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76th EAGE Conference and Exhibition 2014
- Conference date: June 16-19, 2014
- Location: Amsterdam, Netherlands
- Published: 16 June 2014
101 - 120 of 1028 results
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Microseismic Monitoring - Source Characterization and Physical Modeling
Authors O. Akbas, R. Stewart and N. DyaurSummaryThis research provides an overview of the physical modeling procedure using ultrasonic sources and receivers, describes and assesses the hypocenter and source mechanism algorithm, and illustrates the results. We developed a ray tracing and diffraction stack procedure to undertake locations and their evaluation.
Data was acquired using ultrasonic source and 3-component receivers on the natural sandstone. We evaluate how accurately variety of methods locate actual source positions. Location was performed using only P-waves, only S-waves and P-S waves and using traveltime residual, stacked energy, and energy/residual ratio. The most accurate location is obtained using energy/residual ratio. The relative errors of using only P-wave, only S-wave, and P-S waves are 0.8, 0.9, and 0.58 percent, respectively. Furthermore, location uncertainty increases when downhole receivers are left out for all cases. The relative error increased to 0.75 percent from 0.58 percent error when we exclude downhole receivers.
To increase the speed of the algorithm, CPU and GPU computing was implemented. Locating a single microseismic event with seven different methods takes 11.4 seconds on single core CPU, whereas, this number is decreased to 4.2 seconds using multi-core CPU computing. Further, implementing GPU computing decreases the total elapsed time to only 1.9 seconds.
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Quantifying Reservoir Stimulation Using Passive Traveltime Tomography
Authors J.W. Huang, J.M. Reyes-Montes, X.P. Zhao, F.D. Chu and R.P. YoungSummaryHydraulic fracturing stimulates reservoir and imposes stress changes in the surrounding rock that typically induce or trigger seismicity with a wide range of magnitudes. Seismic monitoring provides insight into the reservoir deformation and give critical feedback to the on-going stimulations. We have developed a passive seismic tomography technique adapted from earthquake seismology to jointly locate induced microseismic events and update the velocity of the reservoir illuminated by the microseismicity. We calculate travel-time based on the fast sweeping method to account for complex 3D distribution of velocity and use the adjoint method to transform the inverse problem to a forward problem which can also be solved by the fast sweeping method. In this paper, we apply our algorithm to a two-stage reservoir stimulation project and demonstrate the capability of the microseismic tomography in mapping the stimulated rock volume and in quantifying the reservoir degradation even in the absence of visible P-waves.
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Where is the Proppant? DFN Modeling, Proppant Placement, and Drainage Estimation from Microseismic Data
Authors C.W. Neuhaus, M. Ellison, C. Telker and K. BlairSummaryMicroseismic data for 17 hydraulically stimulated wells in the Marcellus Shale were used to conduct a proppant placement and drainage estimation evaluation in order to optimize the wellbore spacing, and in the future the completion design and landing depth of the wellbores. A calibrated discrete fracture network (DFN) was modeled onto the microseismic events taking into account the magnitude of the events, their source mechanisms, the rock properties of the stimulated reservoir, and the amount of injected fluid in order to distinguish between the total stimulated rock volume (SRV) where microseismic activity was observed and the part of the SRV that contains proppant filled fractures and will therefore be productive in the long term. Evaluating proppant placement in the perpendicular horizontal, parallel horizontal, and perpendicular vertical direction has significance for and direct impact on wellbore spacing, stage length and spacing, and the landing depth of the wellbores.
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Determining Resistivity from Towed Streamer EM Data Using Unconstrained Inversion - Tie to Well and Discovery Examples
Authors A.J. McKay, K. Flisnes Bergh and A.H. BhuiyanSummaryWe show that unconstrained anisotropic 2.5D inversion of Towed Streamer EM data in complex geological settings can produce resistivity models that are consistent with both interpreted log and seismic data, and known discoveries. We consider two cases from recent surveys in the Celtic and Barents Seas offshore Ireland and Norway respectively. In the Celtic Sea case we show an example where we have compared the results of unconstrained inversion to publically available log data. Not only is the overall depth trend recovered, but the main variation of the resistivity is captured as well as, in some intervals, comparable average interval resistivity. For the Barents Sea case we show an example resistivity and anisotropy section from one of eight survey lines that traverse the Skrugard discovery across its short axis (about 2km). While the resistivity section highlights that the sub-surface resistivity is complex, the somewhat simpler anisotropy section reveals an anisotropy anomaly that is co-incident with both the lateral, and depth, extent of Skrugard.
