CN101525996B - Leapfrog neutron tube target voltage control method - Google Patents

Abstract

The invention relates to a leapfrog neutron tube target voltage control method, and mainly solves the problem that the prior neutron tube is broken down due to sudden increment of target voltage. The method comprises the steps of providing power for a logging instrument, increasing the voltage-stabilizing current of the instrument to 108-240mA after the provided power is stable, gradually increasing the target voltage to 10-20kV after the instrument is stable, stopping increasing the target voltage when anode current is decreased from normal 70-90muA to 60-70muA, recovering the anode current to normal 70-90muA after 60-90s and then increasing the target voltage, observing the anode current after the target voltage is increased to 60-80kV, recovering the anode current to normal 70-90muA and finally switching the working interface of the instrument to a water current state to perform production log. The invention has the characteristics that the target voltage is gradually increased such that the neutron tube is not broken down, and the service life of the neutron tube is prolonged.

Description

Leapfrog neutron tube target voltage control method

Technical field:

The present invention relates to a kind of method, the especially Leapfrog neutron tube target voltage control method of the pulsed neutron log of field, oil field.

Background technology:

Adopt the logging method of pulse modulated accelerator neutron generator referred to as pulsed neutron log.Pulsed neutron log refers to utilize the interactional various effects of neutron and stratum, studies a class logging method of drilling geology section.It is a specific character of utilizing rock, and namely the hydrogen content in the rock comes the geological problems such as study of rocks character and degree of porosity.Accelerator for neutron production is the neutron of 14MeV to the stratum emitted energy during well logging, and through interaction processes such as inelastic scattering, elastic scattering and capture radiations, generation can be for epithermal neutron and the secondary gamma-rays measured.In these processes, neutron distribution situation around the probe, and neutron is captured rear gamma ray intensity of emitting, with the rock property around the instrument, particularly the hydrogen content of rock is relevant, and the hydrogen content of reservoir depends on its degree of porosity, and therefore, pulsed neutron log is now widely used a kind of porosity logging.The pulsed neutron log method formed commercialization logger kind and the model that develop now comparative maturity are a lot, and accelerator for neutron production then is the core component of instrument.

Accelerator for neutron production is as compact accelerator neutron source, have light, removable, good, the essentially no γ background of monochromaticjty, use the plurality of advantages such as safety, radiationless harm, especially accelerator for neutron production can according to certain outer triggering signal transmitted pulse neutron, have been brought into play original effect for many years in the nuclear logging field.Develop rapidly along with logging technique, the accelerator for neutron production technology also is greatly improved, by initial major diameter, the consumable products that develops into gradually minor diameter, long-life, high temperature resistant, high yield and can produce in batches, and neutron tube is the critical component of accelerator for neutron production.

In the pulsed neutron log process, neutron tube is the low frequency neutron tube, and yield is higher, is 2 * 10 ⁸Individual/second.Its working method is as follows: be 1～10s each launch time, then interval record 10～60s.Higher neutron yield has guaranteed still can access higher counting rate under this tranmitting frequency, has also shortened neutron tube required service time, has increased its application life.But owing to often having the breakdown phenomenon of neutron tube; on average only be 50～70 hours the application life of existing neutron tube; the length in neutron tube life-span depends on the height that target is pressed; high target pressure can shorten the application life of neutron tube; existing neutron tube target pressure-controlled method is that disposable target is pressed is elevated to required numerical value mostly; target is pressed and is increased suddenly; easily cause neutron tube to puncture; and lower target pressure energy accesses long application life; therefore, be the key that obtains to grow service time to neutron tube target pressure-controlled.

Summary of the invention:

Because pressing, target increases suddenly the deficiency that causes neutron tube to puncture in order to overcome existing neutron tube, the invention provides a kind of Leapfrog neutron tube target voltage control method, thus this Leapfrog neutron tube target voltage control method have target press increase gradually avoid neutron tube breakdown, prolong the neutron tube characteristics in application life.

