Exploring for mammoths

Transcription

1 EXPLORATION Exploring for mammoths The sedimentary basins offshore West-Greenland cover an area comparable to the entire North Sea. Six dry wells so far can therefore not be sufficient reason for writing off the possibility of finding oil and gas here in the future. Furthermore, geologists can now demonstrate the probable presence of prolific source rocks, good reservoirs and enormous structures. Elephants do not enjoy a cold climate. Offshore West-Greenland the search is therefore focused on ``mammoths. New data and solid geological studies confirm GEUS s belief that they can be found.

2 Everyone knows that Greenland has some magnificent scenery. But and this is serious for those concerned with trying to get the oil industry interested in prospecting the belief is widespread that icebergs float around everywhere along the coast. The fact is that ocean currents flow in such a way that the west coast of Greenland south of Disko (70ºN) is for the most part iceberg-free. Instead the majority of these white monsters drift southwards along the east coast of Canada (Baffin Island). Photo: Halfdan Carstens

3 EXPLORATION Halfdan Carstens D espite 6 dry wells and limited interest from the oil industry the search for oil and gas in the large areas west of Greenland will continue. Optimism is greater than for some time past due to several promising news. On the other hand geologists struggle to explain a number of "home truths". Davis S trait Sisimiut Nuuk Tasiilaq 500 m Viking Central graben system of the North S ea at same scale The myths We must work to remove some established myths. Three of these persist: the difficult ice conditions, a lack of suitable source rocks and the presence of oceanic crust between Greenland and Baffin Island, says Flemming G. Christiansen, leader of the stratigraphic department in the Geological Survey of Denmark and Greenland (GEUS). He is also responsible for the geological work which the institution is carrying out in the large sedimentary basins offshore West-Greenland.This takes place in collaboration with the Bureau of Mineral and Petroleum, Government of Greenland ( Råstoffdirektoratet ) in Greenland s own internal administration ( Hjemmestyre ) responsible for licensing. One of the myths which has survived is that oceanic crust is widespread between Greenland and Canada. Hence, without knowledge of the new research results, it is natural to choose other areas for exploration. But we now have data which show clearly that continental crust exists between 62ºN and 68ºN, claims Christiansen. Seismic data showing 6 seconds with sediments and drill-holes deep into the Cretaceous should be enough to convince most people, he maintains. Former geological misconceptions are therefore in the process of losing ground. Ten years ago it was much more difficult to promote the continental shelf offshore West-Greenland, but today we have good news to offer. The explanation for this is that we now have much more data and several geological studies which, collectively, show that the sediment basins have a completely different character than was thought in the 70 s and 80 s when the myths became established, says Christiansen. The new insight is the result of the strategy which we have pursued. The efforts of the Bureau of Mineral and Petroleum and GEUS have, quite simply, paid off, he maintains. Labrador Sea Qaqortoq It is easy to be taken in by the mere scale of things since Greenland is so large and unknown. But the fact is that the sediment basins outside the West-Greenland coast cover an area about as extensive as the North Sea Rift. Research over recent years has proved once and for all that the shelf offshore West-Greenland lies on continental crust. Experts, however, are slow to accept this knowledge. GEUS struggles therefore with the fact that several oil companies give only low priority to the area believing it to lie on oceanic crust. Finds of sediment and oil The first phase in the search for oil and gas offshore the coast of West-Greenland began in the 1970 s. Six groups of oil companies, Amoco, Arco, Chevron, Mobil, Total and Ultramar, took out licences. Five wells were drilled without any show of oil or gas, 250 km at least in commercial quantities. One of the wells, Kangâmiut-1, detected gas under high pressure but testing yielded only drilling fluid. The results from drilling, combined with poor quality seismic data (which formed the basis for the geological models), caused the oil industry to declare 16 GEO ExPro June 2004

