FIELD OF THE INVENTION

This invention relates to a method of stabilizing an aqueous composition of alkanolamine more specifically, where said composition is used for the on-site blending of a modified acid.

BACKGROUND OF THE INVENTION

In the oil & gas industry, stimulation with an acid is performed on a well to increase or restore production. In some instances, a well initially exhibits low permeability, and stimulation is employed to commence production from the reservoir. In other instances, stimulation or remediation is used to further encourage permeability and flow from an already existing well that has become under-productive due to scaling issues or formation depletion. Acidizing is a type of stimulation treatment which is performed above or below the reservoir fracture pressure in an effort to initiate, restore or increase the natural permeability of the reservoir. Acidizing is achieved by pumping acid, predominantly hydrochloric acid, into the well to dissolve typically limestone, dolomite and calcite cement between the acid insoluble sediment grains of the reservoir rocks or to treat scale accumulation. There are three major types of acid applications: matrix acidizing, fracture acidizing, and breakdown acidizing (pumped prior to a fracturing pad or cement operation in order to assist with formation breakdown (reduce fracture pressures, increased feed rates), as well as clean up left over cement in the well bore or perforations. A matrix acid treatment is performed when acid is pumped into the well and into the pores of the reservoir formation below the fracture pressure. In this form of acidization, the acids dissolve the sediments formation and/or mud solids that are inhibiting the permeability of the rock, enlarging the natural pores of the reservoir (wormholing) and stimulating the flow of hydrocarbons to the wellbore for recovery. While matrix acidizing is done at a low enough pressure to keep from fracturing the reservoir rock, fracture acidizing involves pumping acid into the well at a very high pressure, physically fracturing the reservoir rock and etching the permeability inhibitive sediments. This type of acid treatment forms channels or fractures through which the hydrocarbons can flow, in addition to forming a series of wormholes. In some instances, a proppant is introduced into the fluid which assists in propping open the fractures, further enhancing the flow of hydrocarbons into the wellbore. There are many different mineral and organic acids used to perform an acid treatment on wells. The most common type of acid employed on wells to stimulate production is hydrochloric acid (HC1), which is useful in stimulating carbonate reservoirs. Some of the major challenges faced in the oil & gas industry from using hydrochloric acid include the following: extremely high levels of corrosion (which is countered by the addition of 'filming' type corrosion inhibitors that are typically themselves toxic and harmful to humans, the environment and equipment) reactions between acids and various types of metals can vary greatly but softer metals, such as aluminum and magnesium, are very susceptible to major effects causing immediate damage. Hydrochloric acid produces hydrogen chloride gas which is toxic (potentially fatal) and corrosive to skin, eyes and metals. At levels above 50 ppm (parts per million) it can be Immediately Dangerous to Life and Health (IDHL). At levels from 1300-2000 ppm death can occur in 2-3 minutes. The inherent environmental effects (organic sterility, poisoning of wildlife etc.) of acids in the event of an unintended or accidental release on surface or downhole into water aquifers or other sources of water are devastating and can cause significant pH reduction of such and can substantially increase the toxicity and could potentially cause a mass culling of aquatic species and potential poisoning of humans or livestock and wildlife exposed to/or drinking the water. An unintended release at surface can also cause hydrogen chloride gas to be released, potentially endangering human and animal health. This is a common event at large storage sites when tanks split or leak. Typically if near the public, large areas need to be evacuated post event and a comprehensive, expensive to implement, emergency evacuation plan needs to be in place prior to approval of such storage areas. Because of its acidic nature, hydrogen chloride gas is also corrosive, particularly in the presence of moisture. The inability for mineral acids with common corrosion control additives and blends of such to biodegrade naturally results in expensive cleanup -reclamation costs for the operator should an unintended release occur. Moreover, the toxic fumes produced by mineral & some organic acids are harmful to humans/animals and are highly corrosive and/or produce potentially explosive vapours. Transportation and storage requirements for acids are restrictive and taxing. As well, the dangers surrounding exposure by personnel handling the blending of such dangerous products constrict their use/implementation in areas of high risk such as within city limits and environmentally sensitive areas such as offshore.

Another concern is the potential for exposure incidents on locations due to high corrosion levels, even at ambient temperatures, of acids causing potential storage tank failures and/or deployment equipment failures i.e. coiled tubing or high pressure iron failures caused by high corrosion high rates (pitting, cracks, pinholes and major failures). Other concerns include: downhole equipment failures from corrosion causing the operator to have to execute a work-over and replace down hole pumps, tubulars, cables, packers etc.; inconsistent strength or quality level of mineral & organic acids; potential supply issues based on industrial output levels; high levels of corrosion on surface pumping equipment resulting in expensive repair and maintenance levels for operators and service companies; the requirement of specialized equipment that is purpose built to pump acids greatly increasing the capital expenditures of operators and service companies; and the inability to source a finished product locally or very near its end use; transportation and onsite storage difficulties. Typically, acids are produced in industrial areas of countries located some distance from oil & gas producing areas, up to 10 additives can also be required to control various aspects of the acids properties adding to complications in the handling and shipping logistics. Having an alternative that requires minimal additives is very advantageous. Extremely high corrosion and reaction rates with temperature increase causes conventional acids to spend/react or "neutralize" prior to achieving the desired effect such as deeply penetrating an oil or gas formation to increase the wormhole or etched "pathway" effectively to allow the petroleum product to flow freely to the wellbore. As an example, hydrochloric acid can be utilized in an attempt to free stuck drill pipe in some situations. Prior to getting to the required depth to dissolve the formation that has caused the pipe/tubing to become stuck many acids spend or neutralize on formation closer to the surface due to increased bottom hole temperatures and greatly increased reaction rate, so it is advantageous to have an alternative that spends or reacts more methodically allowing the slough to be treated with a solution that is still active, allowing the pipe/tubing to be pulled free. When used to treat scaling issues on surface equipment due to water mineral precipitation, conventional acids are exposed to human and mechanical devices as well as expensive equipment causing increased risk and cost for the operator.

