Method for dividing high-frequency cycle period of barrier island sedimentary body

Abstract

The invention relates to a dividing method for high-frequency cycle periods of a barrier island sedimentary body, and belongs to the technical field of oil exploration and development. According to the dividing method for the high-frequency cycle period of the barrier island sedimentary body, on the basis of the correlation between the content of three radioactive elements of uranium, thorium and potassium reflected by natural gamma-ray spectrum logging and sea level rising and falling and lithology changes, natural gamma-ray spectrum logging data serves as an indication curve to be applied to the barrier island sedimentary cycle identification process; smooth processing and discrete wavelet transformation are carried out on an indication curve to obtain a plurality of wavelet coefficient curves, finally, a target indication curve is selected, and then the high-frequency cycle period can be divided according to the target indication curve, so that the oil and gas reservoir development precision and the oil and gas reserve utilization degree are improved. The economic benefit obtained by guiding the remaining oil and gas potential tapping is improved, and the method has important guiding significance for fine development of oil and gas fields.

Description

Technical Field

[0001] The invention relates to a method for dividing high-frequency cycle periods of a barrier island sedimentary body, and belongs to the technical field of petroleum exploration and development. Background Art

[0002] Barrier islands refer to a long and narrow sandstone body that is higher than the sea level and is distributed parallel to the coast. It is often separated from the coast by a lagoon and acts as a barrier to the lagoon. The tight sandstone reservoir of marine barrier islands is one of the important phases for oil and gas exploration and development at home and abroad. The formation of barrier islands is controlled by specific sedimentary environments such as tides, waves, and strong hydrodynamics. Traditional theory believes that the interior of the sand bar is homogeneous and develops in an overall block shape. However, actual drilling data and field outcrop observations show that a variety of impermeable lithologies such as coal, mud, and ash are commonly developed inside barrier islands. The sand bars are stacked and connected as a whole, but not connected laterally. The distribution of interface interlayers is complex, and the formation mechanism of the barrier zone is unclear, which restricts the fine characterization of the reservoir and the reasonable division of the development strata. According to the analytical approach of the anatomy of the reservoir architecture of clastic fluvial sedimentary reservoirs, the research on the reservoir architecture of barrier islands has made certain progress. Based on the analysis of outcrop, modern sedimentary and underground reservoir data, the internal curtain structure of the sedimentary body was finely dissected using flume sedimentation simulation experiments, and it was clarified that sea level fluctuation is the dominant factor controlling the development of interlayers inside barrier islands. However, due to the diverse lithological combinations inside barrier islands, unclear spatial distribution characteristics, and the difficulty in dividing base level cycles, conventional fluvial sequence stratigraphy cannot be directly applied to marine barrier island sedimentary bodies. It is urgent to explore a method for vertical stage division of marine barrier islands, reconstruct the sea level fluctuation curve, analyze the control of sea level fluctuation frequency on interlayers, and form a reasonable basis for the division of development strata, so as to better conduct efficient exploration and potential development of oil and gas reservoirs.

[0003] Natural gamma ray spectrum logging uses gamma rays of different energies such as potassium K, thorium Th, and uranium U to determine the types and contents of radioactive elements contained in formation rocks by spectrum analysis. The contents of potassium, thorium, and uranium are related to the lithology of the formation, the physical and chemical conditions during the formation process, and the sedimentary background. The contents of potassium and thorium in sedimentary mudstones in clastic rocks are high and usually have a good correlation, while the content of uranium is low. Uranium mainly comes from the adsorption of organic matter. Under oxidizing conditions, organic matter is oxidized and the content of uranium is low. Thorium is not controlled by redox conditions and is only related to the particle size of the rock. The smaller the particle size, the greater the thorium content. In general, the oxidizing and reducing environments during the deposition of the formation can be determined based on the thorium-uranium ratio. Under oxidizing conditions (sea regression), the thorium-uranium ratio decreases, and under reducing conditions (sea transgression), the thorium-uranium ratio increases. Therefore, the reconstructed thorium-to-uranium ratio curve can be used to analyze the trend of sea level change. Low values ​​indicate regression, and high values ​​reflect transgression. The interlayers formed at the transgressive-regressive interface reflect the end of the previous period of the high-frequency sedimentary cycle and the beginning of the next period. The fine division of the high-frequency cycle periods can be achieved through the comparison of interface characteristics and frequency.

