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Second EAGE Passive Seismic Workshop - Exploration and Monitoring Applications 2009
- Conference date: 22 Mar 2009 - 25 Mar 2009
- Location: Limassol, Cyprus
- ISBN: 978-90-73781-59-7
- Published: 22 March 2009
35 results
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Improved Event Location with Single Well Monitoring – A Case Study from Ekofisk
Authors G.A. Jones, D.G. Raymer and J.M. KendallWe relocate microseismic events from the Ekofisk reservoir in the North Sea that were recorded over an 18-day period in April 1997. A array of six 6-component sensors deployed in a vertical borehole with a 20 m spacing detected nearly 4500 events. Events are located using P- and S-wave travel times and azimuthal particle directions, which are calculated using a recently developed noise-weighted analytical-signal singular-value-decomposition method. A inherent 180 degree ambiguity in event locations exists with data recorded by sensors in a signal borehole and 1D velocity model. We remove this ambiguity using dip information estimated as part of the particle motion analysis. The relocation yields 1333 events, which are primarily concentrated in the producing part of the reservoir. In general, our location accuracy is 15m, but most events locate to within 10m. In comparison to the original event locations, the new locations show less scatter and cluster into more linear patterns, we interpret as fault structure.
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Non-linear Calibration of Complex Velocity Models in Microseismic Jobs
Authors T. Bardainne and E. GaucherThe calibration of the velocity model in microseismic jobs is critical to achieve statistically reliable microseismic locations. Indeed, the lack of knowledge of the wave propagation medium is the main source of location inaccuracy. This paper presents a non-linear calibration method of velocity models for passive, microseismic surveys. This method analyzes multiple time and polarization arrivals and uses a non-linear inversion, simulated annealing algorithm, which prevents the velocity solution from converging to a local minimum, to minimize the residuals and the location error measurements. This method calibrates complex velocity models which can be described, by velocities (P&S), velocity gradients, dip of layers or 3d surface layers. We present an example that demonstrates a significant decrease in location errors of microseisms as compared to typical methods.
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Passive Seismic Monitoring of a Heavy Oil Field
Authors A.C. Rosca, R.T. Langan, A.J. Jupe, S.C. Maxwell and P. DillettA pilot project was designed to monitor induced seismic activity in a relatively shallow heavy oil reservoir located in a low permeability, high porosity, silicious shale. Several hundred microseismic events have been located over the past two years using data recorded at two borehole seismic arrays. Microseismic activity occurs predominantly in two separate depth zones: one within the reservoir and one in the shallow overburden. Larger events are located at the top of the reservoir close to the injection well; shallow clusters of smaller events could identify fluid migration pathways in the overburden.
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Automatic Determination of Full Moment Tensor Solutions from P-wave First Motion Amplitudes
Authors D. Kuehn, H.N. Gharti, V. Oye and M. RothStandard microseismic monitoring nowadays focuses on event locations, but information on detailed source parameters is rarely extracted. The estimation of full moment tensor solutions of microearthquakes may provide valuable information on presence and geometry of faults as well as stress fields and changes thereof. Therefore, we included a full moment tensor inversion using automatically picked P-wave first motion amplitudes in addition to the computations of source spectra and related source parameters. We tested the routine using synthetic polarities and synthetic waveforms computed in a complex 3-D velocity model. In a first application, we investigated mining-induced seismicity in the Pyhäsalmi ore mine, Finland. Approximately 50% of the events show strong non-double couple components. Known explosions could be retrieved, being used as quality control of the method.
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Microseismic Measurements and Results in a Flowing Well During Well Stimulation
Authors U.G. Rinck, L.B. Barzaghi, L.V. Vetri, F.F. Ferulano, A.S.B. Boivineau and M.D. DibitettoThe measurement of low magnitude microseismic signals is a challenge inside a producing or injecting well with the high amplitude level of flow noise. We will present a recent deployment of the PS3-FW sensor tool technology for flowing wells and the results from the monitoring of a stimulation operation together with the reservoir understanding derived from it.
