Thin Sand Research Articles

Geochemical behavior of uranium and thorium in sand and sandy soil samples from a natural high background radiation area of the Odisha coast, India.

Owing to their natural radioactivity, uranium (U) and thorium (Th) play significant roles in environmental sciences for monitoring radiation dose and in geological sciences for understanding sedimentary processes. The Odisha coastal area, in eastern India, is a well-known high background radiation area that is rich in monazites and rutile. This area was selected to study geochemical characteristics of U and Th in sand and sandy soil samples. The concentrations of U and Th were measured using inductively coupled plasma mass spectrometry (ICP-MS). The median, geometric mean, and standard deviation for U were determined to be 6, 4.5, and 2.5μg/g and for Th were186, 123.3, and 3.1μg/g, respectively. Major element concentrations were evaluated using X-ray fluorescence spectroscopy to get the mineralogical composition and state of chemical weathering. The ratios of Th/U and Th/K varied from 4 to 37 and from 13 to 1058, respectively. These results clearly indicate that the samples from the coastal region were formed in an oxidizing and intense chemical weathering terrestrial environment with an enrichment of radiogenic heavy minerals (monazites and zircon) and clay mineral association. Since the majority of the samples have undergone moderate to intense weathering in the oxidizing environment, U is leached from the soil and sand matrix. Eventually, Th resides in the matrix and becomes a major source for radiation exposure in the environment. The high ratios of Th/U, along with the strong positive correlation between Th and P2O5, evidence the enrichment of the Th-bearing radioactive mineral, monazite, in these samples.

Stratigraphic evolution of the Nakdong River valley in response to late Quaternary sea-level changes

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley yielded a good example of a river-valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo-valley, varying sediment supply, and Holocene sea-level change associated with coastal currents. The late Quaternary stratigraphic sequence in the Nakdong River Estuary, approximately 60–70 m thick, forms a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuarine, coastal/shoreface, and deltaic. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed before 12 ka. The transgressive systems tract (TST), showing a succession of retrograding or backstepping depositional arrangements, can be divided into two depositional systems (Unit II and III). The riverine sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 7 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the Holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka.

Application of ultra-deep sandstone reservoirs prediction technology under controlled seismic facies in Yudong block of Tabei Uplift, Tarim Basin, China

Thin sand layers are widely developed in the Cretaceous Baxigai Formation in the Yudong area, western Tabei Uplift, and series of lithologic traps controlled by the structures are formed. The thickness of the target layer is 3–5 m, which is beyond the resolution of conventional seismic data; this causes the prediction of the reservoir to be difficult. Starting from the forward simulation, a forward model was designed based on the well logging data and characteristics of the strata in the well area to analyze the impact of different thin reservoir development modes on the seismic waveform. The experimental results show that the amplitude of thick sandstone is strong, while that of the thin sandstone is weaker. When mudstone barriers develop in sandstones, the amplitude decreases and the trough widens. Based on the results above, the seismic facies plan is formed by clustering the two attributes of wave trough width and amplitude, and the qualitative prediction of the reservoir can be realized on the plane by referring to the drilled rock information. Based on this, high-resolution seismic waveform inversion was carried out to achieve vertical reservoir prediction. The inversion results on the profile are higher than those of well logging. Furthermore, geological knowledge is achieved on the plane and good application results are obtained.

Controls on microbial and oolitic carbonate sedimentation and stratigraphic cyclicity within a mixed carbonate‐siliciclastic system: Upper Cambrian Wilberns Formation, Llano Uplift, Mason County, Texas, USA

AbstractThe upper Cambrian Wilberns Formation in central Texas records deposition on a low‐gradient shelf within a mixed carbonate–siliciclastic tidal‐flat system that changes offshore to subtidal shelf and open‐marine oolitic skeletal shoals with large microbial mounds. Siliciclastic sediment is interpreted to have been delivered to the tidal flat by aeolian processes because of the narrow range in grain size and paucity of clay. Tidal influence is dominant as evidenced by reversing currents and desiccation on the tidal flat, and megaripples with reversing current indicators in offshore shoals. Intraclastic conglomerates were deposited in broad channels on the tidal flats during storm surges. Microbialite deposition is interpreted to be controlled by accommodation favouring amalgamated thin biostromes developed in the tidal flat vs. larger mounds with greater synoptic relief in the offshore, and current energy resulting in preferential elongation of offshore mounds in a NE–SW orientation. Intertidal mounds and biostromes grew in the presence of significant siliciclastic flux and trapped it within their structure, whereas offshore large buildups incorporated little siliciclastic component. Oolite and skeletal grainstone formed in tide agitated shoals associated with large subtidal microbial mounds. Storms extensively recycled and redistributed skeletal and oolitic sands from the offshore shoals across the shelf as thin sand sheets. Spatial mixing of siliciclastic and carbonate sediment occurred across the tidal flat and shelf. Low‐frequency and intermediate‐frequency stratigraphic cycles were driven by shifts in the shoreline and changes in rate of siliciclastic flux in response to relative sea‐level fluctuation. Random facies stacking and the lack of metre‐scale cyclicity are interpreted to reflect stratigraphic incompleteness and an episodic signal introduced by storms.

