**3. Sequence stratigraphic model of fluvial facies**

Fluvial sedimentation is the result of several allogenic factors, including sea level, environmental energy flux, source area tectonic movement, and basin subsidence [3, 4] (**Figure 2**). The relative importance of these factors is hard to determine, although related stratigraphic criteria can be derived from field studies and from experimental work [25]. The tectonism, the relative sea level fluctuations, and the climatic controls may be interpreted from the changes through geologic time in the directions of tectonic tilting during the deposition and from the variations of the landscape gradients. They can also be interpreted from the variations in the depths of burial, as inferred from the analyses of paleocurrent directions, architectural elements, fluvial styles, and late diagenetic clay minerals, coupled with isotopic geochemistry and petrographic studies of framework and early diagenetic constituents [26–28].

**Figure 2.** Allogenic controls on fluvial sedimentation [16].

The base level control on fluvial cyclicity represents the bulk of the first-generation sequence stratigraphic models, which assume a direct correlation between rising and falling base level on one hand, and fluvial aggradation and downcutting on the other hand [1, 29, 30]. The predictable relationship between fluvial processes and base level changes reflects a most likely scenario, but exceptions do exist [16]. This relationship is valid for the downstream reaches of fluvial systems, where rivers respond to "downstream controls" (i.e., interplay of sea level changes, basin subsidence, and fluctuations in environmental energy flux induced by climate change). In such settings, which may be characterized by either low or high accommodation space in the Leckie and Boyd's [31] scheme of fluvial stratigraphy, the fluvial deposits may be integrated within the standard lowstand, transgressive, and highstand systems tracts.

Wright and Marriott [2] believe that lowstand system tracts are mainly composed of amalgamated channel deposits. The thick transgressive systems tracts are characterized by the deposits of floodplains that are mainly wrapped with isolated channel sand bodies. The upward highstand systems tracts are characterized by higher density sandstones and paleosol deposits, representing good stratigraphic markers. Shanley and McCabe [4] considered that fluvial strata can be traced to marine strata from the same period. Laterally amalgamated fluvial sheet sandstone can overlap the unconformities. In the upper alluvial parts, amalgamated channel deposits turn into relative isolated and fine-grained sediments interbedded with meandering channel deposits. This sedimentary feature shows the tidal influence from the ocean. Catuneanu [16] made a summary of these two representative models (**Figure 3**). Thus, the fluvial sequence boundaries are placed at the bottom of base level cycles. Incised valleys form when the base level falls, while lowstand systems tracts occur at the beginning of base level rise [32].

Holbrook et al. [11] introduced the useful buttresses and buffer concepts to explain longitudinal changes in fluvial facies and building upstream coastline. One is some fixed point of control on the river equilibrium profile in the ocean basin. It is a base level (sea level) in the main river inland basin. The reaction buffer space with and below the current gradient profile

**Figure 3.** Stratigraphic model of fluvial facies modified from [16].

The base level control on fluvial cyclicity represents the bulk of the first-generation sequence stratigraphic models, which assume a direct correlation between rising and falling base level on one hand, and fluvial aggradation and downcutting on the other hand [1, 29, 30]. The predictable relationship between fluvial processes and base level changes reflects a most likely scenario, but exceptions do exist [16]. This relationship is valid for the downstream reaches of fluvial systems, where rivers respond to "downstream controls" (i.e., interplay of sea level changes, basin subsidence, and fluctuations in environmental energy flux induced by climate change). In such settings, which may be characterized by either low or high accommodation space in the Leckie and Boyd's [31] scheme of fluvial stratigraphy, the fluvial deposits may be integrated within the standard lowstand, transgressive, and highstand

