While mining no precious (ordinary), semiprecious and precious minerals, such as silver and gold, people learned to extract from the depths of the earth huge amounts of unique mineral resources known as oil which is rightfully called the “black gold”
There is not a single branch of industry that can do without products obtained in the course of oil cracking such as paraffin, kerosene, petrol, ligroin, fuel oil, asphalt and lubricant grease. However, in spite of all positive progress in the sphere of oil extraction from the depths of the earth the existent technologies of oil extraction are not able to prevent sedimentation of oil components such as sulphur, paraffin and tar on the walls of oil wells. In the course of long-term extraction of oil these components may partially or fully clog up pump pressure pipes through which oil is transferred. Oil pipe clogging is a disease of all oil-extracting businesses. There are methods of cleaning clogged oil wells from tarry paraffin-asphalt deposits (TPAD) all over the world. However, some of the methods are very expensive, thus making oil-well cleaning process very expensive, other methods are ineffective.
Let us discuss certain methods of cleaning oil wells from TPAD. There is a scraping method when a scraper comprising cone-shaped metal lobes is lowered on a cable into a partially paraffmized tube. When the cable is pulled up, the lobes are extended so that they come into contact with the walls of the well, i.e. a pump pressure pipe (PPP) through which oils is transferred, and tarry paraffin-asphalt deposits are removed from the PPP walls. The disadvantage of this method is that the lobes cannot be proportionally engaged in contact with the PPP walls and clean away the deposits to the shining effect, therefore particles of paraffin-asphalt remain on the PPP walls, so that a PPP pipe will quickly get paraffmized again; therefore, this method has to be used at regular two days intervals by stopping the oil production, thus incurring economic losses on the oil-extracting business.
The worldwide practice of cleaning oil wells uses a steam-based method. Steam-generating equipment is produced in the U.S. Steam is discharged at high pressure to melt and remove paraffin-asphalt deposits. The disadvantage of this method lies in the large size and heavy weight of the steam-generating equipment. High cost is another drawback of the equipment, worth $1,200,000, and the self-cost of one-day operation of this equipment amounts to $45 thousand. Yet another drawback consists in the fact that steam cools down as it moves down the oil well, as a result it gets condensed and transformed into cool water, which cannot melt paraffin-asphalt deposits formed at lower depths. Therefore, this method can be used for deparaffinization of deposits existent at the depth of down to 80 meters from the head of the well. Another method utilized is the air method; The equipment pumps air at 600 atmospheres into a PPP pipe and the paraffin-asphalt plug descends into the bottom hole of the oil well, and into the layer of hot oil, where it melts. The disadvantage of this method is that it is only applicable when plugs are small; however, if the paraffin-asphalt plugs have formed within a section of more than100 meters of a PPP pipe, then such plugs will not move or descend into the layer of oil even when acted upon by such huge pressure. Another disadvantage consists in the metal fatigue that occurs in metal tubes in the course of long-term operation of the well, the strength of metal is reduced, whereas the pressure of 600 atmospheres may break the integrity of the oil well, i.e. the PPP pipe.
In addition to air method, there is an acid method through which the well is filled with acid to decompose paraffin. Yet, the disadvantage of this method revolves around the acid, while decomposing paraffin, comes into contact with the metal PPP pipe and corrodes its walls, completely brakes the pipe’s integrity and makes it inoperable. This method incurs large-scale economic and ecological losses on the business.
Our company LLC Everest-2000 has developed a device and implemented a point-junction heating method of cleaning clogged-up wells from TPAD deposits by means of the H-l device.
Mechanical Method of Oil Extraction
This method is subdivided into two types:
A) Electro-centrifugal pump (ECP): the electric cable is connected to the pump of the PPP pipe from the exterior, while the pipe itself remains hollow.
B) Deep sucker rod pump (DSRP): the pumping jack is placed over the well. It has a 20 mm diameter screwed-in metal rod, which runs down along the centre of the well and is connected via a plunger with the pump that pumps the oil. Through this method, customers are obliged to remove the rod from the PPP pipe, otherwise the rod will prevent the H-1 device from being lowered into the PPP pipe and the cleaning thereof will be impossible.