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Fracture Characterisation Using Estimates of Shear-wave Splitting from Microseismic Data
Authors J-M. Kendall, O. Al-Harrasi, J.P. Verdon, A. Wuestefeld and A. Al-AnbooriWe summarize observations of shear-wave splitting from passive seismic monitoring in a range of petroleum settings. Such measurements are relatively rare, but the emerging picture is one of fracture-induced anisotropy where a number of factors control both spatial and temporal variations. These observations offer insights into the state of stress in a reservoir and can serve as a ground-truth for geomechanical models.
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Reservoir Monitoring Using Induced Seismicity Magnitude – A Case Study from Oman
Authors S. Sarkar, M.N. Toksöz, H. Zhang, F. Al-Kindy, H.J. Lewandowski and N. Al-TouqiWe present a case history of passive seismic monitoring with location and characterization of seismic events induced by oil and gas production and water injection at a petroleum field in Oman. Two different monitoring networks have recorded thousands of microseismic events in the field over the last 9 years. We used data from both networks to locate the events and to analyze the patterns and causes of induced seismicity in the field. Locations of these events correlate with preexisting fault maps derived from surface seismic, and delineate structures that were previously unmapped by the same. Spatial and temporal analyses of event locations indicate large scale fault reactivation in the field. Comparisons between induced seismicity and production/injection data in the field suggest gas production as the primary cause of inducing seismicity in the field. The use of passive seismic technology in this field has been very effective in the characterization and surveillance of the reservoir.
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A Review of Crosscorrelation and Multidimensional Deconvolution Seismic Interferometry for Passive Data
Authors E.N. Ruigrok, K. Wapenaar, J.R. van der Neut and D.S. DraganovIn the search for new hydrocarbon reservoirs a number of sedimentary basins have so far been underexplored due to exploration challenges, like, e.g., difficult terrains to employ vibrator sources. Instead of conducting an active seismic survey, the first exploration data could be delivered by using natural seismicity and seismic interferometry (SI). For this purpose, arrays with continuously recording receivers would need to be installed in the exploration area. With SI, seismicity due to natural sources in the subsurface can be remapped to receiver positions on the Earth’s surface. The remapped responses can subsequently be used to create a (low-frequency) reflectivity image of the subsurface. Initially, SI was proposed as a crosscorrelation (CC) of responses. Recently, an alternative remapping procedure for passive data was proposed, by performing a multidimensional deconvolution (MDD). We evaluate both methods. We show that with both methods physical events can be retrieved correctly, also when there are moderate losses in the medium. In realistic situations, for both methods, additionally, specific artifacts are created, so-called internal events. We show how these artifacts could be recognized and removed.
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Recent Microseismic Monitoring Results from VSP and Permanent Sensor Deployments in Saudi Arabia
Authors M. Jervis and S.N. DasguptaA large surface and downhole microseismic network is complemented with a temporary VSP tool deployment to investigate water flooding in Ghawar. Water injector rates are varied to induced microseismicity in the Arab-D reservoir to map possible fracture zones and flood front variations.
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Focal Mechanism Determination from Few Sensors – Application to the Arkema-Vauvert Site, France
Authors M Godano, A. Pussacq, T. Bardainne, E. Gaucher and M. ValetteWe developed a method that enables computing focal mechanisms with only a few sensors. This method is based on a non-linear inversion of the P, SV and SH amplitudes of microseisms recorded on a set of sensors. Information brought by the focal mechanism enables determining the direction of the mechanism and the associated geological structure. Moreover, the computation of the mechanism enables a better estimate of the conventional source parameters. This full analysis has been performed on two microseismic clusters in the Arkema-Vauvert site in the south-East of France. Results of the focal mechanism study highlight that the two clusters are totally different in terms of source behaviour: one is characterized by the occurrence of the seismicity along an important identified thrust fault; the other is characterized by the reactivation of a well-known listric fault.
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Detection of Micro-seismic Events Using a Surface Receiver Network
Authors E. Schisselé and J. MeunierA new micro-seismic detection method is presented. It uses the redundancy offered by large horizontal arrays of geophones to automatically detect micro-seismic events without any time picking and this, even in poor signal-to-noise ratio conditions. The various performances of this method (precision versus computational time, signal-to-noise ratio, source grid parameters,) will be discussed and compared with those of the full semblance method on numerical signals. Results obtained using a real data set will be shown.
