Complex Depositional Environment Research Articles

Seismic attribute analysis with a combination of convolutional autoencoder and random forest in a turbidite reservoir

Due to the complex depositional environment of a turbidite reservoir in the Niuzhuang Delta, China, the traditional seismic facies classification is a challenge to perform accurately and continuously. Due to the thin turbidite layers in the reservoir, machine-learning-based prediction of sandstone thickness is challenging. Inspired by the autoencoder, we develop an open-source deep-learning workflow that combines unsupervised and supervised learning with jointed latent eigenvalues of the convolutional autoencoder (CAE) and traditional seismic attributes for seismic facies classification and sandstone thickness prediction constrained by the facies distribution. First, we extract lower-dimensional latent eigenvalues as a category of novel seismic attributes from the seismic data using a CAE. To accurately and effectively extract lower-dimensional latent eigenvalues, we develop a hybrid loss function based on the mean-squared error loss and the smooth L1 loss in this CAE. Then, we use principal component (PC) analysis to extract the first four PCs of these seismic lower-dimensional latent eigenvalues. Using unsupervised K-means, we cluster the first four PCs to form seismic facies. Finally, we take the first four PCs with the traditional seismic attributes as input and the sandstone thickness as labels for the random forest to predict the sandstone thickness distribution. The results of seismic facies and sandstone thickness distribution confirm the potential and advantages of our workflow, which can speed up the identification of seismic facies with smoother boundaries, improve the prediction accuracy by 16% over than that of traditional seismic attributes, and provide more depositional insight for a turbidite reservoir of the Shahejie Formation in the Niuzhuang Delta, China.

Coquina depositional model, Buzios Field, Brazil

Increasingly relevant as petroleum reservoirs, the coquina deposits of the pre-salt section of the Santos and Campos Basin display a wide variety of sedimentary systems that reflect a complex storm-dominated depositional environment. This complexity resulted in the deposition of numerous sedimentary facies distributed among structural lows and highs, and their understanding is an essential aspect in order to reduce exploration risks. Therefore, the aims of this contribution are twofold: (a) to understand the depositional processes during the generation of the Itapema Formation coquina deposits in the offshore pre-salt Buzios Field, Santos Basin, and (b) to establish a depositional model and identify stacking patterns in the coquina section. The facies analysis was based on rock texture, structure, allochemical composition, taxonomic composition, and taphonomic characteristics of bivalve shells, such as fragmentation, abrasion, sorting, thickness, orientation, and articulation. We described 695 thin-sections and sidewall samples distributed among ten wells in the field area. The analysis resulted in sixteen facies grouped into eight facies associations: (1) bioclastic bars, (2) washover deposits, (3) backshore, (4) bioclastic beaches, (5) tempestites, (6) tempestites with articulated shells, (7) offshore and offshore transition deposits, and (8) offshore siliciclastic mudstones. These carbonate facies associations were deposited mainly under the influence of waves and currents in isolated ramp-shaped margined platforms with low continental input associated with active faults, characteristic of the rift phase of the basin evolution. The stacking of the facies associations indicates that the Itapema Formation coquinas were deposited in an environment that became progressively shallower towards the top contact with the overlying Barra Velha Formation. Siliciclastic mudstones mark the top of the Itapema Formation immediately below the Pre-Alagoas unconformity, indicating a significant lake deepening that drowned the coquina section. The depositional model is the first one about the Buzios Field and the first about the pre-salt fields coquinas based on field-scale information.

Reliability analysis of pile-founded T-walls using the random variable method and random field method

The pile-founded walls (e.g., T-walls) are important civil infrastructure for flood protection. The stability analysis of floodwalls in the face of flooding hazards is a critical problem for the design and maintenance of floodwalls. However, most current studies for the stability assessment of floodwalls are based on deterministic analyses. The uncertainties of soil properties, which cannot be avoidable due to complex geological processes and depositional environment, are not sufficiently studied. To address the uncertainties of soil properties, a two-dimensional pile-founded T-wall system with several clay layers on the top and a sand layer on the bottom is taken as an example for the reliability analysis. Both the random variable method and random field method are adopted for the probabilistic analysis of floodwalls. The effect of the coefficient of variation (COV) and scales of fluctuation of soil properties are investigated by parametric studies. The results show that the probability of failure increases with the COV of soil properties for both methods. For the random field method, the effect of the vertical scale of fluctuation of soil properties is more profound than the horizontal scale of fluctuation. The probability of failure derived from the random variable method is generally larger than that from the random field method at high flood water elevations when the same COV of soil properties is applied. This study can provide useful references for risk-informed decision-making in the stability assessment of floodwalls in the face of flooding hazards.