[0004] The document "Application of Spectral Analysis in Identifying Milankovitch Cycles and High-frequency Sequences - Taking the Lower Ordovician Yingshan Formation in the Tazhong-Bachu Area of ​​the Tarim Basin as an Example" discloses a method for identifying high-frequency cycles using spectral analysis. Based on the three-level sequence division of actual wells, high-frequency cycles with Milankovitch cycle characteristics are identified by filtering, fast Fourier transform, wavelet time-frequency analysis and tuning of natural gamma ray spectrum logging. However, this method has only been applied to uranium resource evaluation, carbonate reservoir lithology analysis, and carbonate sequence stratigraphic research. Due to differences in geological characteristics, this method has not yet been applied to the development and comprehensive adjustment of oil and gas resources in terrigenous clastic sediments (barrier island sediments), and research on improving reserve utilization and recovery rates. In addition, Chinese patent document CN102436013A discloses a method for dividing the sedimentary periods of sandstone and conglomerate using Fischer diagrams. This method uses a combination of logging curves, lithology change surfaces, and the first principal component obtained by principal component analysis inside the sandstone and conglomerate to perform discrete wavelet decomposition and analyze frequency changes, determine the high-frequency base level cycle, and use time-frequency analysis to obtain the dominant period of the high-frequency base level cycle. However, this method needs to verify whether the average thickness of the divided high-frequency base level cycle conforms to the dominant period of the high-frequency cycle. If not, the analysis needs to be repeated continuously, which is cumbersome and time-consuming, and cannot achieve the purpose of quickly and accurately dividing the high-frequency cycle periods in sandstone.

[0005] Therefore, there is an urgent need to develop a simple and fast method for dividing the high-frequency cycles of barrier island sediments. Summary of the invention

[0006] The purpose of the present invention is to provide a method for dividing the high-frequency cycle periods of barrier island sediments, which can solve the problem that the current division of the sedimentary periods of barrier island sediments is complicated and time-consuming.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the method for dividing the high-frequency cycle periods of barrier island sediments of the present invention is:

[0008] A method for dividing high-frequency cycle periods of barrier island sediments comprises the following steps:

[0009] (1) Determine the mid-term base level cycle of the barrier island sediments in the study area, and then establish the sequence stratigraphic framework of the barrier island sediments in the study area;

[0010] (2) Based on the lithofacies and logging data of the target intervals of the target coring wells in the study area, determine the correspondence between lithofacies and logging response characteristics, and then identify the short-term sedimentary cycles of the target intervals of the target coring wells within the sequence stratigraphic framework of the barrier island sedimentary bodies in the study area;

[0011] (3) performing pairwise correlation analysis on the natural gamma logging curves of the target layer section of the target coring well in the study area and the uranium curve, thorium curve and potassium curve of the natural gamma spectral logging, and selecting a curve with poor correlation with the other three curves from the four curves as the target curve according to the correlation analysis results; then calculating the ratio curves of the other three curves other than the target curve and the target curve, and then comparing the three ratio curves with the lithological combination characteristics of the target layer section in the target coring well in the study area, and selecting the ratio curve that best reflects the characteristics of the short-term sedimentary cycle identified in step (2) as the indicator curve;

[0012] (4) The indicator curve is smoothed, and then the smoothed indicator curve is subjected to discrete wavelet transform to obtain a number of wavelet coefficient curves. The wavelet coefficient curve with the highest matching degree with the oscillation trend of the indicator curve is selected from all the wavelet coefficient curves as the target indicator curve; and then the high-frequency cycle periods of the target coring wells in the study area are divided according to the target indicator curve.

