A deuterium-tritium source neutron porosity logging instrument for open hole wells

Abstract

The present invention discloses a deuterium-tritium source neutron porosity logging instrument for open hole wells, which relates to the technical field of oil and gas development. The instrument comprises a shell, in which a deuterium-tritium neutron tube, a neutron energy attenuation block, a neutron detector and a shield are installed. The deuterium-tritium neutron tube is wrapped in the neutron energy attenuation block. The neutron detector includes a near-disk spacer close to the deuterium-tritium neutron tube. 3 He neutron tube and the distance from the deuterium-tritium neutron tube 3 The He neutron tube, and the shielding body includes a first shielding body and a second shielding body. The open-hole deuterium-tritium source neutron porosity logging instrument proposed in the present invention effectively applies a deuterium-tritium source to the open-hole neutron porosity logging instrument by using a small-diameter deuterium-tritium neutron tube, providing a neutron energy attenuation block, and adjusting the optimal near- and far-detector source distances. This improves the low sensitivity of the open-hole deuterium-tritium source neutron porosity logging instrument and provides a new guiding idea for the development of open-hole deuterium-tritium source neutron porosity logging instruments.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and natural gas development, and in particular to a deuterium-tritium source neutron porosity logging instrument for open hole wells. Background Art

[0002] Conventional neutron porosity logging instruments use chemical sources made of americium and beryllium that continuously emit neutrons, causing irreversible damage to the surrounding environment and instrument operators. If the instrument becomes stuck during logging, the neutron emission reaction cannot be stopped, resulting in severe radioactive contamination of the formation and even the abandonment of the well. Compared to chemical sources, controlled deuterium and tritium sources offer the advantages of safety, environmental protection, and controlled radioactivity. With increasingly stringent environmental regulations both domestically and internationally and the shortage of isotope neutron sources, the use of controlled sources, instead of chemical sources, for neutron porosity measurements has become a trend in nuclear logging technology.

[0003] At present, research on using deuterium-tritium sources instead of americium-beryllium sources for neutron porosity measurement while drilling has made breakthrough progress. Major oil service companies have launched mature controlled-source neutron porosity logging instruments while drilling. However, under open hole conditions, the low sensitivity of deuterium-tritium source neutron porosity logging has hindered the promotion and application of related technologies.

[0004] Therefore, there is an urgent need to develop a deuterium-tritium source neutron porosity logging instrument that can improve the low sensitivity of open hole controlled source neutron porosity logging. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention discloses an open hole deuterium-tritium source neutron porosity logging instrument, which improves the problem of low sensitivity of open hole controlled source neutron porosity logging.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A deuterium-tritium source neutron porosity logging instrument for an open hole includes a shell, a deuterium-tritium neutron tube, a neutron energy attenuation block, a neutron detector, and a shielding body installed in the shell, the deuterium-tritium neutron tube is wrapped in the neutron energy attenuation block, and the neutron detector includes a near-field detector close to the deuterium-tritium neutron tube. 3 He neutron tube and the distance from the deuterium-tritium neutron tube 3 He neutron tube, the shielding body includes a first shielding body and a second shielding body, the first shielding body is located between the deuterium-tritium neutron tube and the vicinity 3 Between the He neutron tubes, the second shield is located near 3 He neutron tube and 3 The space between the He neutron tubes is used to shield the neutrons directly emitted by the deuterium-tritium neutron tubes.

[0008] Optionally, the diameter of the deuterium-tritium neutron tube is not greater than 30 mm.

[0009] Optionally, the neutron energy attenuation block is composed of two semi-cylindrical heavy metal blocks, and a semi-cylindrical groove is provided in the middle of the two semi-cylindrical heavy metal blocks for wrapping the deuterium-tritium neutron tube. The neutron energy attenuation block can significantly reduce the energy of high-energy fast neutrons emitted by the deuterium-tritium neutron tube, and can improve the sensitivity of the open hole deuterium-tritium source neutron porosity logging instrument.

[0010] Optionally, the neutron energy attenuation block completely fills the space between the deuterium-tritium neutron tube and the inner wall of the shell.

