Hydraulic fracturing technology is a synergistic mining technology applied to low-abundance, low-permeability oil and gas fields. This technology will fracture the formation by injecting a high pressure (~70MPa) fracturing fluid into the well, and use the proppant in the fracturing fluid to fill the fracture to change the seepage flow of oil and gas to achieve an increase in production. During the construction process, fracturing balls and bridge plugs must be used to block the construction columns of different working layers. Tools such as fracturing balls made of ordinary alloys, if trapped in wells, can reduce well productivity. Once the fracturing ball is stuck on the packer, special tools are needed to cut it, which not only prolongs the construction period but also increases the construction cost. In response to these problems, foreign oil companies have developed soluble fracturing balls (resin, magnesium, or aluminum composites), but tools such as dissolvable bridge plugs and ball seats have not yet been successfully developed.
Fracturing technology has been widely used in North America. Although it has been applied in China for nearly 40 years, related tools still rely on imports, which severely limits the efficiency of China's oil extraction. Therefore, the development of fracturing tools with soluble functions is of great significance for ensuring stable production and high production of China's oil fields.
The Research Institute of Hydrogen Storage Alloys and Applications of the Institute of Materials and Devices for Metals uses the existing aluminum water reaction research basis to develop soluble aluminum alloy materials that can be dissolved in pure water, and can regulate the reaction of the alloy with water. Initial temperature and dissolution rate in water.
Generally, it is difficult to observe the dissolution of aluminum in water because a continuous and dense oxide film on the aluminum surface hinders the aluminum water reaction. If aluminum is alloyed with some of the low-melting-point metals (Ga, In, Sn), the interfacial low-melting phase formed by these low-melting metals on the surface of the aluminum grains will disrupt the continuity of the aluminum surface oxide film. The research group carried out a series of work on some basic issues of aluminum water reaction and found that when the alloy is in contact with water, the aluminum and water in the low-melting phase of the interface undergo an exothermic reaction, and the aluminum atoms in the aluminum crystal grains can flow to the liquid interface. The low melting point continuously diffuses. With the aid of the low melting point relative to the destruction of the aluminum oxide film and the transport of aluminum atoms, aluminum can continue to react with water. Further study found that the starting temperature of the reaction of aluminum water is closely related to the melting point of the low-melting phase of the interface, and the melting point of the low-melting phase of the interface can be regulated by the composition of the alloy, and the reaction rate and the low melting point on the surface of the aluminum crystal grains are covered. The area is proportional to the area. In addition, the research group also studied the effect of other alloying elements such as Cu, Mg, Zn, and Ti on the dissolution performance of the alloy, and found that these metals also have different degrees of influence on the initial temperature and reaction rate of aluminum water reaction.
The use of soluble aluminum alloy as a structural member requires not only good dissolution properties but also sufficient strength and plasticity. In order to meet the solubility and mechanical properties of soluble aluminum alloys, low-melting-point metals (Ga, In, Sn) and various strengthening alloying elements must be added to the alloy. However, the low-melting phase distributed on the grain boundaries of aluminum alloys is generally detrimental to the strength and the plasticity of the alloy, and particularly to plasticity. On the other hand, strengthening alloying elements also changes the dissolution properties of the alloy while strengthening the alloy. Because the effects of these two types of alloying elements are mutually constrained, it is essential for the preparation of the alloy to select the appropriate type, content, and proportion of alloying elements to balance the solubility and mechanical properties. Based on a large number of experiments, the researchers optimized the composition of the alloy, refined the alloy grains and improved the quality of the molten aluminum to improve the plasticity of the alloy. The quenching and aging processes were used to control the alloy's overall performance, and finally prepared to meet the actual requirements. Working conditions for aluminum alloy materials.
The strength of the developed alloy is more than 350 MPa, Vickers hardness is close to 150, and the compressive strength meets the requirements of hydraulic fracturing. The initial reaction temperature of soluble aluminum alloy water can be adjusted from room temperature to 85Â°C. The dissolution rate of the alloy can also be adjusted according to different working conditions.
Compared with the soluble aluminum alloy developed by the research group, the current soluble materials of resin and aluminum composite materials are comparable in strength, but the former needs to be dissolved with a special etching solution, and the latter reacts with the initial reaction temperature of water. The dissolution rate in water is not easily controlled, and the alloy shows excellent overall performance. In addition, the alloy can be smelted and cast by conventional techniques, with low cost and high productivity, suitable for large-scale application and promotion.
The research group cooperated with relevant companies to develop a number of products such as fracturing balls, ball seats and bridge plugs. Fracturing balls have been used in fields such as Daqing and Changqing, and soluble aluminum alloy bridge plugs and ball seats have also been tested in Daqing's wells. At present, the world's oil wells that are extracted by hydraulic fracturing technology are roughly estimated at several hundred thousand, and there are nearly 10,000 ports in Daqing alone. There is a huge market demand for soluble aluminum alloys.
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