James L. Simmons

3-D seismic evidence of the effects of carbonate karst collapse on overlying clastic stratigraphy and reservoir compartmentalization

A multidisciplinary team, composed of stratigraphers, petrophysicists, reservoir engineers, and geophysicists, studied a portion of Boonsville gas field in the Fort Worth Basin of north‐central Texas to determine how modern geophysical, geological, and engineering techniques can be combined to understand the mechanisms by which fluvio‐deltaic depositional processes create reservoir compartmentalization in a low‐ to moderate‐accommodation basin. An extensive database involving well logs, cores, production, and pressure data from more than 200 wells, 26mi2 (67km2) of 3-D seismic data, vertical seismic profiles (VSPs), and checkshots was assembled to support this investigation. We found the most important geologic influence on stratigraphy and reservoir compartmentalization in this basin to be the existence of numerous karst collapse chimneys over the 26-mi2 (67km2) area covered by the 3-D seismic grid. These near‐vertical karst collapses originated in, or near, the deep Ordovician‐age Ellenburger carbonate ...

Waveform-based AVO inversion and AVO prediction-error

A practical approach to linear prestack seismic inversion in the context of a locally 1-D earth is employed to use amplitude variation with offset (AVO) information for the direct detection in hydrocarbons. The inversion is based on the three‐term linearized approximation to the Zoeppritz equations. The normal‐incidence compressional‐wave reflection coefficient R0 models the background reflectivity in the absence of hydrocarbons and incorporates the mudrock curve and Gardner’s equation. Prediction‐error parameters, ΔRsh and ΔRρ, represent perturbations in the normal‐incidence shear‐wave reflection coefficient and the density contribution to the normal incidence reflectivity, respectively, from that predicted by the mudrock curve and Gardner’s equation. This prediction‐error approach can detect hydrocarbons in the absence of an overall increase in AVO, and in the absence of bright spots, as expected in theory. Linear inversion is applied to a portion of a young, Tertiary, shallow‐marine data set that conta...

AVO modeling and the locally converted shear wave

The locally converted shear wave is often neglected in ray‐trace modeling when reproduction of the AVO response of potential hydrocarbon reservoirs is attempted. Primaries‐only ray‐trace modeling in which the Zoeppritz equations describe the reflection amplitudes is most common. The locally converted shear waves, however, often have a first‐order effect on the seismic response. This fact does not appear to be widely recognized, or else the implications are not well understood. Primaries‐only Zoeppritz modeling can be very misleading. Interference between the converted waves and the primary reflections from the base of the layers becomes increasingly important as layer thicknesses decrease. This interference often produces a seismogram that is very different from one produced under the primaries‐only Zoeppritz assumption. For primaries‐only modeling of thin layers, synthetic seismograms obtained by use of a linearized approximation to the Zoeppritz equations to describe the reflection coefficients are more...

3-D instantaneous frequency used as a coherency/continuity parameter to interpret reservoir compartment boundaries across an area of complex turbidite deposition

In previous unpublished work, we found that anomalous values of instantaneous frequency (that is, frequency values that are negative or that have positive magnitudes greater than Nyquist limit) are valuable indicators of alterations in reflection waveshape that occur commonly at stratigraphic terminations. Inspection of 3-D seismic data across Nash Draw Field on the northwest slope of the Delaware Basin showed that appreciable wavelet alterations occurred at the boundaries of distinct seismic facies within the targeted Brushy Canyon reservoirs that are being produced in this field. Based on this observation, we used instantaneous frequency as the fundamental database to define the edge positions and areal shapes of individual reservoir facies within this complex, slope‐basin distribution of siltstones and sandstones, commonly thought to be a succession of turbidite depositions. We compared the compartmentalization detail derived from this frequency‐based approach with compartmentalization models provided ...

3-D seismic imaging and seismic attribute analysis of genetic sequences deposited in low‐accommodation conditions

A multidisciplinary team, composed of stratigraphers, petrophysicists, reservoir engineers, and geophysicists, studied a portion of Boonsville gas field in the Fort Worth Basin of North‐Central Texas to determine how modern geophysical, geological, and engineering techniques could be combined to understand the mechanisms by which fluvio‐deltaic depositional processes create reservoir compartmentalization in a low‐ to moderate‐accommodation basin. An extensive database involving well logs, cores, production, and pressure data from 200‐plus wells, 26-mi2 (67km2) of 3-D seismic data, vertical seismic profiles (VSPs), and checkshots was assembled to support this investigation. The reservoir system we studied was the Bend Conglomerate, a productive series of gas reservoirs composed of Middle Pennsylvanian fluvio‐deltaic clastics 900 to 1300 ft (275 to 400 m) thick in our project area. We were particularly interested in this reservoir system because evidence suggested that many of the sequences in this stratigr...

Linearized tomographic inversion of first-arrival times

A linearized tomographic‐inversion algorithm estimates the near‐surface slowness anomalies present in a conventional, shallow‐marine seismic reflection data set. First‐arrival time residuals are the data to be inverted. The anomalies are treated as perturbations relative to a known, laterally‐invariant reference velocity model. Below the sea floor the reference model varies smoothly with depth; consequently the first arrivals are considered to be diving waves. In the offset‐midpoint domain the geometric patterns of traveltime perturbations produced by the anomalies resemble hyperbolas. Based on simple ray theory, these geometric patterns are predictable and can be used to relate the unknown model to the data. The assumption of a laterally‐invariant reference model permits an efficient solution in the offset‐wavenumber domain which is obtained in a single step using conventional least squares. The tomographic image shows the vertical‐traveltime perturbations associated with the anomalies as a function of m...

3-D seismic imaging and interpretation of Brushy Canyon slope and basin thin-bed reservoirs, northwest Delaware Basin

A study was done at Nash Draw field, Eddy County, New Mexico, to demonstrate how engineering, drilling, geologic, geophysical, and petrophysical technologies should be integrated to improve oil recovery from Brushy Canyon reservoirs at depths of approximately 6600 ft (2000 m) on the northwest slope of the Delaware basin. These thin‐bed reservoirs were deposited in a slope‐basin environment by a mechanism debated by researchers, a common model being turbidite deposition. In this paper, we describe how state‐of‐the‐art 3-D seismic data were acquired, interpreted, integrated with other reservoir data, and then used to improve the sitting of in‐field wells and to provide facies parameters for reservoir simulation across this complex depositional system. The 3-D seismic field program was an onshore subsalt imaging effort because the Ochoan Rustler/Salado, a high‐velocity salt/anhydrite section, extended from the surface to a depth of approximately 3000 ft (900 m) across the entire study area. The primary imagi...

A matched-filter approach to impedance estimation

Stacked seismic data are modeled as a superposition of simple‐interface and thin layer reflections. This parameterization permits a parsimonious blocky model of the impedance. The method is an alternative to the classical least‐mean‐squared‐error approach and is similar in spirit to minimum‐entropy deconvolution and sparse‐spike inversion, although much different, and simpler, in implementation. A specified number of events on a seismic trace are modeled (inverted) independently. The selected set of basis functions used to represent the data includes a simple interface and a suite of high and low impedance layers covering a range of layer thickness. The simple interface basis function is the seismic wavelet, which is presumed to be known. Each event is classified using a normalized zero‐lag crosscorrelation of the basis functions with the seismic trace. Modeled events are prevented from overlapping, thereby ensuring a sparse earth model. Real data results show that a portion of a shallow‐marine data set c...

Multiple reflections as an additive noise limitation in seismic reflection work

A principal problem in seismic exploration is the heterogeneous partially reflecting medium that makes up the transmission zone to the target reflectors of interest. Multiple reflection between the free surface and the shallower reflectors produces additive noise that interferes with our view of the bedding plane geometry and rock properties in the target zone. Residual multiple energy on the interpreters record section display can easily be mistaken for signal. Because the magnitude of multiples is dependent on reflectivity products, and because subsurface reflectivities are normally small, the importance of multiples is highly variable. The complementary combination of predictive deconvolution and common depth point stack is routinely used for the reduction of multiple reflections. Predictive deconvolution achieves a temporal prediction and subtraction of that class of short-period multiples that is most predictable, and common depth point stack reduces that class of multiples distinguishable from primaries on the basis of local horizontal phase velocity in the x, t observational space. Each of these methods can be justified in terms of a simplified one-dimensional model of the earth. However, a major reason for their success is that they are employed with an empirical, statistical approach. As a result, these two processes are particularly robust and forgiving and respond imperfectly, but often constructively, to real-world deviations from the simplified models. Both processes are capable of distorting or destroying the desired signal, and their noise-reduction effectiveness is dependent on the manner of application. Quality control methods are imperfect, and there is an element of human artistry in seismic data processing. Predictive deconvolution employs a one-dimensional (t) filter designed on a purely statistical basis. Seismic data represent observations in (x1, x2, t), a four-dimensional space, and multiple reflections are deterministically predictable (in principle) from the shallower primary reflection data. Common depth point stack operates in (x1, t) as an array steered for the arrival of the roughly spherical target reflection wavefront. Multidimensional filter design aimed at coherent noise rejection, based on the nonrandom noise structure in (x1, t) is often used in problem areas. More effective reduction of multiple reflections is one of many potentially useful improvements in the seismic method.

Case History: 3-D Shear-wave Processing And Interpretation In Radial-transverse (SV-SH) Coordinates

Summary A 9-C 3-D seismic reflection data set from Clark County, Kansas is processed to produce SH and SV data volumes. Data processing is quite straightforward; rotation of the data from field coordinates to radial-transverse coordinates, static corrections (elevation, shot, and receiver) derived from the SH data, NMO correction with a single velocity function, inside-trace mute, and stack. Super gathers monitor the convergence of the shear-wave statics, which are found to be relatively small (+/- 40 ms), and simple to estimate from the dominantly 12 Hz SH data. Single velocity function NMO (velocities derived from SH) show the SV data to be slightly overcorrected, suggesting the presence of vertical transverse isotropy. An inside-trace mute eliminates the surface-wave noise cone. Dominant reflections in the stacked data are from the top and base of the Morrow clastic interval. Reflection signal quality is superior on the SH data.