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Dual Treatment Monitoring with a Horizontal Receiver Array
Authors G.C. Michaud, W.S. Leaney, L. Bennett, M. McClay, K. Ainsworth, M. Kaiser and B. McPhersonMicroseismic monitoring from a horizontal well poses some challenges in terms of accurately determining the depth of the microseismic events. To handle data recorded by receivers distributed generally in deviated or horizontal wells, the full polarization vector in addition to event times must be included in the location algorithm. A 3D waveform-based grid search method is described and is applied to a dataset recorded with a horizontal receiver array to monitor a simultaneous dual well treatment. The results of the data processing workflow show a good estimation of the fracturing positions and growth on both sides of the receiver array.
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Microseismic Estimation of Permeabilities of Tight-gas Sands
Authors V. Grechka and S.A. ShapiroThe objective of hydraulic well stimulation is creating a network of fractures in a tight rock that enhance its natural permeability and make hydrocarbon production economic. As both the geometry of fractures and the permeability of treated formation influence the subsequent production, their assessment is important for development of tight-gas fields. While the fracture shapes and orientations are conventionally inferred from microseismic data acquired in the process of stimulation, here we demonstrate that the same data also allow quantifying the formation permeability. We discuss the permeability-estimation technique that utilizes the dynamics of microseismic clouds and apply it to data recoded during hydraulic fracturing of two wells drilled in the Pinedale Field, Wyoming, USA. The obtained permeabilities are then used to predict the gas rates.
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Microseismic and 3D Seismic Anisotropy Fracture Mapping – A North America Tight Gas Case History
By J.E. WolfeA tight gas case history from the North America Rocky Mountains shows the capability of borehole microseismic and 3D seismic anisotropy to delineate fracture systems induced in a clastic reservoir by hydraulic fracturing of a horizontal well. Dual monitoring of the horizontal well completion indicates improvements in fracture mapping by compressing hypocenters of the microseisms to more linear features that are corroborated by production logging flowmeter. Fracture half-lengths and vertical heights of fractures are indicated for reservoir modelling. Advanced processing of the microseismic 3-component geophone first motions indicates fracture azimuth and dips from a moment tensor inversion and suggests a conjugate set of orthogonal fractures in the reservoir. 3D seismic anisotropy results, using a fast and slow velocity direction calculated from the data, suggest inherent microfractures present in the rock prior to completion. Surface fault mapping in the field supports fractures mapped by both the microseismic and the 3D seismic anisotropy. Multiple regression analysis of drilling, completion and 3D seismic anisotropy parameters versus initial production for 30, 90 and 180 days results show independent contributions to production. A predictive production model based on the multiple regression analysis allows for future well planning and completions to optimise well performance.
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Understanding Hydraulic Fracture Growth by Mapping Source Failure Mechanisms
Authors T.I. Urbancic, T. Morrish and V. ShumilaDeveloping a model of hydraulic fracture development to characterize the effective fracture volume and identify potential means for re-stimulation of previously treated wells by utilizing seismic moment tensor inversion techniques
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Location Uncertainties in Passive Seismic Monitoring
Authors L. Eisner, W. Heigl and P.M. DuncanIn this study we shall address the effects of the receiver geometry, arrival time uncertainty and velocity model errors on location uncertainties. The effect of the velocity model error will be limited to a consideration of homogeneous media, although heterogeneity may have as profound effect on location accuracy as receiver distribution. Although many different sensor distributions are conceivable, we will focus on those that are most commonly applied in practice to include a 2-D grid of receivers on the earth’s surface and linear arrays of receivers in vertical boreholes.
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Microseismic Deformation Rate Monitoring
Authors S.C. Maxwell, J. Shemeta, E. Campbell and D. QuirkMicroseismic monitoring of hydraulic fractures is an important tool for imaging fracture networks and optimizing the reservoir engineering of the stimulation. The range of magnitudes of the recorded microseisms depends at the lower limit on the array sensitivity; while the upper limit varies significantly from site to site. In this paper the variation in the microseismic magnitude range is examined and compared with the injection and site characteristics. Although there are numerous potential factors effecting the seismic deformation, the energy of the pumping and state of stress appear to be the two dominant factors. However, interaction with pre-existing faults also results in increased deformation. In this paper these factors are examined using the seismic injection efficiency, defined as the ratio of seismic energy release to the hydraulic energy expended during the injection. Ultimately, this can potentially be used to design the stimulation to maximize the deformation. Characterization of the seismogenic potential is also important for seismic hazard assessment, as well as the design of passive monitoring.
