With the exploitation of energy for meeting the demand of the rapidly development of human society, oil and gas resources that are easy to exploit in the shallow surface are increasingly scarce, the water content of old oilfields is getting more higher, and the mining environment is getting worse. The development of new drill pipe materials has become an urgent task.
For the drill pipe, steel drill pipe, aluminum drill pipe, and titanium drill pipe are common, among them steel drill pipe is the most widely used drill pipe currently.
Although some thin-walled, lightweight ultra-high strength steel drill pipe can be used to solve the drilling problems of extended reach wells, ultra-deep wells and deep water drilling, high strength steel is brittle at low temperature, and the impact toughness and tensile strength of drill pipe do not match with the environment. Incomplex wells, the drill pipe needs to be cycled at a high stress level for a long time under a small curvature radius.
Conventional steel drill pipe will sharply shorten their life or even fail due to the fatigue cracks, wear and high bending stress, which will bring safety hazards to drilling operations.
Therefore, light and high strength drill pipe should be selected in deep wells、 ultra-deep wells、 horizontal wells and other unconventional oil and gas wells。
According to the research, it is also found that titanium alloy drill pipe has high hardness and specific strength, which is beneficial to the corrosion resistance and fatigue resistance, and the fatigue life of titanium alloy drill pipe still has significant advantages under the multi-factor coupling of H2S, mud and temperature.
Features and advantages of titanium alloy when it be used for oil well tubing
1) Significantly reduce the overall quality of oil well pipes and reduce the load on mining institutions
Compared with traditional oil well pipe materials such as carbon steel and nickel-based alloys, the density of titanium (approximately 4.5g/cm3) is about 57% of carbon steel and 50% of nickel. Titanium alloys have better mechanical properties. The specific strength of titanium alloy is about 1.7 times that of nickel-based alloys and 1.6 times that of ordinary carbon steel pipes. Titanium alloy is beneficial to reduce the load of oil well pipe strings, reduce the weight of structural parts, and reduce the power of mining equipment, thereby increasing the safety factor of deep oil well pipe strings and improving the safety of equipment.
2) Excellent corrosion resistance
The dense oxide film formed on the surface of the titanium alloy will hinder the further reaction of the substrate with the external environment. It has excellent corrosion resistance in the environment of different corrosive media, and the titanium alloy hardly corrodes in the flowing seawater.
3) Excellent welding performance, good adaptability under high temperature and high pressure environment
Titanium alloy has excellent welding performance. At present, welding methods such as argon tungsten arc welding, plasma arc welding, and laser welding are often used to weld titanium alloy oil well pipes. The tensile strength of the weld is high, usually reaching 90% of the strength of the pipe body. The linear expansion coefficient of titanium is 10. 2×10-6 K-1, and its elastic modulus is about 43% smaller than that of steel. Titanium alloy oil well pipes have lower thermal expansion internal stress and are more adaptable to high temperature and high pressure oil and gas wells. In addition, titanium alloy oil well tubing is non-magnetic and can be equipped with conventional logging and logging tools, which is convenient for downhole use.
4) Abundant resources and good comprehensive economy
According to statistics from the United States Geological Survey, the global ilmenite reserves in 2018 were about 880 million tons, of which China`s ilmenite reserves accounted for about 26.14% of the global reserves. Titanium alloy pipes have a higher fatigue life than conventional carbon steel pipes.
The quality of チタンパイプ of the same specification is 40% lighter than nickel-based alloy pipes, which greatly reduces maintenance costs. Therefore, the vigorous development of titanium alloy oil well pipes not only conforms to China`s oil and gas resource strategy, but also has great advantages of High economy.