Differential Compaction of Winnipegosis Reefs: A Seismic Perspective

Winnipegosis Formation reefs in southern Saskatchewan are typically encased in the thick, apparently incompressible salts of the Prairie Evaporite. Illustrates the usefulness of seismic data to separate postdepositional compaction features from primary features to determine the primary morphology of a reef better and to determine the relative amounts of postdepositional compaction with the different reef environments

A Seismic Analysis of Black Creek and Wabumun Salt Collapse Features, Western Canadian Sedimentary Basin

These salt remnants and their associated collapse features are often associated with structural or stratigraphic traps. As a result of the relationships between dissolution and hydrocarbon entrapment, the distribution (areal extent and thickness) of these salt remnants is of significant interest to the explorationist. Seismic information about the thickness and the extent of these salts should be used together with well log control to generate subsurface distribution maps. These maps will facilitate both the delineation of prospective structural and stratigraphic play fairways and the determination of the timing of salt dissolution. In addition, an appreciation of regional salt distribution will decrease the likelihood that remnant salts will be misinterpreted as either reefs and/or faulted structures

An Integrated Surface Seismic/Seismic Profile Case Study: Simonette Area, Alberta

On the basis of conventional surface seismic data, the 13-15-63-25W5M exploratory well was drilled into a low-relief Leduc Formation reef (Devonian Wood-bend Group) in the Simonette area, west-central Alberta, Canada. The well was expected to intersect the crest of the reef and encounter about 50-60 m of pay; unfortunately it was drilled into a flank position and abandoned. The decision to abandon the well, as opposed to whipstocking in the direction of the reef crest, was made after the acquisition and interpretive processing of both near-and far-offset (252 and 524 m, respectively) vertical seismic profile (VSP) data, and after the reanalysis of existing surface seismic data

Hydrogeophysical Investigation at Luxor, Southern Egypt

Over the past 35 years, the exposed stone foundations of the ancient Egyptian monuments at Luxor have deteriorated at an alarmingly accelerated rate. Accelerated deterioration is attributable to three principal factors: 1) excavation and exposure of foundation stone; 2) construction of the Aswan High Dam; and 3) changes in the regional groundwater regime. In an effort to better elucidate the hydrostratigraphy in the Luxor study area that extends from the River Nile to the boundaries of the Nile Valley and covers about 70 km2, a geophysical/hydrological investigation was conducted. Forty Schlumberger vertical electrical soundings (VES), two approximately 6 km long seismic refraction profiles and a total number of 39 groundwater and surface water samples were acquired. Based on the integrated interpretation of the acquired geophysical/hydrological data, the main contributions of this study were the geophysical definition of the hydrostratigraphy using resistivity (seven distinct geologic/hydrologic units were mapped), the mapping of the water table using seismic refraction and the mapping of groundwater salinity trends through geochemical sampling. The factors contributing to the rise of groundwater and its accompanying increase in salinity were identified and documented. This characterization establishes a model for evaluating various plans to lower groundwater levels and salinities in the areas of archeological monuments

A Comparison Study Using Particle Swarm Optimization Inversion Algorithm For Gravity Anomaly Interpretation Due To A 2D Vertical Fault Structure

A new approach to the inversion of gravity data utilizing the Particle Swarm Optimization (PSO) algorithm is used to model 2D vertical faults. The PSO algorithm is stochastic in nature; its development was motivated by the communal in-flight performance of birds looking for food. The birds are represented by particles (or models). Individual particles have a location and a velocity vector. The location vectors represent the parameter value. PSO is adjusted with random particles (models) and searches for targets by updating generations. Herein, the PSO algorithm is applied to three synthetic data sets (residual only with and without noise, residual plus regional, residual plus anomaly generated by a buried cylinder structure) and two field gravity data sets acquired across known faults in Egypt. Assessment of the synthetic data demonstrates that the PSO algorithm generates superior results if a first horizontal gradient (FHG) filter is applied first. The robustness of the PSO inversion algorithm is demonstrated for both synthetic and field gravity data

Spectral Analysis of Surface Waves to Detect Subsurface Voids

Systems and methods for detecting a subsurface cavity. A source applies a force to ground under inspection and a plurality of sensors coupled to the ground detect resulting surface waves. A processor is configured to extract phase and frequency components of the acquired seismic data, identify a phase shift in surface waves in the ground under inspection based on the extracted phase and frequency components, and determine one or more physical characteristics of a subsurface cavity based on the identified phase shif

An Assessment of Concrete over Asphalt Pavement using Both the Ultrasonic Surface Wave and Impact Echo Techniques

A portable seismic property analyzer (PSPA) was used to simultaneously acquire both ultrasonic surface wave (PSPA-USW) and impact-echo (PSPA-IE) data at predetermined locations along a section of multi-layered pavement. The pavement consisted of a basal concrete layer (~220 mm), an intervening layer of hot-mix asphalt (~60 mm), and a concrete overlay (~220 mm). The section of multi-layered pavement was cored at multiple PSPA test locations for verification purposes. The conditions of the extracted cores were assessed visually, and the static elastic modulus, as well as the compressional wave velocity of each concrete overlay core, were measured in the laboratory. Results from this study demonstrated that the PSPA-USW tool can be used to evaluate the conditions of concrete overlay, the interlayer (hot-mix asphalt), and their bonding conditions from a qualitative perspective. A good correlation between the static and laboratory dynamic modulus from core specimens of concrete overlay were confirmed based on laboratory testing results. However, the field dynamic modulus of core specimens, based on PSPA-USW tests, was lower than both the static modulus and laboratory dynamic modulus. Furthermore, the PSPAIE tool was not able to estimate the depth of the entire pavement and to various pavement layer interfaces due to the interference of flexural mode vibration. Fortunately, the difference between intact and deteriorated pavement can be qualitatively identified from the amplitude spectrum. More core specimens are needed for further studies in order to verify the performance of both PSPAUSW and PSPA-IE techniques for multi-layered pavement condition assessment

