Conference Agenda

In this study, we investigate CO₂-foam injection as a promising technology to increase the security of CO₂ sequestration process. To evaluate the performance of CO₂-foams in saline aquifers, the Delft Advanced Research Terra Simulator (DARTS) is used to predict CO₂-foam dynamic behavior. A consistent thermodynamic model has been implemented in DARTS to describe the phase-behavior of the CO₂-brine system with impurities. This phase-behavior module is combined with representation of foams by an implicit-texture (IT) model. An Operator-Based Linearization (OBL) approach is utilized for fully implicit approximation. The OBL approach reduces the nonlinearity of the physical problem by transforming the discretized nonlinear conservation equations into a quasi-linear form based on state-dependent operators. In our work, a small 2D domain with the presence of a capillary transition zone (CTZ) is used to investigate the effect of capillarity on the CO₂ dissolution rate at different thermodynamic conditions. Then we use a 3D unstructured reservoir to examine CO₂-foams behavior and its effects on CO₂ storage. The results show that foam-assisted CO₂ injection can reduce gas mobility effectively by trapping gas bubbles and inhibit CO₂ from buoyancy-driven migration upward, thus enhancing storage efficiency. At the same time, the CO₂ convective dissolution trapping enhanced by the presence of a CTZ is more limited in the CO₂-foam scenario comparing to pure CO₂ injection. The results of our investigation suggest that CO₂-foam co-injection is a promising technology to mitigate risks at short time scales while pure CO₂ injection has advantages from a long-term sequestration perspective.

An old play has recently been extended across the border from Germany into the Netherlands, an area previously thought to be barren of reservoir sandstones. The combination of core evaluation with observations from modern analogues help to refine the depositional geometries and architecture of the basal Upper Rotliegend play.

The study area is located in the Southern Permian Basin, comprising wadi and dune sandstones and a central desert lake. The dimensions of the desert sand facies belts in North Oman are similar to those in the Southern Permian Basin and, similar to the base Upper Rotliegend situation, a relief characterises the hinterland of the desert system while a large desert lake is missing. For this setting lake Eyre (Australia) is an example. Here, the mountain ranges from which the fluvial feeder systems originate are more than 500 km away and the landscape surrounding the lake is flat.

Flood events in the Rotliegend are usually thought to be unconfined sheet-type floods, leaving behind sheet-like sediments. However, the Lower Slochteren Member was characterised by a relief, which confined rivers and thereby channel deposits could develop. Fluvial events in desert systems from Oman and near Lake Eyre rather resemble braided streams during waning flow stages, where a water sheet is only present during maximum discharge. This is consistent with fluvial deposits in the study area, which are characterised by a depositional sequence reflecting a change from high density currents to low density currents to standing water deposits. Indeed, desert river floods are typically short-lived events with strongly changing sediment/water ratios and current velocities leaving behind a characteristic depositional “flashflood sequence”, analogue to the classic Bouma sequence.

It is mostly assumed that fluvial sands entering the Silverpit lake were deposited by a sediment plume. After drying out, the sediment is assumed to be reworked by wind, leaving few traces of the fluvial activity. In addition to overprinted sediments, coarsening-upward subaqueous bar type deposits are locally common in the study area. Also in Lake Eyre, subaqueous delta facies and channel systems representing pro-delta features occur, which remain visible during periods of drought. Evaporitic cements and a high groundwater table may help to preserve the pro-delta deposits, which can be good quality reservoir sands.

These improvements of the depositional model help to unravel the depositional settings of the basal Upper Rotliegend sandstones and allow for exploration of sweet spots in yet underexplored areas.

The work was carried out to evaluate the petrophysical characteristics of Nubian sandstone in Sarir field. The data used in this study were mainly wire-line logs from three wells (D11-BLK9, D13-BLK9 and D14-BLK9).

The aim of this study is to do the formation evaluation using petrophysical parameters from wire-line logs in order to determine lithology, porosity, permeability and fluid saturation and to understand the importance of the analysis and distribution of petrophysical properties on reservoir and predict oil recovery.

In this work, Interactive Petrophysics (V3.4) software was used to perform a solid computation of petrophysical properties and then give summaries of the results.

It is important to identify properly the lithology and the reservoir to allow an accurate petrophysical calculation of porosity, water saturation and permeability.

The determination of lithology based on cross-plot neutron versus density log was important step to come up with the reservoir petrophysical properties. The quality of the reservoir is determined by set the cut-off values of the petrophysical properties and describe the change in lithologies.

It worth to mention that, the presence of shale in the entire reservoir influenced negatively in the quality of the reservoir and net pay values. The petrophysical properties of the reservoir in Sarir oil field are good enough to permit hydrocarbon production.

Geological models, as 3-D representations of subsurface structures and property distributions, are used in many economic, scientific, and societal decision processes. These models are built on prior assumptions and imperfect information, and this aspect results in uncertainties about the predicted structures and property distributions, which will affect the subsequent decision process. We examine here uncertainties at different steps in the model construction process and discuss recent approaches in the consideration of these uncertainties.

Specifically, we will present an integrated probabilistic geomodelling approach, based on the open-source geomodelling package GemPy, that enables the consideration of uncertainties in geological interface observation points and orientation data, and the combination with random property fields. This workflow is based on an implicit geometry representation and a cokriging interpolation of point and orientation information. Subsequently, property kriging can be performed inside deformed domains. We also show how additional information, e.g. geophysical measurements, or information about geological topology, can directly be integrated in the workflow, and how the resulting model ensemble can be used to visualize and communicate uncertainties, and further combined with a framework to estimate optimal decisions under uncertainty.

