Preface In January 1996 a total of 270 conference participants gathered for 3 days in Trondheim, Norway, to focus on and to discuss the complex topic of hydrocarbon seals particularly related to deformation zones and to caprocks. All together 32 oral papers and 9 poster were presented. There was also a ple- nary discussion and informal gatherings. The conference was the first in Norway and one of the first in Europe to exclusively address this very important subject. The purposes of the conference were to present some of the most recent re- search results, to establish state-of-the-art with respect to understanding hydrocarbon seals and to dis- cuss where to go from here to find some of the keys to successful future exploration and enhanced oil and gas recovery. Out of the presented papers and posters, 71 are compiled and published in this vol- ume. These provide a good overview of and an introduction to the numerous aspects covered during the fruitful days in Trondheim. In the introductory paper by K.J. Weber, a wide-ranging and well illustrated historical overview, the development of theories and methods to predict and quantify trapping mechanisms is presented. The paper covers the period from the early days of the oil business around 1850 up to now and it contains a significant amount of previously unpublished historic material. The section on fault seals comprises a total of 01 papers ranging from case studies to in-depth studies of specific sealing mechanisms. R.J. Knipe et al. provide an introduction to fault seals and processes, describe how properties and evolution of seals within fault zones can be evaluated and sug- gest ways forward to improve fault seal risk evaluation. F.K. Lehner and W.F Pilaar document some previously unpublished observations from a study of clay smears in synsedimentary normal faults dis- played in lignite mines at Frechen in Germany. Although several earlier studies covered these beauti- ful outcrops, a new approach to the well documented observations confirm that substantial clay smears can occur if ductile shale source beds are faulted at slow displacement rates. J.R. Fulljames with co-authors present a method to systematically analyse fault seals and to quantitatively approach the prediction of two types of fault seals, namely juxtaposition seals and fault gouge seals. C. Childs et al. provide a description of the complexity of fault zones based on outcrop studies. They outline a model for the development of the complex internal structures which seem to be important for the evaluation of the sealing potential. The way forward in fault seal prediction is in the authors' opinion by refinement of current empirical and comparative methods through more detailed characterisation of sub-surface faults. A study of fracture systems and rock mechanical properties of the cap rocks of the Late Jurassic Fuglen and Hekkingen Formations in the south-western Barents Sea, Norway, is presented by R.H. Gabrielsen and O.S. Klcvjan. They propose that leakage of hydrocarbons to the surface caused by the Tertiary uplift and erosion could be related to one of four fracture groups associated with major fault zones. To predict deformation mechanisms and cementation of faults in sandstones, E. Sverdrup and K. BjCrlykke developed models by studying cores and outcrops. Timing of faulting relative to the di- agenetic processes is critical and fault characteristics and cementation can be predicted by relating fault episodes to the diagenetic history of the basin. T. Fristad et al. describe a methodology to predict fault-seal behaviour from analysis of a detailed depth model in conjunction with detailed lithological mapping. The case study concentrates on the Oseberg area in the North Viking Graben, Norway. An- other case study done by A.I. Welbon et al. documents a fault seal analysis of the Greater Heidrun area in Mid-Norway. The study assesses the control of fault seal on migration, trap integrity and fill- ing history, which serves as a basis for assessment of risk parameters for exploration prospects and their subsequent ranking. A. Makurat et al. present results from laboratory tests to study flow behav- iour associated with fractures. They conclude that five factors in addition to the fracture orientation affect the flow along and across fractures. These are uniaxial compressive strength, permeability and porosity of the intact rock, fracture roughness, shear displacement and the ratio between effective iv ecaferP stress on the fracture and the compressive strength of the intact rock. T.R. Harper and E.R. Lundin