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On the basis of field observation, four principal styles of hydraulic breccia are recognised, and their characteristic features noted. In practice, hybrid styles are most commonly encountered. Numerous examples will be illustrated during the oral presentation, and the potential for definition of a formative environment is emphasised. In one example presented, it is suggested that more than 50 episodes of hydraulic fracturing can be recognised. In all cases at least sane useful conclusions can be drawn in the context of modeling for drill targets.

Jan 1, 1987

By Marion Rice

THE copper-mining district of Jerome, Ariz., is of such economic importance that the following brief notes may be of interest. The ore deposits are said by Ransome1 to be pre-Cambrian, and are contained in the pre-Cambrian schists of the region. In the vicinity of the mine (the United Verde) the schist stands nearly vertical .and strikes a little west of north. At least three varieties are distinguishable-(1) a green rock, schistose, on its margins but grading into massive material, which is evidently an altered dioritic intrusive; (2) a rough gray schist with abundant pheno-crysts of quartz, apparently an altered rhyolite; and (3) a satiny, greenish gray, very fissile sericitic schist that may be a metamorphosed sediment. The ore occurs in varieties (2) and (3), the main belt of dioritic rock (1) lying just west of the orebodies. The ore is said to follow as a rule the layers of fine sericitic schist. T. A. Rickard2 says that the ore at the United. Verde Extension mine is found at the contact of diorite and schist, that both diorite and ore are earlier than the regional metamorphism, and that the quartz porphyry (" rhyolite" of Ransome) is of post-Cambrian age.

Jan 9, 1918

By D. A. Lowrie

Environmental concerns and increasing mine development costs have created a need for early information on gold recovery from its host environment. The habit, association, and approximate abundance of minerals which contain unacceptable metallic ions which may be released during process of concentration of gold should be identified in exploration drill core. One case of a "clean" gold orebody is described to show that early petrographic studies contributed to a rapid decision to mine a small deposit by open pit and to custom mill the ore in an already restricted effluent environment. A second example describes identification of an undesirable mercury content and resulting action taken.

Jan 1, 1985

By A. N. Winchell

Petrographic studies of over 1400 rock and mineral samples, and studies of their field relations, show that there is a complete gradation between sandstone and limestone; the lime-silicate rocks were produced by recrystallization of limestone; mineralization and silicification occurred after silication and at considerably lower temperature; carbonation occurred at still lower temperatures. IN CONNECTION with law suits between mining companies at Bingham, Utah, a few years ago, the writer made petrographic studies of more than 1400 rock and mineral samples in thin sections, and also careful studies of their field relations. In petrographic studies, even when an area is studied intensively, attention is commonly centered very largely on the unusual features of special interest, so that the relative abundance of rock types (or minerals or textures) can only be determined by a study of map areas outlined largely by field methods, and cannot be based directly on microscopic work. It is very uncommon, and usually impossible, to take samples at regular short intervals along and across formations. It is precisely because such methods were used at Bingham that the work presents a rare opportunity for determining, on a microscopic basis, the relative abundance of rock types and the continuity of gradations between rock types. At the same time, a study was made of the alteration of sediments under the influence of igneous intrusions, with results that are believed to be of interest and importance.

Jan 3, 1924

By Li Shibo, C. Halls

The compositions of olivine, pyroxene and chromite from the Proterozoic ultramafic complex are analagous to those of cumulate ultramafic rocks of tholeiitic origin, suggesting that the parent magma may have been tholeiitic rather than komatiitic. The complex contains economically significant Ni-Cu sulphide mineralisation. The high sulphide/silicate ratio is best explained in terms of the segregation of sulphides from a large volume of magma, of which all but the ultramafic cumulate fraction has since been eroded. Platinum-group minerals that have been identified include sperrylite, moncheite, native platinum, froodite, merenskyite, michenerite and Pd-rich pentlandite lamellae exsolved from pyrrhotite. They are characteristically found in close association with chalcopyrite, either along the contacts between hydrosilicate and sulphide grains or in cracks within pentlandite and chalcopyrite, which may also be intergrown with galena. Crystallisation from a Cu-rich residual magmatic liquid also enriched in Pt, Pd, As, Sb, Bi, Te, Zn and Pb is postulated.

