Geological Datasets Research Articles

Special considerations of determining the gas saturation factor of reservoir rocks of Dnieper-Donets depression gas fields on the basis of petrophysical studies

Introduction. The gas saturation coefficient is one of the most important parameters for calculating gas reserves. The parameter can be determined by laboratory petrophysical methods applying the residual water saturation coefficient. The latter, in turn, is determined by direct or indirect methods. The direct method is used extremely rarely, while indirect methods are very common - primarily the methods of a semipermeable membrane and centrifugation. The first method is considered the most reliable. Formulation of the problem. When applying the semi-permeable membrane method, the issue of setting the maximum displacement pressure is the key factor that determines the result, as it determines the value of the residual water saturation, and, consequently, the value of the gas saturation coefficient of the reservoir. There are numerous cases when the results of laboratory studies of residual water, and hence the gas saturation coefficient, are clearly discordant with the whole set of geophysical and geological data. This problem is possibly caused by the wrong choice of the laboratory research modes, and specifically, the maximum pressure that is created in the course of the experiment. The research objective is to analyze the ways of setting the maximum water displacement pressures during the experiment in terms of the most reasonable, basic method of a semipermeable membrane; to evaluate their applicability taking into account the best practices and propose their optimal combination for practical work. Previous research. The paper considers various approaches to setting the maximum pressure, including an attempt to model the process of deposit formation, achieving irreducible water saturation, an express method using a centrifuge, determining water-holding capacity, limiting pressures by the size of filter pores, and calculating pressures on the basis of the deposit height. Main material. Two approaches have been distinguished from the considered ones: calculation of the maximum pressure on the basis of the deposit height and calculation on the basis of the maximum pore radius, at which a meniscus can be formed. It is shown that it is rational to combine these two approaches into one, which will allow obtaining more reliable values of the residual water saturation, and hence the gas saturation coefficient. The ultimate maximum displacement pressure for the semi-permeable membrane method, which should be created during the experiment, has been determined. The limiting height of the deposit has also been determined. Any calculation above this parameter does not make sense. The discrepancies between theoretical calculations and actually observed heights of capillary rise and the influence of the layered structure of the reservoir have also been considered. The area of possible practical application of the method has been determined. It is noted that extensive knowledge of the reservoir geometry is crucial for the practical application of the method. Besides, the data on the deposit height should be included in the research proposal. Practical value. The application of the method of calculating the maximum displacement pressure on the basis of the deposit height, taking into account the restrictions on the maximum pore diameters, at which a meniscus can be formed, will certainly increase the reliability of gas reserves calculations in the gas fields of Ukraine.

The robustness of geodetically derived 1-D Antarctic viscosity models in the presence of complex 3-D viscoelastic Earth structure

SUMMARY Earth structure beneath the Antarctic exerts an important control on the evolution of the ice sheet. A range of geological and geophysical data sets indicate that this structure is complex, with the western sector characterized by a lithosphere of thickness ∼50–100 km and viscosities within the upper mantle that vary by 2–3 orders of magnitude. Recent analyses of uplift rates estimated using Global Navigation Satellite System (GNSS) observations have inferred 1-D viscosity profiles below West Antarctica discretized into a small set of layers within the upper mantle using forward modelling of glacial isostatic adjustment (GIA). It remains unclear, however, what these 1-D viscosity models represent in an area with complex 3-D mantle structure, and over what geographic length-scale they are applicable. Here, we explore this issue by repeating the same modelling procedure but applied to synthetic uplift rates computed using a realistic model of 3-D viscoelastic Earth structure inferred from seismic tomographic imaging of the region, a finite volume treatment of GIA that captures this complexity, and a loading history of Antarctic ice mass changes inferred over the period 1992–2017. We find differences of up to an order of magnitude between the best-fitting 1-D inferences and regionally averaged depth profiles through the 3-D viscosity field used to generate the synthetics. Additional calculations suggest that this level of disagreement is not systematically improved if one increases the number of observation sites adopted in the analysis. Moreover, the 1-D models inferred from such a procedure are non-unique, that is a broad range of viscosity profiles fit the synthetic uplift rates equally well as a consequence, in part, of correlations between the viscosity values within each layer. While the uplift rate at each GNSS site is sensitive to a unique subspace of the complex, 3-D viscosity field, additional analyses based on rates from subsets of proximal sites showed no consistent improvement in the level of bias in the 1-D inference. We also conclude that the broad, regional-scale uplift field generated with the 3-D model is poorly represented by a prediction based on the best-fitting 1-D Earth model. Future work analysing GNSS data should be extended to include horizontal rates and move towards inversions for 3-D structure that reflect the intrinsic 3-D resolving power of the data.

