A method for rapid identification of hydrate occurrence forms based on electromagnetic wave resistivity while drilling

Abstract

The present invention proposes a method for quickly identifying the occurrence form of hydrates based on electromagnetic wave resistivity while drilling. It proposes to identify sensitive parameters of hydrates with different occurrence forms based on the difference between phase and attenuation resistivity and annular resistivity, and then combine the intersection analysis of high-frequency and low-frequency phase resistivity at different source distances, in order to achieve the purpose of quickly and accurately identifying the occurrence form type of hydrates. First, the logging data including annular resistivity, P-wave velocity, density, and gamma of the logging while drilling are analyzed, and the logging data are compared with the saturated water background resistivity to determine whether the hydrate reservoir is a fracture-filled type or a pore-filled type; then, for the medium-saturation fracture-filled hydrate and pore-filled hydrate, both of which have the characteristics of high annular resistivity and high P-wave velocity anomalies, the phase and attenuation resistivity and their ratio at different source distances are analyzed and compared with the annular resistivity to finally determine the occurrence form of the hydrate.

Description

Technical Field

[0001] The invention relates to the field of oil and gas hydrate exploration and reservoir evaluation, and specifically to a method for quickly identifying hydrate occurrence forms based on while-drilling electromagnetic wave resistivity. Background Art

[0002] Natural gas hydrates (hereinafter referred to as hydrates) existing in the earth are mainly ice-like cage compounds formed by hydrocarbon molecules (usually methane) and water molecules under low temperature and high pressure. They are widely present in the marine environment at the edge of the continental shelf.

[0003] At present, my country's oil and gas resources are all developed in deepwater areas. After a large number of drilling results, it is shown that there are three different hydrate occurrence forms: pore filling type, fracture filling type, and coexistence of pores and fractures. It is known that hydrate is an electrical insulator. The reservoir containing hydrate has a high resistivity anomaly, which is often used to evaluate the hydrate saturation index in sediments. However, affected by the anisotropy of fractures, the hydrate saturation results calculated based on isotropic and anisotropic resistivity are quite different. For example, in the NGHP-01-10A well in India, the hydrate saturation calculated using the isotropic Archie equation and the annular resistivity while drilling is as high as 50%, which is much higher than the saturation of 10-20% calculated by pressure coring. Pore-filling hydrates develop in the pore space of sediments. In muddy silt and sandy reservoirs, the hydrate saturation calculated based on the isotropic resistivity model is similar to the rate and core calculated saturation index. Therefore, the occurrence form of hydrates must be identified first, so that a suitable rock physics model can be selected and the accurate calculation and evaluation of hydrate saturation can be finally achieved.

[0004] The existing traditional methods are mostly to identify the occurrence form of hydrates by CT scanning of samples taken from drilling cores, or to qualitatively identify the occurrence form of hydrates through logging while drilling data, such as through comprehensive analysis of P-wave velocity and annular resistivity, that is, to judge whether the occurrence form of hydrates is fracture-filling hydrates by obvious high resistivity anomalies and no obvious change in P-wave velocity. However, when the saturation is relatively low, the annular resistivity shows high value anomalies because both the formation fracture inclination and the hydrate saturation affect the measured resistivity; but the velocity may be similar to that of the saturated water layer, or it may be higher than that of the saturated water layer. In the high-saturation fracture-filling hydrate layer, the annular resistivity and P-wave velocity both show high value anomalies, but in the relatively high-saturation pore-filling hydrate, the P-wave velocity and annular resistivity also show abnormally high values. Therefore, when the annular resistivity and velocity show high value anomalies, it may indicate hydrate layers with different occurrence forms. It is difficult to accurately determine the occurrence form of hydrates by only using the changes in annular resistivity and P-wave velocity, which in turn affects the selection of saturation evaluation models.

[0005] If the core CT imaging scanning technology is used to perform non-destructive testing of the core structure through X-rays, the precise location and occurrence form of hydrate development can be identified. However, due to the absorption of heat by hydrate decomposition, the core samples show abnormal low temperatures. The distribution of hydrates can be roughly identified through infrared thermal imaging, and the occurrence of hydrates can be qualitatively identified through the abnormal characteristics of temperature imaging. Therefore, the core can quickly determine the occurrence form of hydrates, but the cost and difficulty of coring are high, and a large number of drilling wells have not carried out related coring operations.

