A 3D Multi-scale geology modeling method for tunnel engineering risk assessment

Section-constrained local geological interface dynamic updating method based on the HRBF surface

This paper reports an application of uncertainty visualisation of a regional scale (1:50 000) 3D geological geometry model to be involved in GIS-based 3D mineral potential assessment of the Xiangxibei lead-zinc mineral concentration area in northwestern Hunan District, China. Three-dimensional (3D) geological modelling is a process of interpretation that combines a set of input measurements in geometry. Today, technology has become a necessary part of GIS-based deep prospecting. However, issues of sparse data and imperfect understanding exist in the process so that there are several uncertainties in 3D geological modelling. And these uncertainties are inevitably transmitted into the post-processing applications, such as model-based mineral resource assessment. Thus, in this paper, first, a big-data-based method was used to estimate the uncertainty of a 3D geological model; second, a group of expectations of geological geometry uncertainty were calculated and integrated into ore-bearing stratoisohypse modelling, which is one of the major favourable parameters of assessment for Lead-Zinc (Pb-Zn) deep prospectivity mapping in northwestern Hunan; and finally, prospecting targets were improved.

Combining the requirements for refined modeling and dynamic update of fault slope geological models in open-pit coal mines, we systematically elaborated on the elements and rules of slope 3D geological modeling and proposed a fine modeling and dynamic updating method based on digital elevation model (DEM) and half-edge boundary representation (B-Rep) data structures. Initially, the stratigraphic division of the study area is conducted based on borehole and section data, combined with the geological evolution history and the level set theory. Applying inverse distance weighting (IDW) for estimation, the geological interface triangular irregular network (TIN) is constructed using the TIN algorithm. Secondly, fine reconstruction of fault surfaces through Morphing transformation improves the accuracy and smoothness of fault surface shape reconstruction under sparse data conditions. Then, the intersection-cutting processing method of fault-fault and fault-stratum for slope geological ground state model modeling under complex fault segmentation is investigated. Finally, constructing 3D geological models of fault slopes and the integrated correction of surface and subsurface are realized through dynamic updating methods for 3D surfaces and strata. Taking the 3D geological modeling of a fault slope of an open-pit coal mine in China as an example, the feasibility of the technical method is verified.

We review five deformation models generated for the 2023 update to the U.S. National Seismic Hazard Model (NSHM), which provide input fault-slip rates that drive the rate of earthquake moment release. Four of the deformation models use the Global Positioning System-derived surface velocity field and geologic slip-rate data to derive slip-rate estimates (Evans, Pollitz, Shen-Bird, and Zeng), and one model uses geologic data (the “geologic model”). The correlation between the geologic model preferred slip rates and geodetically derived slip rates is high for the Pollitz, Zeng, and Shen-Bird models, and the median of all slip-rate models has correlation coefficient of 0.88. The median geodetic model slip rates are systematically lower than the preferred geologic model rates for faults with slip rates exceeding 10 mm/yr and systematically higher on faults with slip rates less than 0.1 mm/yr. Geodetically derived slip rates tend to the low end of the geologic model range along sections of the San Andreas fault and the Garlock fault, whereas they tend to be higher across north coast California faults. The total on-fault moment rates agree well across models with all rates within 18% of the median. Estimated off-fault strain rate orientations and styles vary considerably across models and off-fault moment rates vary more than on-fault moment rates. Path integrals across the western U.S. accounting for fault-slip rate and off-fault deformation are generally consistent with Pacific-North America plate motion with the median deformation rates recovering about 98% of the plate motion with about 20% of the total plate motion accommodated by off-fault strain rate. The geologic model, which has no off-fault deformation, accounts for about 82% of plate motion with fault slip. Finally, we make a recommendation for relative weighting of the models for the NSHM as well as several recommendations for future NSHM deformation model development.

