WO2017165954A1

WO2017165954A1 - Using synthetic acid compositions as alternatives to conventional acids in the oil and gas industry

Info

Publication number: WO2017165954A1
Application number: PCT/CA2017/000054
Authority: WO
Inventors: Clay Purdy; Alexander David JAMIESON
Original assignee: Fluid Energy Group Ltd
Current assignee: Fluid Energy Group Ltd
Priority date: 2016-03-31
Filing date: 2017-03-15
Publication date: 2017-10-05
Anticipated expiration: 2018-09-30
Also published as: CA2925634A1

Abstract

A synthetic acid composition for use in downhole oil industry activities, said composition comprising: urea and phosphoric acid or a derivative thereof in a molar ratio of not less than 0.1 : 1.

Description

USING SYNTHETIC ACID COMPOSITIONS

AS ALTERNATIVES TO CONVENTIONAL ACIDS IN THE OIL AND GAS INDUSTRY FIELD OF THE INVENTION

This invention relates to compositions for downhole use in performing various operations in the oil & gas industry, more specifically to synthetic acid compositions as alternatives to conventional acids where chrome exposure is expected. 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 is used to further encourage permeability and flow from an already existing well that has become under-productive due to scaling tendencies of water producing formations.

An acid scale 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 acid treatment, the acid dissolves the sediments and scale that are inhibiting the permeability of the rock or blocking down-hole production equipment, enlarging the natural pores of the reservoir (wormholing), opening the perforations, cleaning down-hole pumps and tubulars while stimulating the flow of hydrocarbons. Typically a service rig unit is required to pull all of the downhole equipment out of the hole prior to the acid treatment due to incompatibilities with chrome parts. It is highly advantageous to have a product that can treat scaling issues with the downhole equipment left in the well, eliminating the need for an expensive workover of the well.

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 or treat scaling is hydrochloric acid (HCI), which is useful in stimulating carbonate reservoirs but corrodes chrome aggressively resulting in the need to remove these components from the well prior to treatment

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 for steel exposure 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 some metals, such as aluminum, magnesium and chrome, are very susceptible to major effects causing immediate damage. Because chrome plated components are common in the industry having a product that attacks calcium based scale but does not affect chrome is highly advantageous. Hydrochloric acid also 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. Having a product that is non- fuming is very advantageous.

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 which 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 a hydrogen chloride gas cloud 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. Because of its acidic nature, hydrogen chloride gas is also corrosive, particularly in the presence of moisture.

The inability for acids 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 or vapours produced by mineral & organic acids are harmful to humans/animals and are highly corrosive and/or potentially explosive. Transportation and storage requirements for acids are restrictive and taxing in such that you must haul the products in acid approved tankers or intermediate bulk containers (1BC) that are rated to handle such corrosive products. As well, the dangers surrounding exposure by personnel handling the blending of such corrosive/dangerous products limits their use/implementation. Another concern is the potential for exposure incidents on locations due to high corrosion levels of acids causing storage container failures and/or deployment equipment failures i.e. coiled tubing or treatment iron failures caused by high corrosion rates (pitting, cracks, pinholes and major failures). Other concerns include: in particular, chrome plated downhole equipment failures from corrosion causing the operator to have to execute a work-over and replace down hole pumps, drilling motors, tubing, 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, in particular chrome plated plunger rods and other fluid end chrome plated parts; 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 far from oil & gas applications, up to 10 additives can 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 chrome friendly and can be deployed statically for many hours or days is very advantageous.

When used to treat scaling issues on surface due to water contamination or production, conventional acids are exposed to humans, animals, the environment, water sources and mechanical devices as well as expensive pumping equipment causing increased risk for the operator and corrosion effects that damage equipment and create hazardous fumes. When mixed with bases or higher pH fluids, acids will create a high 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 on-site with field/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) causing the acids to become very corrosive and resulting in damage to downhole equipment/tubulars. Conventional acids are also very destructive to most elastomers found in the oil & gas industry such as those found in blow out preventers (BOP's) /downhole tools/packers/submersible pumps/seals/mud motors/stators 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. It is advantageous to have an acid blend that can be exported to production facilities through pipelines that once spent or applied, is commonly close to a neutral pH greatly reducing disposal costs/fees.

