Radioactive logging-while-drilling system, logging method and drilling tool combination

Abstract

The invention provides a while-drilling radioactive logging system, a logging method and a drilling tool assembly, and belongs to the technical field of oil-gas exploration, and the system comprises at least one perovskite semiconductor detector which is used for directly absorbing gamma rays from a stratum and generating corresponding electric pulse signals; the electronics module is electrically connected with the perovskite semiconductor detector and used for processing the electric pulse signal to obtain while-drilling radioactive logging data, and the while-drilling radioactive logging data comprises at least one of natural gamma counting data, natural gamma energy spectrum data and gamma-gamma density data; the protection packaging body comprises a metal shock-resistant and high-pressure-resistant shell, a heat insulation and heat preservation layer and a heat channel which are arranged in the metal shock-resistant and high-pressure-resistant shell, and a high shock-resistant and impact-resistant connecting piece for fixing internal devices, and the protection packaging body is used for accommodating the perovskite semiconductor detector and the electronics module; and the safety and the accuracy of radioactive logging while drilling are improved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, specifically to a radioactive logging-while-drilling system, logging method, and drill string assembly. Background Technology

[0002] In the field of oil and gas exploration and development, logging while drilling (LWD) technology is crucial for achieving geological guidance, real-time formation assessment, and drilling optimization. Radioactive logging, especially natural gamma ray (GR), natural gamma ray (SGR), and bulk density (RHOB) measurements, is an indispensable component of LWD, used to identify lithology, calculate clay content, assess reservoir properties, and delineate formation interfaces.

[0003] In related technologies, downhole gamma-ray detection technology mainly relies on an indirect conversion system consisting of a scintillation crystal and a photomultiplier tube (PMT). This system has the following inherent limitations: First, due to the multi-stage conversion from "γ-ray to visible light to electrical signal," the system suffers from numerous signal losses and noise introductions, resulting in generally poor energy resolution. This severely restricts the reliable resolution of characteristic peaks of potassium (K, 1.46 MeV), uranium (U, 1.76 MeV), and thorium (Th, 2.62 MeV) in the natural gamma spectrum, affecting the accuracy of quantitative elemental analysis. Second, the PMT and its glass vacuum housing are sensitive to high temperatures and mechanical stress. Gain and stability drop sharply in environments exceeding 125°C, and the failure rate is high under drilling conditions with high vibration (>10 g RMS) and high impact (>50 g), making it difficult to meet the stringent requirements for long-term instrument stability in deep wells, ultra-deep wells, and rotary steered drilling. Logging-while-drilling instruments are installed in the drill string assembly (BHA), where space is extremely limited and the bandwidth of telemetry methods such as mud pulses is strictly constrained. Therefore, the detection system is required to have high integration, low power consumption and miniaturization characteristics.

[0004] In summary, there is an urgent need in this field for a logging-while-drilling solution that can operate stably in extreme high-temperature, strong vibration and shock, and strong magnetic field environments, while providing better energy resolution, higher system integration and reliability, and enabling safer and more accurate measurement of radioactive parameters while drilling. Summary of the Invention

[0005] In view of this, it is necessary to provide a radiometric logging system, logging method and drill string assembly to solve the technical problems of poor environmental adaptability, poor stability, high signal loss and high power consumption of existing methods under complex geological conditions, which lead to low safety and accuracy of radiometric parameter measurement during drilling.

[0006] To address the aforementioned technical problems, in a first aspect, the present invention provides a radioactive logging-while-drilling system, wherein the radioactive logging-while-drilling system is installed inside a drilling instrument and is used to perform logging simultaneously with drilling by the drilling instrument. The radioactive logging-while-drilling system includes: At least one perovskite semiconductor detector is used to directly absorb gamma rays from the strata and generate corresponding electrical pulse signals. An electronics module, electrically connected to the perovskite semiconductor detector, is used to process the electrical pulse signal to obtain logging-while-drilling (LWD) data, wherein the LWD data includes at least one of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data. The protective package includes a metal shockproof and high-pressure resistant shell, a heat insulation layer and a thermal channel disposed within the metal shockproof and high-pressure resistant shell, and a high vibration and shock resistant connector for fixing internal components, wherein the protective package is used to house the perovskite semiconductor detector and the electronics module.

[0007] In one possible implementation, the perovskite semiconductor material of the perovskite semiconductor detector is selected from at least one of CsPbBr3, MAPbI3, and FAPbBr3, or is other semiconductor materials with a perovskite crystal structure and their derivatives; if the logging-while-drilling radiometric data is natural gamma-ray count data; the electronics module includes: A bias power supply unit, electrically connected to the perovskite semiconductor detector, is used to provide a stable bias voltage to the perovskite semiconductor detector; The signal amplification and shaping unit is electrically connected to the perovskite semiconductor detector and is used to amplify the electrical pulse signal with low noise and shape the waveform to obtain the shaped electrical pulse signal. The counting window unit is used to count the shaped electrical pulse signal to obtain natural gamma count data.

[0008] In one possible implementation, if the logging-while-drilling radioactive data is natural gamma ray spectroscopy data, the electronics module includes: A bias power supply unit, electrically connected to the perovskite semiconductor detector, is used to provide a stable bias voltage to the perovskite semiconductor detector; The signal amplification and shaping unit is electrically connected to the perovskite semiconductor detector and is used to amplify the electrical pulse signal with low noise and shape the waveform to obtain the shaped electrical pulse signal. A pulse amplitude analysis unit, connected to the signal amplification and shaping unit, is used to analyze the peak amplitude of the shaped electrical pulse signal; A multi-channel analyzer unit, connected to the pulse amplitude analysis unit, is used to count and statistically analyze the peak amplitude by energy level to obtain natural gamma spectrum data.

