Transcript for:
Geologic Model for a Single Well

[Music] you hello I'm Doug weibull's today out presenting a video that shows much of the basic workflow in creating a good geologic model for a single well we'll start with a rough model that was based on several concepts and assumptions about the tectonic depositional and thermal history of the model location which sits in a complex area that appears to have experienced at least one major erosional and conformity will examine the model in detail beginning with the geologic data and very importantly a clear acknowledgement of the gaps in our data and uncertainty about the assumptions involved in building our original model I'll then propose some significant modifications to those assumptions that will lead to significant revisions of the ideas in the original model the purpose of this video is to show both the thought process in building good models and the importance of using the best possible assumptions data and data interpretations in building the models our model for this video is the Munster line one well drilled to a depth of about 6,000 meters in 1961 for scientific purposes by the West German government data from the well were subsequently studied thoroughly by a large team of German scientists the Muenster line 1 or M 1 well is shown in the lower map here as a red dot in the middle of the munster Ron basin which sits to the north of the current exposure of the Rhenish Massif that Massif consists of many thrust slices in place during the ver ISKCON orogeny in the late carboniferous the upper map places our small study area in the context of northwest Europe the location is very close to the Dutch German border not far south of the North Sea the Muenster line Mason also known as the Munster line cretaceous basin or the MCB is just south of the larger and better known Lower Saxony Basin and somewhat north of the well studied tertiary age round robin as we will see later however there are a number of major and critical differences between the Munster line region and the nearby basins the Munster line one well was in fact the first well for which a burial history curve was ever published by Nicolai lapatin in his landmark 1971 paper that introduced his TTI method the precursor the modern Basin modelling m1 was not coincidentally also the first model I ever created so there's a good bit of nostalgia for me as I revisit it today we'll be analyzing the wells history in detail in a way that was not only impossible to do in the 1970s but impossible to even imagine do it we've truly come a long way in the past five decades all models are created using a mixture of facts and assumptions and we must be vigilant about keeping what we know separate from what we think may be true the geo history plot presented on this slide is no exception it was created quickly using a variety of data and ideas and possibly even a few concepts but it is not a finished and proven reconstruction our specific objectives today are to break down the components of this Muenster line one model and examine them to improve our understanding of the integrated geologic history at the modern location and finally to build a better model our broader objective in this video of course is to learn how to do this type of critical thinking and analysis routinely the shape and details of the m1 geo history plot quickly indicate several important details that we with a bit of knowledge of local and regional geology and plate tectonics can relate to specific geologic events for example on this slide we see a period from about 335 ma to 300 ma a very rapid sediment accumulation a portion of this part of the model is essentially fact supported by the well known ages and thicknesses of the Carboniferous rocks present in the well but the geo history plot also includes a hypothesis shown in the annotation that the rapid Carboniferous deposition corresponds to development of a foreland Basin in front of the veux risk and orogeny once those two sets of information are juxtaposed in one's mind this is easy to make the mistake of believing they are inseparable and that both are entirely factual rather than partly interpretive here I have added a second interpretive common varistor Niraj derived from the well-documented existence of a major unconformity that is believed to have begun near the end of the Carboniferous the precise age at which subsidence change to uplift at this location is unknown but I have assigned it here an age of 300 million years which is surely not far from the truth the change from deposition to erosion is a fact but the timing is an assumption that has some range of uncertainty fortunately probably no more than a few million years we also interpret with our comment that the uplift means the variscan orogeny sensu stricto had arrived at our modeled location and that the forlán Basin stage was now over logical and obvious as this comment seems it is still an interpretation rather than a fact that uplift and erosion occurred is a fact that they are related to the risk and origin is an interpretation this model also shows our interpretation of the elevation of the veriscan mountains as a function of time the elevation histories shown here is not based on data but rather develops from our interpretation of the magnitude and timing of uplift and of timing and amounts of erosion both syn orogenic and post orogenic we'll discuss those points later in more detail please note that the ages and thicknesses of the eroded rocks are not data since they are inferred rather than directly measured as we will see later those inferences can be tested using measured thermal indicator data during the model optimization process a vital part of this initial model is the reconstruction of the period from the late permian through the middle jurassic where our model proposes accumulation of a thick marine section that has subsequently been completely eroded and thus isn't present today the thickness of the postulated section was not extreme it doesn't present a problem in terms of the sedimentation rates required the concern lies elsewhere the model as proposed requires bringing the top of the verr ISKCON Mountains down below sea level in quite a short time what mechanism or driving force would justify this proposed subsidence the concept of rapid subsidence is not unusual or particularly difficult but juxtaposing it with a thrusting event does create mechanistic issues that must be addressed in addition to the complex mechanics involved we must also ask why we would even be tempted to deposit and erode the promote jurassic section why not simply assume continuing erosion of the verse can mount ins permitting them a gradual and graceful rather than abrupt subsidence into the sea is the per mo jurassic sedimentation event pure fantasy or does it have its foundation in real data from near my areas and if such data exists how trustworthy relevant and convincing are they for the moment we have no answer well we shall return to this key issue in the very near future deposition of perm Oh Jurassic strata in our model creates another problem since those layers aren't present today they must have been eroded in this case knowing the timing of erosion isn't much of a problem since a thick sedimentary section spanning two-thirds of the Cretaceous sits atop the eroded Carboniferous we therefore know that erosion of the proposed per mo Jurassic started no earlier than late Jurassic and then did no later than albeit if it was deposited at all but we also need a mechanism for this erosion in the current model after a hundred million years of subsidence we must uplift and erode those same sediments during the next 50 million years what would be the driving force for this significant