Hydrate - free gas exploration target selection method based on evaluation of natural gas transmission efficiency

Abstract

The present invention discloses a method for selecting exploration areas of hydrate-free gas based on the evaluation of natural gas conduction efficiency. The present invention obtains a high-resolution 3D seismic data volume; establishes a complete sequence geological framework; searches for enhanced reflection axes, i.e., "bright spots", along the top of the conduction structure, i.e., the shallow surface layer, on the seismic profiles intercepted from the high-resolution 3D seismic data volume, extracts amplitude attribute slices along the direction of the enhanced reflection axes, and the total area of multiple enhanced reflection axes is S 总 ; conducts numerical simulation studies on oil and gas migration using PetroMod software based on basic geological data, and extracts the effective parameter, the total gas volume G, which can reflect the amount of oil and gas migrating to a specific shallow position, i.e., above the conduction structure; calculates the logging saturation S h of natural gas hydrate using Archie's formula; combines the evaluation of the conduction efficiency of different conduction structures and the drilling saturation of natural gas hydrate to select exploration areas of natural gas hydrate-free gas and guide the strategic selection of oil and gas areas.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration, and particularly relates to a method for exploring and selecting areas for hydrate-free gas based on the evaluation of natural gas conduction efficiency. Background Art

[0002] There has been little attention paid to the migration efficiency of natural gas in different conduction structures and evaluation methods, and there is a lack of effective quantitative analysis means. The spatial relationship between the occurrence of natural gas and the dominant conduction channels has not been established, thus restricting the exploration and strategic area selection evaluation of free shallow gas and natural gas hydrates in oil and gas bearing basins. Summary of the Invention

[0003] The purpose of the present invention is to propose a method for exploring and selecting areas for hydrate-free gas based on the evaluation of natural gas conduction efficiency in view of the above deficiencies of the prior art.

[0004] A method for exploring and selecting areas for hydrate-free gas based on the evaluation of natural gas conduction efficiency of the present invention includes the following steps:

[0005] S1: Collect and process 3D seismic data of the marine research area to obtain a high-resolution 3D seismic data volume;

[0006] S2: Based on the high-resolution 3D seismic data volume, conduct fine closed interpretation of sequence stratigraphy and conduction structures, clarify their spatial development positions and planar distributions, and establish a complete sequence geological framework;

[0007] S3: On the seismic profile intercepted from the high-resolution 3D seismic data volume, search for enhanced reflection axes, i.e., "bright spots", along the top of the conduction structure, that is, the shallow surface layer, count the number a of enhanced reflection axes, extract amplitude attribute slices along the direction of the enhanced reflection axes, and respectively finely depict the boundaries of strong amplitudes, i.e., the boundaries of the enhanced reflection axes, on the obtained amplitude attribute plan view to obtain the planar distribution areas S1, S2,... S a , S1, S2,... S a Sum them up to obtain a total area of S 总 ; The area unit is km 2 ;

[0008] S4: Based on basic geological data, carry out numerical simulation research on oil and gas migration using PetroMod software to obtain a cross-section showing the oil and gas migration path, and further obtain the information of the oil and gas pointing area of the numerical simulation;

[0009] S5: According to the information of the oil and gas pointing area of the numerical simulation, extract the effective parameter total gas volume G that can reflect the amount of oil and gas migrating to a specific shallow position, that is, above the conduction structure, and the unit is Mtons;

[0010] S6: Combine the S of all the obtained conduit structures 总 , G, and obtain the average value of all S 总 and the average value of all G, and compare the parameters S of the enhanced reflection axis at the top position of different conduit structures 总 , the total amount of gas G obtained by numerical simulation, comprehensively judge the gas conduction efficiency of different conduit structures, and divide the high and low values of S 总 and G with the average value as the boundary. Values greater than the average value are high values, and values less than the average value are low values; if S 总 and G are both low values, it means that the gas conduction efficiency of this type of conduit structure is low; if S 总 is high while G is low or S 总 is low while G is high, it means that the gas conduction efficiency of this type of conduit structure is medium;