Generating unrepresented proportions of geological facies using Generative Adversarial Networks

In this work, we investigate the capacity of Generative Adversarial Networks (GANs) in interpolating and extrapolating facies proportions in a geological dataset. The new generated realizations with unrepresented (aka. missing) proportions are assumed to belong to the same original data distribution. Specifically, we design a conditional GANs model that can drive the generated facies toward new proportions not found in the training set. The presented study includes an investigation of various training settings and model architectures. In addition, we devised new conditioning routines for an improved generation of the missing samples. The presented numerical experiments on images of binary and multiple facies showed good geological consistency as well as strong correlation with the target conditions.

Integrating Different Databases to Offer a Geological Perspective of Coastal Management: A Review Case from the Northern Tuscany Littoral Cell (Italy)

A multidisciplinary approach to coastal process research has been increasingly encouraged in the last decade, and it is now widely accepted for a thorough, in-depth analysis of any issue related to such an environment. In this study, we emphasized the need for the integration of different time-scales, not just disciplines. Many geological datasets provided by several sources contribute to the knowledge of coastal processes. We retrieved the available datasets about morphodynamic, geomorphological, and geological aspects of the northern Tuscany (Italy) littoral cell, and we merged all of them with QGIS (Quantum Geographic Information System) applications to provide an assessment of the current situation starting from a geological perspective. Data processing resulted in maps and stratigraphic sections that confirmed that sediment supply is the main factor driving the evolution of the littoral cell. Such a perspective is also useful for the development of reliable coastal evolution future scenarios, not just for a better definition of the present situation. As these datasets are now available for many sectors of coast around the world, this approach may be easily replicated elsewhere to improve coastal management policy making.

Conditions to Preserve the Sedimentary Record of Channel Planforms in Temperate Rivers of the Northern Hemisphere

AbstractWe aim to identify conditions that influence the preservation of a complete record of channel planforms in the topmost layer of floodplains, prior to the maintenance in the rock record. We have tested a hypothesis that a successive decrease of stream power and channel belt width are necessary to preserve the record of channel planforms in the topmost floodplain layer over 103 to 104‐year time scales. A literature review was conducted for rivers of the temperate zone of the Northern Hemisphere. Stream power, valley, and channel belt widths, paleodischarges, sediment grain‐size, and age of paleochannels were used to identify four groups of rivers with preservation potential ranging from tens of thousands years to annual time scales. The decrease in stream power followed by sustained low stream power, and successive decrease of channel belt width were identified in rivers preserving a 103 to 104‐year record of channel planforms. River valleys with the record of at least two generations of paleochannels, and valley width/channel belt width ratios between 6 and 12, potentially preserve fluvial records over 103 to 104‐year time scales. We analyzed unusually well‐preserved records of channel planforms from the Obra and Sió Rivers (central Europe). A determination of trends in changes of stream power and channel belt widths based on an extensive set of geophysical, geological data, and sediment dating from earlier studies, confirmed the tested hypothesis. The proposed framework can be extended by fluvial records preserved by large, and coastal rivers, with the potential to include ancient fluvial records.