Jan 12, 1993

By R. Sweennen, A. Vervoort, J. Caers

A case study is presented of the mechanical behaviour of fractures in the Westphalian A and B siliciclastic succession of mud-, silt- and sandstones with intercalating coal layers in the Campine basin of northeast Belgium. Mining ceased in the area in 1992 and a pilot well was drilled to assess the feasibility of methane extraction by hydraulic fracturing. Work was carried out to study the influence of types of cement fill in fractures on the shear behaviour of the rocks by comparison with that of the coal seams. X-ray computerised tomography was used for visual appraisal and selection of jointed rocks before destructive shear testing was carried out. Two major type of veins were found to be present, one cemented with carbonate and the other with kaolinite or kaolinite/carbonate. Uniaxial compressive strength and shear tests showed that differentiation of the two types of veins was vital in evaluating the strength of the sandstones, as cementing of the fractures by rigid carbonate minerals can reinstate the strength of the rock masses to that of the intact material. Kaolinite was more susceptible to plastic deformation than carbonates

Jun 19, 1905

By Richard D. Harvey

Relative quantitative analyses of certain mineralogical and textural properties of carbonate rocks were made with an image analysis computer. The instrument, referred to by its manufacturer as a Quantimet; consists of a petrographic microscope, a television camera and monitor, a detector, an electronic computer, and a read-out meter. Measurements were made on polished and etched specimens, standard thin sections, and on scanning electron micrographs of carbonate rocks. Critical to the success of the analysis is the preparation of the specimen in such a way that good optical contrast is obtained between the various petrographic components. The dolomite content, the pore volume, pore boundary projection, and pore size distribution of high-purity carbonate rocks were measured by image analysis methods. The frequency and size distribution of void inclusions in dolomites were determined by image analysis of scanning electron micrographs of cleaved surfaces. Image analysis methods permit rapid and quantitative assessment of various microscopic properties. The results are of reasonable accuracy and certainly are relative quantities that may be used to characterize carbonate rock materials.

Jan 1, 1972

Preliminary petrographic investigations of eight Upper Permian coal seams of the Muja sub-basin, Collie Coalfield, reveal that the coal is high in inertinite and relatively low in vitrinite and exinite contents. The exinite content of Collie coal is relatively high when compared to other Australian coal of similar age. In addition the mineral matter content of the coal is very much lower than comparable Permian coal of Eastern Australia. The higher exinite content could be attributed to the type of Glossopteris flora, and the lower mineral matter content to the environment of deposition postulated for the Collie Coal Measures.

Jan 1, 1982

By Walter Gaby

L. C. GRATON, Cambridge, Mass.-May I ask, in connection with one point in the summary, to what extent the author regards actinolite equivalent to tourmaline as an index of high-temperature and presumably magmatic conditions of deposition of the accompanying sulphides? W. E. GARY.-I merely advanced the idea that the mineral actinolite might have some such significance. In the copper deposit at Braden in South America, the ore occurs in an andesite breccia which is cemented by a matrix of sulphides, quartz, and tourmaline. Tourmaline is a high-temperature mineral, and when we find it associated with ores, these are regarded as having come from a volcanic or deep-seated source, hence a primary hypogenetic deposit. Thus we can count on greater continuation of the ore with depth than in some other kinds of deposit, and I thought that the actinolite, being also a high-temperature mineral, might have some such bearing in the case of Mount Morgan. I did not advance this idea as a final conclusion from a study of such phenomena, but thought that it might bear some discussion in view of the fact of the peculiar occurrence of this mineral in a notable orebody. It also occurs with the copper ores at Ducktown, Tenn., and in both cases may only be due to general regional metamorphism.

