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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
881 - 900 of 980 results
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Method of Stress Direction Determing by Three Calipers
More LessSummaryStress direction is one of the important parameters in petroleum exploration and development. Logging data can be used to calculate stress direction. Some researches of this study have carried out. To achieve the rapid qualitative identification and precise quantitative evaluation of stress direction, a new method to determine stress direction is established by three calipers based on the borehole breakout ellipse method. A wall ellipse can be fitted with three calipers. Four cases based on the length relationship between the three calipers are studied. Each case corresponds to a formula. Then the direction of long axis is got. The minimum stress direction is determined by combining the angles of the long axis of ellipse and the plate 1. This method is applied well in the real data and can fix the minimum stress direction within 30 degree quickly. It can also provide the whole interval accurate minimum stress direction and be easy to operate.
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Improving Constraints on Fracture Behaviour in Geomechanical Models Using Uncertainties in Input Data
Authors H. Deckert, S. Abe and W. BauerSummaryAn important step in the exploration of a geothermal project is determining the stress state of the faults in the project area. While of course the main aim of exploration is to find structures allowing high production rates, the prevention of perceivable seismicity during geothermal production is also an important issue, as especially in Europe many geothermal projects are situated or planned in densely populated areas.
Therefore the dilation tendency, influencing fluid flow properties, and the slip tendency of the faults, which influences seismic risk, are of particular importance. An issue frequently encountered, in particular in greenfield explorations, is insufficient data availability regarding stress boundary conditions and fault properties. Here we present a workflow based on ensemble modelling and statistical analysis, which allows to mitigate the problems cause by the lack of data and to quantify the resulting uncertainties. We also present results from an application of the workflow.
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Quantifying the Impact of Natural Fractures on the Performance of Unconventional Wells Using Geomechanical Modeling
Authors A. Ouenes, N. Umholtz, Y.E. Aimene and J.A. NairnSummaryA geomechanical workflow that combines Geophysics, Geology and Geomechanics (3G) is discussed and applied to a Wolfcamp well. The new workflow uses the Material Point Method (MPM) to simulate the geomechanical interaction between hydraulic and natural fractures. The realistic distribution of the natural fractures input in the geomechanical simulation is derived from seismic. The workflow leads to multiple deliverables that provide a quantitative measure of the impact of natural fractures on the performance of the fraced unconventional wells. First, the quantitative impact of the natural fractures on the regional stress is provided through the differential stress. The second impact is through the proper modeling of the interaction between the hydraulic and natural fractures which is validated with microseismic data. Lastly, the impact of the natural fractures is measured in the J Integral where poor frac stages are identified in areas where there are too many fractures (near faults) or not enough fractures. The best frac stages seem to cluster where there are enough fractures to create a complexity, proximal to large natural fracture trends interpreted from seismically-derived coherency.
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The Role of Faults and Fractures in Local and Regional Perturbation of Present-day Horizontal Stresses - An Example from the Clarence-Moreton Basin, Eastern Australia
Authors M. Rajabi, M. Tingay, O. Heidbach and R. KingSummaryThe present-day stress field has numerous applications in both conventional and unconventional hydrocarbon reservoirs, particularly for borehole stability, reservoir drainage and flooding patterns, pore pressure and fracture gradient prediction, fluid flow in naturally-fractured reservoirs, hydraulic fracture stimulation, seal breach by fault reactivation and any geomechanical modelling.
The orientation of present-day maximum horizontal stress (SHmax) in most tectonic plates, such as North America, South America and Western Europe, is primarily parallel to absolute plate motion; suggesting that the plate boundary forces that drive plate motion also control the intra-plate stress field. However, the Australian continent displays a complex pattern of stress and is not oriented parallel to its north-northeast absolute plate motion.
In this study we conduct the first analysis of drilling-related present-day tectonic stress in the Clarence-Moreton Basin, which is located in the New England Orogen of eastern Australia. We analysed 11.3 km of acoustic image logs in 27 coal seam gas wells and interpreted more than 2800 drilling induced stress indicators (borehole breakouts and drilling induced tensile fractures) with a total length of 1.6 km, which suggest a mean SHmax of 068°N for the basin. However, there are significant localised perturbations of the horizontal stress orientation, both spatially and with depth due to presence of faults, fractures and lithological contrasts; suggesting that geological structures are a key control on the stress pattern in the basin.