Tectonics of the Colorado Plateau and Its Margins

The Cenozoic Colorado Plateau physiographic province overlies multiple Precambrian provinces. Its ∼2-km elevation rim surrounds an ∼1.6-km elevation core that is underlain by thicker crust and lithospheric mantle, with a sharp structural transition ∼100 km concentrically inboard of the physiographic boundary on all but its northeastern margin. The region was uplifted in three episodes: ∼70–50 Ma uplift above sea level driven by flat-slab subduction; ∼38–23 Ma uplift associated with voluminous regional magmatism and slab removal, and less than 20 Ma uplift associated with inboard propagation of basaltic magmatism that tracked convective erosion of the lithospheric core. Neogene uplift helped integrate the Colorado River from the Rockies at 11 Ma to the Gulf of California by ∼5 Ma. The sharp rim-to-core transition defined by geological and geophysical data sets suggests a young transient plateau that is uplifting as it shrinks to merge with surrounding regions of postorogenic extension. ▪ The Colorado Plateau's iconic landscapes were shaped during its 70-million-year, still-enigmatic, tectonic evolution characterized by uplift and erosion. ▪ Uplift of the Colorado Plateau from sea level took place in three episodes, the youngest of which has been ongoing for the past 20 million years. ▪ Tectonism across the Colorado Plateau's nearest plate margin (the base of the plate!) is driving uplift and volcanism and enhancing its rugged landscapes. ▪ The bowl-shaped Colorado Plateau province is defined by ongoing uplift and an inboard sweep of magmatism around its margins. ▪ The keel of the Colorado Plateau is being thinned as the North American plate moves southwest through the underlying asthenosphere.

Data-Analysis Approach Aids Reservoir-Quality Prediction of Microporous Carbonates

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19972, “Improving Reservoir-Quality Prediction of Microporous Carbonates Using a Multiscale Geophysical Data-Analysis Approach,” by Ahmad Ramdani, SPE, Viswasanthi Chandra, and Thomas Finkbeiner, SPE, King Abdullah University of Science and Technology. The paper has not been peer reviewed. Copyright 2021 International Petroleum Technology Conference. Reproduced by permission. Understanding the effect of microporosity on reservoir quality and predicting the spatial distribution of microporosity at the reservoir scale accurately is required to improve the recovery of remaining hydrocarbons from reservoirs. Using an integrated data-analysis approach applied to multiscale geological and geophysical data sets from micrometer-scale scanning-electron-microscope (SEM) imagery to decameter-scale seismic data, the authors predict the distribution of microporosity at the reservoir gridblock scale. The proposed methodology is applied in the complete paper to the Arab-D reservoir equivalent outcrop data from the Upper Jubaila formation in Saudi Arabia. Methodology This methodology is tested at an 800-m-long roadcut along the Riyadh-Mecca Highway in Saudi Arabia, stratigraphically equivalent to the Upper Jubaila Formation in the subsurface (Fig. 1). A 35-m-long core was drilled from the top of the same roadcut (dubbed the DQ-1 well), from which 106 cylindrical horizontal core plugs were obtained, drilled with an average spacing of 30 cm. This outcrop location was chosen because the pore volume in this interval is characterized by porosity with pore-diameter distribution of less than 10 µm. This outcrop provides an excellent analog to study microporosity-dominated carbonate rocks irrespective of their diagenetic origin. Moreover, the Upper Jubaila formation is a part of the Arab-D reservoir in the subsurface, which has been acclaimed as the most prolific oil reservoir in the world. Because this study used outcropped rocks, the authors acknowledge that differences in petrophysical properties with the subsurface rock formations will exist. Therefore, the study is not intended as a one-to-one analog for the Arab-D reservoir. Instead, the aim is to establish a general methodology that links micrometer-scale morphology of microcrystals that hosts microporosity with macroscale petrophysical properties and seismic attributes. Details of the methodology of seismic data acquisition and petrographic and petrophysical analysis are provided in the complete paper.

