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Mattsson J.,Petroleum Geo Services
76th EAGE Conference and Exhibition 2014, Workshops | Year: 2014

Towed streamer electromagnetic (EM) data along a survey line at the Alvheim Boa oil field in the North Sea has been inverted using an open-source 2.5D inversion code. The electric field data was acquired in 4 kn with a single vessel using a horizontal bipole source atlOm depth and densely populated electrode pair receivers housed in a towed streamer towed at 50 m depth in water depths between llO and 125 m. The inversion algorithm is based on a parallel adaptive 2.5D finite element algorithm and uses a regularized variant of a Gauss-Newton minimization algorithm. This inversion method has proven to be fast and efficient for and suitable for towed streamer EM data. In this case, the resulting anisotropic resistivity cross section corresponds well with the high resistive part of the sand layer in the vicinity of the reservoir depocenter. The low noise in the frequency response data and the low navigation and measurement uncertainties made it possible to obtain a final misfit as low as 2 %. The towed streamer EM technology has proven to be a robust and useful CSEM method in shallow waters. The densely sampled frequency response data is suitable for anisotropic inversion.

Long A.,Petroleum Geo Services
Society of Petroleum Engineers - International Petroleum Technology Conference 2014, IPTC 2014 - Innovation and Collaboration: Keys to Affordable Energy | Year: 2014

3D seismic imaging attempts to reconstruct a continuous image of the subsurface based upon discretely sampled reflectivity traces. The spatial sampling is typically irregular, coarse, and may even be under-sampled according to the classic Shannon-Nyquist sampling theory. In addition to primary reflections, unwanted energy in form of coherent noise is recorded in many forms, and is typically more prone to spatial aliasing than the primary signal. As a consequence, traditional processing approaches follow a flow that may be collectively referred to as pre-conditioning. Pre-conditioning removes coherent and incoherent noise, modifies the phase of the data, and attempts to interpolate/regularize/reconstruct the data in a band-limited manner. Velocity model estimation and imaging are then applied, followed by additional noise removal and signal enhancement as required. Attention has moved in recent years to so-called broadband seismic imaging. A variety of deghosting solutions have emerged for removing the effects of both the source-side and receiver-side ghost effects within towed streamer seismic data. Attendant claims are made about whether such solutions are 2D, have azimuth-specific assumptions, are 3D, or even "true 3D". So how do we measure whether the 3D broadband solution obtained by a particular acquisition-processing-imaging methodology is really "true 3D" in a broader imaging context? This question is complicated recently by imaging methods that exploit the illumination from surface multiples in addition to the illumination from primary reflections. I introduce a frame of reference that begins with 3D towed dual-sensor streamer marine seismic acquisition and dual-source shooting. There is no theoretical limit to how many orders of the corresponding surface multiple wavefield may be sampled for a given streamer separation. I demonstrate that by pursuing dual-sensor wavefield separation at the first stage of pre-conditioning and sampling densely enough in the cross-line direction, an uncompromised 3D image of the earth may be achieved for most target depths without any loss of temporal resolution in the frequency range afforded by natural attenuation to each respective target depth. In the case of shallow geology affected by the imprint of the acquisition geometry, imaging with surface multiples will typically yield a better result than any approach based solely on primary reflections. I differentiate between the most significant approaches used for pre-conditioning data during deghosting, and provide a path towards an optimal ghost-free 3D seismic image of the earth. Copyright © 2014 by the Society of Petroleum Engineers.

Ampilov Y.P.,Petroleum Geo Services
Geomodel 2015 - 17th Scientific-Practical Conference on Oil and Gas Geological Exploration and Development | Year: 2015

The paper addressed to issues related to the changes of the Russian oilfield services market in the fall of oil prices and sector of sanctions imposed by the US and the European Union on Russia. The factors that affect the foreseeable future on the oil quotations, marked the key trends in the global and Russian oilfield services market. Emphasis is placed on the need for a long-term individual domestic exploration and production technologies for the most key process steps.

Ampilov Y.P.,Petroleum Geo Services
Geomodel 2015 - 17th Scientific-Practical Conference on Oil and Gas Geological Exploration and Development | Year: 2015

The paper addressed to issues related to the changes of the Russian oilfield services market in the fall of oil prices and sector of sanctions imposed by the US and the European Union on Russia. The factors that affect the foreseeable future on the oil quotations, marked the key trends in the global and Russian oilfield services market. Emphasis is placed on the need for a long-Term individual domestic exploration and production technologies for the most key process steps.

