Seismic-Sedimentary Facies Analysis of Es3x Formation in Southern Region, Laizhou Bay Depression, Bohai Bay Basin, China

Xudong Y, et al., J Atmos Earth Sci 2019, 3: 011 DOI: 10.24966/AES-8780/100011 HSOA Journal of Atmospheric & Earth Sciences

Research Article

Seismic-sedimentary Facies Introduction The southern region is located in Laizhou bay Depression of Bo- Analysis of Es3x Formation in hai bay Basin. Due to the research area is just in the early exploration Southern Region, Laizhou Bay phase, there are few drilling wells, low research degree of seismic data, incomplete sedimentary evolution, and no similar oil fields have Depression, Bohai Bay Basin, China been developed, the relevant researches on the formation, deposition of this area will mainly rely on seismic1 and well logging data. And Yang Xudong, Xie Jun*, Zhou Liang, Wang Mengqi, Jiang Xinyu previous studies on seismic facies and sedimentary facies in this area were relatively weak. For the study on seismic facies, Dong conduct- College of Earth Science and Engineer, Shandong University of Science and ed in-depth discussion on the seismic facies in the Liaodong bay area Technology, Qingdao, China of Bohai bay Basin, reclassified the seismic facies, and combined the seismic facies and sedimentary facies to identify favorable reservoir facies zones [1]. In the study of sedimentary facies, Liu analyzed the Abstract mixed sedimentary characteristics, development patterns and main The southern region in the Laizhou bay Sag of the Bohai bay Ba- controlling factors in the south of Laizhou bay Depression in detail, sin has a good oil and gas display in Es3x formation (the lower third and identified the dominant reservoir sub facies[2]. There are some sub-member of the Shahejie Formation) through a few wells, indicat- differences between the previous studies and the study area. There- ing that large or medium-sized oil and gas fields may be discovered. fore, it is particularly important to further study the seismic-sedimen- Due to less drilling, low seismic reflection interface and low the degree tary facies based on some previous views. In this paper, the distribu- of evolutionary research, it is still difficult to study the sedimentary fa- tion of sedimentary facies in the study area is studied by using the cies in the study area. In this paper, both seismic facies analysis and regional sedimentary environment combined with logging data and logging data analysis are used to infer the sedimentary environment. Firstly, the study of seismic sections are used to identify the seismic seismic data, and thecharacteristics of seismic sedimentology are dis- facies of the study area. There are mainly four seismic phases in study cussed and summarized, so as to provide guidance and basis for the area: parallel and sub-parallel seismic facies, foreset seismic facies, research and application of seismic facies and sedimentary facies in wedge-shaped seismic facies and filling seismic facies. Secondly, the the study area in the future. distribution of sand bodies is predicted by seismic attributes. It is found that there is a strong amplitude region in the south of the study area, Basic Geological Features and there is a medium-strong amplitude region in the west, which is The southern region is located in the southern sea area of Bohai- the sand body development area. The sedimentary characteristics of the study area are clarified by converting seismic facies to sedimenta- sea, China (Figure 1A). It is a favorable zone for oil and gas migra- ry facies and researching logging data. The research indicates that the tion and accumulation in Nan sag (Figure 1B). Structural traps are braided river delta deposits developed in the western part of the study well developed and formed (Figure 1C). The structural area is close to area, the fan delta deposits developed in the south and southwest part the source material, the spatial location of hydrocarbon source rocks, of the study area, and the mixed sediments deposits developed in the faults and sandstone reservoirs is well matched, and oil and gas mi- middle of the study area. gration is unobstructed, which is a favorable exploration target in the southern slope area of Laizhou bay Sag. Keywords: Laizhou bay sag; Mixed deposits; Sedimentary facies; Seismic facies; Seismic attribute The tectonic evolution of Laizhou bay Sag in Bohai bay Basin is mainly influenced by the four stages of tectonic activities. Cenozoic *Corresponding author: Xie Jun, College of Earth Science and Engineer, strata are well developed in the study area. The main oil-bearing strata Shandong University of Science and Technology, Qingdao, China, E-mail: [email protected] are Shahejie formation, especially Es3x formation, which is revealed by drilling data. From top to bottom of stratum is Nm formation, Ng Supported by the Natural Science Foundation of China (51674156). formation, Ed formation, Es formation. The lithology of Nm forma- Citation: Xudong Y, Jun X, Liang Z, Mengqi W, Xinyu J (2019) Seismic-sedi- tion is medium sandstones, fine sandstones and mudstones. The li- mentary Facies Analysis of Es3x Formation in Southern Region, Laizhou Bay Depression, Bohai Bay Basin, China. J Atmos Earth Sci 3: 011. thology of Ng formation is medium sandstones, grits and mudstones. The lithology of Ed formation is fine sandstones and mudstones. The Received: July 21, 2019; Accepted: August 05, 2019; Published: August 12, 2019 lithology of Es formation is siltstones, fine sandstones and mudstones. The color of siltstones and fine sandstones is light grey. The color of Copyright: © 2019 Xudong Y, et al. This is an open-access article distributed under mudstones is gray. On the whole, it is a set of sedimentary sequence the terms of the Creative Commons Attribution License, which permits unrestrict- ed use, distribution, and reproduction in any medium, provided the original author from semi-deep lake to shore-shallow lake delta [2], The sedimen- and source are credited. tary range gradually becomes larger from small, and the shoreline Citation: Xudong Y, Jun X, Liang Z, Mengqi W, Xinyu J (2019) Seismic-sedimentary Facies Analysis of Es3x Formation in Southern Region, Laizhou Bay Depression, Bohai Bay Basin, China. J Atmos Earth Sci 3: 011.