[0013] The method for dividing the high-frequency cycle periods of barrier island sedimentary bodies of the present invention is based on the correlation between the contents of three radioactive elements, uranium, thorium and potassium, reflected by natural gamma ray spectrum logging and sea level rise and fall and lithology changes. The natural gamma ray spectrum logging data is used as an indicator curve in the barrier island sedimentary cycle identification process. By smoothing and discrete wavelet transforming the indicator curve, a number of wavelet coefficient curves are obtained, and finally a target indicator curve is selected. Since the high and low value changes of the target indicator curve can intuitively and clearly reflect the rise and fall process of the sea level in a short-term cycle, the high-frequency cycle periods can be divided according to the target indicator curve, thereby improving the development accuracy of oil and gas reservoirs and the degree of utilization of oil and gas reserves, and improving the economic benefits obtained by guiding the potential tapping of remaining oil and gas, which has important guiding significance for the fine development of oil and gas fields.

[0014] Preferably, the target curve is selected as follows:

[0015] (1) Perform pairwise correlation analysis on the natural gamma logging curves of the target layer of the target coring well in the study area, as well as the uranium curve, thorium curve and potassium curve of the natural gamma spectral logging, and obtain the correlation coefficient between each curve and the other three curves. The array composed of the correlation coefficients of a certain curve and the other three curves is defined as the correlation determination array of the curve;

[0016] (2) Then calculate the sum of the three correlation coefficients in the correlation determination array of each curve. If the sum of the three correlation coefficients in the correlation determination array of a certain curve is the smallest and the three correlation coefficients in the correlation determination array of the curve are not greater than 0.3, then the curve is the target curve.

[0017] Preferably, the method for determining the indicator curve is as follows: if a ratio curve is similar to a natural gamma curve in shape and change trend, and the ratio curve has the most lithology change coincidence points, then the ratio curve is the indicator curve; the lithology change coincidence point refers to a data point that meets the following conditions: if a peak value A on a ratio curve corresponds to a formation depth B, and a maximum value on the natural gamma curve corresponds to a formation depth C, and if the difference between B and C does not exceed 3m, then a peak value A on the ratio curve is a lithology change coincidence point.

[0018] Preferably, the smoothing method is a sliding average filtering method.

[0019] Preferably, the discrete wavelet transform is performed using a Meyer wavelet function.

[0020] Preferably, the method for determining the medium-term base level cycle of the barrier island sediments in the study area is as follows:

[0021] (1) Establish a sedimentary model for barrier islands in the study area based on modern sedimentary and field outcrop studies;

[0022] (2) Comprehensively analyze the core and logging response characteristics to identify the marker layers in the barrier island sedimentary bodies in the study area;

[0023] (3) Using the marker layer as a constraint, the mid-term base level cycle of the barrier island sediments in the study area is determined through stratigraphic comparison and division.

[0024] Preferably, after dividing the high-frequency cycle periods of each target coring well in the study area, a high-frequency cyclic sequence stratigraphic framework of the barrier island sedimentary bodies in the study area is established and the stratigraphic framework closure in the region is achieved.

[0025] Preferably, after establishing the high-frequency cyclic sequence stratigraphic framework of the barrier island sediments in the study area, the type of interlayers at the secondary interface of the high-frequency cyclic period is determined, the distribution position of the interlayers in the barrier island sediments in the study area is clarified, and then the development of oil and gas reservoirs in the barrier island sediments in the study area is guided. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the results of the sedimentation pattern of the barrier islands in the study area established in an embodiment of the present invention;

[0027] Figure 2 It is a schematic diagram of the result of mapping the geological layering information, depth, GR curve, SP curve, LLD curve, AC curve and lithology information of each coring well and two sets of marker layers determined according to the coring well in an embodiment of the present invention;

[0028] Figure 3The rock phase variation curve with formation depth, natural gamma curve, porosity curve, permeability curve, uranium curve (U), thorium curve (Th), Th / U ratio curve, smoothed thorium-uranium ratio curve (Th / U_Ma), d7 wavelet coefficient curve, and d9 wavelet coefficient curve in the embodiments of the present invention;

[0029] Figure 4 It is a schematic diagram of the locations of SL1, SL2, and SL3 wells and the horizontal trajectory design and deployment results of the SL1 well in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0031] Example

[0032] The method for dividing the high-frequency cycle periods of barrier island sediments in this embodiment takes a gas reservoir as the research area and specifically includes the following steps:

