WO2011021125A1

WO2011021125A1 - Methods for increasing the recovery rate of a hydrocarbon from an underground reservoir

Info

Publication number: WO2011021125A1
Application number: PCT/IB2010/053466
Authority: WO
Inventors: Marina Bulova; Dmitry Eskin
Original assignee: Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development Limited
Priority date: 2009-08-20
Filing date: 2010-07-30
Publication date: 2011-02-24
Also published as: CA2675903A1

Abstract

Methods for increasing the recovery rate of hydrocarbons from an underground reservoir. The methods involve injecting into the reservoir a first acid solution at a sufficient concentration to stimulate flow of the hydrocarbon in the reservoir, wherein the concentration of the first acid solution minimizes matrix acidizing and/or acid fracturing of the reservoir. The concentration of the first acid is sufficient to increase the hydrophilicity of the surface formations present in the underground reservoir, which stimulates the flow of hydrocarbons in the reservoir. The first acid may interact with connate water and form a second, stronger acid in situ.

Description

METHODS FOR INCREASING THE RECOVERY RATE OF A HYDROCARBON

FROM AN UNDERGROUND RESERVOIR

BACKGROUND OF THE INVENTION

Field of the Invention

The petroleum industry is constantly researching new techniques and methods to increase oi! and gas production from reservoirs. To increase production, more and more complicated stimulation techniques are applied to overcome problems related to underground formation and reservoir fluid properties. These techniques are often very expensive and involve the use of highly concentrated acids. In general, these techniques involve liberating oil and gas from either carbonate formations, sandstone formations, or a combination of both. One approach involves dissolving underground formations in order to create passages for the petroleum product to flow through the underground reservoir. Examples of this approach include matrix acidizing and acid fracturing.

Description of Related Art

[0002] Matrix acidizing involves injecting a concentrated acid or acids into carbonate rock formations. In this technique, wormholes are created by injecting into an underground reservoir highly concentrated acid solutions that react with the formation. For example, high concentrations of inorganic acids, such as hydrochloric and hydrofluoric acid, are typically used. These acids react with the underground formation and dissolve the bulk of carbonate rock to produce hollow channels or wormholes.

[0003] Acid fracturing involves injecting concentrated acid into the well a! pressures sufficient to fracture underground formations. Thus, a large flow channel is produced in the underground reservoir where hydrocarbons can freely move from the underground reservoir to the wcllbore,

[0004] Although matrix acidizing and acid fracturing permit enhanced oil and gas recovery from underground formations, there are several drawbacks to using these techniques. For example, strong acids, such as hydrochloric acid, are very corrosive to oil recovery equipment. Additionally, concentrated acids can be very dangerous to handle, especially when used in large quantities. Finally, strong aeids can degrade valuable hydrocarbons, which ultimately reduces recovery rates,

BRIEF SUMMARY OF THE INVtNTlON

[0005] Described herein are methods for increasing the recovery rale of hydrocarbons from an underground reservoir. The methods involve injecting into the reservoir a first acid solution at a sufficient concentration to stimulate flow of the hydrocarbon in the reservoir, wherein the concentration of the first acid solution minimizes matrix acidizing and/or acid fracturing of the reservoir. The concentration of the first acid is sufficient to increase the hydrophilicity of the surface formations present in the underground reservoir, which stimulates the flow of hydrocarbons in the reservoir. By increasing surface hydrophilicity within the reservoir, hydrocarbon recovery from the underground reservoir is increased.

[0006] The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

BRIEF DF SCRIP TlON OF THE DRAWINGS

[0007] The accompanying drawings, which are incoiporated in and constitute a part of this specification, illustrate several aspects described below.

[0008] Figure 1 shows oil liberation from calcium carbonate powder impregnated with oil and brine and subsequently treated with various dilute acids.

DF TAILED DESCRIPTION OF THE INVENTION

[0009] Before the present compounds, compositions, and methods are disclosed and described, it is to be understood that the aspects described below arc not limited to specific compounds, synthetic methods, or uses, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

3] In this specification and in the claims that follow, reference will be made to a number of term;, that shall be defined to have the following meanings:

[0011] The singular forms "a," '"an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a first acid solution" includes mixtures of two or more such acids, and the like.

[0012] Throughout this specification, unless the context requires otherwise, the word "comprise,¹" or variations such as "comprises" or "comprising," will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0013] "Optional" or 'Optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. For example, the phrase "optionally a surfactant" means that the surfactant may or may not be included in the first acid solution.

