Underground real-time double-dessert identification method based on laser-induced breakdown spectroscopy

Abstract

The invention provides an underground real-time double-dessert identification method based on a laser-induced breakdown spectroscopy. The underground real-time double-dessert identification method based on the laser-induced breakdown spectroscopy comprises the following steps: step 1, establishing a breakdown spectrum database of representative rock samples and formation fluid through a laser-induced breakdown experiment; 2, emitting high-energy laser to break down drilling cuttings and fluid in the well to obtain a plasma spectrum; 3, comparing the obtained plasma spectrum with the breakdown spectrum database to obtain reservoir real-time key parameter quantitative data; and 4, calculating real-time dessert distribution of the reservoir according to the obtained data, and drawing a single well dessert distribution profile. According to the underground real-time double-dessert identification method based on the laser-induced breakdown spectroscopy, reservoir dessert distribution can be efficiently and accurately identified in real time, errors caused by manual lithology identification are avoided, and fracturing design parameter optimization is effectively guided.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploitation, and in particular to an underground real-time double sweet spot identification method based on laser induced breakdown spectroscopy. Background Art

[0002] The exploitation of unconventional oil and gas is inseparable from hydraulic fracturing. The effect of hydraulic fracturing is based on the premise of high-quality wellbore trajectory and accurate selection of the transformation location in the later stage. However, the heterogeneity and anisotropy of unconventional oil and gas reservoirs make it easy for the drilling trajectory of horizontal wells to deviate from the target layer and enter the relatively poor geological sweet spot reservoir. In addition, the current logging method is time-consuming, and the interpretation results are affected by the subjective factors of the testers. This makes it difficult to accurately select the location of the fracturing transformation. The selection of layers and the determination of perforation positions in the current fracturing scheme are mostly based on experience, resulting in a large uncertainty in the implementation effect of hydraulic fracturing, which increases the cost of unconventional oil and gas exploitation. In order to reduce the input-output ratio of unconventional oil and gas resource exploitation, there is an urgent need for a method that can accurately and real-time obtain the formation information near the drill bit, timely guide the drilling trajectory, and improve the objectivity and accuracy of the interpretation of reservoir information.

[0003] At present, the most commonly used methods to obtain formation information are logging and mud logging. Among them, logging is the fastest way to obtain formation information, but there is still a long delay time. Sand is sampled from the wellhead, sorted in batches, flushed, and dried, and then the color, hardness, lithology and other characteristics of the cuttings are described. Finally, a logging profile is drawn and a logging report is written. The identification of the lithology of the cuttings is greatly affected by human subjective factors. With the continuous improvement of drilling technology, drilling efficiency is gradually improved, and the number of cuttings returned to the ground per unit time is also more and smaller. Lithology identification cannot fully meet the requirements of drilling operations in terms of efficiency or accuracy, and even misleads the later reservoir transformation. With the development of logging technology, logging while drilling (LWD) technology has gradually emerged, but the logging method is no different from before. Real-time and efficient acquisition of formation information is still a problem that plagues oil and gas development.

[0004] In the Chinese patent application with application number: CN202010504219.0, a shale gas sweet spot evaluation method based on gas carbon isotopes is involved, including the following steps: obtaining gas carbon isotope composition data while drilling; collecting geological logging data; drawing the gas carbon isotope composition data and geological logging data into a comprehensive profile; combining geological parameters and dividing the sweet spot layer according to the gas carbon isotope composition parameters. In the above manner, the method disclosed in the invention can be implemented after the vertical well is completed, effectively shortening the sweet spot evaluation cycle and improving the efficiency of oil and gas exploration.

[0005] In the Chinese patent application with the application number: CN202110807234.7, it involves a shale oil sweet spot detection system and data acquisition method based on nuclear magnetic resonance technology. An emission coil is arranged on the ground, and a nuclear magnetic resonance signal acquisition unit is configured with a ground signal receiving sensor and / or a downhole signal receiving sensor; a high-power alternating current source system on the ground supplies an alternating current with a frequency of the Larmor frequency into the emission coil on the ground; after cutting off the current pulse, the ground signal receiving sensor and / or the downhole signal receiving sensor are used to receive the nuclear magnetic resonance signals generated by different excitation pulses. The nuclear magnetic resonance signals received on the ground or in the well are processed to obtain the nuclear magnetic resonance T2 spectra at various positions within the underground shale oil reservoir, and based on the characteristics of the T2 spectra, the saturation of the producible shale oil within the shale oil reservoir and its distribution pattern on the exploration area plane are evaluated and predicted, thereby realizing the prediction of the distribution of high shale oil saturation sweet spot areas within the shale oil reservoir.