[0033] (1) Based on modern sedimentary and field outcrop studies in the study area, the sedimentary model of barrier islands in the study area was established. At the same time, the lithology and natural gamma (GR) curves of single wells with different sedimentary environments with formation depth were plotted, and the level interfaces of sedimentary architecture division (level 3 to level 5, level 3 is the boundary of a single yellow sand body in the figure, and level 4 is the boundary between several sets of sand bodies and the underlying mudstone layer) were marked in the figure. The results are shown in the figure. Figure 1 As shown in the figure, sedimentary model refers to the physical and chemical model of sedimentary environment and its sediments summarized on the basis of comprehensive research on the physical, chemical and biological characteristics of modern sediments in a certain environment. It is a comprehensive summary of the development characteristics, evolution and spatial combination of sedimentary environment, an ideal and generalized sedimentary phase pattern expressed in graphic or text form, and can help to understand complex natural phenomena and their process. Sedimentary model includes the spatial form of sedimentary body, lithological combination, sedimentary structure, biological characteristics, dynamic conditions, tectonic background and other elements.

[0034] Depend on Figure 1It can be seen that the sedimentary environment of the barrier island in the study area in this embodiment includes lagoons, barrier flats, sand dunes and barrier beaches. The sedimentary environment of the single well with well number D89 is a lagoon, the sedimentary environment of the single well with well number DPT-92 is a barrier flat, the sedimentary environment of the single well with well number DPT-109 is a sand dune, and the sedimentary environment of the single well with well number DPT-105 is a barrier beach. Among them, the barrier island deposits are washed by waves on the sea side, and barrier beach deposits with low mud content and coarse sand body grain size are developed. Most of them are smooth box-shaped. The middle part of the barrier island is the main part of the sand body deposition, which is composed of multi-stage sand bodies and dune deposits. The sand body is thick and presents toothed box, bell or funnel-shaped characteristics on the logging GR curve. On the landward side of the barrier island, due to the relatively weak hydrodynamic force, barrier flat deposits with high mud content and fine sand body grain size and lagoon deposits composed of mudstone and limestone formed under calmer water environment are developed. By analyzing the sedimentary model of the barrier island, the combination characteristics of the lithofacies of different sedimentary architecture elements are clarified, laying the foundation for the division of subsequent sedimentary cycles.

[0035] Comprehensively analyze the core and logging response characteristics, and identify two sets of marker layers in the barrier island sedimentary body in the study area, which are stable in development, highly comparable, and have obvious lithological and electrical characteristics. The marker layer refers to a layer or a group of rock layers with obvious characteristics that can be used as stratigraphic comparison markers; the marker layer should have the characteristics of obvious fossils and lithological characteristics, stable stratigraphic position, wide distribution range, and easy identification; in this embodiment, there are two sets of marker layers in the barrier island sedimentary body in the study area, one of which is located at the top of the barrier island sedimentary body, which is a lithological combination of coal seams in the lower part, limestone in the middle part, and coal seams in the upper part; the other is located at the bottom of the barrier island sedimentary body, which is a coal seam with an average thickness of more than 6m. The geological stratification information, depth, natural gamma (GR) curve, natural potential (SP) curve, deep lateral resistivity (LLD) curve, acoustic time difference (AC) curve and lithological information of each coring well and the two sets of marker layers determined according to the coring wells are mapped, and the results are as follows: Figure 2 As shown; SH in the lithology data represents the shale content, SAND represents the sand content, LIME represents the ash content, COAF represents the coal content, and DOLO represents the dolomite content;

[0036] With two sets of marker layers as constraints, through point, line and surface stratigraphic correlation and division (point stratigraphic correlation refers to the stratigraphic correlation between single well points, line stratigraphic correlation refers to the stratigraphic correlation between multiple wells distributed in a certain direction, that is, on the basis of single well point stratigraphic correlation, single wells are connected into a long section to confirm whether the stratigraphic division results of each well are still consistent, and surface stratigraphic correlation refers to the mutual comparison between multiple long sections in a region. At the intersection of sections, it is necessary to ensure that the stratigraphic division is consistent to form a closed stratigraphic framework), determine the mid-term base level cycle interface of the barrier island sedimentary body in the study area, establish the sequence stratigraphic framework of the barrier island sedimentary body in the study area, and achieve the closure of the stratigraphic framework in the region;

