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Article

The Sequence Stratigraphy and Sedimentary Evolution of the Guantao Formation in the Binxian Uplift Area, Bohai Bay Basin, China

by
Qing Li
1,2,
Xuelian You
3,*,
Yu He
4,
Yuan Zhou
1,2,
Renzhi Tang
5 and
Jiangshan Li
1,2
1
National Key Laboratory of Petroleum Resources and Engineering, Beijing 102249, China
2
College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China
3
School of Ocean Sciences, China University of Geosciences (Beijing), Beijing 100083, China
4
Research Institute of Petroleum Exploration and Development, Beijing 100083, China
5
Zigong Earthquake Monitoring Center, Sichuan Seismological Bureau, Zigong 643000, China
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(6), 2518; https://doi.org/10.3390/app14062518
Submission received: 20 February 2024 / Revised: 13 March 2024 / Accepted: 14 March 2024 / Published: 16 March 2024
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Abstract

:
Due to the influence of multiple tectonic movements in rift basins, the sequence and sedimentary filling modes of continental petroleum reservoirs are complex, which makes it difficult to establish isochronous stratigraphic frameworks and thus affects the accuracy of subsequent predictions of effective sand bodies. Taking the Guantao Formation of the Binxian uplift and the surrounding areas as an example, this study established the sequence stratigraphic framework of the Guantao Formation and discussed the controlling effect of sequence stratigraphy on sedimentary filling. According to a combination method of seismic data, well log data, the wavelet transform technique (WTT), and Integrated Prediction Error Filter Analysis (INPEFA) methods, the Guantao Formation in the study area can be divided into 1 long-term cycle (LNG), 4 mid-term cycles (MNG1–MNG4, from bottom to top), and 11 short-term cycles (SNG1–SNG11, from bottom to top). Based on comprehensive analysis of geological and seismic data, three sedimentary facies can be classified: alluvial fan facies, braided fluvial facies, and meandering fluvial facies. The sequence stratigraphic style of the study area has a significant controlling effect on sedimentation and sand body distribution. Different levels of cycles have different impacts on sedimentary facies/microfacies types, the development degree of each sedimentary microfacies, and sand body distribution. The long-term cycle controls the distribution of sedimentary facies, while the mid-term and short-term cycles control the distribution of sedimentary microfacies. The bottom interface of the Guantao Formation (T1) served as the dominant migration channel in the study area, connecting the reservoir and source rocks. When the base-level was in the low stage (MNG1), a large amount of sand bodies developed, forming favorable reservoirs for petroleum. The interlayers at the top of the long- and mid-term cycles served as seal layers to prevent oil and gas from escaping. The MNG1 cycle has a good combination of reservoir and seal, resulting in the accumulation of oil and gas in the MNG1 strata, which became the main oil- and gas-producing layer in the area. These study results can provide effective guidance for future prediction of the distribution of sand bodies and high-quality reservoirs.

1. Introduction

With the advancement of oil and gas exploration and development, the characterization of subtle lithology and stratigraphic oil and gas reservoirs is gradually becoming more elaborate and the prediction of effective sand bodies is becoming more important. However, due to the influence of multiple tectonic movements in rift basins, the sequence and sedimentary filling modes of continental petroleum reservoirs are complex, with strong heterogeneity, which makes it difficult to establish isochronous stratigraphic frameworks and thus affects the accuracy of subsequent predictions of effective sand bodies [1,2]. The establishment of a fine-sequence stratigraphic framework is the basis for accurately predicting effective sand bodies. Clarifying the impact of sequence stratigraphy on sedimentation and reservoirs can provide useful information for predicting efficient exploration and development of oil and gas. The proposal of high-resolution sequence stratigraphy theory provides new solutions for the interrelationships between sequences and reservoirs. The sequence stratigraphy theory proposed by Vail uses unconformity surfaces as sequence boundaries [3,4], while the high-resolution sequence stratigraphy theory proposed by Cross is based on the base-level cycle to determine sequence boundaries [5]. The base-level cycle is a comprehensive factor influenced by tectonic factors, the climate, sediment supply, and accommodation space. Clarifying changes in the base-level is the basis for establishing a high-resolution sequence stratigraphic framework. High-resolution sequence stratigraphy is widely and effectively applied in continental strata to establish a regional stratigraphic correlation framework using core, logging, and seismic data [6,7,8].
The Binxian area is located in the northwest of the Jiyang Depression, Bohai Bay Basin, China. The Guantao Formation of Neogene is the main oil-bearing layer in this area, with great exploration potential. The Guantao Formation in the Binxian area is mainly composed of alluvial fan and fluvial facies. The establishment of sequence stratigraphy of alluvial fan and fluvial facies strata has always been a difficult point in sequence stratigraphy research [9]. The main reasons for this include (1) the fact that alluvial fan and fluvial facies commonly exhibit the characteristic of rapid lithology changes in both horizontal and vertical directions, making it difficult to correlate isochronous sequence stratigraphy in the entire region; (2) the lack of a widely developed marker bed, such as a maximum flooding surface sediment, which makes it difficult to identify a typical marker bed for stratigraphic correlation.
Replacing the sea level with the base-level (the surface where erosion and sedimentation reach equilibrium) is the key to establishing high-resolution sequence stratigraphy of alluvial fan and fluvial strata in continental environments [10]. A base-level is a dynamic interface that balances erosion and sedimentation, representing the relationship between stratigraphic stacking patterns and changes in base-level cycles. A base-level cycle is commonly composed of a rising semi-cycle and a falling semi-cycle. “Accommodation space” refers to the amount of space available for sediment to fill up [11]. An increase in the base-level will to an increase in the accommodation space, while a decrease in the base-level will reduce the accommodation space.
Previous studies have focused on hydrocarbon accumulation and the reservoir characteristics of alluvial fans. However, there is limited understanding of the sequence stratigraphic division and sedimentary evolution of alluvial fan–fluvial systems, which has constrained the accurate exploration and development of the Guantao Formation in the Bohai Bay Basin [12,13,14].
Taking the Guantao Formation of the Binxian uplift and surrounding areas as an example, the purpose of this study was (1) to identify the long-term, medium-term, and short-term cycle sequence stratigraphy of strata filled with an alluvial fan and fluvial depositional system by using seismic, logging, and core data; (2) to establish the sequence stratigraphic framework of the Guantao Formation; and (3) to understand the controlling effect of sequence stratigraphic framework on sedimentary filling. The results of this study can be utilized for hydrocarbon exploration in the Guantao Formation in the Bohai Bay Basin and other similar basins.