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Goodbye Noise, Hello Signal! Improving Microseismic Monitoring in Noisy Environments
Authors F.H. Kindy, G. Engen, I. Ismaily, N. Touqi and A. YahyaiOver the last decade, Petroleum Development of Oman have deployed several microseismic monitoring systems. Due to the maturity of many of the oilfields in Oman, anthropogenic noise is in abundance. Given that the magnitude of some of the microseismic events can be as low as M = -3, noise can seriously hamper the detection and/or processing of such events. This paper describes PDO's experiments on new hardware and software to increase S/N. We show some examples of how our implementaion techniques improved event detection thresholds. In addition, we propose simple solutions that are not only more effective at noise reduction, but are also cheaper both in implementation and in reducing the subsequent cost of data processing.
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Predicting Microseismicity from Coupled Fluid-flow and Geomechanical Simulation
Authors D.A. Angus, J.M. Kendall, J.S. Segura, Q.J. Fisher and M. DutkoIn this paper, we predict microseismicity for a series of simple rectangular reservoir geometries using results from coupled fluid-flow and geomechanical simulation. The results are analysed in terms of their spatial and temporal variations in distribution. We also evaluate the associated failure mechanisms to characterise the type of brittle failure. We find that microseismicity is sensitive to reservoir size. In the small reservoir microseismicity is confined to the edges and in the larger models, where stress arching is significant, microseismicity extends further from the edges as well as up into the overburden. We observe also a transition in the style of faulting, from normal to oblique strike-slip, as well as variation in magnitude of failure of up to 5 orders of magnitude. This work represents some of the research being conducted for the IPEGG (Integrated Petroleum Engineering, Geomechanics and Geophysics) consortium, an industry sponsored research partnership between the University of Bristol, University of Leeds and Rockfield Software Ltd.
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3D Integration of Active and Passive Seismic for Reservoir Monitoring
Authors A.L. Vesnaver, L. Lovisa and G. BöhmIn this paper, we present an integrated procedure for estimating hypocentres and complex 3D velocity models by the joint traveltime inversion of micro-earthquakes and active surface seismic data. Reflection tomography can reconstruct the major formation interfaces along extended areas, but its vertical velocity resolution between interfaces is low. Micro-earthquakes may improve the ray illumination at the reservoir, so improving in sequence the 3D velocity model and their location precision. This data integration improves also the time origin estimation of micro-earthquakes.
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Locate Microseismicity by Seismic Interferometry
Authors X. Xiao, Y. Luo, Q. Fu, M. Jervis, S. Dasgupta and P. KelamisWe present a new seismic interferometry method to locate microseismicity by crosscorrelating the direct P- and S-waves from repeating sources, e.g., hydro-fracture. Typically microseismic data by surface array are below signal-to-noise ratio for a migration-type approach, and barely pickable for a traveltime-base approach. The repeating sources inside a resolution zone give high signal-to-noise ratio arrivals after stacking in a virtual source gather. This gives us superiority over traditional microseismic processing to remove noises, reflections and surface waves in the virtual source gather. Knowledge of the source excitation time is not needed and more reliability is provided. Numerical tests on an elastic model and noisy field microseismic surface array data partly demonstrate its superiority over the traditional microseismic processing.
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Microseismic Monitoring at the Basel, Deep Heat Mining Project
Authors B.C. Dyer, U. Schanz, T. Spillmann, F. Ladner and M.O. HäringThe Deep Heat Mining project in Basel, Switzerland aimed to create a cogeneration pilot plant, producing both electricity and thermal energy for district heating, from an Enhanced Geothermal System (EGS). The project is located in the Upper Rhine Graben within the city of Basel, Switzerland. During 2006 the exploration well BS1 was drilled to a total depth of 5000 m. The granitic basement was found at ~2257 m below ordnance datum (bOD). The estimated temperature at 5000 m depth was 190°C. In December 2006 an hydraulic stimulation of the openhole section of BS1, from 4379 to 4750 m bOD, was performed. The microseismic monitoring techniques and results of the stimulation are discussed here.