Late Jurassic uplift and how much topographic relief would it have created in deposition of the Cretaceous in our model creates still another problem we know Cretaceous strata are present today and we think we have a good idea of their original thickness but we don't yet know how the required accommodation space was created so rapidly after erosion of the perla jurassic section we also don't know yet where the cretaceous sediments would have come from are they derived from the remains of the aging Riskin mountains or do we have a new source terrain perhaps one with different possibilities to produce reservoir faces or seals or since much of the Cretaceous section is calcareous perhaps the sediment source is simply the marine organisms themselves it's all food for thought as we develop our conceptual model perhaps it's time to rigorously compile everything we know or think we know from our data concepts ideas and interpretations in order to deal with all the issues that will arise it's useful to make two lists one is a list of things that we know or think we know the other will be a list of things that we don't know here I've begun by compiling a list of the data and facts we have at our disposal and that we must honor we could make an even longer list but our time is limited so I will stop here for the moment in dealing with the issues we have just mentioned we will undoubtedly discover other questions that need answering that's part of the excitement and value of this journey let's start with the easiest items which most people would think are either trivial or irrelevant but present-day location and elevation are both important the present day location will enable us to track our models latitude and position with respect to other tectonic plates through time while the present day elevation will have to connect to the Paleo elevation history that we eventually reconstruct the red dot on this map marks the Muenster line one location very close to the Dutch border in North West German that it's elevation is only 25 meters today is no surprise in this figure we also see its location with respect to thrusts on the Rhenish Massif and what used to be the veriscan Mountains the well is just at the northern edge of the thrusts which advanced from the southeast this information will be important in understanding the paleo elevation story during and following the varistor Niraj by the way the names ver ISKCON and hercynian are largely interchangeable although Virizion which I am using in this video seems to be slightly preferable in this area we also know the present-day stratigraphy in wind sterlin one quite well in fact the model Street Tigre shown here is a rather simplified representation of the known stratigraphy however it will work quite well for our purposes what the present-day stratigraphy lacks is obvious information about strata that have been removed by erosion a definite statement on whether missing time intervals actually included depositional events and if so what were the details of those events we've already seen one complete reconstructed geo history plot showing our starting version of the geologic history at Munster line one however is we have already discussed that geo history included a large amount of interpretation now I want to show a different type of geological history plot that contains very little interpretation and thus serves as a more neutral beginning for the model building process this is a burial history plot in which water depth and elevation which are included as crucial components of geo history plots are omitted in fact this special version is even simpler and less accurate than a normal burial history plot because it has made no effort to reconstruct events at the unconformity it has simply considered each unconformity to be a hiatus to repeat it is not a realistic model but it is a useful unbiased starting point based only on data the red arrow is at the right designate the two unconformity x' that are definitely present in our model the earlier one is between the Carboniferous and the cretaceous and the later one is at the surface above the cretaceous please note that the plot doesn't show the per mo Jurassic section or its deposition or erosion since there is no conclusive evidence from the present stratigraphy alone that it was ever present or what it might have consisted of similarly there is no information about possible eroded rock above the preserved Cretaceous this approach more than makes up for its deficiencies by allowing us to reconstruct the details of those unconformity x' with fresh eyes by the way I consider the concept of fresh eyes to be crucial to successful modeling of geological histories so don't be reluctant to discuss your models even unfinished or difficult ones with your colleagues and with other geo scientists who might not even be directly interested in Basin modelling everyone sees some things that others would miss down hold temperature data are of great value in modeling of thermal histories fortunately in the moon's der Laan one well we have a nice set of down whole temperatures obtained from numerous wireline logging runs this plot shows the temperature data that I was originally given for the Munster Line one well the temperature profile is excellent and certainly seems at first glance to give a clearer answer about the present-day thermal regime unfortunately I was not told whether or not the temperatures had been corrected and if they had been what method had been used I was concerned because the data were published in 1963 long before modern methods for correcting wireline log temperatures had been published and I was concerned the trend of temperature data was too perfect to be believable anyone who has worked with real down hole temperature data would likely be just as suspicious as I was of a trend as nice as this one this is the information I had to start with about present day temperatures I'll tell you the rest of the story a bit later it does have a very happy ending but probably not the one you are anticipating Thermal indicator data are also of great value in modeling especially where there are major and conformities and major uncertainties about those unconformity x' or where paleo heat flow might have been different from present-day heat flow fortunately in the Muenster line one well we have an incomparable set of Vautrin height reflectance values measured on a large number of Carboniferous coal samples by world-renowned experts the reflectance data range from moderate maturity levels to extremely high ones unfortunately low maturity data are absent in the Paleozoic samples analyzed apparently no reflectance data were obtained from the cretaceous the lack of reflectance data from the Mesozoic is understandable in an historical context 1962 reflectance had only ever been applied to Cole's it had never been used for carriage ins or rocks that didn't contain Coley material the Carboniferous in Munster line 1 was very rich in Cole's but the cretaceous was not this is one of those rare and extremely happy occasions where the auro data appeared to be completely trustworthy the increasing scatter and data at the bottom of the section where maturity is extremely high is unavoidable since it stems from increasing NIS atrophy of the veteran ID particles moving on with our list we know today with reasonable accuracy the plate tectonics setting and history of nearly any location on the planet this reconstruction shows the Muenster line one location the red dot in the late carboniferous at 302 ma just before uplift created the frisk and unconformity the well sits in the middle of Pangaea at the complex intersection of several agglomerated continents and micro continents the green dot