2. Geological Setting

The Binxian uplift and its surrounding areas are located in the northwest of the Jiyang Depression, Bohai Bay Basin, with an overall exploration area of approximately 240 km2 (Figure 1a). The Binxian uplift is an ancient uplift mainly composed of Archean granite gneiss. Two syn-sedimentary faults, the Binbei fault and Binnan fault, are developed around the Binxian uplift, and multiple secondary faults are developed in the southern part of the Binnan fault (Figure 1 and Figure 2).
The strata in the study area include (from bottom to top) the Archean basement, the Paleogene (approximately 42.5 Ma to 24.6 Ma; including the Kongdian Formation and Shahejie Formation), Neogene (approximately 24.6 Ma to 1.8 Ma; including the Guantao Formation and Minghuazhen Formation), and Quaternary (mainly the Pingyuan Formation). The tectonic evolution in the Cenozoic era can be divided into two evolutionary stages: the rift expansion period and the depression period. The rift expansion period can be further divided into the early rift expansion stage, the peak rift expansion period, and the decline rift expansion period [15,16,17,18]. The Guantao Formation, the target strata of this study, is in the depression period and can be divided into four sand groups (from top to bottom): Ng1, Ng2, Ng3, and Ng4, according to lithology and electrical characteristics (Figure 1c). Among them, Ng4 is the main oil-bearing layer. The Guantao Formation has a thickness of about 200 m and contact with the upper and lower strata in parallel and angular unconformity, respectively.
The study area entered a depression period in the early stage of the Guantao Formation. Due to the presence of the Binxian uplift, the Guantao Formation in the study area developed a sedimentary system of alluvial fan and fluvial facies. In the early stage of the Guantao period, alluvial fans developed near the Binxian uplift, and a braided fluvial system developed in the areas surrounding the Binxian uplift. In the middle and late stages of the Guantao Formation, the Binxian uplift was gradually covered, and the sedimentary facies changed from alluvial fans to fluvial gradually [19,20,21,22].

3. High-Resolution Sequence Stratigraphic Division

3.1. Methods

The accurate establishment of a sequence stratigraphic framework is a prerequisite for conducting research on predicting the distribution patterns of sedimentary facies and sand bodies [23]. At present, the sequence stratigraphic division in the Binxian area is not clear. Guided by the theory of high-resolution sequence stratigraphy, the different levels of sequence stratigraphic boundary characteristics in the Guantao Formation have been reorganized and determined.
The Integrated Prediction Error Filter Analysis (INPEFA) and wavelet transform technique (WTT) can highlight the cyclic features hidden in the original well logging data, thereby more clearly reflecting the trend changes in sedimentary cycles within the strata [24,25].
One-dimensional discrete wavelet transform is a signal processing technique. It is commonly used to decompose signals into sub-signals of different scales and frequencies to better understand and process signals. In discrete wavelet transform, wavelet functions are used to transform a signal into signals of different frequencies.
Maximum Entropy Spectral Analysis (MESA) is a method of extrapolating autocorrelation functions based on the maximum information entropy criterion. It is particularly suitable for signals with poor regularity and high noise, and can improve the resolution of spectrum estimation. Prediction Error Filter Analysis (PEFA) is a method of calculating the difference between the predicted MESA values and the corresponding real values of the logging curve at each depth point based on the MESA results. Integrated Prediction Error Filter Analysis (INPEFA) is a more valuable curve obtained by applying specific integration processing to the PEFA curve, which can display trends and patterns that are usually not easily observed in the original logging curve.
This study identified long-term cycles, mid-term cycles, and short-term cycles in the Guantao Formation by using a combination method of seismic data, well log data, the wavelet transform method, and INPEFA methods.