Acids perform many functions in the oil & gas industry and are considered necessary to achieve the desired production of various petroleum wells, maintain their respective systems and aid in certain functions (i.e. cleaning calcium based scale from tubulars and pumps that are chrome plated). The associated dangers and costs that come with using acids are expansive and tasking to mitigate through controls whether they are chemically or mechanically engineered is very demanding. Eliminating or even simply reducing the negative effects of acids while maintaining their usefulness is a struggle for the industry, especially on chrome surfaces. As the public demand for the use of cleaner/safer/greener products increases, companies are looking for alternatives that perform the required function without most of the drawbacks associated with the use of conventional acids.

Hydrochloric acid is extremely corrosive on metals including chrome. Mineral acids can also have a very negative impact on the corrosion of various metals including chrome. Phosphoric acid is very effective to remove rust but it is an acid which also negatively affects the integrity of chrome when placed in contact with it over time.

Pure phosphoric acid is a white solid. It melts at a little over 42°C into a viscous and colorless liquid which is quite viscous and colorless. The most commonly commercially available forms of phosphoric acid are aqueous solutions of 75% to 85% concentration. These solutions are colorless, odorless, viscous / syrupy, and non-volatile. Known common industrial uses of phosphoric acid includes rust removal, where iron (III) oxide is converted to ferric phosphate (FeP04). This ferric phosphate can then be manually removed.

Similarly, phosphate salt which consists of salts formed by the neutralization of phosphorous or phosphoric acid with a NaOH or KOH. Orthophosphates are phosphoric acid (H₃P0₄) salts, where 1 , 2 or 3 of the hydrogen ions are neutralized. Neutralization with NaOH gives three sodium orthophosphates: (a) monosodium phosphate (MSP), (b) disodium phosphate (DSP) or (c) trisodium phosphate (TSP). Their solutions are buffers in the 4.6 to 12 pH range. TSP is an excellent degreaser. All will precipitate hardness ions such as calcium. Polyphosphates are polymers made from various orthophosphates by dehydration with heat. Sodium acid pyrophosphate (SAPP) is a clay deflocculant and treatment for cement contamination. For clay deflocculation, polyphosphates are limited by the temperature at which they hydrolyze back to orthophosphates, although several that performed up to 280°F [138°C] have been documented in the literature (see reference.

Similarly, polyphosphates (also known as pyrophosphates) are polymers made from various orthophosphates by dehydration with heat. Orthophosphates are phosphoric acid (H₃P0₄) salts, where 1 , 2 or 3 of the hydrogen ions are neutralized. Sodium acid pyrophosphate (SAPP) is a clay deflocculant and treatment for cement contamination.

WO 20061 13735 A2 teaches an aqueous acidic cleaning composition suitable for the cleaning of metal parts is constituted by urea phosphate, a surfactant, a corrosion inhibitor, and water. The corrosion inhibitor can be a phosphatizing compound such as iron phosphate, zinc phosphate, manganese phosphate, and the like. US 20060079424 Al teaches a composition for cleaning oxide discoloration, rust, and high temperature-related scale from stainless steel and other metals. The composition comprises a nitrogen acid salt produced by the mixture of urea and an acid and a gelling agent. The preferred nitrogen acid salt used in the composition is urea hydrochloride, which is a buffered acid cleaner. Synthetic smectite clay is the preferred thixotropic gelling agent. Both of these ingredients are non-hazardous and do not produce any toxic or corrosive fumes. The invention also includes the method of preparing the composition.

US 20040048769 Al teaches a cleaning formulation comprising a cleaning agent, a particulate clay material and an aqueous carrier. The formulation has a pH less than about 4.0 and is characterized by at least a 90% reduction in viscosity at 25° C. at a shear rate of up to about 0.10 s^~' . The cleaning formulation is thixotropic and has a highly desirable combination of acid stability, temperature stability, electrolyte stability and ultraviolet radiation stability. US 20030004080 A l teaches a long-time stable pickling agent for the removal of an oxide layer on a stainless steel after heat treatment, such as welding, which pickling agent comprises nitric acid and fillers and constitutes of a pickling paste or pickling gel to be coated on the heat treated stainless steel, or of a pickling liquid to be sprayed on the steel. According to the invention, the pickling agent also comprises urea for reduced formation of nitrous fumes when the pickling agent is used.