TEM-NLnet: A Deep Denoising Network for Transient Electromagnetic Signal With Noise Learning

Transient electromagnetic (TEM) method is a widely adopted technology in geophysics. TEM signals received by coils will be disturbed by complex noises. Compared with traditional filtering-based methods, deep-learning-based TEM signal denoising methods achieved impressive denoising performance. However, the existing deep-learning-based methods rely heavily on simulated noise with a certain distribution to construct paired datasets for supervised learning. In real scenarios, if the noise distribution of acquired TEM signals has a huge difference (e.g., the type of noise distribution, the level of noise) with that of the simulated datasets, the trained model may not always be valid. To address this issue, a novel noise-learning-inspired deep denoising network (namely, TEM-NLnet) is proposed for TEM signal denoising. Specifically, instead of inserting the simulated noise, we first learn the noise appeared in real-world signals through generative adversarial networks (GANs), such that the generator can produce the learned noise to construct paired datasets for training. Then, a deep-neural-network-based denoiser is imposed to learn mapping from the noise TEM signal to the corresponding noise-free one. Extensive experiments on the simulated and actual geological datasets show that compared with other state-of-the-art TEM denoising methods, our proposed method achieves better performance in terms of quantitative and visual results. Models and code are available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/wmyCDUT/TEM-NLnet_demo</uri> .

Geomorphological and geophysical analyses of the Hebron Fault, SW Namibia: implications for stable continental region seismic hazard

SUMMARYThis study explores the geomorphological expression and geological context of a normal fault scarp in a stable continental region (SCR) which we interpret as having failed in large (Mw &amp;gt;7) earthquakes. Records of such large normal faulting events in an SCR (or even in more rapidly deforming regions) are extremely rare, and so understanding this feature is of international interest. The scarp is exceptionally well-preserved due to the extensive calcrete/silcrete cementation. In areas where this cementation is reduced or absent the scarp is more diffuse, as expected for a feature formed by one or more paleoearthquakes. The exceptional preservation aids comparison with data sets based on scarps which have formed more recently. Our analysis is based on a high-resolution digital elevation model of the Hebron Fault scarp in southern Namibia using pan-sharpened Worldview-3 satellite stereophotos (0.31 m resolution). We make scarp height measurements at 160 locations providing improved estimates of the average displacement (5.9 m), maximum displacement (10.1 m), and the minimum fault length (45 km). No consistent evidence of lateral displacements in water courses or alluvial fan margins were found implying predominantly normal displacement. A newly described section in the northwest has en-echelon scarps consistent with a component of strike-slip motion that may be explained by its difference in strike from the central section. Most channels crossing the fault show a single knick-point. The displacement varies smoothly as it crosses a number of different generations of alluvial fan surfaces. No evidence of a multiscarp or a composite scarp were observed. We have therefore found no evidence for a mutiple-event origin for the scarp, although, this lack of evidence does not conclusively demonstrate a single-event origin. Published regressions, based on the limited data available for SCRs, suggest that the mean expected average displacement ($\bar{D}_{\rm av}$) for a faults of this length is 1.2–3.1 m implying that the scarp is likely to have formed in 2–5 events with an expected Mw = ∼7.1 though displacements in individual events may exceed these average values. Comparison with the regional geology and aeromagnetic data sets suggests that the fault reactivates a Mesoproterozoic ductile structure, the Nam Shear Zone, and that the location, orientation and segmentation of the scarp is controlled by the alignment of pre-existing structurally weak zones with the present-day stress regime. The fault has undergone repeated brittle reactivation, accumulating ∼110 m of vertical offset since the deposition of the Ediacaran-to-Cambrian Nama Group. This is less than expected from global compilations of total displacement and fault length data, suggesting that the fault rapidly attained its current length by recruiting an existing weak zone and is expected to accumulate displacement at a relatively constant length in the future.

Local Dynamic Updating Method of Orebody Model Based on Mesh Reconstruction and Mesh Deformation

In this paper, to update the orebody model based on the given interpreted geological information, we present a local dynamic updating method of the orebody model that allows the interactive construction of the constraint deformation conditions and the dynamic updating of the mesh model. The rules for constructing deformation constraints based on the control polylines are discussed. Because only part of the model is updated, the updated mesh is effective and the overall quality is satisfactory. Our main contribution is that we propose a local dynamic updating method for the orebody model based on mesh reconstruction and mesh deformation. This method can automatically update a given 3D orebody model based on a set of unordered geological interpretation lines. Moreover, we implement a deformation neighborhood region search method based on the specified ring radius and a local constrained mesh deformation algorithm for the orebody model. Finally, we test the method and show the model update results with real geological datasets, which proves that this method is effective for the local updating of orebody models.

