Inversion of refraction data by wave field continuation

The process of wave equation continuation (migration) is adapted for refraction data in order to produce velocity-depth models directly from the recorded data. The procedure consists of two linear transformations: a slant stack of the data produces a wave field in the p - τ plane which is then downward continued using τ = O as the imaging condition. The result is that the data wave field is linearly transformed from the time-distance domain into the slowness-depth domain, where the velocity profile can be picked directly. No travel-time picking is involved, and all the data are present throughout the inversion. The method is iterative because it is necessary to specify a velocity function for the continuation. The solution produced by a given iteration is used as the continuation velocity function for the next step. Convergence is determined when the output wave field images the same velocity-depth function as was input to the continuation. The method obviates the problems associated with determining the envelope of solutions that are consistent with the observations, since the time resolution in the data is transformed into a depth resolution in the slowness-depth domain. The method is illustrated with several synthetic examples, and with a refraction line recorded in the Imperial Valley, California

3-D sedimentological and geophysical studies of clastic reservoir analogs: Facies architecture, reservoir properties, and flow behavior within delta front facies elements of the Cretaceous Wall Creek Member, Frontier Formation, Wyoming

This project examined the internal architecture of delta front sandstones at two locations within the Turonian-age Wall Creek Member of the Frontier Formation, in Wyoming. The project involved traditional outcrop field work integrated with core-data, and 2D and 3D ground penetrating radar (GPR) imaging from behind the outcrops. The fluid-flow engineering work, handled through a collaborative grant given to PI Chris White at LSU, focused on effects on fluid flow of late-stage calcite cement nodules in 3D. In addition to the extensive field component, the work funded 2 PhD students (Gani and Lee) and resulted in publication of 10 technical papers, 17 abstracts, and 4 internal field guides. PI Bhattacharya also funded an additional 3 PhD students that worked on the Wall Creek sandstone funded separately through an industrial consortium, two of whom graduated in the fall 2006 ((Sadeque and Vakarelov). These additional funds provided significant leverage to expand the work to include a regional stratigraphic synthesis of the Wall Creek Member of the Frontier Formation, in addition to the reservoir-scale studies that DOE directly funded. Awards given to PI Bhattacharya included the prestigious AAPG Distinguished Lecture Award, which involved a tour of about 25 Universities and Geological Societies in the US and Canada in the fall of 2005 and Spring of 2006. Bhattacharya gave two talks, one entitled “Applying Deltaic and Shallow Marine Outcrop Analogs to the Subsurface”, which highlighted the DOE sponsored work and the other titled “Martian River Deltas and the Origin of Life”. The outcrop analog talk was given at about 1/2 of the venues visited

Application of Wave Field Continuation to the Inversion of Refraction Data

Three examples of the inversion of refraction data by downward continuation illustrate the applicability of the method to field data. The first example is a refraction profile from the Mojave Desert, California. These data are spatially aliased and contain clear evidence of lateral inhomogeneity. The inversion in this case produces a broken image in the slowness-depth domain due to the lateral inhomogeneity, but a useful average velocity model is still obtained. The second example is a shallow marine reflection profile. Here, the truncation effects due to the finite horizontal aperture of the recording cable produce artifacts in the slowness-depth domain. The velocity model is, however, distinct from these artifacts, and the presence of strong precritical reflections aids in the inversion. The third example is another shallow marine reflection profile. The inversion of these data illustrate the utilization of constraints provided by multiples as well as primary arrivals

Creating Virtual 3-D Outcrop

Because of the high precision of present-day GPS and reflectorless laser technology, geologic information and remotely sensed data (i.e., seismic and GPR grids, wells) can be positioned accurately in 3-D and reconstructed as a virtual image. Hence, we have developed the “virtual outcrop” for applications that require knowledge about the 3-D spatial arrangements of rock types

A 3-D Ground-Penetrating Radar and Wavelet Transform Analysis of the Morphology of Shoreface Deposits in the Upper Cretaceous Ferron Sandstone Member, Utah

Wavelengths of hummocky cross-stratified (HCS) beds (a common sedimentary feature of storm-dominated shorefaces) are documented for the first time using measurements in three-dimensional (3-D) ground-penetrating radar (GPR) data for a well-developed Upper Cretaceous lower-shoreface succession at Dry Wash in the Ferron Sandstone Member, Utah. The shallow-marine sequence consists of upward-thickening HCS sand beds alternating with interstorm deposits. The thickness variation of the storm beds indicates locally steadily growing storm intensity with at least four cycles. Weakly coarsening-upward (mud to very fine-grained sand) fair-weather background deposits suggest a slow progradation of deposition with no significant change in environment. The GPR interpretation mapped three conformable, high-continuity, high-amplitude reflections throughout the 3-D GPR data volume. The interpreted radar surfaces (RSs) are well correlated with tops of HCS sand beds (and thus paleotopographic surfaces); the associated radar units (RUs) have a uniform thickness (on average ~0.8 m [~2.6 ft]). The RUs and the adjacent outcrop observations suggest that the shoreface sandstone at the Dry Wash site has a simple layered internal architecture. The hummocky-swaley surfaces generally dip westerly, as a product of postdepositional structural alterations that are mostly in the shoreline direction, and contain variable-size, structurally undulating rounded features. A 2-D continuous wavelet transform analysis is applied to the detrended RSs, producing a multiresolution image decomposition of the GPR surfaces. Surface features with a wavelength range of 1–7 m (3–23 ft) are in good agreement with the observations on modern hummocky shallow-marine seabeds. Quantitative measurements indicate that the hummocky surfaces at the Dry Wash site are dominated by uniformly distributed circular to elongate bed forms with maximum correlation at 1.5–3.5-m (4.9–11.4 ft) wavelength and that the deltaic sedimentary layers were simultaneously deformed by the middle Campanian compressional stress of the Sevier orogeny transmitted from the northwest. Quantitative information on the subseismic-scale surface geometry of the HCS beds is expected to result in more refined reservoir models. In addition, the connectivity of units indicated by the scale of the morphology can be an indirect indicator of unit correlation and permeability paths