US Patent no. 3,936,3 16 teaches a process and composition for pickling metals, especially iron based metals, prior to metal finishing. A hydrohalide acid pickling solution is used which solution is characterized by the addition of urea. The urea substantially reduces, even completely eliminates, the excessive liberation of noxious and corrosive hydrohalide acid fumes normally associated with such pickling operations. It is stated that it greatly reduces the cost of the pickling operation as the consumption of acid is dramatically reduced. Moreover, there is less injury to personnel and equipment contacted with said fumes. Finally, a metal surface treated with the pickling solution of the invention is improved as there is less pitting and the surface is more active to a metal depositing solution. US patent application no. 2003/0181350 A l discloses a cleaning formulation comprising a cleaning agent, a particulate clay material and an aqueous carrier. In a preferred embodiment, the formulation has a pH less than about 1 .0 and is characterized by: (i) at least a 90% reduction in viscosity at 25° C. at a shear rate of up to about 0.10

and (ii) a substantially unchanged viscosity for a period of at least 60 days. The cleaning formulation is thixotropic and is said to have a highly desirable combination of acid stability, temperature stability, electrolyte stability and ultraviolet radiation stability. Several production operations in the oil industry expose fluids to very high temperatures (some upward of 100°C), the compositions used in these various operations need to withstand these high temperatures without losing their overall effectiveness. These compositions must be capable of being used in operations over a wide range of temperatures while not affecting the equipment with which it comes in contact. Most solutions available in the market damage the metallurgy of down hole pumps and /or tubulars requiring a service rig to pull these items out of the hole prior to treatment. The present invention eliminates the need to do so, saving the operator substantial money and minimising risks to personal and assets. Consequently, there is still a need for compositions for use in the oil industry which can be used over this range of applications and exposures to chrome plated equipment such as pumps, mud motors stators, cables and tubulars which can decrease a number of the associated dangers/issues typically associated with conventional acid applications requiring the removal of these items from the wellbore by a service rig and to the extent that these acid compositions are considered much safer for handling on worksites.

Moreover, it was discovered that the composition according to the present invention exhibits stability for operations at elevated temperatures (above 65°C) and therefore makes them useful in the oil and gas industry. The composition according to the present invention can ideally be used in various downhole oilfield operations, such as: injection - disposal and production well treatments, scale removal treatments (surface and subsurface-, equipment, pipelines, facilities), formation filter cake removal, tubing pickling, matrix acid squeezes and soaks, cement squeeze breakdowns, fluid pH control, and drilling cement plugs, ball drop balls without causing damage to the chrome plated components such as rotors within the mud motors etc. By providing and acid to assist greatly reduce drill out times the operator can save substantial costs compared to drilling with a water based system.

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 chrome and steel corrosion, logistics/handling, human/environmental exposure and formation/fluid compatibilities.

It is an object of the present invention to provide a synthetic acid composition which can be used over a broad range of downhole and surface applications in the oil and gas industry and which exhibit advantageous properties over known compositions. According to one aspect of the present invention, there is provided a chrome friendly synthetic acid composition which, upon proper use, results in a very low corrosion rate of oil and gas industry chrome and steel tubulars/equipment.

According to a preferred embodiment of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which has a controlled spending (reacting) nature that is near linear as temperature increases, non-fuming, low toxicity, and has a highly controlled manufacturing process ensuring consistent end product strength.

According to another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in downhole oil industry activities which has a pH below 1.5.

According to another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which has minimal exothermic reactivity upon dilution or reaction. Typically adding a strong acid to a fluid (water, base etc.) will cause an aggressive rise in fluid temperature. Certain preferred embodiments of the present invention do not exhibit this effect to the same degree such that the exothermic reaction is minimal when combined with typical industrial fluids, such saline water, fresh water or even a high pH fluid.