Optimized rock physics model implementation to characterize the heterogeneous B-interval reservoir facies in the petro-elastic domain, mubarak block, lower indus basin, Pakistan

Rock physics abridges geological and reservoir parameters to quantify the heterogeneous hydrocarbon reservoir facies in the petro-elastic domain. The widely distributed Lower Goru sands across the Lower Indus Basin are proven hydrocarbon reservoirs and exhibit heterogeneity due to their complex depositional environment. Diagenetic detrital quartz overgrowth cementation, sand, shale intercalation, and various fluids add more challenges to characterize facies in the petro-elastic domain. For precise petro-elastic relationship establishment, an extended cemented sandstone rock physics model for B-Interval sands of the Lower Goru Formation was developed. It produced conclusive elastic properties by optimizing the density log and synthesizing the missing shear sonic log. The accuracy of the selected model was authenticated by statistical measures, i.e., good prediction quality, high correlation coefficient, along with less normalized root mean square error for modeled Vp, Vs and density. This comprehensive approach adheres to the interrelationship between pores, minerals, cementation effects and fluids to address reservoir heterogeneity, facies classification and tight sand. Furthermore, these parameters are translated in a ubiquitous way in the petro-elastic domain, illuminating the sweet spots within the reservoir.

Content and distribution of mercury in coal and its relation to depositional environment—A case study on coals from the Shanxi Formation in Huainan Coalfield

Mercury in coals might emit into the environment from coal combination, and finally cause environmental pollution. In this paper, 26 coal samples were selected from No. 1 which is coal in the Shanxi Formation of Zhangji and Xinjier mines in the Huainan coalfield. The mineralogical and geochemical components of coal samples were determined by DMA-80 mercury-measuring instrument, XRF, XRD, ICP-MS, and the relationship between the depositional environment of the coal seam and mercury enrichment was analyzed. The results show that the mercury content of coal in the study area ranged from 0.03 to 0.93 μg/g, with an arithmetic means of 0.21 μg/g, higher than the background values of coal in China and the world. The mercury content of Shanxi Formation coal varied among different mines, the arithmetic mean value of mercury in Zhangji coal mine and Xinjier mine coal is 0.35 μg/g and 0.12 μg/g respectively. Due to the complex depositional environment and depositional facies, the distribution of mercury content in the coal seam is quite different. XRD, Microscopic observation and the ratio of (CaO + MgO + Fe2O3)/(SiO2+ Al2O3) and Al2O3/TiO2 show that the main mineral in the depositional environment of this study area is kaolinite, quartz and pyrite, and the depositional facies are intercontinental and sea-land, so the parent rock type belongs to acid bedrock. The Ni/Co, Sr/Ba, and Sr/Cu ratios were used to indicate a weak oxidation-reduction, Marine salt water, and an arid and hot environment. The vertical distribution of mercury in coal and the characteristics of the depositional environment are combined to show that mercury in coal is easily affected by redox conditions, paleosalinity and paleoclimate in the depositional environment. At the same time, mercury accumulation is more easily in the depositional environment dominated by seawater intrusion than in the terrigenous input.

Expanded Explorations of the Dinaledi Subsystem, Rising Star Cave System, South Africa

The Dinaledi Chamber of the Rising Star cave system has yielded a large assemblage of fossil hominin material, attributed to Homo naledi. The unusual taphonomic and geological situation of the assemblage suggested that the remains may have been deliberately deposited in the chamber. However, the route and mechanism of deposition of the remains within the Dinaledi Chamber are still uncertain. During the 2017—2018 field seasons, we expanded explorations of the passages surrounding the Dinaledi Chamber. These explorations improved our understanding of the cave’s spatial complexity, necessitating a revision of the way the spaces are named and described. The work supported the hypothesis that there is no alternate entrance into the system other than the Chute. The work also identified new fossil deposits in several remote passages, three of which contain material attributable to H. naledi. Here, we clarify the definition of the Dinaledi Subsystem and provide terminology for new fossil localities found in this portion of the Rising Star cave system. These results emphasize the complex depositional environment of the Dinaledi Subsystem and raise new questions about the process and timing of the fossil accumulations.

