A method for comprehensive geological-seismic identification of the origin of fault seismic reflection blank zones

Abstract

The present invention provides a method for comprehensively determining the causes of fault seismic reflection blank zones using a geological-seismic approach, comprising: step 1, comparative analysis of seismic data collected from different periods and using different acquisition methods within a study area; step 2, theoretical analysis of the causes of fault seismic reflection blank zones; step 3, analysis of the fault structure and geological characteristics of the fault cementation-filled zone; step 4, forward modeling to demonstrate the influence of the fault cementation-filled zone on fault reflection characteristics; step 5, dialectical analysis of the relationship between geological phenomena and fault seismic reflection characteristics; and step 6, based on the above analysis, establishing a geological-seismic model to determine the causes of fault seismic reflection blank zones, determine interpretation schemes for such faults, and guide well placement. This method for comprehensively determining the causes of fault seismic reflection blank zones provides valuable support for the detailed characterization of narrow reservoir traps in complex fault blocks, facilitating further exploration of oil and gas potential.

Description

Technical Field

[0001] The present invention relates to the field of geophysical exploration and comprehensive research, and in particular to a method for comprehensively determining the cause of a fault seismic reflection blank zone by geological and seismic analysis. Background Art

[0002] With the application of high-density seismic data, it has been discovered that high-density seismic data has a relatively rich cross-section wave. Compared with conventional sections, although the fault characteristics are clear, the double-track and blank reflection characteristics are more obvious in medium- and deep-layer faults, which greatly affects the detailed characterization of complex fault block sections and the success rate of drilling. This is mainly reflected in the appearance of "reflection blank zones" (generally 3-6 channels) at deep faults in high-density seismic data. The cross-section is relatively wide, affecting the determination of the high point of the fault block. Accurate characterization of the cross-section location is required for accurate well deployment. In particular, complex fault block reservoirs are mostly characterized by narrow oil-bearing strips and multiple vertical oil layers. In the later stages of development, residual oil is enriched along the fault line.

[0003] Currently, there is no research on fault seismic reflection gap zones, and even less is a method for determining their origin. The unclear formation mechanism of these faults makes it difficult to determine the accuracy of interpretation schemes for these faults. Previous researchers simply determined this based on the position of the reflection axis on the seismic profile, resulting in many wells failing to reach the high point of the fault block. Therefore, a comprehensive geological and seismic method for determining the origin of fault seismic reflection gap zones has been developed to address these technical issues. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for comprehensively determining the causes of fault seismic reflection blank zones by geological and seismic means, thereby providing a reliable basis and guidance for the identification and interpretation of faults with seismic reflection blank zones.

[0005] The purpose of the present invention can be achieved through the following technical measures: a method for comprehensively determining the cause of a fault seismic reflection blank zone by geological-seismic means, the method comprising: step 1, comparing and analyzing seismic data of different periods and different acquisition methods in the study area; step 2, conducting a theoretical analysis of the cause of a fault seismic reflection blank zone; step 3, conducting a geological characteristic analysis of the fault structure and the fault cementation filling zone; step 4, forward modeling to demonstrate the influence of the fault cementation filling zone on the fault reflection characteristics; step 5, dialectically analyzing the relationship between geological phenomena and fault seismic reflection characteristics; step 6, establishing a geological-seismic model based on the above analysis, determining the cause of a fault seismic reflection blank zone, determining an interpretation scheme for such faults, and guiding well site deployment.

[0006] The purpose of the present invention can also be achieved by the following technical measures:

[0007] In step 1, by comparing and analyzing the fault reflection characteristics of seismic data collected in different acquisition methods and at different times in the study area, the development law of the fault seismic reflection blank zone is clarified on the basis of judging the polarity of the seismic profile, and it is judged whether the acquisition and processing factors are the cause of the fault seismic reflection blank zone.

[0008] In step 2, a forward model is established under different conditions to conduct a theoretical analysis of the causes of the fault seismic reflection blank zone and determine whether the theory is consistent with the actual situation.

[0009] In step 3, the fault structure is dissected to clarify the geological characteristics of the fault cementation filling zone.

[0010] In step 4, based on step 3 and starting from the actual geological characteristics, a forward model is established to simulate and demonstrate the influence of the fault cementation filling zone on the seismic reflection characteristics of the fault.

