ELECTRICAL SUBMERSIBLE MOTOR PROTECTING SYSTEM AND METHOD WITH CHEMICAL CHAMBER

An electric submersible pump system for use in a wellbore includes a pump; a motor protection component having an oil chamber and an wellbore fluid chamber; a motor component, the motor component including oil and being fluidly coupled to the oil chamber of the motor protection component; and a chemical chamber that includes a neutralization chemical. The neutralization chemical includes a scale inhibitor. The chemical chamber is configured to contact fluid from the wellbore with the neutralization chemical and is fluidly coupled to the wellbore fluid chamber of the motor protection component. The pump is configured to be driven by the motor component. A chemical chamber and a method for operating an electric submersible pump are also disclosed.

FIELD

The technology disclosed herein relates to an electrical pump, in particular for a submersible pump for use in a wellbore.

BACKGROUND

Electrical submersible pump (ESP) systems are a type of artificial lift system used in oil and gas wells to increase the flow of fluids (such as water and/or oil) to the surface. An ESP generally includes a pump that is submerged in the wellbore and is powered by a downhole electric motor. The ESP system is designed to operate under high temperatures, pressures, and corrosive conditions, making it suitable for use in harsh downhole environments.

The main purpose of an ESP system is to increase production of oil and gas. This can be done by either increasing the speed or volume of fluid flow, but most wells have a fixed production rate. Production could also be improved by reducing downtime by making the ESP more reliable, less prone to breaking down, and/or easier and quicker to repair. Replacing or repairing an ESP requires significant time and cost in preparing the wellbore to perform the change out operation. Often the preparation for servicing the ESP involves even more time than the time to replace or repair the ESP. Costs are very significant to pull up piping from a deep well, especially an off-shore well, where a barge and crane must be used for removing the pipeline and replacing it.

Overall, the development of ESP technology has been driven by the need to increase oil and gas production in challenging downhole environments. As such, ongoing research and development in this field are expected to continue to drive innovation and improvements in ESP technology. There is a need for increased reliability for the ESP motor and its related components.

SUMMARY

In some aspects, the techniques described herein relate to an electric submersible pump system for use in a wellbore, which includes a pump; a motor protection component having an oil chamber and an wellbore fluid chamber; a motor component, the motor component including oil and being fluidly coupled to the oil chamber of the motor protection component; and a chemical chamber that includes a neutralization chemical. The neutralization chemical includes a scale inhibitor. The chemical chamber is configured to contact fluid from the wellbore with the neutralization chemical and is fluidly coupled to the wellbore fluid chamber of the motor protection component. The pump is configured to be driven by the motor component.

In some aspects, the techniques described herein relate to a method of operating an electric submersible pump system in a wellbore, including: starting a motor component for driving a pump; flowing wellbore fluid into a chemical chamber; neutralizing the wellbore fluid with a neutralizing chemical; heating oil in a motor component, causing it to expand into an oil chamber of a motor protection component; flowing neutralized wellbore fluid into a wellbore fluid chamber of a motor protection component.

In some aspects, the techniques described herein relate to a chemical chamber device for an electric submersible pump system, including: a chemical chamber cavity bounded by an outer housing, a filter, a chemical chamber inner tube, a head, and a floor portion. Chemical chamber tubing extends from the head of the chemical chamber into the chemical chamber cavity. The head is configured for attaching to a pump, and the chemical chamber inner tube is configured to surround a shaft. A passage is formed between the filter and the chemical chamber inner tube, and the passage terminates at a bottom of the chemical chamber. A neutralization chemical resides in the chemical chamber cavity.

DETAILED DESCRIPTION

Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form. Additionally, as used herein, the term “exemplary” is intended to mean serving as an illustration or example of something, and is not intended to indicate a preference. In addition, the terms “inner” and “outer” are in reference to the longest axis of the devices and systems disclosed herein. The term “fluidly coupled” means a fluid, such as oil, can flow through from one end of the area it relates to, to another. For example, X is fluidly coupled to Y, means fluid can flow through tubing or some channel or chamber from X to Y or vice versa.

Disclosed herein is a motor protecting system for an ESP, particularly for an ESP in a wellbore environment. The protection component is intended to extend the life of the ESP, thereby decreasing downtime of the well for maintenance of the ESP, and consequently improving production from the well.

