Facies Models Research Articles

Fine dissection of meandering river sand bodies under dense well nets

The main oil layer of Grape Flower in X Oilfield has entered the late stage of high-extra-high water cut, and the remaining oil distribution is uneven, so as to ensure the development effect of the purpose block. Based on the theory of fine sedimentology, the sedimentation characteristics of PІ11 and PІ212 deposition time units were studied. Combined with the sedimentary and logging data of the meandering river delta, the logging facies model was classified in detail and established. Eleven microfacies of 2 subfacies in the delta and the delta shunt plain were identified. PІ11 and PІ212 deposition microphase layout maps were drawn. According to the sedimentary microfacies and conventional flooded logging interpretation data, four flooding distribution histograms were plotted to obtain the residual oil distribution law. The research results provide theoretical support for the later development adjustment.

A Deep Learning Method for Facies Recognition from Core Images and Its Application: A Case Study of Mackay River Oil Sands Reservoir

There is a large amount of drilling core data in the Mackay River oil sands block in Canada, and the accurate identification of facies from the cores is important and necessary for the understanding of the subsurface reservoir. The traditional recognition method of facies from cores is by human work and is very time consuming. Furthermore, the results are different according to different geologists because of the subjective judgment criterion. An efficient and objective method is important to solve the above problem. In this paper, the deep learning image-recognition algorithm is used to automatically and intelligently recognize the facies type from the core image. Through a series of high-reliability preprocessing operations, such as cropping, segmentation, rotation transformation, and noise removal of the original core image, that have been manually identified, the key feature information in the images is extracted based on the ResNet50 convolutional neural network. On the dataset of about 200 core images from 13 facies, an intelligent identification system of facies from core images is constructed, which realizes automatic facies identification from core images. Comparing this method with traditional convolutional neural networks and support vector machines (SVM), the results show that the recognition accuracy of this model is as high as 91.12%, which is higher than the other two models. It is also shown that for a relatively special dataset, such as core images, it is necessary to rely on their global features in order to classify them, and, with a large similarity between some of the categories, it is extremely difficult to classify them. The selection of a suitable neural network model can have a great impact on the accuracy of recognition results. Then, the recognized facies are input as hard data to construct the three-dimensional facies model, which reveals the complex heterogeneity and distribution of the subsurface reservoir for further exploration and development.

Multi-condition controlled sedimentary facies modeling based on generative adversarial network

Obtaining reliable sedimentary facies models is critical for geology, which primarily involves inferring conditional distributions from sparse wells. Multiple-point simulation (MPS) captures complex geological patterns by simulating multi-point probabilities, but it is sensitive to the stationarity of training images, and the limited training image is difficult to reflect the uncertainty of the prior geological models. Generative Adversarial Networks (GANs) have recently been proposed to spontaneously simulate multiple geological models that behave differently, generating realizations that respect spatial observations (hard data), with impressive results. In this paper, we explore a more flexible approach to conditioning synthetic realizations beyond hard data, allowing stylistic control over the realizations. We construct a conditional generative adversarial network consisting of a deep generator and a multi-scale discriminator as the conditional mapping model, and obtained realizations with improved visual quality. Based on this, style codes, which are numerical codes representing geological properties, are introduced to extend the existing mapping model. The resulting extended generative model can synthesize images that respect the hard data and exhibit the desired geological style. In addition, we collect and construct a dataset, which contains abundant and realistic fluvial patterns to reflect adequate prior geological knowledge. Extensive experiments have been carried out on this dataset, the results show that the generated images reflect absolute responses to style codes while maintaining the matching rate of 94.78% to the hard data, which can provide new ideas for conditional geological modeling.