A three-dimensional (3D) geological model of known and potential aquifers as well as enclosing materials in the Fargo-Moorhead region of North Dakota and Minnesota was required for a current water supply assessment coordinated by U.S. Department of the Interior, Bureau of Reclamation and their partners. A multi-agency team funded by Reclamation therefore compiled, interpreted, and integrated existing geologic mapping at a scale of 1:200,000 for an area (Figure 1) extending from 46 to 47.5 degrees north latitude and from 98 to 95 degrees west longitude, an area 190 km east to west and 170 km north to south. These maps were merged with drillhole data (Figure 2) for 30,000 sites, 60 Quaternary stratigraphic control sites, and new subsurface correlations to produce a 3D geological model extending down to the top of Precambrian rocks, compiled at a scale comparable to that of a 1:500,000 map. This new 3D geology and an accompanying USGS compilation of the quantitative properties of selected major aquifers will provide the framework necessary to conduct subsequent water resource analyses. To construct the 3D geology, drillhole cross-sections were constructed using ArcView 3.3, ArcGIS 9.0, and custom extensions. Thirty-four regional cross sections were constructed at 5 km spacing. Drillhole logs and surficial geology were displayed along the locus of each cross section to facilitate correlation. Four smaller areas encompassing important aquifers, ranging from 1,300 to 3,200 square km in area, were chosen for more detailed analysis. East-west cross sections were constructed in these areas using 0.5 to 3 km spacing. Creating these cross sections in ArcView allowed sand and till boundaries to be correlated by overlaying shapefiles in the same view window. A series of points for each stratum were extracted from the cross-section shapefile lines and converted into X, Y, & Z values. These points as well as cross-sections scanned and registered in 3D space were then used as the basis for construction of surfaces and volumes in GOcad software (Figure 3). Modeled strata were constructed for a total of 36 lithostratigraphic units (Figure 4), including Quaternary sediments as well as Cretaceous, Ordovician and Precambrian rocks, and these are now being prepared for further application to regional groundwater inventory, to help ensure long-term water supply for the region.

Explicit-implicit-integrated 3-D geological modelling approach: A case study of the Xianyan Demolition Volcano (Fujian, China)

Three-dimensional geological modelling and multivariate statistical analysis of water chemistry data to analyse and visualise aquifer structure and groundwater composition in the Wairau Plain, Marlborough District, New Zealand

Realistic geological modeling can be considered as the first objective in a reservoir characterization workflow. This term describes the process of building static 3-D reservoir models based on available a priori information, geological interpretations and quantitative geological, seismic, and production data. The definition of the best “realistic geological model” to be produced has to be discussed depending on the target objective: to produce a simulation which honors at best the geological parameters and the seismic derived constraints or to produce a simulation which will fit at best the production data. The incorporation of seismic information is a crucial element in reservoir geological modeling. Many recent research works have focused on the introduction in probabilistic models of secondary data characterized by a relationship, often indirect, with the reservoir properties. Due to the different scales of resolution between seismic and geology and to the complex relationship between rock properties and seismic response, a logical process can be to firstly extract geological properties from seismic data and second to constrain the facies simulation using these properties. The extraction of soft geological information from seismic data relies on statistical calibration with well data. Mainly two approaches can be used, either based on supervised segmentation or on estimation techniques. The obtained information consists in variables correlated with the facies distribution. Depending on the available information the variables can be related to the total thickness of the studied stratigraphic unit (leading to 2D constraints as maps) or to small volumes inside the unit (3D constraints). IFP-CG (Institut francais du petrole - Centre de Geostatistique of the Ecole des Mines) have developed an innovative methodology to generate facies proportions grids from well data, sedimentological conceptual models (maps and zonations), and constrained with seismic derived information. The objective of this paper is to present an analysis and evaluation of the real impact of these seismic derived constraints on the reservoir geological model in terms of quantification of uncertainties, heterogeneities distribution, and key geological characteristics. In the geomodelisation workflow, this work takes place when the structural framework of the reservoir is determined and also when the geological conceptual model is defined in terms of interpretation, environment, and layering. Its purpose is to investigate possible variations in parameterization of the scenarios of filling the space with geological properties. Using a real data case, different constraints and different methods of seismic integration are compared. Their impact of seismic in the framework of the truncated gaussian methodology and compared to the impact of the uncertainty on geological data.

