Keynote 1: Thomas Doe
Topic:Faults as Multi-Fracture, Multi-Porosity Hydraulic Systems
Faults and deformation zones are important geologic features with respect to flow and storage in underground environments. They have significance to a large range of different, but related, applications including radioactive waste isolation, oil and gas production, carbon sequestration, and geothermal energy development.
In discrete fracture network (DFN) models, faults are distinct relative to simple fractures. Whilst both are planar features with distinct transmissivity and storage properties, fractures in DFN models are classically viewed using the parallel plate analog, where the fracture is an open space between two solid faces having a separation termed the aperture. The flow, storage, and transport properties of the fracture all relate to the aperture with the best-known relationship being the cubic law of transmissivity derived from the Navier-Stokes equations of fluid mechanics. Such fractures generally form mechanically in tension.
Faults, on the other hand, are formed by shear deformation and have an internal structure that may contain multiple features including fracture damage zones, breccias, solution-enhanced zones, and gouge as well as alteration haloes. Faults and deformation zones may span a large range of scales with thicknesses from millimeters to tens of meters or more and size ranges from meters to tens of kilometers. Unlike simple fractures, where hydraulic properties relate to one another by the aperture, the different internal structures have varying significances for flow and storage. In DFN models, fault zones may be represented either as single discrete features with effective transmissivity and storage properties, or each fault may be its own DFN domain with core and damage zones explicitly represented as fracture networks.
A review of interference and tracer tests from faults and deformation zone shows that a small portion of the fault-zone porosity is associated the major portion of the flow, while the major portion of the storage is functioning as multi-porosity system. This multi-porosity behavior has significant impacts on many applications. For radioactive-waste isolation the storage serves as a reservoir for matrix diffusion with strong retarding effects on radionuclide migration. In oil and gas development, especially in basement reservoirs, the flowing portions of the fault may account for 10% or less of the reservoir storage, while most of the storage lies in the damage zone. Optimizing recovery in the presence of an aquifer or water injection requires managing the rate of displacement of oil in the transmissive cores of the fault with respect to production from the major portion of the oil stored in the damage and alteration zones, which may lag significantly. Similarly in carbon sequestration, managing the transfer from the low-porosity conductive portions of faults to the less conductive but higher porosity portions is essential. Geothermal development in faulted terrain requires an understanding of heat transfer rates from matrix blocks to the conducting portions of the fault’s fracture network.
Keynote 2: Christie Rogers, ExxonMobil
Topic: Fault Juxtaposition And Trap Controls On Original Hydrocarbon Contacts
In oil and gas exploration, ExxonMobil maintains a long-standing approach for understanding and predicting static hydrocarbon accumulations in faulted traps. Namely, the first order control on hydrocarbon fill is cross-fault juxtaposition of porous units which can allow migration away from the trap or the stair-stepping of fluids vertically within traps. Quality mapping with attention to fault architecture is essential, and fault zone materials, while present, are complex and discontinuous over trap extents thereby offering a lesser effect at geologic time scales. Additionally, a full integration of reservoir geometry (i.e. crests, synclinal spills, juxtaposition and erosional windows, and base seal breakovers) furthers contact analysis and prediction. As shared in several publications historically, the juxtaposition and reservoir connectivity analysis approaches have emerged from meaningful corporate experience, with the additional benefit of being tractable for any interpreter. Scenario analysis, deterministic or stochastic, allow us to account for numerous subsurface uncertainties for volumetric assessment and depletion planning.
Keynote 3: Sherilyn Williams-Stroud, Illinois State Geological Survey
Topic: Enhanced Structural Interpretation using Seismic Data at the Decatur, Illinois Sequestration Site
Monitoring of induced seismicity after injection of super-critical CO2 was used to help determine pathways the fluid took during migration over time and to assess the risk of felt seismicity the Illinois Basin – Decatur Project (IBDP). The microseismic activity at the site indicates locations where existing fractures and faults were reactivated, but do not have a direct correlation with locations of faults mapped in the seismic reflection volume. Some microseismic events were large enough to determine focal mechanisms, but no injection-related felt seismicity has been detected. Most of the induced seismicity occurs below the reservoir in fractured low porosity/permeability igneous basement rocks where fault identification proved problematic. The reservoir itself, the Cambrian Mt. Simon Sandstone, has high porosity and permeability, with much less common fracturing and faulting. The temporal development of the microseismicity at IBDP indicates stress perturbations that migrated largely to the north and west of the injection location, and which were concentrated in clusters elongated in a NE-SW orientation. Detailed spatial-temporal analysis of the clusters indicates more complex structure, suggesting reactivations of planes within a fracture corridor rather than a single large fault plane. We suggest that horizontal fluid migration occurring in the Mt. Simon sandstone could be the dominant pathway for transmission of fluid and pressure away from the injection well to locations that are hydrologically connected to the basement rocks. It is possible that fluid directional pathway is also accommodated by open fractures in the basement with orientations that connect the NE-SW oriented reactivated faults. We use this integrated data set to create a fault and fracture model that is consistent with the interpretation of the seismic reflection data and the observed microseismicity as a basis on which to test the potential for induced slip on existing fault planes and the risk for induced felt seismicity.