Although, the depth of TPAD location is insignificant, and its only effect occurs during the cleaning process, the diameter of a PPP is very important, i.e. the lesser the clearance between the interior wall of the PPP and the exterior wall of the device the higher the efficiency and the cleaning quality.
In order to start the utilization of H-1, some information is mandatory to perform the cleaning works: oil extraction method, well depth and the PPP pipe diameter.
Equipment for TPAD cleaning
1. Coring Hoist.
The most popular PKS-3.5 self-propelled coring hoist is designed for the lowering and lifting of oil-well devices (including the H-1 device) to the depth of oil layer. The coring hoist is connected to the 220-380 V power source by means of a single, three or seven-core cable of CG-3-67-180 or CG-1-55-130 (180) or CG-1-30-130 (180) type or a similar type, where CG means cable geophysical; CG-3 means a three-core cable; the next number 67.
The hoist is mounted on the chassis of an off-road vehicle, usually ZIL-131. The body of vehicle is divided by a partition into two parts: the hoist compartment and the operator’s cabin. The hoist compartment contains a hoist in the form of a welded frame fastened to the vehicle body. The frame has a mounted drum with a cable wound on it and wired to a 220-380 V power source. The drum with the cable is powered from the vehicle’s engine. The length of cable depends on the depth of the oil layer location and can be 4.5 km long.
As regards our work, i.e. cleaning of oil wells from TPAD, a cable of up to 1000 meter-length is used, because such deposits form themselves in wells at the maximum depth of 800 meters from the surface of the earth (head of the well). At lower depths the temperature of the earth, and respectively, of the oil layer is high and oil flows through the well as a uniform mass, and starts to cool down only at the depth of 800 meters by disintegrating into the components such as tar, sulphur and paraffin. The closer the oil is to the head of the well the greater amounts of deposits settle down on the walls of the well; deposits completely clog up the well.
This device is designed to assure safety during the oil-well cleaning works. It is a tube with a diameter that corresponds to the one of the well pipe (73 or 89 mm). The lubricator is mounted on the flange of the valve of fountain fittings. The tube has a mounted discharge faucet, designed for reducing pressure in the well, and a valve with an oil seal intended for passing through and sealing of the cable, which is wired to the H-1. Thus, thanks to the lubricator, H-1 placed inside the lubricator has pressure equalized with the pressure inside the well. By heating up to the temperature to 300 degrees, H-1 melts paraffin (melting point 73 degrees) and tar (melting point 123 degrees).
3. SME Mobile Equipment
It is a steam generating mobile equipment with a capacity of 5-7 cubic meter, which has an in-built autonomous heating boiler powered by fuel oil. A compressor, which is a component of the SME, creates pressure up to 320 atmospheres. The SME is necessary for safety during oil-well cleaning works.
4. Mobile Power Station, Special-Purpose Transformer
It is used in the cases where a stationary power source, i.e. a 220-380 V power transfer line, is unavailable. The mobile power station is a motor with a power generator mounted on the motor’s shaft. During operation, its rotation is transferred to the generator to produce electric power of variable capacity. To operate H-1 device, a 10-20 KWt 3-phase 380 V power station with a petrol powered carburetor engine is required. A special-purpose transformer is necessary for a quality technological process of cleaning oil wells from TPAD; therefore, our technology enables connection of the H-l device to the geophysical three-core cable of 1000 and 2000 meter-length and more.
On the average, each core of the cable has 37-Ohm resistance per 1000 m, whereas three cores will have 117-Ohm resistance per 1000 m. The H-1 device operates from a 220 V power source. As soon as it is connected to the cable, the electric circuit is closed and the 117-Ohm resistance will cause the loss of voltage, thus, if the output capacity of the device is 2 KWt/h, the voltage at the end of the cable will fall to 120 V. In order to increase the voltage at the end of the cable to the normal operation level of the H-1 device, i.e. 220 V, we have developed and produced a special-purpose step-up transformer with the following parameters: output capacity 7 KWt/h, voltage 700 V, current 7-10 A.