A cold seep triggered by a hot ridge subduction

The Chile Triple Junction, where the hot active spreading centre of the Chile Rise system subducts beneath the South American plate, offers a unique opportunity to understand the influence of the anomalous thermal regime on an otherwise cold continental margin. Integrated analysis of various geophysical and geological datasets, such as bathymetry, heat flow measured directly by thermal probes and calculated from gas hydrate distribution limits, thermal conductivities, and piston cores, have improved the knowledge about the hydrogeological system. In addition, rock dredging has evidenced the volcanism associated with ridge subduction. Here, we argue that the localized high heat flow over the toe of the accretionary prism results from fluid advection promoted by pressure-driven discharge (i.e., dewatering/discharge caused by horizontal compression of accreted sediments) as reported previously. However, by computing the new heat flow values with legacy data in the study area, we raise the assumption that these anomalous heat flow values are also promoted by the eastern flank of the currently subducting Chile Rise. Part of the rift axis is located just below the toe of the wedge, where active deformation and vigorous fluid advection are most intense, enhanced by the proximity of the young volcanic chain. Our results provide valuable information to current and future studies related to hydrothermal circulation, seismicity, volcanism, gas hydrate stability, and fluid venting in this natural laboratory.

TRANSIENT ELECTROMAGNETIC SOUNDING IN 2D, 3D, AND 4D MODES: SEQUENCE OF GEOLOGICAL EXPLORATION ACTIVITIES

From 1980s, electromagnetic prospecting is an integral component of geophysical techniques for oil and gas exploration in many regions of the Russian Federation. Electromagnetic methods are used at all stages of geological exploration, including reconnaissance, discovery, prospecting and appraisal, and economic mining. In oil and gas exploration, the most commonly used technique is the near-field transient electromagnetic sounding (TEM). On the other hand, for each of these stages, specific tasks of electromagnetic prospecting have not been clearly defined yet. Furthermore, there are no standard requirements to the volume of a priori geological and geophysical information, which is sufficient for solving a geological problem. If such information is lacking or insufficient, a geological problem may be incorrectly stated and/or improperly correlated with the current stage of works. Our study aims to define which geological problems should be addressed by electromagnetic survey at the different stages of geological exploration, and to specify the requirements to the availability of a priori geological and geophysical information. We have analyzed the electromagnetic data from the regions of East and West Siberia, which have different geological settings. The main geological problems that can be solved by the seismic and electromagnetic techniques are determined. We propose a set of geophysical survey operations, which is optimal for oil and gas exploration. An effective sequence of electromagnetic prospecting stages is determined, and preliminary and accompanying surveys are specified. The requirements to the availability of a priori information are proposed, and its volume is defined. Geological problems are defined with respect to the corresponding stages of geological exploration. Special attention is given to approaches to the mineral resource estimation and calculation of hydrocarbon reserves, taking into account electromagnetic survey results. It is proposed to use the electromagnetic data at the stage of prospecting and appraisal, which aims to assess the resources of categories D l and D 0 , as well as at the exploration stage for estimating the reserves of category C 2 in new and explored fields. Approaches to the economic assessment of using electromagnetic surveys as part of the geological exploration are discussed. Our study shows that a correct sequence of electromagnetic prospecting operations at each stage can ensure obtaining an original geological dataset of the given stage and thus providing a proper basis for the next stage of oil-gas field investigation.

