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The reservoir architecture analysis of braided rivers, especially falling-silt seam forms, has played a key role in predicting remaining oil distributions. However, no studies have used architecture analyses that document braided river outcrops and researched the tapping of the few remaining oil distributions based on outcrops in the Songliao basin, northeast China. In this paper, the architecture characteristics and remaining oil distribution of braided river reservoirs are studied using a combination of an outcrop, modern deposition and subsurface well data. The new 8–13 m thick Lower Cretaceous Quantou Formation outcrop of the Songliao basin is a braided fluvial succession arranged in one large fining-upward cycle. Eight facies (Gt, St, Sm, Sh, Sp, Sw, Fl and Fm), four architecture elements (CH, DA, LV, and FF), and three orders of bounding surfaces (third-, fourth-, and fifth-order) are recognized. A new distribution pattern of falling-silt seams and a braided river architecture model are presented according to the analysis of the outcrop. In the mid-channel bar, the falling-silt seams thin from the mid-bar to the bar tail following the flow direction. Each falling-silt seam is oriented tangentially to the basal surface of the mid-channel bar, and the upper falling-silt seam extends farther than the lower one. In a Daqing Oilfield exploitation block in the Songliao basin, while channels and bars are the main reservoir units, they have different remaining oil distribution patterns. For bars, water injection wells located at the mid-bar, zonal injection technology, the drilling of horizontal wells, and proper well patterns are proposed. Fourth-order bounding surfaces, single braided channels, stacking patterns, and the lateral blocking of levees and floodplains are the key factors affecting the remaining oil distribution in channels.

With the exploration of tight oil and gas, shallow-water deltaic reservoirs have been attracting more and more attention. The sedimentary architecture of a shallow-water delta shows distinctive differences with that of a deep-slope delta. These differences may be associated with the mechanism and characteristics of the deposition in the area where the sediments unloaded. Based on modern sedimentary research of the Poyang Lake in China, this paper focuses on the processes of river flow entering a lake with a low dip angle. We conducted six sets of numerical simulations with different initial sedimentary flow velocities using Fluent software for analyzing the hydrodynamics and the sediment transportation in the shallow-water delta. We combined the simulation results with an analysis of the geomorphology of the Gangjiang Delta to reveal the deposition along the shoreline of the lacustrine shallow-water delta. The numerical simulation shows that the shallow-water delta is dominated by bed friction with an extensive hydrodynamical boundary layer. The bed shear stress, which varies with the changes in river flux, dominated the sediment transport and deposition at the shallow-water delta front, where the effluent flow mixes with lake water. The distributary channels show characteristics of repeatedly occurred erosion, scouring, filling, and reoccupation. We argue that the depositional characteristics are associated with the changes in bed shear stress controlled by variation of flow velocity. Mouth bars are less likely to grow to a reasonable scale because of the seasonal scouring of extreme floods. Moreover, the lake flow potentially reworks the mouth bars. Consequently, mouth bar deposits were difficult to preserve as hydrocarbon reservoirs in ancient shallow-water delta.

The sandbodies within braided fluvial deposits are important reservoirs for the oil fields in China, and they usually have complex sedimentary architecture. A lot of research has been concentrated on characterizing the architecture of the sandbodies. Based on the observation that muddy deposits are commonly well preserved in fluvial deposits, we find that understanding the contact relationship between the muddy deposits and surrounding sand bodies can help characterize the depositional process of sandy braided fluvial systems. We have determined the effectiveness of this idea by characterizing a well-exposed outcrop of sandy braided fluvial system in the Datong Basin, Shanxi Province of China. We first define six muddy lithofacies by integrating the thickness of the muddy deposits, the morphology of the muddy deposit, and the lithofacies of surrounding sand deposits. The six muddy lithofacies include floodplain muddy deposits between intermittent channel complex, lateral covering muddy deposits and fall-silt seam muddy deposits between migrated bar complex, muddy gravel deposits in erosional bar complex, and channel-fill muddy deposits and gully-fill muddy deposits in abandoned bar complex. We then analyze the depositional environments according to the defined muddy lithofacies. We finally build the architecture of the outcrops by integrating the lithofacies of sand deposits and evolution of the depositional environments deduced from the muddy lithofacies.