When mixed with bases or higher pH fluids, acids will create a large amount of thermal energy (exothermic reaction) causing potential safety concerns and equipment damage, acids typically need to be blended with fresh water (due to their intolerance of highly saline water, causing potential precipitation of minerals) to the desired concentration requiring companies to pre -blend off-site as opposed to blending onsite with sea or produced water thereby increasing costs associated with transportation. Conventional mineral acids used in a pH control situation can cause rapid degradation of certain polymers/additives requiring increased loadings or chemicals to be added to counter these negative effects.

Many offshore areas of operations have very strict regulatory rules regarding the transportation/handling and deployment of acids causing increased liability and costs for the operator. When using an acid to pickle tubing or pipe, very careful attention must be paid to the process due to high levels of corrosion, as temperatures increase, the typical additives used to control corrosion levels in acid systems begin to degrade very quickly (due to the inhibitors "plating out" on the steel or sheering out in high rate applications) causing the acids to become very corrosive and resulting in damage to downhole equipment/tubulars. Conventional acids can be harmful to many elastomers and/or seals found in the oil & gas industry such as those found in blow out preventers (BOP's) /downhole tools/packers/submersible pumps/seals etc. Having to deal with spent acid during the back flush process is also very expensive as these acids typically are still at a low pH and remain toxic and corrosive. It is advantageous to have an acid blend that can be exported to production facilities through pipelines that, once spent or applied, is much higher than that of spent HCI, reducing disposal costs/fees. Also mineral acids will typically precipitate iron and/or minerals solubilized during the operation as the pH of the spent acid increases causing facility upsets and lost production. It is advantageous to have a strong acid that will hold these solubilized minerals and metals in solution even as pH rises dramatically close to a neutral state, greatly reducing the need to dispose of spent acids and allowing them to be processed and treated in a more economical manner. Acids are used in the performance of many operations in the oil & gas industry and are considered necessary to achieve the desired production of various petroleum wells and associated equipment, maintain their respective systems and aid in certain drilling operational functions (i.e. freeing stuck pipe, filter cake treatments). The associated dangers that come with using mineral acids are expansive and tasking to mitigate through controls whether they are chemically or mechanically engineered. Eliminating or even simply reducing the negative effects of strong acids while maintaining their usefulness is a struggle and risk for the industry. As the public and government demand for the use of less hazardous products increases, companies are looking for alternatives that perform the required function without all or most of the drawbacks associated with the use of conventional acids.

Several operations in the oil industry expose fluids to very high temperatures (some up to and over 200°C/392°F), the compositions used in these various operations need to withstand high temperatures without losing their overall effectiveness. These compositions must also be capable of being applied in operations over a wide range of temperatures while not or at least minimally affecting or corroding the equipment with which it comes in contact in comparison to a conventional mineral acid of which the corrosion effect at ultra-high temperatures is very difficult and expensive to control. Offshore oil and gas operations are highly regulated due to the environmental concerns which arise from their operations and the potential for spills along with confined work spaces offering little chance of egress in the case of an incident. The complexity of drilling and completing offshore wells is always compounded by both safety issues (exposure to dangerous chemicals as an example) for workers on such offshore oil rigs and production platforms as well as environmental concerns. Many countries bordering the waters where offshore drilling and production is routinely carried out have put into play a number of regulations and operational parameters aimed at minimizing the environmental and human exposure impact. These regulations/procedures include the ban and/or regulation of certain chemicals which may be harmful to marine life and/or the environment. In order to overcome these very restrictive regulations, many oil companies employ very costly containment programs for the handling of certain chemicals, such as acids, which have a wide array of uses in the industry of oil and gas exploration and production. Many of the issues related with offshore oil and gas exploration and production stem from the fact that the conditions under which this is carried out are substantially different than those encountered in the same types of operations carried out onshore, including but not limited to confined spaces, lack of escape routes, very expensive down hole and surface safety and operational equipment compared to onshore requirements Acids conventionally used in various oil and gas operations can be exposed to temperatures of up to 200 C. At these temperatures, their reactivity and corrosive properties is exponentially increased and as such their economical effectiveness is greatly decreased. Corrosion is one of the major concerns at high temperatures and is difficult and expensive to control with additional chemistry, if it can be controlled at all. In many situations a mechanical procedure must be utilized as opposed to a chemical solution due to temperature constraints modified and synthetic acids developed and currently patented such as those containing main components of urea and hydrochloric acid are aimed at increasing personnel safety, reducing corrosion effects, slowing down the reaction rate and reducing the toxicity of HC1. However, it has been found that at temperatures above 90°C the urea component in a synthetic or modified acid containing such compound tends to ultimately decompose and produce ammonia and carbon dioxide as a by-product of decomposition. The ammonia component will neutralize the acidic component or HC1 and render the product non-reactive or neutral. Additionally there is the risk of wellbore and/or formation damage due to uncontrolled solubilized mineral precipitation due to the increase in pH caused predominantly by the formation of ammonia during the decomposition phase.

It has been discovered since the introduction of a modified acid comprising an alkanolamine and HC1 in a molar ratio ranging from 1:3 to 1:12.5, that during the shipping of the components in two separate tanks in the hull of a ship (MEA-HC1 in water tank of a ship and commercial grade HC1 in the acid tank of a ship), there were signs that, under some conditions, the MEA-HC1 would recrystallize in the tank prior to being blended with the commercial grade HC1. This undermines the value of the modified acid comprising MEA and HC1 if such cannot be reliably shipped to remote location or even to offshore. In order to maximize the volume of modified acid which is being transported by ship, it is desirable that the modified acid be shipped in separate components. Since there is an acid tank and a water tank on ships capable of transporting acids, and that modified acids cannot be shipped in the water tank, it is thus necessary to optimize the cargo by shipping the acid in the acid tank and the alkanolamine (such as monoethanolamine (MEA)) in aqueous form in the water tank of the ship. The MEA aqueous composition would preferably be in a solution of pure MEA. However, when substantially pure MEA is fuming when in contact with air humidity and can thus be very dangerous to those handling it.

In light of this drawback, there is a need to develop a method to stabilize compositions of alkanolamine to be shipped in the water tanks of ships. The value of modified acid compositions comprising a mineral acid, such as HC1 and an alkanolamine such as monoethanolamine has been recently established, hence a method to overcome one of many of the above-mentioned drawbacks would help enhance its reliability and further increase its value as a reliable replacement of conventional hydrochloric acid.

