Method for depicting narrow river channel sand body based on sand body thickness and inversion body amplitude attribute

Abstract

The invention relates to a method for depicting a narrow river channel sand body based on sand body thickness and inversion body amplitude attributes. The method comprises the following steps: analyzing response characteristics of the narrow river channel sand body on a logging curve; carrying out abnormal value removal and standardization processing on the logging curve with obvious distinguishing characteristics; carrying out sand shale distinguishing capability analysis, and preferably selecting a logging curve with strong sand shale distinguishing capability as an inversion indication curve; waveform indication inversion is carried out, a target area inversion body is obtained, and the sand body thickness is predicted for a target layer section; extracting the average amplitude attribute of the inversion body of the target layer section; determining a river channel sand body judgment threshold value for dividing the river channel sand body and the non-river channel sand body; according to the obtained river channel sand body judgment threshold value, the narrow and small river channel is depicted in combination with well data and geological laws. According to the method, the narrow riverway is depicted through the two parameters, namely the sand body thickness obtained through the waveform indication inversion means and the amplitude attribute of the inversion body, and the identification precision of the narrow riverway sand body is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of petroleum and natural gas geophysical exploration, in particular to a method for depicting narrow and small channel sand bodies based on sand body thickness and inverted body amplitude attribute, which is applied to guide marine oil and gas exploration and development. BACKGROUND

[0002] Narrow and small channels refer to small-scale channels in river sedimentary systems or small-scale, narrow-width underwater distributary channels formed in delta front sedimentary environments. Compared with conventional large meandering rivers and braided rivers, which can reach hundreds to thousands of meters in channel width, narrow and small channels are usually less than 300 meters in width and only 2-3 meters in thickness, and are often difficult to identify. Although small in scale, narrow and small channel sand bodies still have higher physical properties than other types of sand bodies in the same sedimentary environment, providing favorable reservoir space for oil and gas accumulation. During oilfield development, due to low well pattern control, the phenomenon of injection without production or production without injection often occurs, resulting in low production of crude oil in this part of the sand body, which becomes a remaining oil enrichment area and an important target for remaining oil tapping in the fine exploration and development stage of the oilfield.

[0003] Seismic attribute analysis technology is a commonly used means for predicting interwell channel sand bodies. By extracting different types of seismic attributes, the correlation between the attributes and the type of sand body can be directly analyzed, or various attributes can be further processed to improve the prediction accuracy of the sand body. For example, the invention patent document CN202311753857.6 discloses a multi-azimuth seismic channel sand body prediction method that comprehensively utilizes the azimuth information of prestack seismic traces to improve the prediction accuracy of channel sand bodies. Yang Chunsheng et al. in "Small channel thin sand layer well-seismic joint identification technology and application: taking AGL area in western Changyuan of Daqing as an example" published in Petroleum Geophysical Prospecting in 2022 pointed out that three seismic response modes of narrow and small channel sand bodies can be constructed through forward modeling of underground geological structure. The narrow and small channel type reservoir main flow line azimuth prediction device and method disclosed in invention patent document CN202211229430.1 compiles the inner boundary and outer boundary of the narrow and small channel type reservoir according to sensitive seismic attributes, extracts the azimuth of the inner boundary and outer boundary of the narrow and small channel type reservoir, and realizes fine geological modeling of fluvial facies reservoirs. Jiang Yan et al. in "Prediction of narrow and small channel sand bodies using seismic principal component analysis and Fisher discrimination" published in Petroleum Geophysical Prospecting in 2018 pointed out that the seismic PCA analysis method effectively reduces the redundant information between seismic attributes, and combined with the Fisher sand and mudstone discrimination analysis model, the prediction accuracy of channel sand bodies is improved.