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Time Domain EM Soundings for the Delineation of the Fresh Water - Salt Water Interface in Eastern Canada Islands
Authors J. Giraud, M. Chouteau and A. BoucheddaSummaryA hydrogeophysical study involving electromagnetic and electric methods to map depths to the saltwater-freshwater interface into coastal aquifers was carried out. Time domain electromagnetic (TDEM) soundings were acquired along electric resistivity tomography (ERT) profiles perpendicular to the coastline in the Magdalen Islands (Eastern Canada). Departures from hydrogeological models allowed evaluating the influence of water pumping on the studied aquifers. As a result, except in zones closer to the pumping wells, a good agreement between the hydrogeological model and the position of the interface estimated by the coupling of TDEM and ERT is observed.
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First Results from an Electromagnetic Survey of a Gas Hydrate Vent Offshore Mid-Norway
Authors A. Swidinsky, S. Hölz, M. Sommer, M. Jegen, K. Weitemeyer and C. BerndtSummaryWe describe a transient electromagnetic survey to image the resistivity structure of the hydrate vent CNE03, offshore Mid-Norway which located approximately 10 km north of the Storegga Slide sidewall. The experiment is unique in that the electric dipole transmitter has two polarizations for each transmission station. Furthermore, the newly designed transmitter is deployed in a pogo-style acquisition, which is suitable for a detailed investigation of a small scale seafloor target. The geometry of the experiment makes conventional interpretation methods difficult so that we simplify the data by creating a single rotationally invariant quantity from the original four electric field measurements (two electric field measurements for two transmitter polarizations). This invariant is further reduced to an apparent resistivity, which is useful for rapid resistivity mapping of the seafloor. Results show that CNE03 is characterized by increased apparent resistivities which correlate well with increased P-wave velocities determined from ocean bottom seismometer measurements.
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3D Inversion of Vertical Dipole - Time Domain CSEM data
Authors T. Holten, M. Commer, G. Newman and S.L. HelwigSummaryThe EM code of Newman and Commer can be used for inversion of the time domain vertical dipole data of Petromarker. A depth gradient weight function has been calibrated to obtain the original target depth in the inversion. The main goal of the 3D inversion development is to combine all the measurements in an offshore survey so the data fit a resistivity model.
A synthetic data example is presented where the inversion use forward modelled data from a reservoir case. The inversion recovers the depth and horizontal size of the reservoir.
The inversion code has the potential to improve subsurface imaging by geometrical averaging over all transmitter/receiver combination in a survey, and to include seabed topography and known stratigraphic horizons.
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Integral Equation Method for Anisotropic Inversion of Towed Streamer EM Data - Theory and Application for the TWOP Survey
Authors M. Zhdanov, M. Endo, D. Yoon, M. Cuma, J. Mattsson and J. MidgleySummaryWe introduce a 3D inversion methodology for towed streamer EM data that takes into account anisotropy and includes a moving sensitivity domain. Our implementation is based on 3D IE method for computing the responses and Fréchet derivatives, and uses re-weighted regularized conjugate gradient method for minimizing the objective functional with focusing regularization. Interpretation of the towed streamer EM data is a difficult problem because the data are acquired over large areas with huge number of moving towed streamer EM system positions. We overcome this problem by exploiting the concept of moving sensitivity domain, which is implemented using the IE method. In the framework of this concept, for a given transmitter-receiver pair, the responses and Fréchet derivatives are computed from a 3D earth model that encapsulates the towed EM system’s sensitivity domain. The Fréchet matrix for the entire 3D earth model is then constructed as the superposition of Fréchet derivatives from all transmitter-receiver pairs over the entire 3D earth model. This makes large-scale 3D inversion a tractable problem with moderate cluster resources. We present a case study of 3D anisotropic inversion of towed streamer EM data from the Troll West Oil Province.
