A method for characterizing the reservoir architecture of shallow-water deltas using a combination of well-seismic and dynamic data in the early offshore period

Abstract

The present invention provides a method for characterizing the reservoir configuration of shallow deltas in offshore early-stage well-seismic combined methods, comprising the following steps: collecting and analyzing geological data, seismic data, and production dynamic data of the oil and gas reservoir to be characterized; determining a sedimentary configuration hierarchy for shallow deltas; determining the reservoir configuration characterization hierarchy that can be characterized in the sedimentary configuration hierarchy for shallow deltas under conditions of few wells, and obtaining characterizable reservoir configuration units; determining the rock-electro-seismic response characteristics of the characterizable reservoir configuration units at the shallow delta front; dissecting the characterizable reservoir configuration units at the shallow delta front under conditions of few wells, and performing a rational analysis of the characterizable reservoir configuration units. This application achieves a reasonable prediction of the morphology, scale, direction, and superposition relationship of sand bodies of different genetic hierarchies in shallow delta sediments, providing important geological basis and guidance for well site deployment, well pattern design, and remaining oil prediction for such oil and gas reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of reservoir characterization, and in particular to an offshore early-stage well-seismic-vibration combined shallow water delta reservoir configuration characterization method. Background Art

[0002] As oilfield development continues, the distribution of remaining oil is often controlled by the internal structure of the reservoir sand bodies. Reservoir architecture characterization—the study of the morphology, scale, orientation, and stacking relationships of the different levels of reservoir units—has become a crucial geological foundation for recovering remaining oil and adjusting well deployment in oilfields.

[0003] Reservoir architecture research began in the 1980s, mainly focusing on outcrops and modern deposits, and has achieved a large number of research results, covering almost all channelized deposits, such as alluvial fans, overbank deposits, fan deltas, delta plains, turbidity deposits, tidal channels, braided rivers and meandering rivers.

[0004] In terms of underground reservoir configuration research, for onshore dense well network areas (well spacing of about 50m), the idea of ​​multi-well model fitting is used, that is, using abundant core well and dense well network data to carry out configuration research, which has achieved remarkable results in improving oil and gas recovery rates and maximizing the development of oil and gas resources.

[0005] However, research on reservoir architecture under offshore conditions of large well spacing (average well spacing of 300-500 m in the mid-to-late stages of offshore development) is currently lacking, and conventional methods for characterizing reservoir architecture using dense well patterns are not suitable for offshore oil and gas fields. Currently, some researchers have conducted a hierarchical analysis of the architecture of meandering river sand bodies under large well spacing in the Qinhuangdao Oilfield, establishing a forward conceptual model for the architectural boundaries of meandering river sand bodies of varying orders, enabling detailed identification of these boundaries under large well spacing. Other researchers have also established seismic response characteristics for reservoirs of varying architectural styles, combining frequency-separation attributes and frequency-separation inversion methods to achieve detailed analysis of the architecture of fluvial reservoirs of varying orders in the Minghuazhen Formation of the Qinhuangdao Oilfield in the Bohai Sea. However, methods for characterizing the architecture of shallow deltaic sedimentary reservoirs under large well spacing have not yet been systematically and in-depth studied. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide an offshore early-stage well-seismic-dynamic combined shallow water delta reservoir configuration characterization method suitable for offshore oil and gas fields.

[0007] To achieve the above object, the present invention provides a method for characterizing the structure of an offshore early-stage shallow-water delta reservoir by combining well-seismic and dynamic data, comprising the following steps:

[0008] A. Collect and analyze geological data, seismic data, and production performance data of the oil and gas reservoir to be characterized;

[0009] B. Determine the classification scheme of sedimentary architecture for shallow water deltas;

[0010] C. Determine, based on the data obtained in step A, the reservoir architecture characterization level that can be characterized in the sedimentary architecture level classification scheme for the shallow water delta under the condition of few wells, and obtain the corresponding reservoir architecture unit that can be characterized in the reservoir architecture characterization level;

[0011] D. Determine the rock-electro-seismic response characteristics of the reservoir architecture units at the shallow-water delta front;

[0012] E. Dissecting the reservoir architecture units that can be represented at the shallow delta front under the condition of few wells includes the following steps:

[0013] E1. determining the boundary identification features of the reservoir architecture unit;

[0014] E2. Delimiting a plane of a unit capable of representing a reservoir structure using the boundary recognition feature;

[0015] E3. establishing a filling pattern of the reservoir architecture unit;

[0016] E4. establishing a spatial superposition pattern of the units capable of representing the reservoir architecture;

[0017] E5. Using the plane delimitation, filling pattern and spatial superposition pattern of the reservoir architecture unit, a three-dimensional geological model of the reservoir architecture unit is established, and the rationality analysis of the reservoir architecture unit is carried out.