Keynote 4: Cindy Ong, CSIRO Energy
Topic: Fugitive Methane Emissions Related To Australian Onshore Gas Operations
Australia has significant onshore gas resources that will continue to meet national and global energy demand well into the second half of this century. As Australia and the world strive to meet climate-change goals, gas may have an important role to play as a transition fuel bridging between fossil fuels and renewable energy because it has lower direct greenhouse emissions compared to other fossil fuels. However, to fully understand the viability of gas as a transition fuel, fugitive emissions associated with the industry need to be quantified to determine the actual greenhouse benefits. Methane is the primary component of natural gas, and is a significant greenhouse gas, second most significant (with a greenhouse warming potential of some 28 times that of carbon dioxide) after carbon dioxide. Historically, knowledge and data regarding fugitive methane emissions related to onshore gas were primarily adopted from the USA or other countries because of a lack of local data. Although this overseas knowledge and data could be used as proxies, much of it is not transferable due to the different geological conditions and different engineering and infrastructure. In recent times, CSIRO Energy and its collaborators have conducted significant research and development via the Gas Industry Environmental and Social Research Alliance (GISERA) and other industry and government projects to close the gap in understanding on fugitive emissions related to the Australian onshore gas industry. Comprehensive studies have been conducted deploying new technologies and methods in the Surat Basin in Queensland, the Pilliga region in New South Wales and more recently in the Beetaloo sub-basin in the Northern Territory. These studies provide a comprehensive understanding of baseline levels, characterisation of sources and quantification of methane emissions in those gas producing regions. This presentation will provide an overview of the studies conducted, the technologies used, methodologies developed and new insights on fugitive methane emissions related to onshore gas in Australia.
Keynote 5: Scott Mildren, Tech Limit
Topic: Fault seal in a world moving towards net zero emissions
Environmental, social and political forces are affecting the context in which we consider fault seal and flow properties. Australia is considering a commitment to net zero emissions by 2050 and APPEA itself states that they "support the science of climate change and the need to reduce global emissions, consistent with the objectives of the Paris Agreement”. The body of previously published work, assessing fault seal integrity and migration pathways of traditional hydrocarbon traps, remains relevant, however, there exists specific challenges associated with the storage/utilisation cycle of hydrogen that do not affect CCS. Physical and chemical changes occur over time altering rock properties and stress conditions with repeat pressurisation/depressurisation cycles. These changes can in turn affect injection capacity and the risk of geomechanical breach through a variety of mechanisms. Solutions that will move us towards a net zero future are very much dependent on understanding the nature of structural elements in the subsurface and we now have the added challenges of cyclic operations and a dramatic increase in operational scale. Additionally, predicting properties between wells and within faults has always been a challenge and these issues will also follow us into the future. Seismic data will become an increasing important tool to help us address this, perhaps with the aid of machine learning techniques, to fill the data gaps and allow us to make our fault integrity and fluid flow predictions.
Keynote 6: Ralf Oppermann, OPPtimal Resource Solutions Pty Ltd
Topic: Small-scale Faults and Fluid Flow – a New Understanding Emerges
High-resolution fault imaging provides new opportunities to detect smaller-scale faults and evaluate their impact on the drilling and production of resources. Smaller-scale faults newly visualised through high resolution seismic fault processing have been shown to significantly impact drilling operations and also explain fluid flow and productivity within a reservoir. Seismically identified small-scale faults match with image log fractures and indicate that fracture clusters observed in image logs are directly linked to the proximity of wells to seismic faults, particularly larger-throw (high confidence) seismic faults that are oriented parallel and in close proximity to wellbores. The same seismically identified small-scale faults also provide a means to explain fluid losses during drilling and with this delineate preferential flow pathways within reservoirs. Various studies around the world have shown that hi-res fault imaging delivers groundbreaking insights into the 3-dimensional geometry and distribution of fault networks and how these can affect fluid flow in the subsurface. The studies have shown that fault geometry is the key for the understanding of fluid retention and fluid movements within reservoirs and also seals/aquitards. High-resolution fault processing provides opportunities to reduce operational risks and costs and also increase resource recoveries, and with this provides a step-change in understanding and avoiding drilling, production and safety issues in wells or mines. It is proposed as Best Practice tool for resource development planning and execution.
