BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

The present disclosure relates generally to compositions and methods for treating or completing a subterranean well having a borehole. More particularly, the disclosure relates to cement slurry compositions for cementing a subterranean well and, in the alternative, methods for subterranean well completions and/or cementing a subterranean well having a borehole. The present disclosure also relates to cement-slurry compositions and methods for preparing cement slurry compositions having hydrophobic polymer particles as additives.

In a typical well cementing operation, a cement slurry is prepared at the surface and then pumped into the subterranean well through a liner or casing to fill the annulus between the casing and borehole wall. Once the slurry sets, the cement may provide a number of functions, including providing zonal isolation and segregation, corrosion control, and structural support. A properly prepared slurry and set cement form a strong, nearly impermeable seal around the casing.

Generally, the cement slurry should have relatively low viscosity to facilitate pumping and maintain effectively constant rheological properties during both preparation at the surface and delivery into the well and the target zone. Assuming the cement slurry is properly prepared and delivered to the target zone, the properties of the set cement will depend primarily on the components of the slurry and the additives included in the slurry composition. Ideally, the properly placed cement will develop high compressive strength in a minimum of time.

In recent years, organic polymeric particles have been employed as additives in the cement slurry to achieve or enhance certain cement properties. Generally, the addition of the polymeric particles leads to improved joining of the slurry constituents, which may help achieve improved strength and durability characteristics, among other things. The hydrophobic character of the particles may, however, also present some undesirable issues. In particular, mixability and foaming problems may be observed in the polymer-modified cement slurry. In the field, cement slurries are often prepared using the continuous mixing method, also known as mixing on-the-fly. Solid blends are mixed with water and liquid additives by using a jet mixer. The jet mixer generates a regulated flow of solids that creates a void to draw a dry powder component (due to a venturi effect) into the mix. Unfortunately, the drawing action also draws and entrains air in the slurry. If allowed to stabilize, excess air in the slurry can lead to densely packed air bubbles collecting and then forming at the slurry surface, i.e., foaming. Excessive entrained air and foam can adversely affect the slurry design. For example, it can alter the slurry composition and performance, including deviating from optimal slurry density or increasing slurry viscosity. Such conditions may also cause pumping problems and inefficiencies. Operators attempt to mechanically remove as much of the entrained air from the slurry before pumping, often through further mixing. However, for slurries containing a large amount of hydrophobic polymer particles, such de-aerating efforts often fall short of removing enough of the entrained air from the slurry to avoid slurry quality issues or pumping problems.

To mitigate foaming problems in cement slurry preparations, different traditional measures are available. Antifoam and defoamer additives may be added to the slurry to prevent or minimize foaming. Separator equipment may also be used in conjunction with traditional slurry mixers to mechanically remove the entrained air from the slurry. For example, the SlurryAirSeparator device from Schlumberger Ltd. employs a hydrocyclone mechanism to separate and remove entrained air from the cement slurry. As another option, the slurry may be transferred to a large tank for batch mixing. Much of the remaining entrained air may be removed from the slurry. While any of the aforementioned options may be effective in reducing entrained air and foam in the slurry, the employment of these options may not be feasible. For example, operating time and cost associated with using additional equipment or additives may not be acceptable, or the equipment may not be readily available in some field locations. Also, some of these measures have proven less than satisfactory in reducing entrained air and foam under certain operating conditions.

SUMMARY

The present disclosure is directed to cement slurry compositions having hydrophobic particles.

Embodiments relate to methods for improving the mixability of cement slurries comprising hydrophobic particles. Further embodiments relate to methods for cementing or completing subterranean wells comprising a borehole.

In an aspect, embodiments relate to compositions comprising an inorganic cement, water, hydrophobic particles and a non-ionic surfactant. The particles have an average particle size between 1 micron and 1000 microns.

In a further aspect, embodiments relate to methods for cementing a subterranean well comprising a borehole. A cement slurry composition is prepared and placed in a zone of the subterranean well. The cement slurry comprises an inorganic cement, water, hydrophobic particles and a non-ionic surfactant. The particles have an average particle size between 1 micron and 1000 microns. The cement slurry is then allowed to set and form a solid mass in the zone.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the effect of a lignosulfonate coating on the contact angle of water applied to a polypropylene or an acrylonitrile-butadiene rubber surface.