review the predictability of juxtaposition and deformation seals, describe the mechanisms of shear bands and clay smear, estimate the sealing capacity of shear bands and assess the influence of present- day stress on the sealing capacity of faults. G.M. Ingram and M.A. Naylor introduce the section on migration and top seal integrity totalling 6 papers by presenting an approach to top seal assessment. They review the physics of capillary sealing and flow barriers, discuss static versus dynamic sealing and present a technique for assessing the ef- fect of sub-seismic fault populations within the top seal. A model for gas migration is developed by D. Kettel based on history matches of gas flow by diffusion and Darcy flow through nine known gas fields sealed by salt. The model can be used to derive permeability/depth functions for rock salt that may be used in the prediction of the degree of gas fill for a prospect. N.C. Dutta describes a technique to predict pore pressure before drilling based on seismic velocity data. Examples from deep water ar- eas of the Gulf of Mexico are shown. The technique allows seal failure risk assessment for prospects. R. Olstad et al. has studied the porewater flow and petroleum migration in the SmCrbukk area, Nor- way. They found that a major sealing fault zone has affected lateral migration and has caused the de- velopment of high overpressure cells. The authors conclude that petroleum migration cannot be in- ferred from the pressure distribution because the permeability changes continuously due to diagenetic processes. The Njord Field, Norway, is an interesting case of reservoir compartmentalization as dem- onstrated by T. Lilleng and R. Gundesr Formation pressure data confirms the presence of sealing faults creating hydraulic compartments. A dynamic model of active hydrocarbon migration coupled with vertical leakage through breaching of the reservoir top seal is discussed. D.M. Hall et al. review the processes for top seal failure in the greater Ekofisk area, Norway. There is no evidence that a sig- nificant amount of leakage has occurred as a result of hydraulic breaching, tectonic breaching or cap- illary leakage. The authors argue that pressure-inhibit charge is an alternative explanation for the lim- ited extent of the hydrocarbon columns in some structures. The editors hope that this volume will make a contribution towards a better understanding of hy- drocarbon seals and that it may stimulate further research and studies. The aim would be to improve understanding and promote proper application for the numerous cases where sealing prediction might be the key for enhanced recovery or more effective exploration. We would like to thank all the con- tributors for their interest in the topic and their cooperation during the preparation of this volume. The important work done by reviewers of the papers is highly acknowledged. Thanks are given to NPF, who made this conference possible. Finally, we would like to encourage further research within this field of geology and engineering to make creative steps towards unraveling the true potential of seal evaluation and predictions to improve hydrocarbon exploration and production. Per MOller-Pedersen The Norwegian Oil Industry Association, P.O. Box 547, N-4001 Stavanger, Norway Andreas .G Koestler Geo-Recon A/S, Munkedamsveien 59, N-0270 Oslo, Norway vii List of Contributors L. BACKER Norwegian Technical Institute, P.O. Box 3930 Ullevaal Hageby, Sogns- veien ,27 N-0806 Oslo, Norway A. BEACH Alastair Beach Associates Ltd., 11 Royal Exchange Square, Glasgow, 1G A3 ,J UK K. BJORLYKKE Department of Geology, University of Oslo, P.O. Box 1047, N-0316 Oslo, Norway P.J. BROCKBANK Alastair Beach Associates Ltd., 11 Royal Exchange Square, Glasgow, 1G A3 ,J UK C. CHILDS Fault Analysis Group, Department of Earth Sciences, University of Liver- pool Liverpool L69 3BX, UK M.R. CLENNELL Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK B.A. DUFF PetroFina ,as Rue de l'industrie ,25 B-1040 Bruxelles, Belgium N.C. DUTTA BP Exploration Inc., 200 Westlake Park Boulevard, Houston, TX 77079, ASU M. ELIAS Fina Italiana, Viale Premuda ,72 1-20129, Milano, Italy A.B. FARMER Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK Q.J. FISHER Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK O. FJELD Phillips Petroleum Company Norway, P.O. Box 220, 4056 Tananger, Norway R.C.M.W. FRANSSEN Shell Oil Company, OPA, P.O. Box 4704, Houston, TX 77210-4704, ASU B. FREEMAN Badley Earth Sciences Ltd., North Beck House, North Beck Lane, Hundleby, Spilsby, Lincolnshire, PE23 5NB, UK