Jerry Kapoor

What is the next step after WAZ for exploration in the Gulf of Mexico

The concept of circular geometry for towed-streamer marine acquisition was introduced in the early 1980s by French (French, 1984). Due to the limitations in marine technology and processing methods at the time, circular geometry had a short time span. Recently, it was proved that is feasible to use this type of geometry to acquire fullazimuth (FAZ) data using a single vessel, if the vessel sails along a pattern of overlapping circles (Moldoveanu, 2008). This technique is called Coil Shooting* single-vessel full azimuth acquisition. In this paper we demonstrate the benefits of implementing coil shooting acquisition with multiple vessel configurations.

Developing Earth models with full waveform inversion

Exploration in more geologically complex areas requires new methodologies. In its quest to answer these new challenges, the oil and gas industry has moved from ray-based imaging to finite-difference, wave-equation migration to achieve better subsurface descriptions of target zone and reservoirs. Notable in this progression is the movement from ray-traced Kirchhoff algorithms through one-way wave-equation methods to use the acoustic two-way wave equation.

Full-azimuth imaging using circular geometry acquisition

Wide-azimuth (WAZ) towed-streamer acquisition has improv-ed the quality and reliability of subsalt imaging in the Gulf of Mexico, where WAZ surveys have typically been ac-quired using 3–4 seismic vessels, each shooting in straight parallel lines. However, acquisition of WAZ data using a single vessel and a circular geometry offers several potential ad-vantages, both for operational efficiency and geophysical analysis of subsurface rock properties. Modeling exercises indicate that circular acquisition geo-metry can deliver a better range of azimuths and offsets than parallel WAZ geometry. A feasibility test in the Gulf of Mexico shows that it is possible to sail along circles while main-taining constant streamer separation and achieving very accurate receiver positioning. Single-sensor recording enables effective attenuation of the additional coherent noise introduced by shooting in a curve. Prestack depth-migrated data from the circular geometry test compare favorably with a parallel geometry WAZ data set...

Predicting and removing complex 3D surface multiples with WEM modeling--an alternative to 3D SRME for wide azimuth surveys?

Summary Wave equation modeling of multiples predicts multiples by performing one way propagator modeling using only a previously produced velocity model and migrated seismic image. Test results show that wave equation modeling of multiples using a v(x,y,z) velocity and the complete seismic image is effective for predicting complex 3D multiples for subsequent removal. The results appear competitive with 3D SRME methods in certain situations where multiples have 3D complexity or the acquisition geometry provides a challenge for 3D SRME. One situation where this approach is promising is wide-azimuth surveys.

Subsalt imaging The RAZ–WAZ experience

Is the salt winning? This was the question Paul Singer of Total posed at the subsalt workshop held at the Colorado School of Mines in the summer of 2005. This workshop was unique in that presenters from oil companies and contractors discussed their inability to successfully image under salt instead of the usual success stories generally related at most conferences.

Depth imaging examples and methodology in the Gulf of Mexico

Advances in seismic imaging over the past several years have revolutionized interpretation of geologic structures in complex areas. Nowhere has the impact of this technology been greater than the Gulf of Mexico, where the ability to interpret structures in subsalt areas has led to very large oil discoveries. Interestingly, although many techniques used in imaging these complex areas are new, the basis for many may be found in the classic methods of time imaging, many of which are still used in large-scale production depth imaging. Inherent in these techniques has been the assumption of a locally flat-layered earth consistent with hyperbolic moveout, which although incorrect for complex areas such as the subsalt imaging in the Gulf of Mexico, carries with it a robustness and determinism. Gradually, depth-imaging techniques are evolving to overcome the limitations of a local flat-layer earth assumption but at the cost of this determinism. For a true depth model, velocities, densities, and other parameters must be determined in a spatially varying way, so there is an explosion in the number of parameters to be determined. A consistent earth model from the depth-imaging perspective relies on measurement redundancy—i.e., reflections from the subsurface appear on traces from numerous source-receiver pairs in the acquisition geometry. The imaging process is then done in a way that produces not one but many images, each created using energy that has traveled through different parts of the earth. Consistency requires that these images agree. Hence, difficulties have shifted from the imaging algorithms themselves, as with the local flat-layer assumption in time imaging, to those associated with the data, their redundancy, and the uncertainty in determining a consistent model. In this article we examine a number of examples of depth imaging in the Gulf of Mexico. In the process we chronicle depth-imaging methods as they …

Shooting direction: A 3-D marine survey design issue

In the mid-1970s, 3-D marine survey design was primarily constrained by the ability to locate the position of the boat and streamer. Line spacings were, therefore, typically greater than 100 m. (Even if the navigation technology had been more accurate, it is likely that denser grids would not have been acquired because of the cost. This new method, 3-D, carried a price tag that was often considered uncomfortably high for a technology that was as yet unproven.) To minimize crossline aliasing effects, it was most prudent to record data in the dip direction.

Full-waveform Inversion Application In Different Geological Settings

After the synthetic data inversion examples, real 3D data sets have been undertaken by the industry for the last three years. As field data are dominated by P-waves, one feasible approach is to use acoustic approximation. Fullwaveform inversion (FWI) determines parameters related to the acoustic wave equation but mostly velocities by minimizing the misfit between the observed data and the model data. It has shown tremendous potential especially in 3D wide-offset acquisitions. This includes wide-azimuth streamer, ocean-bottom surveys and land type of geometry where the advantage of FWI has convinced the oil industry to pay close attention to the technology and apply it in complex geological settings. We demonstrate FWI applicability in different geological environments including marine from the Gulf of Mexico (GOM), the North Sea, and land data examples from desert type of settings for the geology.

Pore-pressure-constrained, rock-physics-guided velocity model building method: Alternate solution to mitigate subsalt geohazard

AbstractWe developed an integrated method that can better constrain subsalt tomography using geology, thermal history modeling, and rock-physics principles. This method, called rock-physics-guided velocity modeling for migration uses predicted pore pressure as a guide to improve the quality of the earth model. We first generated a rock-physics model that provided a range of plausible pore pressure that lies between hydrostatic (lowest possible pressure) and fracture pressure (highest possible pressure). The range of plausible pore pressures was then converted into a range of plausible depth varying velocities as a function of pore pressure that is consistent with geology and rock physics. Such a range of plausible velocities is called the rock-physics template. Such a template (constrained by geology) was then used to flatten the seismic gathers. We call this the pore-pressure scan technique. The outcome of the pore-pressure scan process was an “upper” and “lower” bound of pore pressure for a given earth ...

A single-vessel method for wide-azimuth towed-streamer acquisition

Summary Wide-azimuth (WAZ) towed-streamer acquisition has been established as a successful method for exploration and development of the complex subsalt structures in the Gulf of Mexico. Wide-azimuth data acquired so far have proved to have better illumination, higher signal-to-noise ratio, and improved seismic resolution. The acquisition geometry used for WAZ surveys is a parallel geometry that employs multiple vessels. In this paper, we propose to acquire WAZ surveys with a single streamer vessel using a circular geometry and we describe the features of this new WAZ method. We also present the results of a feasibility test performed with circular geometry acquisition.