Take the lacustrine delta in the second member of Paleogene Shahejie Formation in block Wang43, Dongying depression, Bohai Bay Basin as an example, the deposition architectural characteristics of lacustrine deltaic sand bodies controlled by syn-depositional faults in complex fault blocks of rift basin are examined from the aspect of the tectonic-deposition response, using cores, well logs and three-dimensional seismic data. The small-scale syn-depositional faults in complex fault blocks are dense and different in dip, the activity along the strike of syn-depositional fault varies in different positions, and all these control the sedimentary process of deltaic sand bodies. Influenced by syn-depositional faults, the deltaic distributary channel is more likely to pass through the position with weak fault activity, and be deflected or limited at the position with strong fault activity. In downthrown side of a single syn-depositional fault or micro-graben areas, sand bodies increase in thickness and planar scale, and sand bodies of multiple stages are likely to stack over each other vertically. In micro-horst areas controlled by syn-depositional faults, the sand bodies decrease in abundance, and appear in intermittent superimposed pattern vertically. This study can provide new research ideas and theoretical basis for exploration and development research in complex fault blocks.

The limited knowledge of Late Cretaceous terrestrial environments and their response to tectonic events in mid-latitudes can be addressed through continental basin deposits such as paleosols. Paleosols have been discovered in the Late Cretaceous Yaojia Formation in the southern Songlaio Basin and are recognized by evidence of soil structures controlled by pedogenesis. Sedimentary facies research on red paleosols was conducted on the Late Cretaceous Yaojia Formation in the outcrop of the southern Songliao Basin to interpret the depositional environments and tectonic significance of red paleosols during the greenhouse period. Mudflat, lake margin, and shallow lake depositional environments in a semi-arid climate are interpreted from the outcrops based on sedimentary descriptions and interpretation as well as geochemical and micromorphological analyses of paleosols in outcrops. We reconstructed the paleoenvironmental and paleoclimatic conditions through the paleosols in the mudflats and lake margin. The red paleosols in the mudflats and lake margin deposits formed in a stable landscape influenced by the tectonic uplift of the Songliao Basin, which is considered as new important evidence for tectonic uplift influenced by the collision of the Okhotomorsk Block with East Asia. The tectonic uplift process in East Asia is identified from the evolution of the depositional environments and drainage conditions inferred from different types of paleosols. Thus, the paleosols-bearing red bed deposits in outcrops provide an important contribution of the Late Cretaceous terrestrial paleoclimate and the tectonic setting research.

Shallow water delta developed during the Late Cretaceous greenhouse climate depositing in the red bed succession of the Yaojia Formation in the Southern Songliao Basin, NE China. The shallow water delta deposits provide an opportunity to understand the influence of high discharge variability in a semi-arid climate on the fluvial patterns, internal sedimentary details, and reservoir quality of distributary channels. The sedimentary process of the shallow water delta in the Yaojia Formation was controlled by a dual-stage process, including a high-flow stage and a low-flow stage within a semi-arid paleoclimate. During the high-flow stage, crevasse channels formed through avulsion of major distributary channels on the delta plain. Subaqueous terminal distributary channels and mouth bars formed at the delta front during progradation of the delta. During the low-flow stage after flood events, crevasse channels were abandoned and frequently exposed becoming reddish in color. This process can be reason for the classification for two main types of distributary channels: major distributary channels and crevasse channels in the delta plain. Sand bodies in distributary channels are distinguished by sedimentary structures indicate critical and supercritical flow conditions. Based on well logs and 3D seismic data, the sand distribution of was analyzed from the sandstone isopach map of the 2nd sand bed in the first member of the Yaojia Formation. The framework sand belts develop coincides with distribution of the major distributary channels. Based on detailed observational and reservoir test data from cores, the distribution of major distributary channels revealed a belt of high-quality reservoirs in the shallow water delta. This study provides a new perspective on the sedimentary pattern of distributary channels in shallow water deltas with high discharge variability, which has important implications for reservoir exploration in lacustrine basins.