SUMMARY OF THE INVENTION

Compositions according to the present invention have been developed for the oil & gas industry and its associated applications, by targeting the problems of corrosion, logistics & handling, human & environmental exposure, reaction rates, toxicity levels, biodegradation tendencies and formation/fluid compatibilities and facility and/or production and water treatment infrastructure operational compatibilities. 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 method to improve and/or ensure the stability of an aqueous composition comprising an alkanolamine and HC1 where such a composition is typically saturated or a near saturated state.

It has been surprisingly and unexpectedly discovered that by adding a first acidic component to a saturated aqueous composition comprising an alkanolamine, one can improve the stability of the composition. Preferably, the stability refers to the temperature stability. According to a preferred embodiment of the present invention, the alkanolamine is selected from the group consisting of: monoethanolamine; diethanolamine and triethanolamine. The most preferred being monoethanolamine. Combining a premix composition (also referred to as pre-blend) comprising water, said alkanolamine and said first acidic component with a commercial grade acid such as hydrochloric acid, leads to the generation of a reconstituted modified acid composition.

According to an aspect of the present invention, there is provided a method to stabilize a MEA- HC1 composition having a pH preferably ranging between 7 and 11 and more preferably between 7.5 and 10.5 (especially during shipping or long term storage) prior to its combination in a vessel or on the fly with HC1 to provide an aqueous synthetic acid composition for use in oil and gas activities, said modified acid composition comprising: a strong 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 4.1:1; and yet even more preferably in a molar ratio of not more than 3:1. According to another aspect of the present invention, there is provided a modified acid composition comprising: a strong acid and an alkanolamine in a molar ratio ranging from 3:1 to 15:1, preferably from 3:1 to 10:1; more preferably from 4:1 to 8:1, also preferably from 5:1 to 6.5:1.

According to an aspect of the present invention, there is provided a method to increase the stability of an aqueous composition comprising an alkanolamine, said method comprising the steps of: providing a vessel; adding a pre-determined amount of water into said vessel; adding a pre-determined amount of an acid to said water; and adding said alkanolamine to said vessel; and mixing the blend until resulting mixture is homogeneous; wherein the resulting mixture of alkanolamine and said acid has a pH ranging from 7 to 11 , is stable down to a temperature of -5°C and said resulting mixture comprises said alkanolamine and HC1 in a molar ratio ranging from 1:1 to 1:0.1 of alkanolamine: acid.

According to a preferred embodiment of the present invention, the resulting aqueous composition comprising said alkanolamine and acid in a molar ratio ranging from 1:1 to 1:0.2 of alkanolamine: acid. Preferably, the resulting aqueous composition comprising said alkanolamine and acid in a molar ratio ranging from 1:1 to 1:0.4 of alkanolamine:acid. More preferably, resulting aqueous composition comprising said alkanolamine and acid in a molar ratio ranging from 1:1 to 1:0.6 of alkanolamine: acid.

According to a preferred embodiment of the present invention, the acid is selected from the group consisting of: organic acids; mineral acids; and combinations thereof. Preferably, the organic acid is selected from the group consisting of: citric acid; acetic acid; and the like. Preferably, the mineral acid is selected from the group consisting of: HC1; nitric acid; sulfuric acid; and the like. More preferably, the mineral acid is HC1.

According to a preferred embodiment of the present invention the alkanolamine is selected from the group consisting of: monoethanolamine; diethanolamine; and triethanolamine.

According to another aspect of the present invention, there is provided a stabilized aqueous composition of alkanolamine-acid wherein said composition consists of:

- an alkanolamine present in an amount ranging from 9 wt.% to 15 wt.%.

- water; and - an acidic component adapted to stabilize said alkanolamine; wherein said composition has a pH ranging from 7 to 11 and is stable down to a temperature of -5°C, wherein stable is meant to understand that the alkanolamine does not precipitate out from the composition.

According to a preferred embodiment of the present invention, said alkanolamine is present in an amount ranging from 10 wt.% to 13 wt.%. Preferably, said alkanolamine is present in an amount ranging from 10.5 wt.% to 12 wt.%.

According to yet another aspect of the present invention, there is provided a use of a stabilized aqueous composition of an alkanolamine for the preparation of a reconstituted modified acid composition, wherein said stabilized aqueous composition of alkanolamine consists of:

- said alkanolamine in an amount ranging from 9 wt.% to 15 wt.%;

- water; and

- an acidic component adapted to stabilize said alkanolamine; wherein said stabilized aqueous composition of alkanolamine has a pH of no more than 10.0 and is stable down to a temperature of -10°C, wherein stable is meant to understand that the alkanolamine does not recrystallize out from the composition; and wherein said reconstituted modified acid composition has a pH below 1 and comprises said alkanolamine and HC1 in a molar ratio ranging from 1:3 to 1:15.

According to another aspect of the present invention, there is provided a method of preparing a reconstituted modified acid composition comprising an alkanolamine and an acid, said method comprising the steps of: providing a vessel; adding a pre-determined amount of water into said vessel; adding a pre-determined amount of a first acid to said water; and adding an alkanolamine to said vessel; and mixing the blend until resulting mixture comprising said alkanolamine and said first acid is homogeneous; wherein the resulting aqueous composition of alkanolamine and said first acid has a pH ranging from 7 to 11, is stable down to a temperature of -5°C and said resulting mixture comprises said alkanolamine and said first acid in a molar ratio ranging from 1:1 to 1:0.1 of alkanolamine:acid; providing a predetermined amount of mineral acid such as HC1; nitric acid; sulfuric acid; and the like; admixing said mineral acid with said resulting aqueous composition comprising said alkanolamine and said first acid until reconstituted modified acid is homogeneous; wherein said reconstituted acid composition comprises said alkanolamine and said mineral acid in a molar ratio ranging from 1:3 to 1:15, said reconstituted acid composition has a pH of less than 1 and a freezing point of less than -10°C. Preferably, the mineral acid is HC1. Preferably, the reconstituted acid composition has a freezing point of less than -18°C.

