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Fifth International Conference on Fault and Top Seals
- Conference date: September 8-12, 2019
- Location: Palermo, Italy
- Published: 08 September 2019
1 - 20 of 76 results
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Numerical Simulation of Fault Compartmentalisation in CCS Reservoir
Authors L. Langhi, L. Ricard, J. Strand and D. DewhurstSummaryTo improve the South West Hub Carbon Capture and Storage Project (Western Australia) site characterisation and reduce uncertainties around CO2 capacity, injectivity and containment, conceptual fault hydrodynamic models are defined, and reservoir simulations are carried out to investigate the CO2 plume development and its interaction with faults. The conceptual fault hydrodynamic models are defined to incorporate host rock and fault properties accounting for fault zone lithology, cementation, and cataclastic processes. The primary focus was to study the impact of different faulting depth scenarios on reservoir compartmentalization and across-fault and up-fault migration of CO2. Selected flow simulations in the lower injection unit highlight a transition from partially sealing to totally sealing faults that occurs for the most probable faulting depth scenarios. This suggests some degree of compartmentalization in the injection unit resulting in potential restriction of reservoir volume affecting the plume distribution with a preferential CO2 migration aligned along the local N–S structural trend. The compartment bounding faults however, are expected to be composed of overlapping segments unlikely to represent extensively continuous barriers and lateral flow pathways are expected to intermittently exist between compartments reducing risk of pore pressure build up at depth.
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The CO2CRC Otway Controlled CO2 Release Experiment in a Fault: Geomechanical Characterisation Pre-Injection
Authors E. Tenthorey, E. Tenthorey, A. Feitz, A. Feitz, A. Credoz, M. Lavina, E. Coene, A. Idiart and S. JordanaSummaryThe CO2CRC Otway Research Facility is one of the world’s pre-eminent CO2 storage demonstration projects, focussed on carbon storage research and development. The latest injection test that is being planned is based around a small injection test into a shallow fault at depths less than 100 m. The main goal of the controlled CO2 release into the fault is to use a diverse array of geophysical and geochemical monitoring techniques to image the CO2 plume migrating into, around and ultimately up the fault toward the surface. In doing so, we expect to acquire significant learnings around fault permeability, the ease by which CO2 can migrate through minor faults and also gain some understanding about the portions of the fault that are most prone to allowing vertical gas migration. Preliminary geomechanical modelling presented here indicate that the Brumbys fault is a good candidate for a CO2 injection experiments, as it is expected to maintain its integrity and not introduce any geomechanical complications to the equation.
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Fault Seal Analysis Using Seismic Inversions: Pitfalls and Limitations
Authors V. Schuller and M. VögeleSummaryIf only few data available how can we assess the risk and uncertainty of a hydrocarbon accumulation which relies on the sealing capacity of a fault? We want to present a Fault Seal Analysis approach based on the strong integration of geophysical data. The purpose of this workflow is to deliver prediction on Fault Seal Capacity in areas and prospects where no well data is available or offset wells are too far away to be used for Fault Seal input (e.g. Vshale log). Our study suggests that 3D seismic inversion can be exploited to create a Vsh cube which can be used to “read-out” Vsh values along a planned exploration well path in an underexplored setting. The generated Vsh curve is used for a full 3D FSA which delivers distinct values on the fault sealing capacities and uncertainty ranges on expected hydrocarbon column heights. In order to verify the results of this approach, the inverted VSH data was subsequently compared to CPI data from a drilled exploration well in the AOI. Pitfalls and limitations, especially with regards to lithology and fluid effects, are highlighted.
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Fracture Reactivation in Shale: Laboratory Testing and Analytical Modeling
Authors B. Bohloli, J.C. Choi and M. SoldalSummaryThis paper presents a tool for first-order evaluation of fracture/fault reactivation due to fluid injection. It also provides frictional strength parameters of a shale from direct shear testing. The in-house tool, FracStress, was developed based on the analytical Mohr-Coulomb failure criteria and 3D transformation of in-situ stress conditions. The software accounts for the geometry of fracture/fault, 3D stress field, pore pressure and frictional properties. It calculates and visualizes the state of stress for any given fracture orientation. Friction and cohesion of a pre-fractured shale is determined through a direct shear test. The state of stress and frictional strength envelope of material are plotted to estimate the critical injection pressure for the material. The developed tool was tested using the stress condition and test results of Draupne shale in the Ling Depression, the North Sea. The analysis shows that for stress conditions present at the depth of 2582 m, Ling Depression, fractures dipping 60° are close to failure condition. However, fractures dipping 30° and 45° will sustain injection pressure of between 2 to 9 MPa depending on the state of horizontal stresses in the area and the friction coefficient of material.