Thin sand identification in complex depositional environment by supervised artificial neural networks

The thin sands within the study interval developed in a complex fluvial-to-shallow marine environment. This variety results in extremely heterogeneously distributed thin sands. The objectives are to identify heterogeneous thin sands via machine learning and evaluate the impact of tuning thickness on the recognition. Multi-attribute classification using supervised ANNs is employed to predict the distribution of these thin sands within six subintervals. Before the prediction, the investigation of the six subinterval shows that the major part of each subinterval is greater than the tuning thickness and can be resolved by the available seismic data. An integrated workflow of multi-attribute classification based on supervised ANNs was established. The supervised classification cannot only add significant details and enhanced lateral resolution, but also allows the interpreters to avoid manual labelling. The thin sands of the six intervals predicted by the supervised ANNs are verified qualitatively and quantitatively. The predicted sand thickness is validated by a log-based thickness map and shows similar distribution of thin sands. The cross plots of the sand thickness between the seismic predictions and the log measurement at well locations quantify the seismic prediction. Therefore, both verifications show seismic prediction characterizes the thin sands in the study area and supervised ANNs have great potential in solving the challenge of thin bed identification. The positive correlation of the coefficients between the predicted and log-based thickness at the well locations and the average thickness of the subintervals suggest that seismic prediction still depends on the tuning thickness though multi-attribute classification based on the supervised ANNs used.

Pliocene–Pleistocene glacimarine shelf to slope processes in the south‐western Barents Sea

AbstractThe glacimarine shelf‐edge is a complex depositional environment in which the interplay between accommodation and glaciation has played an important role in influencing sediment deposition and margin architecture. It can be challenging to unravel the history of basin infill in these areas, particularly where landforms are deeply buried. This study presents an integrated workflow for deciphering the architecture and evolution of erosional and depositional elements in a crucial location of the south‐western Barents Sea margin, with a focus on the comparatively poorly understood processes and patterns of glacimarine sedimentation that occurred during the Pliocene and Early Pleistocene. Wellbore interpretations of lithology are combined with the analysis of seismic facies, geomorphology and attributes using merged 3D seismic reflection data to investigate the morphology and development of buried landforms and depositional features on the outer‐shelf, shelf edge and upper‐slope. The Pliocene (preglacial) slope system is dominated by upper‐slope channels, upper‐slope channels with associated sediment lobes, and mass‐transport deposits. The first appearance of mega‐scale glacial lineations in the study area is close to the onset of the Pleistocene (around 2.58 Ma), suggesting that an ice stream reached the palaeo‐shelf edge during the earliest Pleistocene. The prevalence of upper‐slope channels and mass‐transport deposits throughout the Pleistocene stratigraphy shows that the basinwards transfer of sediment took place mainly by evacuation of sediment through relatively linear channels combined with mass‐movement events. The results presented in this study have implications for understanding the glacial history of the south‐western Barents Sea and sedimentary processes on glacimarine shelf edges more generally.

The importance of transects for characterizing aged organic contaminant plumes in groundwater

A complex mixture of dissolved organic contaminants, emanating from a many decades-old, residual, dense non-aqueous phase liquid (DNAPL) source, migrates through unconfined, moderately heterogeneous, glacial-derived sediments and sedimentary rock in a residential area of Dane County, Wisconsin, USA. A portion of this contaminant plume intersects a large man-made pond, roughly 400 m downgradient of the source zone. Depth-discrete, multilevel groundwater sampling, detailed sedimentological logs, and hydraulic head profiles were used to delineate the spatial distribution of hydraulic, geologic, organic contaminant, and redox hydrochemical conditions within the established plume along two transects immediately upgradient of the pond. Twenty-one contaminants were detected and classified into four major contaminant groups: chlorinated ethenes, chlorinated ethanes, aromatics (BTEX: benzene, toluene, ethylbenzene, xylene), and aliphatic ketones. Within the glacial sediments and shallow bedrock, zones of reductive dechlorination of chlorinated ethenes and ethanes were juxtaposed with zones of BTEX and ketone degradation. Spatial heterogeneity in the concentration and distribution of contaminant groups and redox conditions was observed over lateral distances of tens of meters and vertical distances of tens of centimeters along the two transects. Although the site was situated in a complex glacial depositional environment, lithologic and hydraulic heterogeneity surprisingly only had a modest influence on the spatial distribution of plume contaminants. Depth-discrete sampling along paired, closely spaced transects (~20 m apart) was essential to assess internal plume composition/concentration evolution along flow paths with strong attenuation over short migration distances. This study shows how paired, highly resolved transects can enhance understanding of transverse and longitudinal variability in areas where contaminant-induced redox conditions control reaction zones and strong plume attenuation.