Preferred embodiments of the present invention provide a modified acid composition which, upon proper use, results in a very low corrosion rate on oil and gas industry tubulars down-hole tools and equipment. According to a preferred of the present invention, there is provided a modified acid composition for use in the oil industry which is biodegradable. According to a preferred of the present invention, there is provided a modified acid composition for use in the oil industry which will provide a thermal stability at temperatures above 90°C and up to 190°C. According to a preferred embodiment of the present invention, there is provided an aqueous modified acid composition for use in the oil industry which affords corrosion protection at an acceptable oilfield limit at temperatures ranging up to 190°C. According to a preferred embodiment of the present invention, there is provided an aqueous modified acid composition for use in the oil industry which has minimal exothermic reactivity upon dilution or during the dilution process with water.

According to a preferred embodiment of the present invention, there is provided a method to maintain the stability of an alkanolamine solution (especially during shipping or long term storage) prior to its combination in a vessel or on-the-fly (OTF) with hydrochloric acid to provide a reconstituted modified acid composition for use in oil and gas activities. Preferably, the stability refers to temperature stability where, conventionally, an alkanolamine solution would precipitate at temperatures below +10°C. Preferably, said composition can be used to reconstitute a modified acid, where said modified acid comprises: - an alkanolamine & hydrogen chloride in a molar ratio ranging from 1:2.1 to 1:12.5; more preferably, said alkanolamine and hydrogen chloride are present in a molar ratio ranging from 1 :3 to 1 : 12.5 ; even more preferably said alkanolamine and HC1 are present in a molar ratio ranging from 1:3.5 to 1:9; yet even more preferably in a molar ratio ranging from 1:4.5 to 1:8.5; and yet even more preferably in a molar ratio ranging from more than 1:5 to 1:6.5.

It has been surprisingly and unexpectedly discovered that by combining an acidic component to a saturated or near saturated aqueous composition comprising an alkanolamine selected from the group consisting of: monoethanolamine; diethanolamine; and triethanolamine. Reconstituted modified acid compositions according to the present invention have been developed for the oil & gas industry and its associated applications, by targeting the problems of corrosion, logistics & handling, human & environmental exposure, reaction rates, toxicity levels, biodegradation tendencies and formation/fluid compatibilities and facility and/or production and water treatment infrastructure compatibilities. It is an object of the present invention to provide an aqueous synthetic 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 a preferred embodiment of the present invention, there is provided a process to stabilize a saturated or near saturated aqueous alkanolamine solution when such is exposed to temperatures below 0°C. The inventors have noticed that an alkanolamine solution as a premix (also referred to as preblend) for the preparation of a modified acid comprising HC1 and an alkanolamine is being shipped to a destination prior to mixing this alkanolamine composition with commercial grade mineral acid, preferably HC1 (such as but not limited to 32% HC1, 37% HC1) would sometimes exhibit some issues of stability. The inventors have surprisingly discovered that by adding up to 1% wt/wt of an acid (such as, but not limited to HC1) into a saturated alkanolamine (such as monoethanolamine), they could enhance the stability of such a solution and subsequently ensure that the monoethanol amine would not reprecipitate out of solution during the time it was exposed to conditions which typically cause the precipitation of the alkanolamine.

According to a preferred embodiment of the present invention, the resulting reconstituted modified acid composition will, upon proper use, results in a very low corrosion rate on oil and gas industry tubulars and equipment compared to mineral acids, such as HC1.

According to a preferred embodiment of the present invention, the reconstituted alkanolamine-HCl- containing modified acid composition can be used in the oil industry and is biodegradable.

According to a preferred embodiment of the present invention, the reconstituted alkanolamine-HCl- containing modified acid composition can be used in the oil industry as it possesses a controlled, more methodical spending (reacting) nature that is near linear as temperature increases, low-fuming/vapor pressure, low- toxicity, and has a highly controlled manufacturing process ensuring consistent end product strength and quality. According to another preferred embodiment of the present invention, there is provided a reconstituted aqueous modified acid composition for use in the oil industry which has a pH below 1. According to another preferred embodiment of the present invention, there is provided a reconstituted aqueous modified acid composition for use in the oil industry which will keep iron particles and solubilized carbonate in solution even as the pH rises to a level > 4 pH. According to another preferred embodiment of the present invention, there is provided a reconstituted aqueous modified acid composition for use in the oil industry which will provide a thermal stability at temperatures above 100°C. According to another preferred embodiment of the present invention, there is provided a reconstituted modified acid composition for use in the oil industry which will provide corrosion protection at an acceptable oilfield limit when said composition is in contact with metal components and is at temperatures ranging from 100°C to 220°C. According to a preferred embodiment of the present invention, there is provided a reconstituted synthetic acid composition for use in the oil industry which has minimal exothermic reactivity upon dilution or during the reaction process.

Preferably, the reconstituted aqueous modified acid composition for use in the oil industry is compatible with existing industry acid additives. According to another preferred embodiment of the present invention, there is provided an aqueous synthetic acid composition for use in the oil industry which has higher salinity tolerance. A tolerance for high salinity fluids, or brines, is desirable for onshore and offshore acid applications. Conventional acids are normally blended with fresh water and additives, typically far offsite, and then transported to the area of treatment as a finished blend. It is advantageous to have an alternative that can be transported as a concentrate safely to the treatment area, then blended with a saline produced water or sea water greatly reducing the logistics requirement. A conventional acid system can precipitate salts/minerals heavily if blended with fluids of an excessive saline level resulting in formation plugging or ancillary damage, inhibiting production and substantially increasing costs. Brines are also typically present in formations, thus having an acid system that has a high tolerance for brines greatly reduces the potential for formation damage or emulsions forming down-hole during or after product placement/spending (reaction) occurs. According to another aspect of the present invention, there is provided an aqueous synthetic acid composition for use in the oil industry which is immediately reactive upon contact/application. According to another aspect of the present invention, there is provided an aqueous synthetic acid composition for use in the oil industry which results in less unintended near wellbore erosion or face dissolution due to a more controlled reaction rate. This, in turn, results in deeper formation penetration, increased permeability, and reduces the potential for zonal communication during a typical 'open hole' mechanical isolation application treatment. As a highly reactive acid, such as hydrochloric acid, is deployed into a well that has open hole packers for isolation (without casing) there is a potential to cause a loss of near-wellbore compressive strength resulting in communication between zones or sections of interest as well as potential sand production, and fines migration. It is advantageous to have an alternative that will react with a much more controlled rate or speed, thus greatly reducing the potential for zonal communication and the above potential negative side effects of traditional acid systems. According to a preferred embodiment of the present invention, there is provided an aqueous synthetic acid composition for use in the oil industry which provides a controlled and comprehensive reaction rate throughout a broad range of temperatures up to 220°C.

