- Home
- Conferences
- Conference Proceedings
- Conferences
Fifth International Conference on Fault and Top Seals
- Conference date: September 8-12, 2019
- Location: Palermo, Italy
- Published: 08 September 2019
21 - 40 of 76 results
-
-
Depth-Dependent Fault Sealing in the Greater Oseberg Area
Authors C. Hermanrud, G.M.G. Teige, T. Lien and M.O. OsnesSummaryWe have re-examined the hydrocarbon distribution in the Greater Oseberg Area to get a more complete understanding of migration and trapping in the area. This work has included observations of oil vs gas, fluid pressure and fault sealing in the area, as well as re-examination of previous modelling work. We suggest that diagenetic fault sealing trapped hydrocarbons in several structures in the Greater Oseberg Area. The faults were largely open when the reservoirs were at shallow burial depths. Therefore, oil could migrate to the Oseberg Alpha structure from the north, and to the Omega structures from the west. The faults started to seal off as the rocks entered the temperature zone that is favourable for quartz diagenesis. This resulted in fault sealing at some places, and open fluid communication along faults (possibly below the fluid contact positions) at other places. Further burial resulted in complete sealing of the fault planes and therefore in pressure build-up. The diagenetic reactions progressed despite the high fluid pressures and resulted in pressures that reached the fracturing limit at Huldra. These high pressures resulted in leaked and underfilled segments here.
-
-
-
Fault Seal Prediction and Production Experience. Fault Behavior in Upper Jurassic Sands, Halten Terrace
Authors S. Ottesen, H.S. Solli Fossmark, R. Worthington, J. Van Hagen and N. FredmanSummaryThis study reports the findings of a regional investigation of fault seal prediction and production behaviour including several fields in the Halten Terrace area, on the Norwegian Continental Shelf. The Upper Jurassic quartz rich, shallow marine deposits of the Garn Fm are investigated. Faults where Garn Fm. is self-juxtaposed are considered and in short; the study compares production data (fault properties from dynamic flow history matching), 4D and initial pressure data) with fault permeability predictions from a combination of SGR calculations and petrophysical measurement of cored faults. One field also give a calibration point for smearing potential of the shale below the Garn Fm as the faults in this field only provide very limited communication across the shale even if Garn Fm is juxtaposed against deeper stratigraphy.
-
-
-
Validation of the Membrane Seal Capacity Workflow Using a Case Study and MICP Database
Authors S. Martinez, T. Harrold, G. Saceda and K. MeyerSummaryIn this article a workflow to predict membrane seal capacity and maximum hydrocarbon column potential is applied in two exploratory wells in a new basin. The aim is to prove that the results from the workflow are in the range of the results obtained from laboratory MICP measurements. In addition to the workflow validation, the second objective is to present a regional database built over several years to help refine the hydrocarbon column prediction in new prospects and analog seals.
-
-
-
Modelling how Faults Influence the Trapping of Oil & Gas
By N. GrantSummaryFaults are known to have a significant role in the migration and trapping of hydrocarbons, either offering conduits for, or barriers to, fluid flow. Faults may also influence fluid phase trapping and hence potentially phase fractionation in the subsurface. A Monte Carlo approach is used to model these effects for trap analysis. The aim its to show how varying both fault seal capacity, the fault orientation, the regional stress tensor, and the trap geometry can all affect how oil and gas are retained within a trap. The model reduces the problem to a 1D analysis with a structural description depth-referenced to the crest of the prospect. Both juxtaposition and membrane fault seal are included, together with hydrodynamic effects and fault reactivation risk. A trap scenario is modelled using input parameter distributions and governing equations. The potential of a prospect to trap hydrocarbons is then evaluated in a roll-up of results with the outputs including a predicted hydrocarbon column height distribution and column height control statistics. The technique also offers an insight into potential fluid phase partitioning that may occur dependant on the active leakage mechanism and spill control, enabling gas versus oil columns to be predicted in certain charge scenarios.