Jan 12, 1916

By W. E. Gaby

INTRODUCTION SINCE the time of their discovery, the genesis of the ores at Mount Morgan, and the nature of the changes which have affected the surrounding rocks, have been the subject of investigation and speculation by geologists and mining engineers. Developments at this mine, for a long period the greatest gold producer of the world, show that with depth the orebody grades into copper, of which metal it now furnishes a large output, exceeding in value the gold. In earlier times, the purity of the gold and the first extremely heterogeneous character of the ore made it an interesting problem. Now, the probable depth of the copper enrichment, genesis, and true relations of the neighboring rocks furnish equally profitable material for investigation, and the present somewhat detailed description of these ores and rocks, from microscopic study, may prove of interest. The mine occupies a highly silicified portion of a belt of quartz-porphyry, which is believed to be the oldest rock of the region. This belt of quartz-porphyry and allied rocks runs north and south between two areas of a later intrusive granite, as shown on the geologic map,1 Fig. 1. Near the orebody the quartz-porphyry has been intruded by a dense basaltic mass called the "Old Basic." Cutting all three of these igneous masses are two sets of basaltic dikes, one running northwest-southeast, and the other, cross dikes, northeast-southwest. These dikes may be contemporaneous with, instead of later than, the ore. Their number has caused peculiar difficulties in extracting it, as the clay selvage of decomposed material affords no adhesion between dike and ore, causing great blocks to loosen and come down.

Jan 9, 1916

By G. J. Jansen

Introduction Coal petrography is the microscopic study and description of coal and other organic substances in terms of the microscopically recognizable organic constituents and of the rank of the material. Petrography studies of coal and other organic substances are useful in themselves, and have a number of practical applications. Some of these include determining coking quality of coal, estimating yields of methane from coal beds, and assisting in coal preparation. Petrography studies can also help in mine planning, in source rock studies, in combustion problems, and in synthetic fuel applications. Most recently, petrography has been found to be useful in studying sediment-hosted ore deposits. Microscopic constituents-macerals Under the microscope, coal is a heterogeneous assemblage of the coalified remains of woody matter and plant remains from the swamp or bog from which the coal was formed. The individually recognizable materials making up the organic mass are termed macerals by petrographers. They are the organic equivalent of the minerals that make up rocks. Coal petrographers can examine coal in two ways. Those interested primarily in the microscopically transparent macerals or in the study of very low rank materials, lignites for examples, like to use transmitted light microscopy where light passes through a microsection about 3 to 6 µm (0.0001 to 0.0002 in.) thick (Fig. 1). The dominant red color of the section in Fig. 1 is inherent, not a stain or produced by a filter. Distinct suggestions of textures in the reddish constituents can be seen. The red material is vitrinite and is thought to be the coalified remains of woody tissues. The yellow, lenticular substance is exinite. It is what remains of the waxy coating on a spore. Also seen are white dots of mineral matter and black opaque material that is better seen and described in polished sections. A polished microsection is prepared by grinding and polishing to a mirror polish a compact of coal and embedding resin or a coherent chunk of coal. The resulting microsection is then examined in a reflecting microscope. High magnification, 200X to 400X, and an oil immersion lens are needed to resolve fully the macerals of the organic matter so prepared. Figure 2 shows two macerals, an even gray vitrinite, unstructured and fusinite, a whitish, more or less cellular constituent. Fusinite is thought to represent more or less completely carbonized cellular material. Coal petrographers appreciate that coal is a heterogeneous material. Figure 3 is a view of another section. The generally structureless gray material is vitrinite. The bean-shaped dark constituents are exinites. The long, narrow, somewhat scalloped dark constituent is cutinite. Cutinite is thought to be derived from leaf coatings. Some coal petrographers would describe the large white, structureless mass as micrinite. Others might prefer the term macrinite. A few fragments of fusinite can also be seen. Figure 4 shows a coalified fungal remain, termed sclerotinite. It is surrounded by vitrinite and crushed fragments of fusinite all floating in a sea of embedding resin. Sometimes the microscope reveals the great heterogeneity of coal even on the microscope scale. Figure 5 shows a section with semi-fusinite, inertodetritinite, vitrinite, and micrinite. The nature of the heterogeneity may be judged by noting that the long dimension of the photomicrograph is about 70 µm (0.0027 in.). Measurement of rank Hoffmann and Jenkner (1932) discovered that measuring the reflectance of the vitrinite constituent of coal in a polished section gave a good measurement of the rank of the coal. In practice, a photomultiplier is used to mea-