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Anisotropic 2.5D Inversion of Towed Streamer EM Data from Three North Sea Fields Using Parallel Adaptive Finite Elements
Authors K. Key, Z. Du, J. Mattsson, A. McKay and J. MidgleySummaryWe present anisotropic inversion results from towed streamer electromagnetic (EM) surveys of the Bressay, Bentley and Kraken (BBK) heavy oil fields in the North Sea. The BBK discoveries pose several challenges to conventional controlled-source EM surveying since the relatively shallow water dampens the anomaly magnitudes due to airwave coupling, and the reservoirs are in close proximity to other resistive features. The 160 m spacing of the 44 receiver bipoles on the towed streamer offers much higher data density than is typically achieved with conventional seafloor receiver surveys. We tested the resolving capabilities of the towed-streamer by inverting the survey data using a new code based on a 2.5D parallel goal-oriented adaptive finite element method and a modified implementation of the Occam inversion algorithm. The inversion successfully images the 1–2 km wide Bressay and ∼5 km wide Bentley reservoirs, illustrating that the high data density of the towed streamer offers improved resolution over sparsely sampled nodal seafloor receiver data. The results also demonstrate the importance of allowing for anisotropy when inverting data from this region. Whereas anisotropic inversion clearly recovers the lateral edges of the known reservoirs, isotropic inversion results in inter-bedding of resistive and conductive layers that conceal the reservoirs.
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3D Anisotropic Inversion of Towed Streamer EM Data over the Mariner Field in the North Sea
Authors J. Mattsson, M.S. Zhdanov and M. EndoSummaryTowed streamer electromagnetic (EM) data over the Mariner oilfield in the UK sector of the North has been inverted using a fast and efficient 3D anisotropic inversion code. The electric field data were acquired with a single vessel using a horizontal bipole source and sensors housed in a towed streamer in a densely sampled grid over the subsurface volume of interest. The inversion algorithm is based on the 3D contraction integral equation method and utilizing a re-weighted regularized conjugate gradient technique to minimize an objective functional. This inversion method is proven to be fast and efficient for large data sets and is here shown to be suitable for towed streamer EM data from complex geological environments such as the Mariner area. In this case, the final 3D resistivity cube after inversion and with a corresponding misfit of 6.4 %, agrees well with the expected structure from seismic data and well logs. In particular, the 3D cube contains a resistive anomaly of 8–10 Ωm corresponding to the Maureen and Heimdal reservoirs on top of the resistive chalk and basement.
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Cableless Seismic Acquisition Technology Evaluation and First Full Field Implementation in France and Uganda
Authors J.M. Mougenot, C. Cardama, P. Faure and R. SanchezSummaryThe use of cableless recording units for land acquisition has been widely increasing in the last 10 years with almost 900 000 units produced at this time. During recent years Total has been investigating how this new technology could facilitate its land acquisition operations and what are the most appropriate systems. There are more than 10 vendors competing for this market with systems with different functionalities. After a market evaluation and field tests of some systems, Total selected two different systems to acquire its first full-field 3D cableless acquisitions in Uganda and in France. This experience gave very encouraging results in term of potential of this technology to reduce acquisition environmental footprint and recording downtime, manpower and logistics.
The presentation will focus on the evaluation of this technology and the reasons why two cableless systems with very different functionalities were selected to meet the specific constraints of these two surveys.
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Cableless Sesimic Acquisition to Reduce Environmental Footprint in Murchison Falls National Park Uganda
Authors C. Cardama, R. Sanchez and J.M. MougenotSummaryIn the quest of increasing hydrocarbon reserves and oilfield development, it has been necessary for the oil industry to work in frontier and more sensitive areas than ever before. New developments in equipment and methodologies provided the means to tackle some of these problems. Seismic data acquisition in the Murchison Falls National Park in Uganda (the largest protected area in the country) proved to be a demanding project in terms of seismic acquisition methodology, biodiversity care and operational planning. The use of cable less technology, small efficient servo hydraulic vibrators were the pillars on which the acquisition strategy was based. This equipment provided the possibility of minimizing the environmental foot print in the Park and obtaining very high quality data that will be instrumental in the development of the fields discovered in the EA-1 block in northern Uganda
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Allowing Seismic Surveys to Boldly Go Where No Surveys Have Gone Before
Authors S. Baris, N. Badel, H. Ribeiro, F. Layan, P. Herrmann, O. Lamerain, A. Jacques and P. FaureSummarySingle Source - Single Receiver wireless systems reduce acquisition to its most elementary components, allowing high flexibility to adapt to all environments. Small to medium size single sources can be used in any type of terrain, with minimal to zero footprint. Cableless single receivers adapt easily to any topography or natural, agricultural, or urban organization. Their reduced weight also means highly efficient deployment. The advent of these new solutions enables a shift from equipment-driven and access-driven to image-driven survey planning. In the Lussagnet-Izaute case study, we illustrate how such advanced systems lead to highly efficient operations to produce high resolution 3D seismic volumes.