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Integration of Multiple Tools for Geomechanical Models Across Fractured Formations
SummaryGeomechanics is a multidisciplinary discipline where geologists, reservoir engineers, geophysicists and drilling engineers work together in order to improve the drilling campaign to drill fast, safe and cost-effcient. The determination of the in-situ stresses, rock mechanical properties and pore pressure inferred in the geomechanical models is useful to predict well behavior and assess future stability problems.
This study presents a case study where a geomechanical model is generated for an offset well drilled through a fracture formation. The workflow consists of three phases: data analysis, fracture interpretation and geomechanical model. The fracture study is based on micro-CT images and image log interpretation. The definition of the pore pressure profile is one of the most important steps in the geomechanical model. The estimation of the pore pressure has to be done in detail when formations are fractured. The pore pressure profile along the well is calculated based on the normal compaction method, which highlights the effect of fractures on the measurements and hence on the pore pressure prediction. The study presents the importance of detecting fractures prior to the generation of geomechanical models in order to introduce the appropriate considerations in the generation of the geomechanical model.
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Predicting the Brittleness of Rocks From a Crushability Index
Authors S. Kahraman and O.Y. ToramanSummaryThe determination of brittleness, an important mechanical property of rocks, requires some standard tests which are time consuming and expensive. The sample preparation and testing methods are easy in the crushability test suggested in this study and a small amount of crushed rock is enough for testing. That the crushability test can be applied on the drill cuttings is another important advantage. The prediction of brittleness from the crushability test will be useful for some cases. 500 g oven-dried crushed samples, in the size range of 19.0–9.52 mm, were prepared from twenty four different rock types. After charging the samples to a jaw crusher, the crushed materials were passed through the 9.52 mm mesh and the percentage of oversized material was described as the crushability index (CI). The brittleness B1 determined from the Protodyakonov impact test and the brittleness B2 determined from compressive and tensile strength were evaluated in this study. A significant strong correlation was found between the CI and the brittleness B2. Because the tested rocks cover sedimentary, igneous, and metamorphic rocks, the derived relation can be generalized. It can be concluded that the crushability test is a practical and easy method for the prediction of brittleness B2.
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Stress Studies Using 3D Seismic Interpretation Results and Earthquakes in a Gas Field, Southern Iran
Authors S. Pourbeyranvand, B. Lund, I. Abdollahie Fard and A. JavaherainSummaryPaleostress studies play a major role in understanding of the geodynamics and tectonic evolution of the earth’s crust. In this study, the paleostress history of and area covering an oil fields in Southern Iran, where the usual outcrop data for paleostress studies was not available so far, has been revealed by using 3D seismic interpretation results. The strike and dip of the fault planes extracted directly from the triangles consisting the 3D model of the fault plane while a new method implemented to estimate slip direction from seismic interpretation data. The Allan lines were used to extract the separation data for each horizon and the slip direction calculated from heave and through of the separation pairs. To compare the paleostress direction with the present state of the stress in the study area, the stress tensor inversion performed on the fault plane data from available earthquake focal mechanisms from the Global CMT project. A significant clockwise rotation from older layers up to the younger ones and finally the present day state of the stress was observed. The starting point of the rotation coincides with the initiation of the collision between Arabia and Eurasia which affected the SHmax direction at Eocene time.
