CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to Canadian Patent Application No. 3,054,052, filed Sep. 4, 2019. The entire specification and figures of the above-referenced application are hereby incorporated, in their entirety by reference.

FIELD OF THE INVENTION

The present invention is a liquid acidic composition for application in the oil & gas industry, more specifically, the composition is invented to reduce negative friction reducer compatibility issues in higher iron bearing formations.

BACKGROUND OF THE INVENTION

In the oil and gas industry, friction reducers are widely applied in fracturing operations (slick water fracks) to minimize frictional losses during pumping operations. Indeed during several types of operations, namely, drilling, completion and stimulation of subterranean wells, injected fluids are often pumped downhole at very high rates, in particular during fracking operations. During the injection, there is often frictional losses of energy due to fluidic turbulence and friction. Without the use of friction reducers, these frictional energy losses may require additional horsepower to pump or place the fluids and proppant at a rate capable of achieving the designed or engineered stimulation program injection rates. To minimize frictional energy losses, certain friction reducing polymers have been incorporated in the fluids prior to their injection downhole.

To achieve this high molecular weight (Mw) polymers are utilized. The drag reduction properties of high Mw polymers arise from polymer elongation, which dampens the quasi-streamwise vortices that are characteristic of turbulent flow. The drag reduction properties increase with increasing Mw due to the more pronounced stretching of the very long polymer chains. Typically, three classes of polymers are used for this application: non-ionic-; anionic; and cationic polymers. Characteristic for all three classes is that at least one monomer is acrylamide and therefore the resulting polymers are polyacrylamides, co-polyacrylamides or ter-polyacrylamides. The hydrolyzed form of Polyacrylamide (HPAM), a co-polymer of acrylamide and acrylic acid, is the most widely used anionic friction reducer in oil and gas applications.

Polyacrylamides (PAM, HPAM etc.) can undergo different degradation processes. The one of interest for the current invention is the further hydrolysis at a low pH (acidic conditions) under downhole conditions (elevated temperature and pressure). The hydrolysis of amide groups leads to the generation of carboxylic acid groups and therefore to an increased number of negative charges along the polymer chain. If in the formation increased Fe2+/Fe3+concentrations are present, this can lead to the formation of complexes, which are crosslinking polymer chains. With increased crosslinks the high Mw polymers have tendency to form a gel, similar to super absorbers.

It is theorized that the described gel formation becomes a more severe problem, if during the individual stages of fracturing operations (slick-water fracs) a spearhead acid for the initial cement and/or formation break down is utilized. With such an operational procedure the risk increases that the utilized friction reducers are undergoing the described hydrolysis. If then Fe2+/Fe3+ions are present the described gel formation can cause major production shut-offs and costly remediation procedures to remove the formed gel plugs downhole.

Some prior art documents describe slick water problems and propose solutions. Among them, U.S. Pat. No. 7,846,878 teaches a method that comprises: introducing a treatment fluid into a subterranean formation, wherein the treatment fluid comprises water and a concentrated polymer composition comprising a complexing agent and a friction reducing polymer. Also disclosed is a method that comprises combining at least water and a concentrated polymer composition to form a treatment fluid, wherein the concentrated polymer composition comprises a complexing agent and a friction reducing polymer; and introducing the treatment fluid into a subterranean formation. Also disclosed is a concentrated polymer composition comprising: a friction reducing polymer in an amount of about 15% to about 60% by weight of the composition; and a complexing agent.

U.S. Pat. No. 6,265,355B1 teaches a composition containing a chelating agent and an amino carboxylic acid and a method for breaking a gel formed by a crosslinkable polymer and a crosslinking agent. The composition may also be used for selectively removing crosslinked polymer gels from an oil-bearing zone in a subterranean formation in the presence of a water formation plugged by a crosslinkable polymer and a crosslinking agent. Aqueous solutions of phosphonates and sulfonates are also useful in the method.

U.S. Pat. No. 4,815,537A teaches an improved sweep efficiency obtained in an oil recovery process wherein oil is recovered from a subterranean, viscous oil containing formation having relatively highly permeable zones and relatively low permeability zones penetrated by at least one injection well and at least one spaced apart production well in fluid communication with a substantial portion of the formation. It is stated that first, a predetermined amount of gel solution is injected into the formation at high pressure to deeply penetrate and plug the fracture face and highly permeable zones of the formation. Thereafter, a breaker material such as hydrochloric acid is injected into the formation at a low pressure to break the gel and displace it from the fracture face and highly permeable zones in the vicinity of the injection well thereby reestablishing injectivity into the formation in the vicinity of the injection well. Thereafter, a flooding agent such as carbon dioxide, steam or water is injected into the formation that displaces oil through the low permeability unswept zones of the formation and fluids including oil are recovered from the formation through the production well.