T. FRISTAD Norsk Hydro, P.O. Box 200, N-1321 Stabekk, Norway J.R. FULLJAMES Shell International Exploration & Production BV., P.O. Box ,06 2280 AB Rijswijk, ehT Netherlands R.H. GABRIELSEN Department of Geology, University of Bergen, All~gaten ,14 N-5007 Ber- gen, Norway A. GROTH Norsk Hydro, P.O. Box 200, N-1321 Stabekk, Norway R. GUNDESO Norsk Hydro Produksjon a.s., N-5020 Bergen, Norway M. GUTIERREZ Norwegian Technical Institute, P.O. Box 3930 Ullevaal Hageby, Sogns- veien ,27 N-0806 Oslo, Norway S.R. GYTRI Fina Exploration Norway, SkOgstostraen, P.O. Box 4055, Stavanger, Nor- way D.M. HALL PetroFina ,as Rue de l'industrie ,25 B-1040 Bruxelles, Belgium iiiv List of Contributors T.R. HARPER Geosphere Ltd., Netherton Farm, Sheepwash, Beaworthy, Devon EX21 5PL, UK A. HARRISON Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK G.M. INGRAM Shell International Exploration and Production, Research & Technical Services, P.O. Box ,06 2280 AB Rijswijk, ehT Netherlands G. JONES Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK D.A. KARLSEN Department of Geology, University of Oslo, P.O. Box 1047, N-0316 Oslo, Norway D. KETTEL Kettel Consultants, Ch~tellon de Cornelle, 01640 Boyeux .tS Jgr6me, ecnarF B. KIDD Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK O.S. KLOVJAN Norsk Hydro U&P Research Centre, N-5020 Bergen, Norway R.J. KNIPE Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK S.D. KNOTT 3 Creagbat Avenue, Quarriers Village, Bridge of Wear, UK F.K. LEHNER Institute for Geodynamics, Bonn University, Nussalle ,8 D-53115 Bonn, Germany T. LILLENG Norsk Hydro Produksjon a.s., N-5020 Bergen, Norway E.R. LUNDIN Statoil Research Centre, Postuttak, 7005 Trondheim, Norway A. MAKURAT Norwegian Technical Institute, P.O. Box 3930 Ullevaal Hageby, Sogns- veien ,27 N-0806 Oslo, Norway E. MCALLISTER Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK M.A. NAYLOR Petroleum Development Oman LLC, PDO Office, Mina al Fahal, Muscat, Oman R. OLSTAD Esso Norway ,SA PO Box ,06 N-4033 Forus, Norway T. PEDERSEN Conoco Norway Inc., Randberg, PO Box 488, N-4001 Stavanger, Norway W.F. PILAAR J.F. Kennedy plantsoen ,36 2252 EV Voorschoten, ehT Netherlands J.R. PORTER Rock Deformation Research Group, Department of Earth Sciences, Uni- versity of Leeds, Leeds, LS2 9JT, UK E. SVERDRUP Saga Petroleum ,sa P.O. Box 490, N-1301 Sandvika, Norway S. THOMAS Statoil a.s., 4035 Stavanger, Norway J.L. URAI Geologie-Endogene Dynamik, RWTH Aachen, Lochnerstrasse4-20, D- 52056 Aachen, Germany J.J. WALSH Fault Analysis Group, Department of Earth Sciences, University of Liver- pool Liverpool, L69 3BX, UK J. WATTERSON Fault Analysis Group, Department of Earth Sciences, University of Liver- pool, Liverpool, L69 3BX, UK K.J. WEBER Faculty of Applied Earth Sciences, Delft University of Technology, P.O. Box 5028, 2600 AG Delft, ehT Netherlands tsiL of srotubirtnoC xi A.I. WELBON Alastair Beach Associates Ltd., 11 Royal Exchange Square, Glasgow, G1 3A ,J UK (now at Statoil a.s., Stavanger, Norway) E.A. WHITE Rock Deformation Research Group, Department of Earth Sciences, Uni, versity of Leeds, Leeds, LS2 9JT, UK G. YIELDING Badley Earth Sciences Ltd., North Beck House, North Beck Lane, Hundleby, Spilsby, Lincolnshire, PE23 5NB, UK L.J.J. ZIJERVELD 21 Oxford Street, Edinburgh EH8 9PQ, UK A historical overview of the efforts to predict and quantify hydrocarbon trapping features ni the exploration phase and ni field development planning K.J. Weber The story of the development of theories and methods related to trapping mechanisms is a fascinating succession of brilliant observations, ludi- crous misconceptions, empirical trials, and eventually the breakthrough of sound geological and physical principles. It took some 30 years from the start of the oil industry before petroleum geology began to have an impact. The period from 1885 to 1915 was very fruitful although the pendulum swung too much the other way and exploration focussed on anticlinal traps only. However, by 1915 considerable progress had been made and most trapping configurations had been recognised. Also the basic physical principles of trapping were understood in a qualitative sense. The years from 1915 to 1935 saw the development of most of the important exploration tools and also the invention of wireline logging and many petrophysical analysis methods. Consequently, the structural control on traps and the petrophysical characterisation improved significantly. By 1935, so much oilfield data had become available that several geologists in succession designed detailed classification systems for trapping