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New Advanced Rock Removal Technique Using Laser Technology - An Update
Authors R. Hafizi, M. Bakhtbidar and M. BakhtbidarSummaryNo other scientific discovery of the 20th century has been demonstrated with so many exciting applications as laser acronym for (Light Amplification by Stimulated Emission of Radiation). Lasers are employed over a wide range of applications from scientific research, biomedicine, and environmental sciences to industrial materials processing, microelectronics, avionics, and entertainment. Laser drilling tests showed that high power lasers have the ability of drilling good clean holes to a certain depth, at which point melting occurs and a layer of glassy phase forms. Additional laser energy either did little or created fractures due to a combination of the effects of reflecation loss from the glassy surface, heat release from the bottom edge, and poor purging. This paper will present study results on using a pulsed CO2 laser to drill through the given rock samples. Preliminary test shows that CO2 laser can drill the rock as efficiently as the other types of high power lasers and the permeability of the rock lased by pulsed CO2 laser beam increases up to 150% compared to non-lased rocks due to clay dehydration and microfractures induced by the high temperature gradient and phase transformation volume expansion generated in the rock while lasing.
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Multi-component Seismic Noise Attenuation with Multichannel MTM Filtering Method
More LessSummaryVector relationship between multi-component seismic data is very important for multicomponent processing and interpretation, but this relationship could be damaged when each component is processed individually. We extend the modified trimmed mean (MTM) filtering method to attenuate the random noise of multicomponent seismic data simultaneously. We implement multichannel MTM filtering along local event, and the optimum track of local event is detected according to the spatial distance between the hodographs of vector waves. The multichannel MTM filter is applied to synthetic and field data sets. The results are compared to those generated by using single channel MTM filter and low-pass filter. Results indicate that the multichannel MTM filter can attenuate noise while preserving the relative amplitude information of multi-component seismic data more effectively than the alternatives.
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A Simple Simultaneous Estimation of Water Static, Non-linear Clock Drift and Node Depth Error for Deep Water OBN
Authors B.W. Hootman, P. Kristiansen, A. Ogunsakin, O.K. Zdraveva and E. QuadtSummaryOcean bottom node (OBN) acquisition presents some interesting challenges and opportunities for data processing. Among these are the statics caused by water velocity variations over time, node depth error, non-linear clock drift, and water height variation due to tides. Each one is a tractable problem in the absence of the three other effects; however, when all three are acting simultaneously the interaction makes it difficult to solve them.
We explain the problems associated with determining these effects due to their interactions, and propose a simple and efficient method to simultaneously estimate the effects of all. We describe the simplifying approximations that reduce the problem to source and receiver consistent static corrections. We introduce a dynamic binning procedure used to correct the asymmetry of OBN ray paths. Using a deep water OBN dataset from offshore Nigeria, we present the results of the procedure and show static corrections due to water velocity variation, non-linear clock drift, node depth error and tidal variations. We show the final images of the down-going wave mirror-migration, verifying that the application of the static corrections improve the image.
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A Ghost Prediction Based OBC PZ Summation Method for Comolex Seabed
More LessSummaryIn ocean bottom acquisition, receiver side deghosting is normally done by summing together the hydrophone P and geophone Z data. A prerequisite for this method to work effectively is the precise calibration of geophones to hydrophones, so as to compensate for the differences in sensitivity and coupling. A “cross-ghosting” approach has been proposed to extrapolate geophone and hydrophone data to have the same manner for matching. However, as far as we know, existing cross-ghosting methods are based on a 1D geology assumption. In this paper, we describe a cross-ghosting method using 2D wave-equation extrapolation, which accurately predicts the ghost according to the structure of the sea-floor. By honoring the geology and angle dependency of ghosts, more data can be included for calibration, providing a more accurate geophone calibration filter with which to separate up-going and down-going wavefields. The method only needs the water depth information and water velocity, and has no limitation on subsurface geology or structure. We compared this algorithm to the conventional 1D method and results show the superiority of our approach.