3.2. Long-Term Cycle Identification Based on Well Logging–Seismic Data Combination

The bottom boundary of the Guantao Formation exhibits characteristics of medium to strong amplitude and medium to high continuity on its seismic profile (interface T1), which can be tracked throughout the region. The seismic down-lap reflection structure can be identified above the T1 interface, and obvious truncation reflection texture can be identified below the interface (Figure 3), indicating an angular unconformity contact relationship between the Guantao Formation and the underlying strata. The obvious unconformity between the upper and lower sedimentary bodies reflects an important tectonic movement and can serve as a marker bed for identifying long-term cycles (third-order sequences).
There are two types of contact interfaces between the Guantao Formation and the underlying strata in the study area. One type is the Guantao Formation’s contact with the Shahejie Formation (Es), and the other is its contact with the Archean strata. These two types of strata contact interfaces have different well logging curve characteristics. The well logging curves of the contact surface between the Guantao Formation and the Shahejie Formation have the following characteristics (Figure 4c): the well logging curve SP value above the T1 interface is relatively low, while the SP value is relatively high below the T1 interface; the well logging resistivity curve shows an increasing trend below the interface; the well logging CAL and AC curves exhibit more severe serration above the T1 surface, gradually returning to low values below the T1 surface. The well logging curves of the contact surface between the Guantao Formation and the Archean strata have the following characteristics (Figure 4d): the well logging resistivity curve above the T1 interface shows a straight and continuous low value, with an increasing trend under the T1 interface; the well logging AC and CAL curves often exhibit a combination of serrated box-shaped and serrated bell-shaped shapes above the T1 interface, with a downward trend under the T1 surface. The differences in these logging curve shapes indicate the differential sedimentary facies and lithologies on different sides of the interface [26].
The interface between the Guantao Formation and the overlying Minghuazhen Formation in the seismic profile (interface T0) shows characteristics of medium to strong amplitude and medium to low continuity (Figure 3). The T0 interface is a parallel unconformity surface, reflecting geological erosion caused by rapid structural uplift and lake level decline [27]. Under the T0 interface, the well logging GR, SP, CAL, and AC curves are mainly of medium to high values, and the resistivity curve is mainly of medium to low values (Figure 4a,b).
Based on comprehensive analysis of seismic and well logging data, it is believed that the bottom interface (T1) and top interface (T0) of the Guantao Formation are typical third-order sequence boundaries, and the entire Guantao Formation corresponds to a long-term cycle (third-order sequence).
The long-term cycle includes a rising base-level semi-cycle in the lower part and a falling base-level semi-cycle in the upper part. The identification marker of the interface between the rising and falling semi-cycles is the thick mudstone section layer, which was formed in the inter-river floodplain and continuously developed in the upper parts of the Guantao Formation. The thick floodplain mudstone was deposited during a maximal flooding period, which can be recognized in the large number of drilling wells in the study area (Figure 5).

3.3. Identification of Mid-Term Cycles using WTT

Well logging curve characteristics reflect the comprehensive signal response of sedimentary bodies controlled by different levels of cycles. It is difficult to effectively distinguish sedimentary cycles of different levels solely based on the characteristics of original well logging curves. Wavelet transform technology (WTT) can extract the development characteristics of different levels of cycles hidden in the original logging data. Therefore, WTT can reflect changes in sedimentary cycles more clearly within the formation. Due to the different rhythms of sediments corresponding to different cyclic levels, WTT of logging curves can be used to explore the cyclic characteristics of different levels and establish corresponding sedimentary cycles at different levels [28,29,30]. For drilling wells with complex logging curves and unclear cycle characteristics, WTT can be used to assist in identifying cycles.
One-dimensional discrete wavelet transform of the original well logging curve was performed in MATLAB software to generate 12 different levels of transformation curves, including d1, d2, d3, d4, d5, d6, d7, d8, d9, d10, a10, and s, where s represents the original curve. The transformation curves had the following relationship:
s = a10 + d10 + d9 + d8 + d7 + d6 + d5 + d4 + d3 + d2 + d1
By comparing and verifying the wavelet transform effects of various logging curves, the well logging GR curve was finally selected as the dominant curve. Through wavelet transform of GR curves for each well, it was found that the transformation curves d7 and d8 could better reflect the variation in the sedimentary cycles. The periodic characteristics of transformation curve d8 were well matched with the mid-term cycle, while the periodic characteristics of transformation curve d7 were well matched with the short-term cycle (Figure 6). Wavelet transform was used to identify mid-term sedimentary cycles in this study. Based on wavelet transform curves and supplemented by original logging curves, the Guantao Formation was divided into four mid-term cycles, named MNG1 to MNG4, from bottom to top (Figure 6).