shows the munster line one location in a more zoomed in view at about the same time that Vilonia baltic 'e and Lorenza that is North American plate names are circled in red note the wells position on the leading edge of one of the risk and thrust on the Rhenish Massif that moved from the southeast those thrust edges are shown by the dotted lines to the east and south of the green dot the plate tectonics history helps us understand the nature of the complex collision during the late Paleozoic that resulted in the forest and erosion this knowledge is crucial for creating a realistic model for the erosion and for the post orogenic history the small red dot shows the approximate location of the Muenster line one well 400ma as various continents and micro continents approach each other well before the start of the variscan orogeny another reconstruction from about the same time confirms the same basic pattern of the preliminary stages in the Assembly of the northwestern part of Pangaea our well is again indicated by the red dot slightly later the major docking of Leroux CEO with Gondwana is well underway the Muenster line one location the red dot is not involved in a major collision finally by the late carboniferous the Muenster line one location is surrounded by the gathered continental fragments and so as wikipedia says the variscan orogeny involved a complicated heterogeneous assembly of different micro plates and heterochromatic elisions the allegheny in orogeny is the north american name for what is called the hercynian orogeny in Africa and in parts of Europe it is shown here is the western portion of the yellow mountains which have an east-west orientation the small six pointed red star sits approximately at the eastern end of that orogeny some people might take the allegheny an erogenous a good model for what happened at mr. Lenoir however the Allegheny Anu Rajan II involved a straw in direct collision between two massive plates Lorenza and the African portion of Gondwana whereas the collision further east that directly affected Munster Lang 1 shown by the red dot was much less direct the collision that m1 might be compared to a group of bumper cars coming together in an amusement park rather than as a head-on collision on the freeway when we think of continental collisions and suturing the most obvious example to many of us is India colliding with Eurasia this topographic representation shows the net result of that collision a thin line of extremely high peaks the Himalayan ranges that separates the uplifted Tibetan Plateau with an average elevation of about 4,500 meters from low-lying India India striking Eurasia seems to have been rather like a spear into the heart even during the approach of the two continents the potential for major pain and suffering was evident from the eocene to the present day India has pushed itself deeply into the side of Eurasia this striking representation shows clearly the asymmetry and the results of the collision as India was subducted beneath Eurasia the map also shows that the vast majority of the area affected by the collision is not at extreme elevations we therefore shouldn't think that every continental suture produced mountains 5 to 10 kilometers high nor that such mountains where they did form represented a large portion of the landscape but beyond those caveats about misusing the most extreme features of a compressional setting as typical characteristics there are other reasons to believe that India Eurasia may be a poor and analog for Muenster land this slide shows interpretive cross-sections through time with the oldest on the bottom across the Allegheny anuraag which sutured Muraco to the southeastern US India clearly lost the battle with Eurasia and was subducted but the Allegheny and orogeny produced more of a draw than a winner and a loser continental thickening and uplift occurred on both sides of the vanished ocean the variscan orogeny which is considerably to the east of the Allegheny orogeny was probably much weaker because of the aforementioned bumper-car effect subduction or extreme compression seems unlikely the red dot on the map on the Left shows the location of the m1 well in the Allegheny n'ver ISKCON system further to the southeast on the older parts of their Rhenish Massif the 2005 fishin tract data of card and co-workers indicate larger amounts of erosion and thus probably more thrusting and higher mountains we've talked thus far about what we do know and how well we know it but it's necessary to also discuss the things that we don't know about Wednesday like one most of those knowledge gaps are related to the tectonic history these gaps often combine to give us potentially large uncertainties about the thermal history in terms of depth of burial at different times paleo surface temperatures and heat flow out of basement through time the blue items at the bottom of this slide relate to uncertainties about the models calculations of hydrocarbon generation although they are real concerns today we'll focus on issues related to the geological and thermal history and we won't be discussing source rocks kinetics or hydrocarbon generation the items in red at the top of this list are directly related to the unconformity x' they involve reconstruction of events during each unconformity and the implications of events during the major risk an unconformity for paleo temperatures here's our original geo history model again just to refresh your memory and here is that original geo history plot with red arrows indicating a variety of events that we have consciously or unintentionally defined in the process of building this rough draft model we'll go through all of them from the oldest on the left to youngest on the right so that we understand the implications of our data and assumptions in creating this model the green arrow here shows that veriscan defects began to be felt no later than 335 ma with an increase in sedimentation rate one could also argue that the effects actually began earlier at about 365 ma with the increase in water depth a sediment supply initially failed to keep up with a tectonic Li induced increase in subsidence rate the green arrow at the bottom of the slide at 300 MA shows the moment of maximum burial just as the foreland basin began to invert as the veriscan thrusting moved into the monster land one location the timing of this inversion is dictated by the age of the youngest Carboniferous sediment we have allowed to be deposited as noted earlier there is an uncertainty of perhaps a few million years in this exact date the horizontal green arrow at the top shows that we have proposed a maximum elevation of 3,000 metres above sea level at 280 million years we should be able to provide good justifications for both the elevation and the dating and if we can't we should investigate further the blue arrow shows that in our model erosion began at the onset of uplift and continue to tell the start of Permian sedimentation at 256 MA it can't be seen easily on this scale and in this type of diagram but the rate of erosion decreased substantially from relatively high rates between 300 ma and 290 ma to lower rates after 290 ma be prepared to defend the rate or rates of erosion at different times during the unconformity taking into consideration type of sediment climate erosion mechanisms and topographic relief the green arrow here points out the initiation at the late permian through middle jurassic depositional phase that we have proposed even though there is no direct evidence for it at the munster line one location the blue arrow represents the long period allocated for deposition of those per mo jurassic sediments and the down warping that enabled that deposition be prepared to discuss thickness