Chaotic diffusion of the fundamental frequencies in the Solar System

The long-term variations in the orbit of the Earth govern the insolation on its surface and hence its climate. The use of the astronomical signal, whose imprint has been recovered in the geological records, has revolutionized the determination of the geological timescales. However, the orbital variations beyond 60 Myr cannot be reliably predicted because of the chaotic dynamics of the planetary orbits in the Solar System. Taking this dynamical uncertainty to account is necessary for a complete astronomical calibration of geological records. Our work addresses this problem with a statistical analysis of 120 000 orbital solutions of the secular model of the Solar System ranging from 500 Myr to 5 Gyr. We obtain the marginal probability density functions of the fundamental secular frequencies using kernel density estimation. The uncertainty of the density estimation is also obtained here in the form of confidence intervals determined by the moving block bootstrap method. The results of the secular model are shown to be in good agreement with those of the direct integrations of a comprehensive model of the Solar System. Application of our work is illustrated on two geological data sets: the Newark-Hartford records and the Libsack core.

A Laurentian cratonic reference from the distal Proterozoic basement of Western Newfoundland using tandem in situ and isotope dilution U-pb zircon and titanite geochronology

The Humber Margin of Newfoundland preserves the most distal exposures of Proterozoic basement in northeastern Laurentia. Age uncertainty has permitted a range of hypotheses for its origin and links to subsequent tectonic events. One hypothesis has proposed large-scale orogen-parallel displacement between basement blocks in western Newfoundland. The apparent absence of Grenville- (∼1250–950 Ma <i>sensu lato</i>) or Taconic-aged (∼480–450 Ma) magmatism or metamorphism on the Corner Brook Lake Block (CBLB), which are defining features of the Humber Margin, has been reconciled by restoring the CBLB to a pre-Taconic position in Labrador with &gt;400 km of post-Taconic dextral motion along the Humber River Fault. To test this model and better define the basement and Paleozoic rifted margin of North America, we conducted a geochronological study of the CBLB and the basement of the adjacent Humber Margin at Indian Head Range using tandem <i>in situ</i> and isotope dilution U-Pb zircon and titanite geochronology. These basement blocks, separated by the Humber River Fault, consist of <i>∼</i>1500 and <i>∼</i>1250 Ma protoliths, 1140 to 1135 Ma magmatism, 1000 to 970 Ma metamorphism, and <i>∼</i>607 Ma intraplate magmatism. These basement blocks are also overlain by similar late Ediacaran to Cambrian siliciclastic successions with similar detrital zircon age spectra. From this set of geological data, we conclude that the Humber River Fault did not accommodate significant orogen-parallel displacement. New basement ages and a revised compilation of detrital zircon ages from overlying rift-related deposits contribute to a geochronologic cratonic reference datum for western Newfoundland9s crystalline basement, whose protolith has a restricted age range from <i>circa</i> 1500 to 950 Ma. New age constraints for metasedimentary rocks are also used to document a 1250 to 1135 Ma succession at Indian Head Range and a ∼1000 Ma succession on the CBLB associated with Grenvillian orogenesis. Protracted late Grenvillian tectono-thermal events are inferred from cores and metamorphic overgrowths of ∼990 to 920 Ma detrital titanite in late Ediacaran conglomerate overlying CBLB basement.

A kinematic reconstruction of Iberia using intracontinental strike‐slip corridors

AbstractDespite considerable progress in restoring rifted margins, none of the current kinematic models can restore the Mesozoic motion of the Iberian block in full agreement with the circum‐Iberian geology. This conflict requires a revision of the kinematic description at the onset of divergence. The circum‐Iberian region has a unique geological dataset that allows calibration and testing of kinematic reconstructions and therefore it is an ideal candidate for testing intracontinental restoration approaches. Here we define intracontinental deforming regions, referred to as strike‐slip corridors, based on alignments of Mesozoic rift basins and/or transfer zones bordering rigid continental blocks. We use these strike‐slip corridors and data from the southern N‐Atlantic and Tethys to define the motion path of the Flemish Cap, Ebro and Iberia continental blocks. The resulting Mesozoic kinematic model for the Iberian block is compatible with recently published data and interpretations describing the Mesozoic circum‐Iberian geology. Large‐scale intracontinental strike‐slip corridors may offer a valid boundary condition for reconstructing continental block motion at the onset of divergence in intracontinental settings.