[0006] Therefore, how to establish a method for rapid identification of hydrate occurrence forms through comprehensive analysis of LWD data is an urgent issue to be solved in the current hydrate occurrence form identification technology, hydrate resource exploration and its trial production objectives, and is of great significance for the accurate evaluation of hydrate resources.

[0007] In view of this, this patent application is proposed. Summary of the invention

[0008] The method for quickly identifying the occurrence forms of hydrates based on electromagnetic wave resistivity while drilling described in the present application aims to solve the problems existing in the above-mentioned prior art and to accurately evaluate the physical properties of hydrate reservoirs. It is proposed to identify sensitive parameters of hydrates in different occurrence forms based on the difference between phase and attenuation resistivity and annular resistivity, and then combine the intersection analysis of high-frequency and low-frequency phase resistivity at different source distances, in order to achieve the purpose of quickly and accurately identifying the occurrence form type of hydrates.

[0009] To achieve the above-mentioned design purpose, the method for quickly identifying the occurrence form of hydrates based on electromagnetic wave resistivity while drilling is based on the response difference between phase and attenuation resistivity and annular resistivity to identify the occurrence form of hydrates. First, the logging data including annular resistivity, P-wave velocity, density, and gamma of the logging while drilling are analyzed, and the logging data are compared with the saturated water background resistivity to determine whether the hydrate reservoir is a fracture-filled type or a pore-filled type; then, for the characteristics of high annular resistivity and high P-wave velocity anomalies of both fracture-filled hydrates and pore-filled hydrates with medium saturation, the phase and attenuation resistivity and their ratio at different source distances are analyzed and compared with the annular resistivity to finally determine the occurrence form of hydrates.

[0010] Furthermore, the method comprises the following steps:

[0011] Step 1), preliminarily determine the type of hydrate reservoir;

[0012] Using various data including annular resistivity, P-wave velocity, density and natural gamma logging measured by LWD, the velocity and annular resistivity variation characteristics of different formations are analyzed and compared with the resistivity of saturated water layers to preliminarily determine the type of hydrate reservoir.

[0013] Step 2), analyzing the abnormal characteristics of electromagnetic wave resistivity collected at different source distances and high and low frequencies;

[0014] In logging while drilling, geoVISION and NeoScope data are collected simultaneously using the Schlumberger LWD tool suite;

[0015] By comparing and analyzing the attenuation and phase resistivity measured at a low frequency of 400kHz and the attenuation and phase resistivity measured at a high frequency of 2MHz by electromagnetic wave resistivity measurement, several attenuation and phase resistivity curves collected at different source distances and high and low frequencies are compared with the annular resistivity and the calculated water-saturated formation resistivity;

[0016] Step 3), optimizing the sensitive parameters of hydrates of different occurrence types;

[0017] By comparing the electromagnetic wave resistivity and annular resistivity values ​​at different frequencies and different source distances in the above step 2), the high-frequency electromagnetic wave resistivity at the minimum source distance of 16 inches and the maximum source distance of 40 inches is selected as the basis for determining the occurrence type of hydrate;

[0018] Step 4), using sensitive parameter ratios to analyze hydrate occurrence types;

[0019] Based on the comparative analysis of the above steps 2) and 3), the high-frequency electromagnetic wave resistivity (phase resistance P40H and attenuation resistivity A40H) measured at the maximum source distance is first compared with the annular resistivity and saturated water resistivity; among them, the phase and attenuation resistivity at the large source distance (40 inches) are compared with the annular resistivity;

[0020] By comparing the ratio with the saturated water layer, the high-frequency phase at a large source distance of 40 inches is compared with the attenuation resistivity curve, and the ratio analysis is performed with the annular resistivity;

[0021] Step 5) Identify the hydrate occurrence type by using sensitive parameter intersection analysis;

[0022] Extract the sensitive parameters with the largest separation between electromagnetic wave resistance and ring resistivity and the most different measurement results in step 3) and step 4), and perform intersection analysis with the logging data of high-frequency phase resistivity (P40H and P16H) and ring resistivity (RING) at the maximum source distance (40 inches) and the minimum source distance (16 inches), and observe the partition characteristics of the intersection diagram;

[0023] Step 6), using intersection and ratio analysis to jointly identify the hydrate occurrence type;

[0024] From the electromagnetic wave resistivity data measured at different frequencies and different source distances in step 3) to step 5), as well as the intersection results of different sensitive parameters, the upper hydrate layer and the lower hydrate layer show obviously different change trends and different value ranges;

[0025] If the measured phase and attenuation resistivity of the hydrate-bearing abnormal layer are greater than the annular resistivity, it is judged to be a fracture-filling hydrate; if the measured phase and attenuation resistivity of the hydrate-bearing abnormal layer are less than or close to the annular resistivity, it is judged to be a pore-filling hydrate.

