Louis M. Liro

A PHYSICAL MODEL STUDY OF SHEAR-WAVE SPLITTING AND FRACTURE INTENSITY

In a series of physical model experiments, fractured media are simulated by stacks of thin Plexiglas sheets clamped together tightly to form blocks. The plates are assembled underwater, and a very thin water layer between the sheets prevents formation of an effectively welded interface between them. Thus, the stacked material is not a series of welded plates but rather a truly fractured medium simulating a potential petroleum reservoir with only fracture porosity and permeability. Sheets of constant thickness are used, but the intensity of fracturing between the different models is simulated by using different thicknesses of Plexiglas for each model. Observation of direct shear‐wave arrivals through the stack, with propagation parallel to the sheets and polarization of particle motion allowed to be parallel to, normal to, or in any arbitrary angle to the sheets, definitively demonstrate the existence of shear‐wave splitting and hence anisotropy. For Plexiglas sheets 1/16 in thick (0.16 cm) representing a ...

Integrated geochemistry, organic petrology, and sequence stratigraphy of the Triassic Shublik Formation, Tenneco Phoenix # 1 well, North Slope, Alaska, U.S.A.

Abstract The Tenneco Phoenix #1 well recovered continuous core through the Shublik Formation, allowing an uncommon opportunity to comprehensively study organic and lithostratigraphic facies variations in a known hydrocarbon source-rock interval. The lower portion of the cored Shublik Formation represents part of a transgressive systems tract (TST) and is characterized by alternating well-laminated and bioturbated shales. A pronounced condensed section occurs at the top of this interval. The Shublik Formation above the maximum flooding surface (MFS) represents initial deposits of a highstand systems tract (HST); it contains coarser grained material and is more bioturbated than the base of the unit. The distribution of oil-prone facies within the Shublik Formation is dependent on stratigraphic position and is predictable within a sequence stratigraphic framework. The transgressive portion is dominated by oil-prone facies while the upper, regressive portion is predominatly gas-prone to non-source. Well-laminated, organic-rich, oil-prone intervals in the Phoenix core correspond to uranium anomalies on the spectral gamma ray log. An organic petrologic study of 54 core samples from the Shublik Formation is consistent with log analysis and source-rock geochemistry. Both subtle and dramatic organic facies changes characterize the TST. Fluorescent amorphinite, marine alginite, and other exinites are the dominant kerogen macerals. Subtle variation in the maceral concentration of this oil-prone organic debris is typical of this interval; however, there are four major changes in kerogen composition in this transgressive interval. These changes include fluctuations in kerogen composition that reflect likely variations in those factors that controlled deposition and preservation of the organic matter in the Shublik Formation. There is another significant reduction in the amount of oil-prone kerogen in the condensed section at the top of the TST. Non-fluorescent amorphinite is the dominant organic matter type. In general, fluctuations in kerogen composition are much less pronounced in the HST when compared with the TST. Fluorescent amorphinite is the dominant kerogen type, but there is also 10–15% vitrinite with comparable amounts of inertinite. The amount of these maceral types gradually increases stratigraphically upward in the HST. Because of this, source-rocks in this interval tend to be gas-prone. However, there is no significant change in the apparent origin of the organic matter immediately across the MFS; there is still considerable kerogen of marine origin in the HST.

Distribution of shallow salt structures, lower slope of the northern Gulf of Mexico, USA☆

Abstract Shallow salt structures on the lower slope of the northern Gulf of Mexico are interpreted to be the manifestation of a unique geological situation: an unusually thick original salt layer mobilized and deformed by episodic Cenozoic sedimentary loading into a variety of shallow subsurface forms. Salt deformation, observed on seismic data, increases in intensity and complexity from the relatively simple shallow salt canopies of the Florida Escarpment area to partitioned and deformed shallow salt masses of the offshore Texas area. Salt ‘tongues’ (extensive lateral salt bodies in the shallow subsurface, with demonstrable sources) are observed from the Mississippi Fan area to the western edge of the lower slope. Salt tongues vary in style from subhorizontal, very shallow, laterally persistent tongues that comprise the frontal lobe of the Sigsbee Escarpment to adjacent undulatory, landward dipping tongues which rise obliquely through the sedimentary section. The salt tongues form a trend which defines the southern limit of shallow salt in the northern Gulf of Mexico. Shallow salt features landward of this trend are interpreted as earlier formed salt dome and tongue systems, the original shape and distribution of which were modified by partitioning of a precursor shallow salt feature by sedimentary loading. The morphology of the prominent Sigsbee Escarpment is due entirely to lateral and basinward movement of asymmetric salt masses. Lateral displacement of salt in these salt tongues is of the order of only tens of kilometres. The occurrence of dome-like features and withdrawal basins landward of the salt tongues suggests that the tongues originate from or in association with these domes.

A new paradigm for data integration and collaboration using 3-D visualization technology

Seismic interpretation still begins with the simple question “what if…?” in the interpreters mind and translating that question into a working model. However, modern 3-D visualization allows that model to be constructed and evaluated in real time by a technically integrated staff. It is now possible at the onset of a project to review the data, identify prospective regions or reservoir trends, assess key technologic challenges, and determine an efficient work direction in an afternoon.

Application of 3-D visualization to integrated geophysical and geologic model building: A prestack, subsalt depth migration project, deepwater Gulf of Mexico

Application of 3-D prestack depth migration for subsalt exploration in the deepwater Gulf of Mexico requires efficient interaction between geophysical imaging and geologic modeling to obtain optimum imaging quality. When this process is applied to massive 3-D seismic volumes, time and cost concerns are critical. Salt-model building through conventional 2-D vertical section interpretation is too labor-intensive and error-prone to be cost-effective. The ability to visualize a full seismic volume greatly expedites interpretation while offering insight and perspective not possible with 3-D in-line and cross-line interpretations. 3-D visualization techniques, an essential component of our technical strategy, allowed us to build velocity models and complete PSDM processing over approximately 300 OCS blocks (7000 km2) in less than 12 months. In this paper, we discuss techniques applied across the entire project, but we can report our results on only the southern half.