Peter I. Pecholcs

Over 40,000 vibrator points per day with real‐time quality control: opportunities and challenges

To evaluate high-density source and receiver land seismic acquisition designs, two sets of simultaneous highproductivity vibroseis field tests were performed in a relatively flat terrain area with good signal-to-noise ratio. These included distance separated simultaneous sweeping (DSSS) (Bouska, 2009), slip-sweep (Rozemond, 1996), distance separated simultaneous slip-sweep (dynamic slipsweep) and independent simultaneous sources (ISS) (Howe et al., 2008) with unique sweeps. The second dynamic slipsweep field test used a 29 km active fixed super-spread (12 receiver lines separated by 300 m) with 20 point vibrator fleets on a 25 m x 25 m source grid. A group of 10 point vibrators were oriented orthogonal to the receiver spread in the North and 10 in the South direction with a lateral separation distance of 14.5 km. This method achieved 30,346 vibrator points (VPs) in a 24 hour period. The same fixed active receiver spread was reduced to continuously record two unconstrained simultaneous sources (microseismic mode) in 18 sectors (3x6). Each sector was 1.8 km x 1.8 km with 4,320 VPs on a 25 m x 25 m source grid (77,760 total VPs) with 18 unique 12 s pseudorandom sweeps (Sallas et al., 2008) and repeated with 18 unique linear upsweeps (14.5 s average sweep length) from 5 to 110 Hz. We achieved optimum productivity rates of 45,501 and 44,793 VPs per 24 hours, respectively, with real-time quality control (QC) – we were not sweeping blind. Seventy two drivers were organized in three eight-hour shifts along with four vibrator pushers per shift. Three helped with fleet management and one for TDMA real-time communication between the vibrators and the recorder. Even higher productivity rates could have been achieved with stakeless guidance training of the vibrator drivers and pushers.

Estimation of Long-wavelength Near-surface Velocity And Low-relief Structural Anomalies Part I. A Case History In Central Saudi Arabia

Summary Undetected near-surface and subsurface velocity variations greater than an effective spread length produce false structures both in time and depth. The estimation of these variations rely on uphole measurements, high density shallow reflection data and sufficiently long offsets for subsurface reflectors. Despite inadequate near-surface velocity-depth measurements in the study area, we developed a strategy for the detection and estimation of both near-surface and subsurface long-wavelength velocity and low-relief structural variations. We chose two 2D seismic lines (dip and strike) over two existing low-relief fields in central Saudi Arabia, to demonstrate how the velocity-depth ambiguity problem is partially overcome by integrating the refraction delay time solutions derived from multiple refractors below the seismic reference datum with iterative pre-stack depth migration, residual analysis, and reflection tomography. We compare these results with the conventional isopach depthing method and discuss how this strategy improves the structural integrity of potential prospects. Even with the verification of the near-surface velocity and structural anomalies along the dip line and buried velocity anomaly along the strike line through forward modeling and flatness of depth image gathers, these models are non-unique. Based upon this case study, a new constrained tomographic algorithm has been developed which overcomes the above ambiguity and is discussed in Part II.

Spatially Fixed Patterns Illuminate Unresolved Static Anomalies.

Summary In Saudi Arabia, the complex three-dimensional nearsurface overburden can introduce large magnitude shortwavelength time delays greater than half a period and wavelengths greater than half an effective spread length. Since automatic residual statics algorithms fail to resolve these statics, additional geologic information is needed during the interpretation phase to constrain the near-surface model. These errors are overcome by combining this interpretation phase with a new partial-offset stack domain within a stand-alone PC-based interpretation system. This interpretation system uses multiple forward and reverse partial-offset stack displays in the common-receiver point (CRP), common-source point (CSP), and commonmidpoint (CMP) domains to delineate and estimate surfaceconsistent source and receiver statics. However, it is only possible to decouple the source and receiver statics when the offset distance is greater than the anomaly width (i.e., under shoot). This limitation is overcome by using a new 2D or 3D spatially fixed stacking pattern to organize CRP and CSP offset-dependent stacks for spatially fixed sources and receivers, respectively. These patterns are designed to “illuminate” the near-surface anomaly from different directions, discriminate between structural and surfaceconsistent velocity variations, and decouple shot and receiver statics. Each offset trace within a range of receivers or sources from a fixed set of binned sources or receivers will have the same constant surface-consistent static. This constant static term can be easily estimated and removed from the time picks when two patterns are overlapped. Hence, the surface-consistent source and receiver static components are decoupled. This is the only known efficient method for resolving surface consistent short-wavelength large magnitude and medium- to longwavelength statics in three-dimensions.

