Gas layer identification method based on the intersection of secondary inelastic and captured gamma information of drill collars

Abstract

The present invention discloses a gas layer identification method based on the crossplot of drill collar secondary inelastic and capture gamma information, which relates to the field of oil and gas development, and includes: establishing a 1:1 instrument - formation simulation model; simulating the total secondary inelastic and total secondary capture gamma energy spectrum information of an actual instrument under ideal gas layer and water layer conditions, and normalizing; analyzing the total secondary inelastic and total secondary capture gamma energy spectra under ideal gas layer and water layer conditions using standard spectrum information, and simultaneously obtaining the drill collar secondary inelastic and capture gamma yields of the instrument; combining the drill collar secondary inelastic and capture gamma yield information corresponding to the same formation porosity to establish a gas layer identification crossplot; obtaining the drill collar secondary inelastic and capture gamma yield information under actual reservoir conditions, and plotting the yield information on the gas layer identification crossplot to complete the identification of gas and water layers in the actual reservoir. The method of the present invention eliminates the dependence of the gas layer identification method on porosity measurement, and further improves the accuracy and universality of gas layer identification.

Description

Technical Field

[0001] The invention relates to the technical field of oil and natural gas development, and in particular to a gas layer identification method based on the intersection of drill collar secondary inelasticity and captured gamma information. Background Art

[0002] Neutron gas layer identification technology while drilling is of great significance to the exploration and development of unconventional oil and gas. The invention patents that have been published (CN113123779A, CN115030711A) disclose a gas layer identification method based on the inelastic gamma information of drill collars. This method uses the inelastic gamma counting yield of drill collars to identify gas layers, successfully solving the problems of low efficiency of fast neutron detection and the great influence of formation density on total inelastic gamma information, and further improving the sensitivity of gas layer identification. However, the gas layer identification method based on the inelastic gamma information of drill collars still cannot do without the measurement of formation porosity information, and the accuracy of formation porosity measurement directly affects the results of gas layer identification.

[0003] Therefore, it is urgent to study a gas layer identification method that eliminates the dependence on porosity measurement. Summary of the invention

[0004] In order to solve the above technical problems, the present invention discloses a gas layer identification method based on the intersection of secondary inelastic and captured gamma information of drill collars. The secondary inelastic and captured gamma yield information of the drill collars are simultaneously obtained through spectral analysis technology, and the difference between the two in the response of gas and water layers is used to form an intersection plate. While retaining the advantages of the gas layer identification method based on the drill collar inelastic gamma information, the dependence of the gas layer identification method on porosity measurement is eliminated, thereby further improving the accuracy and universality of gas layer identification.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A gas layer identification method based on the intersection of drill collar secondary inelasticity and captured gamma information includes the following steps:

[0007] Step S1, based on the actual parameters of the controlled neutron source gamma gas layer identification instrument while drilling, a 1:1 instrument-formation simulation model is established using a Monte Carlo numerical simulation method;

[0008] Step S2: establishing water-saturated and gas-saturated formation models with different porosities based on actual formation conditions, simulating the total secondary inelastic and total secondary captured gamma spectral information of the actual instrument under ideal gas layer and ideal water layer conditions, and performing normalization processing;

[0009] Step S3, obtaining standard spectrum information of drill collar and formation elements of the instrument, analyzing the total secondary inelastic and total secondary captured gamma energy spectra under ideal gas layer and ideal water layer conditions using the standard spectrum information, and obtaining the secondary inelastic and captured gamma yields of the drill collar of the instrument;

[0010] Step S4: Based on the differences in the responses of the drill collar's secondary inelastic and capture gamma yields to ideal gas layers and ideal water layers in the instrument, combine the drill collar's secondary inelastic and capture gamma yield information corresponding to the same formation porosity, and establish a gas layer identification crossplot based on the drill collar's secondary inelastic and capture gamma information.

[0011] Step S5: Perform spectral analysis on the secondary inelastic and capture gamma spectral information from the actual reservoir based on the standard spectral information obtained in Step S3 to obtain the drill collar's secondary inelastic and capture gamma yield information under actual reservoir conditions, and plot the yield information on the gas layer identification crossplot to complete the identification of gas and water layers in the actual reservoir.

[0012] Optionally, in Step S1, the downhole controllable neutron source gamma gas layer identification instrument includes a drill collar, a D-T neutron source, a shielding body, and a long source-distance gamma detector.

[0013] Optionally, in Step S1, the instrument-formation simulation model consists of two parts: an instrument model and a formation model. Among them, the instrument model changes with the parameters and materials of the actual instrument, and the size and filling material of the formation model are set according to the actual reservoir conditions and formation element composition.

