Joe Stefani

Acquisition using simultaneous sources

We present a technique in which two or more shots are acquired during the time it normally takes to acquire one shot. The two (or more) shots are fired in a near simultaneous manner with small random time delays between the component sources. A variety of processing techniques are applied to produce the same seismic images which would have resulted from firing the simultaneous shots separately. These processing techniques rely on coherency of the wavefield in the common-shot domain and unpredictability in the common-receiver, common-offset, and common-midpoint domains. We present results of its application on synthetic 2D, real 2D, and real 3D data from the Gulf of Mexico. These results demonstrate that, in deep water with modest water-bottom reflectivity, no special processing is required, whereas in shallower water with stronger water-bottom reflectivity, the use of shot-separation techniques is necessary. We conclude that this technique can be used robustly to improve source sampling and, for example, ...

Imaging salt with turning seismic waves

Turning seismic waves, which first travel downward and then upward before (and after) reflection, have been recorded in a 3-D seismic survey conducted over an overhanging salt dome. Careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome.When seismic wave velocity increases with depth, waves that initially travel downward are reflected and may turn so as to travel upward before reflection. A simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com-mon-midpoint (CMP) gathers, in that reflection time decreases with increasing source-receiver offset. This abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves.The most important step in imaging turning waves, assuming that they have been recorded, is the migration process. Simple and inexpensive modifications to the conventional phase-shift migration method enable turning waves to be imaged for little additional computational cost. The examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes.

An implementation of the acoustic wave equation on FPGAs

Hardware accelerators as co-processors are emerging as a powerful solution to computationally intensive problems. A standard desktop PC or cluster node can be augmented with additional hardware dedicated to providing substantially increased performance for particular applications. Previous efforts have shown that FPGA-based hardware accelerators can offer order-of-magnitude greater performance than conventional CPUs, providing the target algorithm performs a large number of operations per data point. FPGAs are off-the-shelf chips with a configurable ‘sea’ of logic and memory that can be used to implement digital circuits. FPGAs can be attached to the compute system either through the main system bus or as PCI Express cards (or similar) and are typically configured as highly parallel stream processors. FPGA acceleration has been successfully demonstrated in a variety of application domains including computational finance (Zhang et al., 2005), fluid dynamics (Sano et al., 2007), cryptography (Cheung et al., 2005) and seismic processing (Bean and Gray, 1997; He et al., 2005a; He et al., 2005b; Pell and Clapp, 2007).

On the Power-Law Behavior of Subsurface Heterogeneity

Summary Analysis of five different types of well-logs from four different basins (20 logs in all) reconfirms the known but under-utilized power-law character of their spatial spectra, and suggests that the power law exponent is only weakly dependent on the log type and basin type. Further, the two new contributions of this paper are (1) the verification of such behavior for permeability logs and horizontal logs, and (2) the use of a horizontal seismic power-law coefficient as a proxy for horizontal well data, both of which are crucially important for proper reservoir characterization at the flow unit scale.

9-C time‐lapse VSP monitoring of steam injection at Cymric Oil Field

The heavy oil of Cymric Field in California’s southwest San Joaquin Basin has been produced by cyclic steaming for more than a decade, but recent efforts to optimize development and increase production have made it a top priority to know the spatial distribution of the steam. Wells are now being drilled very close together on 5/8-acre spacing. Serious problems occur when steam from one well reaches a neighboring well. For example, breakthrough can result in severe mechanical damage that can lead to abandonment of wells. The closer the wells, the more likely the problems, unless you know exactly where the steam is and adjust well locations accordingly.

Integrated use of the Earth model in subsalt seismic prestack imaging

Seismic imaging and the development of accurate earth models enhance geologic understanding and reduce risk in the challenging deepwater areas of the Gulf of Mexico. The standard seismic imaging practice is complicated by extensive sheets of allochthonous salt, which hinder clear imaging of subsalt reflectors due to nonuniform illumination and overprinting by multiples and converted waves. This talk highlights several work practices that we perform to help constrain and validate the subsurface model with respect to the data, and thereby reduce risk within a consistent interpretation. They include complex 3D structural representation and visualization, 3D ray tracing that links the model to the data, visual diagnosis of prestack traces, and integrated displays of earth model, seismic data and inferred earth properties. Rapid iterations and modifications are achieved through software developed on a common computing platform.

Imaging in subsalt shadow zones using post‐critically reflected waves

Structural imaging of sedimentary reflectors is improved within the shadow zone underlying steeply dipping base salt structure by using energy which has reflected postcritically from the base of salt. This concept is tested with both ray traced and wavefield synthetics, and then applied to real subsalt data, with encouraging results. The possibilities and limitations of this approach are discussed and evaluated. Improving subsalt illumination consists of a series of marginal assaults on the problem. This talk presents one such assault