Finally, a probabilistic geomodelling workflow can only capture specific aspects of uncertainty, and the final results have to be interpreted in light of this limitation. These limitations are aspects of active research, and we show promising results of successful applications.

Three-dimensional geological modelling is usually constraint by seismic and borehole data. However, in geological settings of high complexity and sparse, restricted or ambiguous available information additional geoscientific data and methods have to be considered. For this purpose, the incorporation of gravity data holds enormous potential to improve structural interpretations and allows for cross-validation and harmonization of geological models.

Herein, we demonstrate an integrated approach of gravity interpretation and modelling to refine an existing geological 3D SKUA-GOCAD model in the south of the North German Basin (Saxony-Anhalt/Brandenburg cross-border region). The approach comprises at first filtering and gradient calculation to gain insight into the fault system. Second, 3D Euler deconvolution is used to assess the source depth of main gravity anomalies. Subsequently, a 3D density model incorporating density gradients was built with the software IGMAS+. Testing different structural scenarios and evaluating depth uncertainties enabled us to validate the model. In a last step the adjusted layers were incorporated in a volumetric, parameterized three-dimensional geological model.

This integrated modelling approach provided various additional indications for the modelling area: gravity gradients allowed for precise tracing of faults and for contouring of basement structures. 3D Euler depth solution improved depth estimates for the salt-bearing Zechstein formation and basement. Finally, 3D density modelling revealed the extent of structures in the Mesozoic cover and provided insights into the facial composition of the Zechstein formation at the southern edge of the North German Basin.

Geological modelling and flow simulation in the subsurface in heterogeneous and anisotropic media is increasingly common. Unfortunately, conventional modelling using statistical techniques, up-scaling and interpolation to populate the inter-well volume of sparse datasets have a low resolution (> 50 m). Consequently they have difficulty modelling heterogeneous and anisotropic reservoirs. This paper focusses on modelling and simulation of heterogeneous and anisotropic reservoirs using a fractal approach (Advanced Fractal Reservoir Models; AFRMs), which includes variability at all scales such that it can represent the heterogeneity correctly at each scale. These three-dimensional AFRMs can be used to model any fractally complex volume with applications well outside geosciences. In our application AFRMs can be used in generic modelling to understand the effects of heterogeneity and anisotropy, but can also be conditioned to represent real reservoirs. This paper will show how 3D AFRMs can be constructed to represent reservoir parameters (e.g., porosity, permeability, water saturation, relative permeabilities). Results of generic modelling and simulation with AFRMs will be given for a 2 phase system, which show how total and incremental fluid flow and breakthrough all depend strongly on heterogeneity as represented by the fractal dimension the reservoir, and also depends upon anisotropy. The real test of AFRMs is their capacity to be conditioned to real scenarios. Results for moderate to high heterogeneity reservoirs comparing the flow characteristics of such an approach to a conventional kriging/upscaling show that AFRMs was always within 5% of ideal, compared with underestimations by over 70% for the conventional approach.

A large, densely populated part of the Netherlands is located below mean sea level. The risk of flooding is therefore omnipresent. Dikes are vital for safety, and local waterboards apply high standards when monitoring and maintaining the dikes.

The waterboard ‘Hoogheemraadschap de Stichtse Rijnlanden’ (HDSR) has launched a maintenance program to investigate and reinforce the 55km long northern Lek River dike between Schoonhoven and Amerongen. As the dike’s strength depends on both its design and its subsurface, detailed knowledge of the local geology is essential. Along the Lek, the subsurface is characterized by a heterogeneous composition of the shallow subsurface and HDSR requires a higher level of detail than provided by the currently available 3D voxel model GeoTOP (Stafleu et al., 2012. TNO 2012 R10991).

We constructed a 3D geological model, based on the GeoTOP workflow, for three sub-trajectories beneath the dike with a voxel size of 25x25x0.25m. The lithology of each voxel is modelled based on borehole descriptions, cone penetration tests (CPT) and paleogeographic maps. Applying machine-learning to retrieve lithological data from CPT’s increased the data density and allowed for high-resolution modelling.

The new high-resolution model is now used by the waterboard to:

- identify dike-trajectories that need further investigation

- design location-specific and fit-for-purpose dike reinforcement measures

- explain proposed measures to local stakeholders.

The first two applications potentially reduce costs significantly; whereas the third application aids creating social foundation for reinforcement measures. Most importantly, the new high resolution model helps HDSR to enhance safety behind the dikes.

The utilization of geothermal energy comes with a high economic risk. Many of the parameters that control the quality of a geothermal reservoir are heterogeneously distributed and therefore difficult to predict in a rock volume.

We carried out a numerical sensitivity study using a large number (1027) of 4D numerical models of a geothermal doublet. We systematically varied each parameter (e.g., porosity, permeability, background hydraulic gradient (BHG)) and tested the longevity of the simulated reservoirs, by calculating the time until the temperature of the produced fluid fell to 100°C. We increased complexity of the models by introducing permeability anisotropy and contrast to simulate layering, fracture anisotropy, and a fault-zone.

Our results confirm the positive effect of porosity on heat capacity. However, they show also that the BHG, together with permeability, if sufficiently high, can outperform the other parameters. In the more complex models, certain configurations of the parameters constitute tipping points, i.e. small modifications of the parameters decide between extreme longevity and early thermal breakthrough.

For example, highly permeable zones, as is common in faults, can provide high initial yields, but also channel the fluid flow and thus can restrict the exploitable reservoir volume. The BHG can be outperformed by small variations in permeability contrast caused by layering and fracture anisotropy. Even low permeability contrasts (10³) or fracture-induced permeability anisotropies (10¹) can channel fluid flow and thus significantly restrict the utilizable reservoir volume. In such cases, the initial yields may be high, but the lifetime of the reservoir is short.