-
-
-
Top Seal Membrane Capacity Prediction: A Practical Workflow for Exploration
Authors G. Saceda Corralo, T. Harold, S. Martinez and A. VayssaireSummaryAn empirical approach to estimate capillary pressure in conventional mud rock seals is proposed based on estimates of compaction state, porosity or effective stress of shales / mud rock sealing formations. This workflow covers how to infer or estimate shale porosity from different sources of data, the relationships to calculate the capillary entry pressure and maximum hydrocarbon columns. The equations and empirical relationships are based on published work and exploration industry software.
-
-
-
Evolution of Clay-Gouge Volume and Sealing Capacity during Fault Growth Insight from Present and Paleo Oil-Column
More LessSummaryIt has been demonstrated that increased clay-gouge volume within a fault zone increases a fault’s ability to inhibit hydrocarbons migration across or along it. And Yielding et al. (1997) compared clay-gouge volume (such as shale gouge ratio) vs. the across-fault pressure difference in various fields around the world, calibrated of fault sealing capacity, the quantitative evaluation of fault sealing capacity was realized, and this method is currently widely used in petroleum exploration. However, the result of calibrating fault sealing capacity only reflect the sealing capacity of fault during the stable period, less attention is given to the errors of evaluating fault sealing capacity due to fault activation in field scale. In this paper, we calibrate of fault sealing capacity based on present oil-reservoir analysis from Qinan area, Bohai Bay Basin, China, and analyze the effect of fault reactivation on fault sealing capacity by means of identification of paleo-oil columns. Then we confirm the evolution of clay-gouge volume during fault growth and analyze the effect of fault reactivation on the nominal sealing capacity and the true sealing capacity. At last, we establish an evolution mode to illustrate the relationship between clay-gouge volume and sealing capacity during fault growth.
-
-
-
Closing the SeAM - Linking Seal Analysis and Mechanics to Improve Fault Stability Prediction
Authors M. Kettermann, V. Schuller, A. Zamolyi, M. Persaud and B. GrasemannSummaryThe reactivation of critically stressed faults during production-induced pressure changes bears a big risk and limits the total recoverable volume as for safety reasons pressure changes must be kept lower than potentially possible. Reservoir pressure and regional stresses can be reasonably well measured and estimated before the start of production. However, to maximize recovery while minimizing the risk of fault reactivation, assessing fault strength as accurately as possible is crucial. The strength of a fault depends on the mechanical properties of the fault rock (friction angle, cohesion), which can vary strongly over short distances, depending on displacement, complexity of fault geometries and available host rock lithologies. Especially clay minerals entrained in the fault core can tremendously reduce the strength of faults. We develop a workflow that uses standard fault seal algorithms (e.g. Shale Gouge Ratio) to estimate shale content in the fault rock and subsequently provide corresponding frictional properties for each fault cell in a reservoir model. This will be a function of the statistical distribution of shale smears in a fault depending on mechanical properties at time of faulting, as well as present day effective stress.
-
-
-
A Review of Fault Modelling Approaches
Authors A.E. Lothe, B.U. Emmel, A. Lavrov and P.R. CerasiSummaryDifferent approaches are used for large scale fault modelling for CO2 storage, pressure prediction on production scale or on geological time scale. In this contribution we give a short overview of several numerical methods targeting different aspects of fault properties on different scale. We show examples of fluid flow along and across faults, effect on pressure build up and stress changes due to production and injection in a neighbouring fault block, using four different simulation methods. These are a) 3D pressure basin modelling, b) reservoir modelling, c) modified discrete element modelling and d) finite element modelling. The different methods address different challenges related to fault behaviour for a) pressure build up over geological time scale, b) effect of pressure depletion in one part of a basin, and how it is controlled by fault transmissibilites, c) permeability and d) stress changes along a single major fault, due to pressure changes on production time scale.