[0014] Optionally, in Step S2, the water-saturated and gas-saturated formation models are obtained by replacing the filling material in the formation simulation model in Step S1 with the elemental materials of the ideal water layer and the ideal gas layer.

[0015] Optionally, in Step S2, the ideal gas layer refers to a gas layer with a single lithology and different porosities, and the ideal water layer refers to a water layer with a single lithology and different porosities.

[0016] Optionally, in Step S3, the standard spectra of the instrument drill collar and formation elements refer to the inelastic gamma spectra and capture gamma spectral information generated by the interaction of the instrument drill collar and a single formation element material with the neutrons emitted by the controllable neutron source.

[0017] Optionally, the standard spectrum of the instrument drill collar is obtained by normalizing the detector energy spectrum information during the instrument's self-simulation.

[0018] Optionally, the standard spectrum of the formation element is obtained by normalizing the energy spectrum information recorded by the instrument gamma detector when the formation filling in the model established in Step S1 is a single element material.

[0019] Optionally, in Step S3, the method for analyzing the total secondary inelastic and total secondary capture gamma energy spectra refers to the least squares method or the singular value method.

[0020] Optionally, in step S4, the gas layer identification crossplot uses the formation porosity parameter as the bridge for the crossplot of the information of the secondary inelastic and capture gamma yields of the instrument drill collar. By combining the two pieces of information on the secondary gamma yields of the drill collar, the dependence of gas layer identification on porosity measurement is eliminated.

[0021] The beneficial effects of the present invention are as follows: The present invention obtains the information of the secondary inelastic and capture gamma yields of the drill collar during the logging with a controllable neutron source while drilling, and forms a crossplot using the differences in the responses of gas and water layers of the two. While retaining the advantages of the gas layer identification method using the inelastic gamma information of the drill collar, the dependence of the gas layer identification method on porosity measurement is eliminated, further improving the accuracy and universality of gas layer identification. Description of the Drawings

[0022] Figure 1 is a flowchart of the gas layer identification method based on the crossplot of the secondary inelastic and capture gamma information of the drill collar according to the present invention;

[0023] Figure 2 is a graph showing the relationship between the secondary capture gamma yield of the drill collar and thermal neutrons of the instrument shown in the embodiment of the present invention;

[0024] Figure 3 is a response diagram of the secondary inelastic gamma yield and the secondary capture gamma yield of the drill collar in the water-saturated and gas-saturated formations shown in the embodiment of the present invention, where (a) is the secondary inelastic gamma yield of the drill collar and (b) is the secondary capture gamma yield of the drill collar;

[0025] Figure 4 is the gas layer identification crossplot based on the crossplot of the secondary inelastic and capture gamma information of the drill collar shown in the embodiment of the present invention. Detailed Embodiments

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] A gas layer identification method based on the crossplot of the secondary inelastic and capture gamma information of the drill collar, as Figure 1 shown, includes the following steps:

[0028] Step S1, based on the parameters of the actual logging with a controllable neutron source gamma gas layer identification instrument, use the Monte Carlo numerical simulation method to establish a 1:1 instrument-formation simulation model;

[0029] Optionally, the logging with a controllable neutron source gamma gas layer identification instrument includes a drill collar, a D-T neutron source, a shielding body, and a long source distance gamma detector;

[0030] Optionally, the instrument-formation simulation model consists of two parts: an instrument model and a formation model. Among them, the instrument model changes with the parameters and materials of the actual instrument. The various parameters of the instrument part are consistent with the measured instrument, and the size and filling material of the formation model are set according to the actual reservoir conditions and formation element composition.

[0031] In this embodiment, according to the parameters such as the actual instrument material, length, and detector position, a Monte Carlo numerical simulation method is used to establish an actual logging-while-drilling (LWD) controllable-source neutron instrument-formation model.

[0032] Step S2: Based on the actual formation conditions, establish formation models with different porosities that are saturated with water and saturated with gas, simulate the total secondary inelastic and total secondary capture gamma energy spectrum information of the actual instrument under ideal gas layer and ideal water layer conditions, and perform normalization processing.

[0033] Optionally, the ideal gas layer refers to a gas layer with a single lithology and different porosities, and the ideal water layer refers to a water layer with a single lithology and different porosities.

[0034] In this embodiment, according to the actual formation conditions, formation models with different porosities that are saturated with gas and saturated with water are established under ideal conditions. Simulations are carried out to obtain the total secondary inelastic and total secondary capture gamma energy spectrum information of the gas layer and the water layer, and normalization processing is performed. Using the established LWD controllable-source neutron instrument-formation model mentioned above, the formations of the model are respectively set as ideal formations that are saturated with gas and saturated with water. The formation porosities are respectively from 0 to 35%. The counts of different time windows of the gamma detector for the two models are the inelastic and capture gamma energy spectrum information of the LWD gas layer identification device in the gas-saturated and water-saturated formations. Among them, the ideal formation refers to a pure rock formation that does not contain shale and has the main lithology of the formation.