[0037] A rise and fall of the base level is called a base level cycle. According to different standards, base level cycles can be divided into grades. The medium-term base level cycle is composed of a series of short-period base level cycles with progradation, aggradation and retrogradation superposition styles. The medium-term base level cycle is the basic unit for reservoir heterogeneity research, reservoir prediction and source-reservoir-cap combination analysis; the medium-term base level cycle obviously controls the changes in the lithology and physical properties of the reservoir and the changes in sedimentary microfacies; the medium-term base level cycle is more obvious and easy to identify than the short-term base level cycle, which can reflect the changes in sedimentary microfacies and can be directly identified and divided through well point logging curves, while the short-term base level cycle needs to be divided and determined based on the division of the medium-term base level cycle and combined with other factors such as core characteristics for comparative analysis. The long-term base level cycle has a poor identification effect due to its large time span;

[0038] The sequence stratigraphic framework is the geometrical form and mutual combination relationship of sedimentary sequence units, which is established by orderly incorporating the rock layers formed in the same era into the time stratigraphic framework of related ages for isochronous stratigraphic correlation;

[0039] (2) Obtain the rock phase of the target coring well in the study area (the target coring well is located in the sand dune deposits of the barrier island, and the well number is X). Then determine the change curve of the rock phase with the formation depth in the target layer section (the formation depth is 2670-2700 m) in the target coring well. The results are as follows: Figure 3 As shown ( Figure 3 lithology column curve in the target coring well); at the same time, the logging data of the target coring well is obtained (the logging data includes natural gamma logging data, porosity data, and permeability data), and then the curve of the change of natural gamma logging data with the formation depth in the target layer section (the formation depth is 2670-2700m) in the target coring well is determined, that is, the natural gamma logging curve, the curve of the change of porosity data with the formation depth, that is, the porosity curve, and the curve of the change of permeability data with the formation depth, that is, the permeability curve, are respectively as follows: Figure 3 As shown ( Figure 3 Natural gamma curve, porosity curve, permeability curve);

[0040] In addition, the uranium value, thorium value and potassium value of the natural gamma spectral logging of the target coring well are obtained, and then the variation curves of the uranium value, thorium value and potassium value of the natural gamma spectral logging with the formation depth in the target layer section (formation depth of 2670-2700m) in the target coring well are determined, and the uranium curve, thorium curve and potassium curve of the natural gamma spectral logging in the target layer section (formation depth of 2670-2700m) in the target coring well are obtained respectively. The uranium curve and thorium curve of the natural gamma spectral logging are as follows: Figure 3 As shown ( Figure 3 U curve, Th curve in );

[0041] According to the rock phase and logging data of the target layer in the target coring well (the logging data includes natural gamma log curve, porosity curve, and permeability curve), the corresponding relationship between the rock phase and the logging response characteristics is determined, and then the short-term sedimentary cycle of the target layer in the target coring well is identified within the sequence stratigraphic framework of the barrier island sedimentary body in the study area;

[0042] (3) The natural gamma logging curves of the target layer (stratum depth of 2670-2700 m) in the target coring well in the study area (the target coring well is located in the sand dune deposits of the barrier island, well numbered X) and the uranium curve, thorium curve and potassium curve of the natural gamma spectral logging were analyzed pairwise. The results are shown in Table 1.

[0043] Table 1 Correlation coefficients between different curves

[0044] Curve Name Curve Name Correlation coefficient Natural gamma ray logging curve Uranium curve of natural gamma ray spectrum logging 0.08 Natural gamma ray logging curve Thorium curve of natural gamma ray spectrum logging 0.26 Natural gamma ray logging curve Potassium curve of natural gamma ray spectrum logging 0.31 Uranium curve of natural gamma ray spectrum logging Thorium curve of natural gamma ray spectrum logging 0.17 Uranium curve of natural gamma ray spectrum logging Potassium curve of natural gamma ray spectrum logging 0.28 Thorium curve of natural gamma ray spectrum logging Potassium curve of natural gamma ray spectrum logging 0.42

