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

Abstract

The present application relates to a method for depicting narrow and small channel sand bodies based on sand body thickness and inversion body amplitude attribute, which comprises: analyzing the response characteristics of narrow and small channel sand bodies on logging curves; performing abnormal value removal and standardization processing on logging curves with obvious distinguishing characteristics; carrying out sandstone and mudstone distinguishing ability analysis, and preferably selecting logging curves with strong sandstone and mudstone distinguishing ability as inversion indicating curves; carrying out waveform indicating inversion, obtaining target area inversion bodies, and predicting sand body thickness for target intervals; extracting average amplitude attribute of target interval inversion bodies; determining channel sand body discrimination threshold for dividing channel sand bodies and non-channel sand bodies; and depicting narrow and small channels according to the obtained channel sand body discrimination threshold, in combination with well data and geological rules. The present application depicts narrow and small channels by using two parameters of sand body thickness and inversion body amplitude attribute obtained through waveform indicating inversion means, which greatly improves the recognition accuracy of narrow and small channel sand bodies.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration of oil and gas, specifically to a method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties, which is applied to guide marine oil and gas exploration and development. Background Technology

[0002] Narrow channels refer to smaller channels in fluvial sedimentary systems, or small-scale, narrow underwater distributary channels formed in deltaic front sedimentary environments. Compared to conventional large meandering rivers and braided rivers, which can reach widths of hundreds to thousands of meters, narrow channels are typically less than 300 meters wide and only 2-3 meters thick, often making them difficult to identify. Despite their small size, narrow channel sand bodies still possess higher physical properties compared to other types of sand bodies within the same sedimentary environment, providing favorable reservoir space for hydrocarbon accumulation. During oilfield development, due to low well network control, injection without production or production without injection often occurs, resulting in low utilization of crude oil in these sand bodies. These areas become rich in residual oil and are important targets for tapping residual oil potential during the refined exploration and development phase of oilfields.

[0003] Seismic attribute analysis is a common method for predicting inter-well channel sand bodies. By extracting different types of seismic attributes, their correlation with sand body types can be directly analyzed, or various attributes can be further processed to improve the prediction accuracy of sand bodies. For example, a multi-azimuth seismic channel sand body prediction method disclosed in invention patent document CN202311753857.6 comprehensively utilizes the azimuth information of pre-stack seismic gathers to improve the prediction accuracy of channel sand bodies. In 2022, "Petroleum Geophysical Exploration" published Yang Chunsheng et al.'s "Well-Seismic Joint Identification Technology and Application of Thin Sand Layers in Small Channels—Taking the AGL Area in Western Daqing Changyuan as an Example" pointed out that three seismic response models of narrow channel sand bodies can be constructed through forward modeling of underground geological structures. The invention patent document CN202211229430.1 discloses a device and method for predicting the azimuth angle of the main flow line of narrow channel reservoirs. Based on sensitive seismic attributes, it constructs the inner and outer boundaries of narrow channel reservoirs and extracts the azimuth angles of these boundaries, achieving refined geological modeling of fluvial reservoirs. In 2018, the journal *Petroleum Geophysical Exploration* published Jiang Yan et al.'s work, "Prediction of Narrow Channel Sandbodies Using Seismic Principal Component Analysis and Fisher Discriminant Analysis," which points out that the seismic PCA analysis method effectively reduces redundant information between seismic attributes and, combined with the Fisher sandstone and mudstone discriminant analysis model, improves the prediction accuracy of channel sandbodies.

[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, transforming seismic data into a data volume that more directly reflects the differences in physical properties between formation sand bodies and surrounding rocks. This compensates for the insufficient vertical resolution of seismic data, clearly highlighting the differences in physical properties between reservoirs and non-reservoirs, greatly improving the accuracy and reliability of sand body identification. For example, the 2018 issue of *Progress in Geophysics* published "Characterizing Single Channel Sand Bodies Using Geostatistical Inversion Methods," which pointed out that the trend of sand body thickness variation can be obtained through inversion, thus characterizing the channel distribution.

[0005] Limited by the narrow channel scale and resolution of conventional seismic data, seismic attribute analysis techniques struggle to directly identify thinly interbedded narrow channels. While statistical processing of multiple seismic attributes has achieved high matching with well data in specific regions, its applicability to other areas is uncertain due to the lack of geological support. Although reservoir inversion prediction techniques can quantitatively characterize thin sand bodies, the thinness of narrow channel sand bodies, which is not significantly different from other types of sand bodies, makes it difficult to directly distinguish narrow channel sand bodies from non-channel sand bodies based solely on thickness. A highly accurate, practical, and geologically sound method for characterizing narrow channel sand bodies is needed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties. This method is used to solve the problem of low identification accuracy of narrow channel sand bodies in the prior art.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: This method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties includes the following steps:

[0008] 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.

[0009] Step 2: Perform outlier removal and standardization on the logging curves with obvious distinguishing features from Step 1;

[0010] 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;

[0011] 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.

[0012] Step 5: Extract the average amplitude attribute of the inverted volume of the target layer segment;

[0013] 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;

[0014] 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.

[0015] Step three in the above plan specifically refers to:

[0016] 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.

[0017] Step four in the above scheme is specifically as follows:

[0018] 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.

[0019] Step six in the above scheme is specifically as follows:

[0020] 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.

[0021] Step seven in the above scheme is specifically as follows:

[0022] 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

[0023] 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.

[0024] 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

[0025] Figure 1 These are logging response characteristic diagrams of different sedimentary microfacies in the example area;

[0026] Figure 2 These are the sand body thicknesses and natural gamma curve amplitudes of different sedimentary microfacies in the example area;

[0027] Figure 3 This is a comparison chart of the natural gamma curves of all wells in the example area before and after standardization processing;

[0028] Figure 4 It is a histogram that distinguishes the value range distribution of sandstone and mudstone by different logging curves;

[0029] Figure 5 This is a cross-sectional view of the waveform indication inversion result;

[0030] 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;

[0031] Figure 7 This is a cross-plot of post-well inspection sand body thickness and gamma inversion amplitude;

[0032] Figure 8 It is a diagram depicting the process of carving a narrow river channel. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings:

[0034] This method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties includes the following steps:

[0035] 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.

[0036] Step 2: Perform outlier removal and standardization on the logging curves with obvious response differentiation characteristics from Step 1;

[0037] 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:

[0038] 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.

[0039] 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:

[0040] 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.

[0041] Step 5: Extract the average amplitude attribute of the inverted volume of the target layer segment;

[0042] 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.

[0043] 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.

[0044] 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:

[0045] 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

[0046] This method for characterizing narrow channel sand bodies based on sand body thickness and inversion volume amplitude properties includes the following steps:

[0047] Step 1

[0048] 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.

[0049] Step Two

[0050] 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.

[0051] Step 3

[0052] 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.

[0053] Step Four

[0054] 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.

[0055] Step 5

[0056] 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.

[0057] Step Six

[0058] 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.

[0059] Table 1:

[0060] Predicted river channel area Suspected river area Predicting non-river areas Actual river channel (well / layer) 46 40 17 Actual non-river channel (well / layer) 8 43 59 Prediction accuracy rate (%) 85.2% — 77.6%

[0061] Step Seven

[0062] 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; 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. Step 7: Based on the river channel sand body discrimination threshold obtained in Step 6, and in conjunction with well data and geological patterns, characterize the narrow river 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.

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.

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