the beginning and end age for each depositional event and lethality is deposited as well as comparable details for all phases of erosion the green arrow on this slide shows the uplift and erosion of the entire promote jurassic sequence be prepared to discuss the uplift and erosion mechanisms and details such as timing and rates the blue arrow indicates deposition of the Cretaceous section which is not in doubt however the arrow serves to remind us of the need to understand both the cause of the creation of accomodation space and the source of the Cretaceous sediments the horizontal green arrow again serves to remind us of the need to distinguish the tectonically active Cretaceous from the very quiet Cenozoic and to understand the mechanism that terminated Cretaceous subsidence and sedimentation this slide provides a rewritten summary of most of the work points made on the previous geo history plots it's mainly here for future reference many tectonic events are associated with thermal anomalies so it's always a good idea to investigate that possibility of particular interest here is the veriscan event because it appears to be the strongest tectonic event in the Welles history and because it is associated with proposed maximum burial and temperature well we're going to defer discussion of all thermal issues until we finish with the tectonic events as we just saw it's important in building a good geologic model to understand cause-and-effect relationships many such relationships begin with tectonics I therefore think it's very useful to attempt to recreate and understand the tectonic events in the models history we have already seen this philosophy in action to some degree but now we're going to take a slightly different approach I've begun by very quickly assigning several tectonic events to the geo history as overlays the earliest of the events are development of the Fordland Basin followed by the virus can uplift itself then to explain the collapse of the virus can mount ins and the deposition of a moderately thick late permian middle jurassic section i've proposed a long sagging event probably relaxation devolving from the disintegration of Pangaea the fourth event is largely a guess we need some mechanism to terminate jurassic deposition and provide a platform for erosion of the entire lower Mesozoic section here I've just called it unknown uplift I hope to be able to clarify its origin later in the analysis finally the fifth event which enabled deposition of the Cretaceous section suggests some kind of rapid extension as either a pull apart or a rift again I hope to shed more light on the details as the analysis proceeds these five events will help us get started is very likely that our list of events will change significantly as we learn about the moon sterlin ones history there are obvious improvements that could be made in our estimates of the timing of the various events the start of the veriscan portland episode shown by the red arrow could easily be pushed back from 318 ma to 365 ma as it initially developed as a starved Basin with increasing water depth before a flood of sediments from the veriscan origin filled in' the end of the verse can uplift indicated by the blue arrow might be better placed at peak elevation 280 ma then at 271 ma that new date might also be a better time to initiate the disintegration of Pangaea we might push the end of the disintegration phase back to a hundred and sixty ma to correspond better with the end of jurassic sedimentation we could initiate the period of unknown uplift at the same time as shown by the green arrow the end of the uplift probably occurs earlier than this diagram says and doesn't necessarily coincide with the onset at the Early Cretaceous extension the proposed extension event in the Cretaceous shown by the orange arrow appears to have begun with the renewal of sediment accumulation in the actia and ended at 82 ma when the most rapid phase of subsidence ended the rift phase seems to have been followed briefly by a drift phase from 82 ma to 67 ma before it was terminated by another uplift event the same geo history plot with the revised event superimposed is shown here it doesn't provide a complete or quantitative analysis of the tectonic history but it does give us a better guide in going forward with the analysis analysis of tectonic uplift and subsidence provides another invaluable tool for understanding the integrated geological history this slide shows insane geo history with the tectonic events removed for clarity and with a red tectonic subsidence curve now superimposed upward movement of the red line indicates that tectonic forces are moving the rocks upward with respect to the data which in this case and in most cases in this presentation is paleo sea level while downward movement indicates tectonic subsidence our other geo history plots all use paleo sea level as the data so the surface of the ocean was that in a constant elevation of 0 through time however when one wants to emphasize the role of eustatic sea level it may be more useful to take present-day sea level as the data in such cases as shown here the surface of the ocean goes up and down through time these plots are actually more realistic than the ones with flat sea level but as they are new they are unfamiliar and even disconcerting to some people in this presentation I'll use a mixture of the two styles depending on what I am trying to say the development of the verr ISKCON foreland Basin involves considerable tectonic subsidence as shown by the blue arrow and the verse can orogeny in orange requires tectonic uplift but what is most interesting here is the massive tectonic subsidence required to bring the high proposed for risk and mountains back down below sea level in order to initiate deposition of the upper Permian marine 16 evaporites this tectonic subsidence shown by the red arrow parallels the decrease in surface elevation erosion alone is not adequate to bring the veriscan Mountains to sea level since isostatic forces keep pushing the land surface back up nearly as fast as it erodes ice aesthetic responses even imperfect ones are important to the story here and in many other places this result from combining these various technologies and phenomena used to see isostasy tectonic uplift and subsidence curves and geo history plies shows us very clearly that our proposed model is probably not realistic in particular I think we need to reduce the required amount of tectonic subsidence of the veriscan Mountains the next slide shows one possible improvement in the model if we reduce the Paleo elevation of the veriscan Mountains it of course becomes easier to eventually bring them down to sea level in this slide we have reduced the maximum Paleo elevation by half from 3,000 meters to 1500 meters with a proportional decrease in the amount of required tectonic subsidence it is very important to understand that this change only affects paleo elevation the amount of erosion wasn't changed we're simply saying that more of the erosion was sin orogenic if the amount of required tectonic subsidence is still more than we can accept we can further reduce the Paleo elevation as shown on the next slide here I've reduced the maximum Paleo elevation to only 500 meters and our variscan Mountains have become the veriscan Hills our model still requires some tectonic subsidence but that amount may be acceptable for some tectonic models at this point we haven't proven that this solution is geologically acceptable for me it is much more attractive than the original high mountain scenario especially given the lack of evidence that high mountains actually existed but it is not the only possible model for the Primeau Jurassic history at Munster line 1 