[0006] In the Chinese patent application with the application number: CN201811603533.3, it involves a method and device for δ13C isotope logging of multi-alkane component gases. According to the principle of spectral gas isotope detection, a δ13C isotope logging device for alkane component gases is used to detect the sample gas separated by a degasser from the drilling fluid carrying formation fluid information, and the δ13C isotope information in alkane component gases such as methane, ethane, and propane is detected to achieve the purpose of δ13C isotope logging of multi-alkane component gases. The isotope logging information of multi-alkane component gases can accurately realize reservoir correlation of oil and gas resources, evaluate water-flooded layers, guide geosteering, identify shale gas sweet spots, prevent the occurrence of drilling construction accidents, and improve the efficiency of oil and gas exploration and development.

[0007] In the Chinese patent application with the application number: CN202210539291.6, it involves a method for predicting comprehensive sweet spots of continental shale oil, including: obtaining the comprehensive sweet spot evaluation indexes of the area to be determined, where the comprehensive sweet spot evaluation indexes include geological sweet spot evaluation indexes and engineering sweet spot evaluation indexes; conducting experimental calibration on the comprehensive sweet spot evaluation indexes to obtain the parameters of each comprehensive sweet spot evaluation index and determine each comprehensive sweet spot evaluation index, where the comprehensive sweet spot evaluation index is the product of the normalized geological sweet spot index and the engineering sweet spot index; determining the prediction result of continental shale oil sweet spots according to the comprehensive sweet spot evaluation index, and analyzing the vertical distribution characteristics of continental shale oil sweet spots through an improved logging method; determining the lower limit value of the comprehensive sweet spot index according to the relationship between the vertical distribution characteristics of continental shale oil sweet spots and shale oil production, and applying the lower limit value to other areas to be determined to determine the exploration potential of their oil and gas resources.

[0008] The above prior arts are all quite different from the present invention and fail to solve the technical problems we want to solve. Therefore, we have invented a new downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy. Summary of the Invention

[0009] The object of the present invention is to provide a downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy that can identify the distribution of reservoir sweet spots in real time, efficiently, and accurately, avoiding the errors caused by manual lithology identification and effectively guiding the optimization of fracturing design parameters.

[0010] The object of the present invention can be achieved by the following technical measures: A downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy, the downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy includes:

[0011] Step 1, establish a breakdown spectral atlas database of representative rock samples and formation fluids through laser-induced breakdown experiments;

[0012] Step 2, emit high-energy laser to break down drilling cuttings and well fluids in the well to obtain plasma spectra;

[0013] Step 3, compare the obtained plasma spectra with the breakdown spectral atlas database to obtain quantitative data of key real-time reservoir parameters;

[0014] Step 4, calculate the real-time sweet spot distribution of the reservoir based on the obtained data and draw a single-well sweet spot distribution profile.

[0015] The object of the present invention can also be achieved by the following technical measures:

[0016] In Step 1, establish a breakdown spectral atlas database of various lithologies, mineral contents, and formation fluids according to laser-induced breakdown experiments. The lithologies include mudstone, sandstone, shale, and volcanic rock, and the formation fluids include drilling fluid, oil, gas, and water.

[0017] In Step 1, collect a large number of samples of drilling cuttings, drilling fluid, and reservoir fluids in the early stage of the research block. In particular, for drilling cuttings, a large number of indoor experiments need to be carried out on different mineral compositions or mineral contents under the same lithology to establish a relatively comprehensive breakdown spectral atlas database.

[0018] The downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy further includes, after Step 1, establishing a geological sweet spot evaluation method and an engineering sweet spot evaluation method according to lithology, mineral content, and formation fluid distribution.

[0019] When establishing the geological sweet spot evaluation method and the engineering sweet spot evaluation method, the geological sweet spot mainly considers lithology and fluid characteristics, and the engineering sweet spot mainly considers brittle mineral content, drilling time, and drilling mechanical specific energy.

[0020] In Step 2, a drilling tool with a geological parameter monitoring sub-section is used during the drilling operation. During the drilling process, cuttings flow towards the wellhead through the annulus. When passing through the geological parameter monitoring sub-section near the drill bit, they are captured and a laser breakdown experiment is conducted. The plasma spectrum obtained from laser breakdown of the mixed sample is transmitted to the ground.