Jan 9, 1987

By Walter Miller

The remarkable strides which have been made in recent years in the art of petroleum refining are not fully apparent until we attempt to compare the scientific status of the industry today with the basic conditions existing a decade or so ago. The spotlight has played so strongly on the development of cracking that many of the wonderful steps brought about in other departments have crept upon us unawares. A number of causes have contributed to this highly accelerated rate of progress. Constant effort by both companies and individuals to obtain the honors and prizes rewarding new discoveries has played its usual important part in our industry as in others. Competition has applied its continuous pressure on the refiner to reduce costs and losses and increase the proportionate yields of the higher-valued fractions. Advances in the engineering professions and growth in chemistry and allied sciences have contributed much. But there are other factors which deserve particular mention. The rapid development of the internal combustion engine, with the rigorous quality requirements and large quantity consumption of both fuel and lubricants has been a tremendous influence in adding impetus to natural progress. The teaching of petroleum principles and practices in many of our best universities and technical schools, and the calling into the industry of ever greater numbers of scientifically trained men to supplement the efforts of the practically trained operators, as well as to apply at close hand the fundamentals of science as a life work, has had and is having an incalculable influence. Important Improvements Let us consider briefly some of the most important improvements: First, distillation, which constitutes the greatest single phase of refinery operations, even with cracking excluded; that phase of distillation being handled as an individual subject in this symposium. Today we are distilling crude oil and redistilling by-products at a rate very much faster than was possible with the lesser knowledge of the art which we possessed

Jan 1, 1927

By Charles Parmelee

When Professor Silliman made his first examination of the newly-discovered Pennsylvania rock oil in 1859, he noted that different rates of heating produced different results in fractionation—longer heating produced larger percentages of light fractions. In 1862, it was found that when petroleum vapors are condensed in the still crown and dropped back into the hot liquid, the result of the distilling operation is materially modified. These early dates mark the beginning of what is called cracking petroleum and is explained as separating the component parts of the hydrocarbon molecules into more and smaller groups of the same elements. The phenomena were utilized for the next 30 years to increase the yield of burning oil. The procedure was that regularly practiced today in dry or destructive distillation. Considerable scientific study was given to the subject from 1862 to 1905, and a number of patents were obtained, but the work done was not continuous or intensive until about 1905, when the increasing demand for gasoline attracted attention of petroleum refiners to the possibilities of cracking. The first equipment built and operated essentially for cracking petroleum on a large scale was placed in successful operation in 1912. The commercial practice is, therefore, less than 15 years old. Comprehensive intense study of the controlling factors during this period has resulted in rapid increase in our knowledge, and material improvement has been made in the practice of the art. It is the purpose of this paper to outline briefly the state of our knowledge and to suggest some of the questions which are attracting attention of researchers at the present time. The major purposes for which petroleum hydrocarbons, including natural gas, are or have been cracked are: 1. To obtain products used to increase the heat value and illuminant content of artificial gas. 2. During the World War, to increase the supply of toluol. 3. To increase the amount of products capable of conversion into industrial chemicals. 4. To produce pure carbon.