[0026] Further, in step 2), the saturated water resistivity is calculated using the following Archie formula:

[0027]

[0028] Among them, Rw is the formation symbiotic water resistance, which is generally 0.28Ωm; φ is the formation porosity; a and m are Archie constants, which are fitted by the intersection of formation factors and porosity. In the NGHP-02-17 well, the values ​​are: a = 2.44, m = 1.12.

[0029] In summary, the method for quickly identifying the occurrence form of hydrates based on while-drilling electromagnetic wave resistivity proposed in this application has the following advantages: 1. This application innovatively utilizes the characteristics of electromagnetic wave resistivity that is sensitive to cracks, and based on the phase and attenuation resistivity ratio and annular resistivity ratio or intersection analysis at different source distances, it can quickly determine the occurrence form of hydrates and significantly improve the accuracy of selecting a suitable rock physics model for quantitative calculation of hydrate saturation results.

[0030] 2. This application combines the intersection analysis of high-frequency and low-frequency resistivity at different source distances, which can effectively overcome the cost and sampling difficulties of using cores to identify the occurrence form of hydrates, and fully utilizes the phase and attenuation resistivity measured at different source distances for the differences in fracture inclination, hydrate saturation and other characteristics. It combines multiple parameters to quickly and quantitatively determine the occurrence form of hydrates, which helps to quantitatively calculate the saturation of hydrates, solve the problem of rapid identification and quantitative evaluation of hydrate layers, and provide strong support for the accurate prediction of target hydrate resources.

[0031] 3. The present application can overcome the difficulty of the prior art in identifying medium-saturation fracture-filling hydrates and pore-filling hydrates, and realize rapid judgment and calculation on-site during logging while drilling without the need for drilling and coring. Therefore, a large amount of drilling costs and working hours can be saved, and the operating efficiency is relatively high. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the method proposed in this application for quickly identifying the occurrence form of hydrates based on electromagnetic wave resistivity while drilling;

[0033] Figure 2 This is a schematic diagram of the logging while drilling data of India's NGPH-02-17 well;

[0034] Figure 3 This is a schematic diagram of the electromagnetic wave resistivity data while drilling measured at different source distances and frequency bands in the NGPH-02-17 well in India and the calculation results of the saturated water resistivity R0;

[0035] Figure 4 The diagram shows the annular resistivity, 40-inch source distance, high-frequency measurement of attenuation and phase resistivity curves and saturated water resistivity of the NGHP-02-17 well in India, as well as the ratio of attenuation and phase resistivity to annular resistivity.

[0036] Figure 5 This is the intersection diagram of the high-frequency phase resistivity at a source distance of 40 inches and the high-frequency phase resistivity at a source distance of 16 inches in the NGHP-02-17 well in India, and the intersection comparison diagram of the high-frequency phase resistivity at a source distance of 40 inches and the high-frequency phase resistivity at a source distance of 16 inches, and the ratio of the high-frequency phase resistivity to the annular resistivity. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings proposed in the present application. It is obvious that the described solutions are part of the embodiments of the present application rather than all of the embodiments. Based on the embodiments proposed in the present application, ordinary technicians in this field may make improvements or changes without making creative work, and all these improvements and changes should fall within the scope of protection of the claims attached to the present application.

[0038] Embodiment 1, as Figures 1 to 5 As shown, the present application proposes a method for quickly identifying the occurrence form of hydrates based on electromagnetic wave resistivity while drilling, which only analyzes the logging data while drilling without drilling coring operations, starting from the characteristics of phase and attenuation resistivity being sensitive to fractures, because fracture-filling hydrates are formed in fractures, they are greatly affected by fracture characteristics. However, the existing technology ignores the influence of fractures themselves in the study of identifying hydrates, and only focuses on the resolution of measurement parameters, which is only effective for identifying pore-filling hydrates.