[0009] In one possible implementation, if the logging-while-drilling radioactive data is gamma-gamma density data, and the gamma-gamma density data includes formation bulk density and formation photoelectric absorption cross-section index, then the system includes: A sealed gamma radiation source is used to emit initial gamma rays into the formation to generate scattered gamma rays through the interaction between the initial gamma rays and the formation. A shielding and collimation assembly is used to collimate the scattered gamma rays toward the formation; At least two perovskite semiconductor detectors, serving as near and far detectors respectively, are arranged along the axial direction at different source distances of the sealed gamma radiation source to directly absorb scattered gamma rays scattered by the strata and generate electrical pulse signals. The electronics module includes: An energy window sorting unit is used to perform pulse amplitude analysis on the electrical pulse signals from the near detector and the far detector respectively, and obtain the count rate of the first energy window and the second energy window according to their respective pulse amplitudes, wherein the energy of the first energy window is greater than the energy of the second energy window; The count rate processing unit is used to determine the formation volume density based on the count rate of the far detector in the first energy window; and to determine the formation photoelectric absorption cross section index based on the count rate of the near detector in the second energy window.

[0010] In one possible implementation, the electronics module further includes: The wellbore effect compensation unit is used to correct the formation volume density using the count rate of the near detector in the first energy window, and to correct the formation photoelectric absorption cross section index using the count rate of the near detector in the second energy window, so as to obtain the compensated formation volume density and formation photoelectric absorption cross section index.

[0011] In one possible implementation, the system further includes an environment and attitude sensing module; the environment and attitude sensing module includes a triaxial accelerometer and / or a magnetometer for detecting the rotational phase of the instrument; The electronics module includes a binning processing unit, which performs rotation synchronization and azimuth binning processing on the radiometric logging data while drilling based on the rotation phase to obtain azimuth-based logging data.

[0012] In one possible implementation, the electronics module further includes a gain management and calibration unit; The gain management and calibration unit is used to perform energy calibration correction and gain drift compensation by periodically injecting standard calibration pulses or soft calibrations downhole, in order to adapt to high-temperature environments.

[0013] In one possible implementation, the system further includes a telemetry while drilling module and a power supply module; The telemetry while drilling module is used to transmit the radiometric logging data while drilling to the surface; The power module is used to provide high-voltage power to the perovskite semiconductor detector and low-voltage power to other modules of the logging-while-drilling radioactive logging system.

[0014] Secondly, the present invention also provides a drill string assembly that integrates the above-mentioned radioactive logging-while-drilling system.

[0015] Thirdly, the present invention also provides a method for logging while drilling (LWD) using radioactive materials, applied to the aforementioned LWD system, comprising: Using the at least one perovskite semiconductor detector, gamma rays from the formation are directly absorbed in the downhole drilling environment, and corresponding electrical pulse signals are generated. The electronic module processes the electrical pulse signal to obtain radioactive logging data while drilling, which includes at least one of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data.

[0016] The beneficial effects of this invention are as follows: The logging-while-drilling (LWD) radiometric logging system provided by this invention directly absorbs gamma rays from the formation and generates corresponding electrical pulse signals through a perovskite semiconductor detector, eliminating the light conversion and photoelectric amplification stages in the traditional scintillator-photomultiplier tube (PMT) system, thus improving energy resolution. Furthermore, the perovskite semiconductor detector is heat-resistant, improving the high-temperature resistance of the LWD radiometric logging system. Simultaneously, perovskite semiconductor materials (such as CsPbBr3) have a higher gamma-ray linear attenuation coefficient and a better signal-to-noise ratio than traditional NaI(Tl) scintillators, reducing the radiation source activity of the LWD radiometric logging system and enhancing its safety. The electronics module transforms the high-resolution potential of perovskite detector materials into high-performance output at the system level, enabling logging while drilling (LWD) of natural gamma counts, natural gamma energy spectra, and gamma-gamma density. This ensures the accuracy and real-time performance of LWD radiometric logging data under conditions of high rotation speed, high vibration, and high count rate. The protective enclosure allows for high integration and miniaturization of the entire detection front end, reducing system power consumption and overcoming the industry bottleneck of high failure rates of traditional instruments in deep and ultra-deep wells. Therefore, the LWD radiometric logging system of this embodiment can operate stably under extreme high temperatures, strong vibration and shock, and strong magnetic fields, while providing better energy resolution, higher system integration and reliability, and improving the safety and accuracy of LWD radiometric logging. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the drilling radioactive logging system provided by the present invention. Figure 2 This is another structural schematic diagram of the radioactive logging-while-drilling system provided by the present invention; Figure 3 This is another structural schematic diagram of the radioactive logging-while-drilling system provided by the present invention. Figure 4 Another structural schematic diagram of the radioactive logging-while-drilling system provided by the present invention; Figure 5 This is a schematic diagram of an embodiment of the radioactive logging-while-drilling method provided by the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] In the description of the embodiments of the present invention, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0021] The terms "first," "second," etc., used in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a technical feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] Before demonstrating the embodiments, the following terms will be explained.

[0024] Logging While Drilling (LWD) is a logging technology performed simultaneously during the drilling process. It places extremely high demands on the high temperature resistance, shock resistance, and reliability of the instruments, which is the application scenario that the embodiments of this application aim to adapt to.

[0025] The radioactive logging-while-drilling system provided by this invention is applicable to deep wells, ultra-deep wells, high geothermal wells, horizontal wells, and geological steering scenarios. In practical applications, its output high-precision GR, SGR, RHOB, and Pe data can be jointly interpreted with drilling parameters such as neutron-density, acoustic imaging, and resistivity imaging, thereby improving the efficiency of sand / mud identification, carbonate rock Pe discrimination, thin interbedded layer identification, and geological steering decision-making.

[0026] This invention provides a radioactive logging-while-drilling system, logging method, and drill string assembly. The technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] Figure 1 This is a schematic diagram of the structure of the radioactive logging-while-drilling system provided by the present invention. The radioactive logging-while-drilling system includes: At least one perovskite semiconductor detector 101 is used to directly absorb gamma rays from the strata and generate corresponding electrical pulse signals.

[0028] The radioactive logging-while-drilling system described in this invention can be integrated into the drill string assembly (Bottom) The system operates within the Hole Assembly (BHA), such as in the BHA stabilizer or near-bit sub. In this embodiment, the logging-while-drilling (LWD) radiometric system is installed inside the drilling instrument for logging operations during drilling.

