight ethoxylates at the opposite end of the curve, which increases the uniformity and performance of the surfactant. Conventional surfactants that have a broad distribution range of EO can be unpredictable in light of the high variability. Lower concentrations of NRE surfactants are needed in the solid surfactant composition due to the targeted EO content. This allows for lower concentrations of NRE surfactants to be utilized in the surfactant package, while achieving the same clean interface across the temperature gradient. The surfactants preferably comprise 30-70 % of the solid surfactant composition.

The surfactants used in the present invention are considered NRE because the shoulders of the distribution are dramatically reduced. This is achieved by dramatically reducing the mol% of short and long chain surfactants created in the ethoxylation process. Primarily the distribution of short chain surfactants become mobile at lower temperatures than the bulk of the distribution, allowing them to phase segregate or sweat out of the solid surfactant over many solidification/liquification cycles. This has led the market into 2 distinct directions. The first is coating or absorbing liquid and solid surfactants into or onto solid inorganic carriers. This addresses the sweating by only having very small amounts of short chain surfactant in one place that can phase segregate out at a given time. This also means one would need to use a much larger amount of substrate to coat a small amount of surfactant, which will cause them to brick up over many temperature cycles.

The second direction is to reduce the energy or temperature that the solid surfactant will be subjected to. This is impractical because a warehouse in the field will surpass the ambient temperature unless special care is taken. If the package phase segregates at 37 °C while the field temperature reaches 49 °C for 5 months out of the year, it is unusable. By using NRE surfactants in the present invention, both of these problems are solved by having a high percentage active densely packed solid surfactant that can withstand field temperatures and solidification/liquification cycles without excessive sweating while maintaining performance, enhanced surfactant selection, foam control and mixing time.

The solid soluble matrix is an organic polymer functioning as the entrainment matrix to immobilize the surfactants into its solid structure. The desirable properties of a suitable polymer matrix for entraining a liquid surfactant to form a solid surfactant composition include water solubility, a melting point of approximately 60 °C, and a sufficiently firm polymer to provide the required supporting structure for the surfactants. In the present invention, the polymer matrix is preferably polyethylene glycol (PEG), typically with an average molecular weight of 3000 to 20 000 g/mol. PEG with a molecular weight below 3000 g/mol lacks the required hardness to serve as a matrix to the surfactants and quickly transitions to a liquid state rather than remaining stable as a solid, particularly in the ambient temperature of a warehouse environment where the PEG would typically be stored. On the other hand, PEG with an average molecular weight over 20 000 g/mol is too rigid to function as a matrix, has a high dynamic viscosity and forms a gel in solution. In view thereof, in the present invention PEG is preferably selected with an average molecular weight of between 5000 and 10 000 g/mol.

Alternative polymers for the entrainment matrix include polypropylene glycol (PPG), blends of PEG and PPG, block PO/EO and EO/PO polymers, ethers with side carbon chains lengths typically between C12-C30 or other linear or branched surfactants. The matrix may also contain branched or linear alcohols with carbon chains between C4 and C24.

Polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) are alternative organic polymers that present shortcomings in comparison to PEG as a suitable entrainment matrix for the present invention. High molecular weight water soluble PVA has a very high melting point (between 90 and 120 °C). In the presence of a surfactant, PVA takes approximately 30 minutes to melt and combine with the surfactant. This provides large hurdles for manufacturing and can prove impractical. Further, PVA has relatively low strength and is elastic, which makes it unsuitable to physically contain the liquid surfactant. Similarly, PVP has a high melting point of 150-180 °C, which makes it impractical for melt blending with surfactants. The solid surfactant composition of the present invention displays several advantages over conventional liquid surfactant packages:

• It is versatile, able to entrain a wide range of ethoxylates as surfactants in both liquid and solid format, including branched, linear and cyclic C6-C30 non-ionic and anionic surfactants, making the surfactant package’s hydrophilic lipophilic balance (HLB) tunable while retaining its solid structure;