Subaqueous clinoforms created by sandy wave-supported gravity flows: Lessons from the Central California shelf

Subaqueous clinoforms are an important shelf feature. Their origins are typically associated with subaerial deltas but recent work has identified similar features in settings without a significant fluvial source (Mitchell, 2012; Patruno et al., 2015; Patruno and Helland-Hansen, 2018). These other studies have shown that such subaqueous clinoforms, also known as infralittoral prograding wedges (IPWs), are created largely by wave-induced processes. This study uses geophysical, sedimentological, and radiocarbon data to determine the sedimentary characteristics and genesis of a shore-parallel subaqueous clinoform developed far from any significant river on the central California continental shelf; a sedimentary shelf buildup known locally as the Cross Hosgri Slope. Sediment cores through the clinoformal sedimentary unit reveal that it is composed of beds with an erosive base, overlain by a thin (∼ 15 cm) coarsening upward sequence of shelly fine sands transitioning to a fining upward sequence marked by alternating parallel and ripple cross laminated very fine sands. The sedimentary succession is often capped by fine silts that are commonly interbedded with thin very fine sand beds. Radiocarbon dating of shells collected just above the erosive base indicate the subaqueous clinoform initiated progradation ∼7 ka, nucleating on an older Younger Dryas relict shoreface. We suggest the Cross Hosgri Slope was created by winter-storm waves mobilizing sands in water depths up to ∼70 m that transitioned into wave-supported gravity flows. The wave-supported gravity flows traveled downslope to water depths of up to ∼80 m, corresponding to the foot of the subaqueous clinoform. They did not travel beyond this depth as wave influence at these depths is negligible and the shelf gradient is insufficient to maintain movement of the load alone. Our work suggests that wave-supported gravity flows can entrain very fine sands and silts and build subaqueous clinoforms, even in the absence of a significant river source. Furthermore, we provide a facies model for sandy wave-supported gravity flow deposits.

Quantifying thin heterogeneous gas sand facies of Rehmat gas field by developing petro elastic relationship in fine stratigraphic layers through bayesian stochastic seismic inversion

The Lower Goru Formation (LGF) sand intervals are prolific producers in the Central Indus Basin (CIB), Pakistan. The B-Interval of LGF is a proven reservoir of the Rehmat gas field, having heterogeneous and thin sand layers (14–17 m) below seismic tuning thickness. To quantify these potential layers, a petro-elastic relationship is developed using seismic and well data. Well data although having high resolution, lacks in many aspects, such as poor density logs due to bad boreholes along with the missing shear sonic (Vs), adding more challenges to characterize a complex reservoir. Therefore, an extended cemented sandstone model is established by incorporating the petro-elastic models (PEMs) of the reservoir's litho-fluid facies in the rock physics modeling (RPM) framework. RPM compensated for the lithological variability, quartz cementation impact, missing and bad density logs. The missing low and high frequencies of band-limited seismic data are retrieved through constraining wells by geostatistical parameters for enhanced visualization of thin-bedded heterogeneous sand. Bayesian stochastic seismic inversion (BSSI) addressed reservoir challenges by incorporating the PEMs responses along with consigning the frequencies limitation, through a low-frequency model and variograms from the sparse well data for high frequencies. For optimized reservoir characterization, a 3D seismic dataset is inverted in a fine-scale stratigraphic grid of 0.1 ms interval yielding high-resolution elastic properties. These enhanced elastic attributes are integrated with petrophysical relationships simulated through probability density functions that permit elastic attributes to be translated into reservoir characteristics (geological facies). So, an integrated technique of rock physics modeled logs with BSSI successfully identified thin heterogeneous gas sands through several high-resolution realizations with associated uncertainty.

Reservoir quality and facies modeling of the early Eocene carbonate stratigraphic unit of the Middle Indus Basin, Pakistan

The early Eocene carbonate reservoir, Sui Main Limestone (SML), is the largest gas reservoir in Pakistan. In the Qadirpur area, more than 30 wells have been drilled, some of which have been declared dry or abandoned due to poor reservoir characteristics or facies variation. The aim of this work is to re-evaluate the reservoir characteristics and facies identification of Sui Main Limestone by using petrophysical analysis and rock physics modeling in the Qadirpur field in the Middle Indus Basin of Pakistan. The reservoir characterization of carbonate rocks is difficult because of their complex pore networking. The well data on five exploratory wells drilled in this gas field are used. The log-derived porosity varies in a very large range of 2%–36%, with an average of 14%–34%. The average porosity of the clean carbonate intervals is 10%–14% and thus has the capacity to accumulate hydrocarbon. The high porosity value indicates the presence of micro-fractures in Sui Main Limestone. These micro-fractures and secondary pores are well interconnected and allow the pore fluids to communicate. The secondary porosity is mainly due to the presence of vuggs and fractures in Sui Main Limestone. The volume of shale varies from 11%–38% in the wells. The net pay zones have hydrocarbon saturation in the range of 40%–70%, which is mainly gas. Using wireline log response, the formation is divided into three facies: limestone, shale, and shaly limestone. This comprehensive work may help improve the prediction of the reservoir quality in heterogeneous carbonate reservoirs and optimize field development.