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Seismic Attenuation Assessment in Passive Seismic Investigations Using Pulse Width Analysis and Considering Source Effects
Authors G.A. Tselentis, P. Paraskevopoulos, N. Martakis, A. Serpetsidaki and E. SokosKnowledge of attenuation can be very useful in many stages of conventional seismic data processing as its removal increases resolution. Recent advances in passive seismic investigations involving microearthquakes indicate that attenuation assessment has a great potential as a direct hydrocarbon indicator and reservoir structural delineation. The purpose of this investigation is to assess the use of pulse width analysis to invert for attenuation structure.
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The Detectability of Microseismic Events Using Surface Arrays
Authors K. Chambers, J.M. Kendall, S. Brandsberg-Dahl and J. RuedaRecently there has been much interest in using data from surface arrays for passive seismic monitoring, where migration-based processing methods can be used to locate events in both space and time. Here we test the sensitivity of such methods to signal to noise ratio using signals embedded in different amounts of realistic noise. The data for this study consist of signals recorded across a temporary array of surface instruments in Wyoming, whilst a perforation shot was detonated in the subsurface. Applying a stacking procedure to the data with different signal to noise ratios demonstrates that surface arrays in conjunction with migration style processing methods can successfully image sources that are too weak to be observable in the raw data. The results show that the imaged shot position is relatively insensitive to the level of added noise. The primary effect of adding noise is that it defocuses the image of the shot location. We find that given our migration approach, the experiment geometry and recording conditions for the Wyoming dataset, signals embedded in noise with signal to noise ratios >0.1 can be successfully used to image and locate events.
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Correlation between the Reservoir Dynamics Performance and Production/Injection Induced Microseismicity – A Field Case
Authors J.G. Osorio Ltd and G. Peñuela Ltd LtdMapping passive seismics in Cusiana and Cupiagua fields has revealed a strong correlation between reservoir dynamic performance and production induced microseismicity. Fluid production/injection causes changes in reservoir pore pressure and, therefore, in local effective stresses. The changes in effective stresses cause natural fracture deformations which, in turn, change local transmissibilities and triggers microseismic events. The interplay of these two latter effects determines the relationship between microseismicity and reservoir dynamics (pressures and fluid saturations among other factors).
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Kinematic Features and Magnitudes of Fluid Induced Seismicity – Case Studies and Their Interpretation
Authors S.A. Shapiro, C. Dinske and J. KummerowSometimes fluid injections are characterized by a risk to induce a seismic event of a significant magnitude. Here we address magnitude distribution of seismicity induced by borehole fluid injections. However, firstly we give a short introductory review of microseismicity interpretation in geothermic reservoirs and by hydraulic fracturing. Then, we introduce a simple theoretical model, which predicts the earthquake magnitude distributions for fluid injection experiments. The temporal distribution of microearthquake magnitudes depends on the injection pressure, the size of the borehole injection section, the hydraulic diffusivity of rocks, and is also inherited from the statistics of pre-existing crack/fracture systems controlling the local seismicity. We consider different case studies and show how our model can be used to optimise the design of fluid injection experiments and reduce their seismic risk.
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Location Accuracy of an Integrated Microseismic Monitoring Network: A Saudi Arabian Case Study
Authors J. Vernier, E. Gaucher, S.N. Dasgupta and M. JervisA Saudi Arabian oil field was monitored during 28 days using three different networks of receivers: a digital wireline array set close to the reservoir depth, a permanent analogue array set at mid-depth and a dense surface array. A total of 267 receivers monitored the area when three 4-day injection tests occurred. About 9,500 microseisms were recorded. Recorded and picked microseisms ranging from magnitude -2.2 to 1.1 and were separately located using the different networks. The locations were consistent despite their uncertainties, especially in shape. The location using all networks strongly improved the location thanks to the monitoring coverage. However, this was only possible for 1% of the detected events because it required phase-picking on surface and a signal-to-noise ratio higher than one.