[0018] This application uses a combined approach of early offshore well-seismic-vibration data to effectively characterize reservoir architecture units that can be characterized in offshore oil and gas fields, achieving a reasonable prediction of the morphology, scale, direction, and superposition relationship of sand bodies of different orders of shallow-water deltaic deposits, and providing important geological basis and guidance for well site deployment, well pattern design, and remaining oil prediction for such oil and gas reservoirs.

[0019] A preferred embodiment of the above technical solution is as follows: in step A, the geological data of the oil and gas reservoir to be characterized includes well data of the target area to be characterized, geological stratification data, geological interface structure map, and sedimentary facies plane map of the target layer to be characterized;

[0020] The seismic data of the oil and gas reservoir to be characterized include a three-dimensional seismic data volume of the target area to be characterized, and seismic horizon interpretation data of the top and bottom of the sand layer group and its internal small layer level interface of the target layer segment to be characterized;

[0021] The production performance data of the oil and gas reservoir to be characterized includes the production performance data of the production wells in the target area to be characterized;

[0022] The data analyzed include the well pattern and spacing of the wells drilled in the target area to be characterized, the sedimentary facies type of the target layer to be characterized, and the quality of the seismic data of the target layer to be characterized.

[0023] A preferred embodiment of the above technical solution is as follows: Step C comprises the following sub-steps in sequence:

[0024] C1. Establish the relationship between the well pattern and spacing of the wells drilled in the target area to be characterized, as well as the production performance of the production wells and the sedimentary facies type of the target layer to be characterized; establish the correlation between the seismic attributes of the target area to be characterized and the thickness of the reservoir sand body;

[0025] C2. Determine the reservoir architecture characterization level that can be characterized and meets the requirements of offshore development and production under the condition of few wells.

[0026] A preferred embodiment of the above technical solution is as follows: in step B, the sedimentary configuration level division scheme of the shallow water delta includes:

[0027] Level 6: It can characterize the reservoir architecture unit as a level 6 architecture unit, the level 6 architecture unit is a shallow water delta sedimentary system, the corresponding phase belt level, and the corresponding stratigraphic unit is a sand layer group;

[0028] Level 5: It can characterize the reservoir configuration unit as a level 5 configuration unit, the level 5 configuration unit is a composite underwater distributary channel, the corresponding subfacies level, and the corresponding stratigraphic unit is a small layer;

[0029] Level 4: It can characterize the reservoir architecture unit as a level 4 architecture unit, wherein the level 4 architecture unit is an underwater distributary channel and a sand bar, corresponding to the microfacies level, and the corresponding stratigraphic unit is a single layer;

[0030] Level 3: It can characterize the reservoir architecture unit as a level 3 architecture unit. The accretion body within the large-scale bottom shape of the level 3 architecture unit corresponds to the rhythmic layer level.

[0031] In the sedimentary architecture classification scheme for this shallow delta, the levels are increasingly precise, from level six to level three, and more data are required; thus, the reservoir architecture characterization level that can be characterized is determined based on the data that can be obtained.

[0032] A preferred embodiment of the above technical solution is that the reservoir architecture unit that can be characterized at the shallow delta front is a four-level architecture unit. In step D, the rock-electric-seismic response characteristics of the reservoir architecture unit that can be characterized include:

[0033] subdividing the underwater distributary channel into a main channel, a secondary channel and a channel edge;

[0034] The rock-electric-seismic response characteristics of the main channel include sand body thickness, lithologic characteristics, sand-to-sand ratio, electrical logging curve morphology, and response characteristics on seismic profiles;

[0035] The rock-electric-seismic response characteristics of the secondary channel include sand body thickness, lithologic characteristics, sand-to-sand ratio, natural gamma ray curve morphology, and response characteristics on seismic profiles;

[0036] The rock-electric-seismic response characteristics of the river channel edge include lithologic characteristics, sand-to-soil ratio, natural gamma-ray curve morphology, and response characteristics on seismic profiles;

[0037] The rock-electric-seismic response characteristics of the sand bar include lithologic characteristics, sand-to-ground ratio, natural potential curve shape, natural gamma ray curve shape, and response characteristics on seismic profiles.

[0038] A preferred embodiment of the above technical solution is as follows: in step E1, the boundary identification features include the position of change in seismic phase or amplitude, the position of change in sand body thickness, the boundary position determined based on the relationship between horizontal well lithology change and seismic reflection characteristics, and the boundary position determined based on the difference in production performance of production wells;

[0039] In step E2, based on the boundary identification features of the reservoir architecture unit, a planar delineation of a composite underwater distributary channel is performed, and a planar delineation of a single underwater distributary channel is performed for a local well pattern densification or an area with high-quality seismic data;

[0040] In step E3, the filling pattern of the microfacies of the single underwater distributary channel is determined. The microfacies types include main channel, sand bar and secondary channel. The filling pattern is sand bar, main channel and secondary channel from the center to the edge of the channel.