configurations. After 1935, the physics of rock mechanics, flow in porous media and interfacial tension formed the subject of important studies that put petro- leum geology and engineering on a much more scientific footing. This led in turn to more quantitative analysis of trapping capacity and trap integ- rity. After 1955, there was another upsurge in technical sophistication with respect to seismic quality, wireline logging, geochemistry and labora- tory equipment. More recently, the understanding and quantification of trapping has improved steadily through sophisticated well test analysis, reservoir per- formance monitoring, borehole imaging logs and, in particular, the detailed images provided by 3D-seismic. Outcrop studies have been undertaken to learn more about fault zones. Research is by no means finished and there is still a wide variety of uncertainties and controversies concerning trapping phenomena. Early struggles, 1850-1885 and oil production on anticlinal structures in the Ye- nang Yaung field in Burma already in 1855. That In nearly all oil-producing basins, numerous seeps other types of accumulation existed also was clear exist. Early usage of petroleum goes back to biblical from studies of the Pechelbronn field along the Rhine times in the Middle East. The fact that seeps are often graben in the Alsace, where oil production from mine related to faults and fractures was noted, and it was shafts was started in 1735. even observed that seepages along the Dead Sea were In Indonesia, the oil seeps on Java were studied by activated during earthquakes. a group of mining engineers from the Delft Univer- The beginnings of petroleum production are al- sity who started to inventorise the mineral resources ways around seeps. Some petroleum was collected as in 1850. In 1865 they had located 52 seeps in the medicine, for example, near Modena (Fig. .)1 In this parts of Indonesia accessible at that time. Interest- case, the seep is along a thrust fault and nearby oil ingly, the famous naturalist Junghuhn advised against fields are not situated directly underneath the seep. drilling on Java. He argued that the strongly disturbed However, many seepages take place along crestal and faulted beds were likely to be incapable of hold- fractures of anticlinal structures. The earliest mention ing sizeable accumulations. Nevertheless, present of this fact was made by William Logan, the first di- maps show that the recorded seeps overlie nearly all rector of the new Geological Survey of Canada, in oil provinces that have since been located. 1842. He observed the coincidence of oil seeps with Drilling wells was already common practice by the anticlinal crests in the Gasp6 peninsula near the time the first oil wells were planned. Particularly the mouth of the St. Lawrence. drilling of brine wells for the production of salt was Prior to drilling for oil, some oil was produced carried out in many places. In Pennsylvania this had from hand dug pits in places like Burma and along occasionally led to the inadvertent penetration of oil the Caspian Sea. Thomas Young of the Geological accumulations, which rendered the wells useless. Se- Survey of India reported the occurrence of oil seeps neca Indians in this region used petroleum scooped nobracordyH Seals: ecnatropmI for noitarolpxE and noitcudorP edited by P. M~ller-Pedersen and A.G. Koestler. NPF Special Publication 7, pp. 1-13, Elsevier, Singapore. (cid:14)9 Norwegian Petroleum Society (NPF) 1997 2 K.J. Weber ilblrlu liI lililolllr Ilul~lf:, Ioqiit:llc lltII;illilill cI ploiifllillllr Fig. 1. Oil seep near Modena, Italy, used since medieval times to prepare medicines. from pools to impregnate torches. Thus, the first oil Elsewhere, drilling for oil started at about the same company was named Seneca Oil Company (Fig. 2). time, for instance, in Germany, at Wietze, in 1857, In 1859, Drake drilled the first well which penetrated near a well-known seep. In Rumania, after starting a productive oil accumulation at about 12 m depth. with hand dug wells, drilling started in 1882. In Baku Production amounted to 25 barrels per day, soon and Grosny, in Russia, hand dug wells were followed dropping to .51 by drilling in 1869. In Galicia, which at that time was ~ ~ ' __ 4 ~ j ~ " /de.hd:.'