Abstract A detailed stratigraphy is an essential exploration tool. Stratigraphy can serve as a predictor of lithology prior to drilling. Effective prediction results from accurate regional geology. Regional geology may be thought of as a “momentary”, geologically speaking, view of an area's physiography and understanding the earth-changing processes operative at a given time. A compilation of these physiographic views in sequence with absolute dates in years yields a chronostratigraphy. A legitimate question concerns how geologic time may be understood: is it a series of random events or are there cyclic events? Obviously, there are cyclic events, not totally random. The next logical question concerns the periodicity of the cycles and at what time spacing should they be viewed to be recognized. The Exxon/Vail chronostratigraphy (Vail et al., 1977, Haq et al., 1987, 1988, and Lowrie, 1986) reveal cycles that essentially are exponential: first order cycles have a duration of some (10) 8 years or several multiples thereof; second order cycles have a duration of some (10) 7 years or several multiples thereof; and third order cycles with a duration of some (10) 6 years or several multiples thereof. That the sedimentary cover of our planet is composed of different strata has been known since the days of Aristotle. The present desire is to assign absolute dates to the various layers. Such an effort requires an iterative approach combining the results of paleontology, magnetic stratigraphy, sequence stratigraphy, and radiometric dates, Haq et, al., 1988. The understanding

Abstract Salt wedge – (Sigsbee salt knapp complex, wedge of allochthonous salt) Salt wedge is defined as a general term to include the overall salt mass from any source or time, at present underlying the Louisiana slope. Geometric definition: The geometric shape is an “indefinite” wedge with a blunt pinnacle, up to several thousand feet thick, under the Sigsbee Escarpment. Thus, it is understood that the salt wedge is not continuously salt-filled, nor is it continuous over the Louisiana slope. Interpretative definition: This general term refers to all salt, from any source or time, which has coalesced into the overall lateral salt extrusion; see Worrall and Snelson, 1989, figure 15, for representation of dip section through the wedge, equal to Humphris' 1978 wedge. Salt tongue – Salt tongue is defined as a general term to describe individual salt units that have coalesced into the overall salt wedge (Figure 4). Geometric definition: The geometric shape of a salt tongue is approximately that of a poorly-defined wedge. Usually, the landward blunt pinnacle under the Sigsbee Escarpment. The wedge shape is “indefinite” in that separate and distinct salt units, generally lenticular in the dip direction, occupy portions of the wedge shape. Along strike, the distinct salt units are generally separate from the adjoining units. Length versus width ratios may range from 5: 1 to 10: 1. The various separate units, when summed together from shelf- break to escarpment, along dip, create a salt tongue, (Figure 4). Interpretative definition: Salt tongues are defined as represent

Abstract Upper middle Jurassic (Callovian?) Louann salt is presently found overlying continental, transitional, and ocean crust. Overlying continental crust, extensive salt deposits are found in central and northern Louisiana and southern Arkansas. The basins containing them include the Mississippi Interior, East Texas and North Louisiana basins, the Tampa Embayment, and the more regional Gulf Coast Geosyncline. Along the latter, salt is found west of the Santa Rosa Arch, 86°W, and generally east of the San Marcos Arch, 97°W, and locally within the Rio Grande Embayment. These salts appear to be autocraneous. Overlying transitional crust are the extensive salt deposits generally in the Louisiana offshore, with some salt in the eastern Texas offshore to approximately 96°W, and in the Alabama offshore to approximately 87°W. This salt may be autocraneous, or it was laterally extruded southward from the north (Humphris, 1978; Jackson and Cramez, 1989)”. Overlying oceanic crust, salt extends from approximately 87°W to 96°W. The southern boundary is the bathymetrically significant Sigsbee Escarpment. The northern boundary is transitional, with salt overlying transitional crust. This salt is generally held to have been extruded from the north. (See Humphris, 1978; Jackson, et al., 1988, among others). Mention is made by Lopez (1989) of a stock-like feature underlying this salt extruded wedge near 27°N, 90°20'W. This feature, confirmed by seismic data, may be an isolated salt dome rising to the extruded salt wedge. Also, this dome may have been derived from normal seafloor spreading processes. Here we will