[0035] In this embodiment, the inelastic and capture gamma energy spectrum information of the gas-saturated and water-saturated formations is normalized using the total counts of their respective energy spectra.

[0036] Step S3: Obtain the standard spectrum information of the instrument drill collar and formation elements, use the standard spectrum information to analyze the total secondary inelastic and total secondary capture gamma energy spectra under ideal gas layer and ideal water layer conditions, and simultaneously obtain the secondary inelastic and capture gamma yields of the instrument drill collar.

[0037] Optionally, the standard spectrum of the instrument drill collar and formation elements refers to the inelastic and capture gamma spectrum information generated by the interaction of the instrument drill collar and a single formation element material with the neutrons emitted by the controllable neutron source.

[0038] Optionally, the standard spectrum of the instrument drill collar is obtained by normalizing the detector energy spectrum information during the self-simulation of the instrument.

[0039] Optionally, the standard spectrum of the formation element is obtained by normalizing the energy spectrum information recorded by the instrument gamma detector when the formation in the model established in step S1 is filled with a single element substance.

[0040] Optionally, the method for analyzing the total secondary inelastic and total secondary capture gamma energy spectra refers to the least squares method or the singular value method.

[0041] In this embodiment, the formations in the model in step S1 are respectively set as the simple substances and oxides of common formation elements, and the Monte Carlo numerical simulation method is used to obtain the standard spectrum information of common formation elements and the secondary inelastic and capture of the instrument drill collar. The total secondary inelastic and total secondary capture gamma energy spectra of the gas-saturated and water-saturated formations obtained in step S2 are analyzed with the above secondary inelastic and capture standard spectrum information to obtain the secondary inelastic and capture gamma yields of the instrument drill collar.

[0042] Figure 2 The relationship between the secondary capture gamma yield of the instrument drill collar and the thermal neutron flux in gas-saturated and water-saturated formations of different lithologies after spectral deconvolution is shown. It can be seen that the secondary capture gamma yield of the drill collar roughly shows a linear relationship with the thermal neutron flux, indicating that the secondary capture gamma yield of the drill collar inherits the characteristics of good thermal neutron countability and high sensitivity.

[0043] Step S4: Based on the difference in the responses of the ideal gas layer and the ideal water layer to the secondary inelastic and capture gamma yields of the instrument drill collar, combine the secondary inelastic and capture gamma yield information corresponding to the same formation porosity to establish a gas layer identification crossplot based on the secondary inelastic and capture gamma information of the drill collar;

[0044] Optionally, the gas layer identification crossplot uses the formation porosity parameter as the bridge for the intersection of the secondary inelastic and capture gamma yield information of the instrument drill collar, and eliminates the dependence of gas layer identification on porosity measurement through the combination of the two drill collar gamma yield information.

[0045] Figure 3 The responses of the secondary inelastic and capture gamma yields of the instrument drill collar in gas-saturated and water-saturated sandstone formations under different porosity conditions are shown. It can be seen that there are obvious differences in the responses of the secondary inelastic and capture gamma yield information to the gas and water layers. The gas layer identification sensitivities of the secondary inelastic and capture gamma yields of the drill collar under different porosities are calculated and compared with the gas layer sensitivity of the total inelastic and total capture counts. As shown in Table 1, it can be seen that the gas layer sensitivities of the secondary inelastic and capture gamma yield information of the instrument drill collar are both higher than the total inelastic and total capture information.

[0046] Table 1 Comparison table of gas layer identification sensitivities between instrument drill collar gamma yield and total gamma count

[0047]

[0048]

[0049] Taking the secondary inelastic gamma yield of the drill collar at the same formation porosity as the abscissa and the secondary capture gamma yield of the drill collar as the ordinate, a gas layer identification crossplot for different lithologic formations is plotted. As Figure 4 shown, this crossplot not only maintains a high gas layer sensitivity for the inelastic and capture gamma yield information of the drill collar, but also eliminates the porosity parameter, avoiding the dependence of gas layer identification on porosity and the influence of porosity measurement errors on the accuracy of gas layer identification.