[0004] On the other hand, reservoir inversion prediction technology is also widely used for quantitative prediction of sand body thickness. This technology combines well logging curves as high frequency information with seismic data, converts seismic data into data volume that can more directly reflect the physical property difference between sand body and surrounding rock, makes up for the defect of insufficient vertical resolution of seismic data, and clearly highlights the physical property difference between reservoir and non-reservoir, greatly improving the identification accuracy and reliability of sand body. For example, Geophysical Progress published in 2018 "Geostatistical inversion method for depicting single channel sand body" pointed out that the variation trend of sand body thickness obtained by inversion can depict the channel distribution.

[0005] Limited by the small channel scale and the resolution of conventional seismic data, the technology related to seismic attribute analysis cannot directly identify the small channel of thin interbedded layers. Although the statistical processing of multiple seismic attributes has achieved high matching with well data in a specific area, it is difficult to ensure its applicability in other areas due to the lack of geological support. Although the reservoir inversion prediction technology can realize quantitative depiction of thin sand body, it is difficult to directly distinguish the small channel sand body from non-channel sand body only by thickness because the thickness of small channel sand body is thin and has little difference with other types of sand body. A method for depicting small channel sand body with high accuracy, strong operability and in line with geological rules needs to be proposed. SUMMARY

[0006] The purpose of the present application is to provide a method for depicting small channel sand body based on sand body thickness and inversion volume amplitude attribute, which solves the problem of low identification accuracy of small channel sand body in the prior art.

[0007] The technical solution adopted by the present application to solve its technical problems is that the method for depicting small channel sand body based on sand body thickness and inversion volume amplitude attribute comprises the following steps: Step one, analyze the response characteristics of small channel sand body on well logging curves, and preliminarily screen out well logging curves that show obvious distinguishing characteristics in thickness and amplitude of small channel sand body relative to other types of sand body; Step two, perform outlier removal and standardization processing on the well logging curves with obvious distinguishing characteristics in step one; Step three, analyze the sand-shale discrimination ability, and select well logging curves with strong sand-shale discrimination ability as inversion indicator curves; Step four, perform waveform indicator inversion to obtain inversion volume of the target area, and predict the sand body thickness of the target layer; Step five, extract the average amplitude attribute of the inversion volume of the target layer; Step six, determine the channel sand body discrimination threshold for dividing channel sand body and non-channel sand body, which is the sand body thickness threshold and the average amplitude value threshold of the inversion volume. Step 7: Based on the river channel sand body discrimination threshold obtained in Step 6, and in conjunction with well data and geological patterns, delineate the narrow river channel.

[0008] Step three in the above plan specifically refers to: The histogram method was used to analyze the sandstone and mudstone differentiation ability of the logging curves processed in step two. If the curve values ​​of sandstone and mudstone show a high average value and a small overlap area in the histogram, then the logging curve has a good sandstone and mudstone differentiation ability, and the curve with the best differentiation ability is used as the inversion indicator curve.

[0009] Step four in the above scheme is specifically as follows: Waveform indication inversion is carried out using the inversion indicator curve selected in step three to obtain the inversion body of the target area. During the inversion process, 10% of all wells are retained as post-test wells and do not participate in the inversion. They are used to verify the accuracy of the sand body thickness prediction. If the accuracy requirements are met, the predicted sand body thickness of the target layer is obtained.

[0010] Step six in the above scheme is specifically as follows: The sandstone thickness and inversion volume amplitude values ​​of channel sand and non-channel sand at each well location in the target layer are statistically analyzed, and cross plots are established using these two parameters as the horizontal and vertical axes, respectively. Based on the value range distribution of the two types of sand bodies in the cross plots, the discrimination thresholds for channel sand and non-channel sand are determined. The determined discrimination thresholds are verified using the post-test wells that did not participate in the inversion in step three. If the requirements are met, they are used for the prediction of narrow channels.