Abstract In the previous sections, a series of tectonic and oppositional models for the geologic evolution of the Louisiana offshore have been presented. These models appear to be applicable certainly to the Upper cenozoic, Miocene to present, and quite possibly back to initiation of continental margin deposition in the South Louisiana Basin. The models have depicted lateral Louann Salt migration, suggested possible rates of migration for the several different features, predicted lateral tears in the advancing salt, indicated potential impact of salt ridges onto evolution of shelf-break growth-faults, and computer modeling of fracturing about the various types of migrating salt features, each with their own genetics. Depositional stratigraphy is mixed with the tectonics as the two processes are synergistic. Incoming sediments provide the lithostatic pressures, pushed by omnipresent gravity. The underlying semi-plastic salt and shale masses are pushed into their present configurations by the changing lithostatic and hydrostatic pressures. Lithostatic pressures, resulting from sedimentation, vary with increased deposition and erosion. Hydrostatic pressures vary through geologic time as the potential sediment accommodation volume varies with time, regional subsidence, and sealevel oscillation. It is clearly understood that within the sedimentary record of the Louisiana offshore there are recognizable cycles, from 1st order through at least 4th order, see “Stratigraphic Units” section, and possibly even 5th order sequences. As these global processes are occurring with their own intertwining synergistic effects, they are also impacting, at different frequencies, the semi-plastic salt and shale sheath underlying the encroaching and agrading sediments. Thus, sedimentation shows up to

Abstract In the previous section (Salt Tectonics and Hydrocarbon Plays), there was a brief discussion of salt movements which could create shapes that serve as hydrocarbon traps. In this section, there is a discussion of the thermal conductivity of salt and the thermal impact the salt may contribute to creating mature hydrocarbons and thermally-induced traps. Note that the section is taken from Yu, et al., 1992. Salt has a thermal conductivity 2-3 times greater than that of typical sedimentary rocks (O'Brien and Lerche, 1988; Lerche and O'Brien, 1987). Salt bodies in the subsurface act as conduits for heat transport vertically or horizontally. When salt bodies occur in massive diapirs (sheets), with large vertical (horizontal) relief, they provide a path of low thermal resistance for the conduction of heat in the basin. Local thermal anomalies in the vicinity of salt are expected, owing to the focusing and defocusing of heat by salt. The temperature distribution in the basin has a marked impact on the occurrence of oil and gas, especially through the influence of temperature on hydrocarbon maturation. Maturation can be modeled as a first- order chemical reaction, in which the reaction rate doubles with every 10°C rise in formation temperature (Lopatin, 1971); thus, any effect which causes a significant variation in temperature distribution from the regional trend may have a substantial influence on hydrocarbon generation and accumulation in the subsurface. Here, a two-dimensional fluid flow/compaction model is used, which allows for both thermal conduction and convection

Abstract In this section, various examples of sequence stratigraphy will be presented. The seismic character is employed to assist in determination of deposition environment, whether high- or lowstand, coupled with interpreted regional geology. In analysis of any area, the initial step is to obtain a recognized chronostratigraphy, a stratigraphy containing “absolute” dates. An understanding of global, regional, and local geologic history is essential to produce a chronostratigraphy applicable to the area where the seismic record was collected. Existent global and regional geologic models are correct enough to dictate/influence the evolving local model used to interpret specific data. The geologic model or stratigraphy is a compilation of known tectonic, sealevel, and climate changes, and erosion and deposition characteristics. This “synthetic” stratigraphy is then converted into a geologically reasonable lithologic column and then translated into acoustic impedance and a synthetic seismogram. Comparison of the synthetic and field seismograms evaluates the geologic model. If the two match, then the supposition is made that inputs (acoustic impedances derived from inferred lithologies) into the synthetic model also match the natural inputs (acoustic impedance derived from the natural geologic section effecting the acquisition of the original seismic data). While it is remotely possible that differing velocities and densities may produce acoustic impedances that coincide with those of the natural world, resulting in identity between synthetic and original seismic records, such an occurrence is not realistically very probable. The purpose of this detailed seismic interpretation is to (1) identify and describe each reflection, (2) attribute its origin to

Abstract “Synergisms among tectonics, sedimentation, and climate/sealevel oscillations provide hydrocarbon source, reservoirs, and traps. This book from the SEG Course Notes series examines these traits, as they exist in the on- and offshore region of Louisiana.”

The front matter contains the title page, copyright page, table of contents, and coeditors foreword.

Application of shear (S)-waves in seismic petroleum exploration is in a critical stage of development. Propagation of these waves and of the historically applied compressional (P)-waves in a sedimentary section are affected differently by rock physical properties. Principally, propagation velocity and, in turn, reflection amplitude of P-waves is affected by both rock incompressibility and rigidity, whereas, that of S-waves is affected by rock rigidity only. Because of this difference it is possible, for example, to verify P-wave reflection amplitude variation due to pore fluid change (e.g., brine to a gas-brine mixture), that affects rock compressibility and not rigidity, by the absence of a variation in amplitude of the corresponding S-wave reflection. Additionally, this difference makes it possible to distinguish clastic from calcareous portions of the sedimentary section by comparison of P- and S-wave interval velocities derived from corresponding P- and S-wave reflections bracketing the interval. First to utilize S-waves were earthquake seismologists who deduced composition of the earth from P- and S-wave propagation paths. Application of S-waves in petroleum exploration was delayed by disappointing theoretical and model studies due, principally, to S-wave velocity anisotropy in layered media. Also contributing to this delay was lack of an effective S-wave source of sufficient energy. Viable land S-wave sources now include (1) explosive charges, pioneered by Russian geophysicists, (2) weight-drop devices, and (3) horizontal vibrators, a modification of vertical vibrators used in the Vibroseis® method. Marine S-wave sources presently are not available; nonetheless, reflections of S-waves converted at the ocean bottom from and to pressure waves at the source and receiver end, respectively, provide the possibility of marine S-wave exploration. Current efforts in S-wave exploration, described by papers in this volume, consist of investigation of problems in S-wave recording (e.g., surface wave interference), processing (e.g., reflection static time corrections), and interpretation (e.g., correlation of reflections on P- and S- wave seismic sections). Also described are feasibility studies for determining lithology and porosity, field tests for comparison of P- and S-wave reflection quality, and theoretical studies that may be the basis of novel future exploration techniques. A significant recent development that will advance S-wave exploration considerably is that of a continuously-moving, S-wave velocity well logging sonde.