For lubrication and other purposes, the electrical motor component of the ESP is filled with a dielectric motor oil. Due to the temperature of the motor changing during operation, the volume of motor oil changes accordingly. This change in volume may be described by equation (1)

ΔV is the change in volume, Vois the original volume. β is the coefficient of volume expansion, and ΔT is the change in temperature. As the volume of the oil expands, it must have a reservoir to be pushed into. In an embodiment of an ESP this reservoir is a motor protector component that is an expandable bladder between the motor component and the rotating impellers of the pump. An expandable/contractable motor protector component acts to prevent the motor from well fluid contamination and also maintains a pressure balance between the wellbore and the internal chamber of the motor. This pressure equilibrium allows the expanding oil to freely move from the motor component to the motor protector component as the motor protector component is enabled to expand and contract. Without the ability of the motor protector component to expand and contract, the internal oil pressure in the motor would build up to undesired levels.

In operation, well fluid is allowed to enter and exit the motor protector component constantly as the motor temperature changes to equilibrate the pressure. While well fluid enters and stays in the motor protector component, harsh chemicals in the well fluid react with internal parts of the motor protector and with the motor oil. Eventually, the chemically damaged parts of the motor protector component cause leakage into the internal part of the protector and mix with the motor oil.

Addressing this problem, a system and method is provided herein to reduce the damage to the motor protector component by neutralizing the harsh well fluid that enters the protector component by filtering it through a pre-imbedded chemical material that is in chemical chamber. Accordingly, this system and method is expected to extend the runlife of the ESP in a wellbore and improve the overall production of the well.

With reference toFIG.1, an exemplary system100for oil and gas production is illustrated as an overview exterior view of an ESP110disposed within the walls of a wellbore50. The system100includes an ESP110, which comprises a pump120, a motor protection component130, and a motor component140. A power connector150is also shown at the top of the motor component140. The power connector150is attached to a power conduit160, which runs up the side of the ESP110and continues up to the top of the wellbore50where it is coupled to a power source.

In this embodiment, the motor component140is at a bottom end of the ESP and a top end of the motor component140is coupled to a bottom end of the motor protection component130. A top end of the motor protection component130is coupled to the pump120.

An intake opening125is on the side of the pump120near the bottom end of the pump120. Fluid from the wellbore50comes into the ESP from this intake opening125and is pumped through the pump120up and out of the wellbore50via the production tubing170.

FIG.2is a cross-sectional view of an exemplary first motor protection component230, a second motor protection component290, and a chemical chamber280. A top end of the chemical chamber280is coupled to a pump (seeFIG.1pump120). The bottom of the second motor protection component290is coupled a motor component (SeeFIG.1, motor component140) via a base299circumscribed by a base flange294.

The first motor protection component230, second motor protection component290, and chemical chamber280are coupled through a first coupling body281and a second coupling body291. The first and second coupling bodies281,291are connectors that in an embodiment, function to efficiently attach the different fittings of the first and second motor protection components230,290and the chemical chamber280together. The first and second coupling bodies281,291also include a first tubing277and a second tubing247, which are configured to allow fluid from one component to flow into the other component joined by the first and second coupling bodies281,291.

In the embodiment ofFIG.2, a second motor protection component290is utilized to further protect the motor component. This helps to prolong the life of unit and/or the intervals between servicing the ESP. However, the second motor protection component290is optional.

A shaft250runs through an axial center of the first motor protection component230, second motor protection component290, and chemical chamber280. A bottom end of the shaft250runs from the motor component140to the pump120where it is attached to impellers in the pump120. In an embodiment, the shaft250runs through a bearing chamber245at the bottom of the motor protection component130.