so let's switch gears and focus a bit on late permian through jurassic sedimentation in northern germany this block diagram shows the per mo jurassic section in northwest german represented by the purple pink and blue colors as indicated by the vertical red lines on both the legend and the diagram these are the strata that were deposited and subsequently eroded in our original model those layers are clearly present over the northern part of the area which is to the left in this slide but it's also obvious they are missing in the side on the right side the same area is shown here from a different perspective that includes the Munster Line one well which is indicated by the red dot on the green cretaceous surface Triassic and Jurassic strata are absent in the well but a present not far away is their absence in the well due to erosion as our initial model proposes or perhaps instead to non deposition will now examine the paleo geography at and near the Munster line one well in the context of events from the late permian until the late Jurassic beginning here with Upper wrote ligand to deposited during the late permian this map shows the M one location indicated approximately by the red star as he Mergent at that time with wrote ligand deposition limited to the area further to the north in fact the southern limit of wrote ligand deposition may well have been wholly or in part defined by uplifts created during the veristic thrusting during mu shil cult time from 247 ma to 237 ma in the middle triassic the M one location was right at the margin of the Rhenish Massif if it was on the emergent Massif as I believe it was significant accumulation would have been very unlikely we see the same pattern here during the early Jurassic with the Rhenish Massif emergent and the M one location right at the northwest margin of the mouse another source regarding williamson in their 2012 publication said that quote through permian to late early cretaceous time the Rhenish Massif was an area of Nan deposition and erosion including both the rouga beat and the Muenster lied unquote they and other workers have noted the large difference in Mesozoic history between the Muenster land area and the lower saxony basin just to the north where the upper Permian Triassic and Jurassic are all well developed as we have seen in the preceding slides the apatite fishin tract data of kargh and co-workers from 2005 indicate a possible heating and subsequent cooling event in the Mesozoic that could be explained by sedimentation followed by erosion however their closest dated to the M 1 well do not show this effect and the Mesozoic history of the Ruhr basin where most of their samples were from may well have included at least some per mo Jurassic marine sedimentation that I personally doubt occurred at M 1 the areas that were flooded by marine incursions during the late permian through jurassic were mainly the lowlands that formed as a result of extension as Pangaea disintegrated those areas lay to the north of the Muenster land 1 well there may also have been some sediment accumulation in some of the valleys between thrusts cheese in contrast the thrusted area of the Rhenish Massif itself where we are confident the M 1 well was located because of the erosion it experienced remained high and dry in support of that idea this cross-section shows the Munster line Cretaceous base or MCB where the Muenster line one well is located as shown schematically by the green arrow the red ovals show upper Permian through middle Jurassic strata present in the northern part of the MC B by pinching out depositional II toward the South succinctly stated it seems that if we want to propose large amounts of erosion at the top of the Paleozoic section in the m1 well the well must have been situated at top of thrust a topographic position that would have prohibited it from accumulating sediments during the promo Jurassic this change in our thinking offers us an easy solution to the problem of overly rapid subsidence of the mountains because the development of marine conditions can be postponed nearly a hundred and fifty million years until the aptiom so now let's look at some scenarios in which we don't have to deposit any road sediments of late permian to Jurassic age this geo history plot returns to our original hypothesis of 3000 meters maximum elevation at 280 ma the downward trend in surface elevation from 280 ma to the restart of deposition in the apt II is intentionally more or less exponential reflecting a common and reasonable concept that erosion rates tend to decrease with decreasing topographic relief we note that one consequence of the 3,000 meter maximum elevation is that there must have been a major component of tectonic subsidence during the perma Jurassic as shown by the downward trajectory of the red tectonic subsidence curve erosion alone is not enough to bring the land surface down to sea level because of the rebound effects of isostasy during unloading if we reduce the maximum elevation to 500 meters we note that a minor amount of tectonic subsidence is still required during the main erosional episode in the late permian if we reduce the maximum paleo elevation further 400 meters the need for tectonic subsidence disappears completely as the red tectonic subsidence line remains flat until the beginning of Cretaceous subsidence this is my preferred model for the varus step although there isn't any reason that there couldn't have been some tectonic subsidence during the disintegration of Pangaea in the early Mesozoic we do note however that the fragmentation of Pangaea did not produce any major tectonic events at the em1 location in spite of evidence for major effects a bit further north having reached at least a tentative decision about the early Mesozoic we can turn our attention to the Cretaceous which is definitely present in the monster land one well as we saw earlier the Cretaceous in the m1 well was deposited as the main step in the development of the Muenster line cretaceous basin in the albion the MCV sits between the thrusts that separated from the north german and the lower saxony basins to the northwest and northeast respectively and the thrusts of the Rhenish Massif to the south in fact the northern margin of the Rhenish Massif including the m1 location saying during the Cretaceous allowing the MC b sediments to unlap onto its northern margin as shown here by the blue arrow this block diagram may show the Cretaceous on Lap onto the northern margin of the Rhenish Massif a little more clearly the major global sea level high stand that occurred at 53 ma was nearly 240 meters above present sea level we will see that high sea level stands and variations in sea level were important in the Cretaceous and Cenozoic history of the study area the nearly 2000 metres of preserved Cretaceous section in the m1 well Rep it's a major event with important implications for our entire reconstruction and deserves commensurate attention here we see the standard geo history plot for the well using relatively modest elevations during and after the variscan orogeny because global sea-level was changing greatly during the cretaceous at Cenozoic it is useful now to look at the new type of geo history curve shown here where the datum is present-day sea level and the sea surface this goes up and down through time if we toggle back and forth several times between the two diagrams you can get a feeling for the differences in the two presentation mode in 2012 Rick Hart and Wilson stated quote the global Albion caronian sea-level rise 40 meters as shown by the red arrows marking the beginning and end caused a major on lap of near shore and Hemi pelagic strata under the northern part of the Rhenish Massif transferring the