The architecture analysis of the different orders sedimentary bodies is of great significance to the efficient development of oil and gas fields. In order to investigate the effects of the architectural interfaces on reservoir quality and heterogeneity, this study takes the Gudong oil field as a case to investigate the architectural characteristics of hierarchical bounding surfaces using detailed descriptions of core and wireline logs. Architectural models from the 7th-order to the 3rd-order are analyzed, and the developmental characteristics of the 5th-order braided river, 4th-order single sandstone, and 3rd-order accretion are summarized. The interlayer between two braided rivers is floodplain mud deposition, with poor physical properties, stable thickness, and strong blocking capacity. Two models of interlayers are found in the 4th-order deposition. The first interlayer is between the braided filling channel and midchannel bar, which is composed of generally fine-grained sediments with calcium cementation and poor physical properties. The second interlayer is a transformation belt between two midchannel bars and is generally composed of gravel-scoured deposition with penetration capability. The 3rd-order surfaces are defined as the surfaces of accretions within midchannel bars. Two models of interlayers are also found in the 3rd-order surfaces of accretions. The paleocurrent of the sandy braided river is reconstructed by synthesizing the core data, well logging data, and production performance data. A total of 1 fluvial system (7th-order), 2 compound braided rivers (6th-order), 11 braided rivers (5th-order), 41 midchannel bars (4th-order), and 96 accretions (3rd-order) are developed in the study area.

Paleosols in an outcrop of fluvial–lacustrine red beds have been recognized in the Upper Cretaceous Yaojia Formation in southern Songliao Basin, Songyuan City, Jilin Province, NE China. They are recognized in the field by pedogenic features, including root traces and burrows, soil horizons and soil structures. Root traces are remnants of small herbaceous plants, elongating and branching downwards in the red paleosols. They are filled by calcite, analcime, and clay minerals in spaces created by the decay of the plant roots. Burrows are found near the root traces with backfilled cells made by soil-dwelling insects. Soil horizons include calcic horizons (Bk horizon) with continuous calcareous layers, argillic horizons (Bt horizon) with clay films and dark brown to black iron-manganese cutans, vertic horizons (Bw horizon) with slickensided claystone, and deformed soil structure and gleyed horizons (Bg horizon) with mottles and reticulate mottles. Soil structures of the paleosols include pseudo-anticlinal structures, subangular blocky structures, and angular blocky structures. The micro-pedogenesis characteristics are also observed, including micrite pedogenic minerals and clay skins. Based on the pedogenic features above, paleosols types including Aridisol, Alfisol, and Vertisol are interpreted in the red beds of the Yaojia Formation. Forming in the Late Cretaceous, the paleosols can provide more details about the seasonal climate conditions and terrestrial sedimentary system in lacustrine basin.

Precise discrete fracture network (DFN) is very significant for fractured reservoirs due to its considerable power to help understand the complex nature of reservoir, predict production response, and create a development plan. Typically, many types of static data, including seismic, wellbore, outcrop, geomechanical, and geostatistical data, are integrated to construct a DFN. A potential problem is the mismatching of inter-well connection between DFN and field dynamic data. Therefore, a local optimization method is proposed in this paper to improve DFN for precise inter-well connections using field tracer data based on an improved simulated annealing algorithm. The proposed method is validated with two field case examples by largely improving the performance of numerical simulation. The results of optimization are also reasonable from the perspective of geostatistics and geomechanics. Optimization has a minimum effect on the original fracture density model. Additionally, the percentage of fractures to be updated in each perturbation of the proposed method decides the speed and precision level of the optimization. The improved simulated annealing algorithm can also be widely used for other optimization problems.

