NL8204605A - PREPARATION FOR ACIDIFYING UNDERGROUND FORMATIONS AND METHOD OF APPLICATION - Google Patents

Description

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Preparation for acidifying underground formations and method in which it is applied »

This invention concerns the acidification of underground formations to increase oil and gas production »

Oil and gas accumulations are usually found in underground, porous and permeable rocks. A well is drilled there to obtain oil and gas from these formations. In many cases, the oil and gas are contained in the pores in this formation and are hydraulically connected by connecting those pores. After a well 10 has been drilled in the formation, oil and gas are expanded by expansion, natural and artificial displacement, gravity, etc.? driven to the bore. These different processes can, together or separately, feed the hydrocarbons through the existing compounds to the bore. In many cases, however, production from this well may be too small because not enough channels lead to the bore. In many cases, the formation then undergoes treatment to increase its flowability.

Acidification of an underground formation 20 which has been pierced through an oil well has already been widely used for: increasing the production of crude oil, natural gas, etc. from that formation. The conventional acidification technique consists of introducing a non-oxidizing acid into the well under sufficient pressure to urge the acid into the formation, whereupon the acid-soluble constituents of that formation react. This technique is not limited to high solubility formations in acids such as limestone and dolomite, the technique is also applicable to other types of formation such as sandstone with occasional thin streaks or "streaks" of acid soluble constituents such as various carbonates.

During the treatment with acid, 8204605 * 2 in the formation are liquid passages or existing passages are broadened, thereby increasing the production of liquid from that formation. Acidification operations where the acid is injected into the formation with not enough pressure or in an insufficient flow to cause cracks and fissures in the formation is commonly referred to as "matrix acidification".

Hydraulic fracturing is also widely used to stimulate the petroleum production of underground formations and consists of injecting a suitable "fracturing fluid" from under an oil well and into that formation with enough pressure to overcome the high pressure prevailing thereunder. This leads to the formation of cracks and fractures in the formation, which also promotes the flow of liquid through the formation into the well. When the pressure of that fracturing fluid is lowered, a "proppant" is present in the fracturing fluid that prevents complete sealing of the fracture. The combination of fracturing and acidification is also known in the art.

Gelled acidic liquids containing cross-linked polymers have been used in the acidification or rupture of underground formations. Such liquids cause problems during acidification or rupture if the temperature at the bottom of the bore or where one wants to make breaks exceeds about 90 ° C.

For example, such fluids, when used to break the formation, exhibit gel instability, which is evidenced by deposits and / or syneresis.

The phenomenon of syneresis occurs because the space for the molecules of solvent (water or other medium) in the amorphous network of the gel decreases as the fraction of molecular chains that participate in the crystalline regions within the gel increases. As "the gel thickens," an above layer of liquid also occurs. The thicker, settled layer is in many cases detrimental to the formation.

Still other problems present gelled acidic liquids containing cross-linked polymers when acidifying or breaking up underground formations at high temperatures. In many instances, these polymers undergo degradation, i.e., a decrease in viscosity that leads to poor formation in the formation.

The present invention solves, or at least mitigates, the problem just discussed. This invention provides an improved preparation for acidifying and breaking underground formations, and a method of using them.

An embodiment of the invention relates to a method for acidifying or breaking acidifying an underground formation in which a gelled acidic liquid, which essentially consists of water, contains enough acid to cover an important amount of the gelled acid, through a wellbore. acid-soluble constituents of that formation and an effective amount of a water-dispersible polymer composed of 5 to 60% by weight of acrylamide and the remainder of dialkylaminoethyl methacrylate, trialkylaraononethylethyl methylate and acrylamidoalkanesulfonic acid, and that liquid long enough is kept in contact with that formation to react to a significant degree with the acid-soluble components of that formation and to stimulate the production of liquids therefrom.

Another aspect of this invention relates to a gelled acidic liquid suitable for fracturing and acidifying an underground formation consisting essentially of water, enough acid to react with a significant amount of the acid-soluble constituents of that formation, and from an effective amount of a polymer consisting of 5 to 60% by weight of acrylamide and the balance of dialkylaminoethyl methyl acrylate, trialkylammonioethyl methacrylate and acrylamidoalkanesulfonic acid.

When the above-described acidification or refractive acidification of an underground formation is used, one does not have any problems with handling, pumping the materials to prepare that 8204605 * 4 liquid or with that liquid itself. Surprisingly, this acidic liquid does not exhibit the phenomenon of syneresis at temperatures above 90 ° C, thereby achieving excellent penetration of the formations by the acid.