[0021] In Step 2, the geological parameter monitoring sub-section contains a high-energy laser emission module inside. The captured mixed sample is broken down by a high-energy laser beam, and the generated breakdown spectrum is received by a receiver on the geological parameter monitoring sub-section and transmitted to the ground. After the geological parameter monitoring sub-section captures the mixed sample and conducts a laser breakdown experiment, capturing the breakdown spectrum and transmitting it to the ground is considered as one monitoring. The monitoring interval can be adjusted according to requirements but cannot be less than the time of one breakdown experiment.

[0022] In Step 3, the obtained plasma spectrum is compared with the breakdown spectrum atlas database on the ground to obtain the quantitative mineral content, lithology, and reservoir fluid conditions after removing the drilling fluid of the mixed sample.

[0023] In Step 3, the received plasma spectrum is first decomposed into solid, gas, and liquid spectrograms through Fourier transform, and then compared with the breakdown spectrum atlas database respectively to find the closest atlas and obtain corresponding data such as lithology, mineral content, and hydrocarbon content.

[0024] In Step 4, the data of the mineral content, lithology, and reservoir fluid of the mixed sample are input into the previously established geological sweet spot and engineering sweet spot evaluation methods to obtain a quantitative sweet spot index.

[0025] In Step 4, the geological sweet spot mainly considers lithology and fluid properties, while the engineering sweet spot mainly considers mineral content, drilling time, and mechanical specific energy at different depths.

[0026] The object of the present invention can also be achieved by the following technical measures: The downhole real-time dual sweet spot identification system based on laser-induced plasma emission spectroscopy uses the downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy to analyze the lithology and other formation parameters of the formation near the drill bit, and makes a real-time prediction of the distribution of formation sweet spots.

[0027] The downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy in the present invention includes: establishing a breakdown spectroscopy atlas database of representative rock samples and formation fluids through laser-induced breakdown experiments, where the representative rock samples include but are not limited to mudstone, sandstone, shale, volcanic rock, etc., and the formation fluids include but are not limited to drilling fluid, oil, gas, water, etc.; during the drilling process, a high-energy laser is emitted through a geological parameter monitoring sub-section above the drill bit to break down drill cuttings and wellbore fluids in the well to obtain plasma spectra and transmit them to the ground; comparing the monitored spectra with the atlas database to obtain quantitative data of real-time key parameters of the reservoir; calculating the real-time sweet spot distribution of the reservoir based on the obtained data and drawing a single-well sweet spot distribution profile. This method can identify the sweet spot distribution of the reservoir in real time, efficiently, and accurately, avoiding the errors caused by manual lithology identification and effectively guiding the optimization of fracturing design parameters.

[0028] The downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy can analyze the lithology and other formation parameters of the formation near the drill bit by obtaining the plasma emission spectra generated after a high-energy laser beam emitted by the upper sub-section of the drill bit breaks down the drill cuttings, and can provide real-time guidance for the drilling trajectory and predict the sweet spot distribution of the formation in real time. This method solves the disadvantages that only partial logging data can be obtained in real time during the current drilling process, and information such as lithology needs to be sampled and observed from the drill cuttings, can improve the drilling efficiency and quality, realize the integration of drilling - layer selection - fracturing plan formulation, and effectively shorten the time cycle from well completion to production.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] This method can effectively avoid the subjectivity and inefficiency caused by manual lithology identification, improve the accuracy of lithology identification, and at the same time can master the reservoir information in real time, solving the problems that some current logging information is affected by human subjective factors, there are errors in information acquisition, and the downhole formation information cannot be mastered in real time, making it impossible to evaluate and guide the drilling process in a timely manner and difficult to provide accurate data support for later reservoir transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the radiation process of particles in the plasma in a specific embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of the experimental process of laser-induced breakdown of surface drill cuttings in a specific embodiment of the present invention;

[0033] Figure 3 It is a schematic diagram of the position of the downhole geological parameter real-time monitoring sub-section in a specific embodiment of the present invention;

[0034] Figure 4Schematic diagram of the short - circuit operation for real - time monitoring of geological parameters in a specific embodiment of the present invention;

[0035] Figure 5 Spectrum diagram of a typical rock sample in a specific embodiment of the present invention;

[0036] Figure 6 Flowchart of a specific embodiment of the downhole real - time dual sweet - spot identification method based on laser - induced breakdown spectroscopy of the present invention;

[0037] Each label in the figure is respectively: 1, formation; 2, drill bit; 3, short - circuit for real - time monitoring of geological parameters; 4, cuttings; 3 - 1, plasma emission spectrum receiving device; 3 - 2, laser exciter; 3 - 3, laser beam; 3 - 4, plasma emission spectrum. Detailed implementation manners