• The rate of dissolution of the surfactant composition and package can be controlled by selecting NRE surfactants with higher EO content to allow for complete dissolution within the required two-minute API mixing standards, thus avoiding batch mixing;

• The melting point of the surfactant composition can be adjusted based on the targeted EO content, concentration and structure of the NRE surfactants and polymer matrix. The observed melting points are high, typically between 48.9 and 60 °C (120 and 140 °F), due to the narrow distribution range of lower molecular weight EO and allowing for long-term storage in warm climates without loss of product integrity;

• NRE surfactants have decreased foaming and the foam profile of each surfactant can be further reduced by adding branched, linear or cyclic alcohols in situ to the surfactant composition, decreasing cost of the composition and package, and increasing ease of blending;

• The requirement for specialized equipment at the field site for handling liquid surfactants or the need to batch mix is eliminated and instead the surfactant composition in its packaged form allows for desirable “dry-on-the-fly” field operations;

• The surfactant composition has decreased sweating or exuding due to the NRE surfactants having a reduced mol% distribution of the lower molecular weight EO species due to the narrow range, increasing stability of the composition and package and maintaining its functionality for longer periods; The surfactant composition is designed to allow the resultant spacer fluid to quickly flip the formation from oil to water wet allowing the cement to adhere to the formation and wellbores.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a solid surfactant composition for a spacer fluid, the solid surfactant composition comprising: one or more non-ionic or anionic surfactants of the formula

R - (C₂H₄O)_X- (C₃H₆O)_y - H wherein R is a linear, branched or cyclic hydrocarbon group with between 6 and 30 carbons; - (C2H4O) - is an ethoxylate group and - (CsHeO) - is a propoxylate group; x is from 1 to 30; y is from 0 to 30, wherein at least one surfactant is a liquid at 25 °C and 1 atm; and a soluble solid organic polymer matrix immobilizing the one or more surfactants.

It will be appreciated that a spacer fluid functions in oil and gas applications by displacing oil and drilling fluid from wellbores in order to alter the surface from oil to water wet for cementing. The spacer fluid is prepared by adding a carrier fluid, such as water, to the solid surfactant composition together with other components, such as a weighting agent and a viscosifier.

The polymer matrix may be selected from polyethylene glycol, polypropylene glycol, blends of polyethylene glycol and polypropylene glycol, block polymers of ethylene oxide and propylene oxide, ethers, alcohols and other surfactants.

The polymer matrix may preferably be polyethylene glycol with a molecular weight of 3000 to 20 000 g/mol, and more preferably 5000 to 10 000 g/mol.

The one or more non-ionic or anionic surfactants may comprise a mixture of homologue ethoxylates with a different number of ethoxylate groups, and greater than 80 % by weight of the ethoxylates in the mixture may have a number of ethoxylate groups falling in a distribution range from x-5 to x+5, thereby providing ethoxylates having a narrow range ethoxylate (NRE) distribution.

The advantage of using surfactants with an NRE distribution is the ability to use a decreased concentration of the surfactants in the surfactant composition, which increases the cost of producing the surfactant composition, the surfactant package and ultimately the spacer fluid containing the surfactant package.

The one or more surfactants, of which at least one is a liquid, may be in the form of a liquid or a solid. The surfactants may comprise 30-70 % of the total weight of the solid surfactant composition.

The one or more surfactants may be selected from non-ionic surfactants, anionic surfactants, or a blend of non-ionic and anionic surfactants.

The surfactants may be selected, for example, from one or more of NOVEL 810-3.5, NOVEL 810- 4.5, SAFOL 23E5 to 23E9, ALFOL 20+-20PO-1 EO, ALFOL 20+-20EO, NOVEL S5, and NOVEL S7, alone or in combination.