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Experimental Airgun Survey Using DONET Seafloor Observatories to Estimate Seismic Anisotropy in the Nankai Trough, Japan
Authors T. Kimura, E. Araki, S. Kodaira, S. Miura, H. Mikada, N. Takahashi, M. Takaesu and M. NakanoSummaryThe Nankai Trough, Japan is a major subduction zone, and huge mega-thrust earthquake repeatedly occurred. In this area, DONET (Dense Oceanfloor Network systems for Earthquake and Tsunamis) seafloor cabled seismic network, and IODP C0002G borehole observatory were distributed. In KR13–17 cruise, conducted by R/V Kairei in November 2013, we performed an experimental survey using DONET and IODP C0002G seismometers and airgun shooting to estimate seismic anisotropy in the Nankai Trough. Seismic anisotropy can be a proxy of stress state, which would be a key parameter governing its fault dynamics triggering mega-thrust earthquake in the subduction zone. In KR13–17 cruise, we performed airgun circle shooting around DONET and IODP C0002G seismometers. Then we computed radial and transverse components for each shot-receiver azimuth from original horizontal records of seismometers. In radial and transverse components, P-S converted waves reflected from the bottom of shallow sediment layers were clearly visible. We then obtained azimuthal seismic anisotropy below seismometers in shallow sediment. Obtained results have good agreement with results from another method and dataset. We plan to conduct next survey in the same survey lines to detect temporal evolution of the seismic anisotropy in the seismogenic subduction zone.
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Air Gun near the Sea Floor as Shear-wave Source?
Authors G.G. Drijkoningen, D. Dieulangard, E. Kjos and M. HolickiSummaryThe feasibility of using an air gun near the sea floor as shear-wave source has been investigated. With an air gun near the sea floor, an evanescent P-wave in the water becomes a propagating S-wave in the sea floor, such that it seems that a pure shear-wave source has been used at the sea floor. This type of wave has been called a P*S wave. An experiment with such a set-up has been carried out at the Valhall field. For that case, modelling shows that shear-wave related event of the type of P*S waves can be expected with such a set-up. Especially at larger offsets, P*S waves can be expected. When analysing the field records and Constant-Velocity Stacks, it is hard to find P*S-wave reflected events. On the other hand, P*S-wave refracted events can be discerned in records. These events can be brought up to stack level and imaged, as shown in this paper.
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Computing Near-surface S-wave Velocity Models by Inversion of Converted-wave Traveltime Differences
Authors R. Cova and K. InnanenSummaryCharacterizing the near-surface is an important part of solving seismic static problems. It is also a critical step as input for more general iterative inversion methods applied to land seismic data. In the case of converted waves this becomes even more true due to the large magnitudes of the shear-wave statics. In this study, a solution based on the difference in conversion traveltimes between receivers is proposed. This solution may be useful for inverting delay times retrieved by interferometric techniques. Due to the complexity of the partial derivatives of the forward modelling operator for this case we decided against local descent-based methods, adopting instead a simulated annealing inversion method. This is also justified by the complex topography of the objective function. Performing a representative number of iterations of the proposed algorithm successfully retrieves the true parameters of the model. Since traveltime differences were used, the inverted parameters only allowed us to compute changes in the depth of the base of the near-surface rather than its absolute value. This can be fixed through a calibration process given the depth of the low velocity zone for at least at one receiver location.
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Explosive Source Generated Shear Waves in Elastic Forward Modelling
Authors R.J. Ferguson and M.R. WilsonSummaryRecent field experiments suggest that vertical vibrators and shot-hole explosives generate strong SV-waves, and that SV-P and SV-SV modes are interpretable on vertical component data. Consistent with these field experiments, we find that strong SV-waves are generated in explosive-source, elastic-forward modelling. By using common-source migration to focus a number of reflection modes including SV-P, SV-SV and SH-SH, we demonstrate that, within the context of synthetic data, these modes provide imaged reflections when only an explosive source is used.
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Separation and Imaging of Water-layer Multiples for Walk-away VSP Surveys
Authors S. Fiorentino, M. Codazzi and P. MazzucchelliSummaryWalk-away VSP surveys allow to obtain information about the subsurface structure thanks to the multi-component geophones in the borehole that record the pressure field originating from a seismic source at the surface and reflected by interfaces in the subsurface. Different spurious wavefields can contaminate reflection data: among them, multiple arrivals can be the most energetic source of coherent noise that can hide information recorded at target level for marine acquisitions, especially in shallow water environments. Fully data-driven multiple elimination techniques cannot be directly applied to VSP datasets, because of the lack of recordings at surface level. However, the knowledge of the bathymetry allows to model and subtract water-layer multiples, at least.