[0038] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0039] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0040] As Figure 6 shown, Figure 6 is the flowchart of the downhole real - time dual sweet - spot identification method based on laser - induced breakdown spectroscopy of the present invention. The downhole real - time dual sweet - spot identification method based on laser - induced breakdown spectroscopy includes:

[0041] Step 1, establish a breakdown spectrum atlas database of various lithologies, mineral contents, formation fluids, etc. according to laser - induced breakdown experiments. The lithologies include, but are not limited to, mudstone, sandstone, shale, volcanic rock, etc., and the formation fluids include, but are not limited to, drilling fluid, oil, gas, water, etc.;

[0042] Collect a large number of samples such as cuttings, drilling fluid, reservoir fluids, etc. from the previous wells in the research block. Especially for cuttings, a large number of indoor experiments need to be carried out on different mineral compositions or mineral contents under the same lithology to establish a relatively comprehensive spectrum database.

[0043] Step 2, establish a geological sweet - spot evaluation method and an engineering sweet - spot evaluation method according to the distribution of lithology, mineral content, and formation fluid;

[0044] Geological sweet spots mainly consider lithology and fluid characteristics, while engineering sweet spots mainly consider brittle mineral content, drilling time, and drilling mechanical specific energy.

[0045] Step 3: During the drilling operation, use a drilling tool with a geological parameter monitoring sub-section. During the drilling process, cuttings flow towards the wellhead through the annulus. When passing through the geological parameter monitoring sub-section near the drill bit, they are captured and a laser breakdown experiment is conducted. The plasma spectrum obtained from laser breakdown of the mixed sample is transmitted to the ground.

[0046] The geological parameter monitoring sub-section contains a high-energy laser emission module inside. The captured mixed sample is broken down by a high-energy laser beam, and the generated breakdown spectrum is received by the receiver on the geological parameter monitoring sub-section and transmitted to the ground. After the geological parameter monitoring sub-section captures the mixed sample and conducts a laser breakdown experiment, capturing the breakdown spectrum and transmitting it to the ground is one monitoring. The monitoring interval can be adjusted according to requirements but cannot be less than the time of one breakdown experiment.

[0047] Step 4: Compare the obtained spectrum with the ground spectral library to obtain the quantitative mineral content, lithology, and reservoir fluid conditions after removing the drilling fluid of the mixed sample.

[0048] The received spectrum is first decomposed into solid, gas, and liquid spectrograms through Fourier transform, and then compared with the spectral library to find the closest spectra and obtain corresponding data such as lithology, mineral content, and hydrocarbon content.

[0049] Step 5: Substitute the data such as mineral content, lithology, and reservoir fluid of the mixed sample into the previously established geological sweet spot and engineering sweet spot evaluation methods to obtain a quantitative sweet spot index.

[0050] Geological sweet spots mainly consider lithology and fluid properties, while engineering sweet spots mainly consider mineral content, drilling time, and mechanical specific energy at different depths.

[0051] The present invention establishes a breakdown spectrum atlas database of representative rock samples and formation fluids through laser-induced breakdown experiments. The representative rock samples include, but are not limited to, mudstone, sandstone, shale, volcanic rock, etc., and the formation fluids include, but are not limited to, drilling fluid, oil, gas, water, etc. During the drilling process, multiple high-energy laser beams are emitted by the geological parameter real-time monitoring sub-joint above the drill bit. When the laser encounters the fluid and cuttings in the annulus, physical reactions occur. Due to the differences in the elemental composition of substances, different plasma emission spectra are generated. Then, the different plasma emission spectra are received by the reflection wave receivers above and below the laser emitter. The reflection wave is converted into the vibration of a permanent magnet DC electrode by an encoder and then transmitted to the ground through the casing. It is decoded by the ground receiver and compared with the database to obtain information such as the lithology, oil, gas, and water content of the current formation, so as to avoid the influence of subjective factors on the accuracy of well logging interpretation results and achieve the purpose of accurately and efficiently feeding back formation information.

[0052] The following are several specific embodiments of applying the present invention