Low- and High-Relief Leduc Formation Reefs: A Seismic Analysis

Leduc reefs have grown to widely varying heights and aereal extents along the Rimbey-Meadowbrook trend of central Alberta, resulting in significantly different seismic signatures. Three examples considered in this paper include two high-relief or full reefs from the Leduc-Woodbend field, an atoll and a pinnacle, each around 200 m in height but differing greatly in areal extent, about 100 km2 for the atoll and 1 km2 for the pinnacle. The third example, a low-relief or basalt reef from the Morinville field, is about 100 m high and 1 km2 in areal extent. The Leduc-Woodbend and Morinville reefs exhibit quite different seismic signatures. For example, 25 ms of time-structural drape along the top of the Devonian is observed across the Leduc-Woodbend atoll but only 15 ms across the Morinville reef. There is 30 ms of pullup at the Beaverhill Lake level beneath the Leduc- Woodbend atoll, 15 ms for the Morinville reef. Also, it is very difficult to differentiate the Leduc reflection from the Duvernay reflection, with which it merges, on the Morinville (basal-reef) section. In contrast, the Leduc reflection can be correlated readily on the Leduc-Woodbend atoll section; and reflections from the offreef shales (Duvernay and Ireton formations) terminate abruptly against the reef flank. In addition, the amplitude of the underlying Cooking Lake platform reflection varies laterally, depending on the velocity of the overlying formation (Duvernay shale or Leduc reef) and, to a lesser extent, the thickness of the overlying reef. This variation is not as useful in distinguishing between low-relief and high- relief reefs as it is in indicating the presence or absence of reef

Natural Recession of the Eastern Margin of the Leofnard Salt in Western Canada

The Lloydminster area (T35-65, R15W3M-10W4M) of east-central Alberta and west-central Saskatchewan, Canada, is dissected by the north-northwest trending updip active dissolution margin, of the Devonian Leofnard Member rock salt. West of this margin, up to 150 m of rock salt is preserved; updip and to the east, the salt has mostly been leached from the rock record. The margin is up to 40 km wide and characterized by extreme local variations in net salt thickness. The dissolution of the Leofnard rock salt in the Lloydminster area has resulted in the entrapment of significant hydrocarbon accumulation. Stratigraphic traps, for example, have formed where reservoir facies were either preferentially deposited or preserved in salt-dissolution lows. Structural traps, in contrast, have formed where reservoir facies are draped across residual salt or collapse features. It has been estimated that three trillion barrels of oil (mostly of high viscosity and unrecoverable) are entrapped along the eastern dissolution margin of the Leofnard rock salt in western Canada. A record of the westward progression of the dissolutional edge of the Leofnard salt is locked in the stratigraphic column. This progression is recorded as localized interval thickening in areas where dissolution and deposition were contemporaneous. The horizontal positioning of these interval thicks as a function of their geologic age provides a time record for the positioning of the salt edge. To further explain the process of salt dissolution in the Lloydminster area, we present a suite of contour maps, geologic cross-sections, and seismic profiles. These data depict the present-day distribution of the Leofnard salt in the Lloydminster study area. They support the theses that: (1) the dissolution margin of the Leofnard rock salt originated along the Elk Point outcrop to the east of the study area during the pre-Cretaceous; and (2) the margin receded into the northeastern part of the Lloydminster study area during earliest Cretaceous or pre-Cretaceous time and migrated progressively thereafter into its current position. From the perspective of the explorationist, such information is important because it identifies prospective play areas with high potential for the formation of salt-related stratigraphic traps and/or structural traps

Salt Dissolution and Surface Subsidence in Central Kansas: A Seismic Investigation of the Anthropogenic and Natural Origin Models

Gradual subsidence in the Punkin Center study area, northeast Reno County, Kansas, has resulted in ponding of surface waters, abandonment of at least one oil well, and damage to county roads. Because the Punkin Center area is within the Burrton oil field and is underlain by the Hutchinson Salt Member, surface subsidence historically has been attributed to salt dissolution of anthropogenic origin. Subsidence that occurred significant distances from any known well sites has been attributed to unrecorded abandoned wells or complex asymmetric patterns of salt dissolution that originated at a drillhole. To ascertain the validity of the widely accepted anthropogenic salt-dissolution model, a 4-km seismic reflection profile was acquired along an east-west-oriented county road adjacent to an abandoned oil well. The expectation was that the residual Hutchinson Salt Member would be anomalously thin where maximum recorded surface subsidence occurred and thicker elsewhere. Contrary to expectations, the residual Hutchinson Salt Member is relatively thick (20-30 m) below areas of significant recent surface subsidence. There is no evidence of recent surface subsidence at those locations along the seismic profile where the rock salt has been totally leached. At these sites dissolution and subsidence is interpreted to predate European settlement in Kansas and to be of natural origin. The presence of dissolution and subsidence features related to natural processes has implications for developing an understanding of the potentially complex relationship between anthropogenic activities and pre-existing geologic conditions. Sinkhole development is apparently a natural and expected process along an irregular salt dissolution front. The geometry of this front may be influenced strongly by geologic factors (e.g., fracture patterns and facies distribution). The results are that not all modern sinkhole development has a clear-cut anthropogenic cause, and the potential for adverse impact resulting from anthropogenic activities will be influenced strongly by pre-existing geologic conditions. Efficient management decisions along the dissolution front related to well location and well-site practices should take into account natural processes that previously have and will continue to have an effect on salt dissolution and surface subsidence