This disclosure relates to methods of continuously adding of downhole well treatment chemicals to produced fluids.
Downhole tubular degradation by corrosion attack is often a significant concern in natural gas production operations, especially for these producing from high-pressure, high water volume, high-temperature (HPHT) reservoirs, low pH, high chloride content as well as produced gas containing high levels of acidic gases. CO2 and H2S. Localized, or pitting, corrosion can degrade tubular integrity and the consequences of failure to manage can be costly.
Metallurgical solutions can be effective deterrents of corrosion, but their costs could be beyond the economic limit of many projects. In many cases, low alloy carbon steel is used. In these cases, inhibitor treatment is required to keep the corrosion rate under the acceptable limit. The use of corrosion inhibitors is often considered as the most cost-effective solution for corrosion control in gas production wells. Mild steel corrosion can be significantly reduced by the presence of corrosion inhibitor in small concentrations. Corrosion inhibitors are defined as chemicals that retard corrosion when added to a corrosive environment. Effective corrosion control varies with different fluid compositions, environmental conditions, production rates, and different flow regimes.
Corrosion inhibitors used can create a continuous layer between the metal and the reactive fluids, thus reducing the attack of corrosion elements. They also attach to the surface of corroded metal, altering it and reducing the corrosion rate. In general, they are organic compounds that contain unsaturated bonds and heteroatoms, such as N, O, S, and the like. The corrosion inhibitors can form coordination bonds with empty orbits of metal elements, adsorbing on the metal surface to protect metal material. The most commonly used corrosion inhibitors in downhole tubulars include long chain primary amines, imidazolines, fatty acids, and phosphate esters. Further, a single compound is often insufficient to protect carbon steel because of the different corrosion mechanism associated to CO2, H2S presence but also if increased water production changes on chloride contents creating more severe corrosive environments. Complex formulations containing a wide range of compounds are often used. The development of inhibitor mixtures having a synergistic inhibition effect is the economical and effective way for increasing the inhibition efficiency. Synergistic inhibitors decrease the amount of usage and diversify the application of inhibitors in aggressive medium.
An embodiment described herein provides a method of adding chemicals to downhole produced fluids in a wellbore. The method includes placing a well treatment chemical in a permeable container. The permeable container includes a solid cylindrical body, caps placed at each end of the solid cylindrical body, and holes disposed proximate to each end of the permeable container. The permeable container is hung in a flow of the produced fluids, wherein the holes allow the produced fluid to flow through the permeable container from one end of the permeable container to an opposite end of the permeable container.
Another embodiment described herein provides a system for adding chemicals to a produced fluid in a wellbore. The system includes a gauge hanger and a permeable container. The permeable container includes a solid cylindrical body, end caps placed at each end of the solid cylindrical body, and holes disposed proximate to each end of the permeable container, wherein the holes allow the produced fluid to flow through the permeable container from one end of the permeable container to the opposite end of the permeable container. The system further includes a well treatment chemical disposed in the permeable container.
Embodiments described herein provide a system and method for continuously add well treatment chemicals, such as corrosion inhibitors, encapsulated scale inhibitors, low release foamed agents, sour service scavenger among others, to production fluids in a wellbore. In an embodiment, the system includes a permeable container. The permeable container has holes formed proximate to the top and the bottom to allow the production fluids to flow through the permeable container to add the well treatment chemicals to the production fluids. The holes in the permeable container may be covered by a mesh or wire screen to allow larger holes to be used with smaller particles. The rate of the addition can be controlled by the size, placement, surface riser deployment capacity and number of holes in the permeable container. Further, the rate of addition can also be controlled by the type of well treatment chemical used, downhole temperatures and well drawdown, for example, an encapsulated corrosion inhibitor.
