Architectural Model of a Dryland Gravel Braided River,based on 3D UAV Oblique Photogrammetric Data:A Case Study of West Dalongkou River in Eastern Xinjiang,China

Three-dimensional unmanned aerial vehicle(UAV)oblique photogrammetric data were used to infer mountainous gravel braided river lithofacies,lithofacies associations and architectural elements.Hierarchical architecture and lithofacies associations with detailed lithofacies characterizations were comprehensively described to document the architectural model,architectural element scale and gravel particle scale.(1)Nine lithofacies(i.e.,Gmm,Gcm,Gcc,Gci,Gcl,Ss,Sm,Fsm and Fl)were identified and classified as gravel,sand and fine matrix deposits.These are typical depositional features of a mountainous dryland gravel-braided river.(2)Three architectural elements were identified,including channel(CH),gravel bar(GB)and overbank(OB).CH can be further divided into flow channel and abandoned channel,while GB consists of Central Gravel bar(CGB)and Margin Gravel bar(MGB).(3)The gravel bar is the key architectural element of the gravel braided river,with its geological attributes.The dimensions of GBs and their particles are various,but exhibit good relationships with each other.The grain size of GB decreases downstream,but the dimensions of GB do not.The bank erosion affects the GB dimensions,whereas channel incision and water flow velocity influence the grain size of GB.The conclusions can be applied to the dryland gravel braided river studies in tectonically active areas.

The Anatomy of Shallow Water Sandy Braided River Reservoir Architecture

1 Introduction Reservoir architecture refers to pattern,scale,direction and overlapping relationship of different levels of architecture units.The research of architecture in fluvial phase began in the 1980s(Miall,1985).The braided river

Study on the Distribution of Interlayer in Thick Sandy Braided River under Large Well Spacing—A Case of C Oilfield in Bohai Sea

Using core, logging and other data, combined with field outcrop deposition, this paper studies the sedimentary genetic types and sedimentary stages of thick sandy braided river interlayer in C oilfield, and divides two stages of interlayer and three single-stage braided flow zones. On this basis, geostatistical inversion constrained by logging and discerning River quantitative knowledge base is carried out to predict the distribution range of the main interlayer in the two phases. The production performance test of the blind well and horizontal well shows that the coincidence rate of the prediction results of interlayer with thickness > 1.5 m is 75%. The research shows that the first stage is the main interlayer, mainly composed of mudstone of flood plain origin, with an average thickness of 2.1 m and relatively stable distribution. Based on the interlayer prediction results, the small layer of composite sand body 1 forms a residual oil enrichment area in the high part of the structure due to the wide range of interlayer shielding in the lower part, which is a favorable area for adjusting and tapping potential.

EXPERIMENTS OF THREE-DIMENSIONAL FLOW STRUCTURE IN BRAIDED RIVERS

The braided river is a typical river pattern in nature, but there is a paucity of comprehensive data set describing the three-dimensional flow field in the braided river. A physical model experiment was used to study the flow characteristics in the typical braided river with a mid-bar between two anabranches. In the experiment, two kinds of mid-bar with the ratios of its length to maximal width of 3 and 5 were considered. Moreover, the mid-bar could be moved to adjust the width of two anabranches. The detailed measurements of velocity were conducted using an acoustic Doppler velocimeter over a grid defined throughout the whole braided river region, including the bifurcation, two anabranches and the confluence. In two kinds of mid-bar braided models, a separation zone was observed in the anabranch of the model in which the ratio of length to maximal width of mid-bar is 3, however the separation zone was not found in another model in which the ratio is 5. In addition, the opposite secondary cells were observed at the bend apex of anabranch in two models, and different longitudinal velocity distributions in the entrance region of anabranch account for this opposite flow structure. Finally, turbulent kinetic energy were shown and compared in different situations. The high turbulence occurs at the place with strong shear, especially at the boundary of the separation zone and the high velocity passing flow.

