CN1053763C - Accompanying alpha neutron tube for well logging - Google Patents

Abstract

The invention relates to a adjoint alpha neutron tube for well logging, which is characterized in that the tube is provided with an adjoint alpha particle signal acquisition component. The overall structure and characteristics are suitable for carbon/oxygen ratio spectroscopy logging. The optimal scheme of the accompanying alpha particle signal acquisition component is annular, and can be formed by surrounding deuterium ion incident beams by a plurality of small alpha detectors; the structure of a single alpha detector is: one end of the special-shaped glass light guide is welded on the kovar alloy tube, the other end of the special-shaped glass light guide is shaped into a part of the side surface of the circular truncated cone, and the inorganic scintillator is sintered on the special-shaped glass light guide. The neutron tube is provided with a particle extraction and focusing system and consists of a plurality of annular plane lenses. The neutron tube is used in a carbon/oxygen ratio logging system along with alpha particle fast neutron flight time, can remove the adverse effect of an interference layer outside a gamma scintillation probe, and greatly improves the accuracy of the measured C/O ratio. The basic structure and characteristics of the neutron tube can also be applied to other underground prospecting fields.

Description

Accompanying alpha neutron tube for well logging

The invention relates to a neutron generating device for well logging, in particular to a neutron tube which adopts deuterium-tritium reaction to generate neutrons.

In the carbon/oxygen ratio spectrometer logging tool, a neutron tube is used to generate fast neutrons. The working principle of the neutron tube is: the deuterium ions are generated by the ion source, and after being accelerated, they hit the tritium-containing target and undergo the following reaction: Emit about 14MeV fast neutrons. Use 14MeV fast neutrons to bombard the ore seam around the casing shaft, and the carbon and oxygen in the ore seam emit 4.43 and 6.13MeV non-elastic characteristic gamma rays respectively; measuring their energy spectrum and relative intensity can obtain the ratio of carbon content and oxygen content in the ore seam . There are many carbons in the oil and many oxygens in the water. The oil content of the ore around the oil well can be determined from the ratio of C/O and other relevant data. Existing neutron tubes for carbon/oxygen ratio energy spectrum logging, such as Chinese patent 88220224.3, the neutron tube disclosed by CN2052573U, generally consist of an insulating shell, a Penning ion source, an accelerating electrode and a target. The ion source produces deuterium ions, which hit the tritium-containing target after acceleration, and generate fast neutrons through the above reaction, which bombard the ore seam around the casing well. However, the C/O ratio measured by the existing logging device has great uncertainty. This is because, when the logging device is put into the cased hole for measurement, there are about 60mm thick water, iron, cement and other non-mineral layer materials (hereinafter referred to as interference layer) in the most sensitive area close to the gamma scintillation probe, which contains a large amount of C, O, Si, Ca. The measured thickness of the mineral seam outside the cement casing is about 200mm (hereinafter referred to as the effective mineral seam). Both calculation and measurement show that in the total characteristic γ counts, the contribution from the interference layer such as cement casing accounts for about 50%, and their role is equivalent to the background of interference, which brings a great impact on the C/O ratio. of uncertainty.

The purpose of the present invention is to design a neutron tube for well logging. Using this neutron tube and supporting fast neutron flight time carbon/oxygen ratio logging system can effectively reduce or remove the influence of the above-mentioned interference layer, greatly improving Accuracy of C/O ratio.

The accompanying α-neutron tube for well logging designed by the present invention comprises a sealed casing, a Penning ion source (6) positioned in the sealed casing and fixed thereon, an accelerating electrode (8) and a target (17), and is characterized in that: An ion beam extraction and focusing system (7) is set between the Penning ion source (6) and the accelerating electrode (8), the accelerating electrode (8) is located at the incident port of the ion beam pipeline (9), and Between the other end of (9) and the target (17), there is an accompanying alpha particle detector (15) around the ion beam flow line: said ion beam current extraction and focusing system (7) is three annular plane lenses (7A , 7B, 7C).