[0011] Step seven in the above scheme is specifically as follows: Based on the river sand body discrimination threshold determined in step six, the river sand body prediction area, non-river sand body prediction area, and suspected river area are divided on the plane. Where there are wells, the sand body type determined by the wells shall be used as the standard, and where there are no wells, the prediction results shall be used as the standard. Narrow channels are reasonably depicted according to the direction of the source material in the target area and the morphological pattern of the river. Beneficial effects

[0012] 1. This invention characterizes narrow channels using two parameters: sand body thickness and inversion volume amplitude, obtained through waveform inversion. Compared to seismic attribute analysis techniques, it overcomes the limitations of seismic resolution, significantly improving the identification accuracy of sand bodies in narrow channels. Compared to methods that only utilize the trend of sand body thickness variation in inversion to characterize channels, this invention considers the variation of inversion volume amplitude, solving the problem of small thickness differences between sand bodies in narrow channels and other types of sand bodies in the same environment. Therefore, this invention is advanced in characterizing sand bodies in narrow channels and can meet the requirements of fine exploration and development in oil fields.

[0013] 2. This invention utilizes two parameters—sand body thickness and inversion volume amplitude—to obtain the quantitative discrimination threshold between channel sand bodies and non-channel sand bodies, enabling quantitative prediction of narrow channel sand bodies. Combined with a post-well verification method, it allows for quality control of the application effect and improves the reliability of narrow channel prediction. Attached Figure Description

[0014] Figure 1 These are logging response characteristic diagrams of different sedimentary microfacies in the example area; Figure 2 These are the sand body thicknesses and natural gamma curve amplitudes of different sedimentary microfacies in the example area; Figure 3 This is a comparison chart of the natural gamma curves of all wells in the example area before and after standardization processing; Figure 4 It is a histogram that distinguishes the value range distribution of sandstone and mudstone by different logging curves; Figure 5 This is a cross-sectional view of the waveform indication inversion result; Figure 6 This is a graph showing the intersection of the thickness of the four sub-layers of sand in the example area and the gamma inversion amplitude; Figure 7 This is a cross-plot of post-well inspection sand body thickness and gamma inversion amplitude; Figure 8 It is a diagram depicting the process of carving a narrow river channel. Detailed Implementation

[0015] The present invention will be further described below with reference to the accompanying drawings: This method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties includes the following steps: Step 1: Analyze the response characteristics of narrow channel sand bodies on well logging curves to initially screen out well logging curves that show obvious distinguishing characteristics in thickness and amplitude compared to other types of sand bodies. Step 2: Perform outlier removal and standardization on the logging curves with obvious response differentiation characteristics from Step 1; Step 3: Conduct analysis on the ability to distinguish between sandstone and mudstone, and select the logging curve with strong ability to distinguish between sandstone and mudstone as the inversion indicator curve: The histogram method was used to analyze the sandstone and mudstone differentiation ability of the logging curves processed in step two. If the curve values ​​of sandstone and mudstone show a high average value and a small overlap area in the histogram, then the logging curve has a good sandstone and mudstone differentiation ability, and the curve with the best differentiation ability is used as the inversion indicator curve.

[0016] Step 4: Perform waveform indicator inversion to obtain the inversion volume of the target area, and predict the sand body thickness for the target layer: Waveform indication inversion is carried out using the inversion indicator curve selected in step three to obtain the inversion body of the target area. During the inversion process, 10% of all wells are retained as post-test wells and do not participate in the inversion. They are used to verify the accuracy of the sand body thickness prediction. If the accuracy requirements are met, the predicted sand body thickness of the target layer is obtained.

[0017] Step 5: Extract the average amplitude attribute of the inverted volume of the target layer segment; Step Six: Determine the threshold values ​​for classifying channel sand bodies from non-channel sand bodies: sand body thickness threshold and average amplitude value threshold of the inverted volume. The sandstone thickness and inversion volume amplitude values ​​of channel sand and non-channel sand at each well location in the target layer are statistically analyzed, and cross plots are established using these two parameters as the horizontal and vertical axes, respectively. Based on the value range distribution of the two types of sand bodies in the cross plots, the discrimination thresholds for channel sand and non-channel sand are determined. The determined discrimination thresholds are verified using the post-test wells that did not participate in the inversion in step three. If the requirements are met, they are used for the prediction of narrow channels.