Integration of seismic data in reservoir modeling through seismically constrained facies models

Seismic data are an important source of information to guide and constrain reservoir modeling as it samples the subsurface in 3D away from wells. Seismic interpretations are used to constrain the structure of reservoir models. Different seismic attributes can support the identification and definition of stratigraphic features, and seismic inversion products can help constrain the rock properties. Different methods exist for integration of seismic data in the modeling process. Here, we present two new methods. The first method constrains facies definition and modeling with seismic data through a geobody earth modeling approach. The second method updates existing facies models with new seismic data using a Bayesian approach. Both methods are applied to a case study with good quality seismic data. The results show that the reservoir model becomes more consistent with the observed field seismic data when these fast and repeatable methods are applied (compared to not integrating seismic constraints or using time-intensive manual integration approaches), thus enabling more robust reservoir models and forecasts.

Unlocking the properties of a presalt carbonate reservoir offshore Brazil with facies-constrained geostatistical inversion

A continuing concern regarding presalt carbonate reservoirs offshore Brazil is how to derive accurate quantitative estimates of reservoir properties. It is challenging to understand the link between the facies model and the variation in elastic properties, recover a reliable model of elastic properties from seismic, estimate porosities and permeabilities to use in reservoir simulations, and ultimately close the loop in integrated geology and engineering workflows. This case study describes our use of geostatistical inversion as a tool to unlock reservoir properties. We show how the integration of diverse information from various sources and at different scales is used to produce a meaningful range of probabilistic realizations of this Brazilian deepwater presalt reservoir. We do this while respecting the reservoir properties observed at the locations of drilled wells. We also present a workflow for an optimized implementation of the inversion results at the modeling stage, resulting in fast and geologically consistent history matching in an extremely challenging reservoir management environment. In this way, we achieve accurate history-matched cases on a field level and on a well-by-well basis while remaining within the uncertainty limits. Therefore, we produce geologically plausible and reliable scenarios.

Petrophysical Evaluation of H-field, Niger Delta Basin for Petroleum Plays and Prospects

Abstract in English As a result of a combination of several methodologies, the H-Field, Niger-Delta, has been delineated. To identify probable reservoirs, seals, and source rocks in the study area, this study integrates sequence stratigraphy with petrophysical concepts through a comprehensive analysis of 3D seismic and well logging datasets. According to the 3D facies model, reservoirs are dominated by sand and are laterally extensive. They were then upscaled and stochastically distributed to create a 3D reservoir property model. On average, the porosity of these clastic reservoirs ranges from 22 to 28%. Reservoir net-to-gross (NTG) ratios range from 0.67 to 0.96. Water saturation ranges from 8% to 30%, while hydrocarbon saturation ranges from 70% to 92%. Four gas-bearing units and six oil-bearing units are present in reservoirs P 0.5 and P 1 compartments. All reservoir intervals’ oil and gas volumes are evaluated based on the hydrocarbon distribution. Geological models of the subsurface, such as the one in this paper, are crucial for future reservoir development programs.