[0011] S7: Calculate the logging saturation S of natural gas hydrate using Archie's formula h ;

[0012] S8: Combine the evaluation of the conduction efficiency of different conduit structures and the drilling saturation of natural gas hydrate to select areas for natural gas hydrate-free gas exploration; among them, areas with high conduction efficiency and high hydrate saturation are favorable areas for combined exploitation of hydrate-free gas; areas with high conduction efficiency and low hydrate saturation are favorable areas for free gas, and areas with low and medium conduction efficiency and low hydrate saturation are exploration risk areas for natural gas hydrate-free gas;

[0013] Among them, there is no sequential relationship between S7 and S1-6.

[0014] Furthermore, the conduit structure includes faults, diapir structures, gas chimneys, and blank reflection zones.

[0015] Furthermore, in S4, the basic geological data includes sequence stratigraphic framework, heat flow data, and lithology data.

[0016] Furthermore, in S4, it also includes comparing the obtained information on the oil and gas pointing area from numerical simulation with the distribution area of the conduit structure and the enhanced reflection axis shown above on the seismic profile. If the two have a good coupling relationship, it proves the effectiveness of the simulation results.

[0017] Furthermore, in S5, the logging saturation S of natural gas hydrate h :

[0018]

[0019] where S w is the water saturation, %; R w is the resistivity of seawater, Ω·m; R t is the measured resistivity of the formation, Ω·m; is the formation porosity, %; a, n, and m are constants related to the inherent properties of sediment pores. m is related to the rounding degree of sediment particles. The worse the rounding, the larger m is, and its value range is from 1 to 3; n is the Archie constant, and n is 3; in the marine research area, the porosity is relatively large, and a is equal to 1.

[0020] Further, in S8, S h Greater than 30% means high hydrate saturation, S h Less than 30% means low hydrate saturation.

[0021] The present invention proposes a method for selecting exploration areas of hydrate-free gas based on the evaluation of natural gas conduction efficiency, which combines qualitative and quantitative methods, comprehensively evaluates the natural gas migration efficiency of conduction structures, compares the differences in natural gas migration efficiency of different conduction structures, conducts comparative research, and through the selected efficient conduction structures, according to the results of their planar distribution positions depicted based on high-resolution three-dimensional seismic data, establishes the relationship between the occurrence of natural gas and the efficiency of dominant conduction structures. Then, based on the specific types and distributions of dominant conduction structures, it can provide a reference for further searching for areas rich in high-saturation natural gas hydrates and free shallow gas, directly prospecting for minerals above them, thereby further guiding the process of selecting evaluation areas for free shallow gas and natural gas hydrates, and guiding the strategic selection of oil and gas areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The seismic profile of the Qiongdongnan Basin shows diapir-gas chimney structures;

[0023] Figure 2 The seismic profile of the Qiongdongnan Basin shows a fault conduction system;

[0024] Figure 3 The seismic profile of the Qiongdongnan Basin shows a fracture diffusion system (gas diffusion zone);

[0025] Figure 4 The planar distribution area of enhanced reflection axes of various conduction structures based on amplitude attributes;

[0026] Figure 5 The total amount of shallow natural gas based on the results of numerical simulation of oil and gas migration;

[0027] Figure 6 Calculation of natural gas hydrate saturation based on logging data;

[0028] Figure 7 The comprehensive stratigraphic columnar section of the Qiongdongnan Basin. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following are specific embodiments of the present invention in combination with the drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0030] Step 1: Collect and process 3D seismic data in the study area of the Qiongdongnan Basin to obtain a high-resolution 3D seismic data volume of the study area of the Qiongdongnan Basin.

[0031] Step 2: Based on the high-resolution 3D seismic data volume, conduct a comprehensive evaluation of three types of natural gas conduction structures, namely faults, gas chimney structures, and gas diffusion zones. Conduct a fine closed interpretation of faults, fractures (gas) diffusion zones, and gas chimneys in the 3D working area of the Lingnan Low Uplift in the Qiongdongnan Basin to clarify their distribution positions ( Figures 1 - 3 ), and obtain a sequence stratigraphic framework. Among them, the sequence interface T SB represents the seabed, and T2, T3, T4, T5, T6, T7, T g respectively represent the sub-interfaces of formation groups. See Figure 7 for details.