[0045] As shown in Table 1, the correlation between the natural gamma logging curve and the thorium curve and potassium curve of the natural gamma spectral logging is good, and the correlation between the natural gamma logging curve and the uranium curve of the natural gamma spectral logging is poor. Among the three groups of curves of uranium curve, thorium curve and potassium curve of the natural gamma spectral logging, the correlation between the thorium curve of the natural gamma spectral logging and the potassium curve is good, the correlation between the thorium curve of the natural gamma spectral logging and the uranium curve is poor, and the correlation between the potassium curve of the natural gamma spectral logging and the uranium curve is poor.

[0046] From the above analysis results, it can be seen that the correlation between the uranium curve of natural gamma spectral logging and the natural gamma spectral logging curve, the thorium curve and the potassium curve of natural gamma spectral logging is poor. Therefore, the uranium curve of natural gamma spectral logging, which has poor correlation with other curves, is selected as the target curve, and then the ratio curves of other curves and the target curve are determined, that is, the thorium uranium ratio curve (Th / U), the potassium uranium ratio curve (K / U), the natural gamma spectral logging curve and the ratio curve of the uranium curve of natural gamma spectral logging (GR / U);

[0047] By comparing the Th / U, K / U, and GR / U ratio curves with the lithologic combination characteristics of the target layer in the target coring well in the study area, it is found that the Th / U ratio curve can most clearly reflect the short-term sedimentary cycle structure identified by the coring well section (target layer) in the target coring well in step (2). Therefore, the Th / U ratio curve is used as the indicator curve for high-frequency sedimentary cycle analysis; the Th / U ratio curve is as follows: Figure 3 As shown ( Figure 3 Th / U curve in );

[0048] The Th / U ratio curve and the natural gamma curve that can reflect short-term cycle changes meet the following conditions: the Th / U ratio curve and the natural gamma curve are similar in shape and change trend, and the Th / U ratio curve has the most lithology change overlap points (that is, the Th / U ratio curve can reflect the location of lithology change). The lithology change overlap point refers to the data point that meets the following conditions: if a peak value A on the Th / U ratio curve corresponds to a formation depth of B, and the maximum value on the natural gamma curve corresponds to a formation depth of C, if the difference between B and C does not exceed 3m, then a peak value A on the Th / U ratio curve is a lithology change overlap point; therefore, the Th / U ratio curve can most clearly reflect the short-term sedimentary cycle structure identified by the coring section in step (2), such as Figure 3 As shown;

[0049] (4) The Th / U ratio curve (i.e., the indicator curve) is smoothed using a sliding average filtering method. The linear smoothing method is used for smoothing. The linear function used by the linear smoothing method is shown in the following formula:

[0050]

[0051] Where, T io represents the data point after smoothing, T i+k represents the data point before smoothing, m = 2; this formula means selecting 2m + 1 numerical points before and after the data point to be smoothed to participate in the average calculation, and the average value calculated is used as the data point after smoothing. The thorium-uranium ratio curve (Th / U_Ma) after smoothing is as follows: Figure 3 Said Figure 3 Th / U_Ma curve in );

[0052] (5) Performing discrete wavelet transform on the smoothed thorium-uranium ratio curve (Th / U_Ma);

[0053] The basic principle of wavelet analysis is to use a wavelet function as a basic unit to perform scaling and translation transformation to simulate signal values, and decompose the signal values ​​into multiple signals of different scales and levels. In well logging wavelet analysis, the decomposed wavelet signals show the characteristics of periodic changes and have a good correspondence with the stratigraphic sequences of each level; low-frequency wavelet signals generally correspond to long-term cycles, while high-frequency signals usually correspond to high-frequency short-term cycles, based on which the stratigraphic cycles of each level can be divided;

[0054] In this embodiment, the Meyer wavelet function is used to perform discrete wavelet transform on the smoothed thorium-uranium ratio curve (Th / U_Ma); the formula of the Meyer wavelet function is as follows:

[0055]

[0056] Where ω is the angle vector, reflecting the frequency;