[0011] In step 5, the dialectical method is used to further verify the geological phenomena of the fault cementation filling zone and the fault seismic reflection characteristics; the relationship between the distribution characteristics of the fault cementation filling zone and the fault seismic blank reflection characteristics is dialectically analyzed to determine whether the geological distribution characteristics of the fault cementation filling zone can explain the distribution characteristics of the fault seismic reflection blank zone on the profile.

[0012] In step 6, through the analysis of the above steps, a geological-seismic model is established to determine the cause of the fault seismic reflection blank zone, and combined with the drilled wells, an interpretation scheme for this type of fault is determined.

[0013] The method for comprehensively identifying the cause of fault seismic reflection blank zones, using geological and seismic data, takes full account of the geological characteristics of the fault. Through comparative analysis of different seismic data, dialectical analysis of fault geological characteristics and seismic reflection characteristics, and forward modeling, it studies the relationship between fault geological characteristics and seismic reflection characteristics. It clarifies the influence of the fault cementation filling zone on the fault seismic reflection characteristics, identifies the cause of fault seismic reflection blank zones, and provides guidance for the interpretation of faults with seismic reflection blank zones. This method fills a gap in the technology for studying fault seismic reflection blank zones in complex fault block oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flow chart for a specific implementation of the method for comprehensively determining the cause of a fault seismic reflection blank zone by geological and seismic means according to the present invention;

[0015] Figure 2 A cross-sectional diagram comparing high-density data and pre-stack time-biased data acquired twice in the same area in a specific embodiment of the present invention;

[0016] Figure 3 A comparative cross-section diagram of seismic data from different regions, different periods, and different processing methods in a specific embodiment of the present invention;

[0017] Figure 4 This is a seismic forward simulation cross-section diagram of different velocity differences between the upper and lower walls of a fault in a specific embodiment of the present invention;

[0018] Figure 5 This is a cross-sectional diagram of the velocity of the upper and lower walls of the actual drilling fault and the actual seismic profile analysis in a specific embodiment of the present invention;

[0019] Figure 6 This is an analysis diagram of actual drilling core and logging data in a specific embodiment of the present invention;

[0020] Figure 7 This is a forward modeling cross-section diagram of a fault with or without a fault cementation filling zone based on actual drilling in a specific embodiment of the present invention;

[0021] Figure 8 This is an analysis diagram of the relationship between oil and gas accumulation characteristics and fault cementation filling zone distribution characteristics in a specific embodiment of the present invention;

[0022] Figure 9 This is an analysis diagram of the filling characteristics of outcrop calcite and the seismic reflection characteristics of the fault cementation filling zone in a specific embodiment of the present invention;

[0023] Figure 10 A geological model of a fault cemented filling zone and a forward simulation cross-section thereof in a specific embodiment of the present invention;

[0024] Figure 11 This is a verification diagram of the actual drilling fault interpretation scheme in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the above and other objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings.

[0026] The present invention provides a method for comprehensively determining the cause of fault seismic reflection blank zones through geological and seismic analysis, comprising: performing comparative analysis of fault reflection characteristics of seismic data collected in different modes and at different times, clarifying the development law of fault seismic reflection blank zones, and determining whether acquisition and processing factors are the cause of fault seismic reflection blank zones. If the cause is due to acquisition and processing factors, the cause is explored from a processing perspective; if not, the cause is explored from a geological perspective. Using theoretical guidance, forward modeling models are established under different conditions to conduct a theoretical analysis of the causes of fault seismic reflection blank zones and determine whether the theory and practice are consistent. If they are consistent, the large difference in rock wave impedance on both sides of the fault is determined to be the cause. If not, based on further analysis of the fault structure and the geological characteristics of the cemented filling zone, a geological model is established using existing drilling data. Forward modeling is used to demonstrate the influence of the fault cemented filling zone on the fault seismic reflection characteristics. A dialectical analysis is then used to analyze the relationship between geological phenomena and fault seismic reflection characteristics, determining whether the geological distribution characteristics of the fault cemented filling zone can explain the distribution characteristics of the fault seismic reflection blank zone on the cross-section. Finally, the geological-seismic model is used to determine the cause of the fault seismic reflection blank zone and determine the interpretation scheme for this type of fault. This method for determining the cause of fault seismic reflection blank zones provides valuable support for the detailed characterization of narrow reservoir traps in complex fault blocks and facilitates further exploration of oil and gas potential.