3.4. Identification of Short-Term Cycles via INPEFA

INPEFA technology can obtain preferable trend lines and periodic characteristics (sedimentary cycle characteristics) hidden in well logging curves. The changes and turning points in trend lines can indicate the response characteristics of sedimentary changes and provide more intuitive indicators of cyclic interfaces [31].
By conducting INPEFA on multiple curves, it was found that the well logging GR curve was the most sensitive to changes in lithologies in the formation. Therefore, the GR curve was selected as the dominant logging curve for INPEFA that could reflect the characteristics of sedimentary cycles preferably.
Using the well logging SP curve as the analysis attribute and the well logging GR curve as the result attribute, GR filtering curves for different depth windows were generated, setting multiple depth windows such as 1 m, 5 m, 10 m, 15 m, 20 m, 30 m, and 50 m in Direct software (Figure 7). Through comparative analysis, it was found that the GR filtering curve of the 10 m depth window could best reflect the characteristics of short-term cycles and could assist in identifying short-term sedimentary cycles.
The trend lines generated in the INPEFA can be divided into two categories: positive trend lines (curve shifted to the right) and negative trend lines (curve shifted to the left). A negative trend line indicates an increase in sandstone and a decrease in mudstone, reflecting a decrease in the accommodation space. Conversely, a positive trend line indicates an increase in mudstone content and an increase in the accommodation space.
A negative trend line and an adjacent positive trend line form a periodic oscillation, which corresponds to a short-term cycle. The turning points between two periodic oscillations are commonly an interface between sandstone and mudstone phases, commonly corresponding to a fifth-order cycle boundary. According to the periodic oscillation, the entire Guantao Formation could be divided into 11 short-term cycles (11 fifth-order cycles), named the SNG1–SNG11 cycles, from bottom to top (Figure 7).
Therefore, the isochronous stratigraphic framework of the Guantao Formation in the Binxian area was systematically established with the advantages of identifying unconformity surfaces and continuous tracking through the seismic profile, combined with the high vertical resolution of well logging data with methods of the WTT and INPEFA. The target layer of the Guantao Formation was divided from bottom to top into one third-order cycle (LNG), four fourth-order cycles (MNG1 to MNG4), and eleven fifth-order cycles (SNG1 to SNG11) (Figure 8).

4. The Impact of Sequence Structure on Sedimentary Filling

4.1. Types and Characteristics of Sedimentary Microfacies

According to the seismic reflection characteristics, six typical seismic phases were identified in the study area (Table 1): the broom-shaped progradation phase, the dome-shaped phase, the chaotic phase, the wedge-shaped divergent phase, the lens-shaped filling phase, and the sheet-like parallel phase.
The broom-shaped progradation phase mainly presented a reflection texture of progradation, reflecting the sedimentary process of continuously extending forward. The seismic in-phase axes in this phase were mostly characterized by medium–strong amplitude and medium–low continuity. This phase was mainly distributed in the steep slope zone and the down-dip of syn-sedimentary faults in the area, reflecting the alluvial fan facies (Table 1A).
The dome-shaped phase generally presented a “convex top and flat bottom” dome-shaped reflection, with poor layering and characteristics of medium amplitude and medium continuity. This phase was mainly distributed in steep slope zones. Multiple dome-shaped phases were horizontally stacked, reflecting the transverse cross section of alluvial fans (Table 1B).
The chaotic phase generally exhibited irregular chaotic reflections, with low to medium amplitude levels and low-continuity seismic in-phase axes characteristics. This phase was mainly distributed in the descending plate of syn-sedimentary faults close to faults, which can reflect the rapid sedimentation of alluvial fans (Table 1C).
The seismic reflection of the wedge-shaped divergent phase showed a pattern of gradually decreasing amplitude and continuity towards a certain direction along the same axis. This phase was mainly distributed in depression slopes, reflecting the edge of alluvial fans or the fluvial facies (Table 1D).
The lens-shaped filling phase was generally lens-shaped, with medium to low amplitude and continuity. This phase was mainly distributed in the upper interval of the Guantao Formation and the periphery of the uplift, reflecting channel sand bodies (Table 1E).
The sheet-like parallel phase generally had a sheet-like reflection texture, with medium amplitude and continuity in parallel or subparallel contact with the upper and lower seismic in-phase axes, reflecting a relatively low-energy sedimentary environment. This phase was widely distributed around the uplift, reflecting a floodplain deposit (Table 1F).
Based on comprehensive analysis of geological and seismic data, three sedimentary facies can be classified: alluvial fan facies, braided fluvial facies, and meandering fluvial facies. By combining seismic data and drilling well log information, the sedimentary microfacies in the study area were determined. The typical types of microfacies response in logging curves are as follows.
The braided fluvial facies can be divided into three sedimentary microfacies: center bar, braided channels, and floodplains. The lithology of the center bar microfacies is mainly composed of medium to fine sandstones, with upward-fining rhythms or homogeneous rhythms (Figure 9a). Their SP curve generally presents box-shaped or bell-shaped patterns. The braided channel microfacies are mainly composed of medium sandstone, with upward-fining rhythms. Their SP curve generally shows bell-shaped and box-shaped patterns. The floodplain microfacies are mainly characterized by flat SP curves.
The meandering fluvial facies can be divided into channel and floodplain microfacies. The SP curve of channel microfacies is mainly bell-shaped, with thicknesses generally greater than 2 m. The floodplain microfacies are mainly composed of mudstone, and their SP curve often shows a straight or low-amplitude sawtooth shape (Figure 9b).
The alluvial fan facies can be divided into stream flow deposit, overflow sand bodies, and sheet flow deposit. The lithology of the stream flow deposit is mainly composed of fine sandstone, with good sorting and moderate rounding. The sedimentary rhythm is mainly upward-fining, and the SP curve shows bell-shaped or box-shaped patterns. The sedimentary rhythm of the overflow sand body is an upward-coarsening rhythm, and the SP curve is funnel-shaped. The sheet flow deposit is mainly composed of muddy siltstone and mudstone, and its SP curve is mostly near the mudstone baseline (Figure 9c–e).
Based on the above characteristics and previous studies [19,20,21,22], the sedimentary facies and microfacies of each well in the Guantao Formation have been determined (Figure 10).