[0011] Optionally, the neutron energy attenuation block is made of tungsten.

[0012] Optionally, the first shielding body and the second shielding body are both made of tungsten-nickel-iron material.

[0013] Optionally, the near 3 The distance between the He neutron tube and the deuterium-tritium neutron tube is 35 cm. 3 The distance between the He neutron tube and the deuterium-tritium neutron tube is 40 to 75 cm.

[0014] The beneficial effect of the present invention is that the open hole deuterium-tritium source neutron porosity logging instrument provided by the present invention realizes the application of controllable source in the open hole neutron porosity logging instrument by adopting a small diameter deuterium-tritium neutron tube, a neutron energy attenuation block and adjusting the optimal source distance of the instrument, thereby improving the sensitivity of deuterium-tritium source porosity measurement under open hole conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a structural diagram of an open hole deuterium-tritium source neutron porosity logging instrument of the present invention;

[0016] Figure 2 For the present invention Figure 1 Schematic diagram of the structure of the neutron energy attenuation block;

[0017] Figure 3 A graph showing the relationship between thermal neutron counting flux and source distance according to an embodiment of the present invention;

[0018] Figure 4 A graph of absolute porosity errors corresponding to different remote detector source distances shown in an embodiment of the present invention;

[0019] Figure 5 This is a sensitivity comparison diagram of the well logging tool of the present invention, the deuterium-tritium source tool with a neutron-free energy attenuation block, and the americium-beryllium source tool according to an embodiment of the present invention.

[0020] Reference numerals: 1. Shell, 2. Deuterium-tritium neutron tube, 3. Neutron energy attenuation block, 4. First shield, 5. Near He3 Neutron tube, 6, second shield 4, 7, far He 3 Neutron tube, 8. Heavy metal block, 9. Groove. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] A deuterium-tritium source neutron porosity logging tool for open hole wells, such as Figure 1 As shown, it includes a shell 1, in which a deuterium-tritium neutron tube 2, a neutron energy attenuation block 3, a neutron detector and a shield are installed. The deuterium-tritium neutron tube 2 is wrapped in the neutron energy attenuation block 3, and the neutron detector includes a near-deuterium-tritium neutron tube. 3 He neutron tube 5 and the distance from the deuterium-tritium neutron tube is far 3 The He neutron tube 7, the shielding body includes a first shielding body 4 and a second shielding body 6, the first shielding body 4 is located between the deuterium and tritium neutron tube 2 and the 3 Between the He neutron tubes 5, the second shield 6 is located near 3 He neutron tube 5 and far 3 The He neutron tubes 7 are used to shield the neutrons directly emitted by the deuterium-tritium neutron tubes 2.

[0023] Optionally, the diameter of the deuterium-tritium neutron tube 2 is not greater than 30 mm.

[0024] In this embodiment, the deuterium-tritium neutron tube 2 is a micro self-target neutron tube for well logging. The main structure size of the deuterium-tritium neutron tube 2 is It can emit fast neutrons with an energy of 14 MeV, and the neutron yield can reach 1x10 8 The above can meet the requirements of the present invention.

[0025] Optionally, the neutron energy attenuation block 3 is composed of two semi-cylindrical heavy metal blocks 8, and a semi-cylindrical groove 9 is provided in the middle of the two semi-cylindrical heavy metal blocks 8 for wrapping the deuterium-tritium neutron tube 2. The neutron energy attenuation block 3 can significantly reduce the energy of high-energy fast neutrons emitted by the deuterium-tritium neutron tube 2, and can improve the sensitivity of the open hole deuterium-tritium source neutron porosity logging instrument.

[0026] In this embodiment, Figure 2 As shown, the neutron energy attenuation block 3 is composed of two semi-cylindrical high-density heavy metal blocks 8 with a radius of 4.4 cm. There is a semi-cylindrical groove 9 in the middle of the two semi-cylindrical high-density heavy metal blocks 8 for wrapping the deuterium-tritium neutron tube 2.

[0027] Optionally, the neutron energy attenuation block is made of tungsten.

