ORIGIN OF PETROLEUM

Taranaki Daily News, Volume LV, Issue 89, 31 August 1912, Page 2 (Supplement)

ORIGIN OF PETROLEUM

THE THEORIES ADVANCED. THE TARANAKi FIELD. (By R, Speight, M.Sc., F.G.S., in Lyttelton Times). The success of the oil-boring operations near New Plymouth naturally suggests a consideration of the circumstances which determine the origin and distribution in the earth's crust of one of the most convenient and efficient of present-day heat and power producers. The origin of petroleum, however, is one of these questions concerning which there is at present no finality of opinion, in spite of years of investigation and discussion. When oil was first proved to exist in commercial quantities in the American fields, the United States Government employed geological and chemical experts to examine thoroughly the evidence furnished by these fields as to its origin and mode of accumulation, and they almost without exception came to the conclusion that it was due to the natural distillation of plant l'enHlflS buried ages ago in the earth's crust. Some of these authorities considered land plants as the principal contributors, but others were impressed by the.'enormous quantity of oil yielded by some petroliferous areas, and looked to the cast accumulations of seaweeds known to occur in parts of the ocean as the only vegetable source of supply of carbonacious matter at all commensurate with the amount required. The wide regions of the North Atlantic and North Pacific, known as the Sargasso Seas, were present in their minds when they advanced this theory, and certainly the sea in these localities does contain sufficient plant material to supply carbon for an extensive oil field. Laboratory experiments clearly demonstrate that petroleum can be produced on a small scale by the distillation of vegetable matter and the inference is drawn therefrom that in Nature's own laboratory, where the heat is derived from the practically inexhaustible supply in the earth's interior, and where the pressures are so great that solid rocks are slowly bent, and crushed, analogous results would ensure from buried plant remains. Nature has a special advantage not possessed by human agencies in that she has unlimited time at her disposal, and chemical reactions impossible in a laboratory, can be carried out slowly but surely during the course of geological ages. There can be no possible doubt that she possessi-s the means for turning plants into petroleum, and it appeared to the American geologists only necessary to consider the geological arrangements of the strata favorable for the accumulation of the oil after it had been generated. The first requisite is the presence of a porous or cavernous layer which will allow space for the storage of the oil after it has formed. This is usually sand or sandstone, but limestone also, on account of its somewhat open texture, is occasionally the containing medium. Over this must lie an impervious bed, such as shale, or clay, or slate, through which oil cannot be forced by the heavy pressure to which it is subjected. The conditions are somewhat similar to those necessary for artesian wells, and frequently the oil rises in a bore as a result of mere hydrostatic pressure, as in the ca =e of artesians. In the majority of instances, however, the pressure is due to the elastic force of the gas contained in the pores of the oil-bearing rock. When a pipe is put down, the pressure forces the oil out, and it rises at times like a great fountain, playing night and day, and covering all the neighborhood; with thick, dirty-looking liquid, which fdls hollows in ground and forms miniature lakes. Such "gushers" are often uncontrollable at first, and the waste of oil is enormous; but sooner or later the flow becomes quieter, and they can be managed easily; after a time they cease flowing and only yield their oil on being pumped. The amount of oil given out while the well is in the condition of a constantly playing geyser is incredible, and were not the records fully authenticated they wouldi be treated as idle tales. One well at Baku, near the Caspian Sea, yielded ten thousand tons of oil per day, and kept this going for months, and there are cases which, according to report, exceed even this large amount. A well in Mexico and another in Roumania are each credited with putting out as much as sixteen thousand tons per day. Needless to say, the amount of oil given out from an area with numerous wells approximate to this amount of flow passes all comprehension. The well at Baku just referred to was situated on a section twenty-three acres in area, which produced in the course of a few years sufficient oil to flood it to a depth of two hundred and seventy feet. This is not an exceptional case, for areas in Texas and Galicia run this record very close indeed.