For SH-wave recording, measures taken to suppress noise in the field usually are determined by examining characteristics of the Love waves. The relatively noise-free time window between first arrivals and surface waves, which is often used for compressional p-wave recording with surface sources, does not exist for shear-wave recording. By displaying surface-wave and reflection wavelengths from the record versus slope of the event (inverse apparent velocity) on the record, we determine which wavelengths should be suppressed by irreversible wavelength filtering (source and receiver arrays) in the field and which events should be suppressed by later velocity filtering. The effect of conventional wavelength filtering and combined wavelength and velocity filtering is illustrated in an example which shows the improvement achieved in SH-wave reflection quality.

A new shear (S)-wave source, the M3 Marthor has been developed from a prototype, the M1 Marthor. It is a weight-drop source, producing reversed polarity blows on a baseplate which is adaptable to off- or on-road operations. With internal swings of the hammer and internal strikes on the baseplate, it is a compact, safe, and maneuverable S-wave source. Seismic surveys were carried out to compare effectiveness of the S-wave vibrator and the M3 Marthor in generation of S-waves. In each case recordings were obtained under identical conditions for both sources. Frequency analysis shows that the M3 Marthor source signal spectrum is broader than that of the S-wave vibrator because of high-amplitude, low-frequency components. Onset of the first seismic event with the M3 Marthor is more abrupt than that obtained with the S-wave vibrator, greatly facilitating computation of static corrections. This is an important advantage in view of the usual highly variable S-wave reflection static time differences. S-wave events are enhanced by the M3 Marthor's ability to produce reversed polarity signals to be subtracted, thereby enhancing SH waves and attenuating other wave types. In the case of VSP surveys, the ability to change polarity of the source signal provides identification of events that are difficult or impossible to identify on single-polarity recordings. The distribution of energy along the x,y, and z axes produced by an M3 Marthor blow has been calculated. This study demonstrates the efficiency of the M3 Marthor in restricting source-signal energy to the y component parallel to the desired SH-wave particle motion.

Results from theoretical models, laboratory experiments, and full-waveform sonic log data converge toward a common interpretational model for Vp/Vs ratios in sedimentary rocks. Moreover, we show that Vp/Vs ratios obtained from sonic logs may be significantly different than those obtained from seismic reflection velocity analysis due to dispersion.

This is the bibliography to the book.

This is the index to the book.

Abstract Application of shear (S)-waves in seismic petroleum exploration is in a critical stage of development. Propagation of these waves and of the historically applied compressional (P)-waves in a sedimentary section are affected differently by rock physical properties. Principally, propagation velocity and, in turn, reflection amplitude of P-waves is affected by both rock incompressibility and rigidity, whereas, that of S-waves is affected by rock rigidity only. Because of this difference it is possible, for example, to verify P-wave reflection amplitude variation due to pore fluid change (e.g., brine to a gas-brine mixture), that affects rock compressibility and not rigidity, by the absence of a variation in amplitude of the corresponding S -wave reflection. Additionally, this difference makes it possible to distinguish elastic from calcareous portions of the sedimentary section by comparison of P- and S-wave interval velocities derived from corresponding P- and S-wave reflections bracketing the interval. First to utilize S-waves were earthquake seismologists who deduced composition of the earth from P- and S-wave propagation paths. Application of S-waves in petroleum exploration was delayed by disappointing theoretical and model studies due, principally, to S-wave velocity anisotropy in layered media. Also contributing to this delay was lack of an effective S-wave source of sufficient energy. Viable land S-wave sources now include (1) explosive charges, pioneered by Russian geophysicists, (2) weight-drop devices, and (3) horizontal vibrators, a modification of vertical vibrators used in the Vibroseis © method. Marine S-wave sources presently are not available; nonetheless, reflections of S-waves converted at the ocean bottom from and to pressure waves at the source and receiver end, respectively, provide the possibility of marine S-wave exploration.