According to a preferred embodiment of the present invention, the reconstituted MEA-HC1- containing modified acid composition can be used in a molar ratio ranging from 1 :3.5 to 1 : 12.5 for injection into an oil or gas well to perform a treatment with said composition; recovering the spent acid from the well; and sending the spent acid to a plant.

According to a preferred embodiment of the present invention, the reconstituted MEA-HC1- containing modified acid composition can be used to overcome many of the drawbacks found in the use of compositions of the prior art related to the oil & gas industry.

According to a preferred embodiment of the present invention, the reconstituted MEA-HC1- containing modified acid composition can be used in a method of matrix acidizing a hydrocarbon- containing dolomite formation, said method comprising: - providing a composition comprising a HC1 and MEA mixture and water; wherein the molar ratio between the HC1 and the MEA ranges from 4.5:1 to 8.5:1, - injecting said composition downhole into said formation at a pressure below the fracking pressure of the formation; and - allowing a sufficient period of time for the composition to contact said formation to create wormholes in said formation.

According to a preferred embodiment of the present invention, the reconstituted MEA-HC1- containing modified acid composition can be used in the oil industry to perform an activity selected from the group consisting of: stimulate formations; assist in reducing breakdown pressures during downhole pumping operations; treat wellbore filter cake post drilling operations; assist in freeing stuck pipe; descale pipelines and/or production wells; increase injectivity of injection wells; lower the pH of a fluid; remove undesirable scale on a surface selected from the group consisting of: equipment, wells and related equipment and facilities; fracture wells; complete matrix stimulations; conduct annular and bullhead squeezes & soaks; pickle tubing, pipe and/or coiled tubing; increase effective permeability of formations; reduce or remove wellbore damage; clean perforations; and solubilize limestone, dolomite, calcite and combinations thereof; said reconstituted modified acid comprises: an alkanolamine & hydrogen chloride in a molar ratio ranging from 1:2.1 to 1:12.5; more preferably, said alkanolamine and hydrogen chloride are present in a molar ratio ranging from 1:3 to 1:12.5; even more preferably said alkanolamine and HC1 are present in a molar ratio ranging from 1:3.5 to 1:9; yet even more preferably in a molar ratio ranging from 1:4.5 to 1:8.5; and yet even more preferably in a molar ratio ranging from more than 1:5 to 1:6.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not limitation, of those principles and of the invention.

According to an aspect of the present invention, there is provided a precursor (also referred to as a premix or pre-blend) to a synthetic or modified acid composition comprising: a strong 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 4.1:1; and yet even more preferably in a molar ratio of not less than 3:1.

Preferably, the main components in terms of volume and weight percent of the composition of the present invention comprise an alkanolamine and a strong acid, such as HC1, nitric acid, phosphoric acid, sulfuric acid, sulfonic acid. A preferred strong acid is HC1. An alkanolamine according to the present invention contains at least one amino group, -NH2, and one alcohol group, -OH. Preferred alkanolamines according to the present invention include, but are not limited to, monoethanolamine, diethanolamine and triethanolamine. More preferred are monoethanolamine, diethanolamine. Most preferred is monoethanolamine. When added to hydrochloric acid a Lewis acid/base adduct is formed where the primary amino group acts as a Lewis base and the proton of the HC1 as Lewis acid. The formed adduct greatly reduces the hazardous effects of the hydrochloric acid on its own, such as the fuming/vapor pressure effect, the hygroscopicity, and the highly corrosive nature. The molar ratio of the two main components can be adjusted or determined depending on the intended application and the desired solubilizing ability. While a molar ratio of HC1:MEA of 1:1 can be used, results are significantly optimized when working above a 2:1 ratio and preferably above a 3:1 ratio. According to a preferred embodiment where the strong acid is HC1, one can increase the ratio of the HC1 component to increase the solubilizing ability of the composition while still providing at least one of the following advantages: health; safety; environmental; and operational advantages over hydrochloric acid. While an alkanolamine such as monoethanolamine is a compound known by the person of ordinary skill in the art, the latter knows that such a compound is not to be mixed with a strong acid such as HC1.

In fact, the person skilled in the art will note upon review of the DOW safety data sheet for monoethanolamine LFG 85 that it indicates that one must avoid contact of this compound with strong acids. Various corrosion inhibitors can be incorporated into a preferred composition as disclosed herein which comprises a strong acid and an alkanolamine to reduce corrosion on the steel which is contacted by the reconstituted composition according to the present invention. According to a preferred embodiment of the present invention, the reconstituted composition may further comprise organic compounds which may act as corrosion inhibitors selected from the group consisting of: acetylenic alcohols, aromatic or aliphatic aldehydes (e.g. a.p -unsaturated aldehydes), alkylphenones, amines, amides, nitrogen-containing heterocycles (e.g. imidazoline-based), iminium salts, triazoles, pyridine and its derivatives or salts, quinoline derivatives, thiourea derivatives, thiosemicarbazides, thiocyanates, quaternary amine salts, and condensation products of carbonyls and amines. Intensifiers which can be incorporated into compositions according to the present invention are selected from the group consisting of: formic acid, potassium iodide, antimony oxide, copper iodide, sodium iodide, lithium iodide, aluminium chloride, bismuth oxide, calcium chloride, magnesium chloride and combinations of these. Preferably, an iodide compound such as potassium iodide is used. Other additives can be optionally added to a composition according to a preferred embodiment of the present invention. A non-limiting list of such common additives includes iron control agents (e.g. reducing agents), water-wetting surfactants, non-emulsifiers, de-emulsifiers, foaming agents, antisludging agents, clay and/or fines stabilizer, scale inhibitors, mutual solvents, friction reducer.