Recently, implicit model building techniques have been developed which use, for example, geo-statistical methods to interpolate boundary orientations as a scalar field. Boundaries are implicitly formulated as iso-values of that field. Using more than one potential allows modelling for intrusion and unconformities. This technique is attractive because it makes 3D geological modeling a repeatable task and model uncertainty can be estimated from the geostatistical estimators. However, this uncertainty does not take into account the error on field measurements, nor estimates of how relevant are the measurements to the modelled structures. Lastly, this uncertainty does not take into account possible variation in the knowledge based information which is very often interpretative, such as structural evolution history, fault network, and overprinting relationships with themselves and the different formations. We present an innovative method that will simulate numerous (millions of) geological models from a single initial structural dataset, taking into account these variables. These models are used to estimate geological uncertainty, highlighting future areas of research or data collection. A series of best models are then assessed against potential field inversions and modified to better fit potential field data. In the end, the models that both better fit geological input data and potential field data will be retained. A best probable model will be proposed that will satisfy geophysical data as well as geological data. To assess the models against the initial geological data input, we develop geological objective functions based on (e.g.) locations and gradients of boundaries. It is our intent to combine these objectives functions with classical geophysical objective functions to provide a new method for combined geological and potential field inversions.

<p>The utilization of geothermal reservoirs as alternative energy source is becoming increasingly important worldwide. Details of rock properties, structures, heat transfer and resulting interactions are the basis for the implementation of a sustainable reservoir management, but are often not well enough understood. The investigated warm water reservoir in Waiwera, New Zealand, has been known for many centuries. Triggered by overproduction in the third quarter of the 20th century, the reservoir pressure dropped significantly and in the 1970s the natural seeps on the beach dried up [1]. However, the shutdown of the main user's pumps (Waiwera Thermal Pools) in 2018 led to renewed temporary and location-specific artesian activity. The question now is whether the seeps on the beach will also reappear?</p><p>Hydrogeological models are the basis for a sustainable management of groundwater resources. The key point for the Waiwera reservoir is the amount of geothermal water which is permanently available. However, models are also used to describe the current hydraulic and thermal situation of the study area [2].</p><p>An expedition was carried out in 2019 to investigate the artesian activity of the reservoir, which has been observed again since 2018, and to build a new geological model. For the first time, thermal cameras carried by unmanned aerial systems (UAS) show the emergence of warm water at the beach and photogrammetric analyses carried out allow structural and lithological mapping on exposed cliffs where localized thermal anomalies were identified for the first time. The Waitemata formation found there is considered as analogue of the reservoir rock and thus serves for an improved understanding of the subsurface reservoir properties. The analyses show individual water and heat conducting lithologies and thus provide details about geological units that also constitute the geothermal reservoir at depth.</p><p>Based on the field exploration and the associated structural interpretations, a geological and thermal 3D model is now available for the first time, which will be employed to improve calibration of the hydraulic conditions of the warm water reservoir. Further, the model will be applied in the context of a sustainable reservoir management to clarify the question about the natural seeps on the beach. The reappearance of artesian activity in the Waiwera area due to significant adaptation of production rates is unique but the improved understanding of the interaction between rock properties, existing structures and heat transfer will also enable other reservoirs to be better understood.</p><p>[1] Kühn M., Stöfen H. (2005) A reactive flow model of the geothermal reservoir Waiwera, New Zealand. Hydrogeology Journal 13, 606-626</p><p>[2] Kühn M., Altmannsberger C., Hens C. (2016) Waiwera’s warm water reservoir – What is the significance of models? Grundwasser 21, 107-117</p>

The concept of a geoinformation system for urban geoenvironment is concerned. Geological data is necessary for the sustainable development of city infrastructure. The municipal departments should use geological and environmental information for perspective planning, selecting the location for important infrastructure objects, solving ecologycal problems, and in decision making. The concept includes a preliminary list of system’s users, their informational needs, main functionalities, methodical approaches to the system design and development. Geological data must contain source documents from geological archives “as is” and geodata based on its interpretation for various tasks. These data must be checked carefully and updated with new engineering-geological investigations. Geoinformation system must integrate various geological, engineering-geological, hydrogeological, and environmental data. Sophisticated procedures must be provided to check complicated logical dependences in the system database and to analyze contradictions between source documents. 3D modeling is an adequate language for presenting geological data, therefore, the considered system must include 3D models of various scales. In the suggested concept 3D modeling is considered as a tool for investigations, not only for presentations. The end users should have possibilities to get results of their queries in various formats: tables, geological and thematic maps, geological cross-sections, 2D and 3D grids as source data for mathematical modeling, etc. In conclusion, the paper briefly describes IEG RAS activities in GIS technologies for geological cartography and 3D modeling.