~ f .i. / ,. C,,.l ..... / # # # ~, e, tgtRl ; rre~<. "~ .Lith by ~'undeilioa/r Cris,~nd lqewll~.veRl~t , r,-_~--. .k ...... Fig. 2. Share of the first American oil company that undertook the first dedicated drilling campaign for oil. 1. HISTORY 3 was basic to those plans. He interested a number of people, human primates, including work on yellow fever and a variety including the staff of Harvard's Museum of Comparative Zool- of encephalitis viruses through the 1930s. ogy, the faculty of Columbia University's College of Physicians The Nobel prizewinning achievement of Landsteiner and and Surgeons, and the Columbia University/University of Popper in isolating poliovirus in Vienna (1908, 1909) provided Puerto Rico's School of Tropical Medicine (later to become a the real beginning of serious and widespread use of nonhuman component of the University of Puerto Rico School of Medi- primates in biomedical research, using rhesus monkeys, ba- cine), in the planning effort. He selected Cayo Santiago, a 15.2- boons, and chimpanzees in their work. The unique susceptibil- ha (approximately 38 acres) island 1 mile off Puerto Rico's ity of nonhuman primates to a relatively new and frightening eastern coastal town of Humacao, as the site for the colony. disease threat clearly established their special importance in With the help of a $60,000 grant from a private foundation, research. Carpenter set off for Indochina and India in 1938. He fared well The intense efforts to develop a vaccine against polio that in collecting rhesus monkeys but not gibbons. Survival of the followed was unprecedented. It spanned the next 45 years, was 47-day voyage from Calcutta as deck cargo was a testimonial international in scope, and involved a host of major investiga- to the enduring qualities of the rhesus monkeys and the care tors. However, it was a complex process that experienced seri- that they received. By early 1939, 409 rhesus monkeys, 41 gib- ous setbacks. There were some promising early findings based bons, and 3 pig-tailed macaques were released on Cayo Santi- on nonhuman primate studies using inactivated, or partially in- ago. Eventually only the rhesus monkeys remained. activated, vaccines. However, those findings led to disastrous Maintenance of the island and breeding were not without results when cases of paralytic polio occurred following vacci- problems. Local fruits and vegetables did not provide an ade- nations in human clinical trials (Horstmann, 1985). quate diet and malnutrition was overcome only by feeding fox Nevertheless, nonhuman primates played an important role chow, the early precursor to monkey chow. Wells were dug, but in helping to put polio research back on track. In 1931, throat the water was brackish. Cisterns and a system for collecting washings from patients were inoculated into monkeys and re- rainwater had to be constructed. A number of monkeys were sulted in infection (Paul and Trask, 1932). Later work showed lost through fighting or simply through being crowded out in that poliomyelitis was an enteric and not an olfactory infection. the establishment of a stable social structure. Some escaped by The discovery by Enders and co-workers (1949) that poliovirus swimming the channel to the mainland. Various diseases also could be grown in human tissue culture was a major scientific took their toll and there were few opportunities to limit spread. advance which brought them the Nobel Prize for Medicine in However, persistent efforts did finally result in eliminating 1954. It also provided a means to reduce the need for nonhuman tuberculosis. primates. However, like the promise computers initially offered Another problem was the lack of dependable financial sup- for reduction of paperwork, any reduction in the use of nonhu- port for the project. In 1944, the University of Puerto Rico man primates was soon masked by a vastly expanded dn~: ac- assumed full responsibility for support of the colony. Opera- celerated research effort which required even more animals. tions languished until 1948 when efforts to attract badly needed Salk's report of a formalin-inactivated polio vaccine grown outside support were successful. At that time, the National In- in monkey kidney cell culture paved the way for extensive and stitutes of Health (NIH) awarded the first of a number of federal successful field trials (Salk et al., 1953). Unfortunately, this awards to the University of Puerto Rico to help support Cayo dramatic achievement was clouded by uncertainty when im- Santiago. Eventually, the island operation was incorporated as properly inactivated vaccine caused a number of cases of polio a component of the University's Caribbean Primate Research in 1955 (Horstmann, 1985). Center. At about the same time, Sabin was working on the develop- Cayo Santiago has been a valuable resource through the years ment of a polio vaccine from another direction. Depending