The explanation of the abbreviations above are as follows:

NOVEL 810-3.5 is a NOVEL narrow range ethoxylate non-ionic alcohol produced using the proprietary catalyst from Sasol (USA) Corporation, disclosed in US5627121A, and has a chemical formula CH3(CH2)_X(OCH2CH₂)3.5OH, where x varies between 7 and 9, is a narrow range ethoxylate non-ionic alcohol with 8-10 carbons and average of 3.5 EO groups;

NOVEL 810-4.5 is a NOVEL ethoxylate produced using the above proprietary Sasol catalyst and has a chemical formula CH3(CH2)xCH2(OCH2CH2)4.sOH, where x varies between 6 and 8, is a narrow range ethoxylate non-ionic alcohol with 8-10 carbons and average of 4.5 EO groups;

SAFOL 23E5 is a branched non-ionic C12-C13 oxo alcohol with 12-13 carbons and 5 EO groups;

SAFOL 23E9 is a branched non-ionic C12-C13 oxo alcohol with 12-13 carbons and 9 EO groups (E6, E7, and E8 follow the same trend as E5 and E9); ALFOL 20+-20PO-1 EO is a propoxylated and ethoxylated solid linear alcohol with even numbered carbon chain lengths with over 20 carbons, 20 PO groups and 1 EO group;

ALFOL 20+-20EO is a solid linear ethoxylate alcohol with even numbered carbon chain lengths with over 20 carbons and 20 EO groups;

NOVEL S5 is a NOVEL ethoxylate produced using the aforementioned proprietary Sasol catalyst and is a narrow range ethoxylate non-ionic surfactant with a 12 carbon linear portion, 13 carbon branched portion and average of 5 EO groups;

NOVEL S7 is a NOVEL ethoxylate produced using the aforementioned proprietary Sasol catalyst and is a narrow range ethoxylate non-ionic surfactant with a 12 carbon linear portion, 13 carbon branched portion and average of 7 EO groups.

The solid surfactant composition may be formulated as a flaked, powdered or pelletized product, and may be stored for distribution in a packing means selected from bags, containers, biodegradable packaging, and other suitable means.

According to a second aspect of the invention, there is provided a method of producing the solid surfactant composition of the first aspect of the invention, the method comprising: mixing the surfactants and polymer matrix of the first aspect of the invention; heating the mixture to 5 degrees above the melting point of the polymer matrix; shearing the mixture at 300 rpm until a uniformly mixed composition forms; and cooling the composition at room temperature to harden into the solid surfactant composition.

The mixture may be heated for 10-12 hours or overnight.

The mixture may be sheared using a paddle mixer.

The composition may be cooled for a period of 2 to 3 days.

According to a third aspect of the invention, there is provided a packaged solid surfactant composition comprising: the solid surfactant composition of the first aspect of the invention; and a dissolvable packaging substantially surrounding the solid surfactant composition.

The packaging may be selected from bioplastics, compostable films or papers, plant-based polymers, and similar.

The packaging may substantially surround a plurality of particulates of the solid surfactant composition.

The packaging may disintegrate on reaction with a carrier fluid such that the solid surfactant composition is released from the packaging and available to react with the carrier fluid in forming a spacer fluid. The carrier fluid may be selected from water, oil, or other suitable fluids.

According to a fourth aspect of the invention, there is provided a composition that comprises the solid surfactant package and one or more solid components, such solid components being selected from elements considered in the art to be useful or essential to the function or performance of a composition intended to form part of a spacer fluid.

According to a fifth aspect of the invention, there is provided a spacer fluid precursor comprising the solid surfactant package, where such spacer fluid precursor is a constituent of a spacer fluid.

According to a sixth aspect of the invention, there is provided a spacer fluid that comprises the solid surfactant package, the composition, or the spacer fluid precursor.

According to a seventh aspect of the invention, there is a provided a spacer fluid comprising the solid surfactant composition of the first aspect of the invention or the packaged solid surfactant composition of the third aspect of the invention.