Technical scheme of the present invention is: a kind of Leapfrog neutron tube target voltage control method, logger is powered, power up stable after, the instrument electric current of voltage regulation is heightened to 108～240mA, behind instrument stabilizer, progressively add target and be depressed into 10～20KV; When anode current is down to 60～70 μ A by normal 70～90 μ A, stops to add target and press; Through 60～90s, anode current adds the target pressure after returning to normal 70～90 μ A again, and target is observed anode current after pressing and being added to 60～80KV, and anode current recovers normal 70～90 μ A, then the instrument working interface is switched to streamflow regime, carries out production logging.

The present invention has following beneficial effect: owing to adopting such scheme, target presses segmentation progressively to increase, all add target after anode current is stable presses at every turn again, can rationally control the neutron tube anode current like this, avoided once the neutron tube target being pressed to beat satisfying, cause neutron tube anode, the target utmost point to consume excessively, thereby prolonged neutron tube application life; Simultaneously Leapfrog neutron tube target voltage control method can effectively be avoided consuming excessively of the neutron yield that causes in adding target pressure process, improves service efficiency.

Description of drawings:

Accompanying drawing 1 is the structural representation of neutron tube of the present invention;

Accompanying drawing 2,3, the 4th, the parameter of display interface during each duty of neutron tube of the present invention:

Accompanying drawing 5 is that anode and target are pressed the corresponding relation curve;

The graph of a relation that neutron yield and target were pressed when accompanying drawing 6 was different targets pressure;

Accompanying drawing 7 is graphs of a relation of anode current and heater current;

Accompanying drawing 8, the 9th, the logger display interface of application method of the present invention;

Accompanying drawing 10,11, the 12nd is used existing methodical logger display interface.

1-anode among the figure, 2-glass chamber, the 3-target utmost point, 4-accelerating cavity.

The specific embodiment:

The invention will be further described below in conjunction with accompanying drawing:

Figure 1 shows that this invents the structure of used neutron tube, neutron tube comprises ion gun, accelerating cavity 4, the target utmost point 3 and pressure regulation system, and above-mentioned parts are sealed in a pottery or the glass chamber 2, forms a small-sized extraordinary electron tube.Neutron tube is in fact a kind of small-sized accelerator, and its performance is determining many indexs such as the yield, life-span, stability of accelerator for neutron production.To produce average voltage be that the high direct voltage of 60～80KV is added on the target utmost point 3 to high voltage source during work, the voltage that the ion gun current and power supply produces is added on the ionogenic anode 1, filament heating deuterium holder discharges deuterium gas, become the deuterium ion sucking-off in the ion gun internal ionization, after accelerating cavity 4 accelerates, get on the target utmost point 3 with the about energy of 80～100keV, produce D-T with the tritium of the target utmost point 3, produce the fast neutron of 14MeV.

For fear of once beating neutron tube target pressure full, cause the neutron tube anode, the target utmost point consumes excessively, a kind of Leapfrog neutron tube target voltage control method is provided here, may further comprise the steps: at first, require assembling according to routine, connect logger, the neutron tube power supply will be carried out stage by stage in the well logging, after instrument powered, after each parameter display of logger interface is stable, show that instrument powers up stable, heighten the instrument electric current of voltage regulation to 108～240mA this moment, guarantee the continuity of neutron tube power supply, progressively strengthen target and be depressed into 10～20KV behind each parameter stability of instrument interface of logging well, target is pressed through preliminary and is discharged, produce a small amount of D-T, as shown in Figure 2; Because target is pressed and anode current changes rapidly, therefore to conscientiously observe the variation of anode current, because a small amount of D-T having been arranged, the deuterium ion of anode has slight disengaging, anode current is by normal 70～90 μ A, be down to 60～70 μ A, at this moment stopping to add target presses, greatly behind 60S～90S, anode current reaches equilibrium state after returning to normal 70～90 μ A, and namely anode current keeps stablizing motionless basically, and at this moment the D-T of neutron tube inside is balance, and then add the target pressure, as shown in Figure 3.Target press be added to 60～80KV normal after, at this moment produce higher high-energy neutron bundle, conscientiously observe anode current, anode current recovers normal 70～90 μ A, this process only has 2 seconds, therefore require operator's spirit to want high concentration, careful control instrument electric current of voltage regulation can not be zero, makes the air pressure of neutron tube inside progressively adapt to the impact that high target pressure zone comes, stable output high-energy neutron, then the instrument working interface is switched to streamflow regime, carry out production logging, as shown in Figure 4.Use the neutron well logging that the method is carried out, the NEUTRON EMISSION sequential is stable, and without clutter, without sudden change, record period is clear, noiseless, has improved efficient and the accuracy of well logging.