Said plane lens (7A) of the present invention can be replaced by the bottom surface of the ion outlet of the Penning ion source (6), the plane lens (7B) is a stainless steel cylinder with holes, and the plane lens (7C) is a non-magnetic stainless steel cylinder with holes on the bottom cover, which is secured to the Penning ion source (6).

The accompanying α particle detector (15) of the present invention can be ring-shaped, and is welded by Kovar tube (15A) and special-shaped glass light guide (15B), and the detection end face of glass light guide (15B) is conical frustum side shape, and its A layer of inorganic scintillator is sintered on it.

The ring-shaped accompanying alpha particle detector (15) of the present invention can be made up of several small detectors welded with Kovar tubes and special-shaped glass light guides to surround the incident ion beam, and the detection end faces of all small detectors form a complete Round table side.

The accompanying α particle detector (15) can be formed by welding a Kovar tube (15A) and a glass sheet, on which a layer of inorganic scintillator is sintered.

The accompanying alpha particle detector (15) can be composed of several small detectors welded with Kovar tubes and glass sheets to surround the incident ion beam.

Said annular companion alpha particle detector can be made up of four small detectors welded with special-shaped glass light guides and Kovar alloy tubes, and the detection end face (15C) of each light guide is the side of a quarter-circle frustum.

Said accompanying alpha particle detector can be made up of four small detectors welded by circular glass sheets and kovar alloy tubes.

The neutron tube of the present invention includes a sealed casing, a Penning ion source fixed on the sealed casing, an accelerating electrode and a target, and is characterized in that ion extraction is set between the Penning ion source and the accelerating electrode. and the focusing system, the accelerating electrode is located at the incident port of the ion beam current pipeline, and an accompanying α particle detector is arranged around the ion beam current line between the other end of the ion beam current pipeline and the target.

Compared with the neutron tube used in the original well logging instrument, the present invention has an accompanying α particle detector, through which the effective mine layer area can be selected for measurement, so the use of the present invention can reduce or eliminate γ scintillation probes during well logging Improve the accuracy of the measured C/O ratio due to the adverse effects of the external interference layer

Below in conjunction with accompanying drawing, embodiment further illustrate the present invention.

Fig. 1 is a schematic diagram of the structure of the present invention.

Fig. 2 is a view from the direction of embodiment 1A.

Fig. 3 is a view from the direction of embodiment 2A.

Fig. 4 is a working principle diagram of the present invention.

In the figure 1--exhaust pipe 2A--seal insulator 2B--seal insulator 3A--sealed kovar tube 3B--sealed kovar cover 4--connector 5--insulated shell 6A--Panningyuan magnetic circuit system 6B--Penningyuan cathode magnet 6C--Penningyuan cathode 6D-Penningyuan anode 6E-Penningyuan pair cathode 6F-Penningyuan pair cathode magnet 7A--First lens of ion extraction and focusing system 7B--Ion extraction and focusing system Second lens (focusing electrode) 7C--Ion extracting and focusing system Third lens 8--Accelerating electrode 9--Ion beam pipeline 10--Memory shielding cover 11A--Gas storage 11B--Gas adsorber 12-- Sealing Kovar cover 13A--Sealing insulator 13B--Sealing insulator 14--Welding joint 15A--Sealing Kovar tube for α detector 15B--Glass light guide for α detector 15C--Flash surface for α detector 16-- Target chamber sealing shell 17--tritium target 18--shielding body 19--effective mineral layer 20--γ scintillator 21--interference layer 22--γ photomultiplier tube 23--electronics system 24--cement layer 25 --Oil well steel pipe 26--Water layer 27--Logging instrument casing