The first motor protection component230includes an outer housing232and a flexible bag233. The flexible bag may be made of an elastomeric material, such as butyl rubber, halobutyl rubber, nitrile rubber, natural rubber, styrene-butadiene rubber, or polybutadiene rubber, or mixtures thereof. Inside the flexible bag233is a first inner tube235within which the shaft250rotates upon impetus from the motor component140. The first inner tube235prevents oil from the inside of the flexible bag233from contacting the shaft250. An inner chamber236is formed inside the flexible bag233bounded on the inner circumference by the first inner tube235and on the outer circumference by the flexible bag233. An outer chamber237is formed between the outside the flexible bag233(i.e., its outer circumferential surface) and the inside surface of the outer housing232. The inner chamber236is also referred to herein as an oil chamber, and the outer chamber237is also referred to herein as a wellbore fluid chamber. It is contemplated that in another embodiment, with modifications, the oil chamber could be the outer chamber and wellbore fluid chamber could be inner chamber.

The flexible bag233is attached at the top to a top body234and at the bottom to a bottom body238. These top and bottom bodies234,238and their intersection with the flexible bag233also provide a boundary to the top and bottom of the inner chamber236.

The second motor protection component290in an embodiment is the same as the first motor protection component230, and it includes a second outer housing292and a second flexible bag293. Inside the second flexible bag293is a second inner tube295within which the shaft250rotates upon impetus from the motor component140. The second inner tube295prevents oil from the inside of the second flexible bag293from contacting the shaft250. A second inner chamber296is formed inside the second flexible bag293bounded on the inner circumferential surface by the second inner tube295and on the outer circumferential surface by the second flexible bag293. A second outer chamber297is formed between the outside of the second flexible bag293(i.e., its outer circumferential surface) and the inside surface of the second outer housing292.

The second inner chamber296is also referred to herein as a second oil chamber, and the second outer chamber297is also referred to herein as a second wellbore fluid chamber. It is contemplated that in another embodiment, with modifications, the oil chamber could be the second outer chamber297and the wellbore fluid chamber could be the second inner chamber296.

The second flexible bag293is attached at the top to a second top body264and at the bottom to a second bottom body298. These second top and bottom bodies264,298and their intersection with the second flexible bag293also provide a boundary for the top and bottom of the second inner chamber296.

In operation, the expanding oil flows from the motor component140to the second inner chamber296of the second motor protection component290through a passage between the second inner tube295and the bottom body298. If the second motor protection component290is not present, the oil expands directly into the first motor protection component230. Contracting oil can flow in reverse back down to the motor component140. Excess expanding oil either flows into the first motor protection component130or into the first or second check valve279,239to exit to the wellbore.

Clean oil passes to and from the motor component140, first motor protection component130, and second motor protection component290and flows through internal passages around the shaft or other passages near the shaft that are no further from the axis300than the flexible bag233. The neutralized wellbore fluid passes from the intake opening125through various passages always separated from the clean oil pathways into the first and second outer chambers237,297.

The chemical chamber280incorporates the neutralization chemical289in a chemical chamber cavity286bounded by an outer housing283and a filter284. The filter284is situated around a chemical chamber inner tube285which surrounds the shaft250, for the same reasons as explained above. This filter284can be a cylindrical mesh, or in another embodiment, can be a tube with one or more openings near the top with a metallic mesh covering the openings. In either case, the filter284prevents large solid particles from entering the outer chamber237of the first motor protection component230. In an embodiment, the filter284can be placed at other locations between the intake opening125and the outer chamber237.

At the top of the chemical chamber280is a head282, which is configured to couple (either directly or indirectly via one or more other coupling bodies) to the pump120. A floor portion288bounds the bottom of the chemical chamber cavity286.

Chemical chamber tubing287runs through the head282of the chemical chamber280and at its upper end is in fluidly coupled to an intake opening125for the wellbore fluid. The lower end of the chemical chamber tubing287extends down to near the bottom of the chemical chamber cavity286, for example, the chemical chamber tubing287may extend down to within 25%, within 20%, or within 10% of the bottom length of the chemical chamber cavity286.

The filter284has one or more small openings allowing neutralized wellbore fluid to enter a passage between the inside of the filter284and the outside of the chemical chamber inner tube285. This passage terminates at the bottom of the chemical chamber280where it is coupled to a chamber276that is coupled to first tubing277that runs through the first coupling body281into the first motor protection component230via first and second passages248,249into, specifically, the outer chamber237of the first motor protection component230. The chemical chamber280is thus fluidly coupled to the outer chamber237of the first motor protection component230. Similarly, the second tubing247that runs through the second coupling body291into the second motor protection component290via first and second passages268,269into, specifically, the second outer chamber297of the second motor protection component290. The chemical chamber280is thus fluidly coupled to the second outer chamber297of the second motor protection component290via the first motor protection component230.