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gradually recedes (Figure 2A). In the middle well areas of Y3, Y4 Seismic facies analysis and Y5 wells, terrigenous clastic and carbonate mixed sediments are Seismic phase analysis is to qualitatively identify various types of developed. Sand and gravel bodies are the main favorable reservoirs seismic phase markers on the seismic section, divide seismic phase and typical mudstone reservoirs (Figure 2B). units, make a variety of seismic phase parameter maps, and finally conduct comprehensive analysis of these maps [3]. The external ge- ometry and internal reflection structure of the reflected waves can reflect the overall deposition process, provenance direction and geological background of sediments [4]. In this paper, firstly, the research horizon [5-7] was identified on the seismic profile by means of syn- thetic record and well seismic combination, andthen the planar distribution characteristics of sedimentary bodies were identified by using seismic attributes, including verification of sediment sources. Finally, seismic facies were converted into sedimentary facies by combining different seismic reflection structures and sedimentary environments. According to the north-south seismic profile EF of well Y5 in the research area (Figure 3 and the profile position is shown in figure 1C), obvious foreset and truncated reflection structures can be seen in the profile, which is speculated to be a delta sedimentary environment [8,9], and the overall formation is thinning to the south, indicating that a south-to-north provenance sedimentary system near the profile. By analyzing the characteristics of the seismic profile MN in Es3x Formation of the study area, it is found that both parallel-subparallel reflection structures and fore-integrating reflection structures (Figure 4 and the position of the section is shown in figure 1C). In other sec- Figure 1: Schematic diagram of the location of the study area. tions, the characteristics of seismic facies are not only wedge-shaped and fill-shaped, but also sheet-shaped and other low-energy sedimentary environments, which fully reflect the characteristics of rapid deposition in fan delta, great difference in water energy, and rapid sedimentary phase transition. In the classification of seismic facies in the study area, the seismic profiles of several survey lines are dis- sected and analyzed one by one. It is considered that there are mainly four seismic facies in the study area (Figure 5): parallel to subparallel seismic facies, foreset seismic facies, wedge-shaped seismic facies and filling seismic facies.

Figure 2: Comprehensive stratigraphic section of the southern region in Laizhou bay Sag.

Seismic facies analysis of Es3x formation

The study area is located in the sea, with relatively complex geo- Figure 3: Cross-Y5 well seismic profile (Inline461). logical conditions, low resolution of seismic data (the data is old and not clear). The data collected includes log data from some wells, the 1. Parallel to the horizontal seismic facies: In the study area, it 3d seismic data volume of the study area and some lithologic photo- mainly distributed in the central of Y3 well, Y4 well and Y5 well. graphs. The distribution characteristics of sand body are studied by Internal reflection structure is high amplitude, high continuity, analyzing seismic profile and using seismic attribute analysis to iden- nearly parallel to the shape characteristic. The seismic reflection tify seismic facies. external form for sheet, the lower level is parallel or nearly parallel

Volume 3 • Issue 1 • 100011 J Atmos Earth Sci ISSN: 2689-8780, Open Access Journal DOI: 10.24966/AES-8780/100011

Citation: Xudong Y, Jun X, Liang Z, Mengqi W, Xinyu J (2019) Seismic-sedimentary Facies Analysis of Es3x Formation in Southern Region, Laizhou Bay Depression, Bohai Bay Basin, China. J Atmos Earth Sci 3: 011.

