A method of matching neutron generator emission and acquisition timing

Abstract

The application discloses a method for matching neutron generator emission and collection timing, which obtains the optimal pulse width from multiple pulse widths, and obtains the collection start time of the full spectrum by the optimal pulse width and the position of the falling edge in the time spectrum. The method has high sensitivity, is convenient to operate, and meets the accuracy and integrity of domestic pulse neutron spectrum collection. Compared with traditional neutron instruments, the method is simple to operate, has obvious logging effect, is suitable for cased wells in later production, can accurately evaluate the remaining oil production capacity of oil, the single-layer water injection effect evaluation and the water-out level, has obvious effect, provides important technical support for original spectrum data collection, is simple to operate and convenient to use, and has great practical significance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of oil exploration and well drilling, and particularly relates to a method for matching neutron generator emission and acquisition timing. BACKGROUND

[0002] With continuous exploitation of oil fields, many oil fields have entered the middle and later stages of exploration and development, the development degree of oil fields is continuously improved, the oil production capacity of oil wells gradually decreases, and the water cut is higher and higher. Rechecking and tapping the potential of old wells is an important supplementary means to keep the relative stability of oil and gas production, and is also an effective way to improve the overall development effect of oil fields. Such oil wells have the characteristics of complex underground oil-water relationship and damaged reservoir environment (water injection layer collapse or well wall collapse), and part of the old well logging data is incomplete. These problems bring great difficulties to the further recovery of crude oil. Therefore, for the cased well in the later stage of exploitation, the remaining oil production capacity of the oil well is accurately evaluated, the single-layer water injection effect is evaluated, and the water-out level is provided to provide accurate data for the later development, so as to increase the oil production efficiency and reduce the oil production cost.

[0003] Pulse neutrons interact with the formation to produce non-elastic gamma rays, capture gamma rays and activation gamma rays, and at the same time, neutrons decay due to loss of energy. These ray characteristics are closely related to the lithology, porosity and fluid properties of the formation. Through non-elastic spectrum analysis, the relative content of carbon, oxygen, silicon and calcium in the formation can be determined; through capture spectrum and neutron decay characteristic analysis, the fluid properties and lithology can be determined; through activation spectrum analysis, the water flow condition can be determined. Therefore, the pulse neutron full spectrum logging series is widely used in domestic and foreign oil fields to determine the remaining oil saturation in the oil field water injection development period, judge the water-out degree, find the lost oil layer, find the high water cut layer, carry out water plugging operation, tap the oil production potential in thin layers, and provide the basis for perforation.

[0004] In the process of using the pulse neutron full spectrum logging, in the C / O ratio mode, the pulse neutron emission and acquisition cycle is 50us, in which the neutron emission time is 10us, the emission is completed, and 5us is waited to reduce the influence of residual non-elastic spectrum on the capture spectrum, the next 30us is used to collect the capture spectrum, the collection is completed, and 5us is waited to reduce the influence of residual capture spectrum on the non-elastic spectrum, and then the next emission and acquisition cycle is entered, and the non-elastic spectrum is repeatedly accumulated to obtain the spectrum, and the spectrum displayed on the ground is N seconds accumulated, so that the non-elastic spectrum obtained is mixed with the capture gamma, so that the non-elastic spectrum obtained is not pure, and the non-elastic spectrum information obtained is less, resulting in incomplete non-elastic information obtained. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, and the present application provides a method for matching neutron generator emission and acquisition timing to solve the problems of less non-elastic spectrum information and impure non-elastic spectrum information in the prior art.

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

[0007] A method for matching the emission and collection timing of a neutron generator, comprising the following steps:

[0008] Step 1, set a plurality of pulse widths, obtain the theoretical emission neutron time corresponding to each set pulse width, the neutron generator emits neutrons using the theoretical pulse width corresponding to the set pulse width, read the actual pulse width from the collected time spectrum, compare the theoretical pulse width and the actual pulse width, and then obtain the best pulse width, the best pulse width is the actual pulse width closest to the theoretical pulse width;

[0009] Step 2, use the best pulse width to emit neutrons, read the actual emission neutron time and the position of the falling edge in the time spectrum, and calculate the start time of the energy spectrum collection through the actual emission neutron time and the position of the falling edge in the time spectrum;

[0010] Obtain the best pulse width and the start time of the collected energy spectrum, the neutron generator emits pulsed neutrons and obtains the total spectrum and the capture spectrum, and obtains the inelastic spectrum.

[0011] Further improvement of the present application is that:

[0012] Preferably, in step 1, when the set pulse width is 0, the theoretical emission neutron time is (0+T0)us; when the set pulse width is 5, the theoretical emission neutron time is (5+T0)us; and when the set pulse width is 10, the theoretical emission neutron time is (10+T0)us.