These enormous outputs naturally impressed experts who had drawn all 'their conclusions from the more moderately prolific Pennsvlvanian fields, and they began to doubt if the plant remains likely to occur in a rock stratum were equal in providing such a vast supply. Suggestions were made that the process of manufacture was continuously proceeding in the earth's crust, and that the supply was being renewed as it was drawn out. This idea was based on too short an experience of particular fields, and, in spite of the fact that some wells were known to recover slightly when given a rest, it had to be admitted that such occurrences were exceptional, and exhaustion had to he anticipated sooner or later. This is true of even such fields as Pennsylvania, Baku and, above all, Texas, which had a very short though merry life, some of its "oil pools" yielding for a time sensational returns, and finally petering out without prospect of revival. Other modes or origin had therefore to he sought, in order to account for the vast supply. It was suggested that animal remains helped to swell the stock of carbonaceous material, seeing that plants were probably unequal to the task, ami some geologists drew attention to the prevalence of fish remains and shells of moluscs in petroliferous beds. The conditions might be somewhat similar to those existing now in the estuary of the Avon and ITeathcote. In the sandy accumulations there, millions of shellfish live, and. living or dead, must impregnate their habitat with animal matter. Tf this could be covered up by clay or some impervious material, the hydro-carbons resulting from its partial decomposition would provide a substance like petroleum, and it might be stored up for the use of future generations. No doubt similar conditions occurred again and again in the geological past, and thus it is possible that animals helped to swell the amount of carbonaceous matter turned into petroleum furnished primarily by plants. Recognising the difficulties in the way of purely organic origin, another school, following the lead of the great Russian chemist, Mendeleell', attributed it to tinaction of water on carbides contained in the earth's crust, the oil being formed by a process analogous to the manufacture of acetylene from calcium carbide. No doubt this solution of the difficulty would be perfectly satisfactory if it could be definitely proved that carbides existed in the earth in large quantities. The only positive evidence of their presence is derived from the composition of meteorites, which are supposed to represent the more deep-seated parts of the earth's crust. Meteorites do occa-

