Thermal neutron imaging logging methods and devices

Abstract

This invention relates to the field of well logging technology, specifically to a thermal neutron imaging well logging method and apparatus. The method includes: generating a neutron count rate curve; determining the neutron lifetime at which the neutron count rate curve cuts off based on the curve; and determining the formation boundary based on the neutron lifetime. This application improves the accuracy of formation detection.

Description

Technical Field

[0001] This invention relates to the field of well logging technology, specifically to a thermal neutron imaging well logging method and apparatus. Background Technology

[0002] Thermal neutron lifetime logging involves emitting a 14 MeV neutron beam from a pulsed neutron generator in the wellbore at a predetermined time. High-energy fast neutrons first lose some energy through inelastic scattering, transforming into medium-energy neutrons accompanied by inelastic gamma radiation. These are then further slowed down by elastic scattering, transforming into thermal neutrons, which are gradually captured by the formation. The average lifetime τ of thermal neutrons in the formation is related to formation lithology, formation water salinity, porosity, and water saturation. When formation lithology, formation water salinity, and porosity are known or measurable, the oil, gas, and water saturation of the reservoir can be determined by measuring the neutron lifetime. Current technologies using neutron lifetime measurements employ PNN (Pulsed Near Detector) devices. PNN primarily utilizes the slope of the near-detector count rate curve to determine the interface; however, this method discards the tail end of the curve, resulting in inaccurate results. Summary of the Invention

[0003] Therefore, embodiments of the present invention provide a thermal neutron imaging logging method and apparatus to improve the accuracy of interface demarcation.

[0004] To achieve the above objectives, embodiments of the present invention provide the following technical solution: According to a first aspect of the present invention, a thermal neutron imaging logging method includes:

[0005] Generate a neutron count rate curve;

[0006] The neutron lifetime at which the neutron count rate curve cuts off is determined based on the aforementioned curve.

[0007] The formation boundary is determined based on the lifetime of the neutron.

[0008] Furthermore, the method also includes: generating three detector count rate curves corresponding to the first predetermined value, the second predetermined value, and the third predetermined value when the mineralization is a predetermined value, the porosity is a predetermined value, and the oil saturation is a predetermined value, respectively;

[0009] Determine the first, second, and third ordinates corresponding to the pre-defined horizontal coordinate;

[0010] The first difference between the first ordinate and the second ordinate is calculated.

[0011] The second difference between the second and third ordinates is calculated.

[0012] Determine the minimum difference between the first difference and the second difference;

[0013] Determine whether the minimum difference is less than a predetermined threshold;

[0014] If so, the value of the mineralization is determined to be the minimum threshold for identifying oil and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying oil and water based on the porosity.

[0015] Furthermore, if not, the method further includes:

[0016] The predetermined values ​​of mineralization and porosity are reduced;

[0017] Three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation. The calculation and judgment steps continue until the minimum thresholds for identifying oil and water in terms of mineralization and porosity are determined.

[0018] Furthermore, the method also includes:

[0019] When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of gas saturation, respectively.

[0020] The first, second, and third ordinates are determined based on the pre-defined abscissa and the curve.

[0021] The first difference between the first ordinate and the second ordinate is calculated.

[0022] The second difference between the second and third ordinates is calculated.

[0023] Determine the minimum difference between the first difference and the second difference;

[0024] Determine whether the minimum difference is less than a predetermined threshold;

[0025] If so, the value of the mineralization is determined to be the minimum threshold for identifying gas and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying gas and water based on the porosity.

[0026] Furthermore, if not, the method further includes:

[0027] The predetermined values ​​of mineralization and porosity are reduced;

[0028] The three detector count rate curves corresponding to the first, second, and third predetermined values ​​of the gas saturation are used; the calculation and judgment steps continue until the minimum threshold for identifying the mineralization and porosity of the gas and water is determined.

[0029] A second aspect of this application also proposes a thermal neutron imaging logging device, comprising:

[0030] The image generation module is used to generate neutron count rate curves.

[0031] The determination module is used to determine the neutron lifetime at which the neutron count rate curve cuts off based on the curve graph;

[0032] The formation boundary is determined based on the lifetime of the neutron.

[0033] The image generation module is also used for:

[0034] When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation, respectively.

[0035] In one possible implementation, the determining module is further configured to determine the first, second, and third ordinates corresponding to the pre-defined horizontal coordinates;

[0036] The first difference between the first ordinate and the second ordinate is calculated.

