Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2000-05-26
2003-09-09
Lefkowitz, Edward (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S016000
Reexamination Certificate
active
06618678
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the general subject of the analysis and interpretation of the subsurface from seismic and seismic derived layer property data sets.
BACKGROUND OF THE INVENTION
Seismic data is acquired to provide information about the subsurface structure, stratigraphy, lithology and fluids contained in the rocks. Acquired seismic data records are the response of a seismic energy source after passing through and being reflected by rocks in the subsurface. Seismic data can be acquired at or close to the earth's surface or can be acquired along boreholes. After acquisition, seismic data is typically processed to a set of seismic traces, where each trace represents the seismic response at a certain surface x,y location. The trace itself consists of a series of samples of the seismic response, usually ordered to correspond to increasing seismic travel time or, after depth conversion, increasing depth. Dependent on the acquisition geometry, the seismic traces are usually processed and organized to form lines with regularly spaced traces along the surface. The seismic data along such lines can be viewed as sections through the earth. Seismic data is referred to as 2-D seismic data when the lines are in different directions or are far apart relative to the spacing of the traces. Seismic data is referred to as 3-D seismic data when the acquisition is such that the processing results in a set of seismic lines that are organized sequentially and where the x,y trace locations form a regular grid and such that the spacing of the seismic lines generally is within the same order of magnitude as the spacing of the traces within the lines. In practice, the lines along which the data is acquired are called inlines and lines orthogonal to the inlines are referred to as crosslines.
FIG. 1
shows a seismic section taken from a 3-D seismic data cube. 2-D and 3-D seismic data sets are subsequently analyzed and interpreted, generally on computer workstations with specialized software, to reveal the subsurface structure, stratigraphy, lithology and fluids, and to so predict the location, structure, stratigraphy, lithology and fluid distribution of hydrocarbon reservoirs, associated aquifers and other subsurface features of interest.
The amplitude of seismic data changes with changing angle of incidence of the seismic waves reflecting from a rock boundary. These changes of amplitude with angle can hold valuable information about the types of rocks in the subsurface and fluids they contain. For this reason in modern seismic processing multiple seismic data sets for analysis and interpretation are routinely generated from acquired seismic data. Examples are seismic data sets obtained by stacking seismic traces over different ranges of acquisition offsets or ranges of angles of incidence of the seismic waves. Such data sets typically concern pressure wave data. Connolly (1999) discusses methods for generating such seismic data sets.
FIG. 1
shown above is actually a section from a partial stack over near angles.
FIG. 2
shows the corresponding far angle partial stack. Comparison clearly shows differences in the seismic amplitude behavior caused by the change in incidence angles. Besides pressure wave data, other types of seismic data may also be available. In so called multi-component data acquisition the volumes of pressure wave seismic data are further augmented with one or more volumes of shear wave or converted pressure to shear wave seismic data. This provides further information about the subsurface.
The amplitudes of pressure, shear and converted wave seismic data are primarily determined by the strength of the reflection of seismic waves at layer boundaries. The reflection strength in turn is determined by changes in certain physical parameters of the rocks when going from one layer to the next and the angle of incidence of the seismic waves at the layer boundaries. The physical rock parameters are determined by the physical properties of the rock matrix, i.e. the rock with empty rock pores, and fluids contained in the pores, jointly referred to as ‘rock property data’. Changes in the rock matrix can be caused by changes in the lithology (rock mineral composition, porosity and build-up). Changes in fluids can arise from changes in the relative fractions of the fluid types: water, oil and gas and changes in the properties of the fluid types. Using modern computer algorithms, rock property data that is directly related to the amplitudes of the seismic data can be estimated from the seismic data. Such rock property data which is directly related to seismic data includes acoustic impedance, shear wave impedance, density, pressure wave and converted wave elastic impedance and functionally directly related parameters such as pressure and shear wave velocity or slowness, the Lame parameters and the Lame parameters multiplied by density. For the relationship of such parameters to seismic data see e.g. Castagna and Backus (1993). For the estimation of such rock properties from seismic data see e.g. Goodway et al. (1998), Connolly et al. (1999), Anderson and Bogaards (2000) and Pendrel et al. (2000).
FIG. 3
shows an acoustic impedance section and
FIG. 4
a shear impedance section which are derived from the seismic data shown in FIG.
1
and FIG.
2
. The acoustic and shear impedance have been estimated using a seismic inversion method as described by Pendrel et al. (2000). Further rock property data can also be derived directly or indirectly using functional, statistical or other relationships between the different rock properties. For example geostatistics provides a powerful approach to derive further rock property parameters, see e.g. Torres-Verdin et al. (1999). Seismic derived rock property data can be directly used to analyze changes in lithology and fluids in layers. Also, information about structure and stratigraphy is maintained and often even enhanced relative to seismic data. Use of seismic derived rock property data in subsurface analysis and interpretation is therefore often preferred over the use of seismic reflection data. For the same reason the subject method is preferably applied to seismic derived rock property data.
Importantly, seismic derived rock property data directly characterize the properties of the earth's layers, in contrast to seismic data that directly characterizes the reflection properties of layer interfaces. The fact that seismic derived rock properties characterize the properties of rock layers has as key advantage that they can be directly related to other measurements of the earth's layer properties, such as obtained from well logs. For a further discussion of the benefits of carrying out subsurface analysis and interpretation in the layer domain, see e.g. Latimer et al. (2000).
Besides different seismic derived rock property data sets, further data sets, referred to as layer attribute data sets, may be also be available for analysis and interpretation. An example are the data sets derived from seismic derived rock property data sets where the amplitudes are a measure of the continuity (or discontinuity) of the layers. For example U.S. Pat. No. 5,838,634 describes a method that can also be applied to seismic derived rock property data. Yet further information may be available in the form of estimation uncertainties and other statistical measures about the various rock properties.
In summary, a wide range of seismic derived rock property, layer attribute and layer statistical data can be produced with methods among others from seismic data processing, estimation, inversion and (geo)statistics. As most of these data sets refer to the properties of layers, they are further referred to as ‘seismic derived layer properties’ to contrast them to seismic data and most common attributes directly derived from seismic data which characterize seismic reflections at layer interfaces.
Seismic derived layer properties can be interpreted with the same methods as available for seismic data. However, the seismic derived layer propert
Gutierrez Anthony
Jason Geosystems B.V.
Lefkowitz Edward
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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