Case study: Seismic resolution and reservoir characterization of thin sands using multiattribute analysis and bandwidth extension in the Daqing field, China

The Daqing field, located in the Songliao Basin in northeastern China, is the largest oil field in China. Most production in the Daqing field comes from seismically thin sand bodies with thicknesses between 1 and 15 m. Thus, it is not usually possible to resolve Daqing reservoirs using only conventional seismic data. We have evaluated the effectiveness of seismic multiattribute analysis of bandwidth extended data in resolving and making inferences about these thin layers. Multiattribute analysis uses statistical methods or neural networks to find relationships between well data and seismic attributes to predict some physical property of the earth. This multiattribute analysis was applied separately to conventional seismic data and seismic data that were spectrally broadened using sparse-layer inversion because this inversion method usually increases the vertical resolution of the seismic. Porosity volumes were generated using target porosity logs and conventional seismic attributes, and isofrequency volumes were obtained by spectral decomposition. The resulting resolution, statistical significance, and accuracy in the determination of layer properties were higher for the predictions made using the spectrally broadened volume.

Seismic Bayesian evidential learning: estimation and uncertainty quantification of sub-resolution reservoir properties

We present a framework that enables estimation of low-dimensional sub-resolution reservoir properties directly from seismic data, without requiring the solution of a high dimensional seismic inverse problem. Our workflow is based on the Bayesian evidential learning approach and exploits learning the direct relation between seismic data and reservoir properties to efficiently estimate reservoir properties. The theoretical framework we develop allows incorporation of non-linear statistical models for seismic estimation problems. Uncertainty quantification is performed with approximate Bayesian computation. With the help of a synthetic example of estimation of reservoir net-to-gross and average fluid saturations in sub-resolution thin sand reservoir, several nuances are foregrounded regarding the applicability of unsupervised and supervised learning methods for seismic estimation problems. Finally, we demonstrate the efficacy of our approach by estimating posterior uncertainty of reservoir net-to-gross in sub-resolution thin sand reservoir from an offshore delta dataset using 3D pre-stack seismic data.

Sand injectites: from source to emplacement – an example from the Miocene age Frimmersdorf Seam, Garzweiler Open-cast Mine, Lower Rhine Embayment

Abstract Sand injectites are reported from a Miocene-age lignite seam in the Lower Rhine Embayment, which is exploited in the Garzweiler open-cast mine, Germany. Owing to the ongoing mining of the seam, the sand injectite morphology and extent were documented over a 3 year period. The combination of fieldwork, geophysical and drilling well data, as well as a 3D reconstruction of the host unit, reveal that the sand injectites within the Frimmersdorf Seam (= host unit) are highly variable, and include sills, dykes, reticulate (i.e. an interconnected network of thin sand veins) and irregular-shaped sand bodies. The injectites are connected to the underlying Frimmersdorf Sand or the overlying Neurath Sand (= parent sand units), or can be distributed throughout the seam. The differentiation of sand injectites from syn-depositional sand bodies is based on the orientation (discordant/concordant) and the presence of primary sedimentary structures in the latter. The prevailing stress field across the Lower Rhine Basin, and the coeval nature of fault activity, controlled the formation of sand injectites in the region. While such structures have been noted for over 30 years, this study is the first to provide a detailed analysis of these economically important features, including their classification, extent and morphology.