Keynote 7: Desmond James FitzGerald, Intrepid Geophysics
Topic: Faults in Groundwater Using AEM 2.5D+ Inversion Technology
Intrepid Geophysics (IG) has 40+ years of operations in bleeding edge technology and G & G services, led by the requests from global miners and petroleum companies with strategic input from international experts across mining, petroleum, and water sectors.
A major shift in mining exploration techniques is yet to be taken advantage of by the water sector. Blue resources exploration and management utilize geological and geophysical data that are typically traditional. At the forefront of geophysical workflows there are high cost, high-resolution shallow reflection seismic, low-cost high resolution 2.5D+ AEM products and lower cost emerging tensor magnetics. The data accuracy and resolution of the geophysical techniques are verging for onshore data. The perception that this technique has a computational restriction is now removed with the option of Amazon Web Services elastic scaling.
The intended aim is to support, a substantial step forward in imaging the subsurface has been attained by using the 2.5D AEM industry proven workflows. Clear fault barriers are imaged separating different water salinities within variable geological facies across basin bounding faults. The results apparent within the 2.5D AEM cross sections clearly show fault barriers and fault migration pathways.
The AEM survey became a major component to this project. In this study, the collected AEM datasets were integrated using geophysical inversion modelling to detect the signature of faults and the associated geology with fluid properties.
This study has demonstrated the importance of selecting the most appropriate AEM system and optimizing the AEM inversions for generating a wide range of customized interpretation products to avoid using data products that contain substantial noise, miss leading interpreters and decision makers, extending the project timeframes.
Keynote 8: Stephen Tyson, Universiti Teknologi Brunei
Topic: 30 years of flow simulation, geological modeling and upscaling - Are we making any better decisions?
TBC
Keynote 9: Thomas Manzocchi, University College Dublin
Topic: Representation in Flow Models of Faults in Porous Clastic Sequences: Insights from the Conventional Hydrocarbons Sector
Fault Analysis Group and Irish Centre for Research in Applied Geoscience, University College Dublin, Ireland.This presentation reviews approaches applied within the hydrocarbons sector for describing, parameterising, and representing faults in flow simulation models of conventional clastic reservoirs. The conceptual geological model underlying the most common approaches consider faults to be narrow zone of high-strain fault rock (often called a fault core) with permeability primarily dependent on the clay content of the fault rock, and thickness primarily dependent on the fault displacement. A number of algorithms are used to express fault rock clay content as a function of the faulted geological sequence, of which the simplest and most widely applied is the Shale Gouge Ratio (SGR). Predictions of fault rock properties from clay content are most reliable when calibrated using local data. Fault rock properties are highly heterogeneous and average properties are required at the scale of representation in the flow model. Fault rock permeability and thickness at the scale of individual across-fault cell to cell connection in finite difference flow simulation models are represented most accurately as transmissibility multipliers. These depend on the permeability and size of the host-rock cells as well as on the fault rocks themselves, so in a heterogeneous sequence they are highly variable even if representing a homogeneous fault. In the case of immiscible two-phase flow, relative permeability functions are required in the simulator to calculate fluid-phase specific permeabilities as a function of fluid saturation. It is rare to consider relative permeability of fault rocks in flow simulation modelling, but a few methods to include it have been proposed of which the most robust is via modification of the directional relative permeabilities of the grid-block adjacent to faults. Conceptual models of fault zones often also include a damage zone surrounding the fault core. This can have two important effects on flow. In highly porous sandstones, a damage zone comprising dense networks of small displacement, but low permeability, faults can further attenuate cross-fault permeability, and this effect can be included in the multiplier. More generally, the damage zone consists of systematic arrays of intact and breached fault relay zones resulting in locally high fault displacement gradients and unexpected cross-fault and up-fault juxtapositions. Tools has been developed to predict these juxtapositions probabilistically, and they can be included in flow models using so-called special (or non-neighbour) connections.
Keynote 10: Neil Grant, ConocoPhillips UK Holdings Ltd.