Thus, a procedure to estimate, subtract and separate by order water-layer multiples is described. Furthermore, an iterative schema is proposed to separate by order and then correctly depth–migrate the estimated water-layer multiple reflections.
A so-called “double-mirror” imaging approach is derived, that relies on a simple source geometry modification: imaging of multiples can be performed without the need of any modification of standard depth-migration tools. Results on simulated data prove the feasibility of the proposed approach.
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Determining P-wave Azimuthal Anisotropy from Walkaround VSP with Offset-dependent Slowness Corrections
More LessSummaryP-wave local slowness data from a walkaround VSP can provide a measure of azimuthal velocity anisotropy to characterize fractured rocks or stress fields around a well. When the acquisition is constrained to have irregular shot points, shot-offset-dependent corrections are required. For unconventional plays, a correction for background polar anisotropy might also be necessary to effectively extract the azimuthal anisotropy around the well. This study introduces a modified total slowness and a two-step correction technique to remove the background VTI and minimize the residual offset bias in the walkaround VSP. Field data tests demonstrate that this new technique can provide a quick and quantitative measure for the orientation and magnitude of fracture- or stress-induced azimuthal anisotropy.
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Analysing the Effects of Least-squares Datuming on VSP Multiple Imaging
Authors A. Aldawood, I. Hoteit, G. Turkiyyah and T. AlkhalifahSummaryInterferometric transformations are widely applied to transform seismic data from one acquisition geometry to another. We used a correlation-type interferometric transformation to redatum vertical-seismic-profiling multiples into surface-seismic virtual primaries. Conventional redatuming, based on the cross-correlation of seismic traces, yields virtual surface-seismic records that suffer from correlation artefacts, wavelet distortion, and low-temporal resolution. These effects are mainly caused by the limited recording aperture, the band-limited nature of the source wavelet, and the coarse source-receiver sampling. Least-squares migration of the virtual surface-seismic gathers can partially enhance the seismic resolution and improve the quality of the final migrated sections. However, our results demonstrate that the least-squares datuming step remarkably helps suppress the cross-correlation artefacts, enhance the seismic resolution of the seismic events, and correctly deconvolve the source wavelet. Therefore, the obtained migrated sections suggest that least-squares datuming can be an essential processing step to apply to VSP surface-related multiples prior to imaging subsurface structures.
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Using a Fibre Optic Cable as Distributed Acoustic Sensor for Vertical Seismic Profiling at the Ketzin CO2 Storage Site
Authors J. Götz, S. Lüth, J. Henninges and T. ReinschSummaryFibre optic Distributed Acoustic Sensing (DAS) or Distributed Vibration Sensing (DVS) is a technology that uses an optical fibre cable as a sensor for acoustic signals. Within the last years, DAS/DVS was further developed to record seismic data. We present a successful DAS/DVS-VSP (Vertical Seismic Profiling) field test performed at the Ketzin CO2 storage site, Germany. It was possible to record 23 VSP source points simultaneously within four wells and to build a small 3D VSP cube. The DAS/DVS-VSP cube complements the 3D surface seismic by providing a focused high resolution image below the injection site.
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Feasibility of Cross-well Seismic as CO2 Monitoring Tool
Authors V. Shulakova, R. Pevzner, B. Gurevich, M. Madadi, A. Bona and M. UrosevicSummaryThe next stage of CO2CRC Otway project involves exploration of the ability of various CO2 geosequestration techniques, including cross-hole seismic, to detect and monitor presence of CO2. Despite the limited spatial coverage of a cross-well survey, the acquired data could be used to improve reliability of the whole monitoring and verification program.
Prior to any field experiment we evaluate the feasibility of cross-well seismic using computer modelling. We utilize finite-difference time-domain (FDTD) method for pre- and post- injection stages.
Here we present the results of our study and validate the detectability of CO2/CH4 gas mixture on time-lapse cross-well seismic data on the direct as well as the reflected wave fields.
We demonstrate that the presence of 15,000 t of a gas plume can lead to changes in transit times of up to 1.4 ms (in cross-well setting). The computed seismic tomography detects the difference in velocities up to 80 m/s. The difference caused by gas is also detectable in the migrated time section of reflected waves.
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