[0029] The number of perovskite semiconductor detectors 101 is at least one, which can be configured in counting / spectral mode or in density mode as a near / far-spacing dual detector. The sensitive material of this perovskite semiconductor detector is CsPbBr3, MAPbI3, FAPbBr3, or a mixture thereof, or other semiconductor materials with a perovskite crystal structure and their derivatives [A1]. Its working principle is direct energy conversion. When gamma rays from the strata are incident on the detector crystal, electron-hole pairs are directly generated within it and rapidly collected by electrodes, thereby outputting an electrical pulse signal with an amplitude proportional to the gamma ray energy. The direct conversion mechanism of the perovskite semiconductor detector 101 eliminates the light conversion and photoelectric amplification stages in the traditional scintillator-photomultiplier tube (PMT) system, simplifying the signal chain from a physical perspective, effectively reducing energy conversion and transmission losses, and improving energy resolution. Furthermore, the perovskite semiconductor detector 101 is heat-resistant and can operate in a range of up to 300°C, which greatly improves the heat resistance of the logging-while-drilling system. At the same time, perovskite semiconductor materials (such as CsPbBr3) have a higher gamma-ray linear attenuation coefficient and a better signal-to-noise ratio than traditional NaI(Tl) scintillators, which reduces the radiation source activity of the logging-while-drilling system and can improve the safety of the logging-while-drilling system.

[0030] Electronic module 102 is electrically connected to the perovskite semiconductor detector and is used to process the electrical pulse signal to obtain logging-while-drilling (LWD) radiometric data, wherein the LWD radiometric data includes at least one of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data.

[0031] Specifically, the electronics module 102 and the perovskite semiconductor detector 101 can be electrically connected via high-temperature resistant and vibration-resistant cables. This module can be a specially designed high-temperature, low-noise circuit system, fully covering the entire process from signal conditioning to data processing. It includes a high-temperature, low-noise preamplifier, a pulse shaper, an analog-to-digital converter, and an FPGA-based processing unit. This module is programmed or configured to support the measurement of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data, transforming the high-resolution potential of the perovskite detector at the material level into high-performance output at the system level. This enables logging while drilling of natural gamma counts, natural gamma energy spectra, and gamma-gamma density, ensuring the accuracy and real-time performance of logging while drilling radioactive data under high rotation speed, high vibration, and high count rate conditions.

[0032] The protective package 103 includes a metal shockproof and high-pressure resistant shell, a heat insulation layer and a thermal channel disposed within the metal shockproof and high-pressure resistant shell, and a high vibration and impact resistant connector for fixing internal components, wherein the protective package is used to accommodate the perovskite semiconductor detector and the electronics module.

[0033] Specifically, the protective enclosure 103 is the physical foundation for ensuring the long-term stable operation of the entire system in extreme downhole environments. It employs a multi-layered structure. The outermost metal shock-resistant and high-pressure-resistant shell, made of high-strength martensitic stainless steel or similar alloys, acts as a mechanical barrier, directly withstanding the high pressure (exceeding 100 MPa), high-frequency vibration (>10 g RMS), and instantaneous impact (>50 g) of the drilling fluid. A thermal insulation layer and heat channels, located on the inner wall of the metal shell and composed of high-performance thermal insulation materials, mitigate the heat transfer from external high temperatures (up to 200-300°C) to the internal precision electronic components. Simultaneously, internal heat channels are designed to guide the heat generated by the electronic module 102 during operation to the shock-resistant and high-pressure-resistant metal shell, achieving thermal management. High-vibration- and impact-resistant connectors are used to internally fix all components, including detector crystals and circuit boards, employing an anti-loosening and buffered design to prevent short circuits, breakage, or displacement under severe vibration.

[0034] It is worth noting that the detector in the logging-while-drilling radioactive logging system of this embodiment is a perovskite semiconductor detector. Compared with existing detectors, it can effectively reduce energy conversion and transmission losses, improve energy resolution, and is small in size, easy to integrate, shock resistant, and not easily broken, thus improving the safety and accuracy of logging-while-drilling radioactive logging.

[0035] Understandably, the protective enclosure 103 in this embodiment houses the perovskite semiconductor detector 101 and the electronics module 102, integrating the entire logging-while-drilling (LWD) radiometric system into a dedicated protective enclosure 103. This eliminates the need for additional magnetic shielding and complex vacuum maintenance required by traditional PMTs, allowing for high integration and miniaturization of the entire detection front end. This reduces system power consumption and facilitates sharing of the short section space with other LWD modules such as resistivity and acoustic sensors, enabling multi-parameter measurements during LWD. This improves LWD efficiency and instrument reliability, and allows for long-term stable operation in high-vibration and high-impact LWD environments, solving the industry bottleneck of high failure rates for traditional instruments in deep and ultra-deep wells.

[0036] The logging-while-drilling (LWD) system provided by this invention directly absorbs gamma rays from the formation and generates corresponding electrical pulse signals through a perovskite semiconductor detector 101, eliminating the light conversion and photoelectric amplification stages in the traditional scintillator-photomultiplier tube (PMT) system and improving energy resolution. Furthermore, the perovskite semiconductor detector 101 is heat-resistant, improving the high-temperature resistance of the LWD system. Simultaneously, perovskite semiconductor materials (such as CsPbBr3) have a higher gamma-ray linear attenuation coefficient and a better signal-to-noise ratio than traditional NaI(Tl) scintillators, reducing the radiation source activity of the LWD system and enhancing its safety. The electronics module 102 transforms the high-resolution potential of the perovskite detector material into high-performance output at the system level, enabling logging while drilling (LWD) of natural gamma counts, natural gamma energy spectra, and gamma-gamma density. This ensures the accuracy and real-time performance of LWD radiometric logging data under conditions of high rotation speed, high vibration, and high count rate. The protective enclosure 103 enables the entire detection front end to be highly integrated and miniaturized, reducing system power consumption and solving the industry bottleneck of high failure rates of traditional instruments in deep and ultra-deep wells. Thus, the LWD radiometric logging system of this embodiment can operate stably under extreme high temperature, strong vibration, and strong magnetic field environments, while providing better energy resolution, higher system integration, and higher reliability, thereby improving the safety and accuracy of LWD radiometric logging.