According to another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which is compatible with existing industry additives. According to a preferred embodiment of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which has high 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 may 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 downhole during or after product placement/spending occurs. According to another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which is immediately reactive upon contact/application. Many organic acids that are considered safe have a slower reaction rate, a reduced capacity to solubilize scale, cause substantial damage to chrome, making them ineffective or uneconomical in some applications. Strong mineral acids have very high hazards associated to them, the cause substantial and immediate damage to chrome surfaces, but are immediately reactive. Preferred embodiments of the present invention are immediately active, even at lower concentrations. This immediate activity allows for a standard operating procedure to be followed, minimizing operational changes. Many operations that utilize a mineral acid, such as hydrochloric acid, will not need to alter their standard operating procedure to utilize preferred compositions of the present invention outside of eliminating the need for the removal of down-hole chrome components. The volumes required to complete a typical scale treatment will be linear in most cases.

According to another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which results in less unintended near wellbore erosion or damage due to the controlled reaction rate. This, in turn, results in deeper formation penetration, increased permeability resulting in an increase in production or injection rates, and in some cases 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 another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry said composition having a low evaporation rate. Acids normally utilized in industrial operations typically have a high tendency to evaporate, fume or exhibit a high vapor pressure, especially at higher concentrations. Preferred embodiments of the present invention do not exhibit this tendency and have very low fuming effect and low vapor pressure.. Hydrochloric acid will produce hazardous fumes, such as chlorine gas, which can be fatal in higher concentrations >1300 ppm. Preferred embodiments of the present invention do not produce hazardous fumes, even in high concentrations. According to another aspect of the present invention, there is provided a chrome friendly synthetic acid composition for use in the oil industry which provides a controlled and comprehensive reaction throughout a broad range of temperatures. Preferred embodiments of the present invention have reaction rates that can be controlled/retarded or greatly "slowed or increased" for specific applications where a reduced (or increased) reaction rate is an advantage simply by adjusting the amount of water blended with the product. Preferred compositions of the present invention can be diluted substantially <10%, yet still remain effective in many applications, such as scale through batch treatments or continuous injection and pH control, as well as further increasing the HSE benefits.

Accordingly, the product would overcome many of the drawbacks found in the use of compositions of the prior art related to the oil & gas industry. According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition in the oil industry to stimulate formations.

According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to assist in reducing breakdown pressures during downhole pumping operations.

According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to treat wellbore filter cake post drilling operations.

According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to allow an operator to drill or ream with an acid. According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to descale pipelines and/or production wells and surface equipment

According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to increase the injectivity rate of injection wells.

According to an aspect of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to lower the pH of fluids. According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to remove undesirable scale in surface equipment, wells and related equipment and/or facilities. According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to fracture a well.

According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to perform matrix stimulations.

According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to conduct annular and bullhead squeezes & soaks for treating scaling issues in producing wells

According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to pickle tubing, pipe and/or coiled tubing. According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to increase effective permeability of formations.

According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to reduce or remove wellbore damage.

According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to clean perforations.

According to a preferred embodiment of the present invention, there is provided a use of a chrome friendly synthetic acid composition for downhole use in the oil industry to solubilize limestone, dolomite, calcite and combinations thereof. According to a preferred embodiment of the present invention, there is provided a synthetic acid composition comprising: urea & a phosphoric acid derivative in a molar ratio of not less than 0.1 : 1 ; preferably in a molar ratio not less than 0.5 : 1 , preferably in a molar ratio not less than 0.7: 1 , more preferably in a molar ratio not less than 1.0: 1 ;

optionally other corrosion inhibitors can be added such as Armohib 31 ^® from Azko Nobel.

The term phosphoric acid derivative is to be understood as including compounds such as phosphoric acid, polyphosphoric acid, Orthophosphoric acid (H₃P0₄), pyrophosphoric acid (H₄P₂0₇), tripolyphosphoric acid (H₅P₃0,o), tetrapolyphosphoric acid (H₆P₄0_{! 3}), trimetaphosphoric acid (H₃P₃0₉),and Phosphoric anhydride (P₄O]₀). The preferred phosphoric acid derivative is orthophosphoric acid.

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 invention, there is provided a synthetic acid composition comprising:

- urea & a phosphoric acid derivative in a molar ratio of not less than 0.1 : 1 ; preferably in a molar ratio not less than 0.5 : 1 , more preferably in a molar ratio not less than 0.7: 1 yet more preferably in a molar ratio not less than 1.0: 1.