for both the production of monkeys and for biomedical and greatly on the use of monkeys and chimpanzees, he searched behavioral research. The experiences with Cayo Santiago have for attenuated strains of naturally occurring poliovirus. His also shown that outside support, primarily federal government painstaking work reportedly used 9000 monkeys and 150 chim- support, is essential for the long-term maintenance of nonhu- panzees (Sabin, 1985). The result was the development of an man primate resources. oral polio vaccine that remains in widest use today. While relatively modest in the early years, the use of mon- keys increased dramatically following Salk's discovery of an C. Virological Research and Nonhuman Primates effective vaccine. The high point of this usage was in 1957 and 1958 when about 200,000 monkeys were imported annually Technically, the modern use of nonhuman primates in bio- into the United States (Lecornu and Rowan, 1979). According medical research had its origins in Pasteur's work with rabies to Lecornu and Rowan, the greatest single use of the more than and the studies of others with smallpox and vaccinia in the late 2.1 million rhesus monkeys that were imported into the United 1800s. Kalter and Heberling (1971) and Gerone (1974) have States during the 20 years that followed Salk's discovery was provided comprehensive reviews of virological research in non- for producing and testing polio vaccine. 4 K.J. Weber he had already made several discoveries and his ideas petroleum) is covered by a protective layer, which has began to have influence (Landes, 1951). From this been bent to a so-called saddle or anticline. The saddle time onwards petroleum geology was clearly on the axis runs about parallel to the longitudinal axis of Su- matra and a section perpendicular to the axis is shown in way up in the USA, although one can say that the the adjacent figure (Fig. 4); a-b is the petroleum soaked anticlinical theory got too much attention to the det- layer, which si encountered at 021 m below the surface riment of consideration of other trapping configura- at ,c and produces the large amounts of gas and oil; .d tions. Later geologists have criticized some of era fissures in the coveting rock, in which the oil rises White's publications (White, 1885) and pointed out by the pressures of the gasses in the oil layer to the sur- serious discrepancies with the much more compli- face locally. Some of the covering layers that era more cated reality. However, his influence was what or less porous have been fed by the fissures and have in counted and we must remember the saying: "A pe- that way become secondary locations. (From the special troleum geologist's life is a never-ending struggle commemorative book A Century of ,noitarolpxE 1885- between brilliant concepts and inconvenient facts!" 1985, Shell Internationale Petroleum Maatschappij (Lament of a Shell exploration guru). B.V., The Hague.) Start of petroleum geology, 1885-1915 It is obvious from the above that the basic trapping conditions were well understood. Surface mapping of As an example of the state-of-the-art in petroleum structures also started at this time and on the section geology around 1885, it is interesting to follow the of the Telaga Said field, the surface dips measured history of exploration on the island of Sumatra in around the field are indicated (Fig. 5), This structure Indonesia. The initial story is rather similar to the is situated on the same axial trend as the Telaga To- enggal anticline at a distance of about 1 km towards Pennsylvanian situation. In 1880, a Dutch tobacco planter, A.J. Zijlker, the NW). In the USA this surface mapping became popular after the famous Spindletop discovery in the sheltering on a rainy night, noticed the long-burning torches of the natives and found that these were anticlinical structure overlying a salt dome in 1901. soaked in petroleum scooped from a nearby pool. He However, it would take 25 years before the oil reser- managed to obtain a concession from the Sultan of voir trapped against the flanks of the dome would be Langkat. To obtain capital for his venture, Zijlker found. Good fieldwork and continued drilling near seeps needed the assurance of a competent geologist that an economic volume of oil might be present. For this he resulted in numerous discoveries in the USA but also in Argentina, Venezuela, Trinidad, Mexico, Indonesia had to turn to the government mining department. and very importantly in the Middle East, in Iran. Initially, he only received help in the form of a drill- Typically, the