Muenster land into an area of deposition this was the birth of the Muenster line cretaceous basin which was part of the wide north german epic continental shelves a major period of this transgressive phase occurred during the Cinemania when the coastline shifted far southwards inversion of the lower saxony basin began in the early kayne see locally already in the later oni the inversion converted the former lower saxony basin into the present tectonic lee stable lower saxony tech 2g while simultaneously the Muenster line Cretaceous basin experienced significant subsidence up to 2000 meters thick sediments of keynesian lower campaign Ian M sure formation unquote but the whole story may be even more complex and analyzing the geo history plot provides additional insight we note here that there is considerable tectonic subsidence associated with the Cretaceous deposition the early subsidence phase depicted by the dark red arrow was gentler than the second phase shown by the bright red arrow therefore used to see alone was inadequate to account for the 1800 plus meters of cretaceous sediment we observed the same phenomenon in our study of the Permian Basin in West Texas in the US where rising global sea levels had generally been considered to be the cause of formation of the Cretaceous Western interior Seaway that bisected North America we suggest that both tectonic subsidence and used to see played roles there as well as here mid to late cretaceous tectonic subsidence in the MCB was concurrent with inversion of the lower saxony basin to the north and east this juxtaposition together with the speed and intensity of the second subsidence phase suggests some kind of trains tension now let's shift gears away from the tectonic events and look in detail at the thermal aspects of a model starting with present-day down hold temperatures in the n1 well which are shown in this profile in analyzing temperatures it is normal to begin with the present day because we can directly measure present day subsurface temperatures and because those temperatures will give us clues about paleo temperatures the temperatures in this plot which we saw on an earlier plot are the ones I was originally given without attribution they turned out to be estimates of true formation temperatures based on wireline log temperatures this work was published in 1963 which long predates the development of the standard methods for correcting wireline log temperatures that we use today and as such they needed to be reviewed carefully and possibly revised the basal heat flow required to achieve this fit to the two deepest supposedly true formation temperatures is 54 milliwatts per square meter as shown in this profile if we have chosen to fit any of the other data points instead the required heat flow would have been somewhat lower as shown in this profile the required basal heat flow to achieve the fit to the next two deepest supposedly true formation temperatures is 52 milliwatts it took some research to find the original wireline log temperature data but here they are the uncorrected measured temperatures there's a lot of data and most of it is quite consistent here we see the uncorrected wire line temperatures as open green circles and the estimated true formation temperatures as read open triangles hey demon did not describe his method for correcting the log temperatures but his correction is very small and is least at the greatest depths where temperatures are highest the inclusion of the uncorrupted temperatures doesn't change our fit - he demands corrected temperatures but the very small amount of correction used by Hegeman suggests to me that he has probably underestimated the true formation temperatures modern methods of correcting wireline log temperatures generally give larger Corrections than hedeman used my preferred correction method is based on large studies we carried out in the melee Basin the Gulf of Campeche in Mexico and the Danish central robbing of the North Sea here and in our Nova software it is called the my MX DK method this plot shows the uncorrect along temperatures and hey demands corrected temperatures as before plus the corrected temperatures using the my MX DK method a solid green dots with uncertainty bars the gray calculated temperature profile was chosen to fit the new corrected temperatures and required a basal heat flow of 58 milliwatts per square meter instead of 54 milliwatts this temperature correction method is mainly based on the time since the end of mud circulation one might want to know about other correction methods Nova offers a method calibrated only on the denmark data and given the proximity of Muenster line to denmark it might be reasonable to inquire whether that method might be preferable in this case to the my MX DK method this slide shows applied to the uncorrected temperatures he demands corrected temperatures and the temperatures obtained using the denmark correction that the deepest measured temperatures could not be corrected by this method since their depths are beyond the calibration range for the Denmark method but otherwise the calculated profile and basal heat flow are identical to those used for the my MX DK method the Denmark method is also mainly based on the time since the end of mud circulation Nova also offers the GSMA method which was developed in the late 1960s by combining data from the Permian Basin of West Texas and the Gulf Coast many of the wells were deep so Corrections are available far below the base of the Munster line one well the amount of GS n a correction depends only on the depth at which the temperature was measured Corrections are generally smaller than with the my MX DK method and true temperatures and therefore lower in this case the profile is fit using a Basel heat flow of 55 milliwatts per square meter compared to 58 milliwatts a commonly used but not very scientific correction method is to simply add 10 percent to the measured temperature among its many disadvantages one gets a different answer in Fahrenheit versus Celsius Corrections are generally smaller than with the my MX DK method and true temperatures are therefore lower in this case the profile is fit using a basal heat flow of 55 milliwatts per square meter which is a bit lower than the 58 milliwatts required for the my MX DK method so I think we can conclude that for the lithology x' we are using in our models the temperature data indicate a present-day basal heat flow close to 57 to 58 milliwatts per square meter overall my confidence in our present day temperature profile is extremely high with the present date thermal profile pretty securely in place it's now time to think about paleo heat flow many take time vents are associated with thermal anomalies so it's always a good idea to investigate that possibility a particular interest here is the veriscan event because it is the strongest line and because its association with maximum burial and temperature will ensure its importance but any analysis of the thermal effects of a tectonic event must view that event in a broad context including events leading up to the main event and those events devolving from it one way to begin the discussion of paleo heat flow is to simply try a constant basal heat flow through time and see what happens and here is the result using a constant basal heat flow of 58 milliwatts per square meter through time are calculated reflectance profile shown by the two detached black line segments does not completely fit the measured RO data although the values at the top of the Carboniferous agree pretty well and the calculated slope is only a bit too low the gap or jump or dislocation in the calculated reflectance profile indicated by the red arrow occurs because the Cretaceous rocks