Broadband Full-Azimuth 3D Land Seismic Acquisition - Managing 100,000 Channels, Over 20,000 Vibrator Source Points, and 24 Terabytes of Uncorrelated Data per Day

On land, broadband simultaneous vibroseis acquisition methods and high-channel count recording systems provide key technologies for the acquisition of full-azimuth 3D seismic surveys. This paper focuses on the experience gained in the acquisition and processing of two high density source (1,280 and 3,200 VPs/km2) and receiver (640 stations/km2) surveys, and reviews a new high-productivity field test for optimal de-noising.

Seismic Simultaneous Sources in Land: Challenges and Opportunities

essing of this optimally designed seismic blended dataset without applying any deblending algorithm produces satisfactory results. To improve the prestack analysis such as first break picking, noise removal and velocity analysis, deblending methodologies and workflows were also applied. In this paper, we present processing results related to land simultaneous sources acquisition. Novel deblending schemes will be shown along with their effectiveness in a production environment. Statics, surface consistency, noise attenuation and velocity estimation are seen as the main challenges for the processing of land blended data. Current processing schemes rely mostly on deblending so that conventional workflows can be subsequently employed for data analysis. Full blended data processing in land is still an open issue. Current practice dictates that we have to have well in advance nearsurface and velocity macromodels in order to proceed. Migration will do the rest. The real question therefore is: a) Do we develop tools to fully process blended data? or b) Do we develop effective deblending algorithms & proceed in a conventional manner? We all know the answer…it can be found in the middle!!! Of course everything starts with acquisition…do we play the game safe and acquire optimally distance-separated data or go wild and acquire data in a random fashion? Processing now becomes the key. In short, seismic acquisition and processing must be considered simultaneously!!

Extending the seismic bandwidth — A simultaneous uncorrelated VSP and surface seismic field test study

A controlled simultaneous VSP and surface seismic field test was conducted to evaluate the evolution of the vibroseis chirp wavelet. We verify that the partitioning of seismic energy is independent of sweep rate for different sweep designs. We demonstrate under what conditions the seismic bandwidth can be extended using the semblanceweighted deterministic deconvolution process in the uncorrelated domain for zero-offset VSP, walk-away VSP, and simultaneous borehole and surface seismic data. The deterministic deconvolution process requires knowledge of the chirp wavelet in order to transfer the harmonic energy from the seismic noise domain into the seismic signal domain. Its performance depends on knowledge of the chirp signature and ambient noise. As expected, the ambient noise conditions in the well were extremely low as compared to the higher noise levels recorded in the surface seismic data. Under low ambient noise conditions, the semblance-weighted deconvolution can extend the recoverable bandwidth beyond the predefined pilot bandwidth for both the VSP and surface seismic data independently. The high level of surface ambient noise conditions in our field test limited the effectiveness of the VSP operators to extend the recoverable bandwidth of the surface seismic data.

Universal land acquisition 14 years later

Universal land acquisition means that we are no longer forced to commit to a final processing and/or interpretation sampling grid during the acquisition process, but have the ability to change the processing/interpretation bin dimensions at various later times, depending upon the sampling requirements for the particular processing/interpretation objective under consideration. Ongkiehong et al. (1988) called this “uncommitted acquisition”.