[0053] Embodiment 1

[0054] In a specific Embodiment 1 of applying the present invention, in order to better implement the method, a large number of samples such as drilling cuttings, drilling fluid, and reservoir fluid in the study area need to be collected in advance. Especially for drilling cuttings, a large number of indoor laser-induced plasma emission spectroscopy experiments need to be carried out on different mineral compositions or mineral contents under the same lithology Figure 2 is a schematic diagram of the principle of laser-induced plasma emission spectroscopy experiment. In the laser-induced plasma emission spectroscopy experiment, a high-energy pulsed laser beam is focused on the surface of the sample. When the laser irradiance exceeds the breakdown threshold of the sample, the particles, molecules, and atoms in the laser ablation area will undergo multi-photon ionization to generate initial free electrons. The initial free electrons continue to absorb photons and accelerate, collide with atoms to ionize and generate new free electrons, and these electrons will repeat the behavior of the initial free electrons, continuously ionizing atoms, thus causing an avalanche effect and generating laser-induced plasma. The laser-induced plasma contains electrons, ions, atoms, molecules, and particles, etc., and is overall electrically neutral. Usually, the laser we use is a nanosecond pulsed laser with high output energy. The initial temperature of the plasma generated by such a laser can reach 10 4 to 10 5 K, and the initial electron density is 10 17 to 10 18 cm -3 . When the laser pulse ends, the excited particles in the plasma will transition from high energy levels to low energy levels ( Figure 1 ), and emit characteristic spectral lines. The wavelength λ can be expressed as:

[0055] λ = ch / (E k -E i ) (1)

[0056] where c is the speed of light, h is Planck's constant, E k is the energy of the high energy level, and E i is the energy of the low energy level

[0057] By establishing a relatively comprehensive spectral database as Figure 5 shown, different lithologies will produce wave peaks with different intensities in different bands after being broken down by laser. A mapping relationship is established between the plasma spectra of each lithology and various mineral contents, and at the same time, a mapping relationship is established between the liquid plasma spectrogram and the hydrocarbon content

[0058] During the drilling operation, connect the geological parameter real-time monitoring sub to above the drill bit as Figure 3As shown. During the process of the drill bit (2) drilling into the formation (1), cuttings (4) will be carried to the surface by the drilling fluid in the annulus. During this process, when the cuttings and the original fluids in the formation pass through the geological parameter real-time monitoring sub (3), they will be irradiated by the high-energy laser beam (3-3) emitted by the laser emitter (3-2) in the sub. The plasma emission spectrum (electromagnetic radiation spectrum) (3-4) generated by the interaction of the laser and the substance at the moment of irradiation is received by the spectrum receiver (3-1) on the geological parameter real-time monitoring sub.

[0059] The laser emitter and the spectrum receiver are distributed on the geological parameter real-time monitoring sub at a certain phase angle. In the present invention, the preferred phase angle is 120°.

[0060] Further, the plasma emission spectrum is converted into an electrical signal by the photodiode on the geological parameter real-time monitoring sub, and then converted into an electrical signal for controlling a permanent magnet DC motor through an encoder.

[0061] Further, the permanent magnet DC motor converts the electrical signal into vibration mechanical energy. The electrical signal is transmitted to the surface through the casing by the vibration intensity and vibration frequency. The surface receiver receives the vibration signal and converts the vibration signal into an electrical signal through a decoder, and then converts it into a spectrogram.

[0062] Further, the obtained spectrogram is compared with the spectrograms in the database to judge the formation lithology and formation fluid information at that moment. The obtained formation information is corresponded to the well depth. The location of the geological sweet spot is preferably selected according to the oil and gas bearing property, and the location of the engineering sweet spot is preferably selected according to the lithology and the indirectly obtained rock mechanical parameters, so as to obtain the distribution of the double sweet spots along the well depth trajectory.

[0063] Embodiment 2

[0064] In a specific Embodiment 2 of applying the present invention, in order to better implement the method, it is necessary to collect a large number of samples such as the previous drilling cuttings, drilling fluid and reservoir fluid in the research area in advance. Especially for the drilling cuttings, a large number of indoor laser-induced plasma emission spectrum experiments need to be carried out on different mineral compositions or mineral contents under the same lithology. Figure 2It is a schematic diagram of the experimental principle of laser-induced plasma emission spectroscopy. In the laser-induced plasma emission spectroscopy experiment, a high-energy pulsed laser beam is focused on the surface of the sample. When the laser irradiance exceeds the breakdown threshold of the sample, the particles, molecules, and atoms in the laser ablation zone will undergo multi-photon ionization to generate initial free electrons. The initial free electrons continue to absorb photons and accelerate, collide with atoms to ionize and generate new free electrons, and these electrons will repeat the behavior of the initial free electrons, continuously ionizing the atoms, thus causing an avalanche effect and generating a laser-induced plasma. The laser-induced plasma contains electrons, ions, atoms, molecules, and particles, etc., and is overall electrically neutral. Usually, the laser we use is a nanosecond pulsed laser with high output energy. The initial temperature of the plasma generated by such a laser can reach 10 4 to 10 5 K, and the initial electron density is 10 17 to 10 18 cm -3 . When the laser pulse ends, the excited particles in the plasma will transition from high energy levels to low energy levels ( Figure 1 ), and emit characteristic spectral lines. The wavelength λ can be expressed as:

[0065] λ = ch / (E k -E i ) (1)

[0066] where c is the speed of light, h is Planck's constant, E k is the energy of the high energy level, and E i is the energy of the low energy level.