[0013] Preferably, in step 2, the start time calculation method of the full spectrum collected energy spectrum is: the channel number corresponding to the falling edge of the time spectrum*0.2-actual pulse width.

[0014] Preferably, the channel number corresponding to the falling edge of the time spectrum is located at the inflection point.

[0015] Preferably, in step 3, when the neutron generator emits pulsed neutrons, the long probe time spectrum count is not less than 80000.

[0016] Preferably, in step 3, when the neutron generator emits pulsed neutrons, the H peak is 64 channels.

[0017] Preferably, in step 3, the yield of the neutron generator is not less than 1.5*10 8 .

[0018] Preferably, in step 3, when the neutron generator emits pulsed neutrons, an EILog-06 remote transmission instrument is used.

[0019] Preferably, in step 3, when the neutron generator emits pulsed neutrons, a BGO crystal and a photomultiplier tube are used.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention discloses a method for matching the emission and acquisition timing of a neutron generator. This method obtains the optimal pulse width from multiple pulse widths, and by combining the optimal pulse width with the position of the falling edge on the time spectrum, obtains the full-spectrum acquisition start time. This results in a pure and accurate non-elastic spectrum with high sensitivity and convenient operation, meeting the accuracy and completeness requirements of pulsed neutron energy spectrum acquisition in China. Compared with traditional neutron instruments, this method is simple to operate, provides significant logging results, and is suitable for casing wells in later stages of production. It accurately evaluates remaining oil production capacity, single-layer water injection effectiveness, and water flooding levels, demonstrating significant effectiveness. It provides crucial technical support for raw spectrum data acquisition, is simple to operate and convenient to use, and has significant practical implications. Attached Figure Description

[0022] Figure 1 The time spectrum was collected when the transmission frequency was 20 kHz and the anode pulse width was 10 μs.

[0023] Figure 2 The time spectrum was collected when the transmission frequency was 20 kHz and the anode pulse width was 15 μs.

[0024] Figure 3 The time spectrum collected when the transmission frequency is 20 kHz and the anode pulse width is 20 μs;

[0025] Figure 4 Neutron emission time and measurement timing diagram. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings:

[0027] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] This invention provides a method for matching the timing of neutron generator emission and acquisition. In order to obtain a pure non-elastic spectrum, it is necessary to select an appropriate emission neutron pulse width and the start time of the acquisition total spectrum.

[0029] The operating software has a setting box for the full spectrum start time and pulse width. If the pulse width is not set, the initial value is the anode pulse width T0, which is theoretically the neutron emission time T0. Setting it to a certain value in the setting box will add a certain number of microseconds to T0.

[0030] 1. The method for selecting an appropriate emitted neutron pulse width is as follows:

[0031] The operating software has a pulse width setting box. The default value for the pulse width is 0 if it is not set. At this time, the anode pulse width is (0+T0)us, which means that the theoretical neutron emission time is (0+T0)us. The value set in the setting box is the number of ust added to T0.

[0032] For example, when the neutron emission frequency is 20kHz, T0 is 10µs.

[0033] When the pulse width is set to 0, the theoretical neutron emission time is 10 + 0 = 10 μs;

[0034] When the pulse width is set to 5, the theoretical neutron emission time is 10 + 5 = 15 μs;

[0035] When the pulse width is set to 10, the theoretical neutron emission time is 10 + 10 = 20 μs;

[0036] like Figure 1 , Figure 2 , Figure 3The image shows the time spectrum collected when the pulse widths are 0, 5, and 10. Figure 1 In the case of a neutron emission frequency of 20kHz, when the pulse width is set to 0, the theoretical neutron emission time is 10 + 0 = 10µs. In actual measurement, the upper edge of the pulse is at channel 50 and the lower edge is at channel 70. The actual neutron emission time is (70 - 50) × 0.2 = 4µs.

[0037] Figure 2 In the case of a neutron emission frequency of 20kHz, when the pulse width is set to 5, the theoretical neutron emission time is 10 + 5 = 15µs. In actual measurement, the upper edge of the pulse is at channel 65 and the lower edge is at channel 90. The actual neutron emission time is (90-65) × 0.2 = 5µs.

[0038] Figure 3 In the case of a neutron emission frequency of 20kHz, when the pulse width is set to 10, the theoretical neutron emission time is 10 + 10 = 20µs. In actual measurement, the upper edge of the pulse is at channel 80 and the lower edge is at channel 115. The actual neutron emission time is (115 - 80) × 0.2 = 7µs.

[0039] The graph shows that an anode pulse of 20µs is optimal. Specifically, when the anode pulse (theoretically emitted for 20µs) is 20µs, the actual pulse width is closest to 10µs. Therefore, an anode pulse of 20µs is determined to be optimal.