The spacer fluid may displace a fluid from a wellbore to water wet a formation for cementing operations.

The spacer fluid may include one or more additives selected from monovalent and divalent brine, a weighting agent, a viscosifier, a defoamer, a base oil, and a solvent. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows, for Example 1 , the NOVEL 810-3.5 surfactant (left) and ALFOL 20+- 20EO surfactant (right);

Figure 2 shows, for Example 1, solid surfactant compositions at room temperature, from left to right flaked NOVEL 810-3.5, powdered NOVEL 810-3.5, powdered ALFOL 20+-20EO, and flaked ALFOL 20+-20EO;

Figure 3 shows, for Example 2, foam generated by liquid NOVEL 810-3.5 (left) and by a solid surfactant composition containing NOVEL 810-3.5 (right);

Figure 4 shows, for Example 2, foam generated by ALFOL 20+-20EO (left) and by a solid surfactant composition containing ALFOL 20+-20EO (right);

Figure 5 shows, for Example 3, the rate of dissolution of ALFOL 20+-20EO, at (from left to right) 2 minutes, 5 minutes, 7.5 minutes and 10 minutes of shear at 4000 rpm;

Figures 6A-6C show, for Example 4, the melting points of solid surfactant compositions comprising NOVEL 810-3.5 with ALFOL 20+-20PO-1 EO (far left), NOVEL 810-3.5 (second left), ALFOL 20+-20EO, and ALFOL 20+-20EO (second right) with ALFOL 20+-20PO-1 EO (far right), and temperatures from top to bottom of 48.9 °C, 51.7 °C, 54.4 °C, 57.2 °C, 60 °C, 62.8 °C and 65.6 °C;

Figure 7 shows, for Example 5, a DSC melting curve in oscillation mode showing melting of solid surfactant composition comprising S5:S7 surfactants entrained on PEG 8000;

Figure 8 shows, for Example 5, a DSC melting curve in oscillation mode showing crystallization of solid surfactant composition comprising S5:S7 surfactants entrained on PEG 8000 on removal of heat; and

Figure 9 shows, for Example 5, a DSC melting curve showing melting of solid surfactant composition comprising a 50:50 blend of NOVEL S5: NOVEL S7 surfactants entrained on PEG 8000. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The invention will now be described with reference to the following non-limiting Examples.

Various formulations were tested as potential solid surfactant mixtures, including NOVEL 810-3.5 with ALFOL 20+-20PO-1 EO; NOVEL 810-3.5; NOVEL 810-4.5; SAFOL 23E5; SAFOL 23E7; ALFOL 20+-20EO; and ALFOL 20+-20EO with ALFOL 20+-20PO-1 EO. NOVEL 810-3.5 is a short chain NRE surfactant with an average of 3.5 molecules of EO, it is a free-flowing liquid at room temperature and has a low pour point due to some residual free alcohol. ALFOL 20+-20EO is a long chain surfactant that is a solid at room temperature with an average EO number of 20 and a melting point of 45.6 °C (114 °F).

The performance of solid surfactant compositions comprising the above surfactants is assessed by the four industry requirements discussed above. The four tests employed to evaluate the performance of the solid surfactant compositions are as follows:

• Entrainment of a wide range of surfactants

• Controlling the foam profile

• Controlling the rate of dissolution

• Final blends melting point determination.

Example 1 : Entrainment of NOVEL 810-3.5 and ALFOL 20+-EO in PEG polymer matrix

Figure 1 presents the liquid NOVEL 810-3.5 (left) and solid ALFOL 20+-20EO (right) surfactants at room temperature. It is demonstrated that these two surfactants, one a liquid and one a solid, are capable of being entrained in the PEG polymer matrix. The two surfactants and PEG 20,000 polymer matrix are mixed into solution at a ratio of 25 % NOVEL 810-3.5, 25 % ALFOL 20+-20EO and 50 % PEG. This is heated to at least 5 °C above the melting point of the PEG (at least 60-65 °C) for at least 10-12 hours. The mixture is sheared at 300 rpm using a paddle mixer into a uniform solution and cooled at room temperature for 2-3 days until it completely hardens into a solid surfactant composition.