A novel workflow for geothermal exploration: 3D seismic interpretation of biohermal buildups (Upper Jurassic, Molasse Basin, Germany)

The Upper Jurassic carbonates are the prime target for deep geothermal exploration in the Molasse basin, South Germany. The carbonates have a thickness of over 500m (1640 ft) and consist of two major facies: (1) bedded marly limestone and (2) massive limestone and dolostone. The massive limestone facies is composed of sponge-microbial biohermal buildups It is considered the main geothermal reservoir facies. Only this facies type may be (1) karstified, (2) dolomitized, and/or (3) faulted and fractured, and therefore can yield very high flow rates of >100 l/sec = 26 gps. The main data source used in this study is the 3D seismic survey of the Freiham geothermal field in the western part of Munich/Germany. Blended in were cutting logs to describe the lithology from 2 wells and borehole image logs from the two geothermal wells. Lithologies derived from these wells were upscaled in support of the seismic interpretation. The study presents an integrated workflow of 3D seismic attribute analysis to analyze the distribution and quantification of reservoir facies (massive limestone) versus non-reservoir facies (bedded marly limestone) per time slice. The attribute “sum of magnitude” is mapped for 9-time slices based on the vertical resolution of the Freiham 3D cube. The seismic facies interpretation is compared with upscaled borehole image facies associations of two geothermal wells. BHI log data is calibrated with an interpretation of the depositional environment based on cutting analysis Reservoir geometries were derived from an outcrop analog study to better understand the 3D seismic facies interpretation and to construct the conceptual depositional model of the Upper Jurassic carbonates. This technique is commonly used in hydrocarbon exploration but is not yet adapted to geothermal projects, which are often based on little data, smaller company sizes, tight budgets, and limited access to specialized geomodelling software and experience. The approach of using 3D seismic attribute analysis presented in this study provides a quantitative subsurface model of geothermal reservoir facies in the Freiham geothermal field. It is quick and straightforward and can easily be applied in the exploration workflow for similar fields and reservoirs.

Development of facies model and comparison of Darvin kupesi and Pirallahi fields

The paper reviews two mature fields in long-term development. Both of them have a tectonically complicated structure. Although the fields have been developed since last century, they have quite large oil reserves. Due to this, the structural-lithologic framework of the fields, the lithofacies composition, the balance, and recoverable reserves, as well as the parameters of development have great significance. Our task is the specification and estimation of lithofacies properties of field data. The lithofacies of neighboring Darvin kupesi and Pirallahi fields have not been enough studied. The types of facies of sedimentary rocks of Girmaki, Lower Girmaki, and Gala suites have been researched and 3D models have been developed, the comparisons of the models have been carried out as well. As a result, the changes were observed both by the area and the depth.

Facies model, cementation and sedimentary evolution of a 20th-century beach and beachrock: The Gorrondatxe wave and tidal coastal system (NE Spain)

Lithology, bedding, and sedimentary structures of the Gorrondatxe coastal and beach system show an upper shoreface around the low-water level and containing the coarsest grain sizes; a foreshore in the main intertidal zone, which is mainly composed of sands with minor gravels and a distinctive low-angle, seaward-dipping, planar-parallel lamination; and a backshore zone with a mixture of marine-derived sands (washover) and non-marine sands and muds (aeolian, subaerial ponds) above the high-tide water level. The facies model shows a wave-dominated, mesotidal, composite beach with a fining-upwards and aggradational trend. Over the 20th century, a beachrock developed in this area as a result of heavy-industry waste dumping (steel industry) off the coast, which later became attached to the coast. There are a variety of cements and degrees of lithification in the beachrock, suggesting that the beachrock-related processes, although coetaneous, were not similar in all these zones and that different cements developed at the same time. Sand cementation can be used to recognize such facies in the stratigraphic record or in well cores, when other kinds of data are not available. The upper shoreface sandstones are hard and well-cemented, with a whitish circumgranular aragonite cement and good intergranular porosity; the foreshore sands are medium-hard, with a brown, irregular, aragonite needle cement, which shows higher intergranular porosity; finally, the backshore sands are only lightly cemented, with a brown aragonite and rhombohedral calcite cement, with the highest intergranular porosity. SEM images show the presence of Coccus-type bacteria in all the different facies and zones; these are the best proof of metabolic activity, probably of ureolytic bacteria, in the origin of all these cements. Over the course of the 20th century, Gorrondatxe evolved from a formerly dissipative, ridge and runnel beach to an active, aggrading and prograding, reflective beach, and finally to an inactive beach prone to erosion. The change to a reflective profile and the cementation of the beachrock indicate that anthropic offshore inputs were rapidly recycled into the beachface. Another major change occurred when waste discharges ended, and the former sediments and beachrock started to be eroded to their current state.

