Experimental Seismic Survey Research Articles

A large-scale experiment finds no consistent evidence of change in mortality or commercial productivity in silverlip pearl oysters (Pinctada maxima) exposed to a seismic source survey

High-intensity, impulsive sounds are used to locate oil and gas reserves during seismic exploration of the seafloor. The impacts of this noise pollution on the health and mortality of marine invertebrates are not well known, including the silverlip pearl oyster (Pinctada maxima), which comprises one of the world's last remaining significant wildstock pearl oyster fisheries, in northwestern Australia. We exposed ≈11,000 P. maxima to a four-day experimental seismic survey, plus one vessel-control day. After exposure, survival rates were monitored throughout a full two-year production cycle, and the number and quality of pearls produced at harvest were assessed. Oysters from two groups, on one sampling day, exhibited reduced survival and pearl productivity compared to controls, but 14 other groups receiving similar or higher exposure levels did not. We therefore found no conclusive evidence of an impact of the seismic source survey on oyster mortality or pearl production.

North Sea soundscapes from a fish perspective: Directional patterns in particle motion and masking potential from anthropogenic noise.

The aquatic world of animals is an acoustic world as sound is the most prominent sensory capacity to extract information about the environment for many aquatic species. Fish can hear particle motion, and a swim bladder potentially adds the additional capacity to sense sound pressure. Combining these capacities allows them to sense direction, distance, spectral content, and detailed temporal patterns. Both sound pressure and particle motion were recorded in a shallow part of the North Sea before and during exposure to a full-scale airgun array from an experimental seismic survey. Distinct amplitude fluctuations and directional patterns in the ambient noise were found to be fluctuating in phase with the tidal cycles and coming from distinct directions. It was speculated that the patterns may be determined by distant sources associated with large rivers and nearby beaches. Sounds of the experimental seismic survey were above the ambient conditions for particle acceleration up to 10 km from the source, at least as detectable for the measurement device, and up to 31 km for the sound pressure. These results and discussion provide a fresh perspective on the auditory world of fishes and a shift in the understanding about potential ranges over which they may have access to biologically relevant cues and be masked by anthropogenic noise.

An echosounder view on the potential effects of impulsive noise pollution on pelagic fish around windfarms in the North Sea

Anthropogenic noise in the oceans is disturbing marine life. Among other groups, pelagic fish are likely to be affected by sound from human activities, but so far have received relatively little attention. Offshore wind farms have become numerous and will become even more abundant in the next decades. Wind farms can be interesting to pelagic fish due to food abundance or fisheries restrictions. At the same time, construction of wind farms involves high levels of anthropogenic noise, likely disturbing and/or deterring pelagic fish. Here, we investigated whether bottom-moored echosounders are a suitable tool for studying the effects of impulsive – intermittent, high-intensity – anthropogenic noise on pelagic fish around wind farms and we explored the possible nature of their responses. Three different wind farms along the Dutch and Belgian coast were examined, one with exposure to the passing by of an experimental seismic survey with a full-scale airgun array, one with pile driving activity in an adjacent wind farm construction site and one control site without exposure. Two bottom-moored echosounders were placed in each wind farm and recorded fish presence and behaviour before, during and after the exposures. The echosounders were successful in detecting variation in the number of fish schools and their behaviour. During the seismic survey exposure there were significantly fewer, but more cohesive, schools than before, whereas during pile driving fish swam shallower with more cohesive schools. However, the types and magnitudes of response patterns were also observed at the control site with no impulsive sound exposure. We therefore stress the need for thorough replication beyond single case studies, before we can conclude that impulsive sounds, from either seismic surveys or pile driving, are a disturbing factor for pelagic fish in otherwise attractive habitat around wind farms.

A large-scale experiment finds no evidence that a seismic survey impacts a demersal fish fauna

Seismic surveys are used to locate oil and gas reserves below the seabed and can be a major source of noise in marine environments. Their effects on commercial fisheries are a subject of debate, with experimental studies often producing results that are difficult to interpret. We overcame these issues in a large-scale experiment that quantified the impacts of exposure to a commercial seismic source on an assemblage of tropical demersal fishes targeted by commercial fisheries on the North West Shelf of Western Australia. We show that there were no short-term (days) or long-term (months) effects of exposure on the composition, abundance, size structure, behavior, or movement of this fauna. These multiple lines of evidence suggest that seismic surveys have little impact on demersal fishes in this environment.