[0057] In this embodiment, MATLAB software is used to decompose and reconstruct the smoothed thorium-uranium ratio curve (Th / U_Ma) to realize discrete wavelet transform of the thorium-uranium ratio curve (Th / U_Ma). The wavelet decomposition order is 11, and the wavelet reconstruction order is 11. After discrete wavelet decomposition, 12 discrete wavelet curves (wavelet coefficient curves) are obtained. By comparison, it is found that the oscillation trend of the d7 wavelet coefficient curve (wavelet coefficient curve with a wavelet decomposition order of 7) matches the oscillation trend of the smoothed thorium-uranium ratio curve (Th / U_Ma). Highest (the number of groups of coincident points of the two curves is the largest, and the method for determining the coincident points is as follows: if the formation depth corresponding to the maximum value P1 of curve M is x0, and the formation depth corresponding to the maximum value Q1 of curve N is x1, when the difference between x0 and x1 does not exceed 3m, the maximum value P1 of curve M and the maximum value Q1 of curve N are a group of coincident points; or if the formation depth corresponding to the minimum value P2 of curve M is y0, and the formation depth corresponding to the minimum value Q2 of curve N is y1, when the difference between y0 and y1 does not exceed 3m, the minimum value P2 of curve M and the minimum value Q2 of curve N are a group of coincident points), such as Figure 3 As shown ( Figure 3 The dotted line in the d7 high-frequency cycle is the d7 wavelet coefficient curve. The triangle sequence represents the characteristics of the stratigraphic cycle. The equilateral triangle represents the positive cycle, which means that the sediment grain size becomes finer upward, reflecting the process of the sea-transgressive water body gradually becoming deeper. The inverted triangle (inverted triangle) represents the reverse cycle, which means that the sediment grain size becomes coarser upward, reflecting the process of the sea-regressive water body gradually becoming shallower. The positive and inverted triangles appear alternately, reflecting the sedimentary cycles formed by the rise and fall of sea level. The oscillation trend of the d7 wavelet coefficient curve can be used as the basis for the division of high-frequency cycles. At the same time, it is found that the oscillation trend of the d9 wavelet coefficient curve (the wavelet coefficient curve with a wavelet decomposition order of 9) is consistent with the trend of the short-term cycle, such as Figure 3 As shown ( Figure 3 The dotted line in the d9 short-term cycle is the d9 wavelet coefficient curve. The triangle sequence represents the characteristics of the stratigraphic cycle. The equilateral triangle represents the positive cycle, which means that the sediment grain size becomes finer upward, reflecting the process of the transgressive water body gradually becoming deeper. The inverted triangle (inverted triangle) represents the reverse cycle, which means that the sediment grain size becomes coarser upward, reflecting the process of the regressive water body gradually becoming shallower. The alternating appearance of positive and inverted triangles reflects the sedimentary cycles formed by the rise and fall of sea level).

[0058] (6) Decompose the d7 wavelet coefficient curve obtained in step (5). The specific method is as follows: the low value (minimum value) in the d7 wavelet coefficient curve is taken as the beginning of a cycle and the end point of the previous cycle (i.e., the cycle interface), the adjacent high value (maximum value) is taken as the midpoint of the cycle, and each cycle from a low value to a high value and then to a low value is regarded as a complete high-frequency cycle, thereby achieving a fine division of the four high-frequency cycle periods of the target coring well.

[0059] Then, according to the above method, the high-frequency cycle periods of other target coring wells (in this embodiment, there are 27 target coring wells in total) are finely divided, and then a high-frequency cycle sequence stratigraphic framework of the barrier island sedimentary bodies in the study area is established and the stratigraphic framework closure in the region is achieved (according to the fine division results of the high-frequency cycle periods of each target coring well, the target coring wells are connected and compared to ensure that the high-frequency cycle division results based on the target coring wells correspond to each other and there is no conflict);

[0060] According to the division results of high-frequency cycle periods, the type of interface (the location of high-frequency cycle division, that is, the high-frequency cycle period interface, indicating the end of a sedimentary period) is judged. The high-frequency cycle interface within the short-term cycle is usually an interlayer with a small scale and a thickness of less than 0.2m, and the short-term cycle interface (short-term sequence interface) is usually a continuous interlayer with a thickness of more than 1m.