Nearshore environments before the evolution of land plants

The long-term evolution of the biosphere has caused fundamental shifts in environmental conditions and sedimentation at Earth’s surface. While effects of the evolution of terrestrial vegetation on river systems have been explored in detail, facies models and possible shifts in sedimentation in pre-vegetation nearshore marine settings have not been sufficiently explored. The circa 800-million-year-old Burra Group, exposed in the Adelaide Fold Belt of South Australia, is a terrestrial to nearshore transgressive sedimentary succession associated with rifting. The Burra Group provides a record of marginal and shallow marine environments before the evolution of land plants. Environments are interpreted to record deposition in low energy fine-grained tidal flat, lagoon, tidal inlet, and beach-barrier environments (a beach-barrier system). The thick mudflats (up to 30 m) of the studied units indicate that vegetation is not essential for mudflat accumulation, contrary to some models. The fluvial–marine transition and the back-barrier–tidal inlet–beach-barrier transition is highly regular and there is little interbedding of units. The Tonian beach-barriers of the Burra Group do not backstep into the back-barrier region and aggrade much like stable modern systems backed by peat. These observations are suggestive of a stable barrier system in the absence of land plants. The high mud percentage and/or early carbonate cementation (including microbialite and stromatolite deposition during transgression) may have contributed to the stability of this beach-barrier system.

Contourite channels – Facies model and channel evolution

AbstractDespite the rise in published evidence of deep‐marine bottom current processes and associated deposits there are still very few documented outcrop examples. Herein are reported results of a contourite channel system related to the late Miocene palaeo‐Mediterranean Outflow Water in the Rifian Corridor, Morocco. This work aims to unravel the sedimentary evolution and facies distribution based on the study of large morphological features related to contourite channels and their subsequent sandstone dominated infill sequences. It was found that the channel evolution and facies distribution are related to spatiotemporal changes in flow characteristics of the palaeo‐Mediterranean Outflow Water. The recognized channel facies distribution correlates well with previously established bedform stability diagrams. Erosion and upper‐stage flow regime bedforms are associated with the most vigorous bottom currents, generally related to its core. Laterally, following the decrease in flow velocity towards the adjacent drift, bedforms comprise dunes, lower‐stage plane bedforms and more heterolithic facies. Similar facies changes are also observed down‐channel, related to a decrease in flow velocities resulting from turbulent mixing of water masses, associated decreases in density gradients and the subsequent deceleration due to gravity. Results of this work have been used to propose a three‐dimensional facies model for channelized sandy contourites. This study contributes to understanding contourite systems, thus benefitting oceanographic and climatic reconstructions as well as aiding the predictability of contourite channel systems for industry geoscience applications.

Study on Facies Modeling of Tight Sandstone Reservoir Using Multi-Point Geostatistics Method Based on 2D Training Image—Case Study of Longdong Area, Ordos Basin, China

The Longdong area in the Ordos basin is a typical fluvial reservoir with strong heterogeneity. In order to clarify the distribution law of underground reservoirs in the Longdong area, it is necessary to establish and optimize a 3D geological model to characterize the heterogeneity of reservoirs. This is of great significance for accelerating the exploitation of tight sandstone gas in the southwest of the Ordos basin. This study takes the P2h8 member of the Ct3 research area in the Longdong area as an example, analyzes the core and logging curve shape to divide the sedimentary microfacies, and establishes the facies model. In particular, in view of the difficulty in obtaining 3D training images under the existing conditions in the study area, we use the multi-point geostatistics method combining sequential two-dimensional condition simulation and the direct sampling method to establish the facies model. This method can simulate the 3D geological model by using the 2D training images composed of the digital plane facies diagrams and the well-connection facies diagrams. In addition, we choose the object-based method and sequential indicator method for comparative experiments to verify the feasibility of this method (sequential two-dimensional condition simulation combined with the direct sampling method) from many aspects. The results show that the multi-point geostatistics method based on 2D training images can not only match the well data, but also show the geometric characteristics and contact relationship of the simulation object. The distribution characteristics of sandbody thickness and modeling results are consistent with the actual geological conditions in the study area. This study explores the feasibility of this method in the 3D geological simulation of large-scale fluvial facies tight sandstone reservoirs. Additionally, it also provides a new idea and scheme for the modeling method of geologists in similar geological environments.