[0018] Step 7: Based on the channel sand body discrimination threshold obtained in Step 6, and in conjunction with well data and geological patterns, characterize the narrow channel: Based on the river sand body discrimination threshold determined in step six, the river sand body prediction area, non-river sand body prediction area, and suspected river area are divided on the plane. Where there are wells, the sand body type determined by the wells shall be used as the standard, and where there are no wells, the prediction results shall be used as the standard. Narrow channels are reasonably depicted according to the direction of the source material in the target area and the morphological pattern of the river. Example

[0019] This method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties includes the following steps: Step 1 Observe the logging curve characteristics of typical wells in the case study area, such as Figure 1 As shown, narrow channel sand bodies exhibit box-shaped morphology in microelectrode resistivity, three-lateral resistivity, and natural gamma curves. Compared to other types of sand bodies, they have relatively larger thickness and higher curve amplitudes. However, the amplitude differences in the spontaneous potential curves are relatively small. Taking the natural gamma curve as an example (…). Figure 2 The thickness and amplitude of sand bodies in all wells in the example area were statistically analyzed. It can be seen that the channel sand bodies are significantly different from other types of sand bodies in terms of both thickness and amplitude, with larger thickness and lower amplitude.

[0020] Step Two Outlier removal and standardization are performed on the logging curves with obvious response characteristics from step one. For example... Figure 3 As shown, the natural gamma curves of different wells have significantly different value ranges before processing, but after processing, the value ranges of each well are uniform, which can ensure that the standards for distinguishing sandstone and mudstone are consistent.

[0021] Step 3 Histogram analysis was used to analyze the ability of processed well logging curves to distinguish between sandstone and mudstone. For example... Figure 4 As shown, the natural gamma curve has a high degree of differentiation between sandstone and mudstone, and the overlap between the value ranges of sandstone and mudstone is small. This indicates that the natural gamma curve has a better ability to distinguish between sandstone and mudstone than other curves, and can be used as an inversion indicator curve.

[0022] Step Four The natural gamma curve selected in step three is used as the inversion indicator curve to carry out waveform indicator inversion. During the inversion process, 10% of all wells are retained as test wells and are not included in the inversion; these are used to verify the accuracy of the sand body thickness prediction. If the accuracy requirements are met, the predicted sand body thickness of the target layer is obtained. Figure 5 This is a profile of the inversion results. Since the selected inversion indicator curve is the natural gamma curve, the obtained inversion volume is a natural gamma simulation. In the figure, black represents low gamma values, and white represents high gamma values. According to... Figure 4 The natural gamma curve histogram can be used to obtain a threshold of 100 API for distinguishing sandstone and mudstone. Therefore, the portion of the inverted volume with an API value less than 100 represents sandstone.

[0023] Step 5 Based on the natural gamma inversion volume obtained in step four, the average amplitude attribute is extracted along the layer segment to obtain natural gamma amplitude data at different locations on the target layer plane.

[0024] Step Six The sandstone thickness and inversion volume amplitude values ​​of channel sand and non-channel sand at each well location in the target layer were statistically analyzed, and cross plots were established using these two parameters as the horizontal and vertical axes, respectively. Based on the value range distribution of the two types of sand bodies in the figure, the discrimination threshold between channel sand and non-channel sand was determined. Figure 6 Cross-plots based on data from four sub-layers in the example area are shown. Based on these cross-plots, the sand body thickness threshold is set at 1.5m, and the gamma inversion amplitude threshold is set at 110 API. Using these two thresholds, the cross-plots are divided into three categories: sand body thickness ≥ 1.5m and gamma inversion amplitude ≤ 110 API (predicted channel areas); sand body thickness < 1.5m and gamma inversion amplitude > 110 API (predicted non-channel areas); and other areas (suspected channel areas). The established criteria are verified using post-test wells that did not participate in the inversion in step three. The sandstone thickness and inversion amplitude data from the post-test wells are statistically analyzed, and the verification results are as follows: Figure 7 As shown in Table 1, the accuracy rate of predictions for rivers was 85.2%, and the accuracy rate of predictions for non-rivers was 77.6%, confirming the high reliability of the prediction results.