4.2. The Impact of Long-Term Cycles on Sedimentary Facies Evolution

The base-level cycle has a significant controlling effect on the sedimentary filling in the study area. There are three sedimentary systems filled within the long-term cycles (LNG) in the study area: alluvial fan, braided fluvial, and meandering fluvial facies. According to the analysis and statistics of the proportions of various sedimentary facies in the LNG, it shows that the meandering fluvial facies is most developed in the study area, followed by braided fluvial facies, and finally the alluvial fan facies. The type and characteristics of sedimentary filling have a regular variation with the fluctuation in the base-level in the LNG (Figure 11).
Taking the maximum lake-flooding surface as the boundary, the LNG can be divided into a rising semi-cycle and a falling semi-cycle. The rising semi-cycle of the LNG can be further subdivided into three fourth-order cycles, namely MNG1 to MNG3, from bottom to top. The falling semi-cycle of the LNG corresponds to a fourth-order cycle named MNG4. There were significant differences in the types and development proportion of different sedimentary facies within each fourth-order cycle, which presented regular variation with changes in the base-level (Figure 11 and Figure 12). The alluvial fan facies was most developed in the MNG1 period, accounting for 66%, and decreasing to 11% in MNG2. The proportion of braided fluvial facies in MNG1 was 34%; this proportion increased to a peak of 62.5% in MNG2, and then decreased to 38.5% in MNG3, and disappeared in the MNG4 period. The proportion of meandering fluvial facies increased from 0% in MNG1 to 26.5% in MNG2, then to 61.5% in MNG3, finally reaching 100% in MNG4. During the MNG4 period, the base-level fell and a meandering fluvial facies developed in the entire area, with the distribution area of meandering fluvial sand bodies becoming wider than that of the MNG3 period.
The MNG1 cycle is located in the early stage of the rising semi-cycle of the LNG. Skirt-shaped alluvial fan groups developed surrounding the ancient Binxian uplift near the boundary of the Binbei and Binnan faults during the MNG1 period (Figure 12d). There was no clear boundary between each alluvial fan body. The fan group diverged and connected to the braided river in the southward direction. Stream flow deposits were developed inside the alluvial fan body, extending towards the lower terrain. Part of the stream flow deposits underwent deflection near the descending plate of the syn-sedimentary faults, causing an increase in the width of the stream channel and a change in the direction to parallel to the fault. Braided fluvial facies mainly developed around the periphery of the Binxian uplift.
MNG2 occurs in the middle stages of the rising semi-cycle of the LNG. As the base-level rose, the sedimentary system transitioned from alluvial fans to braided fluvial facies, and the sand body gradually decreased. Only a small number of alluvial fans developed in the central slope area near the uplift (Figure 12c). The braided fluvial channels presented in irregular strips, and their provenance changed, mainly coming from the north of the study area instead of from the Binxian uplift.
The MNG3 cycle develops in the late stage of the rising semi-cycle of the LNG. During the MNG3 cycle, the Binxian uplift was basically filled to flat terrain, with the main facies being meandering fluvial and a small amount of braided fluvial (Figure 12b). The fluvial facies all came from the north. Compared to the MNG2 period, the width of the fluvial channel became narrower and the distribution range of sand bodies became smaller in MNG3, indicating a decrease in material supply. The distribution of the sand bodies became the smallest at the conversion surface between the rising semi-cycle and falling semi-cycle of the LNG.
During the deposition period of MNG4, the base-level of the long-term cycle began to decline. Only meandering fluvial facies were developed in this cycle. Due to the decrease in the accommodation space, the width and distribution range of sand bodies became larger compared to that formed at the conversion surface between the rising semi-cycle and falling semi-cycle of the LNG, showing intertwined strips shaped within the floodplains (Figure 12a).

