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9th International Meeting on Organic Geochemistry
9th International Meeting on Organic Geochemistry University of Newcastle upon Tyne, 17th-20th September, 1979 Opening address by Sir Peter Kent, FRS
Ladies and Gentlemen I have been asked to address you partly because of my long involvement with the petroleum industry, and my awareness of problems both solved and unsolved. I am of course a geologist and to me geochemistry is essentially a tool: a tool which has, of course, increased in importance enormously over the period of my career. Forty or fifty years ago there was already an interest in the implication of varying coal rank, and petroleum geologists began to apply this in the 1930s to problems of looking for oil. It was recognised, for example, that it was no good looking for liquid hydrocarbons, and possibly not even gaseous ones, in basins where anthracite occurs. This was perhaps the thin end of the wedge of a development which has gone so very far in more recent years. When I was a student, stratigraphy, paleontology and petrology effectively constituted the whole of earth sciences. Then geophysics came, as an equal partner with the others, and now we see geochemistry as a science of equivalent status. Thus, in the Research Council with which I have been involved, geochemical research now attracts quite a considerable share of research grants, and very properly so. Geochemists deal with a wide range of problems, and a fundamental one which is now making real headway is the correlation of source rock and crude oils. (My comments, of course, are made as a non-specialist geologist, and maybe at lunch time you will say, we have already solved specific problems. If you can put me right I am very happy to be instructed.) But knowing where the crude oil started from, and what its migration history has been, is a very important aspect in the course of locating economic bodies of crude oil and indeed of gas too. One aspect of the geochemical problems that we don't hear very much about, although I see that there is a paper on it at this conference, is the function of limestones as source rocks. This source can be of very high importance - - for example in the Middle East it is a matter of great difficulty to find any organic rich shale which could have given rise to the enormous oil accumulations of Saudi Arabia. In other places the results are much less spectacular. Nevertheless limestones have had quite a complicated history: initial deposition in either an oxidising or reducing state, then diagenesis of various kinds, finally oxidation when they are brought to the surface. One therefore does have to take seriously the potential of large bodies of limestones as well as argillaceous source rocks in this field. In the last few years, arising from the work of the Deep Sea Drilling Project (DSDP), much interest has been concentrated on the black shales which derive from a Cretaceous oceanic anoxic event, and which have been penetrated by drilling on the ocean floor. We need to know how important as a source was this occurrence. H o w unique was it? Lower Cretaceous oil accummulations are of major importance in a number of parts of the world; the Athabasca tar sands and the Prudhoe Bay oil-field are a m o n g the larger scale ones, but there are many others. The Arabian limestone reservoirs of late Jurassic and basal Cretaceous age, which I have already referred to, as perhaps providing their own source rocks: are these related to the same anoxic event of the oceans, or another one? Although these occurrences relate to the continental shelves and don't have direct access, as far as we know, to oceanic sources, their source potential may have been assisted by general stagnation. But when one comes to other regions, Jurassic sources are ranked as of greater importance. The AOG - A.
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Opening Address
Kimmeridge, Lower Oxfordian and the Lias all have source rock potential, they occur on shelves and to a varying extent are interbedded with shallow water sediment. In the North Sea it is now generally accepted, that the Kimmeridge shale is the critical source. One wonders why the Lower Cretaceous shales appear to be relatively barren, why the Lower Cretaceous, which did so well in other parts of the world, has apparently made no contribution. In other areas in Western Europe, the Netherlands, G e r m a n y , Dorset (Wytch Farm) for example, deeper source rocks must be available, probably Lias, Callovian or Oxfordian shales. One of the problems of which I am sure you are all conscious in this respect, is the attempt to analyse the extent to which multiple sources are responsible in particular reservoirs. Kimmeridge shale may be the dominant source in the North Sea, but was it the only one? If not, then of course one has to solve the problem of the remarkable uniformity of North Sea oil in whatever reservoir it is found. There are alternative sources in the North Sea itself. The Devonian, for example, is deeply buried and on land has an organic content. In the North Sea there are marine limestones; did they produce any hydrocarbons? Another aspect of North Sea exploration, on which geochemists will throw light is relative uplift, and subsidence. The basins seem to have gone down continuously, the blocks on which most of the oilfields are found are fault blocks which, for the most part, have probably also subsided fairly continuously, although less rapidly than the basins. (The fact they are relatively up-thrown does not necessarily mean that they have moved upwards.) It is a matter for determination as to whether a relatively buoyant block has failed to subside equally rapidly or whether it has been uplifted. In this kind of problem it has to be remembered that samples of material from those blocks, the normally available material in oilfieid areas, is not also typical for the surrounding basins. And the blocks themselves may have different thermal histories; in some cases they are known to mask shallow basement and probably have higher temperature histories. In