Fine-scale diagenetic alterations linked to architectural patterns of the sandstones were studied in meter-scale deltaic distributary channels of the Upper Cretaceous Yaojia Formation, Songliao Basin. The deltaic reservoirs of the Yaojia Formation are mostly developed in three types of distributary channels: major distributary channels, crevasse channels, and terminal distributary channels. The three types of distributary channels have different sedimentary architecture and lithofacies. The distribution of reservoir intervals varies greatly in the upward fining distributary channel depositional cycles (meter-scale). From the diagenetic alterations in the distributary channels successions, compaction, calcareous cementation, grain-coating clays with hematite in the red bed sandstones, and dissolution of feldspar or rock fragments are main control factors of high-quality reservoirs . More porosity loss is generated by strong compaction near the top and bottom part of the distributary channel succession. This could be caused by the high clay content and mud clasts which contribute much to the porosity loss in the sandstones. Calcareous cementation is mainly developed near the clay-rich intercalations. Dissolution pores in the sandstones without hematite cement and grain-coating clays are well developed in the middle position of the successions. The cementation is restricted in sandstones with unique hematite cement and grain-coating clays in the reddish crevasse distributary channels. The distribution pattern of high-quality reservoirs within the three different types of distributary channels in red beds is proposed by linking the diagenetic processes to depositional environments and architecture. High-quality hydrocarbon reservoirs are mostly preserved in the massive and cross-bedded sandstones from the middle part of the major distributary channel successions.

Based on outcrop, core, logging and mud logging data, and modern deposition analog, the sandbodies genetic types and spatial distribution in different facies belts of the shallow water delta in the first Member of Cretaceous Yaojia Formation (K2y1) of Qian'an area in Changling sag of southern Songliao Basin were analyzed, and the sedimentary model of shallow water delta was established according to deposition process. Active channel sandbodies, point bar sandbodies and bifurcation bar sandbodies in distributary channels and complex sandbodies formed the main sandbodies in the delta plain, while terminal distributary channels and mouth bar sandbodies formed the main sandbodies in the delta front. The delta prograded gradually under the construction of river mouth and reconstruction of river erosion, the early delta front evolved into delta plain and was reformed by distributary channels, and new delta fronts were formed at the river mouth ahead constantly. Under the control of the above deposition process, the size of main distributary channels in delta plain-delta front declined, while mouth bars developed increasingly. The sandbodies of different genetic types formed framework of river-dominated shallow water delta. The point bar and active channel sandbodies in main distributary channels of the delta, with the best reservoir quality, are lithologic reservoir targets in future exploration. Key words: Songliao Basin, Cretaceous, Yaojia Formation, shallow water delta, sandbody type, sedimentary model

Hyperpycnal flows are river-derived extrabasinal turbidity currents transporting both sand and clay to lacustrine, coastal, shelf and deepwater sedimentary environments. Experimental research in the past twenty years has shown that the presence of clay in sediment-laden flows promotes a transitional behavior between fully turbulent flow and a quasi-laminar plug flow regime. However, to date, most work concerning the fluid dynamic interpretation of lacustrine hyperpycnal flows has been founded on concepts based on fully turbulent flows, and relatively little is known about the influence of clay on the rheological and turbulence characteristics of these flows. With the help of 3D seismic volume and wire-line logging data, the present study undertakes a description and interpretation of subsurface mixed sandstone–mudstone bedforms observed in cores from the Upper Cretaceous Heidimiao Sandstone, Nenjiang Formation, Songliao Basin, NE China. Six lithofacies and five lithofacies associations are recognized from the cores and interpreted as formed under both turbulent and transitional flows. Typical bedforms of transitional flows include large current ripples and low-amplitude bedwaves. The delta-fed shallow lacustrine hyperpycnal flow deposits are characterized by proximal sinuous channels (extending for c. 20 km) and lobe deposits (extending for >20 km), showing a fan-like geometry associated with distributary channel extension in the down-dip direction. Basal erosion in the proximal channels is produced by the initial turbulent and turbulence-enhanced transitional flows, with channel infill dominated by upper transitional plug flows or quasi-laminar plug flows. The lobe deposits possess a fan-like geometry with large aspect ratio, and were formed from turbulence-enhanced and lower transitional plug flows. The downdip transformation of sediment-laden flows in the lacustrine basin varies from an initial turbulent flow, via quasi laminar plug flows to upper and lower transitional plug flows, to turbulence enhanced transitional flows. These transitional flows are interpreted to have experienced gradual dilution and deceleration and eventually transformed to turbulent flows in their distal regions. A new model for delta-fed shallow lacustrine hyperpycnal flow deposits is presented incorporating decelerated transitional flows and flow transformations. This new model can aid understanding of the depositional processes of lacustrine transitional flows and the facies distribution of hyperpynal flows in both modern and ancient sediments.