[0037] In some embodiments of the present invention, the perovskite semiconductor material of the perovskite semiconductor detector is selected from at least one of CsPbBr3, MAPbI3, and FAPbBr3, or is other semiconductor materials having a perovskite crystal structure and their derivatives; such as Figure 2 As shown, Figure 2 This is a schematic diagram of another logging-while-drilling (LWD) radioactive logging system provided by the present invention. If the LWD radioactive logging data is natural gamma-ray count data, the electronics module 102 includes: The bias power supply unit 1021 is electrically connected to the perovskite semiconductor detector and is used to provide a stable bias voltage to the perovskite semiconductor detector. The signal amplification and shaping unit 1022 is electrically connected to the perovskite semiconductor detector and is used to perform low-noise amplification and waveform shaping on the electrical pulse signal to obtain the shaped electrical pulse signal. The counting window unit 1023 is used to count the shaped electrical pulse signal to obtain natural gamma count data.

[0038] Specifically, when the logging-while-drilling radiometric data is natural gamma count data, the logging-while-drilling radiometric system is used to perform natural gamma count measurement (GR-LWD). The electronics module 102 is equipped with a bias power supply unit 1021: electrically connected to the perovskite semiconductor detector 101, providing a stable DC high voltage of 100–600 V to the perovskite semiconductor detector 101 to form a uniform electric field in the crystal and ensure complete charge collection. Specifically, it can be a high-temperature and high-pressure resistant module or a circuit constructed from discrete components.

[0039] The signal amplification and shaping unit 1022, acting as a low-noise front end, is directly coupled to the output of the perovskite semiconductor detector 101. It amplifies the microampere-level or weaker electrical pulse signal output by the perovskite semiconductor detector 101 with low noise and then filters and shapes the waveform to obtain a standard pulse signal with uniform amplitude and fixed time width, thereby optimizing the signal-to-noise ratio and facilitating subsequent processing. It can be a cascaded unit consisting of a charge-sensitive preamplifier and a main amplifier / shaping amplifier.

[0040] The counting window unit 1023 receives the shaped electrical pulse signal and can set one or more energy thresholds. It accumulates and counts pulses exceeding the thresholds to obtain the count rate (cps) data of the shaped electrical pulse signal, i.e., the natural gamma count data. The counting window unit 1023 can be a comparator, a counter, or a logic module for clock management and memory control.

[0041] Understandably, the natural radioactive gamma in the formation is directly converted into electrical pulses by the perovskite detector. After processing by the electronics module, a count rate curve is obtained. Through the coordinated work of the bias power supply unit 1021, the signal amplification and shaping unit 1022, and the counting window unit 1023, the accurate measurement of natural gamma count data is realized, providing an immediate basis for the division of sand and mud interbedded layers, geological guidance, and stratigraphic evaluation.

[0042] In some embodiments of the present invention, such as Figure 3 As shown, Figure 3 This is a schematic diagram of another logging-while-drilling (LWD) radioactive logging system provided by the present invention. If the LWD radioactive logging data is natural gamma ray spectroscopy data, the electronics module 102 includes: The bias power supply unit 1021 is electrically connected to the perovskite semiconductor detector and is used to provide a stable bias voltage to the perovskite semiconductor detector. The signal amplification and shaping unit 1022 is electrically connected to the perovskite semiconductor detector and is used to perform low-noise amplification and waveform shaping on the electrical pulse signal to obtain the shaped electrical pulse signal. The pulse amplitude analysis unit 1024 is connected to the signal amplification and shaping unit and is used to analyze the peak amplitude of the shaped electrical pulse signal. The multi-channel analyzer unit 1025 is connected to the pulse amplitude analysis unit and is used to count and statistically analyze the peak amplitude according to the energy level to obtain natural gamma spectrum data.

[0043] Specifically, when the logging-while-drilling radioactive data is natural gamma spectral data, the logging-while-drilling radioactive system is used to perform natural gamma spectral measurement (SGR-LWD). The bias power supply unit 1021 and the signal amplification and shaping unit 1022 configured in the electronics module 102 are the same as in the above embodiment, and will not be described again here.

[0044] Electronics module 102 is equipped with a pulse amplitude analysis unit 1024, which measures the peak voltage of the shaped electrical pulse signal. This voltage directly corresponds to the energy of the incident gamma rays, and outputs the peak amplitude of the shaped electrical pulse signal. The pulse amplitude analysis unit can be implemented using an analog-to-digital converter (ADC), a dedicated digital signal processor (DSP), and a highly stable clock source. The DSP serves as the processing core, and its internally embedded digital peak detection algorithm is used to analyze the digital waveform sequence sent by the ADC in real time. Through comparison and latching, it accurately finds the maximum amplitude (peak amplitude) of each pulse waveform and records the corresponding digital quantity. The highly stable clock source provides a precise timing reference for the ADC and FPGA, ensuring the synchronization of sampling and processing.

[0045] The Multi-Channel Analyzer (MCA) 1025 receives peak amplitude data from the pulse amplitude analysis unit and classifies it into corresponding energy channels based on the magnitude (i.e., energy) of the peak amplitude for counting, forming an energy spectrum and outputting natural gamma energy spectrum data. The MCA can be implemented using a DSP and high-speed memory. The high-speed memory uses the block memory within the FPGA or an external high-temperature resistant SRAM / DRAM. A portion of it is configured as a spectrum memory; the DSP internally implements an energy-memory address translation algorithm. The DSP performs a "read-increment-write" operation on the corresponding storage cell in the spectrum memory to accumulate the count of the corresponding energy event and obtain the energy spectrum. Through peak position identification and area integration of the 1.46 / 1.76 / 2.62 MeV peaks, the contents of K, U, and Th, as well as clay parameters, are calculated in real time. The MAC has at least 256 channels. By finely dividing the gamma-ray energy range into at least 256 scales, it ensures clear differentiation of characteristic radioactive peaks of potassium, uranium, and thorium in the formation, thereby enabling real-time quantitative analysis of formation elements during drilling.