Jan 1, 1927

By S. B. Sargent, V. J. Collins, Lester C. Uren

[The conclusions arrived at by authors in paper read before the Petroleum Division and the California Sections of the Americam Institute of Mining and MetallurgicaI Engineers and the Standardization Division of the American Petroleum Tnstitute, at a joint session held at Los Angeles, Cal., Jan. 21, 1926, are presented below.] From the theoretical discussion and experimental evidence presented in this paper, the following conclusions may be drawn: 1. The efficiency of the oil-well plunger pump is dependent to an important degree upon the submergence provided. 2. Ample submergence must be secured in order to provide sufficient static pressure to force the oil through the restrictions interposed in the oil path at the standing valve and at the plunger nut surrounding the garbutt rod. These restrictions should be no smaller than is structurally necessary, in order to reduce resistance to oil flow to a minimum. 3. A part of the static pressure developed below the standing valve by submerging the pump is dissipated in overcoming the inertia and in providing upward acceleration for oil left between the pump valves at the conclusion of the down-stroke of the plunger, and of oil below the standing valve in the gas anchor above the oil inlet. This loss in effective static pressure can be reduced to a minimum by dispensing with the garbutt rod and placing the working valve at the lower end of the plunger. The valves should be as near together at the conclusion of the down-stroke of the plunger as is consistent with security in avoiding striking of the lower end of the plunger on the standing-valve crown. Gas anchors should be short, and oil inlets should be as near the standing valve as is consistent with proper gas exclusion. 4. Because of the presence of gas in solution in the oil, which tends to escape from solution under the reduced pressure conditions above the standing valve, the effective length of stroke of the plunger is reduced, and the suction effect of the rising plunger is largely nullified. The influx of oil through the standing valve is therefore chiefly dependent on static pressure developed by submergence.

Jan 1, 1927

By G. S. Rice, J. A. Davis

The Péchelbronn oil field is located in the province of Alsace, in the Rhine Valley, about 30 miles north of Strasbourg. It is approximately 4 miles wide and 12 miles long, extending from the villages of Lobsann on the north to Wintershausen and Ohlungen near Haguenau on the south. (See Fig. 1.) The productive area includes about 44,000 hectares (107,680 acres). The name Péchelbronn signifies "pitch-spring" or "pitch-fountain." The first exploratory galleries were driven in from the hillside in 1735; and in 1745 the first official concession was granted by the French government and the first pit sunk to a depth of about 30 ft. Extraction by drilled wells was begun in 1879, supplementing the mining operations, and during the next 10 years 200 wells were drilled to an average depth of 172 m. (568 ft.). The bringing in of two "gusher" wells, in 1882 and 1888, respectively, was followed by the abandonment of all underground work. Underground mining, with a view to increasing the production of petroleum by recovering the oil left in the sands after drilling wells, was resumed in 1916. This mining operation started by sinking shaft No. 1 to a depth of 150 m. (495 ft.). The underground developments were pushed during 1917 and 1918 and the annual production of the Péchel-bronn field was increased to about 50,000 metric tons or 350,000 bbl. On the signing of the Versailles Treaty the province of Alsace, which had been taken by Germany as the result of the war of 1870, was returned to France, and the proprietary rights were taken over by the French Government. Concessions or leases, which embraced all the known oil-bearing territory of the field, were granted to the present operating company, Mines de Péchelbronn. This company followed both the drilling and the mining methods of the previous company.