[0027] In a specific embodiment, if Figure 1 As shown, Figure 1 This is a flow chart of the method for comprehensively determining the cause of fault seismic reflection blank zones using geology and seismology according to the present invention.

[0028] In step 101, by analyzing the fault reflection characteristics of seismic data collected in different acquisition modes and at different times in the study area, the distribution pattern of the "seismic blank reflection" characteristic faults is clarified, and the influence of acquisition and processing parameters on the fault display effect is clarified.

[0029] like Figure 2 、 Figure 3 As shown in the figure, based on the high-density data of Panhe Development Earthquake and Linyi North 2018, a comparative analysis was conducted with the high-precision data collected from the secondary data. The distribution pattern of faults with the characteristic of "seismic blank reflection" was clarified. First, on the profile: the blank reflection characteristics of the same fault generally appear in the middle and deep layers, that is, in the strata of Sha 4 and below. Second, on the plane: there are different degrees of cross-section wave phenomena in many areas of Huimin; but in the same area, the cross-section waves of single-point high-density data are richer than those of high-precision and pre-stack time deviation data, and the number of faults with "seismic blank reflection" characteristics has increased significantly; the following insights have been obtained through the distribution pattern of such faults:

[0030] Understanding 1: Single-point high-density data has the characteristics of small bins, high coverage, high lateral resolution and good signal-to-noise ratio. It has richer cross-sectional waves and significantly increases the number of faults with "seismic blank reflection" characteristics. Figure 2 As shown in the figure, the high-density data in the same area have significantly more faults with "seismic blank reflection" characteristics than the pre-stack time offset data acquired from the secondary acquisition. This proves that acquisition and processing parameters are one of the factors affecting the seismic reflection characteristics of faults.

[0031] Understanding 2: There are seismic reflection blank zones in different regions and different seismic data to varying degrees. Figure 3 As shown, seismic data from different regions, different periods, and different processing methods all contain seismic reflection blank zones to varying degrees. This demonstrates that acquisition and processing parameters are not the fundamental cause of fault seismic reflection blank zones, but rather geological factors. The following steps will explore the causal mechanism of fault seismic reflection blank zones from a geological perspective.

[0032] In step 102, theoretically, the fault wave is caused by the large difference in wave impedance between the rock on both sides of the fault, so the fault reflection characteristics should be directly related to the velocity of the fault on both sides. Figure 4 ) and found that when the velocity difference between the upper and lower walls is different, the fault will show different reflection characteristics. In conventional strata sedimentation, the velocity of the upper wall of the fault is generally lower than that of the lower wall. When the reflection wave enters the high-speed body from the low-speed body, the velocity difference between the upper and lower walls is small, and no fault wave is generated. Only when the velocity difference is greater than 600m / s, the fault begins to show blank reflection characteristics. However, in the study area, the velocity difference between the upper and lower walls is generally not large, such as Figure 5 While the velocities of Well Pan 40-41 on the upper and lower walls of the fault are comparable, the actual seismic profile shows a distinct single-track blank reflection, contradicting theoretical analysis. By corroborating theoretical analysis with actual geological characteristics, we have ruled out the velocity difference between the upper and lower walls as the cause of the "seismic reflection blank zone" on the fault.

[0033] In step 103, after eliminating external factors in the above steps, the fault structure is analyzed. Through core observation and logging data analysis, it is found that carbonate cementation and filling of sandstone near the fault in Linnan Depression is a common phenomenon. From the core and logging data of Xia 503 well, if Figure 6 As shown, near the fault plane, the sandstone has undergone severe carbonate cementation, causing a sharp deterioration in its physical properties. In terms of its oil content, due to its dense and hard structure, it contains virtually no oil or gas, transforming from a reservoir into a plugging layer. We call the sandstone zone near the fault filled with carbonate minerals the "cemented-fill zone." In the fault-cemented-fill zone, the well logging curve exhibits a sudden change, the natural potential amplitude decreases, and the acoustic time difference decreases significantly.