For effective corrosion inhibition, the surface of a tubular to be protected must be fully covered by the corrosion inhibitor molecules. Interactions with the produced fluids gradually remove inhibitor molecules and they must be replenished with the new inhibitor. Thus, the presence of proper concentrations of inhibitor in the produced fluid is critical to the successful treatment. The proper application in the field is of equal importance. In gas wells, there are two types of inhibitor applications, continuous injection, and batch treatment.
Continuous injection is normally done through a capillary tubing to supply a continuous residual of inhibitor with sufficient concentration to maintain acceptable protection. The disadvantages of this application include high maintenance cost and failure of the injection system. Metering pumps require power and extensive maintenance. Further, the operational cost can be high for some applications, such as remote areas. The solvent in the injected inhibitor product can also be flashed off by produced gas and cause a “gunking” or gelling problem. The gunking problem can plug the injection nozzle, stopping the flow of the inhibitor. This is especially problematic for deep gas wells producing from high temperature reservoirs.
Batch treatment is a more common method of inhibitor application. In a batch treatment, an inhibitor solution is injected into a shut-in well and allowed to flow to the bottom to coat the surface of the tubular with the inhibitor film. The duration of the shut-in time as well as chemical percolation factors are critical factors and for successful batch treatment and is usually several hours. However, in mature gas wells, depleted reservoir pressure may allow the corrosion inhibitor to enter the reservoir near the wellbore. This can result in the inhibitor changing the reservoir rock wettability, which can end-up cause well formation damage, change on near wellbore saturation wettability and else potential for loss of well productivity. Further, the inhibitor film is often stripped off by produced gas, especially at the upper portion of tubular, where pressure is reduced, density change, flow segregate and gas flow rate are high. In these cases, frequent treatment will be required.
The corrosion inhibitors include organic compounds that contain unsaturated bonds and heteroatoms, such as N, O, and S. The corrosion inhibitors can include imidazoline, imidazole, quinoline, pyridine, and their derivatives, primary, secondary, tertiary, and quaternary amines, n-dodecylamine, N-N-dimethyl dodecylamine, amide, amidoamine, amidoimidazoline, isoxazolidine, succinic acid, carboxylic acid, aldehyde, alkanolamine, imidazoline-imidazolidine compound, α, β-ethylene unsaturated aldehyde, polyalkylenepolyamine, diethylenetriamine, or mixtures of these compounds.
For dry gas wells producing small amounts of water, this application method is not suitable due to limited interactions between the produced fluid and solid inhibitor particles.
Holes 312 in the caps, or both the cap and body are formed at each end of the permeable container. The permeable container 304 is suspended from the hangar 302, for example, a gauge hanger, in the flow of the produced fluids. The holes 312 allow the produced fluid to flow through the permeable container from one end of the permeable container to an opposite end of the permeable container, for example, from a cap 308 at a lower end of the permeable container 304 to the cap 310 at the upper end of the permeable container 304.
The device 300 can be used with any number of well treatment chemicals, including encapsulated corrosion inhibitors for protecting downhole tubular in gas wells, among others. The encapsulated corrosion inhibitor, or other well treatment chemical, is placed in the permeable container 304. The well treatment chemical is placed in the permeable container 304 prior to the device 300 being placed in the wellbore.
The permeable container 304 is connected to a hanger 302 which can be installed at a pre-determined depth in a wellbore, such as a gas well, using slickline deployment, digital slickline, E-line, braided line, or coiled tubing. The placement depth can be determined by historical well log data or based on well deviation, drift run results and previous well model predictions. As the produced fluids flow through the permeable container 304, the well treatment chemical is released into the produced fluids. The concentration of the well treatment chemicals in the produced fluid can be monitored from residual samples taken at the wellhead. Once the concentration falls below a targeted level Minimum Inhibitor Concentration (MIC)), the device 300 can be retrieved. The permeable container 304 is then refilled with a new amount of the well treatment chemical. For a corrosion inhibitor, the volume of the corrosion inhibitor material, as well as release mechanism, can be adjusted based upon recorded downhole temperature, water production, downhole drawdown, pipe metallurgy, H2S/CO2 ratios, production chemistry parameters and fluid concentrations.
