Thermoset particles with enhanced crosslinking, processing for their production, and their use in oil and natural gas driliing applications

Abstract

Thermoset polymer particles are used in many applications requiring lightweight particles possessing high stiffness, strength, temperature resistance, and / or resistance to aggressive environments. The present invention relates to the use of methods to enhance the stiffness, strength, maximum possible use temperature, and environmental resistance of such particles. One method of particular interest is the application of post-polymerization process step(s) (and especially heat treatment) to advance the curing reaction and to thus obtain a more densely crosslinked polymer network. The most common benefits of said heat treatment are the enhancement of the maximum possible use temperature and the environmental resistance. The present invention also relates to the development of thermoset polymer particles. It also relates to the further improvement of the key properties (in particular, heat resistance and environmental resistance) of said particles via post-polymerization heat treatment. Furthermore, it also relates to processes for the manufacture of said particles. Finally, it also relates to the use of said particles in the construction, drilling, completion and / or fracture stimulation of oil and natural gas wells; for example, as a proppant partial monolayer, a proppant pack, an integral component of a gravel pack completion, a ball bearing, a solid lubricant, a drilling mud constituent, and / or a cement additive.

Description

[0001] This application claims the benefit of U.S. Provisional Application No. 60 / 689,899 filed Jun. 13, 2005.FIELD OF THE INVENTION [0002] The present invention relates to lightweight thermoset polymer particles, to processes for the manufacture of such particles, and to applications of such particles. It is possible to use a wide range of thermoset polymers as the main constituents of the particles of the invention, and to produce said particles by means of a wide range of fabrication techniques. Without reducing the generality of the invention, in its currently preferred embodiments, the thermoset polymer consists of a terpolymer of styrene, ethyvinylbenzene and divinylbenzene; suspension polymerization is performed to prepare the particles, and post-polymerization heat treatment is performed with the particles placed in an unreactive gaseous environment with nitrogen as the preferred unreactive gas to further advance the curing of the thermoset polymer. When executed in the mann...

AI Technical Summary

Benefits of technology

[0031] The disclosure describes lightweight thermoset polymer particles whose properties are improved relative to prior art. The particles targeted for development include, but are not limited to, terpolymers of styrene, ethyvinylbenzene and divinylbenzene. The particles exhibit any one or any combination of the following properties: enhanced stiffness, strength, heat resistance, and / or resistance to aggressive environments; and / or improved retention of high conductivity of liquids and / or gases through packings of the particles when the packings are placed in potentially aggressive environments under high compressive loads at elevated temperatures.

[0035] Any rigid thermoset polymer may be used as the polymer of the present invention. Rigid thermoset polymers are, in general, amorphous polymers where covalent crosslinks provide a three-dimensional network. However, unlike thermoset elastomers (often referred to as “rubbers”) which also possess a three-dimensional network of covalent crosslinks, the rigid thermosets are, by definition, “stiff”. In other words, they have high elastic moduli at “room temperature” (25° C.), and often up to much higher temperatures, because their combinations of chain segment stiffness and crosslink density result in a high glass transition temperature.

[0043] If a suitable post-polymerization process step is applied to thermoset polymer particles, in many cases the curing reaction will be driven further towards completion so that Tg (and hence also the maximum possible use temperature) will increase. This is the most commonly obtained benefit of applying a post-polymerization process step. In some instances, there may also be further benefits, such as an increase in the compressive elastic modulus even at temperatures that are far below Tg, and an increase of such magnitude in the resistance to aggressive environments as to enhance significantly the potential range of applications of the particles.

[0054] Any significant increase in Tg by means of improved curing will translate directly into an increase of comparable magnitude in the practical softening temperature of the polymer particles under the compressive load imposed by the subterranean environment. Consequently, a significant increase of the maximum possible use temperature of the thermoset polymer particles is the most common benefit of advancing the extent of curing by heat treatment.

[0061] Without reducing the generality of the invention, in its currently preferred embodiments, the thermoset polymer particles are placed in an unreactive gaseous environment with nitrogen as the preferred unreactive gas during heat treatment. Appropriately chosen equipment is used, along with simulations based on the solution of the heat transfer equations, to optimize the heat exposure schedule so that large batches of particles can undergo thermal exposure to an extent that is sufficient to accomplish the desired effects of the heat treatment without many particles undergoing detrimental overexposure. This embodiment of the heat treatment process works especially well (without adverse effects such as degradation that could occur if an oxidative gaseous environment such as air were used and / or swelling that could occur if a liquid environment were used) in enhancing the curing of the thermoset polymer. It is, however, important to reemphasize the much broader scope of the invention and the fact that the particular currently preferred embodiments summarized above constitute just a few among the vast variety of possible qualitatively different classes of embodiments. C. Applications

[0063] The use of assemblies of the particles as proppant partial monolayers and / or as proppant packs generally requires the particles to possess significant stiffness and strength under compressive deformation, heat resistance, and resistance to aggressive environments. Enhancements in these properties result in the ability to use the particles as proppants in hydrocarbon reservoirs that exert higher compressive loads and / or possess higher temperatures.

Problems solved by technology

As discussed above, particles made from polymeric materials have historically been considered to be unsuitable for use by themselves as proppants.

However, these inventors still did not consider or describe the polymeric particles as proppants.

However, embodiments of this prior art, based on the use of styrene-divinylbenzene (S-DVB) copolymer beads manufactured by using conventional fabrication technology and purchased from a commercial supplier, failed to provide an acceptable balance of performance and price.

The need to use a very large amount of an expensive crosslinker (50 to 80% by weight of DVB) in order to obtain reasonable performance (not too inferior to that of Jordan Sand) was a key factor in the higher cost that accompanied the lower performance.

While not improving the extent of covalent crosslinking relative to conventional isothermal polymerization, rapid rate polymerization results in the “trapping” of an unusually large number of physical entanglements in the polymer.

There is no prior art that relates to the development of heat-treated thermoset polymer particles that have not been reinforced by rigid fillers or by nanofillers for use in oil and natural gas well construction applications.

The properties of crosslinked polymers prepared by standard manufacturing processes are often limited by the fact that such processes typically result in incomplete curing.

This situation results in lower stiffness, lower strength, lower heat resistance, and lower environmental resistance than the thermoset is capable of manifesting when it is fully cured and thus maximally crosslinked.

(1996) (see FIG. 1) are compared, it becomes clear that the low performance and high cost of the “as purchased” S-DVB beads utilized by Bienvenu (U.S. Pat. No. 5,531,274) are related to incomplete curing.

This incomplete curing results in the ineffective utilization of DVB as a crosslinker and thus in the incomplete development of the crosslinked network.

This deformation will cause a decrease in the conductivities of liquids and gases through the propped fracture, and hence in the loss of effectiveness as a proppant, at a somewhat lower temperature than the HDT value of the polymer measured under the standard load of 1.82 MPa.

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