Urea and a phosphoric acid derivative is the main component in terms of volume and weight percent of the composition of the present invention. When added to a phosphoric acid derivative, for example orthophosphoric acid, there is a reaction that results in a urea phosphate solution with the chemical composition of CO(NH₂)2' H₃P0 , which binds the phosphate ion within the molecular structure. The low pH of urea phosphate allows Calcium, Magnesium and Phosphorus to co-exist in solution. This reaction greatly reduces the hazardous effects of the orthophosphoric acid on its own, such as the fuming effects, the hygroscopic effects, and the highly corrosive nature.

According to a preferred embodiment, urea & orthophosphoric acid are present in a molar ratio of not less than 0.1 : 1 ; preferably in a molar ratio not less than 0.5: 1 , and more preferably in a molar ratio not less than 1.0: 1. However, this ratio can be increased or decreased depending on the application. It is preferable to add the urea at a molar ratio greater than 1 to the moles of phosphoric acid derivative (in terms of phosphate groups). This is done in order to bind any available phosphate ions, thereby creating a safer, more stable product. Preferably, the composition according to the present invention comprises 1 .00 moles of urea per 1.0 moles of orthophosphoric acid. The urea also allows for a reduced rate of reaction when in the presence of carbonate-based materials. This again due to the stronger molecular or ionic bonds associated over what orthophosphoric acid traditionally displays.

Chrome-friendly is understood to mean that the corrosion on a standard chrome surface upon exposure of the synthetic acid composition is at least 50% less than the corrosion of the same type of chrome surface at a temperature of 20°C for a period of time of 6 hours.

According to the MSDS sheet of Armohib 31^®, this inhibitor is said to be designed for use with phosphoric acid. It is said to contain a proprietary alkoxylated fatty amine salts (in an undisclosed % content), a proprietary alkoxylated organic acid (in an undisclosed content), and Ν,Ν'-dibutyl thiourea in an amount ranging from 20-30 % by weight. This corrosion inhibitor does however not address the fuming and environmental toxicity drawbacks associated with the use of phosphoric acids, nor does it address the corrosion effect on chrome. It mainly addresses the corrosion on steel surfaces.

Example 1 Process to prepare a composition according to a preferred embodiment of the invention

Start with a 50% by weight solution of urea liquor in water. Add a 85% by weight solution of orthophosphoric acid and circulate until all reactions have completely ceased. Immediately add water to a desired concentration of 50%. Armohib CI-31 or an equivalent corrosion inhibition package is added at this point. Circulation is maintained until all products have been solubilized. Table 1 lists the components of the composition of Example 1 , including their weight percentage as compared to the total weight of the composition and the CAS numbers of each component.

Table 1 - Formulation of Example 1

Armohib CI-3 T 0.05% n/a

Example 2

Table 2 lists the components of the composition of Example 2 including their weight percentage as compared to the total weight of the composition and the CAS numbers of each component.

Table 2 - Formulation of Example 2

The resulting composition of Example 1 is a clear, odourless liquid having shelf-life of greater than 1 year. It has a freezing point temperature of approximately minus 30°C and a boiling point temperature of approximately 100°C. It has a specific gravity of 1 .19±0.02. It is completely soluble in water and its pH is 1.

The composition is classified as an irritant according to the classifications for skin tests. The composition is non-fuming and has no volatile organic compounds nor does it have any BTEX levels above the drinking water quality levels. BTEX refers to the chemicals benzene, toluene, ethylbenzene and xylene. Toxicity testing was calculated using surrogate information and the LC₅₀ was determined to be greater than 884 mg/kg.

AQUATIC TOXICITY TESTING

The biological test method that was employed was the Reference Method for Determining acute lethality using rainbow trout (1990 - Environment Canada, EPS l /RM/9 - with the May 1996 and May 2007 amendments).

The Trout 96 hour Acute Test (WTR-ME-041 ) was performed at 5 different concentrations of compositions (62.5, 125, 250, 500 and 1000 ppm) one replicate per treatment, ten fish per replicate. The test results indicate that at concentrations of the composition of Example 2 of up to and including 500 ppm there was a 100% survival rate in the fish sample studied. This is an indicator that the composition of Example 2 demonstrates a highly acceptable environmental safety profile. With respect to the corrosion impact of the composition on typical oilfield grade steel and chrome plated steel, it was established that it was clearly well below the acceptable corrosion limits set by industry for certain applications, such as scale treatments, soaks, injection well treatments, drilling with acid applications (drop ball drill outs, cement drill outs). As the present invention does not corrode or affect chrome plated components it is highly economical for multiple applications where chrome exposure is a concern, as opposed to a full workover which would require removal of all downhole components.