[0037] The second difference between the second and third ordinates is calculated.

[0038] Determine the minimum difference between the first difference and the second difference;

[0039] Determine whether the minimum difference is less than a predetermined threshold;

[0040] If so, the value of the mineralization is determined to be the minimum threshold for identifying oil and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying oil and water based on the porosity.

[0041] In one possible implementation, if not, the image generation module is further configured to:

[0042] The predetermined values ​​of mineralization and porosity are reduced;

[0043] Three detector count rate curves were generated, corresponding to the first, second, and third predetermined values ​​of oil saturation.

[0044] The determining module is further used to continue the calculation and judgment steps until the minimum threshold for identifying oil and water in terms of mineralization and porosity is determined.

[0045] In one possible implementation, the image generation module is further configured to:

[0046] When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of gas saturation, respectively.

[0047] The determining module is further configured to determine the first ordinate, the second ordinate, and the third ordinate based on the pre-set abscissa and the curve.

[0048] The first difference between the first ordinate and the second ordinate is calculated.

[0049] The second difference between the second and third ordinates is calculated.

[0050] Determine the minimum difference between the first difference and the second difference;

[0051] Determine whether the minimum difference is less than a predetermined threshold;

[0052] If so, the value of the mineralization is determined to be the minimum threshold for identifying gas and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying gas and water based on the porosity.

[0053] In one possible implementation, if the determining module determines that the minimum difference is greater than or equal to a predetermined threshold, the image generation module is further configured to:

[0054] The predetermined values ​​of mineralization and porosity are reduced;

[0055] Three detector count rate curves were generated, corresponding to gas saturation levels of 0%, 30%, and 70%.

[0056] The determining module is also used to continue the calculation and judgment steps until the minimum threshold for identifying the mineralization and porosity of the gas and water is determined.

[0057] The embodiments of this invention have the following advantages: This application does not use the slope of the count rate curve, but rather analyzes the lifetime value of neutrons at the tail end to determine the interface between rock, gas, oil, and water. The device improves the accuracy of oil well logging. Attached Figure Description

[0058] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0059] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0060] Figure 1 A flowchart of a thermal neutron imaging logging method provided in an embodiment of the present invention;

[0061] Figure 2 This is a graph showing the distribution of the count rate near the detector.

[0062] Figure 3 This is a schematic diagram showing the curves for a mineralization of 2000 ppm, a porosity of 30%, and oil saturation of 0%, 30%, and 70%, respectively.

[0063] Figure 4 This is a magnified view of the tail of the near-detector count rate distribution curve. Detailed Implementation

[0064] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] In the prior art, see Appendix Figure 2 In this method, PNN utilizes the middle part of the curve, as shown in part 21 of the figure, but ignores the tail end of the curve, part 22.

[0066] Based on this, this application proposes a flowchart of a thermal neutron imaging logging method, see attached diagram. Figure 1 The flowchart shown is a thermal neutron imaging logging method, which includes:

[0067] Step S101: Generate a neutron count rate curve;

[0068] Step S102: Determine the neutron lifetime at which the neutron count rate curve cuts off based on the curve graph;

[0069] Step S103: Determine the formation boundary based on the lifetime of the neutron.

[0070] The TNIS method in this application uses the thermal neutron termination time, i.e., the neutron lifetime, for qualitative analysis, mainly utilizing the tail end of the curve, such as... Figure 2 Part 22 of the text; thereby avoiding the inability to objectively evaluate reservoir properties in cases such as tight layers and low-yield gas layers.

[0071] In order to determine the minimum threshold for identifying the mineralization or porosity of oil-water or gas-water mixtures, the method further includes: generating three detector count rate curves corresponding to the first predetermined value, the second predetermined value, and the third predetermined value for oil saturation when the mineralization and porosity are predetermined values.

[0072] Determine the first, second, and third ordinates corresponding to the pre-defined horizontal coordinate;

[0073] The first difference between the first ordinate and the second ordinate is calculated.

[0074] The second difference between the second and third ordinates is calculated.

[0075] Determine the minimum difference between the first difference and the second difference;

[0076] Determine whether the minimum difference is less than a predetermined threshold;

[0077] If so, the value of the mineralization is determined to be the minimum threshold for identifying oil and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying oil and water based on the porosity.