[0032] Step 3: On the seismic profiles intercepted from the high-resolution 3D seismic data volume, search for enhanced reflection axes (i.e., "bright spots") along the top (shallow surface layer) of the conduction structure, count the number a of enhanced reflection axes, extract amplitude attribute slices along the direction of the enhanced reflection axes, and count the planar distribution areas S 总1 、S 总2 、S 总3 of the enhanced reflection axes corresponding to the three conduction channels of gas chimneys, faults, and fractures (gas) diffusion zones. They are 21.67 km 2 , 19.67 km 2 , 7.32 km 2 ( Figure 4 ).

[0033] Step 4: Based on the sequence stratigraphic framework, heat flow data, and lithology data of the study area of the Qiongdongnan Basin, conduct a numerical simulation study of hydrocarbon migration using the PetroMod software to obtain a cross-section showing the hydrocarbon migration path ( Figure 5 ), and then obtain the information of the hydrocarbon pointing area from the numerical simulation, and compare it with the conduction structure on the seismic profile and the distribution area of the enhanced reflection axes (position of "bright spots") shown above. If there is a good coupling relationship between the two, it proves the effectiveness of the simulation results.

[0034] Step 5: According to the information of the hydrocarbon pointing area from the numerical simulation, that is, the hydrocarbon migration process in different conduction channels, extract the total gas volumes G1, G2, G3 Figure 5 conducted by gas chimneys, faults, and fractures (gas) diffusion zones, which are 1.19 Mtons, 0.95 Mtons, and 0.78 Mtons respectively.

[0035] The results of hydrate drilling often indicate the occurrence state of hydrates and underlying free gas to a certain extent. Use Archie's formula to calculate the logging saturation S of natural gas hydratesh Calculation of Figure 6 As shown, the average hydrate saturation S calculated from the resistivity curves of Well 1, Well 2 and Well 3 (gas chimney, fracture and fracture (gas) diffusion zone) h1 , S h2 and S h3 are 31.9%, 0% and 0% respectively.

[0036] From the above results, it can be seen that the gas chimney in the Lingnan Low Uplift area of the Qiongdongnan Basin has the highest gas conduction efficiency for natural gas, with free natural gas occurring in the shallow layer and abnormal enrichment of hydrates; the fracture has the second highest gas conduction efficiency, with free natural gas occurring in the shallow layer but limited hydrate occurrence or no hydrate enrichment; the fracture (gas) diffusion zone has the lowest gas conduction efficiency, with neither free natural gas nor hydrates being enriched in the shallow layer. Therefore, it is suitable to carry out exploration and development of free natural gas above the gas chimney (the area where Well 1 is located) and the fracture conduction structure (the area where Well 2 is located). It is more suitable to carry out exploration and development of natural gas hydrate resources and free gas above the gas chimney structure, and the current exploration results are consistent with the conclusions obtained by using the method of the present invention. The present invention has the advantages of strong operability, wide coverage, cross-verification between multiple parameters, and high accuracy, and solves the problem of semi-quantitative evaluation of the conduction efficiency of the conduction channel under formation conditions.

[0037] Where not covered above, the prior art applies.

[0038] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and not for limiting the scope of the present invention. Those skilled in the art of the present invention can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made based on the technical essence of the present invention to the above embodiments shall be included in the protection scope of the present invention.