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Sealing, Healing and Fluid Flow in Clay Rocks: Insights on Episodic Flow Events in Fault Zones
Authors V. Nenonen, P. Dick, J. Sammaljärvi, B. Johansson, M. Voutilainen and M. Siitari-KauppiSummaryThe porosity distribution and mineralogical changes in a clay-rich fault core from the Tournemire underground research laboratory are analyzed to determine the mechano-chemical processes in a small-scale vertical strike-slip fault. The results display significant spatial variations in porosity and mineralogy along different gouge zones due to a polyphased tectonic history combined with complex paleo-fluid migrations. Porosity values increase from the center of the gouges to their borders indicating diffusive sealing/healing effects and past hydrothermal activities. The healing and thus the strengthening of the fault is marked by an increase of calcium content, which is concurrent with lower porosities around the gouge zone. Chemical mapping in the gouges reveal clay alteration, iron zonality and the presence of zinc sulphide as well as barium sulphate inside the gouge, further suggesting past hydrothermal activity. Finally, even though the observed porosity variations only occur in subcentimeter-thick gouge bands, the higher porosity sections are pathways for fluid flow during fault activity.
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Effects of Cap Rock and Hydrodynamic on CBM Preservation A Case Study From Ordos Basin, China
More LessSummaryDifferent from other countries, more than 60% of total resources in China occur in medium- to high-rank coal basins and experienced complicated evolution in the long history of tectonic subsidence and uplifting. CBM preservation in these basins requires high sealing conditions. A series of investigations has documented factors influencing CBM enrichment and production. Among the factors, cap rock and hydrodynamic condition were identified as two primary control factors which has a significant influence on CBM preservation. The combination of low permeability mudstone with a high Young’s modulus in the roof and floor is very beneficial to the preservation of CBM. Type NaHCO3 and type NaCl formation water with the TDS (Total Dissolved Solids) value ranges from 1200mg/L to 4000mg/L is an indicator for a suitable preservation of CBM.
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Diagenetic Impact on Polyphase Fault Zones Drain Properties in Micro-Porous Carbonates (Urgonian – SE France)
Authors I. Aubert, P. Léonide, J. Lamarche and R. SalardonSummaryFault zones can act as drains or barriers depending of their architecture, mechanical and diagenetic evolution. Carbonates are very sensitive to diagenetic processes. When they are affected by faults, impact on reservoir properties is enhance. The study focalized on 2 polyphased faults affecting Lower Barremian microporous platform carbonates (Urgonian facies). We realized porosity measurements, observed 92 thin sections under cathodoluminescence, analyzed micrite micro-fabric with SEM and micro-sampled 189 O and C isotopic measurements to determine the diagenetic evolution of both host rock and fault zones. Our result reveal a strong decrease of porosity towards the fault planes. We identified seven cementation phases and 2 different micrit microfabrics from diagenetic analysis. The C and O measured isotopic values ranging from −7.2 to +1.42‰ for δ13C and from −10.40 to −3.65‰ for δ18O. The cross-cutting, overlap and superposition principles allowed to realize the fault zones and host rock paragenesis. Studied Urgonian carbonates have been affected by 3 diagenetic events divided in pre-faulting and fault-related stages impacting reservoir properties during the early stages of fault activity.