[0046] Understandably, the natural radioactive gamma rays in the formation are directly converted into electrical pulses by the perovskite detector. After processing by the electronics module, energy spectrum data is obtained. Through the coordinated work of the bias power supply unit 1021, the signal amplification and shaping unit 1022, the pulse amplitude analysis unit 1024, and the multi-channel analyzer unit 1025, the accurate measurement of the natural gamma energy spectrum data is realized, and the energy spectrum data of K, U, and Th contents are resolved, providing an immediate basis for the division of sand and mud interbedded layers, geological guidance, and stratigraphic evaluation.

[0047] It is worth noting that, in order to ensure the stability of the energy spectrum in a wide downhole temperature range (-20~260℃), the perovskite semiconductor detector 101 can be placed in a closed-loop temperature-controlled environment and provided with a highly stable operating voltage through the bias power supply unit 1021.

[0048] In some embodiments of the present invention, such as Figure 4 As shown, Figure 4 This is a schematic diagram of another radioactive logging-while-drilling system provided by the present invention. If the radioactive logging-while-drilling data is gamma-gamma density data, and the gamma-gamma density data includes formation bulk density and formation photoelectric absorption cross-section index, then the system includes: A sealed gamma radiation source 104 is used to emit initial gamma rays into the formation to generate scattered gamma rays through the interaction between the initial gamma rays and the formation. The shielding and collimation component 105 is used to collimate the scattered gamma rays toward the formation. At least two perovskite semiconductor detectors 101, serving as near and far detectors respectively, are arranged along the axial direction at different source distances of the sealed gamma radiation source to directly absorb scattered gamma rays scattered by the strata and generate electrical pulse signals. The electronics module 102 includes: The energy window sorting unit 1026 is used to perform pulse amplitude analysis on the electrical pulse signals from the near detector and the far detector respectively, and obtain the count rate of the first energy window and the second energy window according to their respective pulse amplitudes, wherein the energy of the first energy window is greater than the energy of the second energy window. The count rate processing unit 1027 is used to determine the formation volume density based on the count rate of the far detector in the first energy window; and to determine the formation photoelectric absorption cross section index based on the count rate of the near detector in the second energy window.

[0049] Specifically, the logging-while-drilling radioactive system includes a sealed gamma radiation source, such as ¹³ 7 The Cs sealed source, a sealed gamma radiation source, is precisely installed in the source chamber and pre-aligned before being lowered into the well. To achieve accurate measurement geometry, the system is equipped with a shielding and collimation assembly made of multi-layered high-Z materials such as tungsten alloy. This assembly rigorously shields the radiation source, preventing direct illumination of the detector. A replaceable collimator module forms a directional radiation cone beam pointing towards the wellbore wall, ensuring that the gamma rays primarily irradiate the formation. Through Compton scattering and the photoelectric effect with the formation, detectable scattered gamma rays are generated.

[0050] To achieve high-precision density measurements insensitive to wellbore effects, at least two perovskite semiconductor detectors are employed, forming a near / far dual-detector configuration. These detectors are positioned axially at different distances from the sealed gamma-ray source. For example, the near detector can be positioned at a shorter source distance (typically 15–25 cm), making it more sensitive to the effects of drilling fluid, wellbore variations, and mud cake. The far detector can be positioned at a longer source distance (typically 35–50 cm), allowing for deeper detection, and the received scattered gamma rays primarily carry information about formation volume density. Both perovskite semiconductor detectors utilize perovskite semiconductor materials (such as CsPbBr3) to efficiently convert the received scattered gamma rays into electrical pulse signals.

[0051] The electronics module includes an energy window sorting unit that analyzes the pulse amplitude of electrical pulse signals from the near and far detectors. Based on the principle of gamma-ray interaction with the formation—that Compton scattering dominates the high-energy portion and the photoelectric effect dominates the low-energy portion—the energy window sorting unit sets two energy windows: a high-energy window (the first energy window) for Compton counting (primarily reflecting density information) and a low-energy window (the second energy window) for estimating the photoelectric index Pe. The energy window sorting unit outputs the count rates of the near and far detectors in real time within each of the two energy windows.

[0052] The count rate processing unit is the core of the density interpretation algorithm. First, based on the count rate of the far detector in the first energy window (which is most sensitive to formation density), the apparent volumetric density of the formation is calculated. Therefore, based on the high-energy-window count rate N_far_high of the far detector, a formation volumetric density ρ_b_apparent is calculated using a pre-calibrated relational formula (usually a nonlinear function). The far detector has a long source distance and a greater detection depth, receiving primarily deep-scattered signals from the formation. It is relatively less directly affected by the drilling fluid within the wellbore, thus its count rate has a stronger and more direct correlation with the formation volumetric density, thereby improving the accuracy of the formation volumetric density. Simultaneously, because the near detector has a shallow detection depth and is extremely sensitive to the wellbore environment (mud cake, drilling fluid), its low-energy-window count rate has high statistical accuracy and a strong signal, and its response contains rich information on the formation photoelectric effect. Therefore, based on the count rate information of the near detector in the second energy window, the formation photoelectric absorption cross-section index is determined, improving the accuracy of the formation photoelectric absorption cross-section index.

[0053] In some embodiments of the present invention, the electronics module further includes: a wellbore effect compensation unit, used to correct the formation volume density using the count rate of the near detector in the first energy window, and to correct the formation photoelectric absorption cross section index using the count rate of the near detector in the second energy window, so as to obtain the compensated formation volume density and formation photoelectric absorption cross section index.

