Wax removal methods commonly used in oil wells include mechanical wax removal, thermal wax removal and chemical wax removal. Mechanical wax removal refers to the wax removal method of scraping off the wall of tubing with special tools and bringing wax to the ground with liquid flow. Wax removal tools used in flowing wells mainly include wax scraper and wax removal bit. Under normal circumstances, a wax scraper is used; However, if wax deposition is serious, use a wax removal bit; Although the wax deposition is serious, it is not blocked yet. Use twist drill; If it is blocked or the wax is hard, stab the drill with a spear.
Mechanical wax removal of sucker rod pumping well is to remove wax from tubing and sucker rod by using movable wax scraper installed on sucker rod. Nylon wax scraper is a common tool in oil field. The stoppers are fixed at a certain distance (generally12 of the stroke length) at both ends of the sucker rod, and the nylon wax scraper is installed between the two stoppers. The sucker rod reciprocates in the tubing with the nylon wax scraper. The wax scraper slides on the sucker rod in the first half stroke to scrape off the wax on the sucker rod, and the sucker rod drives the wax scraper to scrape off the wax on the oil pipe in the second half stroke due to the function of the limiter. At the same time, the oil flow passes through the inclined opening and tooth slot of the nylon wax scraper, which pushes the wax scraper to rotate slowly and improves the wax scraping effect. Because the oil flow speed through the wax scraper is accelerated, the scraped wax is easily taken away by the oil flow, which will not cause siltation and blockage.
Mechanical wax removal can't remove the wax on the sucker rod joint and plug, so other wax removal measures should be added regularly, such as circulating well cleaning with heat carrier or chemical wax removal. Thermal wax removal is to use thermodynamics to raise the temperature of liquid flow and deposition surface and melt wax deposited in wellbore. According to the different heating methods, it can be divided into three methods: hot fluid circulation wax removal, electric heating wax removal and thermochemical wax removal.
1. Hot fluid circulation wax removal method (hot wax removal)
The heat carrier of hot fluid circulation wax removal method is a fluid substance heated on the ground, such as water or oil. Through the circulation of hot fluid in the wellbore, the heat is transferred to the wellbore fluid, so that the temperature of the wellbore fluid is raised, and the wax is deposited and melted and dissolved in crude oil, thus achieving the purpose of wax removal. According to the different circulation channels, it can be divided into four ways: open hot fluid circulation, closed hot fluid circulation, hollow sucker rod open hot fluid circulation and hollow sucker rod closed hot fluid circulation. When circulating hot fluid to remove wax, the medium with large specific heat capacity, strong wax dissolving ability, economy and wide sources should be selected, and crude oil, formation water, active water, clean water and steam are generally used. In order to ensure the wax removal effect, the medium must have a high enough temperature. In the process of wax removal, the temperature of the medium should be gradually increased, and the temperature should not be too high at the beginning, so as to avoid the melting wax block from the upper part of the tubing flowing to the lower part, blocking the circulation channel of the medium and causing failure. In addition, it is also necessary to prevent the medium from leaking into the reservoir and causing blockage.
2. Electric wax removal method
The electric heating wax removal method is to run the hot cable into the wellbore with tubing or use the electric heating sucker rod. After the power supply is connected, the cable or electric heating rod emits heat, which increases the temperature of liquid flow and wellbore equipment and melts the deposited paraffin, thus achieving the effect of wax removal and prevention.
3. Thermochemical wax removal method
In order to remove the wax deposited in the oil layer near the bottom hole or wellbore, thermochemical wax removal method is adopted, and the thermodynamic energy generated by chemical reaction is used to remove the wax plug. For example, the reaction of sodium hydroxide, aluminum and magnesium with hydrochloric acid generates a lot of thermodynamic energy.
Sodium hydroxide+hydrochloric acid = sodium chloride+H2O+99.5kJ.
Mg+2HCl=MgCl2+H2↑+462.8 kJ
2Al+6HCI = 2a 1c 13+3 H2 ↑+ 529.2 kJ
Generally speaking, it is uneconomical and inefficient to generate thermodynamic energy to remove wax in this way, so it is rarely used alone. It is usually used in combination with acid treatment as a stimulation measure for oil wells. Usually, the medicine is added from the air of oil casing or through hollow sucker rod, which will not affect the normal production and other operations of oil wells. In addition to wax removal and prevention, the use of some chemicals can also play the role of pour point reduction, viscosity reduction and plug removal. Chemical paraffin remover includes oil-soluble, water-soluble and emulsified liquid paraffin remover and a solid paraffin remover.