According to a preferred embodiment of the present invention, it is possible to adjust the alkanolamine-HCl ratio in the reconstituted modified acid composition depending on the intended application and the desired solubilizing ability. By increasing the ratio of the HC1 component, the solubilizing ability will increase while still providing certain health, safety, environmental and operational advantages over hydrochloric acid. It is preferable to add the alkanolamine at a molar ratio less than 1 : 1 to the moles of HC1 acid (or any acid). Preferably, the reconstituted composition according to the present invention comprises at most 1 mole of alkanolamine per 3.0 moles of HC1. In a reconstituted composition comprising an alkanolamine component and a hydrochloride component, the alkanolamine allows for a reduced rate of reaction when in the presence of carbonate-based materials. This again is due to the stronger molecular bonds associated over what hydrochloric acid traditionally displays. Further, since the composition according to the present invention is mainly comprised of MEA (which is biodegradable), the product testing has shown that the MEA will maintain the same biodegradability function, something that hydrochloric acid will not on its own.

Typically, ship tanks which are used to carry chemicals are coated with acid-resistant coatings. One widely-used type of coating is epoxy-based. Appropriate epoxy-cased coatings will protect both the steel of the from being affected by the contents and the contents from being contaminated. One such epoxy -based coating used for such purpose is Hempadur® 35760. This coating provides very high corrosion protection properties and excellent chemical resistance and, is especially well-suited for new and old storage tanks containing oils, fuels, bio fuels and a wide range of chemicals. Another epoxy-based coating is Hempadur® 85671, an epoxy phenolic resistant to very aggressive cargos, such as acids.

Another type of coating is Intershield® 300HS which is described as a high solids, abrasion resistant, aluminum pure epoxy coating capable of providing excellent long term anti -corrosive protection and low temperature capability. It comes as a universal primer which can be applied directly to mechanically prepared shop primer or suitably prepared bare steel.

Compatibility testing of pre-blends used in the preparation of a reconstituted modified acid comprising MEA-HC1 (in a 1:5.5 molar ratio) was carried out on coupons coated in Intershield® 300HS and Hempadur® 85671 epoxy was carried out in order to determine the feasibility of transporting acidic precursor compositions comprising hydrochloric acid and an excess of an alkaline component (such as MEA) where the pH of the premix ranges from 7-11 and more preferably between 7.5-10.5 and yet even preferably between 7.8 and 10. Once the alkanolamine premix composition reaches its destination, according to a preferred embodiment of the present invention, an operator may blend such composition with commercial grade HC1 on-the-fly or in batches depending on the situation.

According to a preferred embodiment of the present invention such blending is intended on yielding a reconstituted modified acid composition comprising an alkanolamine and HC1 in a molar ratio ranging from 1:3 to 1:12.5; preferably in a molar ratio ranging from 1:4.5 to 1:9, and more preferably in a molar ratio ranging from more than 1:5 to 1:8.5. Preferably, the composition comprises alkanolamine and HC1 in a molar ratio ranging from 1:4.5 to 1:8.5.

Example 1 - Preparation of a composition according to a preferred embodiment of the present invention To prepare a reconstituted modified acid comprising an alkanolamine and HC1, which both component can be transported on a ship, one first determines the amount of alkanolamine which can be put into the water tank portion of the ship. The other component of the reconstituted modified acid, the HC1, is typically found in the acid tank portion of the ship and thus requires no calculation.

The following describes the steps for the preparation of the alkanolamine-containing pre-mix according to a preferred embodiment of the present invention:

1) weigh required water mass into a container (vessel);

2) weigh required MEA mass into container (vessel);

3) add stir bar;

4) mixing the solution on a stir plate at 190 rpm to disperse MEA/water mixture;

5) slowly adding the required mass of 36 % HC1 slowly to solution to decrease the pf of the MEA water mixture to have the pH fall within a range of 7 to 11, preferably between 7.5 and 10.5. NOTE: this step is exothermic and heat will be generated.

Table 1 indicates the components as well as their amounts in a reconstituted modified acid comprising an alkanolamine and HC1 according to a preferred embodiment of the present invention. Table 2 provides a list of specifications for the reconstituted acid according to a preferred embodiment of the present invention obtained from the example listed in Table 1.

Table 1: Components and amounts to prepare a reconstituted modified acid comprising an alkanolamine and HC1

Table 2: Specifications for the reconstituted acid according to a preferred embodiment of the present invention

According to a preferred embodiment of the present invention obtained from the example listed in Table 1, the number of moles of MEA per kg of reconstituted modified acid is obtained as follows:

Number of moles of MEA per kg of modified acid = 70.47g / 61.08g/mol = 1.15 mol of MEA

The amount of HC1 required to substantially neutralize the MEA present in the pre-blend according to a preferred embodiment of the present invention obtained from the example listed in Table 1 :

Molar weight of HC1 * # of moles of HC1 = mass of HC1 required

36.46 g/mol * 1.15 mol = 42.08 g of HC1 = 116.89g required of 36 % HC1

According to a preferred embodiment of the present invention obtained from the example listed in Table 1, the components and the amounts required to prepare a pre-blend for such a reconstituted modified acid is listed in Table 3. The final pH of the pre -blend is measured to be 7.19. Table 4 provides a list of specifications for the pre -blend according to a preferred embodiment of the present invention

Table 3: Components and amounts to prepare a pre-blend to use in preparing a reconstituted modified acid comprising an alkanolamine and HC1

Table 4: Specification for a pre-blend according to a preferred embodiment of the present invention as set out in Table 3 Table 5: Specification for the reconstituted acid made using a pre-blend according to a preferred embodiment of the present invention

According to a preferred embodiment of the present invention, the above pre -blend can then be mixed on-the-fly with 392.31 g of 36% HC1 to obtain a kilogram of reconstituted modified acid for use in various oil and gas field operations as described herein.

Table 6: Components and amounts to prepare various pre-blends (each having a different pH) to use in preparing a reconstituted modified acid comprising an alkanolamine and HC1

According to a preferred embodiment of the present invention, each one of the pre -blends can then be mixed on-the-fly with 392.03 g of 36% HC1 to obtain a reconstituted modified acid for use in various oil and gas field operations as described herein.