Genesis of an unusual clastic dike in an uncommon braided river deposit

A clastic dike containing unusually large clasts occurs in the Quaternary deposits that unconformably cover the Mesoproterozoic sediments in the Fangshan District,Beijing area,China.The material into which the dike intruded is also uncommon because it consists mainly of loess-type silts that were deposited by braided rivers.The intrusion of the dike is explained as the result of the expulsion of pore water into the coarse,gravel-containing layers of a braided river system.The large size of the clasts in the dike is explained by an exceptionally strong upwards directed flow which owed its high energy to a high hydrostatic pressure that had been built up because pore water could not gradually seep through the impermeable silt-sized material during ongoing burial.This uncommon dike is compared with a second example,in similar Quaternary sediments covering the Mesozoic rocks in the Huairou District.

Study on Geological Genesis and Sedimentary Model of Complex Low Resistivity Reservoir in Offshore Oilfield — A Case of NgIII Formation of X Oilfield in Bohai Sea

In order to study the micro genetic mechanism and main geological controlling factors of low resistivity reservoir in NgIII formation of X oilfield in Bohai sea in China, the clay mineral composition, irreducible water saturation, salinity and conductive minerals of low resistivity reservoir were studied by using the data of core, cast thin section and analysis, and compared with normal resistivity reservoir. At the same time, the control effect of sedimentary environment on low resistivity reservoir was discussed. The results show that the additional conductivity of high bound water content and high montmorillonite content in the reservoir together leads to the significant reduction of reservoir resistivity, which is the main microscopic cause of the formation of low resistance, and is mainly controlled by the sedimentary background such as paleoclimate and sedimentary cycle. During the deposition period of NgIII formation, the paleoclimate was dry and cold, and it was at the end of the water advance of the medium-term sedimentary cycle. The hydrodynamic force of the river channel was weak, the carrying capacity of the riverbed was weak, and the river channel swayed frequently, resulting in fine lithologic particle size, high shale content and complex pore structure of the reservoir, resulting in significant reduction of reservoir resistance. The research conclusion would have strong guiding significance for the development of low resistivity reservoirs in this area.

Depositional characteristics and petroleum geological significance of wetland

Wetland is a new type of sedimentary facies proposed for the first time in this paper. It is a type of sedimentary environment, transitional between land facies and water (sea or lake) facies. In this paper, wetland is redefined as “a type of sedimentary environments whose ground surface is flat and wet throughout the year, which may be covered with very shallow water (less than 2 m deep), and is covered with lush plant growth”. Wetland is reclassified into two types, swamp wetland (swamp in brief) and wet plain wetland (wet plain in brief). Swamp deposits are coal, while wet plain deposits are dark colored mudstones or silty mudstones rich in plant fossils and carbon debris. The deposits of wet plain are different from those of lake and floodplain in the abundance of plant fossils, color, resistivity well logging curve, and other sedimentary characteristics. In boreholes, resistivity logging can be used to distinguish between wet plain mudstones and lake mudstones. Understanding the sedimentary characteristics of wet plain wetland can help to identify wet plain deposits which were formerly classified as floodplain or lake deposits. This will help to reconstruct the palaeogeography and to understand the history of basin and climate evolution accurately, and is especially important in evaluation of the hydrocarbon generating potential of a basin. With the Jurassic Sangonghe Formation of the Yanqi Basin as an example, the identification characteristics of wetland are described.

Research on Thin Layer Structure Identification and Sedimentary Facies of Middle and Deep Layers Based on Reflection Coefficient Inversion—By Taking Dongying Formation of CFD Oilfield in Bohai Offshore as an Example