[0054] Specifically, the core algorithm of the wellbore effect compensation unit is based on the following physical understanding: the count rate of the near detector is much more affected by wellbore environmental factors such as wellbore diameter changes, drilling fluid density, and mud cake thickness than that of the far detector due to its proximity to the source; while the count rate of the far detector mainly reflects formation characteristics, but also retains some wellbore influence. Therefore, the count rate N_near_high of the near detector in the first energy window is used as a direct measure of the wellbore environment's interference with density measurement, and a compensation model (such as multiple linear regression or nonlinear mapping) is established. This compensation model takes the formation volume density ρ_b_apparent and N_near_high as inputs, and eliminates the wellbore contribution represented by N_near_high through the algorithm, outputting the compensated formation volume density ρb, which is closer to the true value.

[0055] The wellbore effect compensation unit utilizes the count rate N_near_low of the near-detector in the second energy window as a direct measure of the interference of the wellbore environment on photoelectric effect measurements. Since low-energy gamma rays are more easily absorbed by the wellbore medium, N_near_low is extremely sensitive to changes in the properties of the mud cake and drilling fluid. The compensation model uses N_near_low to correct the apparent photoelectric absorption cross-section index Pe_apparent, outputting a compensated and more reliable formation photoelectric absorption cross-section index Pe. This effectively suppresses the wellbore / mud cake effect, improves the robustness of the density-Pe joint interpretation, and maintains curve stability and thin-layer resolution even under high well velocity and rotation conditions.

[0056] In one specific implementation, a linear / nonlinear coupling model of the apparent density of the far detector and the wellbore response of the near detector can be established, and the compensation coefficients can be solved online using least squares or Kalman filtering to output the compensated formation volume density ρb.

[0057] Understandably, this embodiment utilizes the responses of the near-detector in two characteristic energy windows—high and low—to correct ρb and Pe. The high-energy window count (N_near_high) primarily corrects for wellbore interference with Compton scattering (density), while the low-energy window count (N_near_low) primarily corrects for wellbore interference with photoelectric absorption (Pe). This provides a more comprehensive physical basis for compensation, fundamentally improves correction accuracy, enhances the robustness of interpretation under complex wellbore conditions, and optimizes geological interpretation and fluid identification capabilities.

[0058] In some embodiments of the present invention, the system further includes an environment and attitude sensing module and a sub-bin module; the environment and attitude sensing module includes a triaxial accelerometer and / or a magnetometer for detecting the rotational phase of the instrument; The electronics module includes a binning processing unit, which performs rotation synchronization and azimuth binning processing on the radiometric logging data while drilling based on the rotation phase to obtain azimuth-based logging data.

[0059] Specifically, the environment and attitude sensing module, as an independent and critical subsystem, is integrated within or adjacent to the protective enclosure 103, and includes at least a triaxial accelerometer and / or a magnetometer. During drilling, the drill assembly (BHA) drives the entire instrument to rotate at high speed within the wellbore. At this time, the triaxial accelerometer accurately senses the periodic centrifugal acceleration changes caused by the instrument's rotation, while the magnetometer measures its azimuth angle change relative to the Earth's magnetic field. Through real-time processing of these sensor signals, the real-time rotational phase of the instrument can be continuously and accurately detected and output, ranging from 0 to 360°. The environment and attitude sensing module also integrates temperature and pressure sensors for real-time monitoring of temperature and pressure in extreme downhole environments, providing input for system health management and data correction.

[0060] The binning unit synchronously acquires two types of data streams with high temporal resolution: one is each gamma photon event (and its pulse amplitude) from the perovskite detector 101, and the other is rotational phase, temperature, and pressure data from the environment and attitude measurement module. Each gamma event is tagged with a precise timestamp; the processing algorithm associates each gamma event with the precise rotational phase of the instrument at the moment of its occurrence based on the timestamp; the system divides the full rotation (0-360°) into several equally divided sectors (e.g., 16, 32, or 64 azimuth bins). Then, all radioactive events with phase tags are assigned and accumulated into the corresponding azimuth bins according to their phase values. This azimuth binning statistics are performed simultaneously for different measurement modes: For natural gamma count data (GR), the total count in each azimuth box is counted to generate a set of azimuth gamma (AzGR) curves.

[0061] For natural gamma spectral data (SGR), pulse amplitude analysis is performed independently in each azimuth box, and the energy spectrum in that azimuth is accumulated to generate azimuth energy spectrum (AzSGR) data, which can be further used to calculate the K, U, and Th contents in different azimuths.

[0062] For gamma-gamma density data (RHOB), the counts of near and far detectors are statistically analyzed by azimuth box, and then the dual detector ratio calculation and compensation algorithm is executed independently in each box, finally outputting the azimuth density (AzRHOB) and azimuth photoelectric index (AzPe) curves.

[0063] To improve the signal-to-noise ratio, especially under high drilling speed conditions, the binning processing unit performs moving average or adaptive filtering on the data in each bin.

[0064] Understandably, the azimuth output of this embodiment enhances the ability to identify wellbore eccentricity, mud cake inhomogeneity, and bedding dip angles. It is based on magnetic / gyro phase output of 0–360° azimuth gamma / energy spectrum / density curves.

[0065] In some embodiments of the present invention, the electronics module further includes a gain management and calibration unit; the gain management and calibration unit is used to perform energy calibration correction and gain drift compensation by periodically injecting standard calibration pulses or soft calibrations downhole to adapt to high-temperature environments.

[0066] Specifically, the electronics module integrates a gain management and calibration unit designed for extreme environments. This unit is a closed-loop control system integrating hardware generation and software algorithms, including a calibration signal generator: the unit contains a highly stable reference voltage source and a precision waveform generation circuit, capable of generating standard calibration pulses with known amplitude and shape. This pulse physically simulates the ideal electrical signal output by the perovskite detector. Simultaneously, the system also supports a "soft calibration" mode, where a digitized reference signal is directly injected into the processing link via the FPGA for logic function verification.

[0067] Periodic injection control logic: Managed by the system's main FPGA, it automatically initiates a calibration cycle according to a preset time interval (e.g., every minute) or trigger condition (such as when a significant temperature change is detected). During this process, standard calibration pulses or soft calibration signals are periodically injected into the input of the signal processing link, completely simulating a real gamma event.