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Quantifying Noise in a Land Seismic Image - Stealth Acquisition Experiment
Authors E. Kragh, M. Daly and J. QuigleySummaryWe wish to quantify the relative contributions of the different components of noise in the land seismic image. We acquired a repeat 2D land seismic line. The first pass used a conventional acquisition technique. The second pass was acquired in exactly the same manner, except that once the vibrator pads were down, the vibrators remained stationary with no pad vibration for the duration of the sweep. We call this “Stealth” acquisition; we record no signal, but we record all the noise that we introduce by the process of acquiring the data (except noise introduced while actually putting signal into the ground). A third acquisition recorded an equivalent time of background noise with no source activity. Analysis of the resulting data shows that we generate a considerable amount of noise simply by the process of acquiring the data, some 10–20 dB above the background noise level below 50 Hz, in the raw data. Our processing workflows can deal with this additional noise very effectively and, in the final image, this is reduced to only a few dB above the background level. While this might still seem considerable, it is out-weighed by the noise introduced when the vibrator trucks shake at full force.
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Field Measurements of the Distortion Resulting from the Use of Tilted Geophones
Authors T. Dean, P. Claasen and B. McCarthySummaryThe moving coil geophone is still the most commonly used sensor for land seismic surveys despite the introduction of other sensors. Modern geophone development has reached the stage where the signal recorded is of very high quality, but it can still be affected by the geophone being placed on an angle relative to the vertical (‘tilt’).
This paper describes the acquisition and analysis of field measurements using tilted geophones. It is shown that the critical angle of the 10 Hz geophones used for this test is 55°. For data recorded using vertically placed geophones separated by only 10 cm the perturbation level (the difference between the data recorded by adjacent geophones) averaged 8% and increased to more than 50% at tilt angles of 40°. The level of perturbation is heavily dependent on the orientation of the tilt angle relative to the source-detector axis, for example, for a geophone tilted at an angle of 30°, the perturbation varied between 14% and 48%. The obvious solution to these issues is to record data using sensors that have been planted extremely carefully or to use other sensors, such as digital accelerometers or 3C sensors that can have the effect of tilt removed during processing.
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Field Measurements of Land Seismic Ambient Noise and Their Implications for the Effectiveness of Geophone Arrays
Authors T. Dean, J.C. Dupuis and R. HassanSummaryHistorically, arrays have been used to attenuate ambient noise under the assumption that the level of attenuation is directly proportional to the square root of the number of sensors in the array. Given the availability of high channel-count point-receiver systems and the cost associated with laying out large arrays this assumption of ‘spatial randomness’ requires further analysis. Using measurements of ambient noise made at various sites in Perth, Australia with closely spaced geophones we show that ambient noise is strongly correlated over distances of up to 10 m. This correlation reduces the signal-to-ambient-noise performance of an array considerably. The correlation coefficient can be modelled using an exponential function and the correlation-distance used to determine the efficient geophone spacing. The optimum geophone spacing on days with a low wind speed (< 10 km/h, observed on 27% of days in the area) is 15 m. For days with a very high wind speed (> 80 km/h) the optimum spacing is 2.5 m, although this wind speed is very uncommon, occurring on average less than once each year. For more than 90% of days the wind speed is such that the optimum geophone spacing required for ambient noise suppression is 7.5 m.
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Simultaneous Mini Sources for Simultaneous Infill and Land Acquisition
Authors C. Berron, E. Forgues, J.B. Laffitte and M. LeclercqSummaryWe present and compare a new alternative technology that can emit simultaneously several tens of small seismic sources alongside a standard land acquisition. This solution fit the infill acquisition purpose where we cannot use standard large vibrators or explosive sources (environmentally sensitive zones, urban areas and so on). This technology is based on continuous mono-frequency emission, allowing many of these Mini Piezo Vibrator sources to emit together.