[0014] Described herein are methods for increasing the recovery rate of a hydrocarbon from an underground reservoir. The phrase "increasing the recovery rate" is defined herein as the ability to enhance the removal of a hydrocarbon from an underground reservoir using the methods described herein when compared to hydrocarbon removal from the same underground reservoir without using the methods described herein.

[0015] The methods involve injecting into the reservoir a first acid for a sufficient time and concentration, wherein the concentration of the first acid minimizes matrix acidizing of the reservoir. The concentration of the first acid introduced into the reservoir is substantially lower than the concentration utilized in matrix acidizing or acid fracturing. At most, a minimal amount of the surface formation present in the underground reservoir is dissolved by the first acid used herein. Thus, in certain aspects, the surface formation is etched to dissolve a very thin layer of the surface formation. This is very different from matrix acidizing, where a significant portion of the underground formation is dissolved by highly concentrated acids to produce large channels. Additionally, the methods described herein for the most part do not fracture underground formations as does acid fracturing. In other words, the methods described herein minimize bulk changes to the underground reservoir.

[0016] Not wishing to be bound by theory, the first acid used herein when introduced into an underground reservoir increases the hydrophificity of surface formations present in the reservoir. Underground formations such as, for example, carbonate formations, are characterized by having an oil-wet surface. Qii-wct surfaces arc generally hydrophobic in nature and prohibit or greatly hinder successful oil recovery from an underground formation. By contacting an underground formation having an oil-wet surface with a first acid solution using the methods described herein, the hydrophiϋeity (i.e., wettability) of the surface is changed from an oil-wet surface to a water-wet surface. Stated differently, the oil-wet, hydrophobic surface becomes more hydropbilic. This change in the formation^'s surface wettability enhances the liberation and isolation of the hydrocarbon from the underground reservoir.

[0017] The methods described herein are useful with underground reservoirs composed of a variety of different minerals and components. For example, the underground reservoir can be composed of carbonate (e.g., limestone, doloraitεj, sandstone, oil sands, and the like. The underground reservoir generally has one or more hydrocarbons that are to be recovered from the reservoir. Examples of hydrocarbons include, but arc not limited to. oil, natural gas, asphaltencs, or other petroleum products, In one aspect, the methods described herein can be useful in the removal of heavy oil from an underground reservoir. The term "heavy oil" is any source or form of viscous oil. For example, a source of heavy oil includes tar sand. Tar sand, also referred to as oil sand or bituminous sand, is a combination of clay, sand, water, and bitumen. Depending upon the underground reservoir, the underground formation may be completely saturated, partially saturated, or slightly saturated with one or more hydrocarbons.

[0018] The first acid can be a variety of different acids, ϊn one aspect, the first acid is an organic acid, an inorganic acid, or any combination thereof. Examples of the first acids include, but are not limited to. phosphoric acid, acetic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, formic acid, benzoic acid, boric acid, huraic acid, citric acid, oxalic acid, or any combination thereof. The acid must have sufficient strength to dissolve a monolayer of the formation, without plugging the formation by forming insoluble salts, as determined by core sample testing. The first acid solution may farther encompass any monoprotic, diprotic, or triprotic acid.

[0019] The first acid solution may vary in acid strength based on the type of underground formation and the acid required. However, the acid concentration is generally low enough to minimize matrix acidizing of the underground reservoir. The first acid solution is generally composed of a first acid and a suitable solvent. The solvent can be water, an appropriate organic solvent used in oil recovery, or a combination thereof. In one aspect, the first acid is less than 5%, less than 1%, less than 0.1%, less than 0.01%, or less than 0.001% by weight of the first acid solution, in another aspect, the first acid is 0.0001 wt%. 0.001 wt%, 0.01 wt%, 0.1 wt%, 0.2 wt°/o, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 Wt⁰Z₀, 1.0 wt%, 1.1 Wt⁰Z⁷O, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 Wt⁰Zo, 1.8 wt%, 1.9 wt%, 2.0 Wt⁰Z₀, 2.1 wt%, 2.2 wt%, 2.3 wt%. 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 Wt⁰Z₀, 3.0 Wt⁰Z₀, 3.1 wt%, 3.2 wt%, 3.3 wt%, 3.4 wt%, 3.5 Wt⁰Zo, 3.6 wt%, 3.7 wt%, 3.8 wt%, 3.9 wt%, 4.0 Wt⁰Zo, 4.1 wt%, 4.2 wt%, 4.3 wt%, 4.4 Wt⁰Zo, 4.5 wt%, 4.6 wt%, 4.7 wt%, 4.8 wt°ό, 4.9 wt°ό, or 5.0 wt% of the first acid solution, where any weight % vaiuε can form a lower and upper endpoint for a weight % range. For example, the first acid may range from 0.0001 wt% to 5.0 Wt⁰Zo, 0.001 wt% to 3.0 wt%, 0.01 wt% to 5.0 wt%, or 0.1 wt% to 3.0 wt% of the first acid solution.