The shaft250runs along an axis300, from the motor component140to the pump120. The shaft250runs through the first and second motor protection components230,290, and through the chemical chamber280. As discussed above, the shaft250is isolated in the interior of the ESP110by the first inner tube235, second inner tube295, and chemical chamber inner tube285. Shaft seals201,202,203are located at the top of each component around the shaft250. The shaft seals201,202,203are configured to prevent arbitrary leakages between chambers through the interface between the first inner tube235, the second inner tube295, and chemical chamber inner tube285that surrounds the shaft250.

In an embodiment, an upper head portion of the motor protection component130is coupled to a base369of the modular chemical chamber380. The modular chemical chamber380can be configured to fit on existing motor protection components130.

In another embodiment disclosed inFIG.3, a modular chemical chamber380is configured for quickly attaching or detaching to a first motor protection component230. The modular chemical chamber380is configured with a base369, and includes a shaft portion350that runs along a central axis400. The first motor protection component230is includes a head362, that is configured to quickly couple to a base369of the modular chemical chamber380. In an embodiment, the head362may be identical to head282(of the device ofFIG.2) and head382on the modular chemical chamber380ofFIG.3.

In an embodiment, each head362/282/382) is configured to quickly connect to the base369. The upper surface of the head362is configured to abut the bottom surface of the head flange364. The base369includes a lip portion367that fits concentrically within the inner surface of the head362. The head362and base369can be attached, for example, by nut-and-bolt type threads on the inner surface of the head362and outer surface of the lip portion367. Other forms of mechanical engagement could be used in addition or instead, such as, multiple nuts and bolts, clamps, or screws into preformed threaded holes.

The shaft portion350of the modular chemical chamber380is configured to engage with and attach at its bottom end351to a top end352of the shaft250residing in the first motor protection component230. In an embodiment, a sleeve459is used to couple the bottom end351to the top end352.

In an embodiment, the sleeve459can, for example, have screw-type threads that engage with matching threads on the bottom end351and the top end352. Alternative connecting mechanisms can also be used, such as a detent pin system or a ball pin on one or more sides of the sleeve459matching with one or more detents on the bottom end351to the top end352. The attachment can be threaded engagement that will be urged to tighten when the shaft250turns. Other mechanical configurations for attachment can be used in other embodiments.

FIGS.6,7, and8are perspective views of an embodiment of the sleeve601and the shaft610. The sleeve601has six raised ridges605, with six depressed surfaces607therebetween each of which run vertically along the axis of the sleeve601. The shaft610includes six matching raised ridges615that run vertically in line with the axis of the shaft and match the width of the depressed surfaces607.

Each end of the sleeve601can be open to receive an end of the shaft610. A shaft610can be inserted from both opens ends or in an embodiment, one shaft610is manufactured with the sleeve601on one end.

The open end of the sleeve601and shaft610, when pressed together can have a tight friction fit, as the depressions619between the matched raised ridges615taper out axially to become less deep as the shaft extends. In an embodiment, the end617of the matched raised ridges615has a tapered width that becomes narrower as the end of the shaft610is approached. This allows for easier engagement with the sleeve601.

FIG.4shows the separate components of the embodiment ofFIG.3assembled together. The modular chemical chamber380is configured for attaching or detaching to a first motor protection component230. This embodiment, is configured to be readily attachable to a conventional motor protection component by a series of bolts.

Other than the head382and the base369components, the modular chemical chamber380is much the same as chemical chamber280ofFIG.2. Chemical chamber tubing387, neutralization chemical389, shaft seals302,304, first tubing377, and outer housing383, are substantially the same as inFIG.2. An additional difference is that in an embodiment, the chamber376is configured differently from the chamber276of the device ofFIG.2, and a head-base chamber458is formed between the base369of the chemical chamber280and the head362of the first motor protection component230. In an embodiment, the neutralized fluid may contact the shaft in the head-base chamber458. Other components inFIGS.3and4are marked with the same numerals as inFIG.2to indicate their similarity.