4.3. The Impact of Mid- and Short-Term Cycles on Sedimentary Microfacies

Statistical analysis was conducted on the sedimentary microfacies of each short-term cycle (fifth-order cycle) within the fourth-order cycles (Figure 13). The types and proportion of different sedimentary microfacies in each short-term cycle was clarified to analyze the control of mid- and short-term cycles on sedimentary microfacies. The MNG1 cycle can be subdivided into three short-term cycles from bottom to top: SNG1 to SNG3. The sedimentary facies in SNG1 was an alluvial fan, with stream flow deposits accounting for 30%, overflow sand bodies accounting for 40%, and sheet flow deposits accounting for 35%. In SNG2, the proportion of the stream flow deposits and overflow sand bodies decreased to 28% and 20%, respectively, while the proportion of sheet flow deposits increased to 42%. Braided fluvial facies began to appear in SNG2, with braided channel microfacies accounting for 3%, center bar microfacies accounting for 5%, and floodplain microfacies accounting for 2%. In SNG3, the proportion of alluvial fans continued to decrease, while the proportion of braided fluvial facies generally increased. The proportion of stream flow deposits, overflow sand bodies, and sheet flow deposits in the alluvial fans decreased to 21%, 14%, and 10%, respectively. On the contrary, the proportion of braided channels, center bars, and floodplains in the braided river facies increased to 30%, 6%, and 19%, respectively. From SNG1 to SNG3, the base-level gradually rose, resulting in a reduction in the sand bodies and an increase in floodplain microfacies and the mud content.
The MNG2 cycle can be subdivided into two short-term cycles, named SNG4 and SNG5. During the SNG4 period, almost all alluvial fan facies were transformed into fluvial facies, with stream flow deposits and overflow sand bodies accounting for only 5% and 7%, respectively. A small amount of meandering river facies began to develop during this cycle, with meandering channels and floodplains accounting for 14% and 11%, respectively. The proportion of braided fluvial facies increased, with 27% braided channel, 17% center bars, and 19% floodplain microfacies. In SNG5, the proportion of meandering channels decreased from 14% to 13%, while the proportion of floodplains increased from 11% to 15%. The proportion of braided channels and center bars decreased from 27% to 24%, and from 17% to 14%, respectively. In these two short-term cycles, the base-level was in the rising stage, with a high mudstone content and the total proportion of floodplain facies being over 30%.
The MNG3 cycle can be subdivided into two short-term cycles: SNG6 and SNG7. From SNG5 to SNG6, the base-level rose and the alluvial fan facies gradually disappeared completely, leaving only meandering and braided fluvial facies. In SNG6, the proportion of meandering fluvial facies (accounting for 57%) began to exceed that of the braided fluvial facies (accounting for 43%). In SNG7, the proportion of meandering fluvial facies increased up to 76%, which was much higher than that of the braided fluvial facies. The main microfacies were floodplains with a high mudstone content in this stage.
MNG4 can be subdivided into four short-term cycles, from bottom to top: SNG8 to SNG11. Only meandering fluvial facies developed in these four short-term cycles. The base-level reached its maximum between SNG7 and SNG8, with the highest accommodation space and mudstone content. The proportion of the floodplains was relatively high, being up to 68% and 70% in SNG7 and SNG8, respectively. On the contrary, the content of sand bodies was very low in this stage. Starting from SNG8, the base-level began to decrease, with a reduction in mudstone and increase in meandering fluvial channels.

5. The Impact of Sequence on Petroleum Reservoir Development

The sequence stratigraphy of the Guantao Formation obviously controlled the sedimentary filling evolution in the study area. The base-level variation during the long-term cycle controlled the type and development degree of the sedimentary facies, while base-level variation during the mid-term cycle controlled the type and development degree of the sedimentary microfacies. As the long-term base-level rose, the sedimentary facies in the study area also shifted from alluvial fans to braided fluvial and ultimately to meandering fluvial facies. With the fluctuation in the base-level in the mid-term cycle, the type, development degree, and distribution of the sedimentary microfacies also changed accordingly. In the alluvial fan facies, the stream flow deposits and overflow sand bodies gradually decreased until disappearing with the rise in the base-level from SNG1 to SNG5. Within the braided fluvial facies, the development of the center bars and braided channels gradually decreased with the rise in the mid-term cycle base-level from SNG4 to SNG7. The meandering fluvial channels increased as the base-level decreased from SNG8 to SNG 10.
The evolution of the sequence stratigraphy also controlled the distribution of high-quality reservoirs in the Guantao Formation. When the base-level was at a low level, a large amount of sand bodies developed, which can form favorable reservoirs for petroleum. The SNG1 to SNG3 cycles were mainly filled with alluvial fan sediments, with well-developed sand bodies, which comprise the main oil- and gas-bearing layers in the study area. Meanwhile, during the evolution of sequence stratigraphy, base-level cycles can control the combination of reservoirs and seals. At the transition surface of the long-term cycle, which corresponds to the maximum lake-flooding surface in the Guantao Formation in the study area, there was a continuous development of thick floodplain mudstone, which can serve as stable regional seal for petroleum reservoirs. This seal combined with the underlying main oil-bearing layers in SNG1 to SNG3, forming a good storage space for the accumulation of oil and gas. At the top of each mid-term cycle, the elevation of the base-level can form relatively stable local seals in the study area. Good reservoir–seal combinations were formed in SNG1 to SNG3, ensuring that oil and gas were not easily dispersed but migrated to the reservoir layers.
The bottom boundary of the Guantao Formation (interface T1) serves as a third-order sequence boundary and has an unconformity contact relationship with the underlying strata. This unconformity surface served as a dominant migration channel in the study area, connecting the reservoir and source rocks and expanding the spatial range of oil and gas migration. Oil and gas migrated through the unconformity surface (third-order sequence boundary) at the bottom of the Guantao Formation in the Binxian uplift to the sand body in MNG1. The interlayers at the top of the mid-term cycles served as seal layers to prevent oil and gas from escaping. The large section of mudstone at the transition of the base-level surface in the long-term cycle further served as a stable seal layer to preserve oil and gas. Therefore, oil and gas were accumulated in the MNG1 cycle strata, becoming the main oil- and gas-producing layer in the area.
Therefore, the sequence stratigraphy plays an important role in the development of petroleum reservoirs. It can be seen that the long-term cycle controls the distribution of sedimentary facies, while the mid-term and short-term cycles control the distribution of sedimentary microfacies. When the base-level is at low levels, a large amount of sand bodies develop, forming favorable reservoirs for petroleum. The interlayers at the top of the long- and mid-term cycles serve as seal layers to prevent oil and gas from escaping. The boundary of the sequence stratigraphy can serve as a migration channel, connecting the reservoir and source rocks. The results of this study can provide effective guidance for future prediction of the distribution of sand bodies and high-quality reservoirs.