38 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

Wright and Marriott [2] believe that lowstand system tracts are mainly composed of amalgamated channel deposits. The thick transgressive systems tracts are characterized by the deposits of floodplains that are mainly wrapped with isolated channel sand bodies. The upward highstand systems tracts are characterized by higher density sandstones and paleosol deposits, representing good stratigraphic markers. Shanley and McCabe [4] considered that fluvial strata can be traced to marine strata from the same period. Laterally amalgamated fluvial sheet sandstone can overlap the unconformities. In the upper alluvial parts, amalgamated channel deposits turn into relative isolated and fine-grained sediments interbedded with meandering channel deposits. This sedimentary feature shows the tidal influence from the ocean. Catuneanu [16] made a summary of these two representative models (**Figure 3**). Thus, the fluvial sequence boundaries are placed at the bottom of base level cycles. Incised valleys form when the base level falls, while lowstand systems tracts occur at the beginning of base

Holbrook et al. [11] introduced the useful buttresses and buffer concepts to explain longitudinal changes in fluvial facies and building upstream coastline. One is some fixed point of control on the river equilibrium profile in the ocean basin. It is a base level (sea level) in the main river inland basin. The reaction buffer space with and below the current gradient profile

systems tracts.

**Figure 2.** Allogenic controls on fluvial sedimentation [16].

level rise [32].

as the representative of the file may not exist an upstream control, such as tectonic or climatic change, the influence of river flow, and sediment. The tectonic uplift may increase the gradient distribution and the upper buffer zone. The decreasing of the butresses, such as in the fall of sea level, may lead to the river system incision, but if the sea level fall blow newly exposed continental shelf as a similar slope, the river profile, there may be little change in the style of the river. In this case, the river system will change into to a new dynamic balance due to new water and sediment flux rate. In the accommodation between the upper and lower areas of the buffer zone, a representative (potential) of the river system to save space is available.

The ratio between channel and floodplain architectural elements during stages of positive accommodation depends on the rates of base level rise. Rapid base level rise leads to increased floodplain aggradation, which results in overall finer-grained successions. Slowly rising base level creates little accommodation available in overbank areas. At the same time, the channel stack in reducing accommodation time may be accompanied by frequent avulsion, which contributes to the spread of excessive lateral sediment [33]. Channel amalgamation under conditions of low accommodation is usually the case with the lowstand and late highstand systems tracts. As the late highstand amalgamated channel fills have a low preservation potential due to the subsequent erosion associated with the subaerial unconformity, the fluvial portion of the depositional sequence commonly displays a fining-upward profile (**Figure 3**). These general principles of fluvial stratigraphy, which relate the stacking patterns of fluvial architectural elements to changes in base level and available accommodation, have also been documented in the case of fan delta systems, which are governed by similar process/ response relationships between fluvial processes within alluvial fans and the base level fluctuations of the standing bodies of water into which they prograde [34].

#### **4. Methodology**

#### **4.1. Sequence stratigraphic analysis**

Geophysical borehole logs represent various rock properties, which can be used for stratigraphic interpretation. The most common type of log, often used for local stratigraphic correlation, is summarized in **Figure 4**. As technology improves, some new types of well logs are being developed. For example, the new micro-resistivity logs combine the methods of conventional resistivity and dipmeter measurements to produce high-resolution images that simulate the sedimentological details of an actual core. This "virtual" core allowed in the details of mm scale visualization, including sediment bedding, cross-bedding, and biological noises. Well logs have both merits and disadvantages compared with outcrops. Geophysical logging in the outcrop of the advantage is that they provide continuous information from the inheritance of relatively thick, often in a range of kilometers. This type of configuration file (log curve) allows one to see the trend in different scales, from single element sedimentary deposition system in the size of the whole basin, to fill. For this reason, data provided by well logs may be considered more complete relative to the discontinuous information that may be extracted from the study of outcrops. Therefore, comparative study of underground relation and formation can usually scale far greater than from the outcrop research. On the other hand, nothing can replace the study of the actual rocks; hence, the wealth of details that can be obtained from outcrop facies analysis cannot be matched by well-log analysis, no matter how closely spaced the boreholes may be [35].