The sand layer B of Dongying Formation of CFD oilfield in Bohai offshore belongs to the middle deep layer of buried hill overlap deposit. Its reservoir distribution has the characteristics of large burial depth, thin thickness and rapidly lateral change. Because of low resolution of seismic data and overlying sand layer. It is difficult to identify and interpret the structure of sand layer accurately. The uncertainty of structure and reservoir restricts the fine development of B sand layer. In order to identify the top surface of reservoir effectively. The seismic data are processed by using the reflection coefficient inversion method. The results show that the inversion resolution of reflection coefficient is significantly higher than that of original data. The top surface of sand layer B and its overlying sand layer can be well identified and traced. Carrying out structural interpretation of B sand layer based on reflection coefficient inversion data and the microstructure and the formation tip extinction point are implemented. Based on the constraint of new interpretation level, the sedimentary facies plane distribution of B sand layer is described and make prediction of dominant reservoir development area in detail combining with sedimentary paleogeomorphology, along layer attribute section and limited drilling data. The research shows that the study area is mainly from the northwest material sources, the slope belt in the northwest is close to the lake shoreline with a gentle slope and shallow water depositional environment, which is located on the main transport and deposition channels. The shallow water gentle slope landform is suitable for forming large-area sand bar deposition, mainly composed of underwater distributary channel and debouch bars facies, which is the dominant reservoir development area. The research conclusion guides the deployment and implementation of the development well location effectively.

Analysis of controls upon channel planform at the First Great Bend of the Upper Yellow River, Qinghai-Tibet Plateau

The 270 km long section of the Upper Yellow River at the First Great Bend is comprised of single channel and multiple channel systems that alternate among anastomosing, anabranching, meandering and braided reaches. The sequence of downstream pattern changes is characterized as： anastomosing-anabranching, anabranching-meandering, meandering-braided and braided-meandering. Remote sensing images, DEM data and field investigations are used to assess ahd interpret controls on these reach transitions. Channel slope and bed sediment size are key determinants of transitions in channel planform. Anas- tomosing reaches have a relatively high bed slope （0.86‰） and coarser sediment bed material （d50 = 3.5 mm）. In contrast, meandering reaches have a low slope （0.30‰） and fine sediment bed material （d50 = 0.036 mm）. The transition from a meandering to braided pattern is characterized by an increase in channel width-depth ratio, indicating the important role of bank strength （i.e. cohesive versus non-cohesive versus channel boundaries）. Interestingly, the braided-meandering and meandering-braided transitions are coincident with variable flow inputs from tributary rivers （Baihe and Heihe rivers respectively）. Theoretical analysis of the meandering-braided transition highlights the key control of channel width-depth ratio as a determinant of channel planform.

Seismic Sedimentology and Its Application in Shallow Sea Area,Gentle Slope Belt of Chengning Uplift

Seismic sedimentology is a new frontier inter-discipline subject, and shows good prospect and potentiality in reservoir deposition research with seismic data and geophysics technologies. We made seismic sedimentology research of shallow sea area, gentle slope belt of Chengning （埕宁） uplift, Bohalwan （渤海湾） basin. In shallow sea area with sparse well coverage, it was difficult to characterize the reservoir architecture with the traditional method based on wells. A new method to resolve the above problems is built： （1） information on plane and in section is inter-ealibrated with each other; （2） recognize the isochronic surfaces by frequency decomposition and interpret the depositional character with technology of stratal slicing; （3） make a comprehensive research with the stratal slice interpreta- tion and the dissection of well group. The depositional model of this area is built and used in the architecture analysis of area without wells. The architecture description reveals that the sedimentary character of pan-connection sand bodies in braided rivers is the reason for high water cut of the new horizontal wells. .

Basin-Scale Sand Deposition in the Upper Triassic Xujiahe Formation of the Sichuan Basin, Southwest China: Sedimentary Framework and Conceptual Model