Jan 1, 1927

By Lester C. Uren

With the depletion of our older, and relatively shallow, oilfields and the necessity for securing new production from deeper horizons, much attention is being given to the improvement of oil-well pumps in order that they may function satisfactorily under the more difficult conditions imposed by increased depth. Until recently, practically all of the world's petroleum was secured from wells less than 3000 ft. deep, whereas horizons are now being explored to depths of from 5000 to 7000 ft. in some of the more prolific fields, and it seems probable that the greater part of the future supply must come from depths in excess of 3000 ft. While much of the early production in a new field is obtained by natural-flow methods, when the stimulus of high gas pressure fails, recourse must be had to some method of pumping. The perfection of a pump capable of economically and efficiently lifting oil from depths ranging from 3000 to 7000 ft. is therefore a matter of prime importance to the oil-producing industry. This paper is offered as an estimate of the present state of development of the oil-well plunger pump and as a review of the general principles involved in its operation in deep-well pumping. A design for a new type of oil-well pump embodying several novel features, is also described. Essential Parts of Oil-well Plungeb Pump The pump commonly used in lifting oil from wells in American practice is of the simple displacement type, in which a plunger equipped with a working, or traveling, valoe is given a vertical reciprocating motion in a stationary working barrel. The latter is suspended from the surface by tubing, submerged in the well fluid, and is equipped at its lower end with a stationary standing valve; Figs. 1 and 2 illustrate two common types of oil-well pumps. The simple cup-leather packed plunger of Pig. 1 has its counterpart in the long, hollow, cylindrical, polished steel plunger of Fig. 2; otherwise the two types are identical in the form and arrangement of their essential parts. Fig. 2 shows the additional feature of a "garbutt

Jan 1, 1927

By F. Julius Fohs

As an industry approaches stabilization, greater and greater stress must be laid on its technologic progress, which becomes a prime aid in improving its condition. The oil industry is tending toward this stage and hence its engineers must be pressed into greater service to prevent stabilization and stagnation from becoming synonymous, and to supply, either by improvements in processes or by new machinery, a means of obtaining savings in raw and finished products. Thus profits can be assured warranting continued investment. It may be repeated, technology must apply a slight improvement here, a change there, or a complete renovation, to eliminate inefficiencies and make each dollar invested yield greater results. The profits of ycstcrday were made of rich strikes, of monopolized patents or processes, of control of prices and of markets. Sixty-five years of growth, of large investment, of healthful competition, and of expanding markets, have put the oil industry in the foremost rank of world industries. .Just as the railroads passed a similar period of expansion and growth, and arc being stabilized with reasonable profits, so the oil industry must take advantage of the efforts of its engineers and experts to promote its healthful growth and a better service to the people. Herein is attempted a review of recent progress in which is presented the advances in exploration, production engineering, transportation, refining and greater efficiency in uses of petroleum, with a view not only to stressing important new processes and methods, but also the problems that press for solution. This review can only touch outstanding developments of recent years, but the several Petroleum Division symposiums of our program will present details worthy of attention. Exploration Geology offers directly little new in the technique of oil-finding— major stress being laid on improvement in subsurface correlation by means of foraminifera1 studies, additions to the knowledge of which are being made, slowly but surely, and by means of mineral, and especially heavy mineral, determinations in well samples. The general application

Jan 1, 1927

By Charles H. Osmond

The rapid progress of basic changes in refining processes, which has characterized this division of the petroleum industry during the last 7 years, slowed up in 1926 and the industry as a whole devoted itself to the enormous task of adopting these changes to its methods of manufacturing. If for no other reason, the year of 1926 will stand out as the first year of widespread activities in placing refining on a true manufacturing basis. A brief survey of each of the important operations and the trend of the changes with their economic results indicate the importance of this period of transition. No attempt has been made to detail the numerous activities in each of the major operations and the writer would refer those seeking such information to the various trade papers and the paper on "Basic Changes in Refining Processes," by Walter Miller.' Distillation.—-Distillation (excluding cracking) is the major item in refining. During the past year there has been a wide application of the improvements developed in former years. Operating costs have been reduced for fuel, labor and capital items. Practically all types of distillations are now carried on as semi-continuous or continuous operations, rather than by the old batch method. Heat-saving devices, such as heat exchangers, or improved combustion chambers, have had a marked effect on the total fuel bill of the industry. The modern pipe-still has been widely used and figures available show that approximately 10 per cent. of the older shell equipment was replaced by pipe-stills during 1926. The range of usefulness of this type of equipment has been extended successfully to the most complicated types of lubricating oil manufacture. These stills afford marked economies in fuel as well as labor costs, also many advantages in older plants where space is limited, as a single pipe-still can replace several batteries of shell stills. Capital expenditure per barrel capacity is decidedly lower and offers economy in this direction. Although there has been considerable discussion of other types of distillation equipment such as the vacuum still, there has been no appreciable increase in these installations during 1926. Cracking.—-Cracking equipment increased rapidly during 1926 as evidenced by the increase in output of cracked gasoline from an average