Figure 2 shows the mixing energy necessary to disperse polypropylene or acrylonitrile- butadiene rubber particles with and without a lignosulfonate coating in water.

Figure 3 shows the effect of a dopamine coating on the contact angle of water applied to a polypropylene or an acrylonitrile-butadiene rubber surface and the variation of the contact angle after immersion of the coated particles in a pH=12 water solution for several hours.

Figure 4 shows the effect of a polysiloxane coating on the contact angle of water applied to a polypropylene or an acrylonitrile-butadiene rubber surface.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation - specific decisions may be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the cement slurry composition used/disclosed herein can also comprise some components other than those cited. In the summary and this detailed description, each numerical value should be read once as modified by the term "about" (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any concentration within the range, including the end points, is to be considered as having been stated. For example, a "range of from 1 to 10" is to be read as indicating each possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to a few specific points, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.

As described herein, cement slurry compositions and methods for preparation are provided in which hydrophobic particles coated with a hydrophilic coating are included as additives. The cement slurry compositions include a suitable amount of an inorganic cement and water to make up the base slurry composition, with particular consideration for an optimal balance of mechanical strength in the set cement and ideal viscosity and quality of the slurry. The hydrophobic particles may achieve or enhance a desired property in the slurry, the set cement or both. The coatings may improve dispersion of the hydrophobic particles into the slurry.

In an aspect, embodiments relate to compositions comprising an inorganic cement, water and hydrophobic particles. A hydrophilic coating is present on the particle surfaces. The particles have an average particle size between 1 micron and 1000 microns. Or, the particles may have an average particle size between 30 microns and 1000 microns. Or, the particles may have an average particle size between 70 microns and 800 microns.

In a further aspect, embodiments relate to methods for cementing a subterranean well comprising a borehole. A cement slurry composition is prepared and placed in a zone of the subterranean well. The cement slurry comprises an inorganic cement, water and hydrophobic particles. A hydrophilic coating is present on the particle surfaces. The particles have an average particle size between 1 micron and 1000 microns. Or, the particles may have an average particle size between 30 microns and 1000 microns. Or, the particles may have an average particle size between 70 microns and 800 microns. The cement slurry is then allowed to set and form a solid mass in the zone.

For all aspects, the compositions are pumpable. To those skilled in art, "pumpable" slurries may be those whose viscosities are lower than 1000 cp at a shear rate of 100 s ^-1 .

For all aspects, the inorganic cement may comprises portland cement, calcium aluminate cement, lime-silica blends, fly ash, blast furnace slag, geopolymers, chemically bonded phosphate ceramics, or zeolites, or combinations thereof.

For all aspects, the composition may comprise about 10% to 50% by weight inorganic cement or cementitious material and about 5% to about 40% by weight hydrophobic particles. The thickness of the hydrophilic coating may be between 10 nm and 10 μιη.

For all aspects, the hydrophobic particles may comprise one or more of the following: rubber particles, poly(acrylic) particles; poly(acrylonitrile) particles; poly(acrylamide) particles; maleic anhydride polymers; polyamides; polyimides; polycarbonates; polymers made from diene monomers; saturated and unsaturated polymers containing ester functionality in the main polymer chain, such as poly(ethylene terephthalate) (PET); polyurethanes'poly(propylene glycol); fluorocarbon polymers; polyethylene, polypropylene, their copolymers; polystyrene; poly(vinyl acetal); poly(vinyl) polymers; poly(vinylidene) chlorides; poly(vinyl acetate); poly(vinyl ether) and poly(ketone); unitaite (more commonly known as Gilsonite™, available from American Gilsonite Company); graphite; coals; and waxes. In certain compositions, the amount of hydrophobic organic polymer particles may be roughly 25% by weight of solid blend, which is relatively high, and in further embodiments, may be about 35% by weight of solid blend.

For all aspects, the hydrophilic coating may comprise a sulfonate, a catecholamine or a polysiloxane or combinations thereof.

For all aspects, the compositions may further comprise an anti-foam agent and a dispersant.