[0039] Specifically, based on the response difference between phase and attenuation resistivity and annular resistivity, the occurrence form of hydrate can be quickly identified; first, the logging data including annular resistivity, P-wave velocity, density, and gamma of LWD are analyzed, and the logging data are compared with the saturated water background resistivity to determine whether the hydrate reservoir is fracture-filled or pore-filled; then, for medium-saturation fracture-filled hydrates and pore-filled hydrates, both have the characteristics of high annular resistivity and high P-wave velocity anomalies. The phase and attenuation resistivity and their ratio at different source distances are analyzed and compared with the annular resistivity to finally determine the occurrence form of hydrate.

[0040] like Figure 1 As shown, the method includes the following implementation steps:

[0041] Step 1), preliminarily determine the type of hydrate reservoir;

[0042] Using various data including annular resistivity, P-wave velocity, density and natural gamma logging measured by LWD, the velocity and annular resistivity variation characteristics of different formations are analyzed and compared with the resistivity of saturated water layers to preliminarily determine the type of hydrate reservoir.

[0043] Specifically, if the measured annular resistivity and velocity both increase significantly and are greater than the resistivity and velocity of the saturated water layer, it indicates that the formation with high annular resistivity and velocity contains hydrates; there are two main types of hydrate layers, one is pore-filling type and the other is fracture-filling type hydrate. The prior art believes that in pore-filling type hydrate layers, both annular resistivity and P-wave velocity increase, while the annular resistivity measured in fracture-filling type hydrate layers increases significantly, while the P-wave velocity is similar to that of hydrate-free saturated water layers. For example, Figure 2 As shown in the NGHP-02-17 well in India, according to the existing technology and the logging data while drilling, the upper formation between 150-247 meters has a higher annular resistivity than the saturated water layer, and the P-wave velocity is similar to the saturated water layer, which is considered to be a fracture-filling hydrate layer; while the lower formation between 270-290 meters, the annular resistivity and P-wave velocity are both higher than the saturated water layer, which is considered to be a pore-filling hydrate. However, in the upper hydrate layer, there are also abnormal layers with high annular resistivity and high P-wave velocity, so it is difficult to determine whether it is a fracture-filling hydrate or a pore-filling hydrate, that is, the existing technology cannot truly identify the type of pore or fracture-filling hydrate at different saturations.

[0044] Step 2), analyzing the abnormal characteristics of electromagnetic wave resistivity collected at different source distances and high and low frequencies;

[0045] In logging while drilling, the Schlumberger LWD instrument combination can simultaneously collect different types of data such as geoVISION and NeoScope. The NeoScope resistivity logging tool uses electromagnetic waves (including attenuation and phase resistivity) of two frequencies, 400kHz (low frequency) and 2MHk (high frequency), and simultaneously measures data of five transmitting pole distances (such as 40 inches, 28 inches, 16 inches, 22 inches, and 34 inches). Once the electromagnetic wave is transmitted, 20 attenuation and phase resistivity curves of different frequencies and different source distance combinations can be measured simultaneously. The geoVISION resistivity tool can collect five different resistivities, such as annular resistivity and drill bit resistivity. The annular resistivity has the highest resolution, reaching 5-8 cm. The traditional method uses annular resistivity for hydrate identification and saturation calculation. This parameter is more effective for pore-filling hydrate identification and saturation estimation. However, for fracture-filling hydrate layers, the measured resistivity is affected by both hydrates and fracture inclination. At low saturation and high fracture inclination, compared with annular resistivity, phase resistivity and attenuation resistivity are more sensitive to fractures, and the measured values ​​are significantly larger than annular resistivity. The range of measured values ​​is related to the fracture inclination and hydrate saturation.

[0046] For example, Figure 2 The 240-247 m depth of the NGHP-02-17 well shows an increase in both annular resistivity and P-wave velocity (shown in the dashed box). Similar to the identification of the lower pore-filling hydrate anomaly, the existing technology usually interprets it as a fracture-filling hydrate layer.