[0078] Furthermore, if not, the method further includes:

[0079] The predetermined values ​​of mineralization and porosity are reduced;

[0080] Three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation. The calculation and judgment steps continue until the minimum thresholds for identifying oil and water in terms of mineralization and porosity are determined.

[0081] Furthermore, the method also includes:

[0082] When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of gas saturation, respectively.

[0083] The first, second, and third ordinates are determined based on the pre-defined abscissa and the curve.

[0084] The first difference between the first ordinate and the second ordinate is calculated.

[0085] The second difference between the second and third ordinates is calculated.

[0086] Determine the minimum difference between the first difference and the second difference;

[0087] Determine whether the minimum difference is less than a predetermined threshold;

[0088] If so, the value of the mineralization is determined to be the minimum threshold for identifying gas and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying gas and water based on the porosity.

[0089] Furthermore, if not, the method further includes:

[0090] The predetermined values ​​of mineralization and porosity are reduced;

[0091] Three detector count rate curves corresponding to the first, second, and third predetermined values ​​of gas saturation;

[0092] In one embodiment, the first predetermined value, the second predetermined value, and the third predetermined value are 0%, 30%, and 70%, respectively;

[0093] Continue with the calculation and judgment steps until the minimum threshold for identifying the mineralization and porosity of the gas and water is determined.

[0094] A second aspect of this application also proposes a thermal neutron imaging logging device, comprising:

[0095] The image generation module is used to generate neutron count rate curves.

[0096] The determination module is used to determine the neutron lifetime at which the neutron count rate curve cuts off based on the curve graph;

[0097] The formation boundary is determined based on the lifetime of the neutron.

[0098] The image generation module is also used for:

[0099] When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation, respectively.

[0100] In one possible implementation, the determining module is further configured to determine the first, second, and third ordinates corresponding to the pre-defined horizontal coordinates;

[0101] The first difference between the first ordinate and the second ordinate is calculated.

[0102] The second difference between the second and third ordinates is calculated.

[0103] Determine the minimum difference between the first difference and the second difference;

[0104] Determine whether the minimum difference is less than a predetermined threshold;

[0105] If so, the value of the mineralization is determined to be the minimum threshold for identifying oil and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying oil and water based on the porosity.

[0106] In one possible implementation, if not, the image generation module is further configured to:

[0107] The predetermined values ​​of mineralization and porosity are reduced;

[0108] Three detector count rate curves were generated, corresponding to the first, second, and third predetermined values ​​of oil saturation.

[0109] The determining module is further used to continue the calculation and judgment steps until the minimum threshold for identifying oil and water in terms of mineralization and porosity is determined.

[0110] In one possible implementation, the image generation module is further configured to:

[0111] When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of gas saturation, respectively.

[0112] The determining module is further configured to determine the first ordinate, the second ordinate, and the third ordinate based on the pre-set abscissa and the curve.

[0113] The first difference between the first ordinate and the second ordinate is calculated.

[0114] The second difference between the second and third ordinates is calculated.

[0115] Determine the minimum difference between the first difference and the second difference;

[0116] Determine whether the minimum difference is less than a predetermined threshold;

[0117] If so, the value of the mineralization is determined to be the minimum threshold for identifying gas and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying gas and water based on the porosity.

[0118] In one possible implementation, if the determining module determines that the minimum difference is greater than or equal to a predetermined threshold, the image generation module is further configured to:

[0119] The predetermined values ​​of mineralization and porosity are reduced;

[0120] Three detector count rate curves were generated, corresponding to the first, second, and third predetermined values ​​of oil saturation.

[0121] The determining module is also used to continue the calculation and judgment steps until the minimum threshold for identifying the mineralization and porosity of the gas and water is determined.

[0122] It is worth emphasizing that other three percentage values ​​can also be selected, and it is not necessarily limited to 0%, 30%, and 70%.

[0123] Appendix Figure 3 This is a schematic diagram showing the curves for a mineralization of 2000 ppm, a porosity of 30%, and oil saturation of 0%, 30%, and 70%, respectively; where the horizontal axis represents neutron lifetime and the vertical axis represents count rate; (See attached diagram) Figure 4 This is a magnified view of the tail section.

[0124] In one embodiment, the minimum threshold for identifying oil-water salinity is determined to be 3000 ppm, and the minimum threshold for porosity is 8%.