The group of copolymers useful in the practice of this invention are 5 to 60% by weight built up from acrylamide and the remainder from (1) compounds of formula 1 wherein R is methyl or ethyl and X is Cl, Br, J or CH 2 OSOg is (2) compounds of formula 2 wherein R is ethyl or methyl and / or (3) compounds of formula 3 wherein R, R 1, R 2 and R 2 independently of one another are hydrogen or alkyl of 1 to 5 carbon atoms and M is hydrogen, sodium, potassium or ammonium.

The copolymer preferred in the invention consists of 20% by weight of acrylamide and the balance of a compound of formula 1 wherein all groups R are methyl and X is methyl sulfate, which polymer has a weight average molecular weight of about 7,000,000.

In general, the amount of acid-gelling polymer used in the invention can vary widely depending on the desired viscosity of the composition and the temperature in the formation to be treated. Generally, the amount of gelled thickener will be between 0.1 and 20% by weight. However, there is essentially no limit to the amount of gelling agent that can be used as long as the liquid can be pumped in the method of the invention.

Generally, the acidic polymer-containing liquid will also contain an inhibitor that counteracts corrosion of metal by acid. Any of the many compounds known in the art can be used. The amount of corro decorative bucket is not very important and can vary widely; usually a small but effective amount will be taken, such as between 0.10 and 2.0% by weight, based on the solution.

If it is desirable to contact the substrate formation with the composition according to 8204605 V.

In the form of a foam, one can use any foaming agent that is compatible with the rest of the composition and which gives a foam in acidic conditions. Many foaming agents are described in U.S. Pat. No. 4,044,083.

Various methods are known in the art for preparing the monomers used in the compositions of the invention. See, for example, U.S. Patent 3,573,263 for the preparation of the monomers of formulas 1 and 2 and U.S. Patent 3,507,707 for the preparation of the monomer of formula 3.

The polymers useful for the practice of this invention may have weight average molecular weights between 5,000,000 and 20,000,000, which are preferably between 5,000,000 and 15,000,000.

In this description and the claims, the weight average molecular weight is defined by the formula _ „u L w * fit 1 1 Σ C.

20 x where C. is the concentration of the type of molecules i and M. is the 1 i molecular weight of that type; there is a sum on all types i.

Any acids which are effective in increasing the flow of liquids (hydrocarbons) through the formation into the wellbore are suitable for practicing this invention. This includes inorganic acids such as hydrochloric, hydrofluoric and phosphoric acids and organic acids of 1 to 4 carbon atoms such as formic acid, acetic acid, propionic acid and butyric acid, as well as all possible mixtures thereof. The concentration or strength of the acid depends on the type of acid, the type of formation to be treated and the above-mentioned compatibility requirement. Generally, the concentration can range from 0.4 to 60 wt%, depending on the type of acid, and preference will be given to concentrations between 10 and 50 wt%, all based on the total composition. If an inorganic acid such as hydrochloric acid is used, it is preferably taken in such an amount that its concentration is between 0.4 and 35% by weight, most preferably above 10% by weight. Concentrations between 5-10 and 30% by weight will often do well. The acids used in the practice of the invention may contain any known corrosion inhibitors, emulsion breakers, metal scavengers, surfactants, frictional moisturizers, etc. The preferred acids in the practice of the invention are hydrochloric, acetic, formic and mixtures thereof.

The acidic gelled liquids of the invention are aqueous preparations. They normally contain a significant amount of water. The amount of water depends on the concentrations of the other ingredients, and in particular on the concentration of acid. For example, if an organic acid such as acetic acid is used in a concentration of 60% by weight, the amount of water in the composition will be significantly less than if an inorganic acid such as hydrochloric acid is used in a concentration of about 35% by weight. It is therefore not possible to indicate a precise range of water contents. However, in view of the aforementioned concentrations of other ingredients, the water content of the compositions will generally be between 30 and 99% by weight, usually between 60 and 90% by weight. But water contents outside that range can also occur.

In the practice of the invention, any propellants known in the art may be used, ie, grains of sand, splinters of nut shells, sintered bauxite, tempered glass beads, nylon spheres or any mixture of two or more such materials. Such agents can be used in concentrations between 12 g and 1.2 kg 3 per m of the breaking liquid. Generally, the proppants will have particle diameters between 0.03 and 3.3 mm, preferably between 0.15 and 2.4 mm, and most preferably between 0.25 and 1.6 mm.