US patent application number US2014/0124205A1 discloses a process for fracturing a subterranean formation comprising a step of fracturing the formation and a step of introducing a treatment fluid containing glutamic acid N,N-diacetic acid or a salt thereof (GLDA), methylglycine N,N-diacetic acid or a salt thereof (MGDA) and/or N-hydroxyethyl ethylenediamine N,N′,N′-triacetic acid or a salt thereof (HEDTA) into the formation, wherein the fracturing step can take place before introducing the treatment fluid into the formation, while introducing the treatment fluid into the formation or subsequent to introducing the treatment fluid into the formation.

U.S. Pat. No. 9,650,299 B2 teaches methods and compositions for the treatment of subterranean formations. In various embodiments, the method includes obtaining or providing a composition including at least one-ion sequestering compound, sequestering at least one ion from a polymer in the composition with the at least one ion-sequestering compound, and contacting a subterranean material downhole with the composition.

U.S. Pat. No. 9,932,516 B2 teaches a composition used to prevent the interaction between a polymer in a water-based fracturing fluid and naturally-occurring metal ions. The composition includes a metal-complexing agent, such as a chelating agent. The chelating agent can also be biodegradable and is citric acid in embodiments. The metal-complexing agent can be coated with one or two coatings to create a time-released form. The time-released form prevents loss of the agent prior to delivery at the shale.

International patent application WO2012/116032A1 discloses a breaker fluid may include a base fluid; and an inactive chelating agent. A process may include pumping a first wellbore fluid comprising an inactive chelating agent into a wellbore through a subterranean formation; and activating the inactive chelating agent to release an active chelating agent into the wellbore.

U.S. Pat. No. 5,497,830A teaches a particulate gel breaker for the controlled reduction in viscosity of aqueous acid compositions used in fracture acidizing of subterranean formations, such as in oil and gas wells, is formed for use with crosslinked polymer gels which are crosslinked with organometallic compounds, such as titanium or zirconium. The gel breaker is composed of particles containing complexing materials such as fluoride, phosphate, sulfate anions and multi-carboxylated compounds, which are capable of complexing with the organometallic crosslinking compounds of the gel. The particles are said to be coated with a water insoluble wood resin coating which reduces the rate of release of the complexing materials of the particles so that the viscosity of the gel is reduced at a retarded rate. It is said that the gel can thus be introduced into the well at a sufficiently high viscosity for fracturing and to allow time for the acid to penetrate the formation before the acid is released.

U.S. Pat. No. 9,932,516 B2 teaches a composition used to prevent the interaction between a polymer in a water-based fracturing fluid and naturally-occurring metal ions. The composition includes a metal-complexing agent, such as a chelating agent. The chelating agent can also be biodegradable and is citric acid in embodiments. The metal-complexing agent can be coated with one or two coatings to create a time-released form. The time-released form prevents loss of the agent prior to delivery at the shale.

U.S. Pat. No. 6,436,880 B1 teaches that an acidic fluid that is useful in stimulation and workover operations, and in particular, for the control of iron in acidizing operations, the removal of alkaline earth carbonate scale in scale removal operations, and matrix or fracture acidizing operations, comprises an acid, such as hydrochloric acid; water; and a hydroxyethylaminocarboxylic acid. Preferred hydroxyethylaminocarboxylic acids are hydroxyethylethylenediaminetriacetic acid (HEDTA) and hydroxyethyliminodiacetic acid (HEIDA). Also disclosed herein are methods of controlling iron, removing alkaline earth carbonate scale, or matrix or fracture acidizing, involving the use of the acidic fluid.

The most commonly used chelating agents are typically EDTA-based agents. Concerns have been raised with the extensive use of these chelating agents as they may exhibit some drawbacks which had not previously been considered. Direct and indirect potential effects of the presence of EDTA in the environment have been studied. EDTA has been found to mobilize contaminant metal ions, particularly heavy metals. Studies have also discovered that EDTA can solubilize radioactive metals and increase their environmental mobility. Other studies have revealed the toxicity of EDTA photosynthetic organisms and as it may inhibit cellular division, chlorophyll synthesis and algal biomass production. The same studies pointed out that the same concentration of EDTA chelated with micronutrients was shown to not have these deleterious properties.

Despite the prior art teachings, there still exists a need for a composition to use in slickwater fracturing or stimulation treatments to avoid and/or minimize the formation of polymer/metal complexes which lead to losses in oil production. Preferably, to overcome this need, the composition should not rely on the use of an EDTA-based chelating agent if at all possible.