[0068] Signal Acquisition and Parameter Analysis: The electronics module performs end-to-end processing on the injected calibration signal. The gain management and calibration unit accurately measures the final digital output (e.g., memory address in the MCA) of the known signal after it has passed through the system. Adaptive Correction and Compensation: The algorithm within the unit compares the measured output with the standard value in real time. Energy Calibration Correction: If the output channel address shifts, the algorithm updates the energy-channel address mapping to ensure that characteristic peaks in the energy spectrum (e.g., ¹³) are corrected. 7 The peak position of Cs (0.662 MeV peak) remains accurate, which is the basis for high-precision energy dispersive spectroscopy (SGR) and correct energy window division (RHOB). Gain drift compensation: If the offset exceeds the predetermined tolerance, it indicates that the system gain has drifted due to temperature changes. The unit will automatically generate adjustment commands to dynamically fine-tune the gain of the preamplifier or the bias voltage of the detector, so that the system gain returns to the nominal value, thereby adapting to the changes in semiconductor characteristics and circuit parameters caused by high-temperature environments. The entire process is ensured to be completed automatically and silently in the downhole background without interrupting normal logging data acquisition, achieving online, real-time performance maintenance.

[0069] In some embodiments of the present invention, the logging-while-drilling radioactive logging system further includes a logging-while-drilling telemetry module and a power supply module; the logging-while-drilling telemetry module is used to transmit the logging-while-drilling radioactive logging data to the surface; the power supply module is used to provide high-voltage power to the perovskite semiconductor detector and low-voltage power to other modules of the logging-while-drilling radioactive logging system.

[0070] Specifically, the logging-while-drilling module can be one or a combination of mud pulse, electromagnetic, or wired drill pipe. It transmits and stores real-time radiometric logging data from the drilling process back to the surface via mud pulse, electromagnetic, or wired drill pipe.

[0071] This application provides a drilling tool assembly that integrates the radioactive logging-while-drilling system described in the above embodiments.

[0072] Figure 5 This is a schematic flowchart of an embodiment of the radioactive logging-while-drilling method provided by the present invention. The method is applied to the aforementioned radioactive logging-while-drilling system, which is installed inside the drilling instrument and used to perform logging simultaneously with drilling. Figure 5 As shown, the radioactive logging-while-drilling method includes: S501. Using the at least one perovskite semiconductor detector, gamma rays from the formation are directly absorbed in the downhole drilling environment, and corresponding electrical pulse signals are generated. S502. The electronic module processes the electrical pulse signal to obtain radioactive logging data while drilling, wherein the radioactive logging data while drilling includes at least one of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data.

[0073] like Figure 5 As shown, the radioactive logging-while-drilling method provided in this embodiment is specifically applied to the radioactive logging-while-drilling system as defined in the preceding claims, and its execution process is as follows: As the drill bit breaks through the formation and the drill string rotates forward, at least one perovskite semiconductor detector installed near the drill bit begins operation. The sensitive material of this detector is CsPbBr3, MAPbI3, FAPbBr3, or structurally equivalent derivatives. When gamma rays from the formation (whether natural gamma emitted by a naturally occurring radionuclide or scattered gamma generated by an artificial source in density mode) are incident on the detector crystal, their energy is directly absorbed, and electron-hole pairs are instantaneously generated within the crystal through the photoelectric effect or Compton effect. These charge carriers are rapidly and efficiently collected under the influence of the electric field inside the detector, thus directly outputting an electrical pulse signal. The amplitude of this pulse is proportional to the energy of the incident gamma photon, and its generation process completely avoids the indirect, inefficient, and noisy conversion chain of "gamma photon → scintillation light → photoelectron" in traditional technologies.

[0074] The electrical pulse signal is immediately sent to the adjacent integrated high-temperature, low-noise electronics module. This module operates stably in the high-temperature (up to 260°C), high-vibration downhole environment, performing a series of signal processing steps: Front-end processing: A low-noise preamplifier initially amplifies the weak pulses, and a pulse shaping circuit optimizes the signal-to-noise ratio and determines the time and amplitude characteristics.

[0075] Pattern processing and data generation: Based on pre-configuration, the electronics module enters a specific operating mode, thereby transforming the raw signal into valuable logging data. In Natural Gamma Counting (GR) mode: The module counts all pulses exceeding a threshold, generating a count rate curve (GR curve) that varies with depth. This mode can be configured to perform omnidirectional counting using a single detector or to achieve azimuth gamma imaging (AzGR) in conjunction with an azimuth sensor.

[0076] In Natural Gamma Spectrometry (SGR) mode: The module's Multichannel Analyzer (MCA) function accurately classifies all pulses by amplitude (i.e., energy), accumulating them to form a natural gamma spectrum. By identifying and integrating the characteristic peaks of potassium (K - 1.46 MeV), uranium (U - 1.76 MeV), and thorium (Th - 2.62 MeV) in the spectrum, the content of K, U, and Th in the formation is calculated in real time. Thanks to the perovskite detector's high energy resolution of better than 1%, the characteristic peaks are clearly separated, and the calculation accuracy is significantly improved.

[0077] In Gamma-Gamma Density (RHOB) mode: The detector assembly is configured as a near / far-spot dual-detector system. The electronics module simultaneously acquires signals from both the near and far detectors and performs energy window sorting (typically, a high-energy window reflects density information dominated by Compton scattering, and a low-energy window reflects lithological information dominated by the photoelectric effect). The module first calculates the ratio of the high-energy window count rate of the far detector or the high-energy window count rate of the near and far detectors to obtain the apparent density; simultaneously, it analyzes the relationship between the low-energy window count and the high-energy window count to obtain the apparent photoelectric absorption cross-section index (Pe). Subsequently, real-time compensation is performed using the near detector count (especially the high-energy window count), which is more sensitive to wellbore effects, ultimately outputting a corrected, high-precision formation bulk density (ρb) and photoelectric absorption cross-section index (Pe) curve. Azimuth density imaging (AzRHOB) can also be generated in this mode. The entire data processing process is highly real-time, and the results can be uploaded to the ground via telemetry methods such as mud pulses.