Application of seismic attribute analysis in fluvial seismic geomorphology

Seismic attributes can be important predictors, either qualitative or quantitative, of reservoir geometries when they are correctly used in reservoir characterization studies. This paper discusses seismic attribute analyses and their usefulness in seismic geomorphology study of Moragot field of Pattani Basin, Gulf of Thailand. Early to Middle Miocene fluvial channel and overbank sands are the reservoirs in Pattani Basin. Due to their limited horizontal and vertical distribution, it is not always possible to predict the geometry and distribution of these sands based on the conventional seismic interpretation. This study utilized various seismic attributes, e.g., RMS amplitude analysis, spectral decomposition, semblance and dip-steered similarity, RGB blending to image the geometry and the spatial distribution of sand bodies in horizon and stratal slices at different stratigraphic intervals. Attribute analyses reveal, at shallow stratigraphic levels, RMS and semblance can successfully identify channel-shaped sand bodies and mud-filled channels associated with channel belts. On the other hand in deeper stratigraphic intervals, sand distribution can be imaged more effectively by using spectral decomposition and dip-steered similarity volumes. High-frequency spectral decomposition slices can image thin sands, and low-frequency slices can image thick sands quite effectively in deeper intervals. RGB blending of different frequency slices is particularly useful in delineating channel systems of various dimensions at deeper intervals. These images show the distribution of sands and mud-filled channels at various stratigraphic levels. The width of channel belts varies from 200 m to 3 km. These channel belts are N–S or NW–SE oriented. From the channel pattern and their dimensions, depositional environments can be predicted. Mud-filled channels identified in the horizon slices will act as a connectivity barrier between sand bodies at either side of the channel. They can also act as lateral and up-dip seal to form stratigraphic traps. The seismic attribute analyses clearly show the geometry and spatial distribution of sand bodies. Hence, this method for predicting sand body geometry might help in field development planning as well as in reducing exploration risk.

Centrifuge model studies on the performance of soil walls reinforced with sand-cushioned geogrid layers

This paper is to investigate the effectiveness of encapsulating geogrid layers within thin sand layers, for enhancing the deformation behavior of vertical reinforced soil walls constructed with marginal backfills. Centrifuge model tests were performed on vertical soil walls, reinforced with geogrid layers, using a 4.5 m radius large beam centrifuge available at IIT Bombay at 40 gravities. The backfill conditions, height of soil wall, reinforcement length, and reinforcement spacing, were kept constant in all the tests. A wrap-around technique was used to represent flexible facing. Three different geogrid types with varying stiffness were used in the present study. The walls were instrumented with vertical linear variable differential transformers to monitor surface settlements during the tests. Marker-based digital image analysis technique was used to determine face movements and distribution of geogrid strain along the wall height. The deformation behavior of soil walls, reinforced with geogrid layers encapsulated in thin layers of sand, were compared against a base model having no sand-cushioned geogrid layers. Provision of sand-cushioned geogrid layers and increase in geogrid stiffness were found to limit normalized face movements (Sf/H), normalized crest settlements (Sc/H), and change in maximum peak reinforcement strain (dεpmax). Sand-cushioned geogrid layers were also found to limit the development of tension cracks behind and within the reinforced zone. Significant reduction in rate of maximum face movement (dSfmax/dt) and rate of maximum peak reinforcement strain (dεpmax/dt) was observed, with an increase in value of normalized reinforcement stiffness (Jg/γH2) of geogrid layers. The analysis and interpretation of centrifuge model tests on soil walls, constructed with marginal backfills and reinforced with sand-cushioned geogrid layers, indicate that their performance is superior to the walls without sand-cushioned geogrid layers.

Stochastic analysis of the capacity of two parallel footings on a thin sand layer

This paper presents a study on the stochastic bearing capacity of two parallel strip footings supported on a heterogeneous sand layer confined by a rigid base. Variability of the sand is represented by a truncated normal distribution function of its friction angle to produce a geostatistical equivalent to the deterministic bearing capacity. A method was first demonstrated to derive an analytical distribution function of the bearing capacity for a single surface footing with a rigid base layer for which an exact bearing capacity function is available. For the twin foundation problem with no explicit deterministic solutions, a Monte Carlo simulation was adopted. The stochastic bearing capacity relative to its deterministic equivalent was determined for a set of layer thicknesses and footing distances in terms of the assumed geostatistical characteristics of the sand and resulting bearing capacity distributions. The Monte Carlo methodology is adaptable in design to model other bearing capacity problems with more complex and random soil distributions.