immediately above the Verushka nonconformity have had a much milder thermal history than the Carboniferous rocks immediately below them the blame for a misfit between the measured dots and the calculated line can be laid either on the measured data if their quality is questionable or on the model because models always have at least some uncertainty since in this case we trust the reflectance data our model must be deficient but what specifically is wrong with it we've already noted that below the veriscan nonconformity where the measured RO day to begin the slope of the black calculated reflectance profile is lower than the slope of the trend of measured reflectance data because both those slopes depend on the temperature grade real or proposed at and near the time of maximum temperature we could improve the fit by changing the heat flow we are using in our calculation of our own since the slope of the calculated trend is too low we would have to increase the models heat flow at the time of maximum burial which we know from our geo history plot must have been very close to 300 ma most people don't realize it but there is a simple and legitimate way to justify a slightly higher heat flow in the past for any model radiogenic heat production from continental basement contributes a significant proportion of the total heat flowing out of basement my own rough estimate is 50% of the total plus or minus about 10% with the proportion varying from place to place so if we have a heat flow of 58 milliwatts per square meter at the top of basement about 23 to 35 milliwatts comes from radiogenic sources my best guess in this case would be 29 milliwatts the amount of radio jamming heat production for basement is important because that quantity decreases slowly through time as shown on this slide each isotope of the main radiogenic elements has its own half-life all of which are very long the fastest decrease in our HP with time is for potassium followed by uranium with thorium having the longest half-life for relatively young Cenozoic or Mesozoic models the decrease in our HP may be too small to worry about but for Paleozoic or older rocks it can represent a few percent of the total as this plot shows our HP from potassium today is about 23% less than it was 500 million years ago the smaller decrease for uranium and the very minor decrease for thorium give us an ad reduction in our HP for a typical granite of 6.4 percent from 300 ma to present-day consequently if our basement keep flow today is 58 milliwatts with a maximum of 60 percent of that heat coming from radiogenic decay in the crust the basement heat flow 300 million years ago when maximum paleo temperature would have been reached could actually have been sixty point four milliwatts per square meter the difference is not large but let's see if it significantly affects the calculated RO values this slide shows the comparison between measured and calculated ro when we consider the maximum likely effect of radioactive decay on basal heat flow through time the inset shows the decreasing basal heat flow through time we can toggle back and forth a few times between the two models that is with and without the decrease in heat flow through time to see that there is a small increase in calculated ro values when the Paleo heat flow is higher however although the changes in the right direction it isn't large enough to change the slope of the calculated ro curve enough to give a fully acceptable fit to the measured ro data so we apparently are going to need another eat source in order for our calculated ro line to have the same slope as the trend of measured RO data so we've made good progress toward the goal of simultaneously fitting thermal data from today temperatures and from the past our own but we have simultaneously uncovered a significant issue the present-day heat flow of 58 milliwatts fits the present day temperature data while a higher heat flow at about 300 million years is required to fit the reflectance data so what is the actual shape of the heat flow curve through time what is our net step in putting the heat flow story together well I pause here and ask your question about data quality before I dive into modifying the model I'm not concerned in this case about the measured reflectance values although ro quality is in fact often a problem I've already said these are Oh data are almost certainly as good as reflectance values can ever be instead my question is about the quality of the calculated our own values which were obtained using the standard Lawrence Livermore National Laboratory easy percent rro equations easy percent ro has been in common use since about 1990 and has been subjected to much scrutiny but not to public testing and the RO values in this well are quite high where applications have been much less frequent than in the main oil window therefore we should be cautious about demanding a perfect fit between measured and calculated iro values since we cannot be completely confident that the calculated values are correct so we'll now begin to change our thermal model to better fit the measured RO data just to refresh your memory here's the model with a constant heat flow of 58 milliwatts and the original proposed ver risk and erosion of 2620 meters increasing the basal heat flow and at a near 300 ma 275 milliwatts per meter squared gives a calculated iro slope that is similar to that of the measured data however we see now that the calculated RO values are much higher than the measured ones in the upper Carboniferous section it is thus clear that in order to fit both the slope of the measured RO trend and the actual measured values we will have to reduce the amount of risk and erosion in our model doing so will reduce the gap in calculated reflectance across the variscan unconformity decreasing the total amount of deposition in erosion at the veriscan nonconformity from 26 20 meters in the previous model by trial and error to nineteen hundred and fifty meters gives us an excellent fit to the measured reflectance data as shown here the discrepancy between the dots and the calculated line at extremely high maturity is mainly a consequence of the limitations in the easy percent ro equations for calculating high reflectance values it is of no significance for this discussion and shouldn't lessen our confidence in the excellent quality of this fit to achieve this fit I reduced the amount of deposition and erosion of each of four striper graphic units Westphalian B C D and Steffi nyan by about 25 percent one of many alternative approaches would have been to omit deposition of the snow Fenian completely and simply begin uplift and erosion earlier the choice of how to partition a change in amounts of deposition and erosion should always be made on geologic grounds the northernmost fishing track data points of card at all that are closest to the M one well actually showed half a kilometre less erosion than in our final n1 model I think this is good evidence that m1 and cards nearby H well are close to the northernmost toes of the veriscan thrusts where thresh sheets were thinner and where there was even very local marine Permian section deposition in some of the erosional valleys between the thrush sheets after achieving the fit to the RO data I rechecked the fit to the present day temperature day now fortunately that fit had not changed noticeably and thus I was able to use the same present-day heat flow a 58 mm what's in this new model changing the maximum depth of burial will sometimes significantly affect compaction which in turn affects thermal conductivity and thus the heat flow required to achieve a target temperature decreasing the amount of deposition in erosion at the various command conformity only