Solubility Testing

The formulation of example 1 was tested for dissolving ability. Its solubilising power (in kg per m³) is lower than other synthetic acids, but it provides steel and chrome protection which other synthetic acids do not. Typically when dealing with scale issues total solubility does not need to be anywhere near as high as for frac blends. The results of the solubilising testing is reported in Tables 3 and 4 below.

Table 3- Calcium Carbonate Dissolution Testing Results for Various Formulations

Table 4- Calcium Carbonate Dissolution Testin Results for Various Formulations

85%

CORROSION TESTING

The formulation of Examples 1 and 2 according to the present invention were exposed to corrosion testing. The results of the corrosion tests are reported below.

Corrosion Testing on J-55 Steel Coupons

Corrosion testing was carried out on J-55 steel coupons at 70°C for 6 hours (density is of 7.86 g/cc , the coupons presenting a surface area 28.992 cm²). Samples of J55 grade steel were exposed to various synthetic acid solutions for periods of time ranging up to 24 hours at 90°C temperatures. All of the tested compositions contained urea and phosphoric acid in a 1 : 1 .00 ratio.

Table 5 - Corrosion Test Results on J-55 Steel Coupons

As a note, compositions where an additive was incorporated contain less water to account for the volume of the additive. Compositions which were diluted after the additive was added. This type of corrosion testing helps to determine the impact of the use of such synthetic replacement acid composition according to the present invention compared to the industry standard (such as HC1 blends or phosphoric acid or organic acid blends). The results obtained for the composition containing only phosphoric acid (at 85% and at 42.5%) were used as a baseline to compare with the formulation of Example 1 according to a preferred embodiment of the present invention. Additionally, the compositions according to the present invention will allow the end user to utilize an alternative to conventional acids that has the down-hole performance advantages, transportation and storage advantages as well as the health, safety and environmental advantages. Enhancement in short/long term corrosion control is one of the key advantages of the present invention. The reduction in skin corrosiveness, the elimination of corrosive fumes, the controlled spending nature, and the high salt tolerance are some other advantages of compositions according to the present invention.

Corrosion Testing on Chrome Coupons

Testing was carried out on Chrome 13 coupons at 70°C for a period of 6 hours. A urea- phosphoric acid composition (Example 2) provided an improvement in the corrosion resistance of 33% versus a phosphoric acid (42.5%) composition. The urea-phosphoric acid with inhibitor composition (Example 1 ) provided a corrosion resistance improvement of 66% over the phosphoric acid (42.5%) composition. This represents a significant improvement as a reduction in pitting on the surface of the chrome component will result in longer equipment life.

Corrosion Testing on Chromed Stainless Steel Coupons

Testing was carried out on stainless steel coupons having a chromed surface at 70°C for a period of 6 hours. The urea-phosphoric acid composition (Example 2) provided a corrosion resistance improvement of 64% over the phosphoric acid (42.5%) composition. The surface area of the coupons was 23.42 cm². The results are reported in Table #6.

Table 6 - Corrosion Test Results on Chromed Stainless Steel Coupons

Testing was carried out on stainless steel coupons having a chromed surface at 23°C for a period of 24 hours. The Urea-phosphoric acid (50%) with additive provided a corrosion resistance improvement of 64% over the hydrochloric acid (15%) composition. The Urea-phosphoric acid provided a corrosion resistance improvement of 64% over the hydrochloric acid (15%) composition. This represents a significant improvement as a reduction in pitting on the surface of the chrome and reduction in the corrosion of the steel will result in longer equipment life. The surface area of the coupons was 23.42 cm². The results are reported in Table #7.

Table 7 - Corrosion Test Results on Chromed Stainless Steel Coupons

wt

15% HC1 24.2276 21.8413 2.386 1862.833 47.316 0.169

Example 1 24.4701 24.469 0.001 0.8587 0.022 0.0001

Example 1 (50%

24.3014 24.2986 0.003 2.185782 0.056 0.0002

diluted)

With HC1 composition, the chromed surface became dull and peeled from the steel. Both of the urea-phosphoric acid compositions (100% and 50%) had barely any impact on the chromed steel.