addition to these basic qualifications, the situation is further complicated because in important areas of the Northwest European basins - - the Dutch Graben is the classic case, with the Sole Pit Trough, the Irish Sea and others - - there has been inversion of areas originally basinal over long periods which have later become relatively buoyant. This again is a subject on which geochemistry will be able to throw a fair bit of light - - from the thermal history of their hydrocarbons, and of shales which have been deeply buried and brought up again by thousands of feet. No doubt this is the sort of subject which will be illuminated in the course of this conference. I would like to refer to another branch of organic geochemistry entirely - - one with which I do not think you will be dealing with here. That is the origin and history oforgano-metallic compounds. There are remarkable cases in the modern seas, as you no doubt know, of organisms accumulating quite abnormal percentages of particular rare elements. The classic case is that of the Tunicates, which concentrate vanadium. Fish accumulate lead in their bones. A number of mollusca put away pollutants such as zinc, lead, and heavy metals in fatty compounds in their bodies. And when one looks at the geological record one finds "hot layers", as they are called in the North Sea, which are high in radioactive elements, black shales which are high in potassium, and also peculiar shales as in the early Lower Lias here in England, in Lincolnshire, which are high in molybdenum. Why does this happen? It must presumably be a function of organic action. In the long run we may need to know by what mechanisms the various organisms produced abnormal concentrations of metals. We may then be able to apply the reactions they are using to extract economic amounts of metals from sea water - - for of course the oceans contain all the metals that mankind could conceivably use as long as man lasts. It does seem that you, as geochemists, should keep in mind these problems because with your studies of the organic-rich sediments there is a reasonable chance that you will be able to throw light on these problems, far out as they are at present, perhaps in the not too distant future. I have touched on some of the problems that directly interest me, although they constitute only a fraction of t h e spectrum that you will be dealing with here. I now have pleasure in formally declaring open this 9th International Meeting on Organic Geochemistry.
Ladies and Gentlemen I have been asked to address you partly because of my long involvement with the petroleum industry, and my awareness of problems both solved and unsolved. I am of course a geologist and to me geochemistry is essentially a tool: a tool which has, of course, increased in importance enormously over the period of my career. Forty or fifty years ago there was already an interest in the implication of varying coal rank, and petroleum geologists began to apply this in the 1930s to problems of looking for oil. It was recognised, for example, that it was no good looking for liquid hydrocarbons, and possibly not even gaseous ones, in basins where anthracite occurs. This was perhaps the thin end of the wedge of a development which has gone so very far in more recent years. When I was a student, stratigraphy, paleontology and petrology effectively constituted the whole of earth sciences. Then geophysics came, as an equal partner with the others, and now we see geochemistry as a science of equivalent status. Thus, in the Research Council with which I have been involved, geochemical research now attracts quite a considerable share of research grants, and very properly so. Geochemists deal with a wide range of problems, and a fundamental one which is now making real headway is the correlation of source rock and crude oils. (My comments, of course, are made as a non-specialist geologist, and maybe at lunch time you will say, we have already solved specific problems. If you can put me right I am very happy to be instructed.) But knowing where the crude oil started from, and what its migration history has been, is a very important aspect in the course of locating economic bodies of crude oil and indeed of gas too. One aspect of the geochemical problems that we don't hear very much about, although I see that there is a paper on it at this conference, is the function of limestones as source rocks. This source can be of very high importance - - for example in the Middle East it is a matter of great difficulty to find any organic rich shale which could have given rise to the enormous oil accumulations of Saudi Arabia. In other places the results are much less spectacular. Nevertheless limestones have had quite a complicated history: initial deposition in either an oxidising or reducing state, then diagenesis of various kinds, finally oxidation when they are brought to the surface. One therefore does have to take seriously the potential of large bodies of limestones as well as argillaceous source rocks in this field. In the last few years, arising from the work of the Deep Sea Drilling Project (DSDP), much interest has been concentrated on the black shales which derive from a Cretaceous oceanic anoxic event, and which have been penetrated by drilling on the ocean floor. We need to know how important as a source was this occurrence. H o w unique was it? Lower Cretaceous oil accummulations are of major importance in a number of parts of the world; the Athabasca tar sands and the Prudhoe Bay oil-field are a m o n g the larger scale ones, but there are many others. The Arabian limestone reservoirs of late Jurassic and basal Cretaceous age, which I have already referred to, as perhaps providing their own source rocks: are these related to the same anoxic event of the oceans, or another one? Although these occurrences relate to the continental shelves and don't have direct access, as far as we know, to oceanic sources, their source potential may have been assisted by general stagnation. But when one comes to other regions, Jurassic sources are ranked as of greater importance. The AOG - A.