The potential for locating hydrocarbon traps in the Rotliegend formation, based on results of experimental seismic surveys

Within the framework of the Operational Programme Innovative Economy 2007-2013, studies were carried out for improving the effectiveness of using seismic surveys in the prospecting and exploration of gas fields in the Rotliegend formation. The completed experimental seismic surveys provided new, very interesting data on the geological structure of the deeper part of the Rotliegend basin (>4000 m), which is practically very important for prospecting for new gas fields. The interesting results were obtained along virtually the entire cross-section, particularly in two segments: the southern segment – in front of and within the Czlopa-Szamotuly tectonic zone (the Szczecin-Gorzow segment) and the northern segment – in the area of the Zabartowo-1 and Zabartowo-2 wells (the Pomeranian segment). In the northern segment, for the first time in the history of studies of the Lower Permian Basin, it was possible to record reflections from the horizon of the aeolian sandstones occurring within the playa silty-clayey deposits (543 m below the top of the Rotliegend formation), which represents a significant achievement from the point of view of prospecting for hydrocarbon resources. This horizon, characterized by favourable reservoir properties, pinches out northward. It is a very important piece of information because systems of lithologic traps may be related to such pinchouts. In the central part of the Obrzycko-Zabartowo profile, in the Chodziez area, a vast structural elevation occurs, approximately 10–12 km wide and with the amplitude of 250–300 m, which may be a potential large structural or structural and lithologic trap. These newly discovered zones of occurrence of gas traps in the seismic profiles made by the AGH University of Science and Technology within the framework of the research project, will be implemented in a detailed seismic exploration during the exploratory work of Polish Oil and Gas Company (PGNiG SA).

Determination and sensitivity analysis of the seismic velocity of a shallow layer from refraction traveltimes measures

In this paper, we are interested in determining the seismic velocity of a shallow under-ground layer from refraction traveltimes measures. We present a study case taken from an experimental seismic survey. The study case is a wide-angle seismic inversion using experimental traveltimes measures and based on ray tracing technique and genetic algorithms. The hypothesis on the velocity distribution, coming from the seismic experiment, makes the computation of some seismic rays expensive in time. We propose to reduce the computations time by introducing a formulation of the inverse problem that avoids such costly rays, hence the inversion becomes feasible. Also we present a sensitivity analysis based on a singular value decomposition of the jacobian of the traveltimes with respect to velocity. We give the relationship between the traveltimes measure errors and the velocity estimation error. We discuss the advantages of this method over the classical one based on the resolution matrix.

Ondas convertidas aplicadas para la detección de fracturas en la zona del área del Catatumbo, Colombia

The multicomponent (3C) seismic method is an emerging technology, which allows recording the complete wave field, including converted (PS) waves. Methods to obtain information about fractured rocks have been developed from these data since anisotropy, an effect of parallel fracture trains, generates birefringence of PS waves. We present here an application of this technology to data from an experimental seismic survey from a setting of NE Colombia. The geological characteristics of this setting were challenging for the current processing methods. A 3C seismic line following geological strike and another one following dip were processed. Coherent noise statics correction and velocity analysis required an iterative approach. The presence of polar anisotropy related to stratification, was taken into account for stacking. This approach greatly improved the resulting section, verifying its suitability. Three seismic sections, each one corresponding to a component, were obtained for the strike line. An azimuthal anisotropy analysis was carried out on them. Significant results were found, that might imply the presence of natural fracturing directions. This result requires to be tested with complementary geological information. About the dip line processing, the method applied appear unsatisfactory. There were identified shortcomings of processing related to dipping strata and complex structures, which became worse by the noisy data. More advanced processing methods would be required in this case.

Biochemical Responses of European Sea Bass (Dicentrarchus labrax L.) to the Stress Induced by Off Shore Experimental Seismic Prospecting

The paper reports the results of an experimental seismic survey in the open sea by an air gun, carried out to evaluate the effects of air gun acoustic waves on marine animals. Air gun blast exposition was found to have a marked influence on confined Dicentrarchus labrax. Our data, in fact, demonstrated a biochemical response to acoustic stress induced by air gun blasts. Variations of cortisol, glucose, lactate, AMP, ADP, ATP and cAMP in different tissues of D. labrax, indicate that fish have a typical primary and secondary stress response after air gun detonations. Radiography indicates that air gun blasts do not induce any macroscopic effect on skeletal apparatus. The variations of biochemical parameters returned within physiological values within 72 h indicating a rapid recovery of homeostasis after acoustic stress and no mortality was observed.