[0078] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware (such as a processor, controller, etc.), and the computer program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0079] The above provides a detailed description of the logging-while-drilling radioactive logging system, logging method, and drill string assembly provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, those skilled in the art will recognize that there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A radioactive logging-while-drilling system, characterized in that, The radioactive logging-while-drilling system is installed inside the drilling instrument and is used to perform logging while the drilling instrument is drilling. The radioactive logging-while-drilling system includes: At least one perovskite semiconductor detector is used to directly absorb gamma rays from the strata and generate corresponding electrical pulse signals. An electronics module, electrically connected to the perovskite semiconductor detector, is used to process the electrical pulse signal to obtain logging-while-drilling (LWD) data, wherein the LWD data includes at least one of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data. The protective package includes a metal shockproof and high-pressure resistant shell, a heat insulation layer and a thermal channel disposed within the metal shockproof and high-pressure resistant shell, and a high vibration and shock resistant connector for fixing internal components, wherein the protective package is used to house the perovskite semiconductor detector and the electronics module.

2. The radioactive logging-while-drilling system according to claim 1, characterized in that, The perovskite semiconductor material of the perovskite semiconductor detector is selected from at least one of CsPbBr3, MAPbI3, and FAPbBr3, or other semiconductor materials and their derivatives having a perovskite crystal structure. If the logging-while-drilling radioactive data is natural gamma count data; the electronics module includes: A bias power supply unit, electrically connected to the perovskite semiconductor detector, is used to provide a stable bias voltage to the perovskite semiconductor detector; The signal amplification and shaping unit is electrically connected to the perovskite semiconductor detector and is used to amplify the electrical pulse signal with low noise and shape the waveform to obtain the shaped electrical pulse signal. The counting window unit is used to count the shaped electrical pulse signal to obtain natural gamma count data.

3. The radioactive logging-while-drilling system according to claim 1, characterized in that, If the logging-while-drilling radioactive data is natural gamma spectral data; the electronics module includes: A bias power supply unit, electrically connected to the perovskite semiconductor detector, is used to provide a stable bias voltage to the perovskite semiconductor detector; The signal amplification and shaping unit is electrically connected to the perovskite semiconductor detector and is used to amplify the electrical pulse signal with low noise and shape the waveform to obtain the shaped electrical pulse signal. A pulse amplitude analysis unit, connected to the signal amplification and shaping unit, is used to analyze the peak amplitude of the shaped electrical pulse signal; A multi-channel analyzer unit, connected to the pulse amplitude analysis unit, is used to count and statistically analyze the peak amplitude by energy level to obtain natural gamma spectrum data.

4. The radioactive logging-while-drilling system according to claim 1, characterized in that, If the logging-while-drilling radioactive data is gamma-gamma density data, and the gamma-gamma density data includes formation bulk density and formation photoelectric absorption cross-section index; then the system includes: A sealed gamma radiation source is used to emit initial gamma rays into the formation to generate scattered gamma rays through the interaction between the initial gamma rays and the formation. A shielding and collimation assembly is used to collimate the scattered gamma rays toward the formation; At least two perovskite semiconductor detectors, serving as near and far detectors respectively, are arranged along the axial direction at different source distances of the sealed gamma radiation source to directly absorb scattered gamma rays scattered by the strata and generate electrical pulse signals. The electronics module includes: An energy window sorting unit is used to perform pulse amplitude analysis on the electrical pulse signals from the near detector and the far detector respectively, and obtain the count rate of the first energy window and the second energy window according to their respective pulse amplitudes, wherein the energy of the first energy window is greater than the energy of the second energy window; The count rate processing unit is used to determine the formation volume density based on the count rate of the far detector in the first energy window; and to determine the formation photoelectric absorption cross section index based on the count rate of the near detector in the second energy window.

5. The radioactive logging-while-drilling system according to claim 4, characterized in that, The electronics module also includes: The wellbore effect compensation unit is used to correct the formation volume density using the count rate of the near detector in the first energy window, and to correct the formation photoelectric absorption cross section index using the count rate of the near detector in the second energy window, so as to obtain the compensated formation volume density and formation photoelectric absorption cross section index.

6. The radioactive logging-while-drilling system according to claim 1, characterized in that, The system also includes an environment and attitude sensing module; the environment and attitude sensing module includes a triaxial accelerometer and / or a magnetometer for detecting the rotational phase of the instrument; The electronics module includes a binning processing unit, which performs rotation synchronization and azimuth binning processing on the radiometric logging data while drilling based on the rotation phase to obtain azimuth-based logging data.

7. The radioactive logging-while-drilling system according to claim 1, characterized in that, The electronics module also includes a gain management and calibration unit; The gain management and calibration unit is used to perform energy calibration correction and gain drift compensation by periodically injecting standard calibration pulses or soft calibrations downhole, in order to adapt to high-temperature environments.

8. The radioactive logging-while-drilling system according to claim 1, characterized in that, The system also includes a telemetry while drilling module and a power supply module; The telemetry while drilling module is used to transmit the radiometric logging data while drilling to the surface; The power module is used to provide high-voltage power to the perovskite semiconductor detector and low-voltage power to other modules of the logging-while-drilling radioactive logging system.

9. A drill string assembly, characterized in that, The drilling assembly integrates a radioactive logging system as described in any one of claims 1-8.

10. A method for radioactive logging while drilling, characterized in that, A logging-while-drilling (LWD) radioactive logging system as described in any one of claims 1 to 8, wherein the LWD radioactive logging system is installed inside a drilling instrument and is used to perform logging while the drilling instrument is drilling, the LWD radioactive logging method comprising: Using the at least one perovskite semiconductor detector, gamma rays from the formation are directly absorbed in the downhole drilling environment, and corresponding electrical pulse signals are generated. The electronic module processes the electrical pulse signal to obtain radioactive logging data while drilling, which includes at least one of natural gamma count data, natural gamma energy spectrum data, and gamma-gamma density data.

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