Improved lithology prediction in channelized reservoirs by integrating stratigraphic forward modelling: towards improved model calibration in a case study of the Holocene Rhine-Meuse fluvio-deltaic system.

Stratigraphic forward modelling (SFM) provide the means to produce geologically coherent and realistic models. In this paper, we demonstrate the possibility of matching lithological variability simulated with a basin-scale advection-diffusion SFM to a data-rich real-world setting, i.e. the Holocene Rhine-Meuse fluvio-deltaic system in the Netherlands. SFM model calibration to real-world data in general has proven non-trivial. This study focuses on a novel inversion process constrained by the top surface and the sand proportion observed at specific pseudo-wells in the study area. Goodness-of-fit expressed by a new fitness function, gives the error calculated as the average of two calibration constraints. Computational efficiency was increased significantly by implementing a new optimization process in two hierarchical steps: a) optimization in terms of sediment load and discharge, which are the most influential parameters having the largest uncertainty and b) optimization with respect to the remaining uncertain parameters, these being sediment transport parameters. The calibration process described allows for the most optimal combination of achieving acceptable levels of goodness-of-fit, feasible runtimes and multiple (non-unique) solutions to obtain synthetic stratigraphic output best matching real-world datasets. By removing model realizations which are geologically unrealistic, calibrated SFM models provide a multiscale stratigraphic framework for reconstructing static models of reservoirs which are consistent with the palaeogeographic layout, basin-fill history and external drivers (e.g. sea level, sediment supply). The static reservoir models that are matched with highest certainty therefore contain the highest geological realism and may be used to improve deep subsurface reservoir or aquifer property prediction. The new methodology was applied to the well-established Holocene Rhine-Meuse dataset which allows a rigorous testing of the optimization and the calibrated SFM allows investigation of controls of the Holocene development on the sedimentary system

A geo-cellular model of a multiphase hydrocarbon field incorporating fault-seal analysis : Bredasdorp Basin, South Africa

Geological 3D static modelling has become an integral tool during the appraisal and developmental stages of a hydrocarbon field lifecycle. The 3D model becomes the basis upon which reservoir heterogeneity and characterisation are understood, hydrocarbon volumetrics are calculated and field development plans are designed. Reservoir compartmentalisation and fault-seal analysis is also an industry topic which has drawn much interest. Having a 3D model allows for fault-seal analyses to be carried out and evaluated using the statistically distributed reservoir properties. This study incorporates the building of a 3D geo-cellular reservoir model with a fault seal analysis of the E-S field, which is located on the north flank of the Bredasdorp Basin. The reservoir model was built using geostatistical methods to populate the several reservoir parameters into the model to calculate a hydrocarbon volume. In addition, a fault-seal analysis was carried out in order to investigate the phenomenon of having an oil accumulation separated from a gas accumulation either side of a fault. The facies modelling was carried out using the object modelling technique, in order to produce a model which is geologically plausible. Most of the remaining reservoir parameters were modelled using a variogram except in the case of water saturation, which was modelled using a J function equation. The volumetrics were assigned per fault block. Using a recovery factor of 75% for gas and 11% for oil, the calculated total recoverable hydrocarbons were 12.6 Bscf and 1.3 MMbbl respectively. The fault-seal analysis showed that the faults separating two of the fault blocks are not completely sealing. All the calculated fault properties supported this view, with the Shale Gouge Ratio (SGR) and threshold pressure relationship indicating a high likelihood for leakage across parts the faults. Pressure data from Repeat Formation Tests (RFT) however, indicates that the hydrocarbon accumulations in both blocks are isolated from each other. This contradiction has informed the recommendation to drill a highly deviated or short horizontal well which will cross the fault and intersect both blocks, and to complete the well using a sliding sleeve, thus providing the flexibility needed in order to manage multi-phase flow