[0040] 2. The method for selecting a suitable start time for acquiring the energy spectrum is as follows: The time spectrum has a total of 256 channels, each with a duration of 0.2 μs. The start time refers to the start time of the total spectrum acquisition. Because the rising edge is not steep enough, there will be a considerable artificial deviation when selecting the start time of the entire spectrum. However, the falling edge is very steep, making it relatively easier to select. Therefore, a backward calculation method is used. When the neutron emission frequency is 20 kHz and the pulse width is set to 10, the theoretical neutron emission time is 20 μs. Figure 3 It can be seen that the actual neutron emission time is 7µs, with the falling edge at channel 110. The actual seed emission time is equivalent to the measured pulse width, therefore:

[0041] Start time = Number of channels corresponding to the falling edge of the time spectrum × 0.2 - Measured pulse width

[0042] =110×0.2-7

[0043] =14

[0044] At this point, the start time of the full spectrum is set to 14.

[0045] See Figure 4In order to establish the correspondence between the emission seed and the measurement using the above parameters, the pulsed neutron emission and acquisition cycle is 50µs, of which the emission time is 10µs, after which there is a 5µs wait, followed by a 30µs acquisition of the capture spectrum, after which there is a 5µs wait, and then the next emission and acquisition cycle begins.

[0046] By setting the parameters mentioned above, the test can be conducted. To improve the accuracy of the data provided during testing, the following four measures are implemented:

[0047] 1. Provide appropriate target pressure so that the time spectrum count of the long probe is greater than 80,000;

[0048] 2. Select appropriate long and short probes with high voltage to stabilize the H peak at channel 64, so that the H peak can be used as a stable reference to obtain other parameters to be measured.

[0049] 3. Calculate the non-elastic spectrum using the fixed coefficient method.

[0050] 4. Select an appropriate threshold to remove counts with fewer than 5 channels in the time spectrum to eliminate the impact of interference on the spectral pattern.

[0051] In the above process, a neutron generator is used, and the yield is no less than 1.5 × 10⁻⁶. 8 The EILog ground system and operating software were used. During the measurement process, the EILog-06 remote transmission instrument, BGO crystal, and photomultiplier tube were employed.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for matching the emission and acquisition timing of a neutron generator, characterized in that, Includes the following steps: Step 1: Set several pulse widths and obtain the theoretical neutron emission time corresponding to each set pulse width. The neutron generator emits neutrons using the theoretical pulse width corresponding to the set pulse width. The actual pulse width is read from the collected time spectrum. The theoretical pulse width and the actual pulse width are compared to obtain the optimal pulse width. The optimal pulse width is the actual pulse width that is closest to the theoretical pulse width. Step 2: Use the optimal pulse width to emit neutrons, read the actual emission time of the neutrons and the position of the falling edge in the time spectrum from the acquired time spectrum, and calculate the start time of energy spectrum acquisition by using the actual emission time of the neutrons and the position of the falling edge in the time spectrum. To obtain the optimal pulse width and the start time for acquiring the energy spectrum, the neutron generator emits pulsed neutrons and obtains the total spectrum and the captured spectrum, thus obtaining the non-elastic spectrum.

2. The method for matching the emission and acquisition timing of a neutron generator according to claim 1, characterized in that, In step 1, among the plurality of pulse widths, when the pulse width is set to 0, the theoretical neutron emission time is (0+T0)us; when the pulse width is set to 5, the theoretical neutron emission time is (5+T0)us; and when the pulse width is set to 10, the theoretical neutron emission time is (10+T0)us.

3. The method for matching the emission and acquisition timing of a neutron generator according to claim 2, characterized in that, In step 2, the calculation method for the start time of the full spectrum acquisition energy spectrum is: number of channels corresponding to the falling edge of the time spectrum × 0.2 - actual pulse width.

4. The method for matching the emission and acquisition timing of a neutron generator according to claim 3, characterized in that, The number of channels corresponding to the falling edge of the time spectrum is located at the inflection point.

5. The method for matching the emission and acquisition timing of a neutron generator according to claim 1, characterized in that, In step 3, when the neutron generator emits pulsed neutrons, the time spectrum count of the long probe is not less than 80,000.

6. The method for matching the emission and acquisition timing of a neutron generator according to claim 1, characterized in that, In step 3, when the neutron generator emits pulsed neutrons, the H peak has 64 channels.

7. The method for matching the emission and acquisition timing of a neutron generator according to claim 1, characterized in that, In step 3, the yield of the neutron generator is not less than 1.5 × 10⁻⁶. 8 .

8. The method for matching the emission and acquisition timing of a neutron generator according to claim 1, characterized in that, In step 3, when the neutron generator emits pulsed neutrons, the EILog-06 remote transmission instrument is used.

9. The method for matching the emission and acquisition timing of a neutron generator according to any one of claims 1-8, characterized in that, In step 3, when the neutron generator emits pulsed neutrons, it uses a BGO crystal and a photomultiplier tube.

Images