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Structural Diagenesis, Early Embrittlement and Fracture Setting in Shallow-Water Platform Carbonates (Monte Alpi Southern Apennines, Italy)
Authors V. La Bruna, J. Lamarche, F. Agosta, A. Rustichelli, A. Giuffrida, R. Salardon and L. MariéSummaryBed-perpendicular diffuse fractures are common features in carbonates that could be affected by early embrittlement process, which may enhance vertically persistent, opening-mode fractures during the first stages of diagenesis. Early-developed fractures could be independent of tectonics and form a background structural network at different scale. This study focuses on the structural, stratigraphic and petrographic characterization, from outcrop- to micro-scale of Lower Cretaceous, shallow-water, tight limestones pertaining to the Inner Apulian Platform paleogeographic/tectonic domain. These carbonates consist of a wide spectrum of inner platform-platform margin calcareous facies, namely mudstones, wackestones, packstones, grainstones, bindstones, floatstones and rudstones. The presented work is addressed on understanding the development of the early diagenetic features which occurred during the first stages of the sediment lithification processes and the description of the formation, geometry and distribution of the contemporaneous and subsequent structural elements. Field analyses in concert with laboratory analyses unrevealed the main structural-diagenetic events which affected the studied shallow-water carbonates. Petrographic analyses highlight early fractures are intrinsically related to the host rock pore type. Finally, evolution of the fracture network is summarized in a conceptual model by taking into account the several tectonic phases which affect the Monte Alpi sector
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Kinematic and Geological Significance of Contractional Deformation Bands in Oil-Bearing Sandstones: Example from Youshashan Anticline, China
More LessSummaryThe contractional deformation bands developed in oil-bearing sandstones of the fold related to the thrust fault in Qaidam basin, China. Deformation bands are organized as distributed and conjugated networks. The offsets of the deformation bands which are characterized by reverse-sense displacement is about 1mm-20mm. The dihedral angles of deformation bands vary in the range of 47–73°, and they bands are characterized by low S/C ratios in the range of 3.9–22.3. In comparison that of the host rock, the porosity of deformation bands decreased by approximately 11.0%–19.7%, the permeability decreases by 1–2 orders of magnitude. Deformation bands show grain “cataclasis” deformation, and can be categorized as contractional CSBs. The period of CSBs formation in the Youshashan anticline is consistent with or slightly later than the period of Youshashan anticline formation. The burial depth of the formation of deformation bands is approximately 2.5km–1.0km. The ability to store fluid of CSBs is worse than host rock, and oil-bearing content within CSBs is less than host rock. CSBs has a negative effect on hydrocarbon migration, resulting in higher oil saturation in the CSBs than the host rock.
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Stochastic Simulation of Sub-Seismic Faults Conditioned on Displacement Intensity Maps
Authors H. Goodwin, E. Aker and P. RøeSummaryWe present stochastic simulations of sub-seismic faults conditioned on displacement intensity and stress orientation maps generated from a geomechanical model. The simulations are performed in an iterative process where new faults are proposed and have a high probability of being accepted if the contribution of the new fault gives a better match with the input displacement intensity map. The algorithm is demonstrated on a synthetic test case and shows that displacement field and strike orientation of the simulated sub-seismic faults matches the pattern of the displacement intensity map and the orientation of the maximum horizontal stress from a geomechanical model.
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Seal Risking Reinvented Using 300 Year Old Math
Authors J.S. Davis, K.C. Hood, K.J. Steffen and J.M. MatthewsSummarySeal constitutes a primary geologic risk within petroleum exploration. Historically, translating seal analyses into risk commonly utilized risk matrices or tables, which combine measures of confidence and risk severity to reach a Chance of Success (COS). Unfortunately, pitfalls abound in the seal risking process, including failure to consider historical success rates, confusion between confidence and risk severity, poorly calibrated ‘gut-checks’, and DHI adjustments. These complications often resulted in inconsistent seal risking, an inability to distinguish more-risky from less-risky prospects, and poorly prioritized exploration portfolios. We present a new seal risking method – the Risking V – which helps to mitigate these obstacles. The method starts with calibrated base rates and explicit Lines of Evidence (LOEs) that address seal risk. Each LOE has clearly articulated confidence and risk criteria, defined by subject matter experts, which lead to Chance of Validity (COV) values. The risking minimum hurdle is a specified hydrocarbon column height. The user works through the LOEs, then applies sequential Bayesian updating to derive a robust COS specific to the characteristics of the prospect being evaluated. This new method results in a clearly documented and consistent seal COS and avoids many of the traditional risking pitfalls.