The Blake Field, Blocks 13/24a and 13/29b, UK North Sea

Abstract The Blake Field is subdivided into two discrete parts, the ‘Channel’ and the ‘Flank’ areas. The two areas are geologically different but also reflect the different levels of maturity in terms of their development. Blake Channel was discovered in 1998, with first production commencing in 2001. Blake Flank was discovered in 1974 and developed in 2003. The field contains saturated light oil, with a field-wide oil–water contact and two significant gas caps. The reservoir comprises deep-water turbidite sands of Lower Cretaceous age. The combination of complex depositional environment and dynamic data resulted in the decision in 2016, to create a new model incorporating a fully integrated approach to subsurface evaluation and modelling. The latest work summarized in this paper incorporates a new geological interpretation along with the addition of aquifer extensions to capture depletion from offset fields, and a palaeo-oil leg, to help limit aquifer influx and improve history match. 4D seismic has also been incorporated to support the evaluation. Blake Channel and Flank have oil-in-place of 230 MMbbl and 300 MMbbl and have produced 94 MMbl and 15 MMbbl, respectively, to date.

Episodic mafic magmatism in the Eyre Peninsula: Defining syn- and post-depositional BIF environments for iron deposits in the Middleback Ranges, South Australia

Banded iron formation (BIF)-derived iron ore deposits of the Middleback Ranges, Eyre Peninsula, South Australia, are hosted within Archean to Paleoproterozoic basement in the southeastern Gawler Craton. Mafic sills and dikes are associated with the orebodies throughout the belt and although described previously, have never been studied in detail. Two main types of mafic rocks, amphibolites and dolerites, are distinguishable from field occurrence and mineralogy. Amphibolites interbedded with BIFs from the southern Iron Magnet deposit are characterized by extensive overprinting. These amphibolites contain metamorphic assemblages of coexisting Mg-Fe- and Ca-amphiboles, garnet, corundum, biotite and relict titaniferous magnetite displaying ilmenite exsolution. Amphibolite petrography and geochemistry in the southern part of the belt indicate formation in a complex BIF depositional environment, with possible detrital input of titaniferous magnetite from igneous rocks. In contrast, NW-trending dolerite dikes occur throughout the belt and contain assemblages consisting of igneous magnesiohornblende and plagioclase. SHRIMP U–Pb zircon ages for amphibolites and dolerites yield two age groups. Amphibolite from Iron Magnet yields a 207Pb/206Pb weighted mean age of 2542 ± 15 Ma. The most robust 206Pb/238U weighted mean age of 782 ± 23 Ma for dolerites comes from the Iron Queen deposit in the central part of the Middleback Ranges. LA-ICP-MS U–Pb geochronology of U-bearing hematite from the Iron Knight South deposit yields ages of ~680 Ma. Taken together, these results suggest mafic magmatism contemporaneous with Archean BIF deposition followed by a high-grade metamorphic event (~2.47–2.41 Ga Sleafordian Orogeny). Dikes from Cape Donington, the southernmost point on the Eyre Peninsula are, instead, associated with the 1.73–1.69 Ga Kimban Orogeny, as evidenced by zircon from a pyroxene-rich dolerite, which yields a 206Pb/238U weighted mean age of 1711 ± 14 Ma. The dolerite ages from the Iron Queen deposit provide the first evidence for the presence of the ~800 Ma craton-scale Gairdner Large Igneous Province in the Middleback Ranges. The young U–Pb hematite age from Iron Knight South and post-emplacement alteration of dikes of Gairdner age from the central part of the Middleback Ranges belt provide additional support for multiple events leading to upgrading of iron ores.