Topic: How faults influence the trapping of oil and gas
Faults may play a significant role in the migration and entrapment of hydrocarbons, either offering conduits for, or barriers to, fluid flow. They may also affect fluid-phase trapping and can influence phase fractionation in the subsurface. A Monte Carlo modelling approach is used to model these effects for trap analysis. The aim is to show how varying fault seal capacity, the fault orientation, the regional stress tensor, and the trap geometry can all affect how both oil and gas are retained within a trap. Both juxtaposition and membrane fault seal are modelled, together with hydrodynamic effects and fault reactivation risk. The potential of a prospect to trap hydrocarbons can be evaluated in a statistical roll-up of results with the outputs including a predicted hydrocarbon column height distribution and column height control statistics. The technique will be shown to offer an insight into the potential fluid-phase partitioning that may occur within a trap dependent on the interplay between the active leakage mechanisms and spill control, thus enabling gas v. oil column heights to be assessed. Application of the model to known accumulations can help with calibration and may also elucidate key controls on observed columns and phases.
Keynote 11: Signe Ottesen, Equinor ASA
Topic: Evaluation of Fault Seal for Co2 Injection in the Norwegian Northern Lights CCS Project
The presentation is based on work performed last year as input to the PDO (plan for development and operation) to the Norwegian authorities on the Northern Lights project, where Equinor was the company in charge with secondees from Shell and TotalEnergies.
The Northern Lights project is the transportation and storage part of the Longship CCS demonstration project recently adopted in the Norwegian Parliament - Stortinget. The Northern Lights joint venture owned by Equinor, TotalEnergies, and Shell will inject and store CO2 in the Lower Jurassic Dunlin Group within the exploitation license EL001 located south of the Troll field. CO2 will be injected in the Johansen Fm. and will, with time, migrate slowly up-dip to the north driven by buoyancy. According to regulations, the stored CO2 shall be contained within the storage complex.
Understanding the effects of the faults are important for predicting CO2 migration within the storage units and for analysis of potential migration pathways for CO2 out of the storage complex. Faults represent potential barriers or baffles for migration of CO2 within the reservoirs and provide potential across fault flow paths between reservoir units. The fault seal evaluation is based on SSF and SGR calculated on triangle diagrams, together with juxtaposition maps made in a new Equinor proprietary RMS plugin FaultRoom.
The Eos well 31/5-7 was the first well drilled into the Dunlin Group in the exploitation license in 2019/2020. Until then the nearest well to the injection site was 18 km to the North. The Eos well was drilled to confirm the reservoir presence, properties, pressure depletion and injection potential of the storage units. The Eos well proves the existence of good reservoirs in high energy shallow-marine sandstones of the Johansen and Cook formations within the Dunlin Group. Furthermore, the well proves the sealing properties of the Drake Formation which constitutes the primary caprock of the reservoir.
Conclusions from the fault seal analysis prior to results from the Eos well had large uncertainty. Applying the data from the Eos well reduced this uncertainty. The post Eos well fault seal analysis confirmed that there is nearly no, or very low, risk for migration through the major faults or upwards migration along faults into shallower stratigraphic units.
Keynote 12: Wendy Timms, Deakin University
Topic: Characterisation and modelling of geological fault zones – a draft explanatory note to help prepare environmental impact assessments
Characterisation and modeling of geological fault zones is often part of environmental impact assessment for coal seam gas (CSG) and large coal mining (LCM) projects. However, fault behaviour is seldom considered in detail, and may vary spatially or change during a coal development project. This often leads to an assumption that a fault is a hydraulic barrier without supporting evidence to support this assumption. The Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development (IESC) is a statutory body under the Environment Protection and Biodiversity Conservation Act 1999. One of the IESC’s key legislative functions is to provide independent scientific advice to the Australian Government Environment Minister and relevant state ministers in relation to coal seam gas (CSG) and large coal mining (LCM) development proposals that are likely to have a significant impact on water resources. To supplement the IESC Information Guidelines (2018), the IESC has developed, with specialist authors, an Explanatory Note (EN) on characterizing and modelling geological fault zones. This presentation will provide an overview of the draft EN that was recently open to public consultation on technical content and relevance. In the context of faulting, this EN provides additional guidance to proponents undertaking an impact assessment of risks to key water assets and groundwater dependent ecosystems (GDEs). It outlines a logical framework for undertaking the assessment and suggests some tools and techniques that may be useful during the assessment. Key recommendations from the EN will be presented, along with a summary of case studies/scenarios that illustrate differing situations and fault risk character.