The Upper Triassic Xujiahe （须家河） Formation in the Sichuan （四川） Basin, Southwest China is distinctive for the basin-scale sand deposition. This relatively rare sedimentary phenomenon has not been well interpreted. Here we addressed this issue by discussing sedimentary framework and conceptual model. Analysis of sedimentary setting implied that the basin received transgression during the deposition. It had multiple provenance supplies and river networks, as being surrounded by old- lands in multiple directions including the north, east and south. Thus, the basin was generally charac-terized by coastal and widely open and shallow lacustrine deposition during the Late Triassic Xujiahe period. This is similar to the modern well-known Poyang （鄱阳） Lake. Therefore, we investigated the framework and conceptual model of the Sichuan Basin during the Xujiahe period with an analogue to the Poyang Lake. Results show that the conceptual model of the deposition can be divided into transgressive and regressive stages. The first, third and fifth mem- bers of the formation are in transgressive stage and the deposits are dominated by shore and shallow lacustrine mud. In contrast, the deposition is mainly of braided river channel sand deposits during the regressive stage, mainly including the second, fourth and sixth members of the formation. The sand deposited in almost the entire basin because of the lateral migration and forward moving of the cross networks of the braided rivers. The multiple alternations of short and rapid transgression and relatively long regression are beneficial to the basin-scale sand deposition. Thus, the main channel of the braided river and its extensional areas are favorable for the development of hydrocarbon reservoir. This provides practical significance to the reservoir evaluation and exploration. In addition, the results also justify the relatively distinctive sedimentary phenomenon in the study area and may also have im- plications for understanding the large-scale sand deposition elsewhere.

A new 'superassemblage' model explaining proximal-to-distal and lateral facies changes in fluvial environments,based on the Proterozoic Sanjauli Formation(Lesser Himalaya,India)

Facies analysis of fluvial deposits of the Proterozoic Sanjauli Formation in the Lesser Himalaya was combined with an architectural analysis. On this basis, a model was developed that may be applied to other fluvial systems as well, whether old or recent. The new model, which might be considered as an assemblage of previous models, explains lateral variations in architecture and facies but is not in all respects consistent with the standard fluvial models. The Sanjauli fluvial model is unique in that it deals with lateral facies variations due to shifts of the base-level along with fluctuations in accommodation space owing to changes in palaeoclimate.

Distribution prediction of the glutenite in Member 3 of Triassic Xujiahe Formation in Yuanba area,northern Sichuan Basin

Although the Triassic Xujiahe Formation in Yuanba area of northern Sichuan has a large amount of resources,the proportion of proved reserves to the amount of resources is low.Production of most of the pilot production wells is high at the initial stage,but it declines rapidly,mainly due to tight rock properties and strong heterogeneity of Xujiahe Formation.Thus,it is important to investigate the distribution of high-quality reservoirs.The Member 3 of Xujiahe Formation develops sandstone interbedded with mudstone,and its lateral thickness of different sandstone groups varies greatly,so it is a challenge to identify appropriate time windows for seismic attribute analysis,thus,so the prediction effect of the glutenite in the Member 3 of Xujiahe Formation.In this study,through analysis of core data and logging facies,single-well sedimentary microfacies subdivision is carried out.Single-well lithological interpretation is also studied with application of lithological identification technique.Then,lithological associations and its seismic responses at the top and bottom interfaces of each sandstone group in the Member 3 of Xujiahe Formation are well investigated,The lithological association with the glutenite above and the mudstone below the stratigraphic interface respectively,corresponds to a trough in seismic profiles;in this case,when extracting the seismic attributes of sandstone groups above the stratigraphic interface,only the difference of between drilling horizons and seismic horizons needs to be considered.The lithological association with the mudstone above and glutenite below the stratigraphic interface respectively,corresponds to a peak in seismic profiles;in this case,when extracting the seismic attributes of sandstone groups above the stratigraphic interface,influence of which should be eliminated;thus,a method of time window determination for seismic attribute extraction is established.Among amplitude,frequency,and phase attributes,the total peak energy has the good correlation with thickness of the glutenite at well sites and it also can reflect the distribution of distributary channels well.The results show that belt-like glutenite in each sandstone group in the Member 3 of Xujiahe Formation extends in a NW-SE direction and thins out toward the southeast,and the distribution of glutenite has certain inheritance in the longitudinal direction,the glutenite in the third sandstone group in the Member 3 of Xujiahe Formation(TX33)and the first sandstone group in the Member 3 of Xujiahe Formation(TX31)are both developed.