[0047] In this embodiment, by comparing and analyzing the attenuation and phase resistivity (AL and PL) measured at a low frequency of 400kHz and the attenuation and phase resistivity (AH and PH) measured at a high frequency of 2MHz by electromagnetic wave resistivity measurement, 20 attenuation and phase resistivity curves collected at different source distances (such as 40 inches, 28 inches, 16 inches, 22 inches, and 34 inches) and high and low frequencies are compared with the annular resistivity and the calculated saturated water formation resistivity (R0), as shown in FIG. Figure 3 As shown, in the NGPH-02-17 well in India, the phase of the upper fracture-filling hydrate layer is separated from the attenuation resistivity, while the phase of the lower pore-filling hydrate layer is not separated from the attenuation resistivity.

[0048] Specifically, the saturated water resistivity is calculated using the following Archie formula:

[0049]

[0050] Among them, Rw is the formation symbiotic water resistance, which is generally 0.28Ωm; φ is the formation porosity; a and m are Archie constants, which are fitted by the intersection of formation factors and porosity. In the NGHP-02-17 well, the values ​​are: a = 2.44, m = 1.12.

[0051] By comparing 20 well logging data with different source distances, the resistivity of the formation with both phase and attenuation resistivity greater than that of saturated water is a hydrate layer containing fracture filling and pore filling types;

[0052] By comparison, it is found that in the fracture-filling hydrate layer, the measured values ​​of low-frequency attenuation resistivity (AL) at different source distances are similar, about 1-3Ωm. At a depth of 182-187.5 meters, the maximum value of low-frequency attenuation resistivity is about 3Ωm, while the measured values ​​of high-frequency attenuation resistivity (AH), low-frequency phase resistivity (PL) and high-frequency phase resistivity (PH) at different source distances are significantly different. The greater the source distance of the same type of resistivity, the greater the resistivity value. The high-frequency attenuation resistivity at a source distance of 40 inches is significantly greater than the measured value at a source distance of 16 inches. At a depth of 182-187.5 meters, the measured value of high-frequency attenuation resistivity collected at a source distance of 40 inches reaches 70Ωm, while the measured value of high-frequency phase resistivity collected at a source distance of 40 inches reaches 60Ωm.

[0053] As mentioned above, by comparing and analyzing the phase and attenuation resistivity curves collected at different source distances and frequencies, it is found that the phase and attenuation resistivity measurements at high frequency (2MHz) and large source distance (40inch) are the largest in the fracture-filled hydrate layer. The above parameters are more sensitive to the identification of fracture-filled hydrates; however, the difference between the phase resistivity measurements at different source distances and high frequencies is the most obvious, mainly because the fracture inclination has the greatest influence on the phase resistivity. The annular resistivity measurement value is only 2-3Ωm, mainly because the fracture has little influence on the annular resistivity.

[0054] Step 3), optimizing the sensitive parameters of hydrates of different occurrence types;

[0055] By comparing the electromagnetic wave resistivity and annular resistivity at different frequencies and different source distances in the above step 2), it can be seen that in the fracture-filled hydrate layer, regardless of the phase and attenuation resistivity measured by high-frequency and low-frequency measurements, the greater the source distance, the higher the measured resistivity; regardless of the phase or attenuation resistivity, the high-frequency measurement result is greater than the low-frequency measurement result, the greater the source distance, the greater the measurement result, and the electromagnetic wave resistivity measurement result is greater than the annular resistivity. Among them, in fractured formations, high-frequency electromagnetic wave resistivity (AH, PH) is more likely to separate than low-frequency electromagnetic wave resistivity (AL, PL), and the degree of separation is also greater, such as Figure 3As shown in the figure, when the electromagnetic wave resistivity is separated, the greater the source distance, the higher the resistivity anomaly value. The electromagnetic wave resistivity value at a source distance of 40 inches is greater than the measurement result at 16 inches.

[0056] Therefore, the selection of high-frequency electromagnetic wave resistivity with a minimum source distance of 16 inches and a maximum source distance of 40 inches can effectively cover the separation and degree of separation of electromagnetic wave resistivity, thus serving as a basis for judging the type of hydrate occurrence.