discovery well in Iran at Masjid-i- ing engineer and the first well was spudded near an Suleiman is only a stone's throw away from a large oil-covered pool. The well encountered some oil at a depth of about 100 m, but deepening only led to wa- seep. The first book on pertroleum geology appeared in ter production. However, a second well, placed by pure luck on the crest of an anticline, resulted in sig- 1915 (Hager, 1915) and in it, several types of trap are described (Fig. 6). Production geological problems nificant oil production at about 30 m and a blow-out such as the gap in a reservoir as a result of a normal of gas, oil and water when a depth of 121 m was reached. This event, in 1885, heralded oil production in Indonesia and is also the origin of the Shell com- pany (Gerritson, 1939). A proper analysis of the find came after a govern- .e,, e,,. ...~ _,, q . ment mining engineer, R. Fennema, was put in tech- nical charge in 1886. Fennema was not only a com- petent engineer but also an accomplished geologist. He carried out geological surveys and showed the anticlinical nature of the oil accumulation at Talaga Toenggal, the site of the discovery well. In one of his letters from 1888 one can read the following: At one boring near Telaga Toenggal really magnificent Fig. .4 Sketch of a section across the Telaga-Toenggal anticline results were obtained. Here the proper petroleum- drawn by the mining engineer .R Fennema (1886). This section reservoir had been reached; geological investigations clearly shows the stratigraphy, structure and fissures which control related with the results of the wells has shown us that the hydrocarbon distribution (from A Century of ,noitarolpxE 1885- this petroleum-reservoir a( thick sand layer soaked with ,5891 Shell Internationale Petroleum Maatschappij B.V., The Hague). A historical overview of hydrocarbon trapping features 5 Beri~l ~ ~ ........ "% Z.W. ~t2 -"" z az,, u s (cid:12)9 " ....... N.O. " ' - I _ I,_ ___v "" ..-- " r-r-" .t. l" ' . .--" .... d=a,,,., , . . r, , , , , (cid:12)9 mndT ~" u, (cid:12)9 "- 2our ~-~ter , -. -- -- -- . . . . . ~, , ,'~ , x x "--; _.._ Dr Z. B/u~ Fig. .5 Section of the famous Telaga Said oil field which was the major oil producer in Sumatra at the end of the 19th century. The surface expres- sions of the structure of this overturned anticline are indicated showing that geological field work had been executed (from Gerritson, 1939). fault had been understood (Fig. 7). Correlations be- Migration can thus be upwards, downwards or - tween wells were carried out with the help of logs laterally. made by glueing cuttings to narrow wooden planks. - Sometimes the more volatile oils will escape Because the regular bailing out of the holes in cable where the strata have been eroded, unless asphal- tool drilling gives a quite accurate depth control on tic or paraffinic deposits coat the faces of the the sampling, this method results in excellent well strata, and act as seals. records. The above gives a good overview of the state-of- From Hager's book, it is worthwhile to paraphrase the-art in 1915. By that time the USA produced 65% some of the keys statements: of the world's oil, Russia was second with 16%, fol- - All oil and gas deposits, so far as known, are lowed by Mexico with 6%. Rumania and Indonesia capped or covered by practically impervious beds produced 3% each, Burma and East Galicia with 2% of shale, sandstone or limestone; also such beds and finally Japan and Iran with 1% close the list of are underlaid by impervious beds. prominent oil producing countries in the fateful year - No beds are actually impervious but are impervi- 1914. ous only in a relative sense. - Where faults or unconformities occur, water will Years of development, 1915-1935 force oil to enter the upper strata by driving it from the lower sands. This is a period in which technical development - Since water has about 50% higher surface tension was rapid. Rotary drilling led to much deeper drilling than oil, it tends to be drawn into the finest capil- compared with the now outdated cable tool drilling. laries with half again as much force as that draw- Surface mapping was insufficient to reveal the traps ing oil into the fine openings. Thus the tendency is at greater depth, and a search was made for other for water to occupy the shale and oil and gas to fill methods. In 1915, the first field use was made of the the pores of the coarser strata. torsion balance in gravimetric surveys in Czechoslo- 1 /k S A ) -- o Fig. .6 Fault trap from the early book on petroleum geology by Hager (1915).