Integrated reservoir, geology, and production data for reservoir damage analysis: A case study of the Miocene sandstone reservoir, Gulf of Suez, Egypt

Reservoir damage is considered one of the major challenges in the oil and gas industry. Many studies have been conducted to understand formation damage mechanisms in borehole wells, but few studies have been conducted to analyze the data to detect the source, causes, and mitigations for each well where damage has occurred. I have investigated and quantified the reasons and mitigation of reservoir damage problems in the middle Miocene reservoir within the El Morgan oil field at the southern central Gulf of Suez, Egypt. I used integrated production, reservoir, and geologic data sets and their history during different operations to assess the reservoir damage in El Morgan-XX well. The collected data include the reservoir rock type, fluid, production, core analysis, rock mineralogy, geology, water chemistry, drilling fluids, perforations depth intervals, workover operations, and stimulation history. The integration of different sets of data gave a robust analysis of reservoir damage causes and helps to suggest suitable remediation. Based on these results, I conclude the following: (1) Workover fluid has been confirmed as the primary damage source, (2) the reservoir damage mechanisms could be generated by multisources including solids and filtrate invasions, fluid/rock interaction (deflocculating of kaolinite clay), water blockage, salinity chock, and the high sulfate content of the invaded fluid, and (3) multidata integration leads to appropriate reservoir damage analysis and effective design of the stimulation treatment. Furthermore, minimizing fluid invasion into the reservoir section by managing the overbalance during drilling and workover operations could be very helpful. Fluid types and solids should be considered when designing the stimulation treatment and compatibility tests should be performed. Long periods of completion fluid in boreholes are not recommended, particularly if the completion fluid pressure and reservoir pressure are out of balance, as well as the presence of sensitive formation minerals.

Inference of the spatio-temporal variability and storage potential of groundwater in data-deficient regions through groundwater models and inversion of impact factors on groundwater, as exemplified by the Lake Victoria Basin

Groundwater is an important resource for supporting domestic water use for people's livelihoods and for maintaining ecosystems. Borehole observations provide the first-hand data that characterise the fluctuation, depth, and aquifer conditions of the groundwater. Unfortunately, such observations are not available or are insufficient for scientific use in many regions. Taking the Lake Victoria Basin (LVB) as an example of data-deficient regions, this study proposes a simple knowledge-based approach that uses the Global Land Data Assimilation System (GLDAS) Catchment Land Surface Model (CLSM) for the main data, with rainfall, hydrological, topographical and geological datasets as supports, by which to infer the spatio-temporal variability and storage potential of groundwater. The method is based on analysis and inversion of impact factors on groundwater, and the feasibility of such a method is proven by showing that the groundwater results from GLDAS CLSM can correctly indicate the seasonality, as well as the link to topographical and geological features. For example, both results from the water balance equation (WBE) and GLDAS CLSM indicate that there are two groundwater recharge seasons in the basin, e.g., March to May and September to November. Compared to the eastern side of the LVB, the western side has mountains blocking surface runoff, and thus, reasonably, has larger storage potential estimates in GLDAS CLSM. Due to the low degree of weathering of the basement rocks, it is expected that there is only small storage potential and variation of groundwater in the southeastern parts of the LVB. GLDAS CLSM also correctly reflects this behaviour. Additionally, the largest groundwater storage potential over the LVB is found in regions near the Kagera River and the western shoreline, since it associates with unconsolidated rocks and behaviours of large groundwater recharge from GLDAS CSLM during the wet year of 2006. The major limitation of this knowledge-based method is that the uncertainty in terms of magnitude on GLDAS CLSM groundwater changes cannot be assessed, in addition to the fact that the reliability of the results cannot be quantified in terms of specific numbers. Therefore, the results and interpretation of groundwater behaviours using such methods can only be a guide for ‘where’ and ‘when’ to find groundwater.