Enhanced denitrification by design modifications to the standard permeable pavement structure

Abstract In this study, six permeable pavement systems (PPS) with different subbase configurations were tested to evaluate their nitrogen attenuation capabilities from urban stormwater runoff. The PPS subbases were configured based on the following rationale for achieving enhanced physical, chemical and biological treatment of nitrogen compounds commonly found in urban stormwater: (i) a layer of natural zeolite to enhance nitrogen removal by ion exchange and adsorption; (ii) a layer of bark chips as a carbon donor to enhance biodegradation; (iii) a saturated zone to maintain required moisture content and reduced oxygen level for enhanced denitrification and (iv) thin sand layer(s) to limit oxygen transport for creating an anoxic zone within the PPS. A laboratory water sampling and testing program was undertaken from these PPS over a six-month period using synthetic stormwater with different pollutant concentrations while simulating varying rainfall intensities to represent typical design rainfall events considered in urban stormwater management. Our results demonstrate an improved denitrification in the PPS when a saturated zone is maintained and an organic carbon source is added in the PPS subbase. Compared with the traditional PPS, the new PPS is found to attenuate twice the amount of the total inorganic nitrogen in stormwater. Also, the attenuation of nitrogen compounds by the standard PPS is found to be reduced with rainfall duration (e.g., 54% attenuation during the first hour and only 3.5% during the 4th hour of the rainfall). The new PPS is found to attenuate 68% of total inorganic nitrogen even in the 4th hour of the rainfall event. The new PPS has the potential to become an effective stormwater quality improvement device that can contribute towards cleaner urban waterways.

Application of geostatistical seismic inversion in reservoir characterization of Sapphire gas field, offshore Nile Delta, Egypt

Seismic reservoir characterization becomes challenging when reservoir thickness goes beyond the limits of seismic resolution. Geostatistical inversion techniques are being considered to overcome the resolution limitations of conventional inversion methods and to provide an intuitive understanding of subsurface uncertainty. Geostatistical inversion was applied on a highly compartmentalized area of Sapphire gas field, offshore Nile Delta, Egypt, with the aim of understanding the distribution of thin sands and their impact on reservoir connectivity. The integration of high-resolution well data with seismic partial-angle-stack volumes into geostatistical inversion has resulted in multiple elastic property realizations at the desired resolution. The multitude of inverted elastic properties are analyzed to improve reservoir characterization and reflect the inversion nonuniqueness. These property realizations are then classified into facies probability cubes and ranked based on pay sand volumes to quantify the volumetric uncertainty in static reservoir modeling. Stochastic connectivity analysis was also applied on facies models to assess the possible connected volumes. Sand connectivity analysis showed that the connected pay sand volume derived from the posterior mean of property realizations, which is analogous to deterministic inversion, is much smaller than the volumes generated by any high-frequency realization. This observation supports the role of thin interbed reservoirs in facilitating connectivity between the main sand units.

Successful infill drilling campaign using fit-for-purpose seismic technologies doubles oil production and extends field life at Lakshmi Field, Gulf of Cambay, western India

The offshore Lakshmi Field, located in the southern part of Cambay Basin in the CB/OS-2 block in western India, is a success story of transitioning from a plateauing gas field to an oil-producing asset. Hydrocarbons sourced from Hazira Shale at Lakshmi Field are trapped in inversion-related four-way dip closures. The reservoirs are within the Miocene-age Tarkeshwar and overlying Babaguru formations; both have excellent reservoir quality with porosity ranging from 25% to 30% and Darcy-scale permeability. During the initial exploration stage, presence of oil was established in the deeper lower Tarkeshwar sands. However, the full oil potential of the field was not realized in the early stage of development due to difficulty in characterizing laterally and vertically discontinuous thin sands. These sands are often not detected in conventional 3D seismic data due to severe attenuation-related masking by overlying thick gas sands. Given the uncertainty of the oil potential of the field, a revised look using advanced seismic technologies was undertaken to drive a new infill drilling campaign. Seismic reprocessing using Q-tomographic inversion was performed to address the gas-attenuation problem, resulting in an improved seismic image. The new seismic data enabled characterization of thin reservoir sands using analytical techniques such as spectral decomposition and amplitude-variation-with-offset (AVO) attribute analysis. An integrated reservoir-characterization approach using field analogs, interpretation within a sequence stratigraphic framework, concepts of seismic geomorphology, and quantitative seismic analysis helped identify optimal areas of the sand fairway for infill well placement. Several infill wells have since been drilled that encountered good pay zones, validating the integrated approach. This successful campaign doubled oil production at Lakshmi and extended the field life by increasing reserves.