Models for managing the deep aquifer in Bangladesh

In southern Bangladesh excessive levels of As in shallow groundwater have led to deeper groundwater becoming the main alternative source of As-free potable water. Hydrogeological configuration indicates that tube-wells pumping from these depths may be vulnerable to As breakthrough from shallow levels. The thesis explores a range of methods of representing lithological heterogeneity of the Bengal Aquifer System (BAS) in models of groundwater flow and travel time. The aim is to support models of arsenic (As) flux to the deep groundwater flow-system of BAS, and hence to aid assessment of the vulnerability of deep groundwater to invasion by As. The research uses an array of geological information including geophysical logs (n=12), hydrocarbon exploration data (n=11), and drillers' logs (n=589) from a 5000 km2 area to characterise the aquifer heterogeneity as a basis for alternative representations of hydrogeological structure in groundwater flow modelling. Groundwater samples from southern Bangladesh were analysed for 14C in order to determine groundwater age (n=23) and for hydrochemical (n=75) and isotopic (n=50) characterisation. A new hypothesis `SiHA (Silt-clay layers influence Hierarchical groundwater flow systems and Arsenic progression in aquifer)' is presented which integrates sedimentological heterogeneities, groundwater flow, and geochemical processes to explain the distribution and geological evolution of groundwater As in the aquifer. The hypothesis explains the spatio-vertical variability of groundwater As concentration by 'groundwater flow systems and differential flushing' in the aquifer. Groundwater flow models based on eight different yet plausible aquifer representations provide adequate simulations of hydraulic head, but contrasting implications for well catchments and travel times. The better representations are judged by comparing model outcomes of travel time with groundwater age determination using 14C. Comparisons demonstrate the importance of incorporating hydrostratigraphy and spatial heterogeneity in order to optimise model representations, and implications for the security of As-free deep groundwater in the BAS

A new perspective to model subsurface stratigraphy in alluvial hydrogeological basins, introducing geological hierarchy and relative chronology

This paper presents a novel perspective for modelling alluvial stratigraphy. It integrates the spatial geological information, geological maps and well-log descriptions, with the rules describing the hierarchy and relative chronology of the geological entities. As geological modelling tools are moving fast forward, the urgent need for expert geological input, codified as modelling rules, persists. Concerning subsurface alluvial architectures, the concepts of \u201cstratigraphic hierarchy\u201d and \u201crelative chronology\u201d provide the most relevant rules which permit to link the modelling procedure to the geo-history of a region. The paper shows how to formalize this knowledge into modelling rules. This is illustrated and implemented in a Python\u2122 module named HIEGEO which is applied on a 2-D cross-section from the Po Basin (N-Italy). The stratigraphic correlation yields 2-D pictures of the hierarchic stratigraphy and relative chronology of the units. The input are: an attribute table of stratigraphic boundaries expressing their hierarchy and chronology; contact points where these boundaries cross the control logs. Since the aim of HIEGEO is to illustrate the principle of the method but not to replace existing 3-D geological modelling tools, it implements a linear interpolation algorithm which creates joins between contact points. It plots linear joins framing polygons based on their hierarchy, at any user\u2019s desired detail. HIEGEO highlights potential inconsistencies of the input dataset, helping to re-evaluate the geological interpretation. The proposed workflow allows to: i) translate geological knowledge into modelling rules; ii) compute stratigraphic models constrained by the hierarchy of stratigraphic entities and the relative chronology of geological events; iii) represent internal geometries of the stratigraphic units, accounting for their composite nature; iv) reduce uncertainty in modelling alluvial architectures. It represents a starting point for multi-scale applications and could be easily integrated into 3-D modelling packages, to couple the hierarchical concept proposed here with existing advanced interpolation methods

The Late Quaternary Evolution of the Southern Vietnamese Continental Shelf

The late Pleistocene-Holocene sedimentary architecture on two different geological setting areas on the Southern Vietnam Shelf has been investigated on the basis of shallow seismic data, sediment core data, sequence stratigraphic concepts and numerical modeling. The late Pleistocene-Holocene sequence stratigraphic models of the SE Vietnam and Nha Trang Shelf show distinctive features which result from the differences in sediment supply regime, shelf morphology and hydrodynamic conditions between the two areas. Sedimentation on the Nha Trang Shelf from the end of the LGM to present has been investigated on the basis of process-based numerical modeling simulations. The results indicate that the sediment supply during TST period (19.6-8.0 ky BP) is 3 to 4 times higher than that of HST period (8.0-0 ky BP). During HST and TST period, 50-80 % of total supplied sediment was contributed by three local river basins (Cai, Dinh and Van Phong) and the rest was transported alongshore from the north

Reconciling sedimentology and numerical modelling to investigate tectonically-driven deposition and landscape evolution within upland incised valleys: the Pliocene - Pleistocene ambra valley-fill (Tuscany, Italy)