Properties

The formulation of Example 1 was analyzed and had the following physical and chemical properties at full strength and upon dilution by half.

Table 8 - Various physical and chemical properties of the formulation of Example 2 at full strength and upon dilution by half.

Additionally, the compositions according to the present invention will allow the end user to utilize an alternative to conventional acids that has transportation and storage advantages as well as health, safety and environmental advantages. Enhancement in short/long term corrosion control is one of the key advantages of the present invention. The reduction in skin corrosiveness, the elimination of corrosive fumes during reactions, the controlled spending nature, and the high salt tolerance and the resistance to damaging chrome are some other advantages of compositions according to the present invention. Salinity tolerance

The formulation of Example 2 exhibited high salinity tolerance of more than 150,000 ppm. Consequentially, this provides the additional advantage of allowing for onsite dilution with produced water while still not precipitating salts, unlike the tendency of HC1 to do so.

Elastomer Testing

This formulation shows little effect on a typical elastomer found within industry upon exposure for 24 hours at room temperature. Table 9 - Elastomer Testing of the Formulation of Example 2 at Full Strength

Elastomer Testing

100%

Viton

Time Thickness 1 / Thickness 2 /

days Weight / g inches inches

0 5.4269 0.35 0.44

1 5.4476 0.35 0.44

Dilution Testing

There is also minimal exothermic reaction when a formulation according to the present invention is blended with water. Comparative testing with phosphoric acid dilution with water showed an increase in temperature from 20°C to 35.8°C. 50ml of the formulation of Example 2 (at 100% strength) and 50ml distilled water mixed together, the temperature was recorded as being 19.2°C (initial T) and 19.1 °C(after dilution). Comparatively, phosphoric acid (85%) yielded an initial temperature of 20.3°C and 35.8°C after dilution. Table 10 - Comparative Exothermic Testing of the Formulation of Example 2 and Phosphoric

Acid (85%) Upon dilution with Distilled Water

The uses (or applications) of the compositions according to the present invention upon dilution thereof ranging from approximately 1 to 100% dilution, include, but are not limited to: injection/disposal treatments; soaks; acid washes; pipeline scale treatments, cement breakdowns or perforation cleaning; pH control; and de-scaling applications. Table 1 1 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 ability to not have to have a service rig come onto the well and pull all down-hole components from the well. This process is a great cost to an operator as well as a high risk operation. Having a chemical option that does not require the removal of this equipment is highly advantageous. As well the reduction of the total loads of acid via dilution, and the required number of tanks by delivering concentrated product to location and diluting with fluids available on location (high salinity production water). Other advantages of the composition according to the present invention include: operational efficiencies which led to the elimination of having to periodically circulate tanks of HC1 acid due to chemical separation; reduced potential corrosion to downhole tubulars; and reduced HC1 acid exposure to personnel by having a non- hazardous, non-fuming acid on location.

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, which various changes in form and detail can be made without departing from the true scope of the invention in the appended claims.

Claims

1 . A chrome-friendly synthetic acid composition for use in downhole oil industry activities, said composition comprising:

- urea and phosphoric acid or a derivative thereof in a molar ratio of not less than 0.1 : 1.

2. The composition of claim 1 wherein the phosphoric acid derivative is selected from the group consisting of : phosphoric acid, polyphosphoric acid, Orthophosphoric acid (H₃P0₄), pyrophosphoric acid (H₄P₂0₇), tripolyphosphoric acid (H5P3O10), tetrapolyphosphoric acid (H₆P₄0i₃), trimetaphosphoric acid (H3P3O9), and Phosphoric anhydride (P4O1₀), wherein the urea and the phosphoric acid derivative are in a molar ratio of not less than 0.5: 1.0.

3. The synthetic acid composition according to any one of claims 1 to 2, further comprising a thiourea derivative, wherein the urea and the phosphoric acid derivative are in a molar ratio of not less than 1.0: 1.0.