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to the contact, the thickness of relatively stable. And the lithol- Only by extracting seismic attributes in an appropriate way according ogy mainly mudstone purpose layer, sand ratio is less than 0.2 to the exploration degree of the research area and the research object by analyzing core samples, it reflecting the weak hydrodynamic can the expected effect be achieved [10]. conditions of deposition as a result, reflects the uneven subsidence of delta platform characteristics 2. Foreset seismic facies: The front end of the foreset reflection layer presents a downward superstate toward the pelvic floor, while the proximal end presents a top superstate toward the basin edge. The wedge-shaped foreset in the study area is characterized by wedge-shaped distributionalong the same direction axis and forward accretion. It is mainly distributed in the south of Y4 well and Y8 well. According to the logging data of Y8 well, it indicates the fan delta deposition on the slope

3. Wedge-shaped seismic facies: The whole profile is wedge- Figure 4: Seismic profile of Y2 well and Y5 well (other well locations are projection shaped, and the internal reflection features are composed of me- wells) (Xline1890). dium-strong amplitude and medium-high continuous reflection in the same phase axis, which is the result of different settlement and deposition rates around the lake basin. In the study area, it is Under the guidance of seismic sedimentology, the target layer mainly distributed in the southwest of Y2 well and located in the properties are accurately extracted. Appropriate time window layer is slope belt. According to the results of coring interval calibration, selected to extract seismic attributes, and seismic attributes are used the wedge-shaped seismic facies in this area belongs to the sedi- to identify the planar distribution characteristics of the sedimentary mentary seismic response of braided river delta system, and the sensitivity of the sedimentary system to seismic attributes is comprehensively considered to determine the characteristics 4. Filling phase: It is characterized by filling shape of the unit.There are two facies in gulch filling phase: open filling (low-energy en- of seismic facies [11]. Extracted RMS (Root-Mean-Square) ampli- vironment) and partial filling (high-energy environment), the fill- tude, mean instantaneous frequency and other attributes for analysis. ing in the study area for filling deposit in valleys. In the seismic Finally, it was found that the root-mean-square amplitude attribute section, in local dent, rendered in valleys. For the waveform char- had a guiding effect on the sedimentary plane distribution in the study acteristics of the region, medium strong amplitude and continui- area. By extracting the seismic attributes of RMS amplitude in Es3x ty well and parallel reflection can be found. It mainly reflect the formation in the 3D seismic working area of the study area, it is found shore and shallow lake, half deep lake, braided delta and delta that there is a strong amplitude area in the south and southeast area of front sedimentary environment the study area (Figure 6ii), indicating that sand bodies in these areas are relatively developed and may be the main developed area of the Seismic attribute analysis delta. In the western part of the study area (Figure 6i), there is a band Different types of sedimentary environments have different char- of mid-strong amplitude area, which is presumed to be braided river acteristics in the seismic profile, which can also be shown in the delta deposition. In the central area of the depression, that is, the south attribute map. Analyzing attribute maps to study sedimentary envi- of Y8 well and around the northeast (figure 6iii) are all weak ampli- ronment and other information can better and more comprehensively tude areas, indicating that these areas are lake mudstone sedimentary reflect the planar distribution characteristics of sedimentary facies. areas and lacustrine sediments.

Figure 5: Regional seismic legend of the study area.

Volume 3 • Issue 1 • 100011 J Atmos Earth Sci ISSN: 2689-8780, Open Access Journal DOI: 10.24966/AES-8780/100011 Citation: Xudong Y, Jun X, Liang Z, Mengqi W, Xinyu J (2019) Seismic-sedimentary Facies Analysis of Es3x Formation in Southern Region, Laizhou Bay Depression, Bohai Bay Basin, China. J Atmos Earth Sci 3: 011.