Application of Individual Foraminifera Mg/Ca and δ18O Analyses for Paleoceanographic Reconstructions in Active Depositional Environments

AbstractMarine and terrestrial material deposited together in Integrated Ocean Discovery Program Expedition 354 cores in the Bay of Bengal offer the opportunity to link the evolution of monsoonal climate and tectonic erosional history. We test the utility of foraminiferal climate reconstructions in this active depositional environment in which turbidity currents transport material to Expedition 354 sites and may mix foraminiferal shells from higher up on the Bengal Fan with local shells. Mg/Ca and δ18O in ~80 modern (<1 kyr) individual Trilobatus sacculifer specimens reconstruct seasonal sea surface temperature (SST) and sea surface salinity (SSS) at three locations: lower fan Expedition 354 Site U1454 near the modern active channel and more likely to be influenced by turbidity currents, lower fan Expedition 354 Site U1449 far from channel activity, and Site 342KL on the continental slope. Because the lower Bengal Fan locations have less seasonally variable SST and SSS than conditions closer to the continental slope, we can determine if foraminiferal populations are local or have been transported from a distal source. Mg/Ca and δ18O from Site U1449 are not likely to be affected by turbidity currents and reflect local conditions. In contrast, Mg/Ca and δ18O from Site U1454 show strong evidence that foraminifera from the active channel record a mixture of local conditions and distal conditions recorded at higher latitudes. Our results suggest that foraminifera can be used to reconstruct SST and δ18O in this complex depositional environment, but caution must be taken when the downcore lithology indicates turbidites and possible sediment transport.

Dating Persistent Short-Term Human Activity in a Complex Depositional Environment: Late Prehistoric Occupation at Saruq al-Hadid, Dubai

ABSTRACTThe archaeological site of Saruq al-Hadid, Dubai, United Arab Emirates, presents a long sequence of persistent temporary human occupation on the northern edge of the Rub’ al-Khali desert. The site is located in active dune fields, and evidence for human activity is stratified within a deep sequence of natural dune deposits that reflect complex taphonomic processes of deposition, erosion and reworking. This study presents the results of a program of radiocarbon (14C) and thermoluminescence dating on deposits from Saruq al-Hadid, allied with studies of material remains, which are amalgamated with the results of earlier absolute dating studies provide a robust chronology for the use of the site from the Bronze Age to the Islamic period. The results of the dating program allow the various expressions of human activity at the site—ranging from subsistence activities such as hunting and herding, to multi-community ritual activities and large scale metallurgical extraction—to be better situated chronologically, and thus in relation to current debates regarding the development of late prehistoric and early historic societies in southeastern Arabia.

Study on the Creep Behaviors of Interactive Marine‐Terrestrial Deposit Soils

The interactive marine‐terrestrial (IMT) deposit soils were formed in the complex depositional environment; their mechanical properties are different from the other deposits. The creep behaviors of Dalian clayey soils were studied according to one‐dimensional creep tests and drained triaxial creep tests. Based on the creep test results, the empirical model was established to describe the one‐dimensional creep behavior and triaxial creep behavior, respectively. The results showed that Dalian deposits have typical nonlinear creep behavior. With the increasing of consolidation pressure, the strain is increased, the stability time is extended, and the demarcation point between primary and secondary consolidation is more obvious. The deposits belong to medium to high secondary compressibility soil, and the secondary consolidation coefficient is decreased with the increasing of consolidation time and increased with consolidation pressure increasing. The ratio between secondary consolidation coefficient and compression index at different depths changes from 0.033 to 0.058, which conform to Mesri conclusion. Under low deviator stress, the creep processes showed the characteristic of attenuation creep and shear contraction. However, it showed the characteristic of acceleration creep, shear contraction, and shear dilatancy under damage deviator stress. The axial strain rate decreased with the increasing of creep time and increased with the deviator stress increasing, while the deviator stress has little effect on the m values. The tests results agree well with the calculation results, which showed that the creep equation is suitable for describing the creep behaviors of Dalian interactive marine‐terrestrial deposits.