Claims

1. A method for selecting exploration areas of hydrate-free gas based on the evaluation of natural gas conduction efficiency, characterized in that: It includes the following steps: S1: Conduct 3D seismic data acquisition and processing in the marine research area to obtain a high-resolution 3D seismic data volume; S2: Based on the high-resolution 3D seismic data volume, conduct fine closed interpretation of sequence stratigraphy and conduit structures, clarify their spatial development positions and planar distributions, and establish a complete sequence geological framework; S3: Search for enhanced reflection axes, i.e., "bright spots", along the top of the conducing structure, namely the shallow surface layer, on the seismic section intercepted from the high-resolution 3D seismic data volume, count the number a of enhanced reflection axes, extract amplitude attribute slices along the direction of the enhanced reflection axes, and respectively and finely depict the boundaries of strong amplitudes, i.e., the boundaries of the enhanced reflection axes, on the obtained amplitude attribute plan view to obtain the planar distribution areas S1, S2, …… S a , S1, S2, …… S a Sum them up to obtain the total area S 总 ; The area unit is km 2 ; S4: Based on the basic geological data, use the PetroMod software to carry out numerical simulation research on hydrocarbon migration, obtain a cross-section showing the hydrocarbon migration path, and then obtain the hydrocarbon target area information of the numerical simulation; S5: According to the hydrocarbon target area information of the numerical simulation, extract the effective parameter total gas volume G, unit Mtons, which can reflect the amount of hydrocarbons migrating to a specific shallow position, i.e., above the conduit structure; S6: Combine the S of all the obtained conduction structures 总 , G, and obtain all S 总 's average value and the average value of all Gs, and compare the parameters S of the enhanced reflection axis at the top position of different conduction structures 总 , the total amount of gas G simulated numerically, comprehensively judge the gas conduction efficiency of different conduction structures, and divide the high and low values of S 总 and G with the average value as the boundary. Values greater than the average value are high values, and values less than the average value are low values; if S 总 and G are both low values, it means that the conduction efficiency of this type of conduction structure for natural gas is low; if S 总 is high while G is low or S 总 is low while G is high, it means that the conduction efficiency of this type of conduction structure for natural gas is medium; S7: Calculate the logging saturation S of natural gas hydrate using the Archie formula h ; S8: Combine the evaluation of the conduit efficiency of different conduit structures and the drilling saturation of natural gas hydrates to select areas for natural gas hydrate-free gas exploration; among them, areas with high conduit efficiency and high hydrate saturation are favorable areas for combined exploitation of hydrates-free gas; areas with high conduit efficiency and low hydrate saturation are favorable areas for free gas; areas with low and medium conduit efficiency and low hydrate saturation are exploration risk areas for hydrates-free gas; Among them, S7 has no sequential relationship with S1-6.

2. The method for selecting exploration areas of hydrate-free gas based on the evaluation of natural gas transmission efficiency according to claim 1, wherein: The said conduit structure includes faults, diapir structures, gas chimneys and blank reflection zones.

3. A method for exploring and selecting areas of hydrate-free gas based on the evaluation of natural gas transmission efficiency as described in claim 1, characterized in that: In S4, the basic geological data includes sequence stratigraphic framework, heat flow data and lithology data.

4. A method for selecting exploration areas of hydrate-free gas based on the evaluation of natural gas transmission efficiency according to claim 1, characterized in that: In S4, it also includes comparing the obtained hydrocarbon target area information of the numerical simulation with the distribution area of the enhanced reflection axis shown above the conduit structure on the seismic section. If there is a good coupling relationship between the two, it proves the effectiveness of the simulation results.

5. A method for selecting exploration areas of hydrate-free gas based on the evaluation of natural gas transmission efficiency according to claim 1, characterized in that: In S5, the logging saturation S of natural gas hydrate h : Among them, S w is the water saturation, %; R w is the resistivity of seawater, Ω·m; R t is the measured formation resistivity, Ω·m; is the formation porosity, %; a, n, and m are constants related to the inherent properties of sediment pores. m is related to the rounding degree of sediment particles. The worse the rounding, the larger m. The value range is 1 - 3; n is the Archie constant, and n is 3; in the marine research area, the porosity is relatively large, and a is equal to 1.

6. A method for exploring and selecting areas for hydrate-free gas based on the evaluation of natural gas transportation efficiency according to claim 1, characterized in that: In S8, S h If it is greater than 30%, the hydrate saturation is high. S h If it is less than 30%, the hydrate saturation is low.

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