The working principle of the present invention is shown in Fig. 1 and Fig. 4. The deuterium ions generated by the Penning ion source 6 pass through the ion extraction and focusing system 7, and after being accelerated by the accelerating electrode 8, they are incident on the tritium target 17. The nuclear reaction produces neutrons ( ₀ ¹ n ) of about 14 MeV and alpha particles ( ₂ ⁴ He ) of about 3 MeV. According to the nuclear reaction kinematics, the neutrons and α-particles produced are in one-to-one correspondence, and are emitted in opposite directions almost on a straight line. The forward-leaning neutrons are incident on the gamma scintillation probe 20 and its surrounding materials (including effective mineral layers and interfering object layers), generating various characteristic gamma rays. Hereinafter, the neutrons incident on the effective mine layer 19 are called the effective neutron group, and the neutrons incident on the gamma scintillation probe 20 itself and the interference layer 21 are called the interference neutron group. The corresponding associated α-particles are ejected backwards along with the α-particles. They can be called effective alpha particle group and interference alpha particle group respectively. In logging tools, the gamma scintillation probe 20 should be as close as possible to the tritium target. It is assumed that the deuterium ions move along the Z axis, and the gamma scintillation probe 20 is located on the Z axis behind the target. Then the accompanying alpha particle detector should surround the Z axis and be in front of the target. The interference layer 19 and the effective mine layer 21 around the gamma scintillation probe 20 are projected on the XY plane as two adjacent rings. The gamma scintillation probe 20 itself and the interfering object layer 19 should avoid incident neutrons as much as possible, and the effective mine layer 21 should accept incident neutrons as much as possible. Like this, according to nuclear reaction kinematics, the alpha particle detector is made into a ring, which can maximize Valid alpha particle populations are effectively accepted, and interfering alpha particle populations are not received. Using the "coincidence method" commonly used in nuclear detection technology, the background formed by various gamma rays generated by the interfering layer can be effectively removed. The size of the inner diameter and outer diameter of the ring is determined by the size of the predetermined interference layer and the effective mine layer.

Of course, the alpha particle detector can also be a non-complete annular detector, but the detection efficiency is lower.

Example 1

As can be seen from Fig. 1, parts 1, 3A, 3B, 5, 12, 9, 15A, 16 and the sealing insulator constitute the sealed shell of the neutron tube of the present invention, and parts 6A, 6B, 6C, 6D, 6E, 6F constitute the Penning ion The source 6, the Penning ion source 6 is fixed on the sealed casing through the connecting piece 4, and the connecting piece 4 can be made of non-magnetic stainless steel. An ion extraction and focusing system 7 is provided between the Penning ion source 6 and the accelerating electrode 8. This is because the photomultiplier tube for making the α detector and assembling the light signal generated by the α needs to occupy a certain space, so that the accompanying α The ion transport length of the neutron tube is longer than that of the ordinary neutron tube, and the measurement principle of the carbon/oxygen ratio logging system accompanied by fast neutron flight time of α particles requires the area of the tritium target to be as small as possible, so On the whole, the ion beam of the neutron tube is approximately a long and thin collimated beam. In order to meet this requirement, the present invention adds an ion extracting and gathering system 7 between the Penning ion source 6 and the accelerating electrode 8 . The system can be composed of several lenses, and the ion extraction and concentration system 7 of this embodiment is composed of three plane lenses. The first plane lens 7A is replaced by the bottom surface of the outlet of the Penning ion source 6, and the second plane lens 7B is an ion extraction and focusing electrode, which is served by a stainless steel cylinder with holes, and a voltage of -3000 to -5000 volts is applied to the first lens , the third lens 7C surrounds the second lens, and is a non-magnetic stainless steel cylinder cover with holes on the bottom, which is fixed with the bottom surface of the ion source 6 outlet. The accelerating electrode 8 is located at the entrance end of the ion beam flow pipe 9 . Between the other end of the ion beam flow pipe 9 and the target 17, an annular α detector is installed around the ion beam flow line.

The process of making a monolithic annular alpha detector is relatively complicated. Multiple small detectors can be fabricated to form a ring. In this embodiment, four small detectors are used to form an annular detector, and one end of each small detector is welded to a Kovar alloy tube with one end of a special-shaped glass light guide, and the area and shape of the cross-section of the Kovar alloy tube match the photomultiplier tube The other end of the light guide is in the shape of a quarter of the side of the circular truncated truncated body, and the inorganic scintillator is sintered on it. In this embodiment, ZnS is used, and four small detectors are combined together, so that the detection end faces form a complete truncated circular truncated side. The receiving surface is shown in Figure 2. The distances from the outer and inner sides of the receiving surface to the center of the tritium target are equal, so that the ranges of the received alpha particles are similar. The receiving solid angle is equivalent to 1/5 to 1/4 of the spherical solid angle.