1. Oil-soluble detergents and waxes
The oil-soluble paraffin remover used in the field is mainly composed of organic solvent, surfactant and a small amount of polymer. For example, the formula of Daqing No.2 paraffin remover and paraffin inhibitor is 30% of bottom oil of platinum reforming tower, 66.6% of 120 straight-run solvent gasoline, 0.3% of polyacrylamide and 0.3% of T penetrant. Among them, the organic solvent mainly dissolves the wax deposited on the pipe wall. The purpose of adding surfactant is to help the organic solvent penetrate along the gap between the deposited wax and the gap between the wax and the oil well pipe wall, so as to increase the contact surface, improve the dissolution speed, and promote the wax deposited on the pipe wall surface to fall off from the pipe wall surface, so as to be taken out of the oil well with the oil flow. The purpose of adding some oil-soluble paraffin remover and paraffin inhibitor to the polymer is to hope that the polymer and the wax crystals precipitated first in crude oil will form * * * crystals. Because the added polymer has a special structure, there are both lipophilic groups and hydrophilic groups in the molecule. Hydrophilic groups and wax crystals, while hydrophilic groups extend outward, which prevents the later precipitated wax from combining with them to form a three-dimensional network structure, thus achieving the purpose of reducing viscosity and pour point, preventing wax deposition and playing a certain wax prevention effect.
Advantages: strong adaptability to crude oil; The wax dissolving speed is fast, and the effect is quick after being added into the oil well; The product has a low freezing point and is easy to use in winter.
Disadvantages: low relative density, not suitable for high water cut oil wells; Low ignition point, easy to catch fire, strict fire prevention measures must be taken when using; Generally, this paraffin remover is toxic.
2. Water-soluble detergents and waxes
Water-soluble paraffin remover is composed of water and various surfactants. The formula used in the field is selected according to the different crude oil properties and wax deposition in each oilfield. However, surfactants, mutual solvents and alkaline substances are all added to the water. Commonly used are sulfonate, quaternary ammonium salt, peregal and polyether. This paraffin remover and paraffin inhibitor can play a comprehensive role. Among them, the surfactant plays the role of wetting reversal, which makes the wax deposition surface reverse to hydrophilic surface. The adsorption of surfactant on the surface of tubing is beneficial to wax shedding from the surface, and is not conducive to wax deposition on the surface, thus achieving the effect of wax prevention. The permeability and dispersity of surfactants are helpful for wax remover and paraffin inhibitor to penetrate into the cracks of loose wax crystals and weaken the binding force between wax molecules, thus leading to the disintegration of wax crystals and dispersion in oil flow. The function of mutual solvent is to improve the mutual solubility of oil (wax) and water. Useful mutual solvents are alcohols and alcohol ethers, such as methanol, ethanol, isopropanol, isobutanol, ethylene glycol butyl ether and ethylene glycol ether. Alkaline substances can react with organic polar substances such as asphaltene in wax to produce water-soluble products, so they can be removed from the wax deposition surface with water-based detergents and paraffin inhibitors. Commonly used alkaline substances include sodium hydroxide, potassium hydroxide and other alkaline substances, as well as sodium silicate, sodium phosphate, sodium pyrophosphate, sodium hexametaphosphate and other salts that dissolve in water to make water alkaline.
Advantages: high relative density and good application effect for high water cut oil wells; Safe to use, no fire hazard.
Disadvantages: slow effect; The freezing point can reach -20 ~-30℃, but its fluidity needs to be improved when used in cold winter.
3. Emulsified paraffin remover and paraffin inhibitor
Emulsified paraffin removal and paraffin inhibitor is an oil-in-water emulsion formed by adding oil-soluble paraffin removal and paraffin inhibitor into water, emulsifier and stabilizer. After this emulsion is added to the oil well, it is demulsified at the bottom of the well, releasing organic solvents and oil-soluble surfactants with good solubility in wax, thus achieving the dual effects of wax removal and wax prevention. Emulsified paraffin remover has the advantages of both oil-soluble paraffin remover and paraffin remover with fast wax dissolving speed. Because the external phase of the emulsion of this wax remover and paraffin inhibitor is water, it is as safe to use as a water-soluble wax remover and paraffin inhibitor, and it is not easy to catch fire, and its density is relatively high. Its disadvantage is that it must be stable during preparation and storage, but it must be demulsified immediately after reaching the bottom of the well. The choice of emulsifier and demulsification temperature at the bottom of the well are strict, and the preparation and use time are high, otherwise it will not play a role in wax removal and prevention.
