OBC Seismic Data Research Articles

Dealing with spatial sampling sparseness and irregularity in 3D OBC seismic data offshore Abu Dhabi

Due mainly to commercial and operational constraints, seismic data are often sparsely and irregularly sampled, leading to several challenges in processing of 3D OBC seismic data offshore Abu Dhabi. Conventional linear noise attenuation techniques based on multi-channel filters are not effective with Scholte waves as they are usually aliased with typical sampling intervals in 3D OBC seismic data (e.g., 25 m source and receiver point intervals), and sometimes scattered because of near-surface heterogeneity. To address them, we apply model-based surface wave attenuation, Surface Wave Analysis Modelling and Inversion (SWAMI), which enables an estimate of local near-surface properties by analysing dispersion curves. Thus, both direct and scattered Scholte waves are effectively modelled and attenuated without suffering from under-sampling. A data interpolation and regularization technique called Matching Pursuit Fourier Interpolation (MPFI) is then applied to enhance spatial sampling. MPFI employs an anti-aliasing capability so optimum data reconstruction can be performed for any frequency range. In addition to the regularization aspect, MPFI with a 5D implementation (4 spatial coordinates and time) is targeted to densify receiver line interval and extend source lines, which consequently enhances fold, offset and azimuth distributions of the data.The implementation of the two techniques successfully addresses processing challenges in sparsely and irregularly sampled OBC seismic data.

Innovative Processing Approaches to Overcome Sampling Sparseness and Irregularity in 3D OBC Seismic Data Offshore Abu Dhabi

Due mainly to commercial and operational constraints, seismic data are often sparsely and irregularly sampled, leading to several challenges in processing of 3D OBC seismic data offshore Abu Dhabi. Conventional linear noise attenuation techniques are not effective with Scholte waves as they are usually aliased with typical sampling interval in 3D OBC seismic data, and sometimes scattered because of near-surface heterogeneity. To address this, we apply model-based surface wave attenuation, Surface Wave Analysis Modeling and Inversion (SWAMI), which enables an estimate of local near-surface properties by analysing dispersion curves. Thus, both direct and scattered Scholte waves are effectively modelled and attenuated without suffering a lack of spatial sampling. We also highlight the shortcomings of the application of interferometry to scattered noise attenuation for sparse acquisition geometry. Matching Pursuit Fourier Interpolation (MPFI) is then implemented to deal with insufficient sampling in crossline direction caused by acquisition geometry. MPFI employs anti-aliasing capability so optimum data reconstruction can be performed for any frequency ranges. In addition to regularization aspect, MPFI with 5D implementation (4 spatial coordinates and time) is targeted to densify receiver line interval and extend source lines, which consequently enhances fold, offset and azimuth distributions of the data.

Recent production and drilling success of the Stag oil field from multidisciplinary evaluation of OBC seismic data

Originally discovered in 1993, the Stag oil field, on the North West Shelf of Western Australia, has proven to be both a prolific and complicated reservoir since production began in 1998. To date, more than 56 million barrels have been produced, in addition to significant volumes of water and glauconite, which has resulted in complex changes to the reservoir over time as the field has produced. Because the reservoir is shallow, at 680 m true vertical depth subsea (TVDSS) with shallow carbonates causing noise issues and imaging challenges, Stag Field remained largely invisible on seismic data. To address these issues, a 220-[Formula: see text] 4C-3D ocean-bottom cable survey (OBC) was acquired in early 2008. Subsequent processing and interpretation of these data, including a joint multicomponent inversion, have resulted in drilling six successful new wells with additional wells currently underway and planned in the near future.

Using high-density OBC seismic data to optimize the Andrew satellites development

The processed data from conventional towed-streamer seismic surveys over the Andrew satellite fields in the Central North Sea are of poor quality because of anomalously fast sand-filled channels in the Eocene overburden. The channels attenuate the primary energy and produce strong multiples. A step change in data quality has been achieved by acquiring a wide-azimuth seismic survey using ocean bottom cables and a high shot density. The new data have much higher signal-to-noise ratio and better resolution. The imaging under the Eocene channels is greatly improved in the processed results of the new survey. Furthermore, the acquisition and processing were completed in time to meet the tight development schedule for the 2008 Kinnoull discovery.

Elastic full waveform inversion of multi‐component OBC seismic data

ABSTRACTElastic full waveform inversion of seismic reflection data represents a data‐driven form of analysis leading to quantification of sub‐surface parameters in depth. In previous studies attention has been given to P‐wave data recorded in the marine environment, using either acoustic or elastic inversion schemes. In this paper we exploit both P‐waves and mode‐converted S‐waves in the marine environment in the inversion for both P‐ and S‐wave velocities by using wide‐angle, multi‐component, ocean‐bottom cable seismic data. An elastic waveform inversion scheme operating in the time domain was used, allowing accurate modelling of the full wavefield, including the elastic amplitude variation with offset response of reflected arrivals and mode‐converted events. A series of one‐ and two‐dimensional synthetic examples are presented, demonstrating the ability to invert for and thereby to quantify both P‐ and S‐wave velocities for different velocity models. In particular, for more realistic low velocity models, including a typically soft seabed, an effective strategy for inversion is proposed to exploit both P‐ and mode‐converted PS‐waves. Whilst P‐wave events are exploited for inversion for P‐wave velocity, examples show the contribution of both P‐ and PS‐waves to the successful recovery of S‐wave velocity.

Improved seismic data processing and interpretation for stratistructural petroleum plays in the north of Al-Khafji area, Middle-East

Seismic data with appropriate processing tools, often come to the rescue of interpretation, minimizing the ambiguities involved in analysing complex geological situations. Stratigraphic features associated with structure, play critical role in hydrocarbon entrapment within the Middle-Late Cretaceous reservoirs in the Al-Khafji offshore area. A total of 61 square kilometres high resolution 3D OBC seismic data were acquired in the North Khafji area, with objectives to explore strati-structural traps and their associated reservoir settings. New petroleum plays are intended to be explored after integrating new 3D seismic vintage with older Al-Khafji seismic data interpretation. Present study is aimed at comparing seismic datasets that are processed by different companies. Authors examine and identify the relative merits of data attributes that are suitable for structural and strati-structural traps interpretation. The initial interpretation done during 1997, reports a possible carbonate build-up, correlatable to Gudair formation, which is equivalent to a horizon associated with Aruma-Wasia unconformity. Comparative study made between Khafji and north of Khafji field could not conclusively establish the extension of this carbonate build-up in the North-Khafji area, because of ambiguous nature of structural and stratigraphic anomalies. At places, there is inconsistency among scales of these datasets. However, based on the interpretation of the newly processed seismic data, seismic structure and attributes have been integrated and reinterpreted for scalable anomalies. Present study strongly suggests an exploration potential in the North-Khafji area and stipulates pursuing further geological studies, detailing these seismic anomalies and converting them into commercial petroleum plays in the offshore basin.

Improved imaging of the Snøhvit field through integration of 4C OBC and dual-azimuth streamer seismic data

Grunde Rønholt, Hans A. Aronsen, Thomas Hellmann and Stian Johansen provide a case study from the Snøhvit field to prove the value of integrating acquisition data from OBC and dual-azimuth streamer seismic surveys for optimal reservoir characterization.