Example 2

The structure of this embodiment is basically the same as that of Embodiment 1, except that a circular glass sheet is used instead of the special-shaped glass light guide 15B in Embodiment 1 to be welded on the Kovar tube, and its detecting and receiving surface is shown in FIG. 3 .

The theoretical calculation and experimental conditions of the target rate in the deuterium ion beam are as follows.

The energy and motion direction of the ions at the exit of the ion source are difficult to be given by analytical expressions, so we use the Monte Carlo method to simulate. Select a target with a diameter of 10mm, the target and the accelerating electrode are at ground potential, the potential of the ion source cathode and the third lens is 115±5KV; the second lens is 3 to 5 kV lower than the ion source cathode. By properly adjusting the apertures and distances of the lenses and electrodes, the target rate of the theoretically calculated beam can reach about 85%, and the experimental measurement is about 82%.

The neutron intensity of the accompanying α-neutron tube for well logging is on the order of 10 ⁷ /s. When used in the matching logging system, the characteristic γ-count of carbon and oxygen can be obtained at more than 1000CPS. It has met the needs of practical use. The basic principle of this type of neutron tube can also be applied to other types of mine measurement fields.

Claims (8)

1. A well logging accompanying α neutron tube comprises a sealed shell, a penning ion source (6), an accelerating electrode (8) and a target (17), wherein the penning ion source (6), the accelerating electrode (8) and the target (17) are positioned in the sealed shell and fixed on the sealed shell, the well logging accompanying α neutron tube is characterized in that an ion beam extraction and focusing system (7) is arranged between the penning ion source (6) and the accelerating electrode (8), the accelerating electrode (8) is positioned at an incident port of an ion beam pipeline (9), an accompanying α particle detector (15) surrounds an ion beam flow line between the other end of the ion beam pipeline (9) and the target (17), and the ion beam extraction and focusing system (7) is three annular plane lenses (7A, 7B and 7C).

2. The neutron tube α according to claim 1, wherein the planar lens (7A) is replaced by the bottom surface of the ion outlet of the penning ion source (6), the planar lens (7B) is a stainless steel cylindrical sheet with holes, and the planar lens (7C) is a non-magnetic stainless steel cylindrical cover with holes on the bottom surface and is fixed on the penning ion source (6).

3. The satellite α neutron tube according to claim 1 or 2, wherein the satellite α particle detector (15) is ring-shaped and is formed by welding a kovar alloy tube (15A) and a shaped glass light guide (15B), the detection end face of the glass light guide (15B) is in a shape of a truncated cone, and a layer of inorganic scintillator is sintered on the detection end face.

4. The adjoiner α neutron tube of claim 3, wherein the ring adjoiner α particle detector (15) is composed of several small detectors welded by kovar tube and shaped glass light guide, and surrounding the incident ion beam, the detecting end faces of all small detectors form a complete round table side.

5. The satellite α neutron tube according to claim 1 or 2, wherein the satellite α particle detector (15) is formed by welding a kovar tube (15A) and a glass plate, and an inorganic scintillator is sintered on the kovar tube.

6. The satellite α neutron tube of claim 5, wherein the satellite α particle detector (15) is comprised of a plurality of small detectors welded to a glass sheet using kovar tubes surrounding the incident ion beam.

7. The satellite α neutron tube of claim 6, wherein said ring satellite α particle detector is comprised of four small detectors welded together with a shaped glass light guide and a kovar alloy tube, the detecting end face (15C) of each light guide being a quarter of a truncated cone.

8. The particle neutron tube of satellite α of claim 7, wherein the satellite α particle detector comprises four small detectors welded together from round glass pieces and kovar tubes.

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