WO2017140543A1

WO2017140543A1 - Method of acidizing silicate containing subterranean formations

Info

Publication number: WO2017140543A1
Application number: PCT/EP2017/052695
Authority: WO
Inventors: Shawn RIMASSA; Christian Spindler; Gary HAWN
Original assignee: Basf Se; Basf Corporation
Priority date: 2016-02-17
Filing date: 2017-02-08
Publication date: 2017-08-24

Abstract

Method of acidizing silicate-containing subterranean formations using HF-containing treatment fluids wherein the fluid comprises at least an additive which is a water-soluble copolymer comprising ethylenically unsaturated carboxylic acids.

Description

Method of acidizing silicate containing subterranean formations

The present invention relates to a method of acidizing silicate-containing subterranean formations using HF-containing treatment fluids wherein the fluid comprises at least an additive which is a water-soluble copolymer comprising ethylenically unsaturated carboxylic acids.

In course of recovering crude oil and/or gas from subterranean formations wells are drilled into the subterranean formation. Owing to the difference between the pressure in the formation and the pressure in the well, the crude oil or natural gas flows through fine channels, pores or the like in the formation to the production well and is conveyed from there to the surface. The pressure in the formation may be of natural origin or may be artificially maintained, for example, by forcing in water, steam or other liquid or gaseous media through an injection well.

In order to ensure an economical production rate for crude oil and/or natural gas, the permeabil- ity of the rock formation must reach a certain degree. Frequently, however, the permeability of the rock formation is too low. On the one hand, the natural permeability may already be too low; on the other hand pores which are sufficiently large per se may become blocked with particles, for example rock particles, in the course of time. It is known in the art to increase the permeability of a subterranean formations by an acid treatment (also referred to as "acidizing treatment" or "acidizing"). For example, aqueous solutions of HF, HCI or also organic acids may be used as acids for an acidizing treatment. Further details in this context are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 6th Edt, 2000 Electronic Release, "Resources of Oil and Gas, 3.4.2. General Production Engineering".

Subterranean, oil-bearing formations may comprise silicon-containing rocks, e.g. sandstone, silicates and/or alumosilicate rocks. For such type of rocks typically HF or HF-containing fluids are used which are capable of dissolving silicon-containing rocks. Consequently, such fluids comprise dissolved silicon-compounds after having been in contact with the silicon-containing rocks which subsequently may precipitate. Precipitates may plug the formation, pipes and other equipment and are thereby highly undesired. It is therefore known in the art to use certain additives in order to prevent or control silica scale. WO 2004/078662 A1 discloses phosphorous containing additives for inhibiting silica scales.

WO 2012/080695 A2 discloses to use ortho-dihydroxybenzene for silica scale control.

US 2008/001 1687 A1 discloses a method of inhibiting silicate/silica scale in aqueous systems using certain esters of carboxylic functional polymers with hydroxyl functional polyethers. The examples describe silica / silicate inhibition at pH 9.

It was an object of the present invention to provide an improved method of acidizing silicon- containing subterranean formations. Accordingly, a method of acidizing a silicon containing subterranean formation penetrated by at least a wellbore has been found, comprising at least injecting an aqueous, HF-containing treatment fluid having a pH < 3 into at least a portion of the subterranean formation, wherein the aqueous, HF-containing treatment fluid comprises additionally 0.1 % to 10 % by wt. -relating to the total of all components of the aqueous treatment fluid- of at least one water-soluble copolymer comprising at least

• 85 to 99 mole % relating to the total of all monomers in the polymer of at least one monoethylenically unsaturated monomer (A) comprising at least one carboxylic acid group and/or salts thereof, and

• 1 to 15 mole % relating to the total of all monomers in the polymer of at least one monoethylenically unsaturated monomer (B) having the following formula

wherein R¹ is selected from H and methyl, R² is selected independently from each other from H, methyl and ethyl with the proviso that at least 80 mol % of the groups R² are H, R³ is selected from H, methyl, ethyl, propyl or butyl, and n is a number from 10 to 100.

With regard to the invention, the following should be stated specifically: Aqueous treatment fluid

In the method according to the present invention an aqueous treatment fluid comprising at least water, HF and a water-soluble copolymer is used.

The aqueous treatment fluid comprises water. Besides water, the treatment fluid may comprise additionally organic, water-miscible solvents. Examples of such additional solvents comprise alcohols, for example methanol, ethanol or propanol. As a rule, the proportion of water is at least 80% by weight, preferably 90% by weight and particularly preferably at least 95% by weight, based in each case on the total amount of all solvents used. In one embodiment only water is used as solvent.

The aqueous treatment fluid furthermore comprises HF. It may comprise further acids besides HF, in particular HCI. The amount of HF may be from 0.1 % by wt. to 10 % by wt. regarding to the total of all components of the aqueous treatment fluid, preferably from 0.5 % by wt. to 3 % by wt..