Mapping Surficial Materials in South of Wager Bay Area (Nunavut) Using RADARSAT-2 C-HH and C-HV, Landsat-8 OLI, DEM and Slope Data

For anarea south of Wager Bay, Nunavut (NTS map sheets 046D, E, 055P, 056A, H), a map detailing 22 surface material classes was produced using a non-parametric classifier, Random Forests, applied to a combination of RADARSAT-2 C-band dual- polarized (horizontal transmitted and horizontal received (HH) and horizontal transmitted and vertical received (HV)) and Landsat-8 OLI images with a digital elevation model and slope data. We show that the addition of RADARSAT-2 C-HH and C-HV images to the optical Landsat-8 OLI image in the classification process increases the overall classification accuracy from 96.7% to 99.3%. Similarly, the accuracy determined by comparing the resulting maps with georeferenced field data (i.e., mapping accuracy) increases from 72.1% to 78.0% when RADARSAT-2 C-HH and C-HV imagesare added to the classification. The material classes with the highest mapping accuracies were flooded alluvium and boulders, both with 100%. The class with the lowest mapping accuracy was thin sand and gravel over bedrock (11.1%), commonly confused with sand and gravel with vegetation and bedrock. Adding RADARSAT-2 data in the classification increases also the mapping accuracy that was established by comparing to georeferenced point observations.

Fusing multiple frequency-decomposed seismic attributes with machine learning for thickness prediction and sedimentary facies interpretation in fluvial reservoirs

Abstract Defining the boundaries, thicknesses and sedimentary facies of fluvial reservoirs (sand bodies) is critical for predicting hydrocarbon volumes, designing schemes for petroleum exploration and development and improving oil recovery. Most reservoirs contain thick and thin sand bodies at the same intervals, while the amplitude values of seismic data usually highlight sand bodies near the 1/4 wavelength for the tuning phenomena. Hence, the application of spectral decomposition to seismic attributes and the combination of multiple frequency-decomposed (spectral-decomposed) seismic attributes have gained increasing attention for the readjustment of tuning thickness to predict sand bodies of various thicknesses. However, the popular method of red-green-blue blending is a simple linear combination of three frequency-decomposed seismic attributes that qualitatively analyzes the sand thickness without well-log interpretation. This research proposes machine learning fusion as a new nonlinear method for fusing high-, middle-, and low-frequency seismic attributes. This method uses machine learning to link well-log interpretation and multiple-frequency seismic attributes for the quantitative prediction of sand thickness, which is important for development work in a mature field. Test results of the conceptual model and the real case indicate that the predicted sand thickness after fusing multiple frequency-decomposed seismic attributes is approximately in line with the actual thickness (correlations between 80 and 90%). Combined with the coherence attribute and the red-green-blue blending results, the distributions and histories of sedimentary facies are analyzed based on the predicted sand thickness and well data. The results suggest that the proposed method can effectively readjust the tuning thickness and improve the resolution of seismic interpretation. This method is a potentially effective technique to characterize the sand thickness and sedimentary facies in other fields using a similar geological setting and dataset.

Evaluation of Practicable Subsurface CO2 Storage Capacity and Potential CO2 Transportation Networks, Onshore North America