[0041] In step E4, based on the planar demarcation of the reservoir-characterizing unit, the seismic response characteristics of the superposition pattern of the reservoir-characterizing unit are studied to determine the spatial superposition pattern between the composite underwater distributary channel and the single underwater distributary channel within it.

[0042] As described above, the shallow water delta reservoir configuration characterization method of the present invention based on the combined well-seismic-vibration method in the early stage offshore has the following beneficial effects:

[0043] This application uses an early-stage offshore well-seismic-vibration combined approach to carry out effective characterization of reservoir architecture units that can be characterized in offshore oil and gas fields, achieving a reasonable prediction of the morphology, scale, direction, and superposition relationship of sand bodies of different orders of shallow-water delta sedimentary genesis, providing important geological basis and guidance for well site deployment, well network design, and remaining oil prediction for such oil and gas reservoirs, and is of great significance for improving the drilling success rate and efficient development of shallow-water delta composite river channel phase oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flowchart of the shallow water delta reservoir configuration characterization method for the early offshore well-seismic-vibration combined method in this application.

[0045] Figure 2 This is a three-dimensional display of the drilled wells in the B3 oil and gas reservoir layer and the top surface structure of B3-2.

[0046] Figure 3 Schematic diagram of the configuration interface identification of B3 oil and gas reservoir seismic data.

[0047] Figure 4a This is the maximum amplitude attribute map of the B3-2 oil and gas reservoir in the study area.

[0048] Figure 4b for Figure 4a Schematic diagram of the seismic response characteristics of the structural boundary encountered at the end of the horizontal section in the middle C2H area.

[0049] Figure 4c for Figure 4a Schematic diagram of the seismic response characteristics of the structural boundary encountered at the end of the horizontal section in the middle C3H area.

[0050] Figure 5a Schematic diagram of the planar demarcation of the composite underwater distributary channel in the B3-2 sublayer of the study area.

[0051] Figure 5b Schematic diagram of the planar demarcation of a single underwater distributary channel in the B3-2 sublayer of the study area.

[0052] Figure 6a Schematic diagram of the response characteristics of the composite underwater distributary channel superposition pattern on the forward seismic section.

[0053] Figure 6b Schematic diagram of the response characteristics of the composite underwater distributary channel superposition pattern on the original seismic section.

[0054] Figure 7 Schematic diagram of the response characteristics of a single underwater distributary channel in the B3-2 layer of the study area on the seismic profile. DETAILED DESCRIPTION

[0055] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0056] It should be noted that the structures, proportions, sizes, etc. depicted in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose of the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0057] The present invention provides a shallow water delta reservoir configuration characterization method based on early offshore well-seismic-vibration integration, which is applicable to offshore oil and gas fields. Figure 1 As shown in FIG, the offshore early-stage well-seismic-vibration combined shallow water delta reservoir architecture characterization method includes the following steps:

[0058] A. Collect and analyze geological data, seismic data, and production performance data of the oil and gas reservoir to be characterized, which are obtained directly or indirectly from existing data;

[0059] B. Determine the classification scheme for the sedimentary architecture of shallow deltas. Different classifications have different data requirements for representing reservoir architecture units. The more precise the classification, the more data is required.

[0060] C. Based on the data obtained in step A, determine the reservoir architecture characterization level that can be characterized in the sedimentary architecture classification scheme for the shallow water delta under the condition of few wells, and obtain the corresponding reservoir architecture unit that can be characterized in the reservoir architecture characterization level;

[0061] D. Determine the rock-electro-seismic response characteristics of the reservoir architecture units at the shallow-water delta front;

[0062] E. Dissecting the reservoir architecture units that can be represented at the shallow delta front under the condition of few wells includes the following steps:

[0063] E1. Determine the boundary identification features that can characterize the reservoir architecture unit;

[0064] E2. Use boundary recognition features to demarcate the plane of the reservoir architecture unit;

[0065] E3. Establish a filling pattern that can characterize the reservoir architecture unit;

[0066] E4. Establish a spatial superposition pattern that can characterize reservoir architecture units;

[0067] E5. Using the plane delimitation, filling pattern and spatial superposition pattern of the reservoir architecture unit, a three-dimensional geological model of the reservoir architecture unit is established, and the rationality analysis of the reservoir architecture unit is carried out.

[0068] This application uses an early-stage offshore well-seismic-vibration combined approach to carry out effective characterization of reservoir architecture units that can be characterized in offshore oil and gas fields, achieving a reasonable prediction of the morphology, scale, direction, and superposition relationship of sand bodies of different orders of shallow-water delta sedimentary genesis, providing important geological basis and guidance for well site deployment, well network design, and remaining oil prediction for such oil and gas reservoirs, and is of great significance for improving the drilling success rate and efficient development of shallow-water delta composite river channel phase oil and gas reservoirs.