results in modest adjustments less than 700 meters in maximum burial depth there was no need to change paleo elevation although it would have been acceptable to do so these relatively modest changes do not invalidate the overall geologic concepts built into our model the biggest conceptual change would be if we had decided to change this definian from a period of deposition to one of erosion toggling back and forth between the original model and the revised model shows the minor differences in depths and in the tectonic subsidence curve so the next important question is the source for the high heat flow of 75 milliwatts around 300 ma this value is nearly fifteen milliwatts above the value that would have been expected even including the variation in basement radiogenic heat production through time we cannot attribute the increase in heat flow to thinning of the lithosphere since this was a period of compression during the Assembly of Pangaea I can think of three candidates perhaps you can think of more one would be hydrothermal effects related to faulting and fracturing that is known to have occurred the second would be volcanism related more to local or regional zones of trans tension or even rifting than decompression the third would be emplacement of plutons it is important to distinguish among these possibilities because they will have different intensities durations aerial extents and geological implications this man shows latest Carboniferous too early permian volcanism in northern Germany and southern Scandinavia with the m1 well location indicated by the green star although there was no volcanism at that location the copious volcanics some hundreds of meters or even kilometers thick to the north and northeast suggest a good possibility of heating at m1 within the period from about 300 ma to 260 ma here we see our final model for paleo heat flow in the m1 well it is derived from the concept of minor heating from the abundant volcanism to the north and northeast and is highly empirical though grounded in solid concepts the baseline curve reflects the small decline in basement RHP with time the high plateau represents rapid heating at the start of the documented volcanism in the late carboniferous followed by about 40 million years with relatively constant heat flow and termination by rapid cooling at the end of the volcanic episode in the late permian all details of this reconstruction are negotiable if better concepts or additional age dating can be found other similar conceptual and numerical models could be created if one wanted to invoke alternative or additional mechanisms such as hydrothermal activity and here we see the result the heat flow history just proposed yields an excellent fit between measured and calculated RO values to summarize in this discussion we have researched and reinterpreted an existing model and have then created a very different new model the combination of significant gaps in the rock record and the tectonic complexity of the area have been responsible for most of the uncertainty in both reconstructions this example is certainly not typical it is far more challenging than an hour every construction but this exercise has sought to show the value of a fresh approach fresh eyes if you will in evaluating a data set it has also shown that even with good temperature and thermal indicator data for calibration important uncertainties can remain those uncertainties represent herein elsewhere opportunities for good scientists to seize an advantage over competitors here we see a standard geo history plot of the original model with its high risk and mountains major VII scanned erosion rapid collapse into the sea to permit deposition of a thick promote jurassic section and the complete removal shortly after its deposition that same lower Mesozoic section the model fits the geologic and calibration data available but is that even approximately correct here in contrast on the same time in depth scales is the geo history plot for the new model with modest variscan hills absence of per mo jurassic deposition and erosion and a slow relaxation of the ver ISKCON landscape into the sea ending in the aptean if we toggle between the two plots a few times we can easily see huge differences the new model also fits all available hard data is it better than the first model I think so but you will have to draw your own conclusions based on additional data if you can find any and on your own interpretation of the missing parts of the story finally here is an annotated geo history plot of the new model using present-day sea-level as the datum rather than the standard paleo sea level also shown are the tectonic subsidence curve and the final set of tectonic reference events I decided to put on the display not shown because it unfortunate overlaps in time with avarice can uplift event is the proposed volcanic thermal event from the latest Carboniferous through the Permian before we conclude I have one final surprise for you when I finished this analysis I decided to see how Nikolai lapatin had handled the poster risk and unconformity in 1971 I hadn't looked at his paper for decades and have forgotten most of the details of his model of course he never discussed the elevation of the risk and mountains because the burial history plot he invented didn't include water depth or elevation but we can see here that he proposed that the maximum burial depth was reached at 288 ma as shown by the red arrow that's a little younger than my estimate we also note that the trajectory of the rock layers is overall upward meaning that the net erosion was occurring during the period from 288 ma to a hundred ma as shown by the green arrow his sequence of events has periods of deposition alternating with slightly stronger periods of erosion one wonders whether lapatin envisioned his early Mesozoic depositional events as marine continental or a mixture of both law patents depositional scenario falls between that offered by my original model with continuous marine deposition from 260 ma to 160 ma and my final one with continuous erosion from 300 ma to 114 ma he proposed that about 2,000 meters of Carboniferous section was removed during the veriscan unconformity very similar to the 1950 meters i used in my final model but less than my original estimate however his model has more total erosion at that unconformity because he removes thermo Jurassic as well as Carboniferous finally like me lapatin proposed a higher geothermal gradient at maximum burial than the one in place today this difference is illustrated by the two temperatures circled in blue the Carboniferous temperature was a hundred and ninety degrees C while the modern temperature at the same depth is about a hundred and seventy C overall his model has stood the test of time remarkably well there are of course a number of aspects of 1d modeling that we haven't discussed here we haven't mentioned pathologies or Rock properties such as compaction or thermal conductivity we haven't discussed porosity optimization we also didn't say much about water deaths little facies depositional environments or eustatic sea level changes in some cases those points are key but they weren't of great importance in this particular investigation of the m1 well we also didn't say much about water deaths little facies depositional environments or eustatic sea level changes in some cases those points are key but they weren't of great importance in this particular investigation of the m1 well finally we didn't mention source rocks hydrocarbon generation expulsion or cracking and all perhaps we'll get a chance in the future video to examine some of those topics thanks for watching I wish you fun and success in your modeling efforts you you you you