[0050] Step S5: Perform spectral analysis on the secondary inelastic and capture gamma spectral information from the actual reservoir based on the standard spectral information obtained in Step S3 to obtain the secondary inelastic and capture gamma yield information of the drill collar under actual reservoir conditions, and plot the yield information on the gas layer identification crossplot to complete the identification of gas and water layers in the actual reservoir, that is, to determine whether the actual reservoir is a gas layer or a water layer;

[0051] In this embodiment, during the above plotting process, first select the gas layer line and the water layer line with the same lithology as the actual reservoir. If the measured point is near the water layer line, it is a water layer; if it is near the gas layer line, it is a gas layer. The less shale and the more homogeneous the lithology of the measured formation, the closer the measured point is to the gas layer or water layer line, and the higher the accuracy of gas layer identification.

[0052] The method of the present invention obtains the secondary inelastic and capture gamma yield information of the drill collar of the instrument from the total secondary inelastic and total secondary capture gamma spectral information recorded by the downhole controllable source neutron gas layer instrument. At the same time, it uses the secondary inelastic and capture gamma yields of the drill collar of the instrument for gas layer identification, improving the sensitivity and accuracy of gas layer identification, and making a crossplot of the secondary inelastic and capture gamma information of the drill collar for gas layer identification, eliminating the dependence of gas layer identification on porosity and the influence of porosity measurement errors on the accuracy of gas layer identification.

[0053] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A gas layer identification method based on the intersection of drill collar secondary inelasticity and captured gamma information, characterized in that: It includes the following steps: Step S1: Based on the parameters of the actual while-drilling controllable neutron source gamma gas layer identification instrument, use the Monte Carlo numerical simulation method to establish a 1:1 instrument-stratum simulation model; Step S2: Based on the actual stratum conditions, establish water-saturated and gas-saturated stratum models with different porosities, simulate the total secondary inelastic and total secondary capture gamma energy spectrum information of the actual instrument under ideal gas layer and ideal water layer conditions, and perform normalization processing; Step S3: Obtain the standard spectrum information of the instrument drill collar and formation elements, use the standard spectrum information to analyze the total secondary inelastic and total secondary capture gamma energy spectra under ideal gas layer and ideal water layer conditions, and simultaneously obtain the secondary inelastic and capture gamma yields of the instrument drill collar; Step S4: Based on the difference in the responses of the instrument drill collar secondary inelastic and capture gamma yields to the ideal gas layer and ideal water layer, combine the secondary inelastic and capture gamma yield information of the drill collar corresponding to the same stratum porosity, and establish a gas layer identification crossplot based on the secondary inelastic and capture gamma information of the drill collar; Step S5: Based on the standard spectrum information obtained in Step S3, perform spectral analysis on the secondary inelastic and capture gamma spectrum information from the actual reservoir, obtain the secondary inelastic and capture gamma yield information of the drill collar under actual reservoir conditions, and plot the yield information on the gas layer identification crossplot to complete the identification of gas-water layers in the actual reservoir; In Step S3, the standard spectrum of the instrument drill collar and formation elements refers to the inelastic gamma spectrum and capture gamma spectrum information generated by the interaction between the instrument drill collar and a single formation element material and the neutrons emitted by the controllable neutron source; In Step S3, the method for analyzing the total secondary inelastic and total secondary capture gamma energy spectra refers to the least squares method or the singular value method; In Step S4, the gas layer identification crossplot uses the stratum porosity parameter as the bridge for intersecting the secondary inelastic and capture gamma yield information of the instrument drill collar, and eliminates the dependence of gas layer identification on porosity measurement through the combination of the two secondary gamma yield information of the drill collar; 2. The gas layer identification method based on the crossplot of drill collar secondary inelastic and capture gamma information according to claim 1, wherein In Step S1, the while-drilling controllable neutron source gamma gas layer identification instrument includes a drill collar, a D-T neutron source, a shielding body, and a long source distance gamma detector; 3. A gas layer identification method based on the intersection of secondary inelastic and captured gamma information of drill collars as described in claim 1, characterized in that, In Step S1, the instrument-stratum simulation model consists of two parts: an instrument model and a stratum model. Among them, the instrument model changes with the parameters and materials of the actual instrument, and the size and filling material of the stratum model are set according to the actual reservoir situation and the formation element composition; 4. The gas layer identification method based on the crossplot of secondary inelastic and capture gamma information of drill collars as claimed in claim 1, wherein, In Step S2, the water-saturated and gas-saturated stratum models are obtained by replacing the filling material in the stratum simulation model in Step S1 with the element materials of the ideal water layer and ideal gas layer; 5. A gas layer identification method based on the intersection of secondary inelastic and capture gamma information of drill collars as described in claim 1, characterized in that, In Step S2, the ideal gas layer refers to a gas layer with a single lithology and different porosities, and the ideal water layer refers to a water layer with a single lithology and different porosities.

Images