In one embodiment of the invention the aqueous treatment fluid comprises at least HF and HCI. In such embodiment, the amount of HCI may be from 10 to 15 % by wt. of HCI and 2 to 5 % by wt. of HF relating to the total of all components of the aqueous treatment fluid. The aqueous treatment fluid has a pH value≤ 3, in particular < 2, and preferably≤ 1. The pH value may be from 0 to 3, for example 0 to 2 and preferably from 0 to 1. The aqueous treatment fluid furthermore comprises at least one water-soluble copolymer comprising acid groups and/or salts thereof. The copolymer serves as a scale inhibitor, in particular for Si-scales but it is also effective against Al-scales.

The copolymer used comprises at least one monoethylenically unsaturated monomer (A) com- prising at least one carboxylic acid group and/or salts thereof. Examples of suitable monomer (A) comprise acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid or fumaric acid. Preferably, the monomers (A) comprise (meth)acrylic acid. In one embodiment of the invention the monomers (A) comprise acrylic acid and methacrylic acid. The amount of all monomers (A) together is from 85 to 99 mole % relating to the total of all monomers in the copolymer, preferably from 90 to 98 mol % and for example from 92 to 95 mole %.

The copolymer used furthermore comprises at least one monoethylenically unsaturated mono- mer (B) having the following formula

In formula (I) wherein R¹ is a group selected from H and methyl.

R² is selected independently from each other from H, methyl and ethyl with the proviso that at least 80 mol % of the moieties R² are H. Preferably, at least 90 mol % of all R² are H and more preferably all moieties R² are H.

R³ is selected from H, methyl, ethyl, propyl or butyl, preferably from methyl, ethyl, propyl or butyl and more preferably R³ is a methyl group.

In formula (I) n is a number from 10 to 100, preferably from 15 to 50 and for example from 20 to 30.

In one embodiment of the invention R² is H and R³ is methyl.

The amount of all monomers (B) together is from 1 to 15 mole % relating to the total of all monomers in the copolymer, preferably from 2 to 10 mol % and for example from 5 to 8 mole %. Besides the monomers (A) and (B) the copolymer may comprise small amounts of ethylenically unsaturated, preferably monoethylenically unsaturated monomers (C) different from monomers (A) and (B). Such monomers may be used to fine-tune the properties of the copolymer to be used as scale inhibitor. The amount of such monomers (C) may from 0 to 14 mole %, for exam- pie 0 to 8 % by wt.. In one embodiment the amount of all monomers (A) and (B) together is 100 mol %; i.e. there are no further monomers besides the monomers (A) and (B).

In one embodiment, the copolymer comprises at least acrylic acid, methacrylic acid and at least a monomer (B), preferably a monomer (B) wherein R² is H, R³ is methyl and n is 15 to 50. Preferably the amount of amount of acrylic acid is from 60 to 75 mol %, the amount of methacrylic acid is from 20 to 30 mole % and the amount of monomers (B) is from 2 to 10 mole %. Preferably, the amount of all monomers (A) and (B) together is 100 mol %. The amount of the copolymer is from 0.1 to 10 % by wt. relating the total of all components of the aqueous treatment fluid. Preferably, the amount is from 0.5 to 6 % by wt., more preferably 1 to 4 % by wt. and for example 1 .5 to 3 % by wt.

Besides the components disclosed the aqueous, HF-containing treatment fluid may comprise optionally further additives and assistants which are typical for an acidizing treatment of oil- or gas-carrying rock formations. Examples of such assistants comprise, for example, polymers for increasing the viscosity, surfactants, foam formers or foam breakers, oxidizing agents, enzymes, complexing agents, assistants for reducing the friction or for controlling paraffin precipitations and biocides.

Method of acidizing

For carrying out the method according to the invention, the aqueous, HF-containing treatment fluid formulation is forced in a manner known in principle through at least one well into a silicon- containing subterranean formation.

The well may be a production well or an injection well. In the case of the production well, it is a well through which mineral oil or natural gas is also withdrawn. The injection well serves for forcing in flooding media for maintaining the pressure in the deposit. A treatment of the injection well reduces pressure drops when the flooding medium is forced in and thus also advantageously contributes to higher productivity.

The term "silicate-containing subterranean formation" relates to formations containing any type of silicates, including but not limited to silicon dioxide. Examples of such formations comprise sandstone formations or formations including other types of silicates such as alumosilicates, feldspar, carbonate, illite, kaolinite, smectite, mixed layer clay, chlorite, mica, zeolite, or quartz. The term shall include silicate-containing impurities which might be present in the subterranean formation.

The formation temperature may be up to 140°C, preferably up to 100°C and more preferably up to 70°C. In one embodiment the formation temperature may be from 20°C to 140°C, preferably from 20°C to 100°C, more preferably from 20°C to 80°C, and for example from 25°C to 70°C. The action time is determined by the person skilled in the art according to the local circumstances at the respective drilling site. It is, for example, dependent on the type of formation or on the deposits and/or impurities to be removed and on the concentration of the acid. The action time may be from a few minutes to several days.

