Method for identifying natural gas hydrate by using incremental ratio between wave impedance of longitudinal and traverse waves

A technology of wave impedance and longitudinal and transverse waves, which is applied in the field of geological exploration, can solve the problems of not being very reliable and increasing the velocity of longitudinal and transverse waves in the formation, and achieve the effects of improving exploration accuracy, reliability and saving drilling costs

Active Publication Date: 2010-02-10
刘学伟 +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0011] The disadvantage of this method is that many non-hydrate factors can also cause the increase of compressional and shear wave velocities in the formation
Therefore, it is not a very credible method to identify hydrates by using the characteristics of P-S wave velocity increase

Method used

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  • Method for identifying natural gas hydrate by using incremental ratio between wave impedance of longitudinal and traverse waves
  • Method for identifying natural gas hydrate by using incremental ratio between wave impedance of longitudinal and traverse waves
  • Method for identifying natural gas hydrate by using incremental ratio between wave impedance of longitudinal and traverse waves

Examples

Experimental program
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Effect test

Embodiment 1

[0050] Ocean Drilling 164 voyage discovered gas hydrates in BlakeRedge wells in the United States, such as Well 995. In this example, using the known P-wave and S-wave velocity curves and density curves in Well 995, the P-S wave impedance increment ratio is calculated. According to the known porosity and the graph of the P-S wave impedance increment ratio threshold relationship curve given in the accompanying drawings, Identify whether the formation contains hydrates. Calculate the depth range of hydrate-bearing formations and compare them with drilling results.

[0051] The method for identifying natural gas hydrates using the ratio of compressional and transverse wave impedance increments of the present invention includes the following steps:

[0052] (1) Multiply the measured formation P-wave velocity and formation S-wave velocity by the actual density of the formation respectively to obtain the compressional wave impedance Z P Curve and shear wave impedance Z S curve. f...

Embodiment 2

[0062] In 2007, my country's first drill in the Shenhu area of ​​the South China Sea successfully obtained hydrate samples. Prior to drilling, hydrate identification was performed prior to drilling using seismic data and the method of the present invention. The identification result shows the presence of hydrates, which provides a basis for determining the well location. Subsequent drilling results confirmed the correctness of the identification results. This embodiment presents the identification process.

[0063] The method for identifying gas hydrates by using the ratio of compressional and shear wave impedance increments includes the following steps:

[0064] (1) Using AVO inversion technology to invert the actual compressional wave impedance Z of the formation from the seismic data P and shear wave impedance Z S Variation curves with depth, respectively, as Figure 5 and Figure 6 As shown, the depth is expressed in two-way travel time, and the unit is milliseconds;...

Embodiment 3

[0074] Both of the above two examples only show the variation curve of the P-to-S wave impedance incremental ratio with depth at the drilling position and the hydrate identification results. We can also perform the same processing on the seismic section to obtain the hydrate identification section, that is, the P-wave and S-wave impedance increment ratio section. This example shows the BlakeRedge hydrate identification section in the United States, which passes through Well 995.

[0075] The method for identifying gas hydrates by using the ratio of compressional and shear wave impedance increments includes the following steps:

[0076] (1) Using AVO inversion technology to invert the actual compressional wave impedance Z of the formation from the seismic data P Profile and shear wave impedance Z S profile, such as Figure 8 and Figure 9 shown;

[0077] (2) For each track on the section, estimate the compressional wave impedance Z of the water-saturated formation accordin...

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Abstract

The invention discloses a method for identifying natural gas hydrate (NGH) by using the incremental ratio between the wave impedance of longitudinal and traverse waves. The method comprises the following steps: (1) inverting the longitudinal wave impedance ZP=VP rho of strata and the transverse wave impedance ZS=VS rho of strata by using seismic data; (2) obtaining the longitudinal wave impedanceZP0 and the transverse wave impedance ZS0 of water-saturated strata; (3) obtaining the longitudinal wave impedance increments delta ZP=ZP-ZP0 and the transverse wave impedance increments delta ZS= ZS-ZS0; (4) obtaining the incremental ratio Ratio of the wave impedance of longitudinal and traverse waves; (5) inverting the porosity of strata; (6) determining the threshold value of the incremental ratio of the wave impedance of longitudinal and traverse waves according to the porosity; (7) judging whether the incremental ratio Ratio of the wave impedance of longitudinal and traverse waves is higher than the threshold value, if so, indicating that the strata contain the NGH; and (8) drawing the bisect where the incremental ratio of the wave impedance of longitudinal and traverse waves is higher than that of the threshold value, wherein the bisect can reflect the distribution range of underground NGH. The method of the invention improves the reliability of the identification results of NGH,greatly improves the exploration precision of NGH and reduces the dry-well rate.

Description

technical field [0001] The invention belongs to the field of geological exploration, and discloses a method for identifying natural gas hydrates by utilizing the ratio of compressional and transverse wave impedance increments. Background technique [0002] Natural gas hydrate is an alternative energy source for oil and coal, and has attracted much attention from governments and academia, as well as industry. Gas hydrates mainly occur in the deep seabed and below the permafrost. Hydrate is a white solid substance produced by the chemical reaction of methane gas and water under low temperature and high pressure conditions. Hydrate occurs in the sandstone pore space. The main technologies for detecting hydrates are: seismic exploration technology, drilling technology, geochemical detection technology, seabed camera and sampling technology. Among them, seismic exploration is the most effective technique for detecting hydrates. At present, seismic exploration technology mainl...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01V1/28G01V1/30G01V1/38
Inventor 刘学伟
Owner 刘学伟
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