[0067] By establishing a relatively comprehensive spectral database, mapping the plasma spectra of each lithology to the contents of various minerals, and simultaneously establishing the mapping relationship between the liquid plasma spectrogram and the hydrocarbon content.

[0068] During the drilling operation, multiple geological parameter real-time monitoring subsections can be installed according to the budget and the requirement for the accuracy of information such as reservoir lithology and fluid to increase the sampling density. The connection position should be above the drill bit. The multiple geological parameter monitoring subsections are connected in series, and the distance L can be determined according to the on-site situation. The geological parameter real-time monitoring subsection is connected above the drill bit as Figure 3 shown. During the process of the drill bit (2) drilling into the formation (1), the cuttings (4) will be carried to the surface by the drilling fluid in the annulus. During this process, when the cuttings and the original fluids in the formation pass through the geological parameter real-time monitoring subsection (3), they will be irradiated by the high-energy laser beam (3-3) emitted by the laser emitter (3-2) in the subsection. The plasma emission spectrum (electromagnetic radiation spectrum) (3-4) generated by the interaction of the laser and the substance at the moment of irradiation is received by the spectral receiver (3-1) on the geological parameter real-time monitoring subsection, as Figure 4 shown.

[0069] The described laser emitter and spectral receiver are distributed on the real-time geological parameter monitoring short joint at a certain phase angle. In the present invention, the preferred phase angle is 120°.

[0070] Furthermore, the plasma emission spectrum is converted into an electrical signal by a photosensitive diode on the real-time geological parameter monitoring short joint, and then converted into an electrical signal for controlling a permanent magnet DC motor through an encoder.

[0071] Furthermore, the permanent magnet DC motor converts the electrical signal into vibration mechanical energy. The electrical signal is transmitted to the ground through the casing according to the vibration intensity and vibration frequency. The ground receiver receives the vibration signal, converts the vibration signal into an electrical signal through a decoder, and then converts it into a spectrogram.

[0072] Furthermore, multiple geological parameter short joints transmit vibration signals to the ground in sequence according to the distance from the bit. A prompt signal is required at the end of each geological parameter monitoring short joint to distinguish the signal intervals of each group.

[0073] Furthermore, the obtained multiple spectrograms are compared with the spectrograms in the database to judge the formation lithology and formation fluid information at that moment. The obtained formation information is corresponded to the well depth. The location of the geological sweet spot is optimized according to the hydrocarbon-bearing property, and the location of the engineering sweet spot is optimized according to the lithology and indirectly obtained rock mechanical parameters, so as to obtain the distribution of the double sweet spots along the well depth trajectory.

[0074] Embodiment 3

[0075] In a specific Embodiment 3 of applying the present invention, in order to better implement the method, a large number of samples such as the previous drilling cuttings, drilling fluid, and reservoir fluid in the research area need to be collected in advance. Especially for the drilling cuttings, a large number of indoor laser-induced plasma emission spectroscopy experiments need to be carried out on different mineral compositions or mineral contents under the same lithology. Figure 2 As shown in the schematic diagram of the principle of the laser-induced plasma emission spectroscopy experiment, in the laser-induced plasma emission spectroscopy experiment, a high-energy pulsed laser beam is focused on the surface of the sample. When the laser irradiance exceeds the breakdown threshold of the sample, the particles, molecules, and atoms in the laser ablation area will undergo multi-photon ionization to generate initial free electrons. The initial free electrons continue to absorb photons and accelerate, collide with atoms to ionize and generate new free electrons, and these electrons will repeat the behavior of the initial free electrons, continuously ionizing the atoms, thus causing an avalanche effect and generating a laser-induced plasma. The laser-induced plasma contains electrons, ions, atoms, molecules, and particles, etc., and is overall electrically neutral. Usually, the laser we use is a nanosecond pulsed laser with high output energy. The initial temperature of the plasma generated by such a laser can reach 10 4 to 10 5 K, and the initial electron density is 10 17 to 1018 cm -3 After the laser pulse ends, the excited particles in the plasma will transition from high energy levels to low energy levels ( Figure 1 ), and emit characteristic spectral lines. The wavelength λ can be expressed as:

[0076] λ = ch / (E k -E i ) (1)

[0077] where c is the speed of light, h is Planck's constant, E k is the energy of the high energy level, and E i is the energy of the low energy level.