Jan 1, 1927

By James H. Gardner

It is a striking fact in the domestic oil statistics of 1926 that with an increase in production of 13,000,000 bbl., there was nevertheless a lowering of both crude and gasoline stocks. It was the first reduction in the last eight years. In 1918, the last year of the war, stocks of crude and refined products were lowered 16,000,000 bbl., but in the following seven years stocks were increased 350,000,000 bbl., due largely to the phenomenal crop of major pools discovered in 1923. The big pools of that year coming as they did through some curious coincidence unprecedented in the oil industry, not only piled up a sudden increase of stocks at a time of large imports but they continued to add their quota to an increase of storage until 1926. With an increase in crude production, according to the Oil and Gas Journal, from 760,000,000 bbl. in 1925 to 773,000,000 bbl. in 1926, and an increase in cracking facilities of about 30 per cent., there was a draft on storage of 22,300,000 bbl. of crude and 1,000,000 bbl. of refined. Crude and refined changed from a stock surplus of 29,130,000 bbl. in 1925, to a deficit of 23,300,000 bbl. in 1926, or a differential total of 52,430,000 bbl. With a stock reserve of 541,700,000 bbl. of crude and refined oil in 1925, the amount drawn from storage was not large in percentage but it marked an important contrast with previous years. It meant a year of stability in prices and a sound condition in the industry. The indicated domestic demand increased from 695,120,000 in 1925 to 743,360,000 in 1926, (7 per cent.), 1 per cent. of which was due to California fires. Most of the gain in consumption was due to the increased demand for gasoline. There was little comparative change in the combined imports of crude and refined oil. There was an increase in exports of 17,200,000 bbl. (1.5 per cent). A petroleum balance sheet for 1926 and a comparativl sheet for the last two years, production in the United States by major districts and pools, and a list of imports are given in Tables 1 to 5, inclusive.

Jan 1, 1927

By W. T. Thom

Interest naturally attaches to fissuring and subsidence of the earth's surface, whatever the cause may be, and the induced movement and fissuring of the impervious strata overlying an oil sand is of even greater practical importance because of its bearing upon the recoverability of the portion of the oil not already extracted or extractable by ordinary production methods. It is probably true that significant ground movement induced by oil production occurs only in oil fields in relatively young formations, where the oil comes from incoherent or only slightly cemented sands and oil-soaked clays, but inasmuch as a great proportion of our "gusher" wells produce from "running" sands and yield a large part of the total oil output, it seems worth while to make an effort to inspire the collection and recording of data indicating the nature and magnitude of oil-field subsidence, both surface and subsurface. Goose Creek Field The single known instance in which the nature and magnitude of the surface subsidence incident to petroleum withdrawal has been accurately ascertained is that in the Goose Creek oil field of Texas, described by Pratt and Johnson.' There subsidence caused the submergence of a considerable area within the oil field, and, because the title to the naturally submerged lands of Texas rests in the State, it became necessary to determine whether the submergence was due to natural or artificial causes. A detailed study revealed that the sunken area conformed very closely to the limits of the productive oil field and that the cumulative depression over an eight-year period ranged from zero at the margin to 3.25 ft. at the center. This depression was accompanied by the development of local marginal surface fractures along which the subsiding ares

Jan 1, 1927