[0020] The acid strength of the first acid solution can also be expressed in molarity (M). In one aspect, the molarity of the first acid solution is less than or equa! to 2.0 M, less than or equal to 1.0 M, less than or equal to 0.5 M, or less than or equal to 0.1 M. In other aspects, the first acid solution has a concentration of 0.001 M, 0.002 M, 0.003 M, 0.004 M. 0.005 M, 0.006 M, 0.007 M, 0.008 M. 0.009 M, 0.01 M, 0.02 M, 0.03 M, 0.04 M, 0.05 M, 0.06 M, 0.07 M, 0.08 M, 0.09 M, 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1.0 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, 1.5 M, 1.6 M, 1.7 M, 1.8 M, 1.9 M. or 2.0 M where any (M) value can form a lower and upper endpoint for a molarity range. For example the first acid solution ranges from 0.005 M to 0.9 M, 0.006 M to 0.5 M, 0.002 M to 0.1 M, 0.001 M to 0.08M, 0.01M to 0.09M, or 0.03 M to 0.08M. In one aspect, the first acid solution is acetic acid, phosphoric acid, or a combination thereof having a concentration of less than or equal to 0.5 M.

[0021] In certain aspects, the underground reservoir may contain connate water. Connate water is defined herein as the endogenous water either trapped within the pores of the underground reservoir during its creation or water naturally occurring within the underground reservoir. Connate water generally includes one or more ions derived from a variety of salts. Examples of such salts include, but are not limited to. alkali salts (e.g., sodium chloride, potassium chloride), alkali earth metal salts (e.g., calcium salts, magnesium salts), sulfates, phosphates, halides, or any combination thereof. In certain aspects, the connate water is brine.

[0022] Not wishing to be bound by theory, when the first acid is introduced into underground reservoir and comes into contact with connate water, the first acid can interact with ions present in the connate water to produce a second acid in situ. For example, a first acid solution composed of II₂SO₄ can be introduced into the underground reservoir containing connate water composed of NaCl. The TI₂SO4 subsequently interacts with NaCl to produce HCi in situ as shown below.

NaCi^■+- H₂SO₄ ~» HCl + NaHSO₄

In this example, both the first acid solution (II₂SO₄) and the in situ acid (HCl) may interact (e.g.. increase hydrophiiicity) of surface formations present in the underground reservoir. Depending upon the first acid selected, the in situ acid produced in the reservoir can be a stronger acid when compared to the first acid.

[0023] In one aspect, the first acid solution, will seek out the "unspent" connate water present in the underground formation. This ensures propagation of the first acid deeper into untouched formation. During this process, the first acid solution is '^"seeking^"' hydrophobic surfaces (i.e., surfaces that have not come into contact with the first, acidi present in the underground reservoir, which will ultimately stimulate the flow of hydrocarbons throughout the reservoir.

[0024] The first acid can be injected into the underground reservoir using techniques known in the art. For example, the first acid can be injected through the wellborc into the underground reservoir. In one aspect, the first acid can be introduced into the underground reservoir on a continuous basis. Here, the first acid can be cycled into and out of the underground reservoir. Alternatively, the first acid can be injected at a specific target in the underground reservoir. For example, a single injection of the first acid solution near the wellbore region can be performed. At higher temperature, the speed of reaction between the injected acid solution and the formation increases. If the reaction occurs with gas release (e.g. carbon dioxide), the accompanying pressure increase can slow the reaction between the acid and the formation. However, the temperature effect will generally be more pronounced. Further, if carbon dioxide is released during the reaction, it will improve heavy oil recovery as it causes precipitation of asphaltenes, thereby reducing the oil^'s viscosity and increasing its mobility.

EXAMPLES

[0025] The following examples arc put forth so as to provide those of ordinary skill irs the art with a complete disclosure and description of how the compounds, compositions, and methods described and claimed herein are made and evaluated, and arc intended to be purely exemplary and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ⁰C or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of reaction conditions, e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.