The acidizing treatment according to the invention can also advantageously be combined with a hydraulic fracturing of the formation. Here, fracturing of the formation by means of any desired flooding medium, for example water, can first be carried out. Hydraulic fracturing can, however, also be carried out with the acidic formulation itself which is used according to the invention. Whether a simple acidizing treatment without hydraulic fracturing of the formation or a combined fracturing/acidizing treatment is effected can be determined by the person skilled in the art in a manner known in principle and by the choice of the pressure at which the acidic formulation is forced into the formation. The examples which follow are intended to illustrate the invention in detail:

Materials used

Inhibitor

For the tests a copolymer comprising ~ 68 mol % of acrylic acid, 25 mol % of methacrylic acid and 7 mol % of the monomer H2C=C(CH3)-COO-(CH2CH20)23-26-CH3 was used as scale inhibitor. The polymer was used as sodium salt.

Silicate

Kaolinite: AI₄[(OH)₈Si₄Oio] Mud acid

Acid mixture comprising 3 % by wt. of HF and 12 % by wt. of HCI. Solubility tests

For the solubility test Kaolinite was crushed and sieved to obtain a fine fraction having a particle size from 45 to 75 μηη. The Kaolinite fraction was mixed with the mud acid as described above at a weight ratio Kaolinite / mud acid of 1 : 10 and stirred for 2 hours. For the tests furthermore the polymer to be tested was added to the mixture. The amounts used are shown below. For comparative purposes tests without the polymer were performed.

Tests were performed at room temperature and at 93.3°C.

The room temperature test were performed by stirring the mixture in a beaker. For the solubility tests at 93.3°C a small amout of a commercially available corrosion inhibitor (Armohib^® CI-31 , 0.7 % by wt.) was added to the mixture and the mixture was put into a Teflon liner (used for testing highly corrosive fluids at high temperatures) which was pressurized (at 2.068^*10⁶ Pa) into an aging cell. The pressurized aging cell was placed into a preheated oven and rotated for 2 hrs.

After two hours the suspension obtained was filtered by filter paper (medium size, 5-10 micron) and the contents of Al ions and of Si ions in the filtrate were analyzed by ICP (Inductively Coupled Plasma).

The results are summarized in table 1.

Table 1 : Results of tests (C indicates comparative example)

The results indicate that the copolymer used in the present invention is effective at RT as Si- Inhibitor as well as Al-lnhibitor. Both, the Si-contents and the Al-contents in the filtrate are higher when adding 2 wt. % of the inhibitor. Interestingly, when adding 5 wt. % of the inhibitor the Si- contents and the Al-contents are still higher compared to adding no inhibitor however not as high as when adding only 2 wt. % of the inhibitor. So, using more inhibitor does obviously not enhance the effect. At 93.3°C adding the inhibitor has no longer a positive effect on the Si- contents of the filtrate but there is still a positive effect on the Al-contents.

Claims

Claims:

1. Method of acidizing silicate containing subterranean formations penetrated by at least a wellbore, comprising at least injecting an aqueous, HF-containing treatment fluid having a pH < 3 into at least a portion of the subterranean formation, wherein the aqueous, HF- containing treatment fluid comprises additionally 0.1 % to 10 % by wt. -relating to the total of all components of the aqueous treatment fluid- of at least one water-soluble copolymer comprising at least

2. Method according to claim 1 , wherein R² is H and R³ is methyl.

3. Method according to claims 1 or 2, wherein n is from 15 to 50.

4. Method according to any of claims 1 to 3, wherein monomer (A) comprises (meth)acrylic acid.

5. Method according to any of claims 1 to 3, wherein monomer (A) comprises acrylic acid and methacrylic acid.

6. Method according to any of claims 1 to 5, wherein the amount of monomer (B) is from 2 to 10 mole %.

7. Method according to any of claims 1 to 6, wherein the total of all monomers (A) and (B) is 100 mole %.

8. Method according to any of claims 1 to 3, wherein the copolymer comprises 60 to 75 mol % of acrylic acid, 20 to 30 mole % of methacrylic acid, and 2 to 10 mole % of monomer (B), and wherein the total of all monomers (A) and (B) is 100 mole %.

9. Method according to any of claims 1 to 8, wherein the aqueous treatment fluid comprises HF and HCI.

10. Method according to any of claims 1 to 8, wherein the aqueous treatment fluid comprises 10 to 15 % by wt. of HCI and 2 to 5 % by wt. of HF relating to the total of all components of the aqueous treatment fluid.

1 1. Method according to any of claims 1 to 10, wherein the pH value of the aqueous treatment fluid is < 1 .

12. Method according to any of claims 1 to 1 1 , wherein the concentration of the polymer is from 1 % by wt. to 4 % by wt. relating to the total of all components of the aqueous treat- ment fluid.

13. Method according to any of claims 1 to 12, wherein the temperature of the subterranean formation is from 20°C to 100°C.