A push-type controllable source neutron porosity measurement device and its usage method

Abstract

The present invention discloses a push-type controllable source neutron porosity measuring device, which relates to the technical field of oil and gas development. It includes a housing and push arms installed outside the housing. Inside the housing, there are a deuterium-tritium neutron tube, a neutron moderator, a neutron detector, a neutron shield, and a neutron absorber. The neutron moderator is used to reduce the energy of the fast neutrons emitted by the deuterium-tritium neutron tube. The neutron shield is used to shield the neutrons directly emitted by the deuterium-tritium neutron tube to the neutron detector. The neutron absorber is used to absorb and shield the thermal neutrons from the wellbore direction. The push-type controllable source neutron porosity measuring device provided by the present invention significantly improves the porosity sensitivity of the deuterium-tritium source neutron porosity logging tool in open-hole wells by using a small-diameter deuterium-tritium neutron tube, a neutron moderator, a neutron absorber, and a measurement method close to the wellbore wall, realizes the application of the deuterium-tritium source on the open-hole well neutron porosity instrument, and ensures the personal safety of the instrument operators.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development, and particularly to a push-type controllable source neutron porosity measurement device and a usage method thereof. Background Art

[0002] In recent years, chemical sources have been commonly used in neutron porosity logging tools. The radioactivity of chemical sources persists, and the neutrons emitted by them are difficult to be shielded. Logging workers and the surrounding public may be exposed to large doses of radiation when in close contact, which may cause irreversible harm to the body. During exploration operations, in case of some unexpected accident conditions, such as the instrument getting stuck or the radioactive source falling into the well, the chemical source will cause great radioactive pollution to the oil well, and even render the oil well useless, resulting in great environmental pollution and economic losses.

[0003] With the increasingly strict environmental protection regulations at home and abroad and the shortage of chemical sources, the state has gradually strengthened the control of chemical sources, promoting technicians to carry out the research and development of controllable neutron sources for logging. Using controllable neutron sources with controllable radioactivity, safety, and environmental protection to replace traditional chemical sources has become a new trend in the development of nuclear logging technology in recent years. Currently, the porosity sensitivity of open-hole neutron porosity instruments is too low after using controllable sources, and controllable sources have not been effectively applied to such logging tools. The neutron source still uses americium-beryllium chemical sources, resulting in many safety hazards still existing. Summary of the Invention

[0004] To solve the above technical problems, the present invention discloses a push-type controllable source neutron porosity measurement device and a usage method thereof, which use a controllable source to replace the americium-beryllium chemical source of the open-hole neutron porosity instrument and improve the problem of too low sensitivity of open-hole controllable source neutron porosity logging.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A push-type controllable source neutron porosity measurement device includes a housing and push arms installed outside the housing. The housing includes a deuterium-tritium neutron tube, a neutron moderator, a neutron detector, a neutron shield, and a neutron absorber. The neutron moderator is used to reduce the energy of the fast neutrons emitted by the deuterium-tritium neutron tube. The neutron shield is used to shield the neutrons directly emitted by the deuterium-tritium neutron tube to the neutron detector. The neutron absorber is used to absorb and shield the thermal neutrons from the wellbore direction. The neutron detector includes a near 3 He neutron tube close to the deuterium-tritium neutron tube and a far 3 He neutron tube far from the deuterium-tritium neutron tube. The neutron shield is respectively arranged between the deuterium-tritium neutron tube and the near 3 He neutron tube, and between the near 3 He neutron tube and the far 3 He neutron tube.

[0007] Optionally, the diameter of the deuterium-tritium neutron tube does not exceed 30 mm.

[0008] Optionally, the neutron moderator is composed of two semi-cylindrical blocks made of high-density heavy metal materials. Among them, a semi-cylindrical groove is provided in the upper middle part of the section of each semi-cylindrical block for placing the deuterium-tritium neutron tube. The neutron moderator is wrapped around the deuterium-tritium neutron tube, which can slow down the high-energy fast neutrons emitted by the deuterium-tritium neutron tube, reduce the overall energy of the neutrons entering the formation, and effectively improve the porosity sensitivity of the open-hole controllable-source neutron porosity logging tool in medium and low porosity formations.

[0009] Optionally, the heavy metal material is tungsten.

[0010] Optionally, the neutron detector uses 3 a ³He neutron tube.

[0011] Optionally, the distance between the near 3 ³He neutron tube and the deuterium-tritium neutron tube is 30 cm, and the distance between the far 3 ³He neutron tube and the deuterium-tritium neutron tube is 60 cm.

[0012] Optionally, the near 3 ³He neutron tube and the far 3 ³He neutron tube are arranged close to the inner wall of the housing. Among them, the diameter and length of the far 3 ³He neutron tube are both larger than those of the near 3 ³He neutron detector.