[0078] By establishing a relatively comprehensive spectral database, mapping the plasma spectra of each lithology to various mineral contents, and simultaneously establishing a mapping relationship between the liquid plasma spectrogram and hydrocarbon content.

[0079] During drilling operations, multiple geological parameter real-time monitoring subsections can be installed according to the budget and the required accuracy of information such as reservoir lithology and fluid to increase the single-point sampling density. The connection position of the geological parameter monitoring subsection should be above the drill bit. Multiple geological parameter monitoring subsections are connected in series. The distances (L1, L2, L3, ……) of each geological parameter subsection from the first geological parameter subsection can be determined according to the on-site situation. The geological parameter real-time monitoring subsection is connected above the drill bit as Figure 3 shown. During the process of the drill bit (2) drilling into the formation (1), cuttings (4) will be carried by the drilling fluid from the annulus to the surface. During this process, when the cuttings and the original fluids in the formation pass through the geological parameter real-time monitoring subsection (3), they will be irradiated by the high-energy laser beam (3-3) emitted by the laser emitter (3-2) in the subsection. The plasma emission spectrum (electromagnetic radiation spectrum) (3-4) generated by the interaction of the laser and the substance at the moment of irradiation is received by the spectral receiver (3-1) on the geological parameter real-time monitoring subsection, as Figure 4 shown.

[0080] The laser emitter and the spectral receiver are distributed on the geological parameter real-time monitoring subsection at a certain phase angle. The preferred phase angle of the present invention is 120°.

[0081] Furthermore, the plasma emission spectrum is converted into an electrical signal by a photodiode on the geological parameter real-time monitoring subsection, and then converted into an electrical signal for controlling a permanent magnet DC motor through an encoder.

[0082] Further, starting from the first geological parameter sub-section, the time S for each subsequent geological parameter sub-section to capture samples for experiments should be based on the first geological parameter sub-section. The sample capture time for the first geological parameter sub-section is S1, the sample capture time for the second geological parameter sub-section S2 = S1 + L1 / v, the sample capture time for the third geological parameter sub-section S3 = S1 + L2 / v, and so on, ensuring that the samples taken in each round are from the same reservoir position, where v is the flow rate of the drilling fluid in the annulus.

[0083] Further, the permanent magnet DC motor converts the electrical signal into vibration mechanical energy. The electrical signal is transmitted to the ground through the casing according to the vibration intensity and frequency. The ground receiver receives the vibration signal and converts the vibration signal into an electrical signal through a decoder, and then converts it into a spectrogram.

[0084] Further, multiple geological parameter sub-sections transmit vibration signals to the ground in sequence according to the distance from the bit. A prompt signal is required at the end of each geological parameter monitoring sub-section to distinguish the interval of each group of signals.

[0085] Further, compare the multiple groups of spectrograms with the spectrograms in the database, conduct multiple groups of experimental verifications at the same reservoir position to ensure the recognition accuracy. Judge the formation lithology and formation fluid information at this moment based on the comparison results, correspond the obtained formation information with the sounding depth, optimize the location of the geological sweet spot according to the oil and gas bearing property, and optimize the location of the engineering sweet spot according to the lithology and indirectly obtained rock mechanical parameters, so as to obtain the distribution of the double sweet spots along the well depth trajectory.

[0086] In summary, the downhole real-time double sweet spot recognition method based on laser-induced breakdown spectroscopy provided by the present invention is based on the plasma breakdown spectrogram library established on the ground. Through the geological parameter real-time monitoring sub-section, the real-time laser breakdown spectrogram of the reservoir is obtained and compared with the spectrogram to obtain parameters such as reservoir lithology, mineral content, and fluid properties. Then, combined with the established geological sweet spot and engineering sweet spot evaluation methods, the real-time reservoir sweet spot distribution profile is obtained. This method can avoid the errors caused by manual lithology recognition, and at the same time can accurately identify the reservoir sweet spot position in real time, effectively determine the favorable horizons, thus assisting in making development decisions and greatly reducing the oil and gas development costs.

[0087] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0088] Except for the technical features described in the specification, the rest are well-known technologies to those skilled in the art.

Claims

1. A downhole real-time dual sweet spot recognition method based on laser-induced breakdown spectroscopy, characterized in that The downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy includes: Step 1: Establish a breakdown spectroscopy atlas database of representative rock samples and formation fluids through laser-induced breakdown experiments; Step 2: Emit high-energy laser to break down drilling cuttings and wellbore fluids to obtain plasma spectra; Step 3: Compare the obtained plasma spectra with the breakdown spectroscopy atlas database to obtain quantitative data of key real-time reservoir parameters; Step 4: Calculate the real-time sweet spot distribution of the reservoir based on the obtained data and draw the single-well sweet spot distribution profile.