[0057] Step 4), using sensitive parameter ratios to analyze hydrate occurrence types;

[0058] Based on the comparative analysis of the above steps 2) and 3), the high-frequency electromagnetic wave resistivity (i.e., phase resistance P40H and attenuation resistivity A40H) measured at the maximum source distance is first compared with the annular resistivity and saturated water resistivity; among them, the phase and attenuation resistivity at the large source distance (40 inches) are compared with the annular resistivity, such as Figure 4 As shown in the figure; in water-saturated formations, the phase and attenuation resistivity are similar to the ring resistivity, and their ratio is stable at 1, while in shallow fracture-filled hydrate formations, the change curves of the ratios of phase and attenuation resistivity to ring resistivity (P40H / RING and A40H / RING) are significantly higher than the ratio of 1 in water-saturated formations; in formations at a depth of 182-187.5 meters, the two ratios are greater than 10, while in the lower pore-filled hydrate layer, the resistivity curve of the ratio is significantly lower than 1, and in some local formations the ratio is 0.1;

[0059] By comparing the ratio with the saturated water layer, and then comparing the high-frequency phase with the attenuation resistivity curve at a large source distance of 40 inches, and performing ratio analysis with the annular resistivity, it is found that the ratio of the fracture-filling hydrate layer is much greater than 1, and the local formation is as high as 10, which varies greatly with the difference of the hydrate filling in the fracture; while the pore-filling hydrate is significantly less than 1, with a local ratio of 0.1, and the saturated water layer without hydrate is approximately 1, indicating that the pore-filling and fracture-filling hydrates have significantly different characteristics. Figure 4 The hydrate ratios of the upper and lower formations in the figure are located on both sides of the saturated water layer ratio, respectively. This ratio is caused by the difference in electromagnetic resistivity and annular resistivity caused by the different occurrence forms of hydrates.

[0060] Step 5) Identify the hydrate occurrence type by using sensitive parameter intersection analysis;

[0061] Extract the sensitive parameters with the largest separation between the electromagnetic wave resistance and the ring resistivity in step 3) and step 4) and the most different measurement results, for example, for electromagnetic wave resistivity, the high-frequency measurement result is greater than the low-frequency measurement result, and the phase resistivity has the largest separation, such as the phase resistivity at a source distance of 40 inches is greater than the phase resistivity at a source distance of 16 inches;

[0062] The high-frequency phase resistivity (P40H and P16H) and ring resistivity (RING) logging data with the maximum source distance (40 inches) and the minimum source distance (16 inches) were used for cross-plot analysis to observe the zoning characteristics of the cross-plot.

[0063] From the cross analysis of the high-frequency phase resistivity at 40-inch source distance (P40H) and the high-frequency phase resistivity at 16-inch source distance (P16H), in the lower pore-filling hydrate layer, the data points are approximately coupled with the diagonal y=x, indicating that the high-frequency phase resistivity at different source distances is not obvious and the values ​​are close. However, in the upper fracture-filling hydrate layer, the data points show an obvious upward deviation, as shown in Figure 2. Figure 5 As shown in the left figure; in addition, the high-frequency phase resistivity ratio (i.e. P40H / P16H) measured at the maximum source distance of 40 inches and the minimum source distance of 16 inches and the annular resistivity are cross-analyzed. In the pore-filling hydrate layer, there is an obvious negative correlation, while in the fracture-filling hydrate layer, there is an obvious positive correlation, as shown in Figure 5 As shown in the right figure;

[0064] The sample points of the electromagnetic wave resistivity sensitive parameters measured above show different obvious change trends. In the fracture-filling hydrate layer, the phase resistivity at high frequency and large source distance is greater than that at small source distance, while in the pore-filling hydrate layer, the two are similar. Similarly, when the ratio of the two intersects with the annular resistivity, different change characteristics appear. The change rate of the fracture-filling hydrate layer is positive, while the change rate of the pore-filling hydrate is negative, showing two obviously different change trends. The change difference is the key basis for distinguishing between pore-filling and fracture-filling hydrates.

[0065] Step 6), using intersection and ratio analysis of sensitive parameters to jointly identify hydrate occurrence types;

[0066] From the electromagnetic wave resistivity data measured at different frequencies and different source distances in step 3) to step 5), as well as the intersection results of different sensitive parameters, the upper hydrate layer and the lower hydrate layer show obviously different change trends and different value ranges.