In an embodiment, the neutralization chemical289is a scale inhibitor. A scale inhibitor delays or prevents scaling. Scaling is a buildup of minerals such as calcium carbonate (CaCO3), calcium sulfate (CaSO4), barium sulfate (BaSO4), strontium sulfate (SrSO4), and iron sulfide (FeS2) on surfaces such as the flexible bag233.

In an embodiment, the neutralization chemical289comprises one or more components selected from the group consisting of: phosphonates, phosphoric acid, ortho phosphates, and high molecular weight polymers (for example, 500,000 g/mol (weight average molecular weight), 750,000 g/mol, or 1 million g/mol or more) such as polyethylene oxide polymer. The neutralization chemical may also include one or more iron chelators, such as, for example, tetrakis hydroxymethyl phosphine chloride (THPC) and/or hydroxymethyl tetrakis phosphonium sulfate (THPS). In an embodiment, the neutralization chemical289is in the solid form at 25° C.

In addition, the neutralization chemical289can be selected to neutralize agents that cause corrosion, scale, or foaming, or to neutralize paraffins and asphaltenes. The neutralization material can include In an embodiment, the neutralization chemical289can be a modified form of the CHEM-STICK material from Odessa Separator, Inc.

In an embodiment, the material is a solid particulate or porous material. The material should have sufficient porosity or low enough density to flow water, oil, or wellbore fluid through the thickness of the neutralization chemical289between the outer housing283and the filter284. This thickness of the chemical chamber cavity286may be, for example, 0.25 to 3 inches, such as, for example, 1 to 2.5 inches, or 1.25 to 2 inches. The height of the chemical chamber cavity286may be 2 inches to 3 feet, such as, for example, 4 inches to 2 feet, or 8 inches to 20 inches.

A volume of the neutralization chemical289is sufficient for neutralization treatment of the wellbore fluid for many hours of use, for example, its entire lifetime, such as up to 60,000 hours, for example, 168 hours to 3000 hours, or 672 hours to 4380 hours. A sufficient volume of the neutralization chemical289in the chemical chamber cavity286is, for example, 1.6 in3to 4070 in3, such as, for example, 3 in3to 2,000 in3, or 100 in3to 1000 in3. The neutralization chemical289is present in the chemical chamber cavity286in a volume sufficient to treat, i.e., neutralize, a wellbore fluid volume of, for example, 0.1 to 5 gallons, such as, for example, 1 to 4 gallons, or 2 to 3 gallons.

In a method of assembling the ESP110, part of the ESP110is assembled in a factory with the motor component140and motor protection component130, these are then filled with clean motor oil. At the wellbore site, the ESP110is assembled by coupling the pump120to the bottom of the production tubing170, coupling the pump120to the chemical chamber280, coupling the chemical chamber280to the motor protection component130(which may optionally be first and second motor protection components230,290) which was preassembled with the motor component140. This method is particularly applicable to the modular chemical chamber380embodiment ofFIG.3. In the embodiment ofFIG.2, chemical chamber280is an added part to motor protection component230and can be manufactured as a single unit, i.e., within the same housing.

The chemical chamber280is preloaded with the neutralizing chemical and the motor component140is preloaded with oil in an amount sufficient to lubricate the motor at a low temperature, e.g., down to 20° C. at standard atmospheric pressure. The ESP110is then dropped down into the wellbore50. The ESP110with the chemical chamber280may be installed in a wellbore50at depths of, for example, 4 to 10,000 foot, such as, for example, 200 to 7,500 feet, or 1,000 to 7,500 feet.

In operation, the ESP110is lowered into the wellbore. The clean motor oil in the motor component140expands as the ambient temperature in the wellbore is elevated at significant depths compared to ambient temperature at the surface. If the expanding oil becomes too high in volume it may overflow via a check valve239/279to exit to the wellbore. Still the motor component140and motor protector component130are filled with clean oil.