[0069] The following provides a specific application example of the present application. The offshore early-stage well-seismic-vibration combined shallow-water delta reservoir architecture characterization method is used to characterize the architecture of the river-controlled shallow-water delta front composite sand body reservoir in the B3 layer of the offshore X oilfield. The oil and gas reservoir to be characterized is the B3 oil and gas reservoir in the study area.

[0070] A. Collect and analyze geological data, seismic data, and production performance data of the B3 oil and gas reservoir.

[0071] The geological data of the B3 oil and gas reservoir include the well data of the B3 oil and gas reservoir drilled in the study area, geological stratification data, geological interface structure map, and sedimentary facies plane map of the target layer section that needs to be characterized. The sedimentary facies plane map of the target layer section that needs to be characterized is the sedimentary facies knowledge that needs to be characterized in the target layer section.

[0072] Well data include: well pattern and spacing, there are 8 wells in the B3 oil and gas reservoir section of the study area, including 4 directional wells and 4 horizontal wells. The horizontal wells have not penetrated the B3 oil and gas reservoir. The drilled wells are all located in the high part of the structure and in the south. The well pattern is irregular, such as Figure 2 As shown, the average well spacing is 500m; the cuttings logging data are: 8 wells; the well logging data are: gamma, resistivity, neutron, density, and acoustic wave data collected by directional wells, and only gamma and resistivity data collected by horizontal wells; the core data are: 2 coring wells in the B3 oil and gas reservoir interval, with core lengths of 8.05m and 18.16m respectively.

[0073] The geological stratification data include: the top and bottom surface stratification data of the B3 oil and gas reservoir sand layer group in the study area, and the top and bottom surface stratification data of the B3-3, B3-2, and B3-1 sub-layers within it, such as Figure 2 shown.

[0074] The geological interface structural map includes: the top and bottom structural maps of the B3 oil and gas reservoir in the study area, and the top and bottom structural maps of the internal B3-2 layer.

[0075] Sedimentary facies characterization of the target interval requires understanding: During the deposition of the B3 oil and gas reservoir in the study area, the lacustrine basin was in a depression phase. This period was characterized by slow sedimentation, a shallow basement slope, weak tectonic activity, and rapid sediment supply, creating a setting suitable for the formation of a shallow-water lacustrine delta. Lithology is dominated by medium-fine sandstone and transitional mudstone, reflecting a depositional environment characterized by rapid transitions from deep to shallow water. The study area also possesses relatively flat topography. The B3 oil and gas reservoir features numerous channels with intermittent positive rhythmic patterns, reflecting shallow-water deposition and paleontological features consistent with shallow-water environments. Comprehensive assessment indicates that the B3 oil and gas reservoir in the study area primarily develops shallow-water deltaic deposits. Florid-like frontal sand bodies are developed in the B3-3 and B3-2 sublayers in the study area, primarily composed of underwater distributary channels and sandbars. Underwater distributary channels are the primary reservoirs in this area, and are therefore further subdivided into primary channels, secondary channels, and channel margins.

[0076] Seismic data for the B3 oil and gas reservoir includes a 3D seismic data volume for the target area to be characterized, as well as seismic horizon interpretation data for the top and bottom of the sandstone groups and their internal sub-layer interfaces within the target interval. Specifically, the seismic data for the target interval in the B3 oil and gas reservoir has a dominant frequency of 28 Hz, an average formation velocity of 2800 m / s, and an optimal resolution of 25 m. The sandstone thickness of the B3-2 reservoir in the study area ranges from 15.5 to 25 m, with the reservoir thickness ranging from one-eighth to one-quarter of the seismic wavelength. The sandstone thickness of the target interval in the B3 study area correlates well with the maximum seismic amplitude.

[0077] The production performance data of the B3 oil and gas reservoir include the production performance data of the production wells in the target area to be characterized; for the B3 oil and gas reservoir, the production performance data of 4 oil wells in the B3-2 oil reservoir were collected and analyzed.

[0078] B. Determine the sedimentary configuration classification scheme for shallow water deltas. This application adopts a six-level classification scheme, and the classification is as follows.

[0079] Level 6: The reservoir architecture unit that can be characterized is the sixth-level architecture unit. The sixth-level architecture unit is a shallow-water delta sedimentary system, corresponding to the facies belt level, and the corresponding stratigraphic unit is the sand layer group, that is, the sand layer group corresponding to the B3 oil and gas reservoir. It can be identified on well logging curves and seismic sections and can be traced between wells.