The surface of log interpretation is largely speculative, under the condition of practical rock data. The core data provide the most clear "ground truth information" [36]. Therefore, the


The ratio between channel and floodplain architectural elements during stages of positive accommodation depends on the rates of base level rise. Rapid base level rise leads to increased floodplain aggradation, which results in overall finer-grained successions. Slowly rising base level creates little accommodation available in overbank areas. At the same time, the channel stack in reducing accommodation time may be accompanied by frequent avulsion, which contributes to the spread of excessive lateral sediment [33]. Channel amalgamation under conditions of low accommodation is usually the case with the lowstand and late highstand systems tracts. As the late highstand amalgamated channel fills have a low preservation potential due to the subsequent erosion associated with the subaerial unconformity, the fluvial portion of the depositional sequence commonly displays a fining-upward profile (**Figure 3**). These general principles of fluvial stratigraphy, which relate the stacking patterns of fluvial architectural elements to changes in base level and available accommodation, have also been documented in the case of fan delta systems, which are governed by similar process/ response relationships between fluvial processes within alluvial fans and the base level fluc-

Geophysical borehole logs represent various rock properties, which can be used for stratigraphic interpretation. The most common type of log, often used for local stratigraphic correlation, is summarized in **Figure 4**. As technology improves, some new types of well logs are being developed. For example, the new micro-resistivity logs combine the methods of conventional resistivity and dipmeter measurements to produce high-resolution images that simulate the sedimentological details of an actual core. This "virtual" core allowed in the details of mm scale visualization, including sediment bedding, cross-bedding, and biological noises. Well logs have both merits and disadvantages compared with outcrops. Geophysical logging in the outcrop of the advantage is that they provide continuous information from the inheritance of relatively thick, often in a range of kilometers. This type of configuration file (log curve) allows one to see the trend in different scales, from single element sedimentary deposition system in the size of the whole basin, to fill. For this reason, data provided by well logs may be considered more complete relative to the discontinuous information that may be extracted from the study of outcrops. Therefore, comparative study of underground relation and formation can usually scale far greater than from the outcrop research. On the other hand, nothing can replace the study of the actual rocks; hence, the wealth of details that can be obtained from outcrop facies analysis cannot be matched by well-log analysis, no matter

The surface of log interpretation is largely speculative, under the condition of practical rock data. The core data provide the most clear "ground truth information" [36]. Therefore, the

tuations of the standing bodies of water into which they prograde [34].

40 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

**4. Methodology**

**4.1. Sequence stratigraphic analysis**

how closely spaced the boreholes may be [35].

**Figure 4.** Types of well logs, properties they measure, and their use for geological interpretations (after [17, 18, 35]).

geophysical data including logging and seismic can only provide indirect information on the solid and fluid phases in the underground that must be calibrated and the interpretation accuracy of verification to verify the geological data of rock [16]. The integration of all available data sets (e.g., outcrop, core, logging, and cuttings, therefore, the seismic) is the best way to correctly identify the stratigraphic contact.

The seismic data can also be used to produce seismic stratigraphic interpretation in the two kinds of materials at the interface of different acoustic characteristics. This can be described by acoustic impedance and is given by the product of density and velocity. The larger is the difference in acoustic impedance between two lithologies, and the stronger is the reflection. Various subsurface layers can be recorded by seismic traces through geophones that receive the reflections. The impedance contrasts control the nature of each wavelet. Such seismograms are time seismic sections. The seismic section generally follows the empirical Faust formula of seismic wave velocity, depth, and age proof [37]:

$$V = 46.5(ZT)^{16} \text{m/s},\tag{1}$$

*V* is seismic velocity, *Z* is buried depth, and *T* is geological age.