English

Fractured carbonated reservoir is one type of unconventional reservoirs which has low permeability rather than conventional reservoirs in terms of complex depositional and diagenetic environment. In most of the fractured carbonated reservoirs, fluid flow characteristics such as permeability and porosity are generally difficult to estimate and the most porous intervals are not always the best reservoirs as the intervals of equivalent porosity. Permeability plays the substantial role in moving the fluid flow from the fractures of the reservoir to the wellbore. Due to the fact that, calculating the appropriate amount of permeability was seriously doubted and there were numerous challenges for petroleum engineers to obtain the accurate quantity. Estimation of permeability using regular methods such as core analysis and well testing methods are outrageously expensive and time consuming. Furthermore, a simple correlation between permeability and porosity cannot be developed. Therefore, the prediction of permeability in heterogeneous carbonates by production logging tools is a preferable methodology to reduce the squander sums of money and time in measuring the fluid properties of a carbonate reservoir such as permeability, measuring the well fluid profile, detection of mechanical problems and evaluation of well completion procedures. That is to say that, production logging tools is performed as a powerful and applicable instrument to estimate the flow rate, water-oil contact, and other fluid properties. Key words: Unconventional reservoirs, permeability estimation, production logging tools, fluid properties.

Pore Type Classification on Carbonate Reservoir in Offshore Sarawak using Rock Physics Model and Rock Digital Images

It has been recognized that carbonate reservoirs are one of the biggest sources of hydrocarbon. Clearly, the evaluation of these reservoirs is important and critical. For rigorous reservoir characterization and performance prediction from geophysical measurements, the exact interpretation of geophysical response of different carbonate pore types is crucial. Yet, the characterization of carbonate reservoir rocks is difficult due to their complex pore systems. The significant diagenesis process and complex depositional environment makes pore systems in carbonates far more complicated than in clastics. Therefore, it is difficult to establish rock physics model for carbonate rock type. In this paper, we evaluate the possible rock physics model of 20 core plugs of a Miocene carbonate platform in Central Luconia, Sarawak. The published laboratory data of this area were used as an input to create the carbonate rock physics models. The elastic properties were analyzed to examine the validity of an existing analytical carbonate rock physics model. We integrate the Xu-Payne Differential Effective Medium (DEM) Model and the elastic modulus which was simulated from a digital carbonate rock image using Finite Element Modeling. The results of this integration matched well for the separation of carbonate pore types and sonic P-wave velocity obtained from laboratory measurement. Thus, the results of this study show that the integration of rock digital image and theoretical rock physics might improve the elastic properties prediction and useful for more advance geophysical techniques (e.g. Seismic Inversion) of carbonate reservoir in Sarawak.

Depositional environments of the Florisbad Spring site and surrounds: a revised synthesis

The Florisbad Spring site displays lithological and stratigraphical complexity within a unique geomorphological setting. Various hypotheses have been proposed to explain this complex depositional environment, and the origins of the spring site and mound are an ongoing topic of debate. To provide a context within which better to understand the depositional environment of Florisbad, the site and its surroundings were investigated. To this end, aerial photographs and Google Earth imagery, combined with field mapping and an analysis of sediments from and around the spring mound, were used to assist in a broad palaeoenvironmental reconstruction. Particular attention was paid to the depositional environment on and around the spring mound. The results did not reveal obvious differences with respect to the sedimentology of lunette dunes in the vicinity, and the spring mound itself. However, there were minor, but potentially significant differences in structure and chemical composition. Evidence suggests that the sediments are primarily of aeolian origin, while geochemical differences suggest that the south-western lunette could predate the spring mound. Optically stimulated luminescence ages confirm reworking of sediment for one of the lunettes. The morphology of the lunettes suggests that this technique would not necessarily yield primary ages for lunette formation due to sediment reworking. The meso-scale geomorphology suggests a shallow depression in which structural control and both fluvial and aeolian processes have worked together to create a unique landscape that promoted the formation and preservation of dune deposits and the unique archaeological site that is Florisbad.