[0080] Level 5: The reservoir architecture unit that can be characterized is the level 5 architecture unit. The level 5 architecture unit is a composite underwater distributary channel, corresponding to the subfacies level, and the corresponding stratigraphic unit is a small layer, that is, the B3-3, B3-2, and B3-1 small layers within the sand layer group of the B3 oil and gas reservoir. It can be identified on well logging curves and seismic sections and can be traced between wells.

[0081] Level 4: The reservoir architecture units that can be characterized are level 4 architecture units. Level 4 architecture units are underwater distributary channels and sand bars, corresponding to microfacies levels and single-layer stratigraphic units. Each architecture unit can be identified on the well logging curve, but the relationship between wells is unclear. It can be partially detected on seismic data.

[0082] Level 3: The reservoir architecture unit that can be characterized is the tertiary architecture unit. The accretionary body within the large bottom shape of the tertiary architecture unit corresponds to the rhythmic layer level. Its interface dip is small, generally less than 15°, and is a low-angle interface. It erodes one or more underlying cross-beds. The interface is usually covered with a layer of mudstone, above which is internal clastic mud and gravel. The lithofacies combination above and below the interface is similar and can be identified on the core. Some architecture units can be identified on the logging curve, but the relationship between wells is unclear and it is extremely difficult to identify on the seismic profile.

[0083] In the sedimentary architecture classification scheme for this shallow delta, the levels are increasingly precise, from level six to level three, and more data are required; thus, the reservoir architecture characterization level that can be characterized is determined based on the data that can be obtained.

[0084] C. Determine the reservoir architecture characterization level and the characterizable reservoir architecture units in shallow water delta under the condition of few wells, which specifically includes the following steps:

[0085] C1. Establish the relationship between the well pattern and spacing of the wells drilled in the target area to be characterized, as well as the production performance of the production wells and the sedimentary facies type of the target layer to be characterized; establish the correlation between the seismic attributes of the target area to be characterized and the thickness of the reservoir sand body;

[0086] C2. Determine the reservoir architecture characterization level that can meet the needs of offshore development and production under the condition of few wells. In the B3 oil and gas reservoir in the study area, the 8 drilled wells are all located in the structural high part, with an irregular well pattern and an average well spacing of 500m, which exceeds the width of the single underwater distributary channel in the study area by 100 to 300m. It is difficult to make inter-well predictions using only well data. Figure 3 The configuration interface identification for the seismic data of the B3 oil and gas reservoir in the study area shows that the seismic data in the study area is of good quality, with a good correlation between the seismic amplitude and the sandstone thickness of the B3 target layer. Therefore, the seismic data of the B3 oil and gas reservoir in the study area can identify the boundaries of fifth-order composite underwater distributary channels and detect the sedimentary boundaries of some fourth-order underwater distributary channels. Therefore, in this example, based on the various data of the B3 oil and gas reservoir, the reservoir architecture that can be characterized is a fourth-order configuration unit, and fifth-order composite underwater distributary channels and fourth-order single underwater distributary channels can be detected.

[0087] D. Determine the rock-electro-seismic response characteristics of reservoir-characteristic units at the shallow-water delta front.

[0088] The B3 oil and gas reservoir in the study area develops a lobate front sand body, which is mainly composed of underwater distributary channels and sand bar deposits. The underwater distributary channels are further subdivided into main channels, secondary channels and channel edges.

[0089] The rock-electric-seismic response characteristics of the main channel include sand body thickness, lithologic characteristics, sand-to-formation ratio, electrical logging curve morphology, and response characteristics on seismic profiles. In the B3 oil and gas reservoir in the study area, the main channel sand body is thick, exceeding 15 meters; the lithology is relatively uniform, often dominated by fine sandstone, with a sand-to-formation ratio of 0.6 to 0.9, generally greater than 0.6; the electrical logging curve morphology is mostly box-shaped, but also bell-shaped and box-bell-shaped combinations; the response characteristics on seismic profiles are strong amplitude, medium-to-low frequency, and lens-shaped.

[0090] The rock-electro-seismic response characteristics of secondary channels include sandstone thickness, lithologic characteristics, sand-to-formation ratio, natural gamma ray curve morphology, and response characteristics on seismic profiles. In the B3 oil and gas reservoir in the study area, the sandstone thickness of secondary channels is thinner than that of the main channel, ranging from 5 to 15 meters. The lithology exhibits a positive rhythmic pattern of coarseness at the bottom and fineness at the top, with a sand-to-formation ratio generally ranging from 0.4 to 0.6. The natural gamma ray curve is bell-shaped. The response characteristics on seismic profiles are medium amplitude and frequency, often associated with both sides of the lens.

[0091] The rock-electro-seismic response characteristics of the channel margin include lithologic characteristics, sand-to-formation ratio, natural gamma-ray morphology, and response characteristics on seismic sections. In the B3 oil and gas reservoir in the study area, the channel margin lithology exhibits an increased abundance of fine-grained sediments, with a sand-to-formation ratio generally less than 0.4. Well logging reveals a medium-to-high amplitude sawtooth pattern on the natural gamma-ray morphology, while the response characteristics on seismic sections are weak amplitude or phase reversal.