Gilsonite Mineral Potential of Gilan-e Gharb to Qasr-e Shirin using FAHP-FTOPSIS Prediction Model

Gilan-e Gharb region has been located in the west of Iran and it has special features in terms of geology. Remote sensing data (satellite images), geology, tectonics and mineral data sets of the region were used to prepare an innovative integrated algorithm for the exploration of Gilsonite mineral. Effective criteria and sub-criteria in the exploration of this mineral were identified and evaluated according to the available exploration data. These criteria were weighted using analytical fuzzy hierarchical process and finally, using the method most similar to the ideal positive and negative solution were ranked in fuzzy environment to prepare a mineral potential map of Gilsonite in Gilan-e Gharb region. Accordingly, a potential map was produced using a combination of the above methods for optimal identification in the early stages of exploration of this valuable mineral to reduce the time, cost, and risk of exploration. Finally, field visit and investigation has been accomplished for the regions with a high potential of Gilsonite mineralization to evaluate the method. The results showed that 82% of the identified points have proper adjustment to the MPM. This high adaptation showed that the method is of good performance for use in Gilsonite exploration.

Latest Mesoproterozoic provenance shift in the southwestern Yangtze Block, South China: Insights into tectonic evolution in the context of the supercontinent cycle

The Huili Group, one of the most representative late Mesoproterozoic strata in the Yangtze Block, bears key information for the tectonic history of the South China Block in the context of the supercontinent cycle. We present an integrated dataset involving field observation, petrology, detrital zircon U-Pb dating, and Hf isotope analyses for the Huili Group. Our new detrital zircon U-Pb ages, in combination with available magmatic age data, confirm that the Huili Group was mainly deposited at ca. 1.1–1.0 Ga. The lower Huili Group is characterized by subrounded to rounded detrital zircon grains with age intervals of 2.80–2.40 Ga (~21%), 2.34–1.72 Ga (~64%), and 1.68–1.19 Ga (~14%). In contrast, zircon grains from the upper Huili Group have variable morphologies and yield two pronounced age populations of 2.00–1.25 Ga (~50%; subrounded to rounded grains) and 1.2–1.0 Ga (~46%; euhedral to subhedral grains). The majority of zircon grains have εHf(t) values and depleted mantle two-stage (TDM2) model ages comparable to those of magmatic rocks or older sediments in the Yangtze Block. Multiple sources are suggested to have contributed older detrital zircon grains to the lower Huili Group, whereas the upper part received greater proportions of zircon grains with ages close to or equal to the depositional age from proximal magmatic sources. This observation indicates a drastic provenance shift most likely occurred within the Huili Group at ~1.04 Ga. Through reappraising our detrital zircon results and available geological datasets, we suggest that the terrigenous clastic and carbonate rocks of the lower-middle Huili Group were deposited on a passive continental margin, but the upper volcano-sedimentary sequences were formed in a back-arc extensional setting. We further propose that the Yangtze Block was spatially separated from (i.e., not yet part of) the Rodinia supercontinent during the sedimentation of the Huili Group, supporting that a global supercontinent did not exist yet in the late Mesoproterozoic.

Determining highway slope ratio using a method based on slope angle calculation

Geographic Information System (GIS) is a vital tool used in numerous areas related to natural science and engineering studies. Managing complex data and obtaining accurate results from the analysis are essential functions of GIS. It is also efficiently used in highway designing both in project and application phases. This study proposes a new calculation method of slope angles to determine the suitable slope modal of a road by using topographic and geological datasets in a GIS environment. Using this method in the preparation phase of the project enables a more accurate calculation of earthwork volume. The proposed method was applied to a highway to prove this idea. The selected road is a significant tertiary of which project was completed by the Turkish General Directorate of Highways. In this study, the calculated values of the project were considered as references. Comparing both results obtained from the proposed method and application project, the accuracy of the slope modal of the proposed method is 71%, and the accuracy of its earthwork volume is 99%. The proposed approach will enable project managers and designers to determine more reliable earthwork volume during project feasibility studies without any application in the field.