The surfactant composition is formulated as a flaked, powdered or pelletized product with between 50 % and 75 % active, shown in Figure 2. Example 2: Foam profiles

The foam profile is determined by adding 0.015 % vol (15 gpt - gallon per thousand gallon) of each surfactant, NOVEL 810-3.5 and ALFOL 20+-20EO, or solid surfactant composition comprising said surfactant, to a blender cup with 400 ml of water at 26 °C and mixing at 4000 rpm for 2 minutes at room temperature. The resulting foam heights of the surfactant on its own are compared with the surfactant as entrained in the PEG matrix, as shown in Figure 3 and Figure 4. Entraining of the surfactants in the PEG matrix decreases the foaming of the surfactants in solution, which is the desirable result for use in a spacer fluid.

Example 3: Rate of dissolution

The rate of dissolution is found by adding 15 gpt of flaked ALFOL 20+-20EO entrained in the PEG matrix to a blender cup with 400 ml of cold water, mixing at 4000 rpm for 2 minutes, and observing the bottom of the cup for solidification every 2.5 minutes. The results are shown in Figure 5 where undissolved flaked ALFOL 20+-20EO is left on the bottom of the blender cup after mixing. The entrained surfactant completely dissolves in cold tap water within 2 minutes.

Example 4: Melting point

The softening behavior of the solid surfactant composition containing different surfactants, alone and in combination, is investigated by placing chunks of each solid surfactant composition in vials and allowing them to come to temperature from 26 °C up to 60 °C (80 to 140 °F) in an oven for 24 hours. The temperature of the oven is increased incrementally each morning, until the surfactant became sticky and ultimately melts. This is shown in Figures 6A-6C The surfactant composition comprising NOVEL 810-3.5 and ALFOL 20+-20PO-1EO becomes sticky between 54.4 and 57.2 °C (130 and 135 °F) and melts between 57.2 and 60 °C (130 and 140 °F). The ALFOL 20+-20EO surfactant composition becomes sticky between 60 and 62.8 °C (140 and 145 °F) and melts between 62.8 and 65.6 °C (145 to 150 °F). The surfactant composition comprising ALFOL 20+-20EO with ALFOL 20+-20PO-1 EO becomes sticky between 54.4 and 57.2 °C (130 and 135 °F) and melts between 60 and 62.8 °C (140 and 145 °F). It is seen that the solid surfactant compositions therefore have melting points sufficiently high enough for optimal storage of the product.

Example 5: DSC melting

DSC is conducted on a solid surfactant composition comprising a 50:50 blend of NOVEL S5 and NOVEL S7, where the concentration of PEG 8000:surfactant is 60:40. DSC allows for the observation of the melting and crystallization of the solid surfactant composition. In Figure 7 the full cycle of the melt in oscillation mode demonstrates the segregation and mass transport of impurities in the bulk composition.

Figure 8 shows in oscillation mode the effect of removing heat from the system wherein from right to left of the curve the large exothermic peak reflects the PEG and bulk of alcohol ethoxylates crystalizing into a solid matrix. The second crystallization peak reflects the light alcohol and impurities in the surfactant blend that will phase segregate from the initially crystalized solid and, over time at elevated temperatures or many thermal cycles, will exude or sweat out of the solid surfactant composition. Decreased exudation or sweating is an advantage of the solid surfactant composition of the present invention as it conserves the functionality and stability of the solid surfactant composition and package. Such decreased exudation is due to the narrow distribution range of ethoxylates of the NRE surfactants, resulting in a decreased concentration of lower molecular weight ethoxylates i.e., the light ethoxylates.