[0067] According to this embodiment, by comparing the phase, attenuation resistivity and annular resistivity changes, if the measured phase and attenuation resistivity are greater than the annular resistivity of the hydrate-containing abnormal layer, the method provided by this patent can be used to identify it as a fracture-filling hydrate; if the measured phase and attenuation resistivity are less than or close to the annular resistivity of the hydrate-containing abnormal layer, the method provided by this patent should be used to identify it as a pore-filling hydrate. The intersection of the identified sensitive parameters and the difference in ratio analysis can further quickly identify the hydrate occurrence form, without the need for drilling and coring, and the hydrate occurrence form can be quickly determined in the field to determine favorable targets for hydrate exploration.

[0068] Although the above embodiments have shown and described the present invention, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for rapidly identifying hydrate occurrence forms based on electromagnetic wave resistivity while drilling, characterized by: Based on the response differences between phase and attenuation resistivity and annular resistivity, the hydrate occurrence form is identified. First, the logging data including annular resistivity, P-wave velocity, density, and gamma from the wellbore are analyzed and compared with the resistivity of the saturated water layer to determine whether the hydrate reservoir is fracture-filled or pore-filled. Then, considering that both moderately saturated fracture-filled and pore-filled hydrates have the characteristics of high annular resistivity and high P-wave velocity anomalies, the phase resistivity and attenuation resistivity at different source distances are analyzed and compared with the annular resistivity to ultimately determine the hydrate occurrence form. The following steps are included: Step 1) Preliminary determination of hydrate reservoir type: Utilizing LWD data on annular resistivity, compressional wave velocity, density, and natural gamma ray logging, the velocity and annular resistivity variations of different formations are analyzed and compared with the resistivity of saturated water layers to preliminarily determine the hydrate reservoir type. Step 2) Analyze the abnormal characteristics of electromagnetic wave resistivity collected at different source distances and high and low frequencies; Compare the attenuation and phase resistivity curves of the electromagnetic wave resistivity at different source distances measured at a low frequency of 400kHz, and the attenuation and phase resistivity curves of the electromagnetic wave resistivity at different source distances measured at a high frequency of 2MHz, with the annular resistivity and the calculated resistivity of the water-saturated formation; Step 3) Optimize sensitive parameters for different hydrate occurrence types. Compare the electromagnetic wave resistivity and annular resistivity values ​​at different frequencies and different source distances in step 2) above, and select the high-frequency electromagnetic wave resistivity at the minimum source distance of 16 inches and the maximum source distance of 40 inches as the basis for determining the hydrate occurrence type. Step 4) Analyze the hydrate occurrence type using the ratio of sensitive parameters. Based on the comparative analysis of steps 2) and 3) above, first compare the high-frequency electromagnetic wave resistivity measured at a maximum source distance of 40 inches with the annular resistivity and saturated water resistivity. Specifically, perform a ratio analysis of the phase and attenuation resistivity at a maximum source distance of 40 inches with the annular resistivity. By comparing the ratio with the saturated water layer, compare the high-frequency phase and attenuation resistivity curves at a maximum source distance of 40 inches, and perform a ratio analysis with the annular resistivity. Step 5) Identify hydrate occurrence types using sensitive parameter cross-plot analysis. Extract the sensitive parameters with the largest separation between electromagnetic wave resistance and annular resistivity measured in steps 3) and 4) and the most divergent measurement results. Perform cross-plot analysis using high-frequency phase resistivity and annular resistivity logging data at a maximum source distance of 40 inches and a minimum source distance of 16 inches to observe the zoning characteristics of the cross-plot. Step 6) Use intersection and ratio analysis to jointly identify the hydrate occurrence type. From the electromagnetic wave resistivity data measured at different frequencies and source distances in steps 3) to 5), as well as the intersection results of different sensitive parameters, the upper and lower hydrate layers exhibit distinctly different change trends and value ranges. If the measured phase and attenuation resistivity are greater than the annular resistivity of the hydrate-bearing abnormal layer, the hydrates contained in the abnormal layer are determined to be fracture-filling hydrates. If the measured phase and attenuation resistivity are less than or close to the annular resistivity of the hydrate-bearing abnormal layer, the hydrates contained in the abnormal layer are determined to be pore-filling hydrates.

2. The method for rapidly identifying hydrate occurrence forms based on while-drilling electromagnetic wave resistivity according to claim 1, characterized in that: in step 2), the saturated water resistivity is calculated using the following Archie formula: ； in, Rw is the formation symbiotic water resistance, which is 0.28Ωm; φ is the formation porosity; a and m are Archie constants, which are obtained by cross-fitting the formation factor and porosity.

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