The Bakken Shale has attracted much attention because of its huge potential for shale oil. To characterize the nanoscale pore structure of the Bakken shale, ten samples were selected from the upper/lower Bakken Shale for N2 and CO2 adsorption, which can provide the pore structure parameters, such as pore size, specific surface area (SSA) and pore volume. The controlling factors of the pore structure were studied through the analysis of the mineral composition, total organic carbon (TOC) content, and thermal maturity (VRo-eq). Also, we investigated the fractal characteristics of samples based upon N2 adsorption. The results exhibited that the composition of the Bakken shale was mainly quartz and clay; the content of clay minerals varies between 24.07% and 53.92%; the content of quartz is between 38.04% and 63.59%. The average value of TOC content of the Bakken shale was 11.49 wt% and the vitrinite equivalent reflectance varied between 0.62 and 1.11%. Micropores (

Formed in extensional structural system, syndepositional faults are widely distributed in rift basins. Large basinal scale syndepositional faults play important roles in controlling the development and dispersion of depositional systems in rift basins. When it comes to the intensively developed small-scale syndepositional faults related to those large basinal scale syndepositional faults in complex fault blocks, the controlling effects to sedimentary architecture in the finer scale are still not well understood in the depositional systems. Thus, commonly used sedimentary models without considering small-scale syndepositional faults related paleogeomorphology are difficult to apply in complex fault blocks of rift basins. In this study, using the interpretation of 3D seismic profiles, wire-line log curves, and cores, patterns of small-scale syndepositional faults and their related finer scale stratigraphic sequences are described in the upper Es2 member, Shahejie Formation of the W43 complex fault block area, Dongying Depression, Bohai Bay Basin. The syndepositional faults are intensively distributed in the W43 complex fault block area. Based on the interpretation of sequence boundaries, four types of syndepositional faults related paleogeomorphology units were identified. They are named the micro slope break belt, micro-horst belt, and the micro-graben belt. The stacking patterns and development scale of individual deltaic sand bodies in the parasequences are controlled by activity of the syndepositional faults. In the hanging wall area near the syndepositional fault of the micro-step and micro-graben, thickened multi-stage continuously individual sand bodies are deposited controlled by low topography during the depositional period with sufficient sediment supply. In the footwall area of single micro syndepositional fault and micro-horst belt, individual sand bodies became thinner and less aggraded in vertical direction. The small-scale syndepositional fault-related paleogeomorphology is a new important factor that controls the sedimentary architecture of the shallow water deltaic sand bodies in the rift basin. This study provides insights into tectonic control of finer-scale sedimentary architecture and hydrocarbon reservoirs development in continental rift basins.

A two-step reservoir modeling process is preferred in the presence of multiple secondary data. In this method, multiple selected secondary data are first combined to generate one spatial probability distribution of primary data by probability combination schemes (PCS), and the intermediate result is then integrated with well data through spatial modeling. Probability combination of secondary data is the key for constructing accurate reservoir models. The traditional PCS assumes that secondary data are independent of each other. However, secondary data are in fact commonly redundant, and it is difficult to fully quantify the data redundancy and obtain the optimal adjustment weights. As a result, the estimated probability by the traditional method is often seriously biased. We propose an improved PCS based on principal component analysis (PCA) and permanence of ratios (PR) model in order to reduce the bias. First, a target-based PCA is developed to create a set of independent principal components that satisfy the assumption made in the PR model. Second, the elementary conditional probabilities of primary data are obtained by calibrating each selected principal component. Finally, the PR model is used to estimate the joint conditional probability of primary data by linking the elementary conditional probabilities from the second step. We illustrate the detailed workflow of the improved PCS by applying it to a fractured reservoir modeling case in the Ordos Basin. In this example, the probability estimated by the improved PCS had 41% less error than the traditional PCS. Furthermore, the established fracture models based on the improved PCS were validated to have a better match with the dynamic data, reducing the error of simulated water cut by 63%. The improved PCS can also be widely used for spatial modeling of all types of categorical or continuous variables.