[0034] Well logging data from multiple wells crossing the fault also revealed that there is indeed a sandstone physical property change zone near the fault. The natural potential amplitude decreases, the resistivity increases, and the acoustic wave time difference becomes significantly smaller, appearing as a high-speed body with a significant velocity difference from the surrounding strata. Analysis of the fault cementation zone shows that it forms a clear reflection interface with the surrounding normal strata.

[0035] In step 104, based on the above-mentioned fault cementation filling zone logging characteristics analysis, forward simulation is used to analyze the impact of the fault cementation filling zone on the fault reflection characteristics. Preferably, the forward model of the well 40-41 well is used for analysis. Figure 7 As shown, the velocity increases near the fault in Well Pan 40-41, with a variation zone of 10 meters. Referring to actual wells, the vertical width of the fault cementation zone is 10 meters, with a velocity of 4200 m / s, and the velocity of the sandstone in the upper and lower walls is 3800 m / s. This shows that when a fault cementation zone exists, the phase of the seismic wavelet at the fault changes, forming a fault wave. The shielding effect of the high-speed cementation zone causes blank reflections in the underlying strata of the fault wave, consistent with the fault characteristics of the actual seismic profile. When the cementation zone is removed, the fault wave and the blank seismic reflection disappear, confirming that the fault cementation zone is the root cause of the blank reflections.

[0036] In step 105, the dialectical method is used to further verify the geological phenomena and the seismic reflection characteristics of the fault. The origin and distribution of the fault cementation filling zone are closely related to the "seismic blank reflection characteristics" of the fault:

[0037] (1) The formation water ion content of each layer in the Linnan Depression (Table 1) shows that the water from the Guantao Formation to the fourth member of the Shahejie Formation is of the CaCl2 type, rich in calcium ions, magnesium ions, and carbonate ions. Therefore, each layer has the conditions to form cemented filling and plugging. However, the older the formation, the more calcium ion and magnesium ion content increases. Therefore, the older the formation, the more likely it is to form calcite and dolomite filling and cementing zones. This is consistent with the fact that the blank zones in the actual seismic profile are mostly distributed in the deep layers.

[0038] Table 1 Ion content of formation water in each layer of Linnan Subsag

[0039] Stratum Mineralization mg / L <![CDATA[Total CO3 2- > <![CDATA[SO4 2- ]]> <![CDATA[Cl - ]]> <![CDATA[Ca 2+ ]]> <![CDATA[K + +That + ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Na + / Cl - ]]> Water type Number of samples Ng 9031 318 40 5955 214 3276 68 0.56-0.92 <![CDATA[CaCl2]]> 36 Ed 18495 484 64 10171 227 6373 94 0.55-0.97 <![CDATA[CaCl2]]> 42 <![CDATA[E31]]> 25224 618 43 14334 567 8659 172 0.41-1.29 <![CDATA[CaCl2]]> 65 <![CDATA[E32]]> 29122 664 165 16534 849 9783 312 0.21-1.57 <![CDATA[CaCl2]]> 181 <![CDATA[E33]]> 18573 630 119 22082 1574 12385 308 0.36-1.33 <![CDATA[CaCl2]]> 78 <![CDATA[E343]]> 57475 345 349 35799 3229 17881 528 0.45-0.97 <![CDATA[CaCl2]]> 43 <![CDATA[E34x]]> 102933 264 610 68757 16351 41790 42084 0.45 <![CDATA[CaCl2]]> 8

[0040] (2) According to the analysis of actual wells drilled, the sand-to-ground ratio in the study area is more than 70%, and oil and gas are blocked by fault cementation filling zones, but the oil and gas accumulation in the study area has the characteristics of oil and water intercalation. Figure 8 In the Pan40-Xie83 reservoir, a thick water layer lies between two oil layers. This reservoir formation is attributed to insufficient carbonate cementation in some sand layers, resulting in an ineffective seal and the resulting oil-water intercalation. This demonstrates that the degree of vertical filling and cementation varies along the same fault.

[0041] Moreover, judging from the filling characteristics of the outcrop calcite ( Figure 9 ) also confirms that the degree of filling and cementation varies across different parts of the same fault. Some faults have wide cementation zones, others have narrower zones, and some have no filling at all. This characteristic of the fault's cementation zone leads to variations and discontinuities in the amplitude of the fault waves on actual seismic profiles. The mutual confirmation of these geological phenomena with seismic reflection characteristics demonstrates that the fault's cementation zone effectively explains the seismic blank reflection characteristics of the fault.