In various embodiments, the permeable container 304 is made of low alloy carbon steels, stainless steel, or corrosion resistant alloy (CRA) metallurgy, depending on sour service scenario and particular well conditions. The number of holes 312, as well as the size and density of the holes, in the caps 308 and 310 and the sides of the permeable container 304 can be adjusted based on the fluid production rate and required concentration of the well treatment chemical to maximize the treatment efficiency and extend treatment life. In some embodiments, the holes 312 may be covered by a mesh screen, such as a wire screen, to allow larger holes to be used with smaller particles.
In operation, a portion of the produced fluids 504 in the tubular 502 enter the permeable container 304 through the holes 312 at the bottom of the permeable container 304. A portion of the well treatment chemical in the permeable container 304 then leaches or dissolves into the produced fluids 504, and the treated produced fluids 506 exit the permeable container 304 through the holes 312 at the top of the permeable container 304.
The concentration of the well treatment chemicals, such as the corrosion inhibitor, in the produced fluid 504 and 506 can be monitored from samples (residuals) collected and monitored at the wellhead. When the concentration is less than the minimum target dosage (minimum inhibitor concentration), the device 300 is latch and retrieved to the surface. In some embodiments, the permeable container 304 is refilled with well treatment chemicals and deployed repeatedly. The well treatment chemicals may be the same as initially used or may be varied as function of surface riser extension, treatment volume design and specific well by well requirement on well integrity monitoring, corrosion protection and other purposes.
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Further, as described herein, the devices 300 and 800 are applicable for other production chemistry problems, such as inhibiting scale deposition or the formation or mitigation gas hydrates in downstream piping and equipment. This may be performed by placing the appropriate chemical products into the inhibitor chamber and container. In cases where different well treatment chemicals are used, a first chemical or chemical type may be placed in the permeable container 304, while a second chemical or chemical type may be placed in the second permeable container 802.
The accessibility of the well is confirmed, and the SL drift is tested. The device 300 or 800 is prepared for RIH, and the depth for placement is determined. The pull out of hole (POOH) drift is set based upon maximum tool Maximum Outside Diameter (OD).
The RIH is set, and the memory tool is activated to set the hanger at the correct depth, for example, using DPU-Programmable or Eline. The RIH is performed, and tool release is confirmed. Gently Tag. The tool is depth correlated, activated for setting and remaining part is pulled out of the hole (POOH) and the equipment is rigged down.
Once the concentration of the well treatment chemical or chemicals falls below a minimum target level, the device 300 or 800 is pulled from the wellbore for refill. This is performed following the opposite procedure from above. The POOH begins with the rigging of the equipment and a pressure test of the wellhead and PCE. The appropriate tool (fishing neck) is selected and identified and for specific hanger (based upon proper tool size) and prepared.
A downhole device, which includes two body segments, is designed to treat gas wells for dispensing chemicals in the flow of production fluids, for example, the protect a tubular from corrosion attack in both H2S and CO2 scenarios. The upper body segment is a hanger that allows the devices to be securely anchored at a given depth and retrieved using conventional slickline, E-line, braided line, or coiled tubing methods. The lower body segment is a permeable container such as a tube with holes in the ends to allow produced fluids to flow through the permeable mesh container. Well treatment chemicals, such as corrosion inhibitors, diffuse into the produced fluid, and are carried into the tubular. The numbers of openings on tube ends and sides can be varied based on the fluid production rate and target dosage. The concentration of the well treatment chemical is monitored over time from samples collected at wellhead. Once the concentration is below the target minimum level, the device is retrieved to the surface, the container is refilled, and the device is redeployed.