Sediment routing in deep-water settings can be significantly different in lacustrine basins from their well-studied marine counterparts, which has been largely overlooked during the past decades. The seismically well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories, which have been studied through the integration of 3D seismic data and well-logging data. In the study area, the Eocene delta-complexes are architecturally manifested as alternating aggradation dominated (AC) and progradation dominated clinothems (PC). The Eocene Dongying clinothem architecture has been documented in terms of shelf–edge trajectory angle (θsht), edge-to-toe distance (ETT), aggradation height (Ah), progradation distance (Pd) and maximum foreset angle (γmfa). Aggradation dominated clinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment delivery into the outlying lake floor. Progradation dominated clinothems, in contrast, are characterized by flat to slightly descending trajectories and generally by a lack of bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequent relative lake level changes (on time-scales of 100s of kyr). Further analysis of seismic images and extensive well-logs suggest the distal aggradational bottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in slope to slope toe areas of progradation dominated clinothems, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply, water salinity and density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with strongly aggradational clinothems, during which sediment can be directly transported to the distant bottomset areas due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradation dominated clinothems start to build under stillstand or falling lake level conditions, sediment generally accumulates at river mouth and collapses due to sediment overload or fault activity. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in both the study of deep-water sequences and deep-water exploration in lacustrine basins.

The Eocene lacustrine carbonates in the western Dongying Depression, Bohai Bay Basin were examined based on integrated analysis of 3D seismic data, cores, thin-sections, and geochemical testing. Seismic profiles and geomorphological mapping revealed a landmass-attached (semi-isolated) carbonate platform restricted by marginal syn-sedimentary faults and surrounded by three deep sags. 3D topographic analysis of the platform revealed six districts characterized by variable buried depths, topographic gradient, and fault combinations, including two flat-topped areas (PFW and SD; topographic gradient

The identification of wireline log shapes is of great significance for research in paleogeography and sedimentology, and further for natural resources characterization. Generally, identification of log shapes is manually achieved by geologists through careful observation of the morphological features of log curves. This process is subjective and tedious, and it may introduce artefacts depending on the bias of the interpreters. Therefore, we developed a model which exceeds average performance of experienced geologists in identifying basic log shapes. The excellence of the model mainly results from a large annotated dataset and a specially designed Recurrent Neural Network (RNN) architecture. The dataset contains 2676 Spontaneous Potential (SP) log segments regarding four basic log shapes (bell, funnel, egg and cylinder shapes). There are six layers in the model's architecture, and the core is a layer of Long Short Term Memory (LSTM) units which are designed to extract the morphological features of the log curve. A committee of four experienced geologists annotated a gold standard testing dataset, based on which different approaches can be compared in regard to their accuracies. We also tried standard artificial neural network (ANN), Support Vector Machine (SVM) and an analytical method (Trendline Matching) for this problem. It turns out the proposed RNN model is more accurate than geologists' manual labelling and also the above three methods. The research for this problem is still at the initial stage and expecting more work and ideas to further improve the robustness of the model. Therefore, we also put forward some ideas for improving the model and enlarging the dataset.

Effective identification of lithology using well logs is one of the most important steps for reservoir characterization. A lot of methods have been developed to identify lithology automatically by analyzing the value or patterns of well logs. However, the response characteristics of log curves for some different lithologies are similar and indistinguishable. As a result, we may obtain results which do not follow the general geologic rules if we only use values or patterns of well logs as the criteria to identify lithology. In this paper, we propose an alternative automatic method to identify lithology by integrating both well logs and sedimentary patterns. First, we obtain the probability of lithology by applying the artificial neural networks (ANN) to the well logs. Then, we obtain the vertical combination patterns of different lithologies by applying a probabilistic statistical method to the cores. Finally, we produce an integrated lithology probability by combining the lithology probabilities calculated using ANN and lithology probabilities computed using sedimentary pattern. We validated our method by applying it to a real case study from China. The results indicate that the accuracy of lithology identification using the proposed method is much higher (91%) than that using neural networks method (83%).