[0028] After research, it was found that heavy metal materials have a significant effect on slowing down high-energy fast neutrons. Therefore, this example uses heavy metal tungsten to make neutron energy attenuation blocks, which plays a role in reducing neutron energy and improving porosity sensitivity.

[0029] Optionally, the neutron energy attenuation block 3 completely fills the space between the deuterium-tritium neutron tube 2 and the inner wall of the shell 1 .

[0030] Optionally, the first shielding body 4 and the second shielding body 6 are both made of tungsten-nickel-iron material.

[0031] like Figure 3 As shown, the zero source distance of the neutron detector in this example is about 16 cm; according to the above zero source distance position, the size of the neutron energy attenuation block and the shielding body, the near 3 The source distance of He neutron tube 5 is 35 cm.

[0032] like Figure 4 As shown in the figure, taking the accuracy of the Americium-Beryllium neutron source porosity logging as the standard, within the allowable error range, the remote sensing accuracy of the instrument in this example is 3 The source distance of He neutron tube 7 should be selected to be 40 to 75 cm. Taking into account the logging sensitivity and accuracy, the source distance of the remote detector in this example is set to 71 cm.

[0033] Optionally, the near 3 The distance between the He neutron tube 5 and the deuterium-tritium neutron tube 2 is 35 cm. 3 The distance between the He neutron tube 7 and the deuterium-tritium neutron tube 2 is 40 to 75 cm.

[0034] like Figure 5 As shown in the figure, compared with the open hole neutron porosity tool that directly uses a deuterium-tritium source and is not equipped with a neutron energy attenuation block, the open hole deuterium-tritium source neutron porosity logging tool of this example has better porosity sensitivity; especially in low porosity formations, the porosity sensitivity of the tool of this example is comparable to that of the americium-beryllium source tool, or even better than the porosity sensitivity of the americium-beryllium source tool.

[0035] The open-hole deuterium-tritium source neutron porosity logging instrument proposed in the present invention effectively applies the deuterium-tritium source to the open-hole neutron porosity logging instrument by adopting a small-diameter deuterium-tritium neutron tube, setting a neutron energy attenuation block, and adjusting the optimal near- and far-detector source distances. This improves the low sensitivity problem of the open-hole deuterium-tritium source neutron porosity logging instrument and provides a new guiding idea for the development of open-hole deuterium-tritium source neutron porosity logging instruments.

[0036] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A deuterium-tritium source neutron porosity logging instrument for open hole wells, characterized in that: The neutron detector includes a housing, a deuterium-tritium neutron tube, a neutron energy attenuation block, a neutron detector and a shielding body. The deuterium-tritium neutron tube is wrapped in the neutron energy attenuation block. The neutron detector includes a near-deuterium-tritium neutron tube. 3 He neutron tube and the distance from the deuterium-tritium neutron tube 3 He neutron tube, the shielding body includes a first shielding body and a second shielding body, the first shielding body is located between the deuterium-tritium neutron tube and the vicinity 3 Between the He neutron tubes, the second shield is located near 3 He neutron tube and 3 Between He neutron tubes; The diameter of the deuterium-tritium neutron tube is not greater than 30 mm; The neutron energy attenuation block is composed of two semi-cylindrical heavy metal blocks, and a semi-cylindrical groove is provided in the middle of the two semi-cylindrical heavy metal blocks for wrapping the deuterium-tritium neutron tube; The neutron energy attenuation block completely fills the space between the deuterium-tritium neutron tube and the inner wall of the shell.

2. The open hole deuterium-tritium source neutron porosity logging instrument according to claim 1, characterized in that: The neutron energy attenuation block is made of tungsten.

3. The open hole deuterium-tritium source neutron porosity logging instrument according to claim 1, characterized in that: The first shielding body and the second shielding body are both made of tungsten-nickel-iron material.

4. The open hole deuterium-tritium source neutron porosity logging instrument according to claim 1, characterized in that: The near 3 The distance between the He neutron tube and the deuterium-tritium neutron tube is 35 cm. 3 The distance between the He neutron tube and the deuterium-tritium neutron tube is 40 to 75 cm.

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