An embodiment described herein provides a method of adding chemicals to downhole produced fluids in a wellbore. The method includes placing a well treatment chemical in a permeable container. The permeable container includes a solid cylindrical body, caps placed at each end of the solid cylindrical body, and holes disposed proximate to each end of the permeable container. The permeable container is hung in a flow of the produced fluids, wherein the holes allow the produced fluid to flow through the permeable container from one end of the permeable container to an opposite end of the permeable container.
In an aspect, combinable with any other aspect, the method includes placing the well treatment chemical in the permeable container comprises filling the permeable container with an encapsulated corrosion inhibitor.
In an aspect, combinable with any other aspect, the method includes selecting a size of the holes disposed proximate to each end of the permeable container based, at least in part, on a target addition rate of the well treatment chemical.
In an aspect, combinable with any other aspect, the method includes selecting a location of the holes at each end of the permeable container based, at least in part, on a target addition rate of the well treatment chemical.
In an aspect, combinable with any other aspect, the method includes selecting a location of the holes at each end of the permeable container based, at least in part, on a flow rate of the produced fluids.
In an aspect, combinable with any other aspect, the method includes selecting a number of the holes disposed proximate to each end of the permeable container based, at least in part, on a target addition rate of the well treatment chemical.
In an aspect, combinable with any other aspect, the method includes selecting a size of the holes, a number of the holes, or both, based, at least in part, on a concentration of hydrogen sulfide in the produced fluids.
In an aspect, combinable with any other aspect, the method includes selecting a size of the holes, a number the holes, or both, based, at least in part, on a concentration of carbon dioxide in the produced fluids.
In an aspect, combinable with any other aspect, the method includes suspending the permeable container in the wellbore using a gauge hanger.
In an aspect, combinable with any other aspect, the method includes suspending a second permeable container in the wellbore.
In an aspect, combinable with any other aspect, the method includes selecting a distance between the permeable container and the second permeable container based, at least in part, on the well treatment chemicals used in each container.
In an aspect, combinable with any other aspect, the method includes placing a first type of chemical in the permeable container and placing a second type of chemical in the second permeable container.
In an aspect, combinable with any other aspect, the method includes placing an encapsulated corrosion inhibitor in the permeable container and placing an unencapsulated corrosion inhibitor in the second permeable container.
In an aspect, combinable with any other aspect, the method includes placing an encapsulated corrosion inhibitor in the permeable container and placing a kinetic hydrate inhibitor in the second permeable container.
Another embodiment described herein provides a system for adding chemicals to a produced fluid in a wellbore. The system includes a gauge hanger and a permeable container. The permeable container includes a solid cylindrical body, end caps placed at each end of the solid cylindrical body, and holes disposed proximate to each end of the permeable container, wherein the holes allow the produced fluid to flow through the permeable container from one end of the permeable container to the opposite end of the permeable container. The system further includes a well treatment chemical disposed in the permeable container.
In an aspect, combinable with any other aspect, the permeable container comprises holes in the end caps, and wherein the holes are sized based, at least in part, on a flow rate of the produced fluid.
In an aspect, combinable with any other aspect, the permeable container comprises holes in the solid cylindrical body proximate to the cap at each end of the solid cylindrical body.
In an aspect, combinable with any other aspect, a mesh screen is disposed over the holes.
In an aspect, combinable with any other aspect, the well treatment chemical comprises particles of an encapsulated corrosion inhibitor disposed in the permeable container.
In an aspect, combinable with any other aspect, the well treatment chemical comprises a kinetic hydrate inhibitor disposed in the permeable container.
In an aspect, combinable with any other aspect, the system includes a second permeable container suspended from the permeable container by a cable. In an aspect, a length of the cable is selected based, at least in part, on a well treatment chemical disposed in the permeable container and a second well treatment chemical disposed in the second permeable container.
In an aspect, a second well treatment chemical disposed in the second permeable container includes a corrosion inhibitor.
In an aspect, a second well treatment chemical disposed in the second permeable container includes a kinetic hydrate inhibitor.
Other implementations are also within the scope of the following claims.