The emulsifier commonly used to prepare emulsified paraffin remover is OP surfactant, the mixture of compound ester of oleic acid, linoleic acid and resin acid and triethanolamine.
4. Solid paraffin inhibitor
Solid paraffin inhibitor is mainly composed of high molecular polyethylene, stabilizer and EVA (ethylene-vinyl acetate polymer). It can be made into particles, or pressed into a certain shape (such as honeycomb briquette) in a mold after mixing, placed in a certain temperature area of an oil well or placed at the bottom of the well, and gradually dissolved at the temperature of the oil well to release chemicals and dissolve them in oil. As a paraffin inhibitor, polyethylene requires a relative molecular weight of 5000 ~ 30000, preferably around 20000, a relative density of 0.86 ~ 0.94, a melting point of 102 ~ 107℃, less crystallization, or amorphous type. EVA in paraffin inhibitor is soluble in crude oil because it has a (CH2-CH2) n segment similar to wax structure and a certain number of polar groups. After cooling, it reacts with wax in crude oil, and then inhibits the growth of wax crystals through polar groups extending outward. When the oil temperature decreases, the polyethylene dissolved in crude oil will precipitate first and become the paraffin crystal nucleus which will precipitate later. Wax crystals will be adsorbed on the carbon chain of polyethylene, and the growth and aggregation of crystals will be hindered by space barriers and barriers, which will reduce the adhesion between EVA and wax crystals, thus reducing wax deposition in oil wells and achieving the purpose of wax prevention.
Advantages: One-time wax prevention cycle is longer (generally up to half a year) and the cost is lower;
Disadvantages: it has strong pertinence to oil products, and its formula must be specifically screened according to the oil well situation and the wax precipitation point of crude oil. Patented mixed biodegradable water-based surfactant/wetting agent/emulsifier contains many ingredients. It is a patented water-based mixed nonionic and anionic surfactant invented by an American company, in which other additives are added to provide unique performance and reduce hydrocarbons. Besoft's product formula is specially optimized for sealing and emulsifying crude oil and hydrocarbons. Emulsifying hydrocarbons by forming micelles is very effective in a series of applications. It is a non-toxic formula, does not contain toxic components listed in CERCLA (Environmental Protection Responsibility Law), and is 100% biodegradable. Gas suppression products certified by ABS (American Bureau of Standards). Besofol can keep the original state of wax block in oil, make the wax block loose and inhibit wax deposition. The field test shows that this patented surfactant formula is more effective, safer and cheaper than hot oil to remove the paraffin accumulation on the formation and oil production equipment. Different from xylyl solvent treatment, Besofol can not only remove sludge and paraffin, but also inhibit the gas generated, leaving no smooth residue, which increases the safety of workers.
Using this surfactant technology to treat hydrocarbons will produce two effects:
(1) solubility increase (solubilization)
(2) The interfacial tension decreases (becomes loose).
One of its technical working mechanisms is to reduce the interfacial tension, so the pressure drop will lead to the inability to "precipitate" paraffin, and the capillary force to prevent paraffin (C-20 ~ C-50) from combining with oil will be reduced. The microorganisms used for wax removal mainly include wax-eating microorganisms and gum-eating and asphaltene-eating microorganisms. The oil well paraffin removal microorganism is a long spirochete with a length of 1 ~ 4 microns and a width of 0. 1 ~ 0.3 microns ... This microorganism can reduce the freezing point and wax content of crude oil and feed on paraffin. After the microorganism is injected into the oil well, it actively swims in the direction of paraffin, feeds and degrades paraffin and asphalt. Sulfate-reducing bacteria in the microorganism proliferate and produce surfactants, which reduces the interfacial tension between oil and water. At the same time, gas-producing bacteria in microorganisms can also produce gases soluble in oil, such as CO2, N2, H2, etc., so as to expand crude oil and reduce its viscosity, thus achieving the purpose of wax removal.