Methodical approach to substantiation of the strategy for the development of residual oil reserves at the final stage of development, taking into account facies analysis

The article considers and solves the problem of finding the optimal strategy for the development of terrigenous deposits of the Bobrikovsko-Radaev horizon of one of the deposits of the Ural-Volga region. Based on the analysis of the behavior of the curves obtained during geophysical surveys in more than three thousand wells, four main types of facies zones were identified, characterized by different porosity and permeability properties and formed development systems. As part of the analysis of the reservoir pressure maintenance system, a direct influence of reservoir properties on the efficiency of waterflooding was established, which made it possible to develop an optimization strategy and the formation of new injection sites. Using the method of multiple regression analysis, two statistical models have been obtained – the reservoir properties model and the facies model, which make it possible to quickly assess the recovery factor and select the optimal development system for fields with a lesser degree of knowledge. Keywords: oil field development; geological structure; facies model; hydraulic fracturing; horizontal wells; hydrodynamic model; multiple regression analysis.

Three‐dimensional bounding surface architecture and lateral facies heterogeneity of a wet aeolian system: Entrada Sandstone, Utah

ABSTRACTAeolian deposits form noteworthy reservoirs (for example, Norphlet Formation and Rotliegend Group) in hydrocarbon extraction and carbon capture and storage contexts, but stratigraphic architecture imparts significant heterogeneity. Bounding surfaces result from autogenic and allogenic controls and can represent important changes in dune‐field dynamics. To further evaluate the impacts of facies heterogeneity and flow‐inhibiting bounding surfaces on reservoir performance and reconstruct ancient erg evolution, the stratigraphic architecture of aeolian systems must continue to be studied at multiple scales. This study pairs traditional methods (for example, measured stratigraphic sections) with advanced technologies (for example, drone‐derived outcrop models) to precisely resolve the metre to kilometre‐scale three‐dimensional stratigraphic architecture of wet aeolian Middle Jurassic Entrada Sandstone outcrops located at Rone Bailey Mesa near Moab, Utah, USA. Five facies are identified, primarily based on sedimentary fabrics, and are grouped into three associations named dune, sabkha and sand sheet. Statistical analyses of gamma‐ray spectrometer and automated mineralogy data indicate a distinct mineralogical difference between dune (quartz‐rich) and sabkha (more feldspathic) packages, suggesting that gamma‐ray logs may be used to better predict facies distribution in the subsurface. Seven modelled super bounding surfaces are planar to undulatory, with no perceived spatial trends. Five modelled interdune migration surfaces are undulatory but exhibit an average 0.09° angle of climb roughly parallel to the palaeocurrent direction. Two modelled superposition surfaces are linear to sinuous in plan‐view. Laterally discontinuous sabkha packages observed are interpreted to be remnants of closed, damp, interdune flats located between ca 8.5 to 17.0 m tall, sinuous, transverse bedforms or patches of such bedforms. Based on stratigraphic architecture interpretations, the Entrada Sandstone preserves signals of allogenic forcing and localized autogenic bedform cannibalization of the substrate. The findings of this study, some of which are not commonly recognized in wet aeolian facies models, enhance the understanding of erg evolution and can parameterize static models of aeolian reservoirs.