When the motor component140is electrically started and begins running, the motor temperature will increase even higher and more expansion of the oil will take place. If there is excess oil over the capacity of the motor protection component130, it can overflow into another motor protection component or through a valve to outside the ESP110. When the motor is running, the wellbore fluid flows into the intake opening125as it is sucked in by impellers of the pump120. Most of the wellbore fluid is sent out of the top of the pump120into the production tubing170. A minor part of the wellbore fluid is sucked into the chemical chamber280due to contraction of the oil volume, specifically into the chemical chamber tubing287that extends to the bottom of the chemical chamber cavity286. The wellbore fluid in the chemical chamber cavity286then contacts and reacts with the neutralization chemical289, is filtered through the filter284, and the neutralized wellbore fluid is flowed through the chemical chamber tubing287and into the outer chamber237/297of the motor protection component130. As the oil in the motor component140begins to heat up from heat generated from the activated motor, the oil expands. The motor component140and the inner chamber236are fluidly coupled such that the expanding oil expands out of the motor component into the inner chamber236of the motor protection component130. If the motor component140is stopped or shut down or the oil cools down due to external temperature changes, the oil in the inner chamber will contract and migrate back into the motor component140, and this volume is replaced by neutralized wellbore fluid from the chemical chamber cavity286.

The method of operation is also shown inFIG.5.FIG.5is a flowchart of an example method for operating an electric submersible pump system in a wellbore. At step510, a motor component for driving a pump is electrically signaled to start. Electric power is supplied and the motor turns, thereby turning shaft and the pump impellers. At step520, wellbore fluid is flowed into a chemical chamber. In an embodiment, this wellbore fluid is, for example, 0.1 to 5 gallons, such as, for example, 1 to 4 gallons, or 2 to 3 gallons. At step530, the wellbore fluid is neutralized with a neutralizing chemical. At step540, oil in the motor component heats up due to friction and movement of parts in the motor. This causes the oil to expand into an oil chamber of a motor protection component. At step550, due to the contraction of oil volume in the motor and the motor protection component, neutralized wellbore fluid will migrate into the motor protection component130. The volume of the neutralized wellbore fluid will be, for example, 0.1 to 5 gallons, such as, for example, 1 to 4 gallons, or 2 to 3 gallons. In an embodiment, once the neutralized wellbore fluid enters into the motor protection component130, the neutralized wellbore fluid will dwell in the motor protection component130for the lifetime of the ESP110, or at least until it is removed from the well and serviced. There may be some fluctuation in the flow of the neutralized wellbore fluid if the motor component temperature or ambient temperature in the wellbore rises or falls during operation, but the majority of the initially neutralized wellbore fluid will remain in the motor protection component130(specifically the outer chamber).

In a method of servicing the ESP110, the motor component140driving the pump120is shut down and pulled up from the wellbore50. In the ESP110according to the embodiment ofFIGS.3and4the modular chemical chamber380can be unscrewed or otherwise quickly detached from the pump120and the motor protection component130. A new modular chemical chamber380can be attached to the pump120and the motor protection component130. Alternatively the neutralization chemical289in the modular chemical chamber380could be removed and replaced with new (unreacted) neutralization chemical289, and then replaced into the ESP110. The motor protection component130, motor component140and pump120could also be inspected and serviced if needed at this time. Oil quality and volume can be inspected and the oil can be changed as well. The assembled ESP110is then inserted back into the wellbore50, and, once in place, the motor component140driving the pump120is restarted and production of hydrocarbons from the well resumes.

The servicing procedure with the ESP110according to the embodiment ofFIG.2would be similar. However, the chemical chamber280of that embodiment is not so easily detachable and reconnectable, and may require detaching the pump120, motor protection component130and motor component140to account for the one piece shaft250. Another advantage of the modular chemical chamber380is that it is configured to be compatible to couple with existing motor protection units.

What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable modification and alteration of the above devices or methodologies for purposes of describing the aforementioned aspects, but one of ordinary skill in the art can recognize that many further modifications and permutations of various aspects are possible. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the details description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim. The term “consisting essentially” as used herein means the specified materials or steps and those that do not materially affect the basic and novel characteristics of the material or method. If not specified above, the properties mentioned herein may be determined by applicable ASTM standards, or if an ASTM standard does not exist for the property, the most commonly used standard known by those of skill in the art may be used. The articles “a,” “an,” and “the,” should be interpreted to mean “one or more” unless the context indicates the contrary.