Carbon Capture, Utilization and Storage (CCUS) is considered to be a potentially important technology for reducing the amount of carbon dioxide (CO2) released into the atmosphere from anthropogenic emission sources. With recent progress on capture technologies, attention is increasingly turning to the identification of key challenges associated with CO2 transportation and storage at the scale being considered for the CCUS industry. Decades of oil and gas production have provided experience in application of technologies required for CO2 transportation and storage, but the challenges unique to CO2 storage still need to be evaluated. This paper describes a scoping-level assessment of practicable subsurface geologic CO2 storage capacity and a potential Carbon Capture, Utilization, and Storage (CCUS) industry in the US and Canada, leveraging publically available data/information, publications, and methodologies. Likely subsurface CO2 storage sites and distribution of storage capacity relative to major anthropogenic sources are first characterized using a probabilistic methodology previously developed by the US Geologic Survey (USGS), which was modified to account for several practical factors affecting storage capacity. Major factors considered include 1) subsurface lateral accessibility restrictions imposed by faulting and/or stratigraphic pinch-outs, 2) the proportion of net storage-quality sand comprised of thin sands unlikely to be good injection candidates, 3) surface access restrictions, and 4) dynamic injectivity/storage efficiency considerations. Potential regional CCUS networks are then modeled using a transportation cost framework to map CO2 sources to storage sinks. The USGS assessment and most other existing assessments of storage capacity are based on the premise that all engineering approaches and hardware required to achieve the highest possible storage efficiency would be employed, and that injection rate and timeframe are not issues, with perhaps hundreds to thousands of years of injection permitted to achieve full storage efficiency. We explore the impact of dynamic injectivity considerations on practical storage efficiency by using reservoir simulation models to account for subsurface pressure limitations and the impact of permeability differences and lateral accessibility on CO2 injectability, and then use the results of the modeling to derive a debiting function that reduces the range of static storage capacity estimated by the USGS. Debiting functions accounting for lateral accessibility, thin sands, and surface access restrictions were also applied to obtain practicable storage estimates. Key conclusions from the study include: 1) Although the modified storage capacity estimates are lower than previously published estimates, the estimated subsurface storage capacity in the US onshore is sufficient to sustain a large-scale CO2 storage industry. We estimate that about 500 Gt of potential US subsurface storage capacity is potentially available (excluding federal offshore capacity) even after accounting for dynamic injectibility considerations, thin sands, surface and lateral access issues. Dynamic injectability factors had the largest impact on the reduction in estimated storage capacity. 2) Significant geographic misalignment exists between current high-volume CO2 emission sources and storage availability in North America. This could affect evolution of CO2 transportation networks with time. Detailed site-specific assessments of subsurface storage capacity are required for site selection and actual project implementation. These efforts could change some of the conclusions of this study. In particular, consideration of legacy wells and geomechanical factors such as induced seismicity, ground surface deformation, and fault activation may further reduce storage capacity relative to the estimates presented here. Nevertheless, the methodology described in this paper may be useful for initial assessment of CO2 storage capacity and matching of CO2 emission sources to storage sinks in geographic locations other than those considered in this study.

A New Example of the Trace Fossil Asteriacites Quinquefolius from Japan and Its Process of Production as Revealed by Observations of an Extant Sea Star

A star-shaped trace fossil here assigned to Asteriacites quinquefolius (Quenstedt) was found in the Miocene Shirahama Formation, Wakayama Prefecture. This is the first report in Japan and stratigraphically youngest record for the ichnospecies. The fossil has five distinct arms and wide striations on both lateral sides of each arm, and the shape is bilaterally symmetrical. To clarify the fossil producing process, we conducted burial experiments of extant asteroids in aquaria and in situ for the first time. Asteroids buried themselves in the substratum using the tube-feet, and when asteroids were covered with thin sand, they escaped slantingly upward onto the sand tilting their body in a bilaterally symmetrical posture. As a result, the remaining trace was very similar to the fossil of A. quinquefolius from the Shirahama Formation. Accordingly, the results suggest the present fossil was formed by the behavior of escaping from thin sand cover by asteroids.

Technology Focus: Mature Fields and Well Revitalization (January 2019)

Technology Focus Mature brownfields contribute significantly to global oil production. A study of the papers presented during the past year at various SPE conferences reveals a continuation of the trend to put in massive effort to minimize decline from mature brownfields. This has been attempted through several means, such as improving well integrity and judicious well interventions to restart production from idle wells. One paper discusses a conceptual platform where all stakeholders (operator and service providers) can share and formulate a win/win strategy wherein operational efficiency and success rate of an activity are the main drives. As an offshoot of such well-intervention activities, low-resistivity pay zones, either shallower or deeper with respect to the main pay and hitherto considered unattractive, have been identified and contribute significantly in sustaining production decline. There is an all-around emphasis on characterizing highly compartmentalized and difficult reservoirs that have thin reservoir sands defying well-to-well correlations because of a lack of marker shales. In some cases, the presence of conductive minerals such as pyrites or siderites further masks the presence of hydrocarbons in conventional log analysis. In addition to efforts on improved reservoir characterization, optimizing ongoing waterfloods is an area where focused efforts are yielding rich dividends. These involve locating the bypassed oil and addressing unswept areas through reservoir surveillance and modeling. Some operators also have focused on innovative enhanced-oil-recovery techniques in mature brownfields to enhance production. Recommended additional reading at OnePetro: www.onepetro.org. SPE 186362 Extending Life of Liquid-Loaded Gas Wells Using Velocity-String Application: Case Study and Candidate Selection by Satria Andrianata, VICO Indonesia, et al. SPE 188443 Novel Reservoir-Modeling and Experimental-Design Approach To Tackle the Challenge of Modeling Highly Compartmentalized Reservoirs Under Large Uncertainties in a Mature Offshore Field, Malaysia by A. Sulaksana, Sabah Shell, et al. SPE 188770 Fluid-Front Monitoring Using Smart and Safe Pulsed-Neutron Technology on Slickline by Rahul Grover, Schlumberger, et al.