6. Conclusions

This study conducted a detailed study on the high-resolution sequence stratigraphy and sedimentary evolution of the Guantao Formation in the Binxian area of Bohai Bay Basin in China. The controlling effect of sequence stratigraphy on sedimentary filling and its significance for oil and gas exploration and development were analyzed.
(1) According to a combination method using seismic data, well log data, WTT, and INPEFA methods, the Guantao Formation in the study area was divided into one long-term cycle (LNG), four mid-term cycles (MNG1–MNG4, from bottom to top), and eleven short-term cycles (SNG1–SNG11, from bottom to top).
(2) The sedimentary facies types of the Guantao Formation exhibited a regular variation with the fluctuation in the base-level. The sequence stratigraphic style of the study area had a significant controlling effect on sedimentation and sand body distribution. Different levels of cycles had different impacts on the sedimentary facies/microfacies type, the development degree of each sedimentary microfacies, and the sand body distribution. The long-term cycle controlled the distribution of sedimentary facies, while the mid-term and short-term cycles controlled the distribution of sedimentary microfacies. During the rising semi-cyclical period of the LNG, the area was mainly filled by alluvial fan and braided fluvial facies. As the base-level rose, the alluvial fan gradually evolved into braided fluvial and then into meandering fluvial facies. During the descending semi-cyclical period of the LNG, the area was mainly filled by braided and meandering fluvial facies. As the base-level decreased, the width of meandering fluvial channels and the distribution range of sand bodies increased.
(3) The bottom interface of the Guantao Formation (T1) served as the dominant migration channel in the study area, connecting the reservoir and source rocks. When the base-level was at a low level (MNG1), a large amount of sand bodies developed, which can form favorable reservoirs for petroleum. The interlayers at the top of the long- and mid-term cycles served as seal layers to prevent the oil and gas from escaping. Therefore, the MNG1 cycle exhibited a good combination of reservoir and seal, resulting in the accumulation of oil and gas in the MNG1 cycle, which became the main oil- and gas-producing layer in the area.
This study analyzed the Guantao Formation in the Binxian uplift in order to clarify the impact of the Guantao Formation sequence stratigraphy on sedimentary filling styles. The study results can provide effective guidance for future prediction of the distribution of sand bodies and high-quality reservoirs.

Author Contributions

Conceptualization, Q.L.; methodology, X.Y.; software, Y.Z. and Y.H.; formal analysis, R.T. and J.L.; investigation, Q.L.; writing—original draft preparation, Q.L.; review, X.Y.; funding acquisition, Q.L. and X.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This study was financially supported by the National Natural Science Foundation of China (Grant No. 42372146 and 41972107) and the Strategic Cooperation Technology Projects of CNPC and CUPB (ZLZX 2020-02).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