[0013] Optionally, the neutron shield is made of tungsten-nickel-iron alloy, which can effectively shield the neutrons directly emitted by the deuterium-tritium neutron tube

[0014] Optionally, the neutron absorber is a cylindrical component with a square groove on the side processed from boron carbide material, including a first neutron absorber and a second neutron absorber. The near 3 ³He neutron tube is placed in the square groove of the first neutron absorber, and the far 3 ³He neutron tube is placed in the square groove of the second neutron absorber. The neutron absorber can absorb the thermal neutrons in the wellbore, reduce the influence of the thermal neutrons in the wellbore on the detector count, improve the signal-to-noise ratio of the instrument, and effectively improve the porosity sensitivity of the open-hole controllable-source neutron porosity tool.

[0015] The present invention also proposes a method for using the above-mentioned push-type controllable-source neutron porosity measuring device.

[0016] In one embodiment, when the push-type controllable-source neutron porosity measuring device is lowered into the well for measurement, the push arms outside the housing are opened, and the measuring device is closely attached to the well wall to start the measurement.

[0017] The beneficial effects of the present invention are as follows. A push-type controllable source neutron porosity measuring device provided by the present invention significantly improves the porosity sensitivity of a barehole deuterium-tritium source neutron porosity logging tool by adopting a small-diameter deuterium-tritium neutron tube, neutron moderators, neutron absorbers, and a measurement method close to the wellbore wall, realizes the application of a deuterium-tritium source on a barehole neutron porosity tool, eliminates various safety hazards brought by using an americium-beryllium chemical source, and thus ensures the personal safety of instrument operators. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a structural diagram of a push-type controllable source neutron porosity measuring device of the present invention;

[0019] Figure 2 For the present invention Figure 1 is a structural diagram of the neutron moderator in the present invention;

[0020] Figure 3 For the present invention Figure 1 is a structural diagram of the neutron absorber in the present invention;

[0021] Figure 4 is a comparison of the sensitivities of barehole neutron porosity logging tools under different design scenarios;

[0022] Reference numerals: 1, deuterium-tritium neutron tube; 2, neutron moderator; 3, first neutron shield; 4, push arm; 5, near 3 He neutron tube; 6, first neutron absorber; 7, second neutron shield; 8, second neutron absorber; 9, far 3 He neutron tube; 10, housing. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] A push-type controllable source neutron porosity measuring device, as Figure 1 shown, includes a housing 10 and a push arm 4 installed outside the housing 10. The housing 10 includes a deuterium-tritium neutron tube 1, a neutron moderator 2, a neutron detector, a neutron shield, and a neutron absorber. The neutron moderator 2 is used to reduce the energy of the fast neutrons emitted by the deuterium-tritium neutron tube 1. The neutron shield is used to shield the neutrons directly emitted by the deuterium-tritium neutron tube to the neutron detector. The neutron absorber is used to absorb and shield the thermal neutrons from the wellbore direction. The neutron detector includes a near 3 He neutron tube 5 close to the deuterium-tritium neutron tube 1 and a far3 The He neutron tube 9, and the neutron shielding bodies are respectively arranged between the deuterium-tritium neutron tube 1 and the near 3 He neutron tube 5, and between the near 3 He neutron tube 5 and the far 3 He neutron tube 9.

[0025] Optionally, the outer diameter of the housing 10 of this example is 10 cm. When the instrument is lowered into the well, the push wall 4 on the outside of the instrument is deployed to realize the measurement of the instrument against the well wall.

[0026] Optionally, the deuterium-tritium neutron tube 1 is a small self-target neutron tube for well logging, and the size of the neutron tube is It can generate fast neutrons with an energy of 14 Mev, and the neutron yield is about 1e8, which can meet the requirements of the example of the present invention.

[0027] As Figure 2 shown, the neutron slowdown block 2 is composed of two semi-cylindrical blocks processed from high-density heavy metal materials. Among them, a semi-cylindrical groove is provided in the upper middle part of the cross-section of each semi-cylindrical block for placing the deuterium-tritium neutron tube 1. The neutron slowdown block 2 is wrapped around the deuterium-tritium neutron tube 1, and can slow down the high-energy fast neutrons emitted by the deuterium-tritium neutron tube 1, reduce the overall energy of the neutrons entering the formation, and effectively improve the porosity sensitivity of the open-hole well controlled-source neutron porosity logging tool in medium and low porosity formations.

[0028] Through simulation research, it is found that heavy metal tungsten has a good slowdown effect on 14 Mev high-energy fast neutrons. Therefore, the material selected for the neutron slowdown block 2 in this example is heavy metal tungsten.

[0029] As Figure 4 shown, after wrapping the neutron slowdown block 2 outside the deuterium-tritium neutron tube 1, the sensitivity of the open-hole well controlled-source neutron porosity tool to medium and low porosity formations can be effectively improved.