-
-
-
An Empirical Approach to Reduce Uncertainty when Predicting Hydrocarbon Column Heights during Prospect Evaluation
Authors I. Edmundson, R. Davies, L. Frette, E. Kavli, A. Rotevatn and A. DunbarSummaryPre-drill volume estimation in exploration involves a number of input parameters that carry a degree of uncertainty. The largest contributor to the pre-drill volume uncertainty is typically the hydrocarbon column height, which is controlled by both charge and seal behaviour. However, it is this parameter that E&P companies often find the hardest to predict, partly due to the lack of sufficient empirical data from existing fields and discoveries. A new empirical dataset has been compiled, which contains hydrocarbon column height, trap height, overburden thickness and trap fill percentage values for over 240 discoveries across the Norwegian Continental Shelf. The data has been aggregated into a probability tree to calculate the likelihood of a discovery containing different ranges of trap fill, depending on its burial depth and trap height. Results show that for a discovery with a given trap height, the probability of recording 100% fill increases when the overburden thickness increases. Equally, when the trap height increases for a given overburden thickness, the probability of discovery 100% trap fill decreases. These findings, amongst others strongly indicate the need to integrate trap height and overburden dimensions to assess suitable hydrocarbon column heights to use when estimating pre-drill volumes.
-
-
-
Shale Smear Geometries and Implications for Fault Seal: An Outcrop Study from Mt Messenger, New Zealand
More LessSummaryFaults in reservoirs can act as both conduits and barriers to fluid flow. Fault seal arises due to a number of mechanisms including, juxtaposition of permeable and impermeable lithologies, fault cementation, and the production of low permeability fault rock by deformation of host beds. This presentation focuses on the production of low permeability fault rock by shale smear. The aim of this investigation was to gain a representative sample of the smearing behaviours of siltstone beds within the Mount Messenger Formation, a poorly lithified unit with a maximum burial depth of 1.5 km. Siltstone beds appear to be incorporated into fault zones by two end-member mechanisms; smearing and meso-scale synthetic faulting. Thin sections of these smears show that they are often deformed by brittle micro-faulting which is generally sub-parallel to the fault zone. Similarly, meso-scale faulting is most often characterized by multiple synthetic slip surfaces that displace the host beds across the fault zone. We suggest that shearing and incorporation of siltstone beds into fault zones is primarily a brittle process. This distinction is important for fault seal as it is more likely to produce variable silt source bed thicknesses within fault zones.
-
-
-
The Influence of Fault Membrane Seal on Hydrocarbon Migration and Accumulation in the South Sesulu
Authors I. Lubis, H. Haryanto, L. Gultom, R. Sipayung and G. FauziSummarySouth Sesulu is tectonically complex hydrocarbon province in the southern part of Kutei Basin, Kalimantan. This study presents the role of fault seal on the interplay of migration and accumulation in the fault bounding trap in the northern part of the South Sesulu are. In particular, the study focuses in the deltaic reservoir, mapped as the “13.5 Ma” horizon that has 350 ft gross thickness. We focus the issues raised due to tectonic development prior to hydrocarbon generation and charge at about 11 Ma and subsequent structural reactivation. The structural reconstruction indicates that closure of the objective trap was generated within 13.5 to 9.8 Ma and structural modelling concludes that normal faulting continued to develop in the prospective trap. Displacement backstripping and fault seal analysis (FSA) shows that the bounding fault to the trap probably acted as a migration pathway when the 11.8 Ma horizon was deposited but later acted as seal after continued displacement. FSA has enabled us to predict the hydrocarbon water contact (HWC) in terms of a membrane seal of fault which is consistent with the hydrocarbon discovery in exploration wells. We have used the same analysis to predict as yet untested column height on other closures along the F8 bounding fault.