Frequency bandwidth enhancement using continuous wavelet transform and random noise attenuation by f-xy filtering technique – a case study from Badin oilfield, Indus basin, Pakistan

Routine seismic data processing does not always meet the quantitative interpreters’ expectations especially in areas like Badin, where prospective thin bed B – sand interval is ambiguous throughout the seismic volume. Continuous Wavelet Transform (CWT) provides detailed description of seismic signal in both time and frequency without compromising on window length and a fixed time-frequency resolution over time-frequency spectrum. We present enhancement of seismic data for effective interpretation using the bandwidth extension technique. Implementing bandwidth extension, the dominant frequency increases from 18 Hz to 30 Hz and the frequency content boosted from 40 Hz to 60 Hz. Noise inclusion by the technique was suppressed by F-XY predictive filter and F-XY deconvolution with edge preserve smoothing. Phase and spectral balancing were applied to partial angle stacks to stabilize the phase rotation across the 3D survey, particularly for far offset stack. Frequency was balanced using surface consistent spectrum balancing, and subjected to trace scaling for amplitudes balance and preservation. Results of the techniques yielded unique improvement on the data resolution and subtle information about the thin sand beds were better delineated. Tuning thickness analysis reveals the usefulness of bandwidth extension, with an increase of 30% in the resolving power of thin beds.

A new method for clastic reservoir prediction based on numerical simulation of diagenesis: A case study of Ed1 sandstones in Bozhong depression, Bohai Bay Basin, China

The use of seismic exploration technique to provide reliable reservoir information is a conventional method. However, due to its quality and resolution reasons, it cannot satisfy the detailed research and characterization of reservoirs, especially the clastic reservoir with thin sand body. Diagenesis is a fundamental process in the development and formation of all petroleum reservoirs and is a major contributor to their ultimate physical properties. Based on numerical simulation of diagenesis, a new prediction method called geology prediction techniques is presented to simulate the evolution of the diagenetic stages, diagenetic facies and porosity of clastic reservoirs and ultimately for favorable reservoir prediction. It emphasizes the idea of dynamic quantitative research dominated by process recovery, the most important of which is the establishment of mathematical models, including mineral dissolution models, mineral cementation models and sediment compaction models using the experimental data in study area and the results of previous studies. The essence of this method is illustrated, and its effectiveness is proved using Ed1 clastic sandstones in the Bozhong depression, Bohai Bay Basin, China. At present, the reservoir is in the early diagenetic stage B (IB) and the middle diagenetic stage A1 (IIA1). The major diagenetic processes that influence the porosity of the sandstones in study area are mechanical compaction, carbonate cementation, quartz cementation, clay cementation, feldspar dissolution and carbonate dissolution. There are three types of sandstones including fine sandstone, siltstone, and argillaceous siltstone, and the variation range of primary porosity of these sandstones is from 26% to 38%. Compaction and carbonate cementation are the main reasons for porosity reduction, with porosity loss percentage by compaction (P-Com) and porosity loss percentage by cementation of carbonate (P-C-Car) being 53.1% ~ 7.8% (av. 41.9%) and 53.1% ~ 7.8% (av. 18%), respectively, while carbonate dissolution and feldspar dissolution can greatly improve reservoir physical property, with porosity increase percentage by dissolution of carbonate (P-D-Car) and porosity increase percentage by dissolution of feldspar (P-D-Fel) being 0 ~ 9.9% (av. 8.9%) and 0 ~ 27.8% (av. 9.4%), respectively. The predicted porosities match the measured porosities well. Cited as : Qian, W., Yin, T., Hou, G. A new method for clastic reservoir prediction based on numerical simulation of diagenesis: A case study of the Ed1 clastic sandstones in the Bozhong depression, Bohai Bay Basin, China. Advances in Geo-Energy Research, 2019, 3(1): 82-93, doi: 10.26804/ager.2019.01.07