Continuous seismic reflection is a "time line" hypothesis; in the basin, it is of great significance to analyze and research the sequence stratigraphy. Seismic records are also complicated by multiples and diffractions. Multiples may be strong enough to obscure deep reflections, but they are now relatively easy to remove by processing. The diffraction from the steep inclined surface is the scripture, such as fault, channel profit, and the erosion of relief unconformity. They are useful indicators of other components showing a steep reflection event but may be confused by the migration. The seismic record can be considerably improved, and interpretation facilitated by the use of two special techniques, the construction of synthetic seismograms, and the use of vertical seismic profiling (VSP) [38]. Synthetic seismograms are generated by the conversion of sonic and density data reflection coefficients. VSP is the recording and analysis of seismic signals received from a geophone lowered downhole. The well is reduced to be recorded on the surface of the signal, when they return to the surface of the detector to incrementally shift. Still, the shortest wavelength signal to each half the length of the T detector was analyzed. Each location has a new record. The synthesis and VSP data is very valuable for calibration of seismic records. For example, they enable a detailed record of seismic velocities to produce depth-corrected cross-sections. However, the VSP technique is far better for various reasons. It can, for example, can be used to calculate the total depth of expansion (TD) of synthetic seismic records, and not. Synthesis methods rely on logging data A, only reflect the conditions close to the hole. In the case of poor hole conditions or seismic reflectors having a very small horizontal extent (less than one Fresnel zone), the synthetic method may not provide a record typical of the area.

In this chapter, the method of stratigraphic analysis we used is an integrated well-seismic correlation. The Wenliu Area possesses abundant available materials, including a 3D seismic database (covering an area of about 35 km<sup>2</sup> ), more than 340 drilling wells and logging data (including core data of over 330 m from 8 cored wells of the area), and plentiful analysis test data. Thus, it is possible to launch a detailed sequence stratigraphic study.

With the 3D seismic database, regional reflection surfaces were traced to the target area. With the correlation of synthetic seismogram and VSP logging data, the relationship between seismic travel time and well depth was established. More than 10 seismic well sections were interpreted and main structures (especially faults) were identified. A more precise analysis was conducted with logging data beyond this. Wavelet transformation and Maximum Entropy Spectral (MEM) analysis with gamma-ray data were also used to enhance the accuracy of the sequence identification.

#### **4.2. Facies mapping**

Logging data are used for stratigraphic and lithologic interpretation, while they can also be used directly in facies mapping. Lithologic information may yield different combinations of logs in the CRO field reconnaissance. These relationships can be converted into a computer algorithm and the log data are digitized and stored in the data bank, a powerful automatic mapping technology. Digital log data can also be displayed and manipulated using interactive computer graphics routines, a facility which can easily compare formation related purposes. Well service company invested a lot of money on design and marketing automation processing and display used in basin analysis and petroleum development techniques, but these techniques suffer from the limited resolution of the physical location is very special. The techniques cannot be used without much initial careful calibration to local petrographic and groundwater conditions.

In addition to logging method as the foundation, extensive additional technique has been developed for underground rock physics for many years, the core and sample data check. These methods have several goals: such as stratigraphic correlation, provenance, reconstructions of paleogeography, regional stratigraphic trends, and tectonic history. Some of these techniques provide a numerical study of the age information. Others are useful or relevant local or regional origin but do not necessarily provide such age information. The grain size, grain shape, and the debris of a stratigraphic unit depend on the initial nature of the clastic source. Yet, after transportation, deposition, and burial process, the debris may experience many metamorphic processes, so that the features of the original source blurred. The analysis of basin detrital composition depends on these main factors: (1) source area geological structure; (2) source area of the climate and terrain; (3) transport process of debris diffusion and mixing mode brings; (4) chemical and mechanical wear, winnowing, transport, and deposition; and (5) diagenetic changes during burial of deposits.