Investigation of Soil Aggressiveness towards Underground Fuel Storage Tanks and Water Pipelines in Parts of Bayelsa State, Southern Nigeria

Structural failure of buried cast/ductile iron water mains and tanks due to corrosion attacks manifests in leaks and is common in most cities throughout Nigeria. The appropriate corrective action, which aims to restore pipe/tank integrity is usually based on proper understanding of the degree of corrosiveness of the soil. In an attempt to determine the potential corrosiveness of the soil to buried metallic structures in Bayelsa State, surface geoelectrical sounding was carried out. Twenty-five Schlumberger Vertical Electrical Soundings (VES) was carried out in the freshwater and meander belt geomorphic zone and the salt water mangrove swamp and estuary complex of the state using a maximum current electrode separation ranging from 200 - 400 m. The data obtained was interpreted by computer iterative modeling using a 1D inversion technique software (1X1D, Interpex, USA). The results show a high degree of heterogeneity, both laterally and vertically, which is typical of a complex depositional environment. Generally, the sub-soil condition within the expected depth of installation of water mains and storage tanks (0 - 10 m) is slightly or moderately aggressive (effective aggressivity) in the freshwater and meander belt geomorphic zone but is very strongly aggressive in the salt water mangrove swamp and estuary complex. Corrosion cells which may lead to significant corrosion failures may occur in the vicinities of strongly aggressive stations. This poses a significant corrosion risk to metallic water pipes and storage tanks. Current day design should therefore either mandate the use of a non-metallic piping product (water mains) or cathodic protection system. Prediction of potential corrosiveness of a soil and thus the application of proper corrosion control measures will not only protect the environment from spillages but will also avert cost of repair, clean-up and replacement.

Multiple Regressive Pattern Recognition Technique: An Adapted Approach for Improved Georesource Estimation

Multiple Regressive Pattern Recognition Technique (MRPRT) is an adapted approach for improved geologic resource estimation. We developed and tested this approach for the Platinum (Pt) bearing region near Goodnews Bay, Alaska, which presents an example of a complex depositional environment. We applied geospatial and pattern recognition methods to assess the spatial distribution of offshore Pt in the Goodnews Bay area from point data collected by various agencies. We used the coefficient of correlation (r) and the Nash–Sutcliffe efficiency (E) to quantitatively assess the degree of accuracy of the estimated Pt distribution. We split the study area, based on trend analysis, into two regions: inside the Bay and outside the Bay. We could not obtain appreciable estimates from the geospatial and pattern recognition methods. Using MRPRT, we were able to improve r from 0.57 to 0.93 and the E from 28.31 to 92.91 inside the Bay. We achieved improvement in r from 0.55 to 0.61 and E from 28.46 to 34.52 outside the Bay. The reasons for a non-significant improvement outside the Bay have been discussed. The results indicate that the proposed MRPRT has wide application potential in georesource estimation where input data is often scarce.

Athabasca oil sands: reservoir characterization and its impact on thermal and mining opportunities

Abstract The heavy oil deposits of Canada are a large resource with an estimated 1.7×10 12 barrels of bitumen in place. The Lower Cretaceous McMurray Formation in the Athabasca area of northern Alberta contains about 900×10 9 barrels of bitumen in place. This resource can be developed through surface mining and thermal in situ techniques. This paper examines the size of this resource in a global context and highlights its position relative to the North American market. The regional geology of the Western Canada Sedimentary Basin and the Athabasca area will also be reviewed. Understanding the regional reservoir distribution of the McMurray Formation is critical to understanding oil sands opportunities. Fluvial estuarine point bar reservoirs are a large portion of the resource that can be developed. Examples will be shown from the type outcrop location, where the stratigraphy can be organized into a hierarchy that subdivides channel-fills into bedsets, storeys, bars and barsets. Inclined heterolithic strata (IHS) surfaces can be identified. Considerable resource delineation drilling has occurred in the basin. The regulator for the Athabasca area specifies minimum drilling densities before project approvals are granted. Regional 2D seismic lines and project-specific 3D and 4D seismic datasets have also been acquired, to reduce the reservoir uncertainty and improve resource definition in this complex depositional environment. These techniques provide a unique opportunity to analyse a complex depositional system with abundant well and core control, outcrop data and seismic information. To determine preliminary deposition environments, software techniques have been successfully used to interpret large datasets quickly. Laser imaging of mine faces has also been used to record stratigraphy and determine the mined volume of ore. The importance of detailed reservoir characterization studies and their impact on thermal in situ recovery mechanisms will also be discussed. Understanding reservoir facies distributions and lateral relationships affects any recovery process, but has an even greater significance in a heavy oil reservoir.