Under good conditions the information extracted can be as detailed as an of the earth in the vicinity of the exploration or development target. Geomechanical information on the overburden, derived from seismic, is an important element to investigating the environmental concerns related to fracking such as caprock integrity and ensuring the safety of our drinking water. We should state now that this is not an all encompassing article. Typically amplitude decreases falls with offset due to geometrical spreading, attenuation and other factors. For example, a water-containing deformation zone in rock mass can conduct electricity better than the surrounding sparsely fractured bedrock.
Sequential Bayesian Gaussian Mixture Linear Inversion of Seismic Data for Elastic and Reservoir Properties Estimation. Delivering an amplitude map with 100 milliseconds of closure is of little value in unconventional exploration. Specifically, such changes may be related to changes in the seismic amplitudes from one 3-D survey to the next. The high resolution reflection seismic method allows exploring the bedrock to a depth of tens of kilometres. One category of well data includes various types of logs recorded in the borehole. Additional attributes of average energy and peak-to-trough ratio are also shown.
These investigations include, among others, reflection seismic 3D measurements in the drillholes 1990 — 2005 and from ground surface in 2006 and 2007 as well as the deep seismic surveys of 2008. The frequency-domain approach, called spectral decomposition, looks for notches in the frequency band representing an interference between the reflections from the top and bottom of the thin bed. The implementation requires that the seismic data are processed in a true amplitude manner and that good log data is available. On the other hand, additional information can be obtained from attributes of the individual seismic traces prior to stacking, in a prestack analysis. The Leading Edge 16 3 : 247. A 100 ton frack at 200m perf spacing has much different economics that a 200 ton fack at 100m perf spacing. It is fortunate that, in many cases, the amplitude of reflection corresponds directly to the porosity or to the saturation of the underlying formation.
The most common attribute is simply amplitude, although its interpretation in thin-layered beds is not necessarily straightforward. Now there are hundreds of seismic attributes out there. It is different than traditional seismic mapping. Incompressibility λ is however non physical unlike rigidity µ, but the extraction method can be seen as a form of stripping off the µ sensitive rock matrix to reveal the most sensitive pore fluid indicator λ. Typically an exploration team evaluates a play for three primary conditions: charge, trap and seal. Seismic resolution becomes especially important in mapping small structural features, such as subtle sealing faults, and in delineating thin stratigraphic features that may have limited areal extent.
To further stabilize the wavelet, deconvolve the data to a desired target waveform with predetermined by knowledge of the input data's usable frequency range. The Leading Edge 16 3 : 241. By contrast the λρ and µρ curves 1b have similar value ranges, that do crossover with λρ µρ is an excellent indicator of thin, tight shale breaks as seen separating gas zone A from B, as well as the capping shale above gas zone B. The time-domain approach involves classifying the character of the reflected wavelet, often using a neural-network technique. Combining the obtained inversion results with lithology and fluid information from the well log using cross-plotting or statistical techniques enables evaluation of lithology and pore fluid variations on both a gross regional scale and a detailed reservoir scale. There are two aspects of seismic resolution: vertical or temporal and lateral or spatial. The unusual behaviour of a very limited ΔVpVp compared to ΔVsVs for this thick, good quality gas sand zone requires some explanation, as most standard measurements concentrate on this non-responsive Vp change.
By recording multicomponent data at the ocean bottom, P-wave and S-wave images can be derived. Both of these techniques run the risk of leading to incorrect interpretations if seismic petrophysical modeling is not performed to direct the analysis and interpretation or to confirm the results. The purpose was to study in particular the rock structures in areas covered by the sea. The upper diagram shows the exact amplitude-vs. The Evolution of Geophysics from Amplitudes to Geomechanics. Using linear regression, a line of best fit can now be calculated that describes how the reflection amplitude varies with offset using just 2 parameters: the intersect, P, and the gradient, G.
It gives us an understanding of the time required for a seismic impulse to travel to and through a reservoir. The situation becomes much more complicated in the case of non-normal incidence, due to mode conversion between and , and is described by the Zoeppritz equations. Journal Geophysical Prospecting — Wiley Published: Mar 1, 2001. Through a series of innovations Figure 6 , we are no longer just producing structural maps with stacked amplitude conformance. The petrophysical properties include porosity, permeability, pore pressure, and fluid saturation.
With the advent of exploration for unconventional reservoirs, there is a perception that the need for geophysics will decline. Historically, they were made up of a Geologist, a Geophysicist and an Engineer. Potential Risks When Using Seismic Attributes as Predictors of Reservoir Properties. Several downhole logging methods have been applied in the deep drillholes. Table 1, shows the justification and power of the method in petrophysical analysis. In the past, marine sediments have been modelled as elastic materials.
The original seismic trace from one location in a seismic volume is shown on the left; the three common attributes of instantaneous amplitude or envelope , instantaneous phase wrapped , and instantaneous frequency follow to the right. Narrow-Band Spectral Analysis and Thin-Bed Tuning. The use of seismic attributes extends well beyond simple amplitudes. The Leading Edge 17 9 : 1286. The geophysical surveys carried out in Olkiluoto are very diverse, not only in the methods used but also in the ways they are implemented. This approximation was popularized in the 1980 book Quantitative Seismology by K. Variation in rock types and pore structures is great, and local calibration is essential, but the empirical results summarized in Fig.