In the methods for cementing a wellbore, a cement slurry composition is first prepared at the surface. Preparation of the cement slurry composition may entail preparing a dry blend of all the solids including the coated hydrophobic particles, and a wet blend that includes water. More additives may be included in the blends as generally known in the art and/or required by the particular cementing operation and wellbore conditions. The dry blend is then added to the wet blend in a standard mixing procedure using, for example, a jet mixer in a single pass operation and at standard mixing speed and time to sufficiently incorporate all the solids into the mixture. After mixing, the cement slurry composition may be pumped into the wellbore. The cement slurry may be delivered into the wellbore, filling the annulus between the drilled hole and the casing string. Once in place, the cement slurry is allowed to cure and harden. Once set, the cement may attain the mechanical properties intended by the design, including high strength. The set cement may also provide an impermeable seal about the casing.

The slurry compositions described herein may employ any one of the types of inorganic cements traditionally used for well completions. These include the more commonly used Portland cement that is produced from limestone and either clay or shale. The cement may meet the chemical and requirements of the American Petroleum Institute and conform to one of the API cement classifications. In any event, it should be understood that the type and formulation of the cement used in an application may depend on several factors, including the conditions expected downhole and the specific purposes or objectives of the cementing operation.

The sulfonate coating may be applied by immersing the organic polymer particles in an aqueous sulfonate solution or spraying the solution onto the particles. The sulfonate concentration in the solution may be between 5% and 80% by weight. The sulfonate compound may be sodium lignosulfonate or calcium lignosulfonate or both. Skilled persons will realize that other types of water soluble sulfonates, including polynaphthalene sulfonates and polymelamine sulfonates, may also be suitable.

The catecholamine coating may be applied by immersing the organic polymer particles in an aqueous medium. A catecholamine compound is then added to the solution, whereupon it crosslinks and deposits on the particle surfaces. The catecholamine compound may be polydopamine, norepinephrine or both. The coating thickness may be controlled by adjusting the polymerization time and the catecholamine concentration in the solution.

The polysiloxane compound may be applied by immersing the organic polymer particles in an aqueous solution in which sol-gel polymerization of an alkoxysilane (e.g., tetraethoxysilane) has taken place in the presence of acidic or basic catalysts. The initial water: alkoxysilane molar ratio may be between 4 and 100. When the polymerization (hydrolysis plus condensation) occurs, water and alcohol are progressively evaporated.

The aforementioned coating processes may take place at temperatures up to 80°C.

EXAMPLES

EXAMPLE 1 To test the effect of sulfonate based coatings on wettability, the contact angle of water was measured using a Tracker tensiometer from Teclis. Since the measurement of contact angles on powders presents some experimental difficulties, contact angle measurements were instead carried out on polymer sheets (polypropylene or acrylonitrile butadiene rubber).

The results, shown in Fig. 1, indicate that the contact angle was below 90° when a 10 wt lignosulfonate solution had been applied to the polymer sheet, either by immersion or spraying, and allowed to dry. EXAMPLE 2

To evaluate the mixability of polymer particles in water, with and without applied coatings, experiments were conducted in beakers and an overhead stirrer was used to apply shear. The particles were coated by immersion in a 10 wt lignosulfonate solution. The mixing speed in RPM necessary to accomplish particle dispersion was recorded. The results are presented in Fig. 2.

EXAMPLE 3 To test the effect of dopamine coatings on wettability, the contact angle of water was measured using a Tracker tensiometer from Teclis. As described in Example 1, the contact angle measurements were performed on polymer sheets. To evaluate the stability of the coating, the contact angle was measured after different immersion times of the polymeric particles in a pH=12 solution simulating the pH of a portland cement slurry.

The results, shown in Fig. 3, indicate that the contact angle remained below 90° for at least 10 hours exposure to a pH=12 environment.

EXAMPLE 4 To test the effect of polysiloxane based coatings on wettability, the contact angle of water was measured using a Tracker tensiometer from Teclis. Tetraethoxysilane was polymerized to polysiloxane through a sol-gel process: 10 mL of tetraethoxysilane were stirred with 50 mL water and 0.1 mL NH ₄ OH at 60°C for 12 hours and at room temperature for 15 hours. A one phase solution was obtained and applied to polymer sheets (polypropylene or acrylonitrile butadiene rubber).

The results, shown in Fig. 4, indicate that the contact angle was below 90° when a the siloxane coating had been applied to the polymer sheet and allowed to dry.

Although various embodiments have been described within respect to enabling disclosures, it is to be understood the disclosed embodiments are not limiting. Variations and modifications that would occur to one of skill in the art upon reading the specification are also within the scope of the disclosure, which is defined in the appended claims.