Further blends according to preferred embodiments of the present invention were prepared. These are identified as Pre -blend #6 and Pre -blend #7 and described in detail in table 7 below. Table 7: Components and amounts to prepare various pre-blends (each having a different pH) to use in preparing a reconstituted modified acid comprising an alkanolamine and HC1

Compatibility testing

The tests were executed on 316 stainless steel coupons coated in Intershield® 300HS and Hempadur® 85671 epoxy submerged in Pre-blend #6 and Pre-blend #7 at ambient temperature and 50°C (122 °F), for 7 and 14 days. After the test period, the integrity of the epoxy resin was observed to not be compromised. Compatibility testing between Pre-blend #6 (having a pH of 7.70) and Pre-blend #7 (having a pH of 10.38) and the Intershield 300HS epoxy coated coupons had shown minimal mass change of < 0.14 % and the Hempadur 85671 epoxy-coated coupons had shown minimal mass change of < 0.15 % after 14 days. Full testing results are reported in Tables 7 and 8.

Compatibility Testing with Intershield® 300HS Epoxy-coated Coupons

Procedure:

To prepare the coupons for corrosion testing, the Intershield® 300HS epoxy was prepared by mixing 2.5 parts of A with 1 part of B as per manufacturers specifications. The 316SS coupons were then coated in the epoxy and hung to allow excess to drip off. The coupons were then placed into an oven at 45 °C (113 °F) for 1 hour and then removed to apply a second layer of epoxy coat to cover any areas that may have had a thin layer or exposed comers. The coupons were then hung to dry overnight in an oven set to 45 °C (113 °F) before the coupons were weighed. A photo of each coupon was taken to document the initial appearance of the surface.

Procedure:

To determine the corrosion properties of Pre-blend #6 and Pre-blend #7, each blend was evaluated at ambient temperature, approximately 20°C (68°F) and at 50°C (122°F) on the epoxy coated coupons. At ambient temperature, the tests were executed on a bench top, while at 50°C (122°F), tests were executed in a heated water bath. After the exposure time, the coupons were removed, washed with warm water and soap, iso-propanol, and dried. The weights of the coated coupons were recorded. A photo of each coupon was taken to document the appearance of the surface after the exposure to the Pre -blend #6 and Pre-blend #7. Test results of the compatibility experiment with Intershield® 300HS epoxy coated coupons are shown in Table 8.

Table 8: Corrosion results of Intershield® 300HS epoxy-coated coupons exposed to Pre-blend

#6 and #7

Compatibility Testing with Hempadur® 85671 Epoxy-coated Coupons

Procedure:

To prepare the coupons for corrosion testing, the Hempadur® 85671 epoxy was prepared by mixing 8.9 parts of A with 1.1 parts of B as per manufacturers specifications. The 316SS coupons were then coated in the epoxy and hung to allow excess to drip off. The coupons were then placed into an oven at 45 °C (113 °F) for 1 hour and then removed to apply a second layer of epoxy coat to cover any areas that may have had a thin layer or exposed comers. The coupon was then hung to dry overnight in an oven set to 45 °C (113 °F) before the coupons were weighed. A photo of each coupon was taken to document the initial appearance of the surface.

Procedure:

To determine the corrosion properties of Pre-blend #6 and Pre-blend #7, each blend was evaluated at ambient temperature, approximately 20°C (68°F) and at 50°C (122°F) on the epoxy coated coupons. At ambient temperature, the tests were executed on a bench top, while at 50°C (12°F), tests were executed in a heated water bath. After the exposure time, the coupons were removed, washed with warm water and soap, iso-propanol, and dried. The weights of the coated coupons were recorded. A photo of each coupon was taken to document the appearance of the surface after the exposure to the Pre -blend #6 and Pre-blend #7. Test results of the compatibility experiment with Hempadur® 85671epoxy-coated coupons are shown in Table 9.

Table 9: Corrosion results of Hempadur® 85671 epoxy-coated coupons exposed to Pre-blend

#6 and #7

Stability Testing

Compatibility and stability testing was performed utilizing Pre-blend #6 (Neutral pH) and Preblend #7 (High pH) at a temperature of 50°C (122°F) over 14 days temperatures to determine fluid stability. A photograph of each solution was taken to document the initial and final appearances of each solution. Review of the photographs taken showed that each solution exhibited no phase separation and each solution was as clear at the end of the stability testing as it was as the beginning.

Corrosion rate testing

Corrosion testing was performed utilizing a composition comprising MEA:HC1 in a molar ratio of 1:5.5 (hereinafter referred to as reconstituted modified acid 1:5.5). This composition was prepared by blending pre-blend #6 (neutral pH), 36% HC1 and CI-9CNE. The resulting modified acid composition was exposed to a stainless steel (316SS) coupon at a temperature of 110°C (230°F). The corrosion testing was performed at a 33 % concentration of the above referred to MEA-HC1 composition comprising MEA:HC1 in a molar ratio of 1:5.5 for a testing period of 6 hours. The corrosion testing results are found in Table 10. CI-9CNE is a corrosion inhibitor comprising a non-emulsifier.

Corrosion tests were executed in a high pressure/high temperature Teflon lined cell. The coupon was washed with acetone, air dried, and weighed, before being suspended in the test fluid and then the cell was pressurized with nitrogen. Each cell was placed in a preheated oven for the specified test duration, plus an additional 30 minutes of heat up time for tests less than 24 hours in duration. After the exposure period, each cell was depressurized, and the coupon was removed, washed with water, followed by an acetone wash, air dried, and then weighed.

Table 10: Corrosion testing of the reconstituted modified acid 1:5.5 (at 33% dilution) at 110"C under a pressure of 400 psi for a duration of 6 hours

NB: The pitting index indicates: No pits. The surface is the same as for the original untreated coupon. This is from the pitting index reported in: Finsgar, M.; Jackson, J. Corrosion Science, 2014, 86, 17-41

The corrosion rate was determined from the weight loss, and the pitting index was evaluated visually at 40X magnification and compared to the literature, and a photo of the coupon surface at 10X and 40X magnification was taken.

Preparation of batch of a modified acid comprising a 1:4.1 molar ratio of MEA and HC1

To obtain a 4.1 : 1 molar ratio of MEA to HC1, one must first mix 165g of MEA with 835g of water. This forms the monoethanolamine solution. Subsequently, one takes 370 ml of the previously prepared monoethanolamine solution and mixes with 350ml of HC1 aq. 36% (22 Baume). Circulation is maintained until all products have been solubilized. Additional components (such as corrosion inhibitors) can now be added as required.