Bekara M.,Petroleum Geo Services | van der Baan M.,University of Alberta
Geophysics | Year: 2010

High-amplitude noise is a common problem in seismic data. Current filtering techniques that target this problem first detect the location of the noise and then remove it by damping or interpolation. Detection is done conventionally by comparing individual data amplitudes in a certain domain to a user-controlled local threshold. In practice, the threshold is optimally tuned by trial and error and is often changed to match the varying noise power across the data set. We have developed an automatic method to compute the appropriate threshold for high-amplitude noise detection and attenuation. The main idea is to exploit differences in statistical properties between noise and signal amplitudes to construct a detection criterion. A model that consists of a mixtureof two statistical distributions, representing the signal and the noise, is fitted to the data. Then it is used to estimate the probability (i.e., likelihood) that each sample in the data is noisy by means of an expectation-maximization (EM) algorithm. Only those samples with a likelihood greater than a specific threshold are considered to be noise. The resulting probability threshold is better adapted to the data compared to a conventional amplitude threshold. It offers the user, through the probability threshold value, the possibility to quantify the confidence in whether a large amplitude anomaly is considered as noise. The method is generic; however, our work develops and implements the method for swell-noise attenuation. Initial results are encouraging, showing slightly better performance than an optimized conventional method but with much less parameter testing and variation. © 2010 Society of Exploration Geophysicists.

Ziolkowski A.,University of Edinburgh | Wright D.,University of Edinburgh | Mattsson J.,Petroleum Geo Services
Geophysical Prospecting | Year: 2011

We discuss the problem of source control in controlled-source electromagnetic (CSEM) surveying and compare and contrast equal energy transient square-wave and transient pseudo-random binary sequence source signatures for the same towed-streamer electromagnetic survey line over the Peon gasfield in the Norwegian sector of the North Sea. The received response of the transient square-wave data was 11 dB greater than that of the pseudo-random binary sequence data, due to diffusive attenuation of higher frequencies present in the more broadband pseudo-random binary sequence signature. Deconvolution of the pseudo-random binary sequence data recovers the total impulse response function, increases the signal-to-noise ratio by 32.6 dB and separates most of the air wave from the earth impulse response by the causality principle. The recovered impulse responses have more detailed information in the frequency domain than the transient square-wave data. The pseudo-random binary sequence data were acquired with a 10 Hz source bit rate but contain no information about the Peon gasfield at frequencies above 2 Hz. The bit rate could have been reduced to 4 Hz, increasing the signal energy below 2 Hz by 150% and thus, potentially, increasing the signal-to-noise ratio by a further 4 dB. Because the total earth impulse response can be recovered from the broad-bandwidth pseudo-random binary sequence data, further time-domain processing may be applied, including correlated noise removal, which can increase the signal-to-noise ratio by as much as 20 dB, and air wave removal using the causality principle. The information in the arrival time of the peak of the earth response provides the potential for traveltime to resistivity mapping to provide a starting model for inversion. © 2011 European Association of Geoscientists & Engineers.

Singh S.C.,CNRS Paris Institute of Global Physics | Moeremans R.,CNRS Paris Institute of Global Physics | McArdle J.,Petroleum Geo Services | Johansen K.,Petroleum Geo Services
Journal of Geophysical Research: Solid Earth | Year: 2013

The sliver strike-slip Great Sumatra Fault (GSF) traverses mainland Sumatra from the Sunda Strait in the southeast to Banda Aceh in the northwest, and defines the present day plate boundary between the Sunda Plate in the north and the Burmese Sliver Plate in the south. It has been well studied on mainland Sumatra but poorly north of Banda Aceh in the Andaman Sea. Here we present deep seismic reflection images along the northward extension of the GSF over 700 km until it joins the Andaman Sea Spreading Centre, and we interpret these images in the light of earthquake, gravity, and bathymetry data. We find that the GSF has two strands between Banda Aceh and Nicobar Island: a transpression in the south and a deep narrow active rift system in the north, dotted with volcanoes in the center, suggesting that the volcanic arc is coincident with rifting. Farther north of Nicobar Island, an active strike-slip fault, the Andaman-Nicobar Fault, cuts through a rifted deep basin until its intersection with the Andaman Sea Spreading Centre. The volcanic arc lies just east of the rift basin. The western margin of this basin seems to be a rifted continental margin, tilted westward, and flooring the Andaman-Nicobar fore-arc basin. The Andaman-Nicobar fore-arc basin is bounded in the west by back thrusts similar to the West Andaman and Mentawai faults. The cluster of seismicity after the 2004 great Andaman-Sumatra earthquake just north of Nicobar Island coincides with the intersection of two strike-slip fault systems. Key Points Diligent fault is a backthrust Presence of continental crust beneath forearc basin Andaman Nicobar Fault is the main sliver strike-slip fault ©2013. American Geophysical Union. All Rights Reserved.

