THE QUEST FOR OIL

Taranaki Daily News, 26 June 1928, Page 2

THE QUEST FOR OIL

GEOPHYSICAL METHODS MANNER OF APPLICATION. DEVELOPMENT IN LAST DECADE. In view of the optimistic reports, based upon the results of geophysical surveys, made about the possibilities of tapping extensive petroleum deposits in Taranaki, it is of interest briefly to examine these newer methode of locating “liquid wealth”, (says the Auckland Herald). While admitting the efficiency and certainty, up to a certain point, of the methods employed by the Elbof "geophysicists in their work for Coal Oil (Ne# Zealand), Ltd., experienced geologists have issued a warning against placing too much faith in over-optimistic statements. The drill, they say, is the final arbiter, and if it were to prove forecasts to be erroneous future legitimate efforts to find oil would be handicapped. At the same time, there is real confidence in ultimate success and a hope that shareholders will have the courage to raise sufficient capital to drill the more promising Taranaki areas. TECHNICAL FEATURES OF SURVEY The technical features of geophysical surveying have been comprehensively dealt with in a report of a sub-com-mittee of the British Committee of Civil Research, covering a scheme for the geophysical survey of portions of Australia at a cost which will probably exceed £27,000, toward which the Empire Marketing Fund will contribute a sum not to exceed £16,01)0. Under tho caption “The Various ■Methods of Geophysical Surveying,” the report of the committee states the methods to be considered are those dependent on properties of the minerals or structures to be surveyed, and which can be detected without direct access. These properties are gravity, electrical conductivity, magnetic attraction and elasticity’. The employment of geophysical methods is comparatively recent. Except for the use of magnetic measurements, of which, particularly in Sweden, advantage was already taken by the middle of the 19th century in searching for deposits of iron ore, these methods were practically unknown until within the last 25 years. Their development has taken place mainly in the last decade. Geophysical methods can be used both directly and indirectly—directly to ascertain the presence, location and bulk of bodies through measurement of the distant effects of certain qualities inherent in them; and indirectly where such effects are not produced actually by the object sought for, but by other elements known to be commonly associated with, and therefore indicating the presence of, the object sought. Prospecting for petroleum provides the most notable instances of indirect applications. INDIRECT LOCATION OF OIL. "Oil itself is only in the most exceptional circumstances directly indicated by the use of these methods,” states the report, "Indirectly, on the other hand, various geophysical methods can be used to locate petroleum deposits by determining the location and exact limits and profile of the salt-domes, to the flanks of which experience shows the deposits to be tied.” The gravimetric method is then described. It consists of ascertaining from the surface of the ground differences in the density of the underlying rock through measuring the force of gravity by a torsion balance. This is a balance consisting of a freely suspended beam which comes to rest in a definite position under the double influence of gravitational forces and of the .twisting of the suspending wire. Set up in a number of positions, it indicates the approximate boundaries, thickness, and depth of the deposits sought. Examples of the success of the method in Britain, Europe and Texas in mining and oil locations, are given. Electrical methods depend on the electrical conductivity of ore bodies as compared with the rocks containing them, ajid the interpretation of results depends largely upon the experience of the man doing the work. The Elbof Company has successfully employed the system in Germany, and it has been useful in Canada, the United States, and other countries. MAGNETIC AND SEISMIC METHODS. Magnetic methods, more recently made applicable to the survey of salt deposits, are now being further used, in combination with the gravimetric method, by leading oil companies. They involve the use of the magnetic compass. Then there are the seismic and sonic sounding methods. Seismic methode take advantage of the greater or lesser elasticity of the materials of the earth’s crust. A dynamite cartridge exploded on the surface of the ground causes elastic waves to emanate in all directions, and by means of seismographs the times taken for the waves to travel from the blasting-point are recorded. During the last few years the method has been successfully employed in Mexico and the United States, notably on the Gulf Coast oilfields of Texas, to locate structures of a pronounced character like salt domes. “There seems little doubt they will prove of considerable application to the discovery of underground oil structures,” the report says. In a survey for oil the first line of attack by geophysicists is the gravimetric method, supplemented, often, by some of the others. “We are satisfied regarding the value of geophysical methods of surveying,” the report continues. "We believe an extensive trial of the principal methods, accompanied by a full publication -of the scientific information and experience so acquired, would .be of great interest and value to the Empire.” It -considers hopefully the proposals of the Development and Migration Commission of Australia as a suitable opportunity for testing these methods, but adds that such a survey cannot be considered as more than a hopeful experi-