nioiiiillv contain iron carbides. so that til ere is some shadow of probability in favor of tin- theory. Nevertheless, American exports who have studied carefully the conditions obtaining in their own and foreign fields, have paid little serious . attention to it. and rely almost entirely on organic agencies. However, a purely chemical origin for petroleum has not yet been disposed of, and there are circumstances which the organic theories do not explain. A most regular attendant on petroleum is common salt; in fact, salt springs may be generally taken as favorable indications of the presence of oil. in those cases, such as Cheshire, in England, ami Stassfurt, in Germany, where salt exists in enormous quantities without petroleum, it has been plausibly asserted that the conditions were not favorable to the storage of the oil, and that it had therefore escaped after being generated-' It is a surprising fact that many oilfields were known first as salt-producers. Baku yielded salt for centuries before it was known as a great oil field, The Pennsylvanian fields were discovered by well-sinkers who were looking for brine, and the discoverers were at first very much disgusted at the contamination it caused to their salt supplies. The Taranaki wells yield large quantities of intensely saline water at tne same time as they give out oil. This association has never yet been satisfactorily accounted for, although ail attempt has been made to explain it by supposing that as the plant remains were buried up at the bottom of old seas the beds became impregnated with salt. But it must be pointed out that marine beds are extremely common in the crust of the earth, while those containing abnormal quantities of salt are an exception. The association of salt with oil certainly points to a chemical relation of which we have at present no satisfactory explanation. The general distribution of oil throughout the world! has also to be considered when framing a theory to account for it. The great oil-tearing regions are generally those lying on the flanks of mountain chains, where the beds have been bent up into, say, series of parallel arches or terraces. It is found that a bore put down on the crest of an arch usually yields gas, and When put down on its flanks it gives oil and salt water; and the amount of the latter increases on approaching the lowest part of the fold. This is a characteristic feature of the Pennsylvanian, Californian, Caucasus, Galician, Roumanian and other noted petroieum-producing areas; but oil also occurs in aesturine and marine deposits where this stricture is absent, It should be noted also that oil may occur in quantity in sedimentary rocks of all ages, so that its formation is not limited to particular periods of the earth's history. NEW ZEALAND FIELDS. The three chief localities in New Zealand where petroleum is known to occur are Taranaki, near Gisborne, and at Kotuku, in the valley of the Grey river. In all these places the age of the beds is approximately the same, and would be classified by geologists as belonging to the Tertiary era. The first-named has attracted most attention up to the present, and it is perhaps the most promising of the three, so that further details may be mentioned concerning it. The province of Taranaki, with the exception of the volcanic mass of Egmont and its outliers, consists of beds of clay —locally known as "papa"—sandy clay, and sand with occasional shell beds, very gently inclined towards the south-west. At Moturoa, near New Plymouth, petroleum has been actually proved to exist by flowing wells, and emanations of gas and other favorable indications are widely distributed throughout the country stretching east and south from this locaiIty. The actual commercial value of this field can, however, be only tested by further boring in likely places. The source of this supply is a most interesting problem, but it is impossible with our limited knowledge, of the existing conditions, to account for the presence of the oil in a satisfactory manner. Sir James Hector, and after him Dr. Bell, attributed its occurrence near New Plymouth to the action of heat from the volcanic rocks of Paritutu and the Sugar Loaves on brown coal measures lying thousands of feet down. These have never been proved to exist below New ■Plymouth, but they are Worked on the Mokau River, some forty miles away to the north-east, and as they dip to the south-west it was conjectured that they might continue underground for some distance and furnish the carbonaceous matter for the Moturoa wells. When Sir James (lector advanced this theory, the study ot oil wells was in its infancy, and volcanic action was frequently credited with being an active agent in its formation, Most oilfields are, however, remarkably free from thermal manifestations, with the solitary exception of mud volcanoes, which frequently occur in districts far from true volcanoes, so that the Taranaki oil supply, if due indirectly to that cause, would be abnormal. Igneous roclcs are certainly found in some oilfields, but no definite connection has been traced between their occurrence and the supply of oil. Since we find in Taranaki, far away from Paritutu and Egmont itself, undoubted indications of petroliferous strata: it is extremely probable that the occurrence here is quite normal and due to the general conditions resembling those of other oilfields, it as certain, too, that the oil which occurs near Gisborne and at Kotuku, in beds geologically similar to those at Taranaki, cannot be assigned to the influence of volcanic action. These fields all belong to the acstuarine type, and, with the exception of Kotuku, are not marked: by the presence of well-defined rock folds or anticlines. It must not be thought, because they have not been located or are actually absent, that indications are unfavorable, since in several rich areas of other countries they are known to be absent. There are areas in New' Zealand where oil undoubtedly occurs, and their capabilities as producers can only be determined by further exploration and development. But one may be allowed to indicate other parts of the country which are possible—l do not say probable—oil producers. It must be admitted that the general conditions are not favorable to extensive, fields, and they will rather be small basins or narrow coastal plains , fringing the chief structural core of the , country. The great Taranaki-Wanganui plain is, perhaps, the greatest of these possible fields, but the major portion of ! Central Otago, the mountainous region of Canterbury, Westland. Xolson, Marlborough. the mountain axis of the North Island, the volcanic plateau, the Coromandel Peninsula are, extensive areas which hold out little or 110 promise. Possibilities do exist where aesuarine deposits contain abundant plant and animal remains, but, after all, it must be remembered that if there are no surface indications such as seepages of oil, gas emanations, salt and sulphur springs, boring on the ofi'-chaiice of striking oil is a pure speculation and not warranted as a commercial investment. So that wide areas without these indications, although acstuarine in character, do not furnish material for hope. It appears better to thoroughly test these areas where surface manifestations do indicate the presence of petroliferous beds below.