-
-
-
Observations on Hanging-Wall Traps that Are Dependent on Fault-Rock Seal
Authors P. Bretan, G. Yielding and E. SverdrupSummaryHanging-wall traps are successful trapping styles with discoveries made in many sedimentary basins worldwide. Examples of hanging-wall traps are documented in the literature but there are very few case studies that describe the role played by fault-rock seal on trap integrity. This contribution focuses on hanging-wall traps that are dependent upon fault-rock seal. Detailed analysis of hanging-wall traps has revealed that the hydrocarbon column height trapped by fault-rock seal appears to be independent of burial depth and is typically less than 190m in height. A similar observation was observed in footwall traps that are dependent on fault-rock seal. Cross-plots of Shale Gouge Ratio (SGR) and buoyancy pressure from hanging-wall traps have a similar data distribution to published SGR – buoyancy pressure calibration plots. Gas-bearing hanging-wall traps are at or close to seal capacity when burial depths are less than 3500m. In contrast, gas-bearing footwall traps are at seal capacity at burial depths greater than 3500m. Published ‘global’ calibration plots of SGR vs buoyancy pressure can be used to evaluate the sealing or non-sealing risk of hanging-wall traps in the same manner as for footwall traps.
-
-
-
An Integrated Calibration Method of Fault-Seal Capacity in Sand-Clay Sequences: Mechanisms, Principles, and Potential Pitfalls
More LessSummaryFault seal failure envelops calibrated by researchers can hardly be interpreted by the variation mechanisms of fault-rock permeability. We attempt to introduce an integrated calibration method of fault-seal capacity from rock deformation mechanisms and their controls on fault permeability and discuss the potential pitfalls in its application. Fisrtly, the sealing capacity of faults have a lower and upper bound which are controlled by cataclasis density and properties of low permeability host rocks. Secondly, periods of fault activation and main stage of oil accumulation should be clarified before calibration to identify whether hydrocarbon reservoirs are damaged by trap-bounding faults, in order to avoid overestimating the sealing capacity of reactivated trap-bounding faults. Then, AFPD-SGR data from faults reactivated after the main stage of oil accumulation can be never used in the calibration of SFE, which may cause the underestimation of sealing capacity of stable trap-bounding faults. Finally, the integrated calibration of SFE from previous compatible work could help not only to identify a potential reactivated fault on the geological time scale and also to understand the sealing capacity or permeability on the production time scale.
-
-
-
Fault Zone Evolution and Architecture in Siliciclastic Turbidites and their Impact on Hydraulic Behaviour
Authors H. Riegel, T. Volatili, D. Jablonska, C. Di Celma, F. Agosta, L. Mattioni and E. TondiSummaryFaults in deep marine siliciclastic rocks are often characterized by great variability in fault zone architecture and relative permeability properties. Siliciclastic rocks found in turbidite successions are commonly represented by alternating layers of various thickness and grain size, which form successions with contrasting mechanical properties. For example, the alternation of sandstone and mudstone layers is responsible for the simultaneous occurrence of brittle (cataclasis) and ductile (clay smear) deformation. In this study, we will investigate the turbidite successions outcropping in Tuscany, Italy, as the study areas contains several faults with varying values of displacement that cut through heterolithic layers. Results of field and laboratory analysis are consistent with both bed thickness and grain size distribution of alternating beds dictating the fault zone architecture in terms of fault core composition and texture, damage zone thickness, fracture intensity and height. Furthermore, presence of thin siltstone/shale layers in alternating patterns with thicker sandstone bed intervals likely enhanced the development of clay smear structures in the investigated outcrops. The analysis of deformation mechanisms and resulting fault zone architecture carried out in the selected siliciclastic rocks allow to better understand the role of inherited depositional, diagenetic, and structural heterogeneities on fault zone permeability properties.
-
-
-
Effect of Shale Volume on the Porosity of Clastic Reservoirs. Case-Study from Mkuki-1 Reservoir, Offshore Tanzania
Authors D.E. Mbaga and G. MwendenusuSummaryThe presence of clay minerals or shale in porous formations presents problems from the interpretation of wireline logs. This mainly affects the porosity and water saturation quantification of the reservoir which result into gross effect in the calculation of hydrocarbon in place (STOOIP). Most of the sand reservoirs show some degree of shaliness. It has therefore become vital to determine the effect of shale content in most of the clastic reservoirs. This project is dedicated in describing the relationship between shale content and the porosity of clastic reservoirs and derive any trend between the two parameters using wireline logging data from Mkuki-1 well, offshore Tanzania.