[0030] Optionally, the neutron detector uses 3 He neutron tube.

[0031] In this embodiment, the distance between the near 3 He neutron tube 5 and the deuterium-tritium neutron tube is 30 cm, and the distance between the far 3 He neutron tube 9 and the deuterium-tritium neutron tube is 60 cm.

[0032] Optionally, the near 3 He neutron tube 5 and the far 3 He neutron tube 9 are arranged close to the inner wall of the housing 10. Among them, the diameter and length of the far 3 He neutron tube 9 are both larger than those of the near 3 He neutron tube 5.

[0033] In this embodiment, the neutron shield includes a first neutron shield 3 and a second neutron shield 7. The first neutron shield 3 is arranged between the deuterium-tritium neutron tube 1 and the near 3 He neutron tube 5, and the near 3 He neutron tube 5 is between the near 3 He neutron tube 9 and the far

[0034] Both the first neutron shield 3 and the second neutron shield 7 are made of tungsten-nickel-iron alloy, which can effectively shield the neutrons directly emitted by the deuterium-tritium neutron tube. 3 He neutron tube 5 is placed in the square groove of the first neutron absorber 6, and the far 3 He neutron tube 9 is placed in the square groove of the second neutron absorber 8. The neutron absorber can absorb the thermal neutrons in the wellbore, reduce the influence of the thermal neutrons in the wellbore on the detector count, improve the signal-to-noise ratio of the instrument, and effectively improve the porosity sensitivity of the open-hole controlled-source neutron porosity tool.

[0035] As Figure 4 shown, on the basis of adding the neutron moderator block 2 outside the deuterium-tritium neutron tube 1, by adding the first neutron absorber 6 and the second neutron absorber 8 to the near 3 He neutron tube 5 and the far 3 He neutron tube 9 respectively, the sensitivity of the open-hole controlled-source neutron porosity logging tool to the low and medium porosity formations can be further improved. At the same time, the sensitivity of the instrument to the high porosity formation has also been improved to a certain extent.

[0036] Compared with the traditional americium-beryllium source open-hole neutron porosity tool, the controlled-source open-hole neutron porosity logging tool in this example has higher sensitivity to the low and medium porosity formations. At the same time, in the high porosity formation, the instrument in this example still has a measurement sensitivity comparable to that of the americium-beryllium source instrument.

[0037] 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 those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A push-type controllable source neutron porosity measuring device, characterized in that, It includes a housing and a pushing arm installed outside the housing. Inside the housing, there are a deuterium-tritium neutron tube, a neutron moderator block, a neutron detector, a neutron shield, and a neutron absorber block. The neutron moderator block is used to slow down the high-energy fast neutrons emitted by the deuterium-tritium neutron tube, reducing the overall energy of the neutrons entering the formation. The neutron shield is used to shield the neutrons directly emitted by the deuterium-tritium neutron tube to the neutron detector. The neutron absorber block is used to absorb and shield the thermal neutrons from the wellbore direction. The neutron detector includes a near 3 He neutron tube close to the deuterium-tritium neutron tube and a far 3 He neutron tube far from the deuterium-tritium neutron tube. The neutron shield is respectively arranged between the deuterium-tritium neutron tube and the near 3 He neutron tube, and between the near 3 He neutron tube and the far 3 He neutron tube; The diameter of the deuterium-tritium neutron tube does not exceed 30 mm; The neutron moderator block is composed of two semi-cylindrical blocks processed from heavy metal materials. Among them, a semi-cylindrical groove is provided in the upper middle part of the cut surface of each semi-cylindrical block for placing the deuterium-tritium neutron tube; The near 3 He neutron tube and the far 3 He neutron tube is disposed close to the inner wall of the housing. Among them, the far 3 He neutron tube has both a diameter and a length greater than those of the near 3 He neutron tube; The neutron absorption block is a cylindrical component with a square groove on the side processed from boron carbide material, including a first neutron absorption block and a second neutron absorption block. Near 3 the He neutron tube is placed in the square groove of the first neutron absorption block, and far 3 the He neutron tube is placed in the square groove of the second neutron absorption block; The heavy metal material is tungsten; The neutron detector uses 3 a 3 He neutron tube; The distance of the near 3 He neutron tube from the deuterium-tritium neutron tube is 30 cm, and the distance of the far 3 He neutron tube from the deuterium-tritium neutron tube is 60 cm; The neutron shield is made of tungsten-nickel-iron alloy.

2. A method for using a push-type controllable source neutron porosity measuring device as described in claim 1, characterized in that, When the push-type controllable source neutron porosity measuring device is lowered into the well for measurement, the push arms outside the housing are opened, and the measuring device is closely attached to the well wall to start the measurement.

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