Oil and natural gas exploration and development can be divided into land exploitation and offshore exploitation. The oil and natural gas contained in the earth's crust roughly accounts for 60% of the land and 40% of the offshore oil. Significantly.
Before the industrialization and large-scale application of titanium alloys, the shells of commonly used logging tools were made of 45 steel, 40Cr steel, and 30 MoVNb steel, but none of them could meet the needs of modern logging technology. Modern high-tech oil and gas exploration And the development requires that the metal shell of the logging tool can withstand the pressure >98 MPa, but also resist the corrosion of underground crude oil and various media, and in the logging, the absorption rate of natural gamma rays must be small. In the magnetic logging , It should not have a shielding effect on the earth's magnetic field. From these performance requirements, titanium alloy is a good material for the casing of logging tools.
In the mid-1980s, the China Petroleum Administration introduced 6 sets of integrated logging tools with Ti-6Al-4V titanium alloy shells from Schlumberger in France and Dresser in the United States. However, the shells of domestic logging tools were not available at that time. Made of titanium alloy. Ti﹣6Al﹣4V is a kind of alloy with good comprehensive performance, mature and good price, but since then, Baoji Nonferrous Metal Processing Plant (now Baoti Group Co., Ltd.) has worked on all aspects of this alloy extruded pipe. Detailed research.
The shell of the logging tool is a thick-walled long cylindrical body, and the force it receives is external pressure. The higher the pressure it can bear, the deeper the formation can be used for logging. Ti-6Al-4V titanium alloy extruded pipe and 40Cr steel pipe The results of the withstand voltage test are shown in Table 1 (data from Yang Xiaoming and Xiong Zhengzhong). It can be seen from the data in the table that the Ti-6Al-4V alloy extruded pipe has no instability failure under the pressure of 112.7 MPa at room temperature and 117.6 MPa at high temperature, while the 40 Cr steel pipe is buckled under the pressure of 80.4 MPa at room temperature. Tests have proved that the critical failure pressure of 40 Cr steel pipe is 78.4 MPa to 80.4 MPa. When the external pressure of the logging tool shell is greater than or equal to the critical failure pressure, the instability failure caused by flattening or wrinkling will damage the measurement system in the shell. Therefore, the critical failure pressure of the logging tool shell will affect the safety and normal operation of the logging tool. Plays a very important role. The mechanical properties and critical failure pressures of Ti-6Al-4V titanium alloy and 40 Cr steel pipe are shown in Tables 2 and 3.
The maximum working pressure of the titanium alloy shell of the comprehensive deep well tool imported from France by China is 137.2 MPa, and the allowable working temperature is 150℃~175℃. According to the data listed in Table 3 above, as long as the casing of the logging tool is made of Ti-6Al-4V titanium alloy with appropriate diameter and wall thickness, the allowable max withstand voltage value of Schlumberger can be fully achieved. China has long been able to fully squeeze all kinds of titanium alloy pipes with excellent straight warp and wall thickness. The pipes produced by Baoti Group and others can not only meet domestic demand, but also export to foreign countries. The pressure resistance of domestic Ti-6Al-4V alloy at 175℃ is far greater than 120 MPa, which can fully meet the domestic high-tech logging requirements; in the range of commonly used logging tool shell sizes, the theoretical max of Ti-6Al-4V alloy The critical failure pressure has reached 248 MPa, and the logging tool casing made from it can withstand pressures greater than 137 MPa.
In petroleum exploration and development logging, detecting natural γ-rays in the formation and analyzing the energy spectrum is one of the main methods to obtain oil-bearing data in the formation. Higher, the more reliable the analysis data obtained. See Table 4 for the test of Ti-6Al-4V alloy and 40 Cr steel pipe against Co60 and Cs137 gamma rays.
The working conditions of the logging tool are very harsh, and the shell material is required to have high corrosion resistance. Studies have shown that Ti-6Al-4V alloy has strong corrosion resistance in crude oil media and in sulfide and chloride-containing media. The corrosion rate is less than 0.017 mm/a. Therefore, the casing of the logging tool made of Ti-6Al-4V alloy can avoid the reduction of the critical damage pressure caused by the thinning of the casing due to corrosion for a long time. Instability and destruction.
In petroleum exploration and development logging, some magnetic physical quantities are also measured. The magnetic susceptibility of the casing of the logging tool will also affect logging. If the magnetic susceptibility is too large, the casing will have a shielding effect and affect the normality of the magnetic measuring instrument. It works, so the magnetic susceptibility of the metal casing is required to be as small as possible. Therefore, titanium alloy is the best material for making the casing of magnetic logging tool. The magnetic susceptibility X of Ti﹣6Al﹣4V alloy is 3.2×10﹣6 cm3/g, which is a non-ferromagnetic material. At the same time, titanium alloy is also good The processing and forming performance.