SUMMARY OF THE INVENTION

The inventors have studied the possibility to mitigate the formation of polymer/polymer complexes via Fe2+/Fe3+crosslinks, by introducing into the spearhead acid an additional chelating agent compound, which has the ability to form a more stable complex with Fe2+/Fe3+. Such chelating agents include: tetra sodium EDTA; EDTA; propylenediaminetetraacetic acid (PDTA); nitrilotriacetic acid (NTA); N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA); diethylenetriaminepentaacetic acid (DTPA); hydroxyethyliminodiacetic acid (HEIDA); cyclohexylenediaminetetraacetic acid (CDTA); diphenylaminesulfonic acid (DPAS); ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA); sodium gluconate; gluconic acid; malonic acid; succinic acid; glutaric acid; adipic acid; pimelic acid; suberic acid; azelaic acid; isocitric acid; citric acid; tetrasodium glutamate diacetate and glutamic acid diacetic acid (GLDA); salts thereof, and mixtures thereof

It is an object of the present invention to provide a modified acid composition which can be used over a broad range of applications in the oil and gas industry and which exhibit advantageous properties over known compositions. According to an aspect of the present invention, there is provided a synthetic or modified acid composition comprising: a chelating agent compound and a synthetic or modified acid.

According to an aspect of the present invention, there is provided a composition for use in reducing the gelation caused when there is contact between a friction reducer and free metal ions during oilfield operations. Friction reducers typically breakdown when exposed to acidic conditions.

According to an aspect of the present invention, there is provided a method of spearheading an acid into a wellbore adapted to avoid the gelation of a friction reducer polymer, wherein said method comprises:

injecting a synthetic or modified acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound, optionally the composition may comprise a corrosion inhibitor package;

allowing sufficient time for the synthetic or modified acid composition to react with material which require acidic treatment;

injecting a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

According to another aspect of the present invention, there is provided a method of spearheading an acid into a wellbore adapted to reduce the gelation of a friction reducer polymer, wherein said method comprises:

injecting a synthetic or modified acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound, optionally the composition may comprise a corrosion inhibitor package;

allowing sufficient time for the synthetic or modified acid composition to react with material which require acidic treatment;

injecting a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

Preferably, the synthetic or modified acid is selected from the group consisting of: Urea-HCl; amino acid-HCl; and alkanolamine-HCl. Preferably, the amino acid is selected from the group consisting of: lysine; glycine; sarcosine, betaine (such as trimethyl glycine), dimethyl glycine (DMG), iminodiacetic acid (IDA), alanine, asparagine, aspartic acid, cysteine, glutamic acid, histidine, leucine, lysine, methionine, proline, serine, threonine or valine or combinations thereof. More preferably, the amino acid is lysine. According to another preferred embodiment, the acid is a sulfonic acid selected from the group consisting of: methanesulfonic acid and toluenesulfonic acid.

According to a preferred embodiment of the present invention, the alkanolamine is selected from the group consisting of: monoethanolamine; diethanolamine; and triethanolamine. Preferably, the alkanolamine is monoethanolamine. According to a preferred embodiment, the acid is an aqueous modified acid composition wherein the hydrochloric acid and alkanolamine are present in a molar ratio of not more than 7.0:1. More preferably, hydrochloric acid and alkanolamine are present in a molar ratio of not more than 4:1. Even more preferably, hydrochloric acid and alkanolamine are present in a molar ratio of not more than 3:1. According to another preferred embodiment of the present invention, the method uses a synthetic or modified acid composition comprising: a strong acid, such as hydrochloric acid and an alkanolamine in a molar ratio of not more than 15:1; preferably in a molar ratio not more than 10:1, more preferably in a molar ratio of not more than 8:1; even more preferably in a molar ratio of not more than 5:1; yet even more preferably in a molar ratio of not more than 3.5:1; and yet even more preferably in a molar ratio of not more than 2.5:1.

According to a preferred embodiment of the present invention, the chelating agent compound is present in the synthetic acid composition in an amount ranging from 0.1 wt % to 5 wt %. More preferably, the chelating agent compound is present in the synthetic acid composition in an amount ranging from 0.5 wt % to 2 wt %. Most preferably, the chelating agent compound is present in the synthetic acid composition in an amount of about 1 wt %.

According to another aspect of the present invention, there is provided a method of selectively depleting divalent cations present in a spent spearheading acid composition into a wellbore, wherein said method comprises:

injecting a synthetic or modified acid composition down a wellbore, said composition comprising: a synthetic or modified acid; a solvent; and a chelating agent compound, optionally the composition may comprise a corrosion inhibitor package;

allowing sufficient time for the synthetic or modified acid composition to react with material which require acidic treatment; and

allowing sufficient time for the chelating agent to remove cations for the spent acid.

Preferably, the method further comprises the injection of a fracturing composition comprising a liquid and a friction reducing polymer down the wellbore.