We extend gratitude to the Exploration and Development Research Institute of Shengli Oilfield for providing the samples and data access, and for granting permission to publish the results.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The geographical location of the Binxian area and the stratigraphic division of the target interval: (a) Tectonic map of the Bohai Bay Basin. (b) Tectonic map of the Binxian uplift and its periphery. (c) Stratigraphic characteristics of the study area.
Figure 1. The geographical location of the Binxian area and the stratigraphic division of the target interval: (a) Tectonic map of the Bohai Bay Basin. (b) Tectonic map of the Binxian uplift and its periphery. (c) Stratigraphic characteristics of the study area.
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Figure 2. Bottom structure of the Guantao Formation around the Binxian uplift.
Figure 2. Bottom structure of the Guantao Formation around the Binxian uplift.
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Figure 3. A typical seismic profile characteristic of the Binxian area.
Figure 3. A typical seismic profile characteristic of the Binxian area.
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Figure 4. Well logging curve characteristics of third-order sequence boundaries: (a,b) Well logging curve characteristics of the top interface between the Guantao Formation and the Minghuazhen Formation. (c) Well logging curve characteristics of the bottom interface between the Guantao Formation and the Shahejie Formation. (d) Well logging curve characteristics of the bottom interface between the Guantao Formation and the Archean strata.
Figure 4. Well logging curve characteristics of third-order sequence boundaries: (a,b) Well logging curve characteristics of the top interface between the Guantao Formation and the Minghuazhen Formation. (c) Well logging curve characteristics of the bottom interface between the Guantao Formation and the Shahejie Formation. (d) Well logging curve characteristics of the bottom interface between the Guantao Formation and the Archean strata.
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Figure 5. Characteristics of long-term cycles and maximum base-level surface.
Figure 5. Characteristics of long-term cycles and maximum base-level surface.
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Figure 6. Characteristics of different wavelet transform curves of GR.
Figure 6. Characteristics of different wavelet transform curves of GR.
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Figure 7. The results of INPEFA with different depth windows.
Figure 7. The results of INPEFA with different depth windows.
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Figure 8. Sequence stratigraphic framework of the Guantao Formation.
Figure 8. Sequence stratigraphic framework of the Guantao Formation.
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Figure 9. Well logging characteristics of different sedimentary microfacies.
Figure 9. Well logging characteristics of different sedimentary microfacies.
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Figure 10. Sedimentary facies of single wells in the Guantao Formation (left well: S106; right well S52).
Figure 10. Sedimentary facies of single wells in the Guantao Formation (left well: S106; right well S52).
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Figure 11. Sedimentary facies changes with fluctuation in the base-level during the LNG.
Figure 11. Sedimentary facies changes with fluctuation in the base-level during the LNG.
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Figure 12. Distribution of sedimentary microfacies of different fourth-order cycles. (a) Distribution of sedimentary microfacies of MNG4; (b) Distribution of sedimentary microfacies of MNG3; (c) Distribution of sedimentary microfacies of MNG2; (d) Distribution of sedimentary microfacies of MNG1.
Figure 12. Distribution of sedimentary microfacies of different fourth-order cycles. (a) Distribution of sedimentary microfacies of MNG4; (b) Distribution of sedimentary microfacies of MNG3; (c) Distribution of sedimentary microfacies of MNG2; (d) Distribution of sedimentary microfacies of MNG1.
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Figure 13. Distribution of sedimentary microfacies in each short-term cycle. Orange arrows show the microfacies changes in mid- term cycles and blue arrows show the microfacies changes in long-term cycle.
Figure 13. Distribution of sedimentary microfacies in each short-term cycle. Orange arrows show the microfacies changes in mid- term cycles and blue arrows show the microfacies changes in long-term cycle.
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Table 1. Characteristics of six typical seismic phases.
Table 1. Characteristics of six typical seismic phases.
Types of Seismic PhaseSeismic Reflection ShapeSeismic Reflection
Texture		Seismic Attribute CharacteristicsDistribution LocationSedimentary Facies
Interpretation		Examples
broom-shaped progradation phasebroom-shapedprogradation reflection texturemid-high amplitude, mid-low continuousuplift periphery, synsedimentary fault downthrown platealluvial fan faciesApplsci 14 02518 i001
dome-shaped phasedome-shapedwave reflection texturemid amplitude, mid continuousuplift peripheryalluvial fan faciesApplsci 14 02518 i002
Chaotic phasewedge-shapedchaotic reflection texturemid-low amplitude, low continuoussynsedimentary fault downthrown platealluvial fan faciesApplsci 14 02518 i003
wedge-shaped divergent phasewedge-shapeddivergent reflection texturemid amplitude, mid continuoussag peripheral slopealluvial fan-fluvial faciesApplsci 14 02518 i004
lens-shaped filling phaselens-shapedfilling reflection texturemid-low amplitude, mid-low continuousgentle area in the sagfluvial faciesApplsci 14 02518 i005
sheet-like parallel phasesheet-likeparallel-subparallel reflection texturemid-high amplitude, mid-highcontinuousgentle area in the sagfluvial faciesApplsci 14 02518 i006
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Li, Q.; You, X.; He, Y.; Zhou, Y.; Tang, R.; Li, J. The Sequence Stratigraphy and Sedimentary Evolution of the Guantao Formation in the Binxian Uplift Area, Bohai Bay Basin, China. Appl. Sci. 2024, 14, 2518. https://doi.org/10.3390/app14062518

AMA Style

Li Q, You X, He Y, Zhou Y, Tang R, Li J. The Sequence Stratigraphy and Sedimentary Evolution of the Guantao Formation in the Binxian Uplift Area, Bohai Bay Basin, China. Applied Sciences. 2024; 14(6):2518. https://doi.org/10.3390/app14062518

Chicago/Turabian Style

Li, Qing, Xuelian You, Yu He, Yuan Zhou, Renzhi Tang, and Jiangshan Li. 2024. "The Sequence Stratigraphy and Sedimentary Evolution of the Guantao Formation in the Binxian Uplift Area, Bohai Bay Basin, China" Applied Sciences 14, no. 6: 2518. https://doi.org/10.3390/app14062518

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