THE PETROLEUM POTENTIAL OF THE EASTERN ARROWIE BASIN AND FROME EMBAYMENT

The eastern Arrowie Basin is a descriptive term for the present-day structurally defined Cambro- Ordovician basin approximately coinciding with the Curnamona Shelf depositional feature which formed on the eastern stable flank of the Adelaide Trough. Remnants of the Arrowie depositional basin are preserved in outcrops of the Flinders Ranges and in the subsurface to the east and west of the ranges. The eastern subsurface sub-basin occupies the area around Lake Frome in South Australia and across the border in New South Wales. Much of the eastern sub-basin is overlain by the Jurassic and Cretaceous rocks of the Frome Embayment of the Eromanga Basin.The area has been explored sporadically over at least the past 20 years but no deep wells have been drilled to test exploration targets. This assessment of the prospectivity of the basin is assisted by shallow stratigraphic and mineral drilling, by extrapolation from outcrop, and by regional geophysics.In the deepest part of the eastern sub-basin the total thickness of the Cambro-Ordovician sediments is expected to exceed 2500 m. Potential reservoirs can be expected within both carbonate and sandstone rocks. Good secondary porosity exists in sandstones of the Middle to Late Cambrian Lake Frome Group and good porosity development is predicted within possible ooid shoal deposits.Source material has been demonstrated in outcrop samples with Total Organic Carbon measured at up to 0.35 per cent. It is suggested that petroleum generation probably occurred in Cambrian sediments in the Adelaide Trough (now the area of the Flinders Ranges) and the petroleum migrated east and west to the stable shelf areas. Sufficient depth of burial may also have been attained on the Curnamona Shelf to allow local generation.In the past, the very poor quality of available seismic data has frustrated the mapping of the subsurface in sufficient detail to justify exploration drilling. Recent experimental seismic surveys, however, have produced data of a much better quality. Potential exists for anticlinal, fault and unconformity traps. There is also some potential for stratigraphic traps such as ooid shoal deposits. At this stage an exploration programme to evaluate the potential of this area is being carried out by the licence holders.

Australia, Geophysical Exploration, and Great Artesian Basin: ABSTRACT

Petroleum exploration began in the Great Artesian basin of Australia in 1900 with the recovery of a strong flow of gas from a depth of approximately 3,500 feet in a hole drilled on Hospital Hill at Roma, Queensland, in an attempt to strengthen the town's artesian water supply. Drilling, both sporadic and intense (including 20 holes in the boom exploration year of 1929), has continued in the area through the years. The lack of significant surface outcrops in much of the basin, and an unconformity at the base of the Mesozoic cover, made structural analysis by means of surface studies difficult, if not impossible. At the request of the exploration companies still operating in the Roma area in 1947, the Bureau of Mineral Resources carried out magnetic and gravity surveys and two experimental seismic surveys from 1947 to 1953. Electric logging of test wells was begun in 1954 but, by the mid-1950s, few of the basin's structural or stratigraphic problems had been solved. Encouraged by liberal concession terms and government subsidies, serious geophysical exploration was started by the Australian-owned Associated Group in 1959. Major world oil firms joined the search in 1960 and the exploration techniques developed in other parts of the world were brought to bear on the problems of the basin. Geophysical data, augmented by information from many test wells, have made it possible to strip the Mesozoic mantle from the basin and have disclosed not a single large basin but many basins. The commercial return from a large exploration investment has been disappointing to date but the chapter is not yet complete. Gas has been found in abundance, yet the Moonie field remains the only oil field of consequence. Moonie and Alton oil are reaching the market but gas still awaits a gathering network of pipelines. The structural and stratigraphic framework of this great basin is still being drawn from a decelerated program of geophysical exploration. Somewhere within the assemblage of data probably lies the key to discovery of a major oil field which, when found, will provide the impetus for completion of the geophysical-geological mapping job. End_of_Article - Last_Page 483------------