[0092] The rock-electric-seismic response characteristics of sandbars include lithologic characteristics, sand-to-ground ratio, spontaneous potential curve morphology, natural gamma ray curve morphology, and response characteristics on seismic profiles. In the B3 oil and gas reservoir in the study area, distributary sandbars are coarser than channel sandbodies, with massive bedding in the cores and often accompanied by boulders. The spontaneous potential and natural gamma ray curves exhibit low-amplitude, jagged box- and bell-shaped combinations. The response characteristics on seismic profiles are strong amplitude and low frequency.

[0093] E. Dissecting the reservoir architecture units of different orders at the shallow delta front under the condition of few wells includes the following steps:

[0094] E1. Determine the boundary identification features of reservoir architectural units using well-seismic-dynamic combination under conditions of few wells. Boundary identification features include the location of changes in seismic phase or amplitude, the location of changes in sand body thickness, the boundary location determined based on the relationship between lithologic changes in horizontal wells and seismic reflection characteristics, and the boundary location determined based on differences in production performance of production wells.

[0095] Changes in seismic phase or amplitude: At the boundaries of sedimentary bodies of different periods, changes in mud content, erosion degree, overlapping relationship, difference in wave impedance between upper and lower layers of the interface, and sand body thickness will cause significant changes in the seismic response characteristics at the boundaries of reservoir structural units, which are mainly manifested in changes in seismic phase and amplitude intensity. Figure 4a As shown, in the B3-2 oil and gas reservoir in the study area, the amplitudes of the C2H and C3H regions are relatively large; Figure 4b and 4c As shown in Figure 3, the seismic response characteristics of the configuration boundary encountered at the end of the horizontal section of the C2H and C3H areas of the B3-2 oil and gas reservoir in the study area.

[0096] Changes in sand body thickness: Using the sedimentary body thickness map, the sand body is thick in the sedimentary center and gradually becomes thinner towards the edge. Based on this, it can be further inferred that the sand body thickness shows a thick-thin-thick change feature. The thinning point may be the edge of the two phases of sedimentary bodies, which may be the boundary position of the architectural unit.

[0097] Based on the relationship between horizontal well lithology changes and seismic reflection characteristics: Figures 4a to 4c As shown in the figure, the reservoir quality at the end of the horizontal section of Well C2H and Well C3H in the study area deteriorates, the mud content increases significantly, and the seismic phase is manifested as weakened amplitude and changed phase axis, which is the boundary of the reservoir architectural unit.

[0098] Based on the differences in production dynamics of production wells: In the B3 oil and gas reservoir area of ​​the study area, Well C2H was put into production in December 2014, and Well C4H was put into production in September 2014. The horizontal distance between the production wells C2H and C4H is 500m, but the production characteristics are very different; Well C2H was put into production in December 2014, and the water-free oil production period was only half a year. It was flooded and shut down in September 2017, and the water cut reached 98% before shutting down; Well C4H was put into production in September 2014, and the water-free oil production period was nearly 3 years. As of the end of 2021, the production situation of the well remained stable, and the water cut was stable at 88%. It is speculated that the connectivity between the production wells C2H and C4H is poor, and there is a structural boundary between them that can characterize the reservoir architectural unit.

[0099] E2. Use the boundary recognition features obtained in step E1 to perform plane demarcation of the reservoir structure unit. Specifically, the plane demarcation of the shallow delta front composite underwater distributary channel series and the composite underwater distributary channel body within the study area is performed based on the boundary recognition features. For composite underwater distributary channel bodies with relatively dense well patterns, the plane demarcation of the single underwater distributary channel level is performed. Figure 5aAs shown in Figure 2, the five-level B3-2 sublayer of the B3 oil and gas reservoir has four stages of composite underwater distributary channel series. The oil reservoir of the B3-2 sublayer is controlled by the second stage of composite underwater distributary channel series, and its interior is composed of three stages of composite underwater distributary channel, namely composite underwater distributary channel 2-1, composite underwater distributary channel 2-2, and composite underwater distributary channel 2-3, referred to as composite channel 2-1, composite channel 2-2, and composite channel 2-3. Figure 5b As shown in the figure, the well data inside the composite underwater distributary channel 2-2 are relatively rich, including the production dynamic data of 4 directional wells, 4 horizontal wells and 4 production wells. The research on the characterization of the reservoir architecture unit can be further refined into four levels of single underwater distributary channels, that is, the composite underwater distributary channel 2-2 is subdivided into three phases of single underwater distributary channels, namely single channel 2-2-1, single channel 2-2-2 and single channel 2-2-3.