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According to the plane distribution characteristics of seismic facies in the study area and combined with the regional sedimentary environment [12-15], the corresponding transformation relationship between seismic facies and sedimentary facies was constructed (Table 1). Single well phase analysis In Y3-Y4-Y5 wells area, it is still difficult to identify the mixed sedimentary characteristics from the seismic facies alone. The lithologic composition analysis of the raised part of similar platform will be conducted by using the single-well facies analysis to guide the sedimentary system. The sedimentary facies were analyzed by drilling data, and through well seismic combination, the over-well profile and single well phase were established to analyze the sedimentary pat- Figure 6: Root-mean-square amplitude attribute map of Es3x Formation. tern of the target horizon. Due to the differences in mixed sediments, the Ex3x formation can be divided into three oil groups (mainly oil Sedimentary distribution characteristics of Es3x groups II and III) (Figure 8). formation Conversion of seismic and sedimentary facies The seismic units were divided by analyzing multiple vertical provenance, parallel provenance profiles and seismic phases, and according to the frequency, amplitude and continuity characteristics of waveform features, the study zones were divided into 4 areas, and the seismic phase distribution map of Es3x formation of the target layer was obtained, which was named as I, II, III and IV (Figure 7).

Figure 8: Waveform characteristics and single well phase diagram of Y5 well.

From single well can be found in the phase diagram, III-2 of oil group to II-2 of oil group deposit gray powder sandstone with thin layers of mudstone, through the core can be found in the development of cross-bedding, wedge cross bedding, wavy bedding and other bar sedimentary characteristics, response on seismic profile characteristics of weak amplitude, medium-low frequency, medium continu- Figure 7: Characteristics of the plane distribution of the seismic facies in the lower ously. II-1 of oil group to I-2 of oil group deposit thin layer powder Es-3. sandstone and argillaceous siltstone with a large set of mudstone.

Phase type Facies marks Area

mixed sedimentary parallel subparallel mid-low frequency mid-strong amplitude middle continuity III platform seismic facies mid frequency mid amplitude middle continuity

wedge-shaped seismic mid-low frequency mid amplitude middle continuity braided river delta I facies low frequency mid-low amplitude low continuity mid-low frequency mid-low amplitude low continuity mid frequency mid-low amplitude middle-low continuity fan delta foreset seismic facies II mid frequency strong amplitude good continuity low frequency low amplitude middle-low continuity

parallel subparallel mid-low frequency mid-low amplitude middle continuity shore shallow lake IV seismic facies low frequency mid-low amplitude good continuity Table 1: Seismic reflection characteristics of typical sedimentary facies of Es3x formation in southern region.

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Bioclastic can be found in the core photos. Sedimentary charac- Conclusion teristics have parallel bedding, tabular and trough cross-bedding delta front. Waveform response on seismic profile for weak amplitude, low 1. The characteristics of fore-accretion seismic facies, with the char- frequency, medium continuously; According to the lithologic combi- acteristics of wedge-like fore-accretion and fore-accretion in the nation characteristics, there are both carbonate rocks and terrigenous same direction axis, indicating the fan delta front deposition on clastic rocks, it can be judged that the Y5 well area has mixed sed- the slope. The uniformly subsided continental shelf delta platform imentary morphology, which reveals the characteristics of the sand is characterized by strong amplitude, medium and high continui- body being transformed by waves, and it is the lakeside sedimentary ty and near-parallel reflection structure, which belongs to parallel environment with shallow water. and subparallel reflection structure. The sedimentary environment of braided river delta is indicated by the seismic facies of sheet It is found that the braided river delta deposits from the far Ken- reflection and plate forward accretion reflection with medium am- dong uplift are developed in the western Y2 well area, while the fan plitude, medium frequency and continuity well delta deposits from the Weibei uplift are mainly developed in the eastern Y6-Y7-Y8 wells area. However, affected by the bottom uplift 2. According to the sedimentary environment, analysis of seismic and faults, Y3-Y4-Y5 wells in the middle blocks the source materi- profiles, seismic facies analysis, seismic attribute analysis, the als from the Kendong and Weibei uplift and deposits the mixed sedi- study area in southern and eastern Y6-Y7-Y8 wells area of fan ments belonging to lacuvial facies (Figure 9). delta sedimentary facies, provided source by Weibei uplift. The study area in western Y2 well area is braided river delta sedimentary facies, provide source from Kendong uplift. Central Y3-Y4- Y5 wells area is affected by the bottom uplift raised for similar platform, sedimentary lacustrine peperite Reference

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Volume 3 • Issue 1 • 100011 J Atmos Earth Sci ISSN: 2689-8780, Open Access Journal DOI: 10.24966/AES-8780/100011

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