Device for TPAD Heating
The product is designed mainly for heating up TPAD, to the temperature of 80-150°C, which are formed in pipes used for transportation of the products containing the abovementioned substances. The device is designed for operation in the following conditions: pipe diameter 50-100 mm, medium free of calcium deposit impurities, power source voltage 200-250 V;
And frequent fluctuations in the power supply network within the 5 percent range of the nominal
The H-1 Advantages
Oil wells are cleaned from TPAD by lowering the equipped device suspended on a load-carrying current-conducting cable into the PPP to the depth of the beginning of paraffin-asphalt deposits. Voltage of 220-1000 V enables quick heating of the device to the temperature of 150-40Q°C depending on the nature of deposits, diameter of oil wells, length and type of the current-conducting cable. When the device conies in contact with TPAD, the latter are quickly melting.
The peculiarity of the developed method of oil well cleaning from TPAD consists in full control of the process due to the built-in temperature sensor fixing any changes in the device and due to the special-purpose transformer indicating the voltage and value.
Among the advantages of this method are simplicity, compactness, small weight, cheapness, absolute explosion, fire safety, absence of negative effects on the whole infrastructure of the oil well and the possibility to work with standard unified geophysical equipment. As regards the speed of cleaning, this method is faster than the traditional ones by a factor of 10 and is more efficient economically.
Let’s discuss each item by an example.
The simplicity of the device consists in a small number of components, one meter height and 15-20 kg weight.The price of this equipment is $1,200,000, one-day operation costs $25-30 thousands. The disadvantage of this equipment is in the clogging of the oil well with suspended rock particles, which was proved by the tests. As a result, one of two oil wells has been irrevocably turned inoperable.
The explosion and fire safety has been achieved by including the SME that pumps hot water into the oil well to the full depth of the device progress of the device. A water column is pressing the device as an additional weight, thus increasing the speed of its progress, which is also increased by the reduction of the frequency of lifts for removing melted paraffin that flow upwards due to the lesser specific weight of paraffin as compared to that of water. The paraffin are constantly emptied into the discharge reservoir through the drain valve thus adding to the ecological cleanness, thanks to the practical incompressibility of water the device is protected from hydraulic hammer. And, the last advantage of water lies in the fact that by filling the whole length of the well it squeezes out air, thus preventing contact of oxygen with oil.
In the course of long-term operation of oil wells, metal pipes are subject to fatigue of metal, i.e. the strength of metal is reduced, whereas the steam-generating equipment of U.S manufacture delivers steam at high pressure thus increasing the danger of breakage of the integrity of the oil well pipe. The H-1 device has no physical impact on the oil well and does not break its integrity.
Connection of the H-1 device is simple because its head is made in accordance with the standard equipment diameters and threads, i.e. the end-piece of the coring plug can be easily screwed on the head of the device. After coordinating and approving the plan of works of oil well cleaning from TPAD by both Parties, we get down to the practical cleaning of oil wells
Cleaning of PPP of oil and gas wells is carried out by means of the H-l heating electrode device that acts on the TPAD on the principle of point-juncture heating. The equipped device is lowered into the PPP through the PPP-mounted lubricator, suspended on a load-carrying current-conducting cable to the depth where paraffin-asphalt deposits begin. Voltage of 220-700 V will heat up the H-l device to the temperature of 150-400°C (depending on the nature of deposits). When the H-l device comes in contact with TPAD, these deposits will quickly melt and be washed out to the surface of the earth by means of hot water (HW).
The advantage of this method consists in the simplicity of cleaning, simplicity of the device design (its diameter is 50 mm, length 830 mm, small weight10 kg), absolute explosion and fire safety due to operation of the device in the water media as oil and gas do not burn or explode in the absence of oxygen. Another advantage lies in the absence of negative effect on the whole infrastructure of well, since the metal fusion point is 1780°C, whereas the operating temperature of H-1 device is 450°C. Therefore, the device is harmless as it does not destroy the crystalline lattice of metal. Moreover, the H-l device has the ability to work with standard unified geophysical equipment. This method is ecologically clean due to the use of a lubricator for controlling oil seals that pressurize the current-conducting cable and prevent the emission of melted TPAD onto the ground and into the environment, whereas the whole melted mass is collected in a special capacity or oil-pipeline up to the last drop. As regards, the speed of cleaning is faster than the traditional methods by a factor of 10 and is 1.5 – 2 times more efficient economically.
By Naftogas of Ukraine, Egypt BranchDownload