ix
X
Opening Address
Kimmeridge, Lower Oxfordian and the Lias all have source rock potential, they occur on shelves and to a varying extent are interbedded with shallow water sediment. In the North Sea it is now generally accepted, that the Kimmeridge shale is the critical source. One wonders why the Lower Cretaceous shales appear to be relatively barren, why the Lower Cretaceous, which did so well in other parts of the world, has apparently made no contribution. In other areas in Western Europe, the Netherlands, G e r m a n y , Dorset (Wytch Farm) for example, deeper source rocks must be available, probably Lias, Callovian or Oxfordian shales. One of the problems of which I am sure you are all conscious in this respect, is the attempt to analyse the extent to which multiple sources are responsible in particular reservoirs. Kimmeridge shale may be the dominant source in the North Sea, but was it the only one? If not, then of course one has to solve the problem of the remarkable uniformity of North Sea oil in whatever reservoir it is found. There are alternative sources in the North Sea itself. The Devonian, for example, is deeply buried and on land has an organic content. In the North Sea there are marine limestones; did they produce any hydrocarbons? Another aspect of North Sea exploration, on which geochemists will throw light is relative uplift, and subsidence. The basins seem to have gone down continuously, the blocks on which most of the oilfields are found are fault blocks which, for the most part, have probably also subsided fairly continuously, although less rapidly than the basins. (The fact they are relatively up-thrown does not necessarily mean that they have moved upwards.) It is a matter for determination as to whether a relatively buoyant block has failed to subside equally rapidly or whether it has been uplifted. In this kind of problem it has to be remembered that samples of material from those blocks, the normally available material in oilfieid areas, is not also typical for the surrounding basins. And the blocks themselves may have different thermal histories; in some cases they are known to mask shallow basement and probably have higher temperature histories. In addition to these basic qualifications, the situation is further complicated because in important areas of the Northwest European basins - - the Dutch Graben is the classic case, with the Sole Pit Trough, the Irish Sea and others - - there has been inversion of areas originally basinal over long periods which have later become relatively buoyant. This again is a subject on which geochemistry will be able to throw a fair bit of light - - from the thermal history of their hydrocarbons, and of shales which have been deeply buried and brought up again by thousands of feet. No doubt this is the sort of subject which will be illuminated in the course of this conference. I would like to refer to another branch of organic geochemistry entirely - - one with which I do not think you will be dealing with here. That is the origin and history oforgano-metallic compounds. There are remarkable cases in the modern seas, as you no doubt know, of organisms accumulating quite abnormal percentages of particular rare elements. The classic case is that of the Tunicates, which concentrate vanadium. Fish accumulate lead in their bones. A number of mollusca put away pollutants such as zinc, lead, and heavy metals in fatty compounds in their bodies. And when one looks at the geological record one finds "hot layers", as they are called in the North Sea, which are high in radioactive elements, black shales which are high in potassium, and also peculiar shales as in the early Lower Lias here in England, in Lincolnshire, which are high in molybdenum. Why does this happen? It must presumably be a function of organic action. In the long run we may need to know by what mechanisms the various organisms produced abnormal concentrations of metals. We may then be able to apply the reactions they are using to extract economic amounts of metals from sea water - - for of course the oceans contain all the metals that mankind could conceivably use as long as man lasts. It does seem that you, as geochemists, should keep in mind these problems because with your studies of the organic-rich sediments there is a reasonable chance that you will be able to throw light on these problems, far out as they are at present, perhaps in the not too distant future. I have touched on some of the problems that directly interest me, although they constitute only a fraction of t h e spectrum that you will be dealing with here. I now have pleasure in formally declaring open this 9th International Meeting on Organic Geochemistry.