[0125] The minimum threshold for the mineralization of the identified gas and water is set at 2000 ppm; the minimum threshold for porosity is set at 5%.

[0126] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A thermal neutron imaging logging method, characterized in that, include: Generate a neutron count rate curve; The neutron lifetime at which the neutron count rate curve cuts off is determined based on the aforementioned curve. Based on the lifetime of the neutron, a minimum threshold for identifying the mineralization or porosity of oil-water or gas-water mixtures is determined, thereby identifying the formation interface; wherein, the method for determining the minimum threshold for identifying the mineralization or porosity of oil-water or gas-water mixtures includes: A. For identifying oil and water: When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation, respectively. Determine the first, second, and third ordinates corresponding to the pre-defined horizontal coordinate; The first difference between the first ordinate and the second ordinate is calculated. The second difference between the second and third ordinates is calculated. Determine the minimum difference between the first difference and the second difference; Determine whether the minimum difference is less than a predetermined threshold; If so, the value of the mineralization is determined to be the minimum threshold for identifying oil and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying oil and water based on the porosity. If not, then reduce the predetermined value of mineralization and the predetermined value of porosity; Three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation. The calculation and judgment steps are continued until the minimum threshold for identifying oil and water in terms of mineralization and porosity is determined. B. For identifying air and water: When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of gas saturation, respectively. The first, second, and third ordinates are determined based on the pre-defined abscissa and the curve. The first difference between the first ordinate and the second ordinate is calculated. The second difference between the second and third ordinates is calculated. Determine the minimum difference between the first difference and the second difference; Determine whether the minimum difference is less than a predetermined threshold; If so, the value of the mineralization is determined to be the minimum threshold for identifying gas and water with mineralization; and the value of the porosity is determined to be the minimum threshold for identifying gas and water with porosity. If not, then reduce the predetermined value of mineralization and the predetermined value of porosity; Three detector count rate curves are generated, corresponding to the first, second, and third predetermined values ​​of gas saturation. The calculation and judgment steps continue until the minimum threshold for identifying the mineralization and porosity of the gas and water is determined.

2. A thermal neutron imaging logging device, characterized in that, include: The image generation module is used to generate neutron count rate curves. The determination module is used to determine the neutron lifetime at which the neutron count rate curve cuts off based on the curve graph; Based on the lifetime of the neutron, a minimum threshold for identifying the mineralization or porosity of oil-water or gas-water mixtures is determined, thereby identifying the formation interface; wherein, the method for determining the minimum threshold for identifying the mineralization or porosity of oil-water or gas-water mixtures includes: A. For identifying oil and water: When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of oil saturation, respectively. The determining module is further configured to determine the first, second, and third ordinates corresponding to the pre-defined horizontal coordinates; The first difference between the first ordinate and the second ordinate is calculated. The second difference between the second and third ordinates is calculated. Determine the minimum difference between the first difference and the second difference; Determine whether the minimum difference is less than a predetermined threshold; If so, the value of the mineralization is determined to be the minimum threshold for identifying oil and water based on the mineralization; and the value of the porosity is determined to be the minimum threshold for identifying oil and water based on the porosity. If not, then reduce the predetermined value of mineralization and the predetermined value of porosity; Generate three detector count rate curves corresponding to the first, second, and third predetermined values ​​of oil saturation; continue the calculation and judgment steps until the minimum thresholds for identifying oil and water in terms of mineralization and porosity are determined. B. For identifying air and water: When the mineralization and porosity are at a predetermined value, three detector count rate curves are generated corresponding to the first, second, and third predetermined values ​​of gas saturation, respectively. The determining module is further configured to determine the first ordinate, the second ordinate, and the third ordinate based on the pre-set abscissa and the curve. The first difference between the first ordinate and the second ordinate is calculated. The second difference between the second and third ordinates is calculated. Determine the minimum difference between the first difference and the second difference; Determine whether the minimum difference is less than a predetermined threshold; If so, the value of the mineralization is determined to be the minimum threshold for identifying gas and water with mineralization; and the value of the porosity is determined to be the minimum threshold for identifying gas and water with porosity. If not, then reduce the predetermined value of mineralization and the predetermined value of porosity; Three detector count rate curves are generated, corresponding to the first, second, and third predetermined values ​​of gas saturation. The calculation and judgment steps continue until the minimum threshold for identifying the mineralization and porosity of the gas and water is determined.

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