[0025] Table 1: Predicted river zone Suspected river zone Predicted non-river zone Actual river (well • layer) 46 40 17 Actual non-river (well • layer) 8 43 59 Prediction accuracy (%) 85.2% — 77.6% Step Seven like Figure 8 As shown, a sand body thickness planar map and a gamma-ray inversion amplitude planar map of the target layer are compiled and then overlaid. Based on the division criteria established in step six, the overlaid map is divided into channel sand body prediction areas, non-channel sand body prediction areas, and suspected channel areas. Where well data is available, the sand body type determined by the well data is used; where no well data is available, the prediction results are used. Narrow channels are reasonably characterized based on the direction of the sediment source and the morphological patterns of the channels in the study area.

Claims

1. A method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties, characterized in that... Includes the following steps: Step 1: Analyze the response characteristics of narrow channel sand bodies on well logging curves to initially screen out well logging curves that show obvious distinguishing characteristics in thickness and amplitude compared to other types of sand bodies. Step 2: Perform outlier removal and standardization on the logging curves with obvious distinguishing features from Step 1; Step 3: Conduct analysis on the ability to distinguish between sandstone and mudstone, and select the logging curve with strong ability to distinguish between sandstone and mudstone as the inversion indicator curve; Step 4: Conduct waveform indicator inversion to obtain the inversion volume of the target area, and predict the sand body thickness for the target layer. Step 5: Extract the average amplitude attribute of the inverted volume of the target layer segment; Step 6: Determine the threshold values ​​for classifying channel sand bodies from non-channel sand bodies: sand body thickness threshold and average amplitude value threshold of the inverted body; Step 7: Based on the river channel sand body discrimination threshold obtained in Step 6, and in conjunction with well data and geological patterns, delineate the narrow river channel.

2. The method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties as described in claim 1, characterized in that: Step 3 specifically involves using the histogram method to analyze the sandstone and mudstone differentiation capabilities of the logging curves processed in Step 2. If the curve values ​​of sandstone and mudstone show a high average value and a small overlap area in the histogram, then the logging curve has good sandstone and mudstone differentiation capabilities, and the curve with the best differentiation capability is used as the inversion indicator curve.

3. The method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties according to claim 2, characterized in that: Step four is as follows: use the inversion indicator curve selected in step three to carry out waveform indicator inversion to obtain the target area inversion body; during the inversion process, 10% of all wells are retained as post-test wells and do not participate in the inversion, but are used to verify the accuracy of the sand body thickness prediction; if the accuracy requirements are met, the predicted sand body thickness of the target layer is obtained.

4. The method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties according to claim 3, characterized in that: Step six specifically involves: statistically analyzing the sandstone thickness and inversion volume amplitude values ​​of channel sand and non-channel sand at each well location in the target layer, and establishing a cross plot using these two parameters as the horizontal and vertical axes respectively. Based on the value range distribution of the two types of sand bodies in the cross plot, the discrimination threshold between channel sand and non-channel sand is determined. The determined discrimination threshold is then verified using the post-test wells that did not participate in the inversion in step three. If the requirements are met, it is used for the prediction of narrow channels.

5. The method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties according to claim 4, characterized in that: Step seven specifically involves: based on the channel sand body discrimination threshold determined in step six, dividing the channel sand body prediction area, non-channel sand body prediction area, and suspected channel area on the plane; where there are wells, the sand body type determined by the wells shall be used as the standard, and where there are no wells, the prediction results shall be used as the standard, and the narrow channel shall be reasonably depicted according to the direction of the source material in the target area and the morphological pattern of the channel.

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