Any suitable method can be used to prepare the acidic gelled liquids of the invention. Thus, any suitable mixing technique and any order of addition can be used, resulting in a composition with sufficient stability against degradation by the underground heat, and that formation penetrates sufficiently and etches sufficiently. Usually, however, it is preferable to first disperse the polymer in a non-hydrating agent such as an alcohol or an oil before contacting the polymer with water or acid. It is therefore within the scope of the invention to stir the polymer with a small amount of a low molecular alcohol (with 1 to 3 carbon atoms) or with a hydrocarbon, such as diesel oil or petroleum, and then use water or acid. add. The acidic gelled liquid of the invention can be stored at room temperature for several days before being placed in the formation.

The acidic gelled liquid of the invention can be prepared on site in a suitable agitated vessel. The liquid is then pumped down the well with the conventional equipment through the well and into the formation. However, it is also within the scope of the invention to prepare the liquids while they are pumped down. For example, a dispersion of the polymer in water can be made in a vessel adjacent to the wellhead and a meter or so downstream from that vessel there may be a connection for adding acid to that polymer dispersion.

The liquid then enters the subterranean formation and its limestone then dissolves, increasing permeability and allowing a better flow of liquid. The flow rate at which the pump is pumped and the pressures applied will of course depend on the nature of the formation and whether one wishes to break the formation or not. After the acidic, gelled liquid has thus been injected, the well will normally be closed and left to stand for several hours to a day or more. When there is pressure on the well, it is then vented and the solution of the salts formed by the action of the acid is allowed to flow back into the bore and pumped up. The bore can then be put back into production or used for other purposes.

The invention is now further illustrated by the following non-limiting example.

The influence of temperature on the viscosity of various polymers in 20% hydrochloric acid was determined by first mixing the components homogeneously with water and heating those liquids in a viscometer (Fann Model 50) from 37 ° to 120 ° C; in this viscometer, rotor and sleeve No. 1 were used at a rotational speed of 50 rpm, and the shear forces in N / dm were read at the temperatures listed in Table A. All samples contained 1 wt% polymer.

Sample A contained a copolymer of 20 wt% acrylamide and 80 wt% trimethylammonioethyl methacrylate salt. Samples B and C contained a copolymer of 60 wt.% Acrylamide and 40 wt.% 2-acrylamido-2-methylpropane sulfonic acid. Samples D, E and F contained 60 wt% acrylamide and 50 wt% 2-acrylamido-2-methylpropanesulfonic acid. The weight average molecular weights of samples A, B, C, D, E and F were between 5,000,000 and 10,000,000. In addition, 25 samples D, E and F were cross-linked with formaldehyde. The results of these tests are shown in Table A.

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The results of this table show that the preparations according to the invention, samples A, B and C, were very stable at high temperatures (even 122 ° C), while samples D, E and F, which were cross-linked with formaldehyde , showed syneresis at temperatures above 90 ° C.

8204605

Claims (12)

An acidic, gelled liquid consisting essentially of 5 (a) water, (b) an acid and (c) an effective amount of a water-deeper-digestible copolymer consisting of 5 to 60 wt.% Acrylamide and for the balance from (1) compounds of formula 10, wherein R is methyl or ethyl and X is Cl, Br, J or CH 2 OSO 2, (2) compounds of formula 2 wherein R is ethyl or methyl and / or ( 3) compounds of formula 3 wherein R, Rj, R2 and Rj independently represent hydrogen or alkyl of 1 to 5 carbon atoms and M is hydrogen, sodium, potassium or ammonium, the weight average molecular weight of that polymer being between 5,000,000 and 20,000,000. Liquid according to claim 1, the acid of which is hydrochloric, hydrofluoric, acetic, formic or a mixture thereof. Liquid according to claim 1 or 2, of which the copolymer consists mainly of acrylamide and the remainder of a compound of formula 1 in which all groups R are methyl and X is methyl sulfate. The composition according to any one of the preceding claims, the copolymer of which has a weight average molecular weight of between 5,000,000 and 15,000,000. Liquid according to any one of the preceding claims, of which the copolymer consists for about 20% by weight of acrylamide. 6. Liquid according to any one of claims 2 to 5, wherein the acid is hydrochloric acid. Liquid according to claim 6, containing between 10 and 30 wt.% Hydrochloric acid. Liquid according to any one of the preceding claims, further comprising a "proppant". 8204605 «· -ν · Liquid according to claim 1, 2 or any one of claims 5 to 8, of which the copolymer consists largely of acrylamide and the remainder of a compound of formula 2, wherein R represents methyl. Liquid according to any one of the preceding claims in the form of a foam. Method for acidifying an underground formation, characterized in that a liquid according to any one of the preceding claims is used for this. The method of claim 11, wherein the liquid is pumped into the formation with sufficient pressure to fracture said formation. 15 8204805