[0061] Based on the results of high-frequency cycle period division, the identification results of interface types (interlayer types) are applied to the construction of interlayer models in barrier islands, realizing the fine three-dimensional characterization of barrier island reservoirs in the study area and applying it to the deployment and tracking adjustment of horizontal wells in barrier island reservoirs. In 2022, 15 horizontal wells were deployed, with a reservoir encounter rate of 91%, an increase of 4.5% over the previous period, and an average initial production of gas wells of 32,000 cubic meters per day, an increase of 9.4% over the previous period. Taking the SL1 well as an example, through the three-dimensional geological model established based on the results of fine division of high-frequency cycle periods, it was found that the horizontal section trajectory of the drilled SL2 and SL3 wells was located in the middle and upper part of the barrier island reservoir, and there was a continuous interlayer with a thickness of more than 4m between the underlying sand body. Therefore, the horizontal section trajectory of the SL1 well was designed and deployed in the first phase sand body in the lower part of the reservoir, such as Figure 4 As shown, in order to fully utilize the remaining gas in the reservoir.

Claims

1. A method for dividing high-frequency cycles of barrier island sediments, characterized in that: The following steps are involved: (1) Determine the mid-term base level cycle of the barrier island sediments in the study area, and then establish the sequence stratigraphic framework of the barrier island sediments in the study area; (2) Based on the lithofacies and logging data of the target intervals of the target coring wells in the study area, determine the correspondence between lithofacies and logging response characteristics, and then identify the short-term sedimentary cycles of the target intervals of the target coring wells within the sequence stratigraphic framework of the barrier island sedimentary bodies in the study area; (3) performing pairwise correlation analysis on the natural gamma logging curves of the target layer section of the target coring well in the study area and the uranium curve, thorium curve and potassium curve of the natural gamma spectral logging, and selecting a curve with poor correlation with the other three curves from the four curves as the target curve according to the correlation analysis results; then calculating the ratio curves of the other three curves other than the target curve and the target curve, and then comparing the three ratio curves with the lithological combination characteristics of the target layer section in the target coring well in the study area, and selecting the ratio curve that best reflects the characteristics of the short-term sedimentary cycle identified in step (2) as the indicator curve; (4) The indicator curve is smoothed, and then the smoothed indicator curve is subjected to discrete wavelet transform to obtain a number of wavelet coefficient curves. The wavelet coefficient curve with the highest matching degree with the oscillation trend of the indicator curve is selected from all the wavelet coefficient curves as the target indicator curve; and then the high-frequency cycle periods of the target coring wells in the study area are divided according to the target indicator curve.

2. The method for dividing high-frequency cycle periods of barrier island sediments according to claim 1, characterized in that: The method for selecting the target curve is as follows: (1) Perform pairwise correlation analysis on the natural gamma logging curves of the target layer of the target coring well in the study area, as well as the uranium curve, thorium curve and potassium curve of the natural gamma spectral logging, and obtain the correlation coefficient between each curve and the other three curves. The array composed of the correlation coefficients of a certain curve and the other three curves is defined as the correlation determination array of the curve; (2) Then calculate the sum of the three correlation coefficients in the correlation determination array of each curve. If the sum of the three correlation coefficients in the correlation determination array of a certain curve is the smallest and the three correlation coefficients in the correlation determination array of the curve are not greater than 0.3, then the curve is the target curve.

3. The method for dividing high-frequency cycle periods of barrier island sediments according to claim 1 or 2, characterized in that: The method for determining the indicator curve is as follows: if the shape and change trend of a ratio curve are similar to those of the natural gamma curve, and the lithology change coincidence points on the ratio curve are the most, then the ratio curve is the indicator curve; the lithology change coincidence points refer to the data points that meet the following conditions: if the lithology change coincidence points on a ratio curve are the most, then the ratio curve is the indicator curve. The formation depth corresponding to a peak value A is B, and the formation depth corresponding to the maximum value on the natural gamma curve is C. If the difference between B and C does not exceed 3m, a peak value A on the ratio curve is the point of coincidence of lithology change.

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