Sedimentation in the upstream reaches of incised valleys is predominantly fluvial and mostly out from any relative sea level fluctuations. Here, the dynamics of facies distribution respond to an interaction of tectonics and climate. Tectonics can directly influence fluvial aggradation and degradation through local changes in gradient, both longitudinal and transverse to the valley slope. This paper deals with a –Pliocene – Pleistocene fluvial valley fill developed in the northeastern shoulder of the Siena Basin (Northern Apennines, Italy). Valley fill aggradation resulted from the interaction of autogenic dynamics and extensional tectonics manifested by normal and oblique-slip faults parallel and near orthogonal to the valley axis, which generated rises of local fluvial base level. This thesis coupled a classical field approach, which aims at analysing the interaction between longitudinal and lateral alluvial plain tectonic tilting and fluvial sedimentation, and numerical modelling, which focuses on the temporal and spatial validation of tectonic forcing on the studied valley fill and on the effects of uplift rate on variable-discharge systems. Longitudinal tilting was generated by a transverse, upstream-dipping normal fault that controlled aggradation of fining-upward strata-sets both upstream and downstream of the fault zone. Aggradation in the upstream sector occurred as a backfilling process and predated that in the downstream one, where sediment was stored as a downfilling. Lateral tilting, spacing out the aggradations, was governed by the interaction between fault-generated subsidence and the topographic confinement of progradational, flank-sourced alluvial fans. Both longitudinal and lateral tilting anomalies are easily recorded in sedimentary succession generated by high-discharge system disturbed by high uplift rates

Visual Techniques for Geological Fieldwork Using Mobile Devices

Visual techniques in general and 3D visualisation in particular have seen considerable adoption within the last 30 years in the geosciences and geology. Techniques such as volume visualisation, for analysing subsurface processes, and photo-coloured LiDAR point-based rendering, to digitally explore rock exposures at the earth’s surface, were applied within geology as one of the first adopting branches of science. A large amount of digital, geological surface- and volume data is nowadays available to desktop-based workflows for geological applications such as hydrocarbon reservoir exploration, groundwater modelling, CO2 sequestration and, in the future, geothermal energy planning. On the other hand, the analysis and data collection during fieldwork has yet to embrace this ”digital revolution”: sedimentary logs, geological maps and stratigraphic sketches are still captured in each geologist’s individual fieldbook, and physical rocks samples are still transported to the lab for subsequent analysis. Is this still necessary, or are there extended digital means of data collection and exploration in the field ? Are modern digital interpretation techniques accurate and intuitive enough to relevantly support fieldwork in geology and other geoscience disciplines ? This dissertation aims to address these questions and, by doing so, close the technological gap between geological fieldwork and office workflows in geology. The emergence of mobile devices and their vast array of physical sensors, combined with touch-based user interfaces, high-resolution screens and digital cameras provide a possible digital platform that can be used by field geologists. Their ubiquitous availability increases the chances to adopt digital workflows in the field without additional, expensive equipment. The use of 3D data on mobile devices in the field is furthered by the availability of 3D digital outcrop models and the increasing ease of their acquisition. This dissertation assesses the prospects of adopting 3D visual techniques and mobile devices within field geology. The research of this dissertation uses previously acquired and processed digital outcrop models in the form of textured surfaces from optical remote sensing and photogrammetry. The scientific papers in this thesis present visual techniques and algorithms to map outcrop photographs in the field directly onto the surface models. Automatic mapping allows the projection of photo interpretations of stratigraphy and sedimentary facies on the 3D textured surface while providing the domain expert with simple-touse, intuitive tools for the photo interpretation itself. The developed visual approach, combining insight from all across the computer sciences dealing with visual information, merits into the mobile device Geological Registration and Interpretation Toolset (GRIT) app, which is assessed on an outcrop analogue study of the Saltwick Formation exposed at Whitby, North Yorkshire, UK. Although being applicable to a diversity of study scenarios within petroleum geology and the geosciences, the particular target application of the visual techniques is to easily provide field-based outcrop interpretations for subsequent construction of training images for multiple point statistics reservoir modelling, as envisaged within the VOM2MPS project. Despite the success and applicability of the visual approach, numerous drawbacks and probable future extensions are discussed in the thesis based on the conducted studies. Apart from elaborating on more obvious limitations originating from the use of mobile devices and their limited computing capabilities and sensor accuracies, a major contribution of this thesis is the careful analysis of conceptual drawbacks of established procedures in modelling, representing, constructing and disseminating the available surface geometry. A more mathematically-accurate geometric description of the underlying algebraic surfaces yields improvements and future applications unaddressed within the literature of geology and the computational geosciences to this date. Also, future extensions to the visual techniques proposed in this thesis allow for expanded analysis, 3D exploration and improved geological subsurface modelling in general.publishedVersio