Coated products and use thereof in oil fields

Details Coated products and use thereof in oil fields Coated products and use thereof in oil fields

1998-11-30

2002-04-30

Tucker, Philip (Department: 1712)

Earth boring, well treating, and oil field chemistry

Preventing contaminant deposits in petroleum oil conduits

C507S902000, C507S219000, C507S244000, C507S224000, C507S229000, C507S261000, C507S227000, C507S939000

Reexamination Certificate

active

06380136

ABSTRACT:

This present invention relates to oil field production chemicals in particular scale inhibitors and their use.
Scale inhibitors are used in production wells to stop scaling in the formation and/or in the production lines down hole and at the surface. Scale is a slightly soluble inorganic salt, such as barium or strontium sulphate, calcium carbonate, calcium sulphate or calcium fluoride. In the production of hydrocarbons from these subterranean formations the deposition of scale on surfaces and production equipment is a major production problem. Scale build-up decreases permeability of the formation, reduces well productivity and shortens the lifetime of production equipment. In order to clean scaled-up wells and equipment it is necessary to stop the production i.e. by killing the well which is time-consuming and costly.
To minimise scale build-up an aqueous solution of a scale inhibitor is injected by force into the formation via a production well-bore. A known scale inhibitor used in such treatments include polyvinyl sulphonate.
After injection the production well is shut-in during which time the scale inhibitor is absorbed within the formation and the inhibitor is slowly desorbed into the fluids in the formation to inhibit scale deposition. After the shut-in period the production well is returned on stream. The fluids produced therefrom are analysed to determine the scale-inhibitor concentration. When the concentration of inhibitor in the fluids has reduced to a certain level then further treatments will be required. An aqueous-based scale inhibitor such as polyvinyl sulphonate has a short lifetime of a few weeks. The continual need for such treatments is therefore costly, not only in terms of production shut down periods but also in the cost of the chemical scale inhibitor used.
Other inhibitors are used in production well environments to stop other deposits e.g. wax or asphaltene and these too need shut-ins to enable the amounts of deposits to be reduced.
It has now been found that coating solid inhibitors, in particular scale inhibitors, can significantly extend the lifetime of the inhibitor thereby increasing the cost effectiveness of inhibitor treatments.
Accordingly the present invention relates to an oil field production chemical in the form of particles each carrying a coating, usually of a dispersing agent.
Another aspect of the invention provides a suspension of the coated particles of the invention in an inert oil.
Yet another aspect of the invention provides a process for the manufacture of an oil field production chemical in the form of particles carrying a coating wherein a solid particulate oil field production chemical is comminuted in the presence of a dispersion of a coating agent in an oil, in particular after the solid particulate chemical has been obtained by spray drying a solution thereof.
In particular the invention also provides for a method of reducing the formation of a separate phase from a liquid phase in a subterranean environment producing oil, or removing said separate phase, which comprises injecting particles comprising an oil field production chemical carrying a coating of this invention into said environment and preferably releasing said chemical into said liquid phase.
The oil field production chemical is usually a charged compound e.g. an organic or inorganic salt, but may be a polar compound especially a polar organic compound. The chemical may be anionic, cationic, neutral or nonionic. Preferably, it is a solid or may be a liquid adsorbed into or onto a solid. Usually it is an inhibitor of deposition of solids, e.g. wax, asphaltenes or scale or of the growth of solids e.g. a scale inhibitor.
The scale inhibitor may be any suitable scale inhibitor used for the purpose of inhibiting scale deposition in well bore formations. It may be a water soluble organic molecule with at least 2 carboxylic and/or phosphonic acid and/or sulphonic acid groups e.g. 2-30 such groups. Preferably the scale inhibitor is polymeric, or may be monomeric with at least one hydroxyl group and/or amino nitrogen atom, especially in a hydroxycarboxylic acid or hydroxy or amino phosphonic or sulphonic acid. Examples of such compounds are aliphatic phosphonic acids with 2-50 carbons, such as hydroxyethyl di phosphonic acid, and aminoalkyl phosphonic acids, e.g. optionally hydroxy substituted poly amino methylene phosphonates with 2-10 N atoms e.g. each bearing at least one methylene phosphonic acid group; examples of the latter are ethylene diamine tetra (methylene phosphonate), diethylene triamine penta (methylene phosphonate) and preferably the polyalkylene triamine and tetramine poly methylene phosphonates with 2-4 methylene groups between each N atom, at least 2 of the numbers of methylene groups in each alkylene being different (e.g. as described further in EP479462, the disclosure of which is herein incorporated by reference). Other scale inhibitors are polycarboxylic acids such as lactic, or tartaric acids, and polymeric anionic compounds such as polyvinyl sulphonic acid and poly(meth)acrylic acids and copolymers thereof, especially with 10-90:90-10 molar ratio of structural vinyl sulphonic groups to acrylic acid, optionally with at least some phosphonyl or phosphinyl groups as in phosphinyl polyacrylates. The scale inhibitors may be in the form of their free acids but are usually at least partly in the form of their alkali metal e.g. Na salts.
The inhibitor is used in the suspension in the form of solid particles having a particle size sufficiently small that the particles disperse in the oily continuous phase. If the particles are too large they will tend to settle out and potentially lead to agglomeration problems. The particle size may be 100% less than 10 microns, preferably 100% less than 7 microns and especially 100% less than 5 microns. Preferably the particle size is not less than 25 nanometres and advantageously not less than 200 nanometres. The average particle size is usually between 1 and 3 microns.
The inhibitors are usually obtained in aqueous solutions; these are dried. Suitable methods of drying include, but are not limited to, spray drying, to obtain a fine powder e.g. of 25-250 microns. The powder then may then, if required, be comminuted using any suitable technique, for example, jet-milling or ball-milling, e.g. wet-milled to obtain particles of the required size e.g. less than 20 microns. Other suitable comminution techniques are described in Section 8 Perry's Chemical Engineers Handbook, 4th Edition, 1963.
The inhibitors may also be obtained as liquids adsorbed into or onto a solid. Usually the solid may be an inert particulate carrier which may be inorganic e.g. silica, alumina or salt or it may be organic e.g. a naturally occurring polymer e.g. starch or a synthetic polymer e.g. a polyurethane or a polyamide. The solid may, if required, be comminuted to obtain particles of the required size using any suitable technique, for example, jet-milling or ball-milling, e.g. wet-milled. Other suitable comminution techniques are described in Section 8 Perry's Chemical Engineers Handbook, 4th Edition, 1963.
The specific gravity of the solid inhibitor may be 0.8-2.0 e.g. 1.0-1.5 while the specific gravity of the solid carrying the inhibitor may be 0.8-3.0, e.g. 1.5-2.5.
The particulate solid inhibitor may then be mixed with a dispersion or solution of a suitable coating agent as described below in a suitable oil e.g. an aliphatic hydrocarbon such as Isopar M oil. The coating agent may be present in the oil e.g. 1-10% by weight, especially 1-5% or 5-10% (based on total solids). While the solid inhibitor may be comminuted to the desired size before mixing with the dispersion or solution, preferably the inhibitor is comminuted (e.g. to reveal freshly cut surfaces) in the presence of the dispersing agent using any suitable technique, e.g. wet milled, to obtain a suspension of coated inhibitor particles of the required average size e.g. 0.4-10 such as 0.4-1.0 or 1-10 microns. The suspension may then if desired be filtered to obtain coated inhi

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