Various sources are compared on seismic data recorded for TOTAL and TIGF during the 2013 Lussagnet survey (France) with no perturbation on the simultaneous standard seismic acquisition. We show that we obtain an acceptable signal above 20 Hz with our Mini Piezo Vibrator after one day of autonomous vibration (approximately nine hours). The signal-to-noise ratio above 50 Hz is even comparable to a Mertz 22. We conclude that this technology is promising and additional work would be required to confirm the ability to image deep reflectors and to optimize low-frequency emission by an adapted vibration sequence.
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Exploring the Extent to which Streamer Separation Can Be Relaxed when Using a Multimeasurement Streamer
Authors S. Mahat, D. Saputra, J.R. Crompton, M. Vassallo and P.A. WattersonSummaryHerein, we explore how we can enable increased efficiency in marine seismic acquisition by using the data recorded by a multimeasurement streamer to allow the relaxation of the usual constraints on crossline streamer spacing - thus, obtaining the desired resolution while towing the streamers farther apart.
Pressure and pressure-gradient measurements acquired by multimeasurement streamers are used to reconstruct the wavefield between the streamers; this is achieved using the generalized matching pursuit (GMP) algorithm. GMP performs wavefield reconstruction and full 3D receiver-side deghosting using multimeasurement data from the streamers, as described by Robertsson et al. (2008) .
Although these scenarios can be modelled using synthetic data, it is important to evaluate real seismic data to understand the impact of variables such as acquisition conditions.
In this work, we analyse the results from a field test acquired in the North Sea using multimeasurement streamers. In the field test, a line of data was acquired using a 75m cable separation and then repeated using a 100m streamer separation.
We consider to what extent we can increase streamer spacing and acquisition efficiency without compromising the spatial resolution, concluding that this experiment supports the case for reconstruction at 100m streamer spacing.
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Assessment Performance Tracking of Multiple Target Prospects - A Statistical Approach
Authors G. Martinelli and C.B. StabellSummarySystematic tracking of exploration results relative to pre-drill predictions is challenging, but important. It is a means both to motivate assessment quality and to improve the assessments produced by the exploration team. Unbiased, accurate and consistent assessments are key for effective exploration decisions. This paper deals with the case where a single well targets multiple zones, compartments or reservoirs in a prospect. Most companies handle the situation as a case of multiple distinct targets. However, while simple, this approach ignores to what extent assessment has handled estimation of risk dependencies and volume correlations between targets. A key challenge for tracking assessments of multiple target prospects is tracking the estimates of risk dependencies between the targets: single well results do not give clear feedback on this estimate. We present an exploration program-level statistical measure of the quality both at the level of aggregate risk dependency estimates and at the level of the individual chance (risk) factor dependency estimates. The procedure is demonstrated with a hypothetical, but illustrative drilling program. Implementation of multiple target prospect assessment performance tracking should both improve assessments of this class of exploration ventures and stimulate more robust, accurate and transparent estimation of prospect-scale risk dependencies.
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Enhanced Seismic Imaging of Permian and Intra-Carboniferous Sections to Define the Dinantian Play Fairway - UK North Sea
Authors K. Rodriguez, N. Hodgson, R. Wrigley and H. NichollsSummaryIn Autumn 2013 the first gas production from the Breagh Field heralded the coming of age of the Dinantian (Early Carboniferous) play on the northern margins of the Southern Gas Basin and threw down the gauntlet to explorers to chase this new play into open acreage within this mature and infrastructure-rich basin.
In 2013 a dense 2D seismic programme was acquired to define the Dinantian play fairway that extends over a large swath of open acreage. Innovative seismic processing techniques resulted in high quality seismic imaging allowing for the first time both intra-Carboniferous and pre- Permian unconformity potential to be mapped with confidence, at the same time high-grading the prospectivity of these plays previously unimaged on poor legacy seismic and providing a new tool for explorers to gain a detailed regional understanding of this new play.
With over 750 BCF of resources discovered to date in this play-fairway, the “Yet To Find” based on Spectrum’s preliminary structure mapping of the new dataset is over 1TCF. A yet unquantified Triassic prospectivity is a secondary target. The identified potential dwarfs that of the established Carboniferous and Permian plays to the south.
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