Figure 9 shows the effect of heat energy on the solid surfactant composition. From left to right, the curve demonstrates how the lower molecular weight ethoxylates readily absorbs heat energy and melts shortly before the bulk of the solid surfactant composition melts. This supports the observation that the softening that is seen before the solid surfactant composition melts is a function of the light ethoxylates segregating from the bulk of the solid surfactant composition and as discussed above is a unique property of the N RE surfactants and the narrow distribution range of ethoxylates. This suggests that it would require many thermal cycles in order for the light ends to melt and crystalize to further phase separate the surfactants in the polymer matrix. Being able to withstand melting at raised temperatures is therefore a further advantage of the solid surfactant composition.

The solid surfactant compositions of the present invention are versatile and compatible with a wide range of end user’s applications. It can comprise one or more of a wide selection of branched, linear and cyclic surfactants with carbon chain lengths C6 to 030. It has decreased foaming compared to its native surfactants, thus eliminating the need for a defoamer in the spacer fluid and increasing ease of blending. Branched, linear or cyclic alcohols can be added in situ to the composition.

Further to this, the solid surfactant composition has several unique advantages in comparison to known surfactant compositions used in spacer fluids, and this is attributed to the innovative use of NRE surfactants entrained to a polymer matrix. As demonstrated, utilising NRE surfactants results in a higher selectivity of ethoxylates within the targeted range, with a narrower distribution of low molecular weight ethoxylates at one end of the distribution curve and high molecular weight ethoxylates at the opposite end of the curve. This allows for the solid surfactant composition and package to have a high rate of dissolution by selecting surfactants with higher percentages of EO, thus promoting complete dissolution within two minutes. As shown, the NRE surfactant mixtures have high melting points due to the narrow distribution range of low molecular weight alcohols and this enables storage in warm environments which is a valuable trait for such a product. In addition, the lower concentration of low molecular weight alcohols in the NRE surfactants reduces exuding from the composition, and thus the solid surfactant composition has decreased sweating, which in turn improves its stability and continued functionality.

Claims

1. A solid surfactant composition comprising: one or more surfactants having a narrow range ethoxylate distribution and of the formula

R - (C₂H₄O)x- (C₃H₆O)_y - H wherein hydrocarbon group R has 6-30 carbons;

- (C2H4O) - is an ethoxylate group and x is from 1 to 30, wherein greater than 80% of ethoxylates in the surfactant fall in a distribution range from x-5 to x+5;

- (CsHeO) - is a propoxylate group and y is from 0 to 30, wherein at least one surfactant is a liquid at room temperature; and a soluble solid organic polymer matrix immobilizing the one or more surfactants.

2. The solid surfactant composition of claim 1, wherein the polymer matrix is selected from polyethylene glycol, polypropylene glycol, a blend of polyethylene glycol and polypropylene glycol, a block polymer of ethylene oxide and propylene oxide, an ether, an alcohol and surfactants.

3. The solid surfactant composition of claim 1 or 2, wherein the polymer matrix is polyethylene glycol with a molecular weight of 3000 to 20000 g/mol, and preferably 5000 to 10000 g/mol.

4. The solid surfactant composition of any one of claims 1 to 3, wherein the one or more surfactants comprise 30-70 % of a total weight of the solid surfactant composition.