Statics fluctuations in surface seismic data result from variations in the near surface, and, therefore, it is important to understand the effect that topography and lithology have on the propagation of seismic waves in the near surface. The approach presented here introduces geomorphologic near-surface characterization from remote-sensing data and shows how topographic and lithologic classification allow the generation of a 3D near-surface geologic model. Using standardized elastic properties for the rock types identified in the classification step, the 3D geologic model can be converted into a 3D elastic model. Statics are estimated assuming vertical propagation of the seismic waves through the layers of the elastic model.

Dynamic simulation and history matching at Ketzin (CO2SINK)

Fully 3D and multidimensional geological models are key for energy, mining and water resources assessment and management, which has a great economic impact. 3D geological models provide critical information regarding geometric properties of the geological bodies of interest, such as ore deposits or reservoirs, allowing inference of volumes and availability to be exploited. However, defining a useful methodology to create a fully digital 3D geological model of volcanic islands is still very challenging due to the intrinsic complexity observed in the structure of volcanic systems. Two-dimensional geological maps, associated vertical geological cross-sectional diagrams and borehole and water-mining tunnels (galleries) logs were examined on El Hierro Island. A geological modelling procedure using the software GeoModeller obtained the first 3D geological model of El Hierro volcanic island, as a basis for volcanic formation definitions and geometric analysis. Surface, volume and center of mass estimations of the differentiated sub-units allowed a better understanding of the spatial distribution and evolution of the volcanic cycles of El Hierro Island over time. The 3D model provided geometry information correlatable with volcanic activity cycles and lava/pyroclast deposition mechanisms that ultimately defines the geometry of the volcanic units. This information provides new variables valuable for the investigation of the existing relationships between rift zones and giant lateral collapses. In addition, the obtained 3D geological model of a volcanic island will support the building of the first hydrogeological and geothermal model of El Hierro Island, allowing advancement of sustainability of isolated systems.

The main objective of this study was to describe the nature, distribution, and physical characteristics of the reservoir, by integrating geophysical, geological, petrophysical, and production data in a three dimensional geological and simulation model that represents the behavior of the Hollin reservoir in Bermejo field. The Hollin reservoir required significantly higher effort due to the strong aquifer, the complex relationship between heterogeneity influences, the movement of the water from the aquifer into the reservoir, water and gas conning, stagnation of unproduced oil zones, and migration of oil towards gas zones. When production data was analyzed, it was determined that even thin shales (on the order of 2-5 ft. or greater) played a role in enhancing reservoir production by delaying water and gas conning and water influx in the Hollin fluvial sandstone. Mapping the shale barriers was as important as mapping the sand bodies. It was decided to correlate the shales interpreted from well log data and introduce shale tops and bases in the geological model. Therefore, in the geological and simulation models shales have been modeled explicitly, down to a five foot resolution. A Stratigraphic geocellular model was constructed to describe the 3D petrophysical properties, calculate hydrocarbons in place and to prepare reservoir simulation grids. Geological models incorporating shales were modeled. If shale was locally absent, the "shale zone" was assigned the appropriate reservoir properties determined from well and/or seismically derived attributes. J-Function analysis was implemented successfully in assigning oil saturation. Calculated oil saturation profiles at initial and current times were compared with initial well log oil saturations. History matching and initialization were conducted to validate geological, petrophysical, PVT, and reservoir models. Flooded and non-flooded regions of reservoir, current WOC and GOC were identified. Areal extent of localized thin shale lenses were modified during history, matching active water breakthrough well by well. The amount of oil invasion in the original gas zone, stagnated oil, and gas contraction volumes were calculated in the most productive marker, Naranja. Current GOC has moved from the original GOC position. Actually, the amount of oil invasion was not significant when it was compared to the volume of stagnated oil. When geological and simulation models are built and data gathered according reservoir specific problems, successful history matching and predictions can be obtained.