Simulated Oil Recovery

[0026] Figure 1 shows the results of an experiment in which different acids were used to test the recovery rate of oil from a carbonate formation. Jn this experiment, calcium carbonate powder was impregnated with brine and oil (hereinafter

"carbonate -oil packs"). All excessive liquid was removed. The carbonate- oil packs were placed into four separate syringes, and each syringe was tilled with (A) water (first syringe), (B) 0.1 M hydrochloric acid (second syringe), (C) 0.1 M acetic acid (third syringe), and (D) 0.1 M phosphoric acid (fourth syringe). After loading each syringe with a liquid, the carbonate-oil pack was allowed to sit at room temperature for one hour. After one hour, no oi! recovery was observed in the water system (A in Figure 1). However, recovery was observed with the hydrochloric acid system (B in Figure I), acetic acid system (C in Figure I), and phosphoric acid system (D in Figure 1). The recovery rate for the acids can be characterized as follows: phosphoric > acetic > hydrochloric. Additional experiments were performed at different acid concentrations. Data revealed that the recovery process occurred faster with 0.01 M acids than with 0.1 M acids; however, no difference was observed between 0.005 M acid and a water environment.

[0027] Various modifications and variations can be made to the compounds, compositions, and methods described herein. Other aspects of the compounds, compositions, and methods described herein will be apparent from consideration of the specification and practice of the compounds, compositions, and methods disclosed herein. It is intended that the specification and examples be considered as exemplary.

Claims

CLAIMS What is claimed is:

1. A method for increasing the recovery rate of a hydrocarbon from an

underground reservoir, the method comprising injecting into the reservoir a first acid solution at a sufficient concentration to stimulate flow of the hydrocarbon in the reservoir, wherein the concentration of the first acid solution minimizes matrix acidizing and/or acid fracturing of the reservoir.

The method of claim 1 , wherein the first acid etches the surface of the underground reservoir.

3. The method of claim i, wherein the first acid solution comprises an organic acid.

The method of claim 1 , wherein the first acid solution comprises an inorganic acid.

5. The method of claim 1 , wherein the first acid solution comprises a

combination of organic and inorganic acids.

6. The method of claim I, wherein the first acid comprises phosphoric acid, acetic acid, sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, formic acid, benzoic acid, boric acid, humic acid, citric acid, oxalic acid, or any combination thereof.

The method of claim I, wherein the first acid solution comprises an acid that is less than 5% by weight of the first acid solution.

8. The method of claim 1 , wherein the first acid solution comprises an acid that is less that! 1% by weight of the first acid solution.

9. The method of claim 1 , wherein the first acid solution comprises an acid that is less than 0.1% by weight of the first acid solution.

10. The method of claim I, wherein the first acid solution comprises an acid that is less than 0.01% by weigh! of the first acid solution.

11. The method of claim 1. wherein the first acid solution comprises an acid that is less than 0.001% by weight of the first acid solution.

12. The method of claim 1 , wherein the first acid solution comprises a

concentration of less than or equal to 2.0 M.

13. The method of claim I, wherein the first acid solution comprises a

concentration of less than or equal to 1.0 M,

14. The method of claim 1. wherein the first acid solution comprises a

concentration of less than or equal to 0.5 M.

15. The method of claim 1 , wherein the first acid solution comprises a

concentration of less than or equal to 0.1 M.

16. The method of claim I, wherein the first acid solution comprises acetic acid comprising a concentration of less than or equal to 0.5 M.

17. The method of claim i, wherein the first acid solution comprises phosphoric acid comprising a concentration of less than or equal to 0 5 M.

18 The method of claim 1 , whcrem the first acid solution comprises a

combination of acetic and pbosphoiic acids comprising a concentration of less than oi equal to 0.5 M.

19 The method of claim 1, wherein the underground reservoir comprises

carbonate.

20. The method of claim 1. wherein the underground reservoir comprises

sandstone.

21. The method of claim 1. wherein the undergiound reservυii compnses oil sands.

22 The method of claim 1 , wherein the hydrocarbon comprises oil, natural gas, or asphaltenes.

23. The method of claim 1, * herein the bydrocaibon comprises heavy oil.

24. The method of claim 1. wherein the first acid is injected into the undergiound reservoir as a single application.

25 The method of claim 1, wherein the first acid is injected into the underground reservoir in a continuous process.

26. A method for increasing the recovery rate of a hydrocarbon from an underground reservoir, the method comprising injecting into the reservoir a first acid solution at a sufficient concentration to react with connate water in the reservoir and form in situ a second acid which will stimulate flow of the hydrocarbon in the reservoir, wherein the concentration of the first and second acids minimizes matrix acidizing and acid fracturing of the reservoir.

27. The method of claim 26, wherein the second acid is stronger than the first acid.

28. The method of claim 26, wherein the first acid seeks unspent connate water and thereby penetrates deeper into the reservoir.

29, A method for increasing the surface hydropbiJtcity of an underground

formation comprising contacting the formation with a first acid solution at a sufficient concentration to increase the surface hydrophilicity of the underground formation.