5. The solid surfactant composition of any one of claims 1 to 4, wherein the surfactants are selected from one or more of a narrow range ethoxylate non-ionic alcohol with 8-10 carbons, an average of 3.5 ethoxylate groups and of a general formula CH3(CH2)x(OCH2CH2)3.sOH where x is between 7 and 9; a narrow range ethoxylate non-ionic alcohol with 8-10 carbons, an average of 4.5 ethoxylate groups and of a general formula CH3(CH2)xCH2(OCH₂CH2)4.5OH where x is between 6 and 8; a branched non-ionic C12-C13 oxo alcohol with 12-13 carbons and 5 ethoxylate groups; a non-ionic C12-C13 oxo alcohol with 12-13 carbons and 5-9 ethoxylate groups; a propoxylated and ethoxylated solid linear alcohol with an even numbered carbon chain length with over 20 carbons, 20 propoxylate groups and 1 ethoxylate group; a solid linear ethoxylate alcohol with an even numbered carbon chain length with over 20 carbons and 20 ethoxylate groups; a narrow range ethoxylate non-ionic surfactant with a 12 carbon linear portion, 13 carbon branched portion and average of 5 ethoxylate groups; and a narrow range ethoxylate non-ionic surfactant with a 12 carbon linear portion, 13 carbon branched portion and average of 7 EO groups.

6. Use of a solid surfactant composition in a spacer fluid, the solid surfactant composition comprising: one or more surfactants having a narrow range ethoxylate distribution and of the formula

R - (C₂H₄O)_X- (C₃H₆O)_y - H wherein hydrocarbon group R has 6-30 carbons;

7. The use of claim 6, wherein the polymer matrix is selected from polyethylene glycol, polypropylene glycol, a blend of polyethylene glycol and polypropylene glycol, a block polymer of ethylene oxide and propylene oxide, an ether, an alcohol and surfactants.

8. The use of claim 6 or 7, wherein the polymer matrix is polyethylene glycol with a molecular weight of 3000 to 20 000 g/mol, and preferably 5000 to 10 000 g/mol.

9. The use of any one of claims 6 to 8, wherein the one or more surfactants comprise 30-70 % of a total weight of the solid surfactant composition.

10. The use of any one of claims 6 to 9, wherein the surfactants are selected from one or more of a narrow range ethoxylate non-ionic alcohol with 8-10 carbons, an average of 3.5 ethoxylate groups and of a general formula CH3(CH₂)_X(OCH2CH2)3.5OH where x is between 7 and 9; a narrow range ethoxylate non-ionic alcohol with 8-10 carbons, an average of 4.5 ethoxylate groups and of a general formula CH₃(CH2)_XCH2(OCH₂CH2)45OH where x is between 6 and 8; a branched non-ionic C12-C13 oxo alcohol with 12-13 carbons and 5 ethoxylate groups; a non-ionic C12-C13 oxo alcohol with 12-13 carbons and 5-9 ethoxylate groups; a propoxylated and ethoxylated solid linear alcohol with an even numbered carbon chain length with over 20 carbons, 20 propoxylate groups and 1 ethoxylate group; a solid linear ethoxylate alcohol with an even numbered carbon chain length with over 20 carbons and 20 ethoxylate groups; a narrow range ethoxylate non-ionic surfactant with a 12 carbon linear portion, 13 carbon branched portion and average of 5 EO groups; and a narrow range ethoxylate non-ionic surfactant with a 12 carbon linear portion, 13 carbon branched portion and average of 7 EO groups.

11 . A solid surfactant package comprising: the solid surfactant composition of any one of claims 1 to 5; and a dissolvable enclosing means substantially and releasably encapsulating at least a portion of the solid surfactant composition.

12. The solid surfactant package of claim 11 , wherein the dissolvable enclosing means is selected from a degradable, bio-degradable or compostable material.

13. A composition comprising the solid surfactant package of claim 11 or 12, and one or more solid components.

14. A spacer fluid precursor comprising the solid surfactant package of claim 11 or 12.

15. A spacer fluid comprising the solid surfactant package of claim 11 or 12, the composition of claim 13, or the spacer fluid precursor of claim 14.

16. The spacer fluid of claim 15, further comprising one or more of a brine, a weighting agent, a viscosifier, a defoamer, a base oil, and a solvent.

17. A method of displacing a liquid in a wellbore, comprising introducing the spacer fluid of any one of claims 15 or 16 into a wellbore.