Moeremans R.,CNRS Paris Institute of Global Physics | Singh S.C.,CNRS Paris Institute of Global Physics | Mukti M.,CNRS Paris Institute of Global Physics | McArdle J.,Petroleum Geo services | Johansen K.,Petroleum Geo services
Earth and Planetary Science Letters | Year: 2014

Seven deep seismic reflection profiles cover the 3000 km-long subduction system from Andaman to Southern Sumatra, including zones that ruptured in 2004, 2007, and 2010. We find that (1) the frontal zone is characterized by a series of thrusts bounding folded blocks of sediments with preserved layering, showing a northward transition from dominantly seaward vergence of the frontal thrusts to dominantly landward vergence of the frontal thrusts, (2) the accretionary wedge is characterized by poor reflection of the seismic energy likely to be due to a high degree of faulting and compaction of the sediments, and (3) the oceanic crust is highly disturbed by faults and topographic reliefs along most of the margin. Landward vergence at the deformation front is associated with a thick incoming sediment section. The segment of the subduction zone where landward vergence is observed corresponds to an area with high near-trench slip during the December 2004 earthquake, the main tsunami source, and lies just west of the hypocenters of several intraplate events (Mw > 7) in the years following the 2004 event. © 2013 Elsevier B.V.

Brown S.P.,Petroleum Geo Services | Thorne M.S.,University of Utah
Geophysics | Year: 2013

Accurate interpretation of seismic traveltimes and amplitudes in the exploration and global scales is complicated by the band-limited nature of seismic data. We discovered a stochastic method to reduce a seismic waveform into a most probable constituent spike train. Model waveforms were constructed from a set of candidate spike trains convolved with a source wavelet estimate. For each model waveform, a profile hidden Markov model (HMM) was constructed to represent the waveform as a stochastic generative model with a linear topology corresponding to a sequence of samples. Each match state in the HMM represented a sample in the model waveform, in which the amplitude was represented by a Gaussian distribution. Insert and delete states allowed the underlying source wavelet to dilate or contract, accounting for nonstationarity in the seismic data and errors in the source wavelet estimate. The Gaussian distribution characterizing each sample's amplitude accounted for random noise. The Viterbi algorithm was employed to simultaneously find the optimal nonlinear alignment between a model waveform and the seismic data and to assign a score to each candidate spike train. The most probable traveltimes and amplitudes were inferred from the alignments of the highest scoring models. The method required no implicit assumptions regarding the distribution of traveltimes and amplitudes; however, in practice, the solution set may be limited to mitigate the nonuniqueness of solutions and to reduce the computational effort. Our analyses found that the method can resolve closely spaced arrivals below traditional resolution limits and that traveltime estimates are robust in the presence of random noise and source wavelet errors. The method was particularly well suited to fine-scale interpretation problems such as thin bed interpretation, tying seismic images to well logs, and the analysis of anomalous waveforms in global seismology.& copy 2013 Society of Exploration Geophysicists.

Zhou C.,Petroleum Geo Services | Jiao J.,Petroleum Geo Services | Lin S.,Petroleum Geo Services | Sherwood J.,Petroleum Geo Services | Brandsberg-Dahl S.,Petroleum Geo Services
Geophysics | Year: 2011

Model building for tilted transversely isotropic media has commonly been performed by a single parameter tomography that updates the velocity in the symmetry direction, while the orientation of the symmetry axis and Thomsen parameters ε and δ are typically estimated from the migration stack and well data. Unfortunately, well data are often not available. In addition, when they are available, their lateral sampling is typically very sparse and their vertical sampling usually spans only a limited range of depths. In order to obtain spatially varying anisotropic models, with or without well data, we developed a multiparameter joint tomographic approach that simultaneously inverts for the velocity in the symmetry axis direction, ε and δ. We derived a set of reflection tomography equations for slowness in the symmetry axis direction and Thomsen parameters ε and δ. In order to address the nonuniqueness of the tomography, we developed a regularization strategy that uses an independent regularization operator and regularization factor for each individual anisotropy parameter. Synthetic tests found that ambiguity exists between the anisotropy parameters and that velocity has a better resolution than ε and δ. They also confirmed that joint tomography provides a better data fit than single parameter tomography. The field example was used to test a way to incorporate the sonic data in the model building process and limit the tomographic updates on certain anisotropy parameters by adjusting the regularization. © 2011 Society of Exploration Geophysicists.

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