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Imaging Conditions for Time-reverse Acoustics
Authors B.W. Artman and I. PodladtchikovThe time reverse modeling (TRM) algorithm is almost identical to making shot illumination maps in shot-profile migration by extracting the zero lag of an autocorrelated wave field after successive extrapolation steps. Time reverse modeling is designed to locate sources within a model domain by producing energy intensity images after propagating reversed data traces into the interior of the domain with wave-equation extrapolators. This is closely related to illumination maps because both procedures require extrapolation of a seismic wave field into the model domain, but differ by utilizing slightly variant imaging conditions. The imaging condition for TRM is conventionally the maximum amplitude value extracted from the time axis after propagation. This assumes that the energy recorded at each receiver will constructively interfere in the model domain at the (x-z) location of the source to produce a maximum. The autocorrelation imaging condition for an illumination map solves the same kinematic imaging problem but differs from TRM by a square-root.
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Acoustic Emission Experiments and Microcrack Modelling on Porous Rock
Authors E. Aker, H.D.V. Khoa, F. Cuisiat and M. SoldalTo exploit the full potential of passive seismic data we study the acoustic emissions (AEs) that are generated as a result of microcracking or movement on microcracks in stressed rock. Microcracking is directly related to the release of stored strain energy inside stressed rock and coalesce of microcracks might result in macroscopic fractures. Therefore, studying AEs and microcracking in rock samples may aid the interpretation of microseismic events recorded around e.g. oil fields. Our work focuses on experimental measurements of AEs with corresponding numerical modelling in order to characterize the AE intensity and capability of typical intact or fractured reservoir rock like sandstone and chalk.
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Passive Seismic Monitoring of Gas Storage – Challenges for Improving Interpretation and Reducing Uncertainties
Authors J.-P. Deflandre, N. Dubos-Sallée and F. HuguetDuring several years passive seismic monitoring was performed at Céré-la-Ronde, an underground gas storage facility located in a saline aquifer. The permanent survey delivers interesting information on the initial reservoir fill-up, especially when considering the geomechanical behavior of the site. Location of microseisms by using two techniques is discussed. A comparison between the 1D and 3D results points out the limit of using simple structural models and gives some idea on associated uncertainties. The discussion deals also with the necessity of improving the workflow to take into account the induced seismic hazard in coupled reservoir and geomechanical modeling and constraining models with passive seismic data too. This experience is very useful in the context of CO2 storage and it constitutes an excellent analogue for short term considerations.
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Microseismic Monitoring of a Carbon Sequestration Field Test
Authors T.I. Urbancic, J. Daugherty, S. Bowman and M. PrinceEvent location and failure mechanism analysis of microseismicity to identify processes associated with a CO2 injection program
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The Challenge for Surface Passive Seismic Measurements in Kuwait
By G.R. RachedSurface passive seismic is a direct hydrocarbon saturation indicator technology. It detects the presence of subsurface hydrocarbons by recording and spectroscopically analyzing the low-frequency acoustic/seismic background noise (between 0.5 - 10 Hz) which is actively emitted by the earth. The measurements after filtering and analysis can be calibrated with well data and integrated with other geophysical data to provide information which can lower the uncertainty level for hydrocarbon exploration, appraisal and field development decisions. Surface passive seismic measurements were carried out in Kuwait to evaluate the suitability of the technology to detect and the map the extent of hydrocarbon occurrences. The main concern was the suitability of the technology to differentiate between various reservoirs in carbonate stacked-reservoir environment. The level of certainty in the result of the measurements could not be accurately assessed as there is a possibility that some deep reservoirs have not been penetrated by the wells in the area of the experiment. It was concluded that the technology (at that point) could not indicate the distribution of the hydrocarbon occurrences among the stacked reservoirs since the measured indicators are the summation of the responses of all the underlying reservoir layers. Nevertheless, the areas with highest hydrocarbon potential indication are considered the most interesting ones. A number of advancements in surface passive seismic have been recently reported and research results are indicating that the distribution of the hydrocarbon occurrences among stacked reservoirs is becoming achievable. However, It remains a challenge for the surface passive industry to demonstrate convincing successful case histories.