The resulting composition is a clear (slightly yellow) liquid having shelf-life of greater than 1 year. It has a boiling point temperature of approximately 100°C. It has a specific gravity of 1.1± 0.02. It is completely soluble in water and its pH is less than 1. The freezing point was determined to be less than - 35°C. The organic component in the composition is biodegradable. The composition is classified as a mild irritant according to the classifications for skin tests. The composition is substantially lower fuming compared to 15% HC1.

The composition thus prepared was also tested for skin corrosiveness and deemed non-corrosive to the skin. Oral toxicity was calculated using the LD50 rat model and deemed to be of low oral toxicity. It is considered readily biodegradable and offers a lower bioaccumulative potential when compared to 15%

HC1.

Canadian Patent 3,006,476 discloses the dermal safety data for modified acid composition comprising an alkanolamine (such as MEA) and HC1 in various molar ratios. The patent also discloses the scale solubility and dissolution power of such compositions, the disclosure in CA 3,006,476 is hereby incorporated in its entirety. These compositions are similar to the reconstituted alkanolamine-HCl- containing modified acid composition (such as, but not limited to MEA-HC1) discussed herein. The teachings of Canadian Patent 3,006,476 are hereby incorporated by reference.

Stability Testing of a reconstituted modified acid composition comprising MEA and HC1

Testing was carried out using pressurized ageing cell with Teflon liner in order to assess the stability of various MEA-HC1 compositions obtained from the mixing of a pre-blend containing MEA when admixed with commercial grade HC1. The tests were conducted at a pressure of 300 psi (denoted by an asterisk) and at 400 psi established that MEA-HC1 compositions obtained mixing a pre -blend (containing MEA, water and HC1 and having a pH ranging between 7 and 11 and preferably between 7.5 and 10.5) with commercial grade HC1 are stable when exposed to temperatures above 200°C.

SCALE SOLUBILITY

The power of a modified acid composition comprising MEA and HC1 obtained from the mixing of an aqueous pre-blend containing monoethanolamine composition according to a preferred embodiment of the present invention with commercial grade HC1 to dissolve scale was assessed. It was determined that a reconstituted modified acid composition (obtained from the mixing of an aqueous pre-blend containing monoethanolamine composition according to a preferred embodiment of the present invention with commercial grade HC1) provides an excellent solubilizing ability when dealing with various oilfield scales. Its solubilizing ability is comparable to the solubility of most many mineral and organic acid packages typically utilized.

ELASTOMER COMPATIBILITY

When common sealing elements used in the oil and gas industry come in contact with acid compositions they tend to degrade or at least show sign of damage. A number of sealing elements common to activities in this industry were exposed to a composition according to a preferred embodiment of the present invention to evaluate the impact of the latter on their integrity. More specifically, the hardening and drying and the loss of mechanical integrity of sealing elements can have substantial consequences on the efficiency of certain processes as breakdowns require the replacement of defective sealing elements. Testing was carried out to assess the impact of the exposure of a reconstituted modified acid composition comprising MEA and HC1 to various elastomers and was found to be stable for the period of time tested.

USES OF RECONSTITUTED MODIFIED ACID COMPOSITIONS COMPRISING MEA AND HCL

The uses (or applications) of the reconstituted modified acid composition comprising an alkanolamine (such as monoethanolamine, MEA) and HC1 according to the present invention upon dilution thereof ranging from approximately 1 to 90% dilution are listed below in Table 11 and include, but are not limited to: injection/disposal treatments; matrix acid squeezes, soaks or bullheads; acid fracturing, acid washes; fracturing spearheads (breakdowns); pipeline scale treatments, cement breakdowns or perforation cleaning; pH control; and de-scaling applications, high temperature (up to 180°C) cyclical steam scale treatments and steam assisted gravity drainage (SAGD) scale treatments (up to 220°C) As would be understood by the person skilled in the art, the methods of use generally comprise the following steps: providing a composition according to a preferred embodiment of the present; exposing a surface (such as a metal surface) to the acid composition; allowing the acid composition a sufficient period of time to act upon said surface; and optionally, removing the acid composition when the exposure time has been determined to be sufficient for the operation to be complete or sufficiently complete. Another method of use comprises: injecting the acid composition into a well and allowing sufficient time for the acid composition to perform its desired function. Yet another method according to the present invention comprises the steps of: providing a composition according to a preferred embodiment of the present; injecting the composition into a well; an optional step of dilution of the acid composition can be performed if deemed necessary prior to injection downhole; monitoring the various injection parameters to ensure that the pressure and rate of injection are below frac pressures and below conventional injection rates used for conventional acids such as HC1; allowing sufficient period of time to act upon said formation to obtain the desired wormholing effect; and optionally, removing the acid composition when the exposure time has been determined to be sufficient for the operation to be complete or sufficiently complete.

Yet another method of use comprises: exposing the acid composition to a body of fluid (typically water) requiring a decrease in the pH and allowing sufficient exposure time for the acid composition to lower the pH to the desired level. Table 10 - Applications for which compositions according to the present invention can be used as well as proposed dilution ranges

The main advantages of the use of the synthetic acid composition included: the reduction of the total loads of acid, and the required number of tanks by delivering concentrated product to location and diluting with fluids available on location (with low to high salinity production water). Other advantages of the composition according to the present invention include: operational efficiencies which lead to the elimination of having to periodically circulate tanks of HC1 acid due to chemical separation; reduced corrosion to downhole tubulars; ultra-high temperature corrosion protection up to 220°C, less facility disruptions due to iron pick up and precipitation, thermal stability of a synthetic acid, and reduced hazardous HC1 acid exposure to personnel and environment by having a non-low hazard, low fuming acid (lower vapour pressure) on location. A synthetic acid composition according to a preferred embodiment of the present invention, can be used to treat scale formation in SAGD operations at ultra-high temperatures (up to 220°C) while achieving acceptable corrosion limits set by industry. This also eliminates the need for the SAGD operation to be halted for a "cool down prior to a scale treatment and said synthetic acid is injected into said well to treat scale formation inside said well at high temperatures. While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by those skilled in the relevant arts, once they have been made familiar with this disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims.