Chris L. Hackert

Quantification of high latitude electric field variability

Variability in the high latitude electric field has been identified as a major contributor to global Joule heating. Electric field patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure are used to characterize the E-field temporal variability over the course of 18 hours. The standard deviation of the E-field magnitude on May 4, 1998 often exceeds the average value of the E-field magnitude. A significant fraction of this variability arises from oscillations with period less than one hour. This confirms that Joule heating calculations based on time-averaged E-fields may significantly under-predict the heating.

Improving Q estimates from seismic reflection data using well-log-based localized spectral correction

Most methods for deriving Q from surface-seismic data depend on the spectral content of the reflection. The spectrum of the reflected wave may be affected by the presence of thin beds in the formation, which makes Q estimates less reliable. We incorporate a method for correcting the reflected spectrum to remove local thin-bed effects into the Q-versus-offset (QVO) method for determining attenuation from seismic-reflection data. By dividing the observed spectrum by the local spectrum of the known reflectivity sequence from a nearby well log, we obtain a spectrum more closely resembling that which would be produced by a single primary reflector. This operation, equivalent to deconvolution in the time domain, is demonstrated to be successful using synthetic data. As a test case, we also apply the correction method to QVO with a real seismic line over a south Florida site containing many thin sandstone and carbonate beds. When corrected spectra are used, there is significantly less variance in the estimated Q values, and fewer unphysical negative Q values are obtained. Based on this method, it appears that sediments at the Florida site have a Q near 33 that is roughly constant from 170- to 600-m depth over the length of the line.

Wave attenuation attributes as flow unit indicators

In this article we present a model-based interpretation algorithm to predict attenuation signatures associated with a reservoirs structure and its intrinsic properties. Scattering losses are caused by multiple reflections associated with the impedance contrast between different reservoir boundaries. Intrinsic losses are due to the fluids in the reservoir, the rock fabric, and the anisotropy due to vertical fractures. Because amplitude data are sensitive to these reservoir characteristics, we calculate the wave attenuation response of the reservoir in the frequency range of surface seismic, VSP, crosswell seismic, and borehole sonic. A model of a plane wave traveling in a poroelastic multilayer earth medium allows us to include anisotropy. The multilayer part of the model simulates elastic scattering; the poroelastic part of the model simulates fluid-flow effects in the reservoir; and the anisotropic part of the model simulates reservoir fractures.

Attenuation analysis of acoustic waveforms in a borehole intercepted by a sand-shale sequence reservoir

We applied a new processing algorithm to extract intrinsic attenuation (1/Q) from the head P-wave of a full waveform sonic log. The sonic log was acquired in an oil reservoir in northeast Texas (USA). The reservoir is a sand-shale sequence characterized at the pore, core, and borehole scales. We found that the attenuation correlates with the lithology, including a sandstone zone partially saturated with oil and water. A comparison of 1/Q with the microseismogram and the petrophysics of other well logs provides a way of evaluating the consistency of Q at each borehole depth location. An analysis of the results explains the different attenuation anomalies found in the Q log.

Permeability and porosity images based on NMR, sonic, and seismic reflectivity Application to a carbonate aquifer

Carbonate formations generally have a large distribution of pore sizes, ranging from microcrystalline to large vugs. Knowledge of these pore spaces and their connectivity is crucial to hydrocarbon reservoir characterization and to hydrogeological and near surface environmental applications. In this paper, we present permeability and porosity images based on crosswell seismic measurements integrated with well logs and petrography from a carbonate aquifer underlying Palm Beach County, Florida, U.S. Petrography and core analyses reveal relationships between the rock physical properties that control the compressional- and shear-wave velocities of the formation. In addition, core data and petrography characterized the matrix permeability and pore spaces as well as the lithology. The lithology integrated with well logs determined the hydraulic and rock properties of a 500-ft zone intercepted by a borehole. We delineated vuggy and permeable/impermeable zones at the borehole and interwell scales in the upper Floridan aquifer in south Florida by inverting reflection seismic data for impedance which, when correlated with borehole permeability and porosity logs, led to empirical relationships that are used to transform impedance images to permeability and porosity images. The images showed continuity between the major geologic units and lateral changes in the porosity image. The high-resolution reflections observed at the field scale in the carbonate formation are associated with changes in porosity due to the presence of vugs. This was corroborated with P-wave and borehole data, which showed that, as P-wave velocity decreases, porosity increases. The images show that porous zones in the carbonate aquifer are laterally continuous up to 200 ft from the well and then become relatively discontinuous, and that these porous and permeable flow units are characterized by interconnected vugs. To analyze the pore structure of the carbonate rocks of the upper Floridan aquifer in South Florida, we processed x-ray CT and optical microscopic (OM) thin …

Detection of guided waves between gas wells for reservoir characterization

Guided seismic waves can be used to predict continuity and discontinuity of reservoir structures between wells, with the low‐velocity beds acting as waveguides. We relate guided‐wave signatures to waveguide targets using experimental data acquired at the Stratton gas field in southeast Texas. The observed seismic data indicate the presence of trapped energy in low velocity shale markers between wells 145 and 151. Guided waves in the form of leaky modes are excited, transmitted, and detected in the low‐velocity shale markers at a well separation of 1730 ft (527 m). Dispersion analysis, modeling, frequency–amplitude depth curves, well logs, and lithological information all support the results. Specifically, the characterization of two low‐velocity shale markers, V2 and V5, demonstrates that V2 is more heterogeneous than V5 between the source well 151 and detector well 145. Finally, images of synthetic and real data show the potential applications of the guided‐wave technology as a tool for reservoir charact...