4. The synthetic acid composition according to any one of claims 1 to 3, wherein the thiourea derivative is selected from the group consisting of: Ν,Ν'-dibutyl thiourea, Ν,Ν'-Diphenylthiourea, 1 ,3-di- tert-butyl-2-thiourea, N-Butylurea, Ν,Ν'-Diethylthiourea, 1 ,3 -Diethyl urea, N,N'-Dimethylthiourea, 1 ,3- Diisopropyl-2-thiourea, Ν,Ν'-Dimethylthiourea, N-Methylthiourea, l ,3-Di-p-tolyl-2 -thiourea, and N- Ethylthiourea.

5. The synthetic acid composition according to claim 4, wherein the thiourea derivative is Ν,Ν'- dibutyl thiourea.

6. The synthetic acid composition according to any one of claims 1 to 5, further comprising an alkoxylated fatty amine salts.

7. The synthetic acid composition according to claim 6, wherein the alkoxylated fatty amine salts is selected from the group consisting of: bis-(2-hydroxyethyl) isodecyloxypropylamine; poly (5) oxyethylene isodecyloxypropylamine; bis-(2-hydroxyethyl) isotridecyloxypropylamine; polyoxyethylene isotridecyloxypropyl amine; bis-(2-hydroxyethyl) linear alkyloxypropylamine; bis (2-hydroxyethyl) soya amine; polyoxyethylene soya amine; bis (2-hydroxyethyl) octadecyl amine; polyoxyethylene octadecylamine; polyoxyethylene octadecylamine; polyoxyethylene octadecylamine; polyoxyethylene octadecylamine; bis (2-hydroxyethyl) octadecyloxypropylamine; bis-(2-hydroxyethyl) tallow amine; polyoxyethylene tallow amine; polyoxyethylene tallow amine; polyoxyethylene 1 ,3 diaminopropane; bis (2-hydroxyethyl) coco amine; bis-(2-hydroxyethyl) isodecyloxypropylamine; polyoxyethylene isodecyloxypropylamine; bis-(2-hydroxyethyl) isotridecyloxypropylamine; polyoxyethylene isotndecyloxypropyl amine; bis-(2-hydroxyethyl) linear alkyloxypropylamine; bis (2-hydroxyethyl) soya amine; polyoxyethylene soya amine; bis (2-hydroxyethyl) octadecylamine; bis (2-hydroxyethyl) octadecyloxypropylamine; bis-(2-hydroxy ethyl) tallow amine; polyoxyethylene tallow amine; polyoxyethylene 1 ,3 diaminopropane; and bis (2-hydroxethyl) coco amine.

8. The synthetic acid composition according to any one of claims 1 to 7, further comprising an alkoxylated organic acid.

9. The synthetic acid composition according to claim 8, wherein the alkoxylated organic acid is selected from the group consisting of: coconut oil ethoxylated fatty acid and derivatives thereof, tall oil ethoxylated fatty acid and derivatives thereof and combinations thereof.

10. The synthetic acid composition according to any one of claims 1 to 9, further comprising a corrosion inhibitor comprising at least one of the following: alkoxylated fatty amine salts; alkoxylated organic acid; and a thiourea derivative.

1 1. The synthetic acid composition according to any one of claims 1 to 10, wherein the urea and the phosphoric acid derivative are in a molar ratio of not less than 0.5: 1.

12. The synthetic acid composition according to any one of claims 1 to 10, wherein the urea and the phosphoric acid derivative are in a molar ratio of not less than 0.7: 1.

13. The synthetic acid composition according to claim 12, wherein the urea and the phosphoric acid derivative are in a molar ratio of not less than 1.0: 1 .

14. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to stimulate formations.

1 . The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to assist in reducing breakdown pressures during downhole pumping operations.

16. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to treat wellbore filter cake post drilling operations.

17. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to assist in freeing stuck pipe.

18. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to descale pipelines and/or production wells.

19. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to increase injectivity rate of injection wells.

20. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to lower the pH of fluids.

21 . The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to remove undesirable scale in surface equipment, wells and related equipment and/or facilities.

22. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to conduct annular and bullhead squeezes & soaks.

23. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to increase effective permeability of formations.

24. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to reduce or remove wellbore damage.

25. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to clean perforations.

26. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to solubilize limestone, dolomite, calcite and combinations thereof.

27. The use of a synthetic acid composition according to any one of claims 1 to 13 in the oil industry to drill out cement plugs.