[0100] E3. Using the rock-electric-seismic response characteristics of the reservoir architecture unit obtained in step D, combined with the boundary identification characteristics obtained in step E1 and the plane demarcation results of the reservoir architecture unit obtained in step E2, establish the filling pattern of the reservoir architecture unit, including determining the filling pattern of the microfacies of a single underwater distributary channel. The microfacies types include main channel, sand bar and secondary channel. The filling pattern from the center of the channel to the edge is sand bar, main channel, secondary channel, as shown in FIG. Figure 5a and Figure 5b shown.

[0101] E4. Using the plane demarcation results of the composite underwater distributary channel obtained in step E2, combined with seismic forward modeling, establish the spatial superposition pattern of the composite underwater distributary channel. Two phases of composite underwater distributary channels are developed in the B3-2 reservoir area of ​​the study area, namely composite underwater distributary channel 2-1 and composite underwater distributary channel 2-2. The two phases of composite underwater distributary channels are in a completely independent superposition pattern. Completely independent superposition means that the sand bodies of the two phases of composite underwater distributary channels have not yet been in contact in the lateral direction, and there are fine-grained deposits in between. The natural gamma logging curve shows a high value, and the composite underwater distributary channel shows a strong reflection on the seismic profile. There are impermeable layers between the isolated sand bodies. According to the elevation difference relationship of different composite underwater distributary channel bodies on the seismic profile, such as Figure 6a and Figure 6b As shown, the order of their formation time can be roughly determined, and the composite underwater distributary channel 2-1 was deposited earlier than the composite underwater distributary channel 2-2.

[0102] Using the plane demarcation results of the composite underwater distributary channel obtained in step E2, combined with the seismic forward modeling method, iteratively performed, such as Figure 7As shown in Figure 2, the composite underwater distributary channel 2-2 is internally subdivided into three phases of single underwater distributary channels: single channel 2-2-1, single channel 2-2-2, and single channel 2-2-3. These three phases of single channels are in contact with each other in a multilateral, merged manner. The edges of the multiple channels are all in contact, with low values ​​on the natural gamma logs of the channel sand bodies and strong reflections on the seismic profile. The sand bodies of the multiple channels exhibit weak to moderate connectivity. Production well C2H is located in single channel 2-2-2, and the horizontal section of well C4H is located on single channel 2-2-3. The two wells are 500 meters apart in horizontal plane, but their production characteristics differ significantly. Production dynamic characteristics confirm that single channel 2-2-2 and single channel 2-2-3 exhibit weak connectivity.

[0103] E5. The planar delimitation results, filling patterns, and spatial superposition patterns of the composite underwater distributary channel and the single underwater distributary channel within it obtained through steps E1 to E4 can be used to obtain the configuration characterization results of the composite underwater distributary channel and the single underwater distributary channel within it. A three-dimensional geological model of the composite underwater distributary channel and the single underwater distributary channel within it is established, and the rationality of the reservoir configuration units that can be characterized is analyzed. The production history fitting of four oil wells in the B3-2 oil reservoir is carried out, and the numerical simulation curve is consistent with the historical production situation. This reflects the rationality of the reservoir configuration anatomy of the shallow water delta composite channel sand body under the condition of few wells.

[0104] In summary, the present invention utilizes a combined offshore early-stage well-seismic-vibration method to characterize the subsurface reservoir architecture, achieving reasonable prediction of the morphology, scale, orientation, and stacking relationships of shallow deltaic sand bodies of varying genetic order. This effectively characterizes the heterogeneity of shallow deltaic composite channel sand bodies, providing important geological evidence and guidance for well placement, well pattern design, and remaining oil prediction in such reservoirs. This is of great significance for improving the drilling success rate and achieving efficient development of shallow deltaic composite channel-facies oil and gas reservoirs. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and possesses high industrial value.

[0105] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for characterizing the structure of an offshore early-stage shallow-water delta reservoir using a combination of well-seismic and dynamic data, characterized by: The following steps are involved: A. Collect and analyze geological data, seismic data, and production performance data of the oil and gas reservoir to be characterized; B. Determine the classification scheme of sedimentary architecture for shallow water deltas; C. Determine, based on the data obtained in step A, the reservoir architecture characterization level that can be characterized in the sedimentary architecture level classification scheme for the shallow water delta under the condition of few wells, and obtain the corresponding reservoir architecture unit that can be characterized in the reservoir architecture characterization level; D. Determine the rock-electro-seismic response characteristics of the reservoir architecture units at the shallow-water delta front; E. Dissecting the reservoir architecture units that can be represented at the shallow delta front under the condition of few wells includes the following steps: E1. determining the boundary identification features of the reservoir architecture unit; E2. Delimiting a plane of a unit capable of representing a reservoir structure using the boundary recognition feature; E3. establishing a filling pattern of the reservoir architecture unit; E4. establishing a spatial superposition pattern of the units capable of representing the reservoir architecture; E5. Using the plane delimitation, filling pattern and spatial superposition pattern of the reservoir architecture unit, a three-dimensional geological model of the reservoir architecture unit is established, and the rationality analysis of the reservoir architecture unit is carried out.