2. The real-time downhole dual sweet spot recognition method based on laser-induced breakdown spectroscopy according to claim 1, wherein In Step 1, establish a breakdown spectroscopy atlas database of various lithologies, mineral contents, and formation fluids according to laser-induced breakdown experiments. The lithologies include mudstone, sandstone, shale, and volcanic rock, and the formation fluids include drilling fluid, oil, gas, and water.

3. The real-time downhole dual sweet spot recognition method based on laser-induced breakdown spectroscopy according to claim 2, wherein In Step 1, collect a large number of samples of drilling cuttings, drilling fluid, and reservoir fluids in the previous drilling of the research block. Especially for drilling cuttings, a large number of indoor experiments need to be carried out on different mineral compositions or mineral contents under the same lithology to establish a relatively comprehensive breakdown spectroscopy atlas database.

4. The real-time downhole dual sweet spot identification method based on laser-induced breakdown spectroscopy according to claim 1, wherein The downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy also includes, after Step 1, establishing a geological sweet spot evaluation method and an engineering sweet spot evaluation method according to the lithology, mineral content, and formation fluid distribution.

5. The real-time downhole dual sweet spot recognition method based on laser-induced breakdown spectroscopy according to claim 4, wherein When establishing the geological sweet spot evaluation method and the engineering sweet spot evaluation method, the geological sweet spot mainly considers lithology and fluid characteristics, and the engineering sweet spot mainly considers brittle mineral content, drilling time, and drilling mechanical specific energy.

6. The real-time downhole dual sweet spot identification method based on laser-induced breakdown spectroscopy according to claim 1, wherein In Step 2, use a drilling tool with a geological parameter monitoring sub during drilling operations. During the drilling process, the cuttings flow towards the wellhead through the annulus and are captured when passing through the geological parameter monitoring sub near the drill bit for laser breakdown experiments. The plasma spectra obtained by laser breakdown of the mixed samples are transmitted to the ground.

7. The real-time downhole dual sweet spot recognition method based on laser-induced breakdown spectroscopy according to claim 6, wherein In Step 2, the geological parameter monitoring sub contains a high-energy laser emission module. The captured mixed samples are broken down by a high-energy laser beam, and the generated breakdown spectra are received by the receiver on the geological parameter monitoring sub and transmitted to the ground. After the geological parameter monitoring sub captures the mixed samples and conducts laser breakdown experiments, capturing the breakdown spectra and transmitting them to the ground is one monitoring. The monitoring interval can be adjusted according to requirements but cannot be less than the time of one breakdown experiment.

8. The real-time downhole dual sweet spot identification method based on laser-induced breakdown spectroscopy according to claim 4, characterized in that In Step 3, compare the obtained plasma spectra with the breakdown spectroscopy atlas database on the ground to obtain the quantitative mineral content, lithology, and reservoir fluid conditions after excluding the drilling fluid of the mixed samples.

9. The real-time downhole dual sweet spot identification method based on laser-induced breakdown spectroscopy according to claim 8, wherein, In Step 3, first decompose the received plasma spectra into solid, gas, and liquid spectrograms through Fourier transform, and compare them with the breakdown spectroscopy atlas database respectively to find the closest spectrograms and obtain corresponding data such as lithology, mineral content, and hydrocarbon content.

10. The real-time downhole dual sweet spot identification method based on laser-induced breakdown spectroscopy according to claim 9, characterized in that, In Step 4, substitute the data of mineral content, lithology, and reservoir fluid of the mixed samples into the previously established geological sweet spot and engineering sweet spot evaluation methods to obtain a quantitative sweet spot index.

11. The real-time downhole dual sweet spot recognition method based on laser-induced breakdown spectroscopy according to claim 10, characterized in that, In Step 4, the geological sweet spot mainly considers lithology and fluid properties, and the engineering sweet spot mainly considers mineral content, drilling time, and mechanical specific energy at different depths.

12. The downhole real-time dual sweet spot recognition system based on laser-induced plasma emission spectroscopy is characterized in that, The downhole real-time dual sweet spot identification system based on laser-induced plasma emission spectroscopy uses the downhole real-time dual sweet spot identification method based on laser-induced breakdown spectroscopy described in any one of claims 1-11 to analyze the lithology and other formation parameters of the formation near the drill bit, and makes a real-time prediction of the distribution of formation sweet spots.

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