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Defining Fault Trap Leakage Pathways via Fault Element Seal Differentiation in Calibration Modelling of Complex Fields
Authors M. Smith and J. ParsonsSummaryDifferentiated seal calibration models of faulted multi-pay oil and gas fields, explaining reservoir fluid fill type in each faulted reservoir, provide a high-resolution quantitative calibration base to explain then predict the industry critical issue of the locations and column heights of fault trapped hydrocarbons. Field calibration models differentiate between working and failed fault seals (matrix and fracture properties) within a fields geologic and stress settings. The models allow testing of seal effectiveness in foot and hanging wall host rock, damage zone and fault core rocks. The calibration objective is to find a ‘best fit’ calibration model and sealing/leaking mechanism that best matches with the observed distribution of water sands, hydrocarbon sands and hydrocarbon column heights. Calibration modelling is conducted to be consistent with the characteristics of fault models as described by Caine et al., 1996 and others. In this method, no prior assumption is made as to the mechanisms of seal success or failure. Success and failure mechanisms vary with different settings and can only be inferred once a best fit model is defined. Calibrated field models are then used as the basis for forward modelling of, in field, exploration targets and for constraining fault zone fluid flow characteristics.
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Incorporating Uncertainty into Fault Seal Analysis
More LessSummaryAnalyzing the sealing capacity of fault rock distributions from clay content distributions modeled from Triangle Diagrams and from data exported from 3D models.
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Understanding the Dynamic Impact of Fault Models Using Fault Properties and Simple Streamline Simulations
More LessSummaryFault zones in porous sandstones can commonly be divided into two parts: a fault core and a damage zone. Both fault zone elements will influence sub-surface fluid flow and must be treated separately to create a geologically realistic model. The fault core can be implemented in the model as a transmissibility multiplier (TM) while the damage zone can be implemented by modifying the grid permeability in the cells adjacent to the model faults. Each of the input parameters used in calculating the TM and damage zone permeability modification is subject to geological uncertainty. We test the impact of varying input parameters through two methods: i) calculating flow indicator fault properties from the static model, and ii) employing a simplified flow-based connectivity calculation, returning dynamic measures of model connectivity. Our results indicate that fluid flow indicator fault properties are weakly correlated with measures of dynamic behaviour. In particular, models with low fault transmissibility show a much greater range of dynamic behaviour, and are less predictable, than models with high fault transmissibility. We ascribe this to the greater complexity of flow paths expected when a highly compartmentalized model contains faults that are likely to be baffles or barriers to cross-fault flow.
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Incorporating Ambiguity and Uncertainty into Subsurface Model Building
Authors J. Solum and K. OnyeagoroSummaryA geological model of a subsurface reservoir is unavoidably less complicated than the geological reality at depth. Two significant factors that contribute to this simplification are ambiguity of the seismic expression of faults and uncertainty caused by the presence of structural heterogeneities that are below the limit of seismic resolution. This is particularly important since fault systems are segmented, and fault architecture will vary with displacement. The fault ranking methodology described in this contribution is a useful way to help quantify interpretation uncertainty, and to identify which faults might need to be revised or might require mutiple realistic interpretations. The scaling relationships described in this work provide a means to estimate a realistic range of the dimensions of fault zone architectural elements, and therefore a way to calculate a realistic range of values for fault properties such as transmissibility.
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Fault Gouge Seal Models: Sensitivity Study of Petrophysical Inputs
Authors R. Locklair, M. Ascanio Regalado, A. Eakin and J. GageSummaryThe study presented here investigates uncertainty in the zonation and composition of host rock stratigraphy that are used in SGR models. For a given stratigraphic sequence, logging data from multiple wells were evaluated to characterize stratigraphic uncertainty related to lateral changes in zone thicknesses. Rock composition uncertainty was evaluated through construction of several derivative log curves in both the rock domain (Vshale) and the mineral domain (Vclay). SGR was calculated for a range of fault throws for all 40 combinations of well and log inputs. As expected, SGR outcomes varied dramatically between cases using Vclay and Vshale inputs, often by a factor of two. This difference could translate to nearly an order of magnitude difference in across-fault pressure differential using published SGR-pressure transforms. This study demonstrates that uncertainty regarding which well(s) and petrophysical input(s) to select for SGR analysis is large enough to influence interpretation of fault zone barriers, baffles, and leaks.