2. The shallow water delta reservoir configuration characterization method according to claim 1, characterized in that: In step A, the geological data of the oil and gas reservoir to be characterized include well data of the target area to be characterized, geological stratification data, geological interface structure map, and sedimentary facies plane map of the target layer to be characterized; The seismic data of the oil and gas reservoir to be characterized include a three-dimensional seismic data volume of the target area to be characterized, and seismic horizon interpretation data of the top and bottom of the sand layer group and its internal small layer level interface of the target layer segment to be characterized; The production performance data of the oil and gas reservoir to be characterized includes the production performance data of the production wells in the target area to be characterized; The data analyzed include the well pattern and spacing of the wells drilled in the target area to be characterized, the sedimentary facies type of the target layer to be characterized, and the quality of the seismic data of the target layer to be characterized.

3. The shallow water delta reservoir configuration characterization method according to claim 2, characterized in that: The step C comprises the following sub-steps in sequence: C1. Establish the relationship between the well pattern and spacing of the wells drilled in the target area to be characterized, the production performance of the production wells, and the sedimentary facies type of the target layer to be characterized; Establish the correlation between the seismic attributes of the target area to be characterized and the thickness of the reservoir sand body; C2. Determine the reservoir architecture characterization level that can be characterized and meets the requirements of offshore development and production under the condition of few wells.

4. The shallow water delta reservoir structure characterization method according to claim 1, characterized in that: In step B, the sedimentary configuration classification scheme of the shallow water delta includes: Level 6: It can characterize the reservoir architecture unit as a level 6 architecture unit, the level 6 architecture unit is a shallow water delta sedimentary system, the corresponding phase belt level, and the corresponding stratigraphic unit is a sand layer group; Level 5: It can characterize the reservoir configuration unit as a level 5 configuration unit, the level 5 configuration unit is a composite underwater distributary channel, the corresponding subfacies level, and the corresponding stratigraphic unit is a small layer; Level 4: It can characterize the reservoir architecture unit as a level 4 architecture unit, wherein the level 4 architecture unit is an underwater distributary channel and a sand bar, corresponding to the microfacies level, and the corresponding stratigraphic unit is a single layer; Level 3: It can characterize the reservoir architecture unit as a level 3 architecture unit. The accretion body within the large-scale bottom shape of the level 3 architecture unit corresponds to the rhythmic layer level.

5. The shallow water delta reservoir configuration characterization method according to claim 4, characterized in that: The reservoir architecture unit that can be characterized at the shallow water delta front is a fourth-level architecture unit. In step D, the rock-electric-seismic response characteristics of the reservoir architecture unit that can be characterized include: subdividing the underwater distributary channel into a main channel, a secondary channel and a channel edge; The rock-electric-seismic response characteristics of the main channel include sand body thickness, lithologic characteristics, sand-to-sand ratio, electrical logging curve morphology, and response characteristics on seismic profiles; The rock-electric-seismic response characteristics of the secondary channel include sand body thickness, lithologic characteristics, sand-to-sand ratio, natural gamma ray curve morphology, and response characteristics on seismic profiles; The rock-electric-seismic response characteristics of the river channel edge include lithologic characteristics, sand-to-soil ratio, natural gamma-ray curve morphology, and response characteristics on seismic profiles; The rock-electric-seismic response characteristics of the sand bar include lithologic characteristics, sand-to-ground ratio, natural potential curve shape, natural gamma ray curve shape, and response characteristics on seismic profiles.

6. The shallow water delta reservoir structure characterization method according to claim 4, characterized in that: In step E1, the boundary identification features include the change position of seismic phase or amplitude, the change position of sand body thickness, the boundary position determined based on the relationship between horizontal well lithology change and seismic reflection characteristics, and the boundary position determined based on the production performance difference of production wells; In step E2, based on the boundary identification features of the reservoir architecture unit, a planar delineation of a composite underwater distributary channel is performed, and a planar delineation of a single underwater distributary channel is performed for a local well pattern densification or an area with high-quality seismic data. In step E3, the filling pattern of the microfacies of the single underwater distributary channel is determined. The microfacies types include main channel, sand bar, and secondary channel. The filling pattern is sand bar, main channel, and secondary channel from the center of the channel to the edge. In step E4, based on the planar demarcation of the reservoir-characterizing unit, the seismic response characteristics of the superposition pattern of the reservoir-characterizing unit are studied to determine the spatial superposition pattern between the composite underwater distributary channel and the single underwater distributary channel within it.

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