[0042] Finally, through comparative analysis of different seismic data, dialectical analysis of fault geological characteristics and seismic reflection characteristics, and forward simulation, it was fully confirmed that the fault cementation filling zone affects the seismic reflection characteristics of the fault and is the main reason for the formation of the fault seismic reflection blank zone.

[0043] In step 106, through geological-seismic model identification, it is recognized that the fault seismic reflection blank zone is caused by the shielding effect of the fault high-speed cementation filling zone. According to the wells drilled so far that have encountered the fault cementation filling zone, the actual fault cementation filling zone is generally narrow, ranging from 30cm to 10m. Using forward simulation, it can be seen that the fault cementation filling zone is difficult to identify on the actual seismic profile, such as Figure 10 Therefore, in practical applications, when interpreting this type of fault, the fault should be interpreted at the end of the hanging wall reflection axis, that is, at the peak of the cross-section reflection.

[0044] Finally, the above interpretation scheme was verified by combining the wells that have been drilled. The wells 40-41 have encountered a fault with the characteristics of “seismic blank reflection”, such as Figure 11 By comparing the layers, the fault point of this well is located at the crest of the fault emission wave, which confirms the correctness of the interpretation scheme of this type of fault and guides the description of faults with the characteristic of "seismic blank reflection".

[0045] The method of the present invention for comprehensively determining the cause of fault seismic reflection blank zones by geological-seismic means determines the cause of fault seismic reflection blank zones and determines the interpretation scheme for faults with seismic reflection blank zones through comparative analysis of different seismic data, dialectical analysis of fault geological characteristics and seismic reflection characteristics, and forward simulation. Determining the cause guides the accurate description of such faults, fills the gap in oil and gas exploration research, promotes the advancement of complex fault block interpretation technology, guides the next step of exploration and development of complex fault block oil and gas reservoirs in the Jiyang Depression, and improves the efficiency of exploration and development of complex fault block oil reservoirs.

Claims

1. A method for comprehensively determining the cause of fault seismic reflection blank zones by geological and seismic methods, characterized in that: The method for comprehensively determining the causes of fault seismic reflection blank zones by geological and seismic integration includes: Step 1: Compare and analyze seismic data collected in different periods and with different acquisition methods in the study area; Step 2: Conduct theoretical analysis on the causes of fault seismic reflection blank zones; Step 3: Analyze the fault structure and geological characteristics of the fault cementation filling zone; Step 4: forward modeling to demonstrate the influence of the fault cementation filling zone on the fault reflection characteristics; Step 5: dialectically analyze the relationship between geological phenomena and fault seismic reflection characteristics; Step 6: Based on the above analysis, a geological-seismic model is established to identify the cause of the fault seismic reflection blank zone, determine the interpretation scheme for this type of fault, and guide well location deployment; In step 2, forward models under different conditions are established to conduct theoretical analysis on the causes of fault seismic reflection blank zones and determine whether the theory is consistent with the actual situation. In step 3, the fault structure is dissected to clarify the geological characteristics of the fault cementation filling zone; In step 4, based on step 3 and starting from the actual geological characteristics, a forward model is established to simulate and demonstrate the influence of the fault cementation filling zone on the seismic reflection characteristics of the fault; In step 5, the geological phenomena of the fault cementation filling zone and the seismic reflection characteristics of the fault are further verified by dialectical analysis. The relationship between the distribution characteristics of the fault cementation filling zone and the fault seismic blank reflection characteristics is dialectically analyzed to determine whether the geological distribution characteristics of the fault cementation filling zone can explain the distribution characteristics of the fault seismic blank reflection zone on the profile. In step 6, through the analysis of the above steps, a geological-seismic model is established to determine the cause of the fault seismic reflection blank zone, and combined with the drilled wells, an interpretation scheme for this type of fault is determined.

2. The method for comprehensively determining the cause of fault seismic reflection blank zones by geological and seismic methods according to claim 1, characterized in that: In step 1, by comparing and analyzing the fault reflection characteristics of seismic data collected in different acquisition methods and at different times in the study area, the development law of the fault seismic reflection blank zone is clarified on the basis of judging the polarity of the seismic profile, and it is judged whether the acquisition and processing factors are the cause of the fault seismic reflection blank zone.

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