-
-
-
Fault Growth and Linkage: Implications for Trap Integrity Associated with Fault Reactivation in the Qinan Slope, Huanghua Depression of Bohai Bay, China
More LessSummary1) Under the differential activities of faults, tilting is the formation mechanism of antithetic fault traps, and fault segment growth and linkage controls the formation and evolution of synthetic fault traps.
-
-
-
Gas Physical Properties and their Implication on Gas Saturation and Leakage in Deep Reservoirs- A Case Study of Cambrian Gas Field, Sichuan Basin, China
More LessSummaryBased on series of experiments and numerical calculation, the gas physical properties (i.e. density, gas-water interfacial tension) were obtained and their implication on hydrcarbon saturation was studied. Furthermore, and evaluation model was established based on the identification of different types of residue water to obtain gas/water saturation in reservoirs. It is concluded that the lower interfacial tension between gas and water helps the gas charges into reservoirs and thus higher gas saturation was observed in the results of calculation. In addition, the more complicated hydrcarbon saturation variation during burial history was studied. It is found that the seal rock is thin thickness(∼50m) and gas in the reservoir tended to loss during the uplift in burial history.
-
-
-
Sealing Properties of Tight Rocks – Experimental Challenges
By A. AmannSummaryThe sealing capacity of sedimentary rocks has been discussed recurrently over several decades and in different contexts. These include the stability and longevity of petroleum and natural gas reservoirs as well as the safe permanent storage of radioactive waste or carbon dioxide in the subsurface.
-
-
-
New Measurements of the Petrophysical Properties of Top and Fault Seals
Authors Q. Fisher, C. Grattoni, S. Allshorn and P. GuiseSummaryThe paper presents new measurements on key petrophysical properties of fault rocks and shale top seals at subsurface conditions. In particular, results are presented from a new instrument that can make mercury injection capillary pressure measurements at reservoir conditions and accurately measure the threshold pressure. Absolute gas permeability from shale caprock samples measured using an extended pressure transient experiment are presented. New relative permeability measurements are also presented from fault rocks. The stressed MICP measurements suggest that the threshold pressures of fault rocks and top seals could be far higher than has previously been assumed. The transient gas permeability measurements indicate that fractures are often present within shales that may not be present in the subsurface indicating that traditional methods may result in an overestimation of shale permeability. The gas relative permeability behaviour of fault rocks appears to be partially related to their absolute permeability. The oil-water relative permeability behaviour of fault rocks seems highly variable and requires further investigation.
-
-
-
Clay Smear: How Predictive Will we Ever Be? Insight From Sandbox Models and Seismic
Authors P.D. Richard and J. UraiSummaryClay smear is an important fault seal mechanism which controls fluid distribution in hydrocarbon fields. Although the idea is four decades old and extensive research and application in the subsurface has improved our understanding, predicting fault seal by clay smear remains a challenge. The complex architecture of fault zones and the difficulties of critically testing subsurface predictions calls for a challenge to the reliability of current methods. Empirical predictions rely on local calibration, but commonly actual findings are quite different from predictions. The objective of this paper is to share some pioneering sandbox experiments 25 done years ago to determine the structural processes and physical parameters that control clay smear formation. Two modes of clay smear formation have been modelled: injection and smear. The mode is determined by the contrast in strength between the clay and the surrounding rocks. If the strength contrast is low (relatively strong clay layer), no injection occurs, and the fault zone is a sheared equivalent of the faulted stratigraphy. If the strength contrast is high enough (soft clay), injection of clay into the fault zone is triggered. These experimental results led to the development of the squeezing block concept of clay injection.
-