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A New Method of Accounting for Uncertainty and Temporal Variability in Studies of Fault Seal Capacity
Authors C. Reilly and M. ValcarcelSummaryA new workflow is presented here combining temporal analysis of fault seal capacity with a newly developed method of determining the uncertainties associated with fault seal studies. Recognised uncertainties in the geometry of geological models and in lithological data used for fault seal calculations are combined and possible deviations due to these uncertainties are run as a Monte Carlo simulation. Results enable quantification of all possible fault seal parameters. Temporal fault seal studies utilising structural restoration techniques to examine geological model configuration, and resultant fault seal throughout the history of hydrocarbon movement in the subsurface is also carried out. Incorporating our newly developed uncertainty modelling workflow with temporal fault seal modelling greatly reduces the risk inherent in resource definition which is dependent on faults for migration/seal. A number of global datasets are utilised to highlight the efficacy of this workflow combination, with this abstract focussing on the Cape Egmont Fault, Taranaki Basin, New Zealand.
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How to Consider Uncertainties in FSA: A-Posteriori Correction and Montecarlo Workflows for Hydrocarbon Column Height Evaluation
Authors M. Meda and L. ClemenziSummaryIn order to consider the main uncertainties related to the Fault Seal Analysis evaluation for the prospect volume prediction, two approaches have been proposed. The first one is based on a deterministic evaluation of the fault behavior, followed by a correction related to the quality and quantity of the available data. The second approach starts from a base case, modeled using Petrel software; according to defined ranges of values and alternatives for each main parameter, with a Monte Carlo approach, the base case is modified and a contact depth distribution is collected.
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Validation of Fault Seal Mechanisms in the Timor Sea: An Outcrop and Subsurface Perspective
Authors T. Murray, W. Power, S. Sosio de Rosar, Z. Shipton and R. LunnSummaryWhen risking faulted structures, across-fault juxtaposition and or membrane seal are key issues. Generally, this work is done on a “best-guess” model. The application of SGR methods in reservoir / seal systems that have moderate Vshale values artificially increases predicted column heights. In a risking processes these large columns are discounted through other geologic risk factors. Faults in Miri, Sarawak, have been systematically mapped in outcrop in great detail to measure the strike variability of fault rocks. This work greatly helps to understand the limitation of membrane seal algorithms. To illustrate the implications to subsurface risking, a validation will be presented in which observed hydrocarbon water contacts are compared with probabilistic models for both juxtaposition and SGR. A comprehensive review of a set of fields in The Timor Sea shows that probabilistic juxtaposition models more accurately predict hydrocarbon water contacts than calibrated SGR single “best” technical models.
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Sub-Seismic Deformation in Traps Adjacent to Salt Stocks/Walls: Observations from Green Canyon, Gulf of Mexico
Authors S. Wilkins, V. Mount, R. Davies, T. Butaud, B. Lindsey, C. Fenn, J. Syrek, H. Adiguna and I. MatthewsSummaryWe use core and image logs to characterize sub-seismic deformation at two adjacent sub-salt hydrocarbon fields, both of which are 3-way structural traps against salt. Microstructural analysis indicates that most of the deformation bands (DBs) are cataclasites, with a lesser amount of protocataclasites. Core calibration with high-resolution oil-based image logs allows interpretation of DBs that were previously unrecognized. Spatial distributions, orientations, and frequencies of DBs are established from structural interpretation of image logs acquired in wells at different structural positions along the salt-sediment interface of each field. The kinematics of the DBs are interpreted from orientation and displacements, and placed in a larger trap scale context to understand their origin and effect on subsurface fluid flow. Bulk effective permeabilities are estimated for each well by incorporating the host sand and DB permeabilities, as well as the reservoir thickness and volumetric fraction of DBs, and then compared to collected pressure and production data.
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