Synthetic seismograms are generated by the conversion of sonic and density data reflection coefficients. VSP is the recording and analysis of seismic signals received from a geophone lowered downhole. The well is reduced to be recorded on the surface of the signal, when they return to the surface of the detector to incrementally shift. Still, the shortest wavelength signal to each half the length of the T detector was analyzed. Each location has a new record. The synthesis and VSP data is very valuable for calibration of seismic records. For example, they enable a detailed record of seismic velocities to produce depth-corrected cross-sections. However, the VSP technique is far better for various reasons. It can, for example, can be used to calculate the total depth of expansion (TD) of synthetic seismic records, and not. Synthesis methods rely on logging data A, only reflect the conditions close to the hole. In the case of poor hole conditions or seismic reflectors having a very small horizontal extent (less than one Fresnel zone), the synthetic method may not provide

42 Seismic and Sequence Stratigraphy and Integrated Stratigraphy - New Insights and Contributions

In this chapter, the method of stratigraphic analysis we used is an integrated well-seismic correlation. The Wenliu Area possesses abundant available materials, including a 3D seismic

(including core data of over 330 m from 8 cored wells of the area), and plentiful analysis test

With the 3D seismic database, regional reflection surfaces were traced to the target area. With the correlation of synthetic seismogram and VSP logging data, the relationship between seismic travel time and well depth was established. More than 10 seismic well sections were interpreted and main structures (especially faults) were identified. A more precise analysis was conducted with logging data beyond this. Wavelet transformation and Maximum Entropy Spectral (MEM) analysis with gamma-ray data were also used to enhance the accuracy of the

Logging data are used for stratigraphic and lithologic interpretation, while they can also be used directly in facies mapping. Lithologic information may yield different combinations of logs in the CRO field reconnaissance. These relationships can be converted into a computer algorithm and the log data are digitized and stored in the data bank, a powerful automatic mapping technology. Digital log data can also be displayed and manipulated using interactive computer graphics routines, a facility which can easily compare formation related purposes. Well service company invested a lot of money on design and marketing automation processing and display used in basin analysis and petroleum development techniques, but these techniques suffer from the limited resolution of the physical location is very special. The techniques cannot be used without much initial careful calibration to local petrographic

In addition to logging method as the foundation, extensive additional technique has been developed for underground rock physics for many years, the core and sample data check. These methods have several goals: such as stratigraphic correlation, provenance, reconstructions of

data. Thus, it is possible to launch a detailed sequence stratigraphic study.

), more than 340 drilling wells and logging data

a record typical of the area.

sequence identification.

and groundwater conditions.

**4.2. Facies mapping**

database (covering an area of about 35 km<sup>2</sup>

The seismic data can also be used for basin mapping. The seismic reflector, the amplitude, and the continuity of seismic facies are the three elements, becoming more and more important to improve the processing and visualization of seismic sections. The concept of seismic facies is the most effective application in the main data including 2D cross-section, but the stratigraphic and sedimentological interpretation is not easy in two-dimensional settings. This problem is not too serious when 3-D data is available, because the nature of the whole volume of 3-D data could be a visual system to provide guidance for the real world. The calibration between the seismic attributes and the lithofacies is specific for each basin to a considerable extent.

The channel environment 3D interpretation of sedimentary system is the most spectacular one, especially in the alluvial and in the submarine fan depositional settings, in the channellevee complexes and crevasse splays, and finally in the coastal plains [39].

In this chapter, the methods to the facies analysis and mapping we used are traditional mapping approach. One of the first step in the facies analysis of a clastic reservoir is the description and interpretation of available conventional cores. Core description was based on 10 cores taken from 7 cored wells of the target interval of the Wenliu Area. The color, the sedimentary structures, and the grain size of deposits were analyzed (the grain size analysis was based on a LS130 Coulter laser micro-granulometer). Sedimentary source analysis was also conducted with heavy mineral combination analysis, which calculates the ratio of stable transparent heavy minerals (mainly zircon and tourmaline) to the entire transparent heavy minerals (zircon, tourmaline, garnet, barite, epidote, etc.). Sedimentary facies were interpreted based on the analysis above. Finally, based on the detailed stratigraphic framework and counted sand body data, the lithofacies paleogeographic characteristics were analyzed, and along with the interpreted types of facies, a depositional model was established and the possible distribution of sedimentary facies was predicted both laterally and vertically.