A borehole-model-derived algorithm for estimating QP logs from full-waveform sonic logs

We develop a processing algorithm to estimate the intrinsic seismic attenuation QP −1 from P head waves of full-waveform sonic logs. The algorithm, based on an extended version of the amplitude spectral ratio (ASR) method, corrects the apparent attenuation for the effects of multiple raypaths within the borehole, geometric spreading of head waves, and formation inhomogeneity. The algorithm is derived from two ray models. The first model simulates the interaction among rays reflected within the borehole and rays reflected from layer interfaces. This model removes these reflections and extracts the leading borehole wavelet. The second model uses a single-ray model for the borehole head wave in layered formations. This model provides the transmission coefficients across the layer interfaces between the source depth and the receiver depth with sectional geometric spreading within these layers. We use these two models to simultaneously separate, correct for, and normalize the effects of the borehole, geometric...

Dispersion and attenuation of acoustic waves in randomly heterogeneous media

We derive the effective displacement relation for acoustic waves in a spatially random heterogeneous one-dimensional medium. This relationship is expressed in terms of parameters σR and σA which represent the standard deviations of the randomly varying density ρ(x) and the randomly varying Youngs modulus α(x), of the medium. In this way, we build the contributions into the total displacement relationship for the spatially random heterogeneous medium and apply this result to determine the dispersion and attenuation of acoustic waves propagating in the random heterogeneous medium. Attenuation and dispersion of waves propagating in media with randomly varying properties has been the subject of much study. Most of this work has neglected the effects of intrinsic dispersion and attenuation in order to concentrate on the effects of the medium inhomogeneities. We demonstrate how intrinsic attenuation may be easily included in the theoretical development, and explore the combined effects of scattering-based and intrinsic attenuation and dispersion on wave propagation. We apply the solution to model interwell acoustic waves propagating in the Kankakee formation at the Buckhorn Test Site, IL. The modeling results show that the strong dispersion in the frequency range of 500–2000 Hz is due to the reservoir heterogeneity. Alternatively, the velocity dispersion for frequencies greater than 2000 Hz corresponds to the intrinsic properties of the reservoir.

Effect of IMF By on thermospheric composition at high and middle latitudes: 2. Data comparisons

[1] The strength and orientation of the interplanetary magnetic field (IMF) has a strong effect on the high-latitude plasma convection pattern, thereby influencing the speed and direction of polar thermospheric winds. The possibility of similar IMF control over the compositional response of the thermosphere during geomagnetic disturbances has not been fully investigated. This study finds that the y-component of the IMF (IMF By) exerts significant control over the development and subsequent equatorward transport of composition disturbances during periods of heightened geomagnetic activity. This is determined using the NCAR-TIMEGCM to simulate the thermospheric conditions during the first 3 weeks far-ultraviolet (FUV) imaging operations of the Dynamics Explorer 1 (DE-1) mission in 1981. The images reveal changes in the relative thermospheric column abundance of O versus N 2 (ΣO/N 2 ). These changes are reproduced by the model, incorporating variable IMF strength and orientation as inputs. It is found that simple reversal of IMF By leads to subsequent changes in ΣO/N 2 at middle latitudes by as much as 30%. This is a manifestation of the effect identified in the companion to this report (Crowley et al., 2006). The study confirms the hypothesis of Immel et al. (1997) that IMF-B y effects on middle-latitude thermospheric composition are important, though more complex than expected. Contrary to previous predictions, early morning local times are shown to be more likely to suffer large decreases in ΣO/N 2 when By is negative. However, the overall magnitude of high-latitude Joule heating is found to be greater when By is positive.

Estimating scattering attenuation from vugs or karsts

Cavities in carbonate rock, such as vugs or karsts, cause scattering attenuation in passing waves. The degree of such attenuation is often difficult to quantify because the exact scale and structure of the cavities is unknown. Taking the exact vug structure from X-ray computerized-tomography scans of two carbonate cores, we use 3D finite-difference modeling to determine the P-wave scattering attenuation in these cores at ultrasonic frequencies. The predicted scattering attenuation is quite high, with Q of 15 and 8 near the source frequency of 250 kHz. In spite of the sharp contrast in medium properties between cavity and rock, and the violation of the small perturbation assumption, the computed scattering attenuation is roughly comparable to that predicted by various random medium scattering theories. This suggests that if the volume fraction and typical size of vugs or karsts can be estimated, then a rough estimate of frequency-dependent scattering attenuation can be made.