On the representability of soil water samples in space and time: Impact of heterogeneous solute transport pathways underneath a sandy field

In Europe, millions of water samples have been collected from sampling points, especially in the saturated zone to assess the water quality among others to fulfil EU water quality directives. Often water samples are collected from sampling points installed in the subsurface without knowing what the water collected represents in space and time. As such, without detailed knowledge of hydrogeological settings and fluctuations in groundwater levels, it is not possible to assess whether water collected represents a hydraulic active sediment setting or an adjacent isolated sediment body. Collecting water from the latter will hence not reveal by analysis potential contamination in the hydraulic active setting. Based on a detailed three-dimensional sedimentary facies model interpreted from geological and geophysical data combined with groundwater level measurements, this study focuses on delineating the impact of changing solute transport pathways underneath a sandy field (2 ha) exposed to bromide and pesticide applications. Hence, the analyses utilize detections in water samples of bromide, pesticides, and/or their degradation products collected through 19 years at 25 sampling points. A special focus is on the relatively high concentration, long-termed leaching of four degradation products (1,2,4-triazole, CGA108906, PPU, and desethyl-terbuthylazine) through the field. The results show that even for sand, knowledge of the hydrogeological setting and in-situ fate knowledge is imperative to assess the representability of water being sampled from both the variably-saturated and saturated zone of the soil-sediment system. Especially, the sub-horizontal layered sediments with numerous facies shifts facilitate horizontal solute transport, and fluctuations in the groundwater table seem to be decisive for, which solute transport pathways are dominating. Such detailed insights are crucial for accurately assessing sources of contaminants, leaching risk of contaminants through the variably-saturated zone, and improving monitoring procedures in the protection of the water resources and hereby the water quality of the future.

Sharp change of the channel bar pattern within the river delta: Insights from modern Ganjiang River delta in Jiangxi province, China

Channel bars (midchannel bars or point bars) in river deltas present challenges to water transportation; meanwhile, they provide a source of building materials, habitats, and farmlands, and they could become targets in hydrocarbon reservoirs. Researchers focus on the channel bar pattern in rivers, while ignoring the channel bar pattern in distributary channels. We have analyzed a sharp change of the channel bar pattern from the river to the delta. The integration of remote map analysis, fieldwork, and a flume experiment has resulted in a quantified sharp change in the channel bar pattern in the Ganjiang River delta and revealed a hydrodynamic mechanism. The result finds that distributary channels develop much finer-grained, smaller-scale, less channel bars with the lower width-length ratio, compared to the upstream river. Distributary channels develop more point bars and fewer midchannel bars than the upstream braided river, and they develop fewer point bars than the upstream meandering river. Sharply weakening bank erosions in distributary channels lead to the formation of the sharp change in the channel bar pattern from the upstream river, due to backwater effect-induced sharp gentling of landform gradient. The backwater effect impedes bank erosions in the distributary channels, but it promotes bank erosions in upstream rivers, which, in turn, enhances the sharp change of the channel bar pattern. We provide insights into channel bars’ growth in modern river deltas and provide new facies models for the river-delta system.

Improving the 3D facies model with the seismic-derived log volumes: a case study from the Asmari Formation in the Hendijan Field, southwest Iran

Abstract The prolific Oligocene-Miocene Asmari Formation is the primary reservoir rock hosting important hydrocarbon resources in Iran and consists of fluvial/deltaic siliciclastic and shallow marine carbonate rocks in the Hendijan Field. Due to the significant facies variability of the formation, the presence and quality of the reservoir pose a significant uncertainty in the characterization of the reservoir. This study compares two facies models, one based on well logs only and the second based on estimated facies volumes as a secondary variable in facies modelling. The petrophysical evaluation with microscopic thin sections and electrofacies analysis were used to classify the facies and determine the reservoir quality. As a result, the Ghar Member was identified as a highly porous interval, while the lower part of the Asmari Formation is characterized by tight facies. A sequential Gaussian simulation (SIS) algorithm was used to build the 3D facies model on the basis of the well logs. Acoustic impedance, shear impedance and density (derived from pre-stack inversion) were used as inputs to an artificial neural network to generate acoustic and density log volumes. Using electrofacies cut-offs, facies volume was constructed and used as a secondary variable to improve the initial facies model. The final facies model was compared with the blind well to check the validity of the prediction and satisfactory results were obtained. Since the values are present in all the cells of the reservoir (the traditional facies model only has values for the well location), the estimated facies volume is an accurate variable in the prediction of the facies model for the Asmari reservoir and for this reason the secondary facies model is more reliable than the primary one.