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Passive Seismic Study at an Oil and Gas Field in Voitsdorf, Austria
Authors M.-A. Lambert, S.M. Schmalholz, E.H. Saenger and B. SteinerWe present the results of a passive seismic survey over two separate reservoirs of an explored oil and gas field near Voitsdorf, Austria. Four different spectral attributes of the ambient seismic wave field are used to identify spatial correlations between anomalies in the surface wave field and the presence of hydrocarbons in the subsurface. The attributes quantify characteristic features of the wave field’s Fourier spectra in the low-frequency range (< 10Hz). The data indicate the position of the southern reservoir. The northern reservoir is less clearly identified. Nevertheless, using several attributes significantly increases the reliability of hydrocarbon reservoir detection compared to using only one attribute. Time-reverse modeling applied to the same data-set shows that the observed attribute anomalies at the surface may be caused by low-frequency seismic energy that is emitted from the reservoir areas. Preliminary results of a time-lapse experiment (comparison of data acquired in April 2007 and in April 2008, respectively) reveals a good reproducibility for two of the four attributes. A first comparison between time reverse modeling applied to the 2007 and the 2008 data-set consistently indicates the presence of seismic sources in the area of the two reservoirs.
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Pilots to Determine if Passive Seismic Technologies Can Aid in Solving Field and Exploration Challenges in Carbonates
Authors W.L. Soroka and M.S. Al-JenaibiIn the Middle East where giant billion barrel oil fields exist and there is the potential to find additional reserves, efforts to pilot advanced geophysical technologies to overcome carbonate challenges are often under consideration. Passive seismic technologies are a new source of information that has the potential to add value in helping overcome field and exploration challenges. Some passive seismic methods are now considered proven technologies in clastic rocks, such as hydro-frac monitoring and microseismic. There are other passive seismic methods which are still considered to be in a research stage. Whether a method will perform the same in a carbonate environment as in the clastic environment is also an important consideration when considering a new technology project in carbonates. When a challenge presents itself and a potential new technology is identified to overcome the challenge it is common practice to first conduct a small pilot. Field and Exploration challenges or problems that the passive seismic technologies have the potential to overcome include among other things, monitoring the impact of faults and fractures on flood front advance, identification of thin thief zones, sweep efficiency and by-passed reserves, water fingering and in exploration the direct detection of hydrocarbons to identify new reserves. Progress in advancing the microseismic technologies suggests that these technologies are not without limitations and should not be treated as a “silver-bullet”. The results of pilots suggest that passive seismic results should be treated like an additional seismic attribute to be integrated with other reservoir characterization and exploration information. The proper matching of passive seismic with other appropriate technologies, such as seismic or VSP images can help overcome limitations and improve interpretation reliability. How to properly pilot a new technology is not always as straight forward and easy as one might think. Difficulties in surface conditions, well integrity, equipment availability and the proper situation to demonstrate value from the passive seismic information often lead to inconclusive results and can make it difficult to get approvals to proceed with yet another redesigned pilot. The following paper documents some of the positive and negative lessons learned from passive seismic pilots.
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Recent Passive Experiments in Abu Dhabi
Authors M.Y. Ali, K.A. Berteussen, J.R. Small, B.T. Anjana and B. BarkatPassive seismic experiments using a small array of 3-component instruments were conducted over an onshore carbonate oilfield in Abu Dhabi. The aim is to confirm and understand the origins of a low frequency signals (2.5-2.8 Hz) that has been observed above several hydrocarbon reservoirs in the area and considered as a hydrocarbon indicator. The results of the experiments indicate that a narrow-band of low frequency signal is present above the hydrocarbon reservoir as previously claimed, but that this signal is also observed over nearby assumed non-reservoir locations. Variations in the character of the signals recorded 12 hours apart during midday and midnight periods were observed. The possible causes of this low frequency energy are not well understood. However, using the array of 3-components instruments, we are able to determine the apparent velocities and the azimuth of the wave fronts as well as the particle motion of the recorded low frequency waves. The results indicate that the observed signals are most likely due to some type of surface waves with the azimuth to the source pointing towards the nearest coastline in the area (the Arabian Gulf).
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