During original neutron tube work, for the stable usually employing that guarantees intraductal atmospheric pressure monitors that the variation of neutron tube heater current comes the operating air pressure in the adjustable pipe, purpose is to make the neutron tube yield stable.Think that the anode current that adopts the supervision neutron tube changes to adjust heater current more reasonable, the variation that anode current or target are pressed can directly cause the variation of neutron yield, only has anode current and target to press stable, and neutron yield has just been stablized naturally.Target is pressed with the corresponding relation of anode current and is seen accompanying drawing 5, can judge by the variation of observing anode current whether the variation of neutron tube target pressure is reasonable.Because the ionogenic duty that neutron tube adopts determines by factors such as magnetic field intensity, anode voltage and target pressures, be relatively-stationary on the impact of neutron yield.And air pressure becomes certain directly proportional to change with anode current, directly affects ionogenic duty.Target was pressed with variation in neutron tube was managed when variations in temperature, also affect the stability of neutron tube work, therefore can be by regulating the duty of target pressure-controlled neutron tube, neutron yield and target are pressed when different targets are pressed relation such as accompanying drawing 6, the change curve that neutron yield was pressed with target when curve 1,2,3 was respectively different targets pressure scope among the figure, curve 1 target is pressed and pressed for 60-80KV, curve 2 targets is that 40-50KV, curve 3 targets pressure are 10-20KV, as seen from the figure, target is pressed less, and the variation that target is pressed is less on the impact of neutron yield.The target pressure-controlled of neutron tube is to realize by the heating current of control filament during work, the relation of anode current and heater current such as accompanying drawing 7, as seen from the figure: the give vent to anger minor variations of rear heater current of neutron tube all can cause the great changes of anode current, thereby cause the variation that target is pressed, therefore when being added to given target pressure, thereby only need to control anode current by the adjustment heater current and just can adjust neutron yield, realize the automatic control of accelerator for neutron production.

The below does not compare with using the interface that the method records the NEUTRON EMISSION of using Leapfrog neutron tube target voltage control method, further specifies the advantage of using Leapfrog neutron tube target voltage control method:

1. the NEUTRON EMISSION sequential of using Leapfrog neutron tube target voltage control method is stable, without clutter, without sudden change, as shown in Figure 8;

2. the record period of using Leapfrog neutron tube target voltage control method is clear, noiseless, as shown in Figure 9;

3. do not use in the power supply process of Leapfrog neutron tube target voltage control method, easily cause wave recording mixed and disorderly, can't work, as shown in Figure 10;

4. do not use the anode drift of the neutron tube of Leapfrog neutron tube target voltage control method, changes and cause recording curve to drift about when larger, can't work, as shown in Figure 11;

5. anode and the target of not using Leapfrog neutron tube target voltage control method are extremely unstable, cause communication maximum to occur, need to readjust the relation between anode and the target pressure, as shown in Figure 12.

Claims (1)

1. Leapfrog neutron tube target voltage control method, comprise assembling, the connection of logger, it is characterized in that: logger is powered, power up stable after, the instrument electric current of voltage regulation is heightened to 108～240mA, behind instrument stabilizer, progressively added target and be depressed into 10～20KV; When anode current is down to 60～70 μ A by normal 70～90 μ A, stops to add target and press; Through 60～90s, anode current adds the target pressure after returning to normal 70～90 μ A again, after target is pressed and is added to 60～80KV, observe anode current, when anode current recovers normal 70～90 μ A, then the instrument working interface is switched to streamflow regime, carry out production logging.

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