4 It is not unusual with oil shows like this on the Nuussuaq Peninsula and Disko Island. Drilling has given quite a good picture of the stratigraphy offshore West-Greenland. Reservoir rocks are proven at several levels, and Statoil s drillhole in particular is interesting because it reveals the presence of sandstones in Upper Cretaceous rocks. the area to be totally uninteresting, says Christiansen. These conclusions remained unchallenged until The Geological Survey of Greenland (GGU, now a part of GEUS) began a re-study of the area. A project involving reprocessing the old seismic data was of crucial significance, relates Flemming G. Christiansen. Large, faulted blocks now became evident in deep water where oceanic crust was formerly thought to occur. Now it could be established that continental crust covered a much larger area in the deep sea areas than previously supposed. Therefore it was necessary to re-evaluate the possibility of finding hydrocarbons in these areas. At the same time oil seepages were detected on the surface of volcanic rocks on the Nuussuaq peninsula. A well drilled down to 448 m showed oil to be present throughout the whole volcanic rock sequence. The subsequent prospecting well drilled on land in 1996 by a Canadian company was dry, but later investigations indicated that it penetrated sandstones with oil shows. A big programme involving collection and detailed analyses of oil samples has shown that at least two source rocks are present and these can have wide regional distributions. One is of Upper Cretaceous age (Cenomenian/Turonian) and the other of Paleocene age. There is no doubt that the discovery of this oil is a strong contributory reason for the return of the oil industry to Greenland. Earlier, the absence of source rocks was the most negative parameter in risk assessment studies, says Christiansen. The re-processed seismic data, which revealed the possible presence of thick sedimentary packages offshore West-Greenland, resulted initially in additional and more modern seismic being carried out. It so happened that the absolute last line of the seismic programme from 1992 showed the presence of fault blocks and flat spots which indicated the possible presence of hydrocarbons in the structures. Four years later Statoil together with Phillips, Dopas and Nunaoil took out a licence based on these data. Oil activity was now in full swing for the second time in the history of Greenland. A dry well Statoil was very optimistic, mostly on account of a prominent crosscutting reflector (flatspot) which could indicate the presence of hydrocarbons. Disappointment was therefore great when, after drilling 2000 m (Qulleq 1), it became apparent that the flat spot was due to diagenetic changes related to temperature and lithology in a thick shale package (transition from opal CT to microquartz). In a regional context, however, the well was very important. It showed good reservoir quality rocks (porosity over 20%) in the Upper Cretaceous Generalised stratigraphy of southern West Greenland (Santonian) sandstones. Their existence was not previously known, and they have given us a new target which, with seismic data, we have tried to extend across the whole basin, says Christiansen. Statoil had hopes of finding large amounts of gas in the Fylla licence area. This was based on seismic evidence which showed what we called a "cross-cutting" reflector (CCR). In advance, 8-9 different interpretations for the CCR were considered, of which one was that it could represent a gas/water contact, partly because it coincided with the mapped spill point of several structures.the potential volumes of hydrocarbons were so large that the gas alone could be of interest for LNG, says Ånon Spinnangr in Statoil who was responsible for Statoil`s licence. The well showed no sign of source rocks or of hydrocarbons. Based on drilling results and regional considerations Statoil nevertheless believe that this well does not in any way detract from the possibility of finding hydrocarbons in other parts of the shelf area off West-Greenland. The presence of source rocks at the right levels will, GEO ExPro June

5 EXPLORATION meanwhile, still be a major factor of uncertainty. This is the view of Ånon Spinnangr who has wide experience in the search for oil in many parts of the world. After a new licence round in 2002 the Canadian company EnCana was awarded a licence with an area of 3985 km 2 (some 50 km north of Statoil s well). No wells have been drilled yet. A new licence round has recently been announced in Copenhagen and Houston. Substantially more data and knowledge is available this time enabling the companies to focus better. We have been in contact with both the oil companies and seismic companies regarding the areas which should be given priority. The conclusion was that smaller areas should be targeted. In the previous licensing rounds the whole area was open, but the companies had too little time. We have now built on the interest shown at that time, and since the database was not good enough more seismic by TGS NOPEC and Fugro is now available. Our impression is that industry prefers this way of doing things, claims Christiansen. GEUS has selected four areas which cover 32,000 km 2 (equivalent to more than 50 North Sea blocks). We have done the first screening based on principles favoured by those companies which have shown interest, explains Flemming who himself has wide experience from Greenland after more than 15 summers in the field.we have chosen to focus the investigations on prospects we believe to have a very good potential, he says. Will only be looking for mammoths A seismic line through the Fylla structure showing the flat spot one hoped for but perhaps did not completely believe should represent the border between gas and oil or between gas and water. GEUS, in close cooperation with the Bureau of Mineral and Petroleum, is now pursuing another strategy than previously in an attempt to attract the oil industry to new ventures on the Greenland Shelf. We have worked hard to gain attention, says Christiansen, by giving talks at conferences, writing scientific articles, visiting the oil companies and inviting them to Denmark. The geological work has been concentrated on a regional mapping of two possible reservoir formations, one in the Paleocene and one in the Cretaceous, the sandstones of which first became interesting after Statoil s well. The oil industry only looks for elephants or mammoths and therefore we have ignored all structures less than 100 km 2 and concentrating on those larger than 400 km 2.Structures which lie at less than 1000 m below sealevel have also been excluded from the map. We have also Focus on four areas Based on geological studies and subsesquent discussions with both oil compnies and seismic companies, four areas have been selected to be included in the third licensing round. They each differ from each other in structural style, petroleum systems and operating conditions. Common to all of them, however, is giant size leads with potentially more than one million barrels of recoverable oil. Area 1 Lady Franklin Basin cover 10,500 km 2 with water depth ranging from m. Area 2 Kangaamiut Ridge and Basin cover some 4900 km 2 with fairly shallow water depth from m. Area 3 Ikermiut Ridge and Basin is with 7000 km 2 somewhat bigger but with similar water depth ranging from m. Area 4 Paamiut Basin is with 11,200 km 2 the largest area. Water depth is from shallow (150 m) to deep (1750 m). 2D seismic is available inall four areas, while 3D seismic has not yet been acquired. 18 GEO ExPro June 2004

6 excluded prospects which lie far from supposed mature source rocks or which are inadequately mapped, explains Christiansen. Nevertheless, four areas remain as well as a large number of structures which qualify as hunting grounds in which mammoths can be found, he says. Faith in source and reservoir rocks - I am worried about the source rocks west of Greenland, says Thomas Ahlbrandt of the United States Geological Survey (USGS) in Denver. As World Energy Project Chief for the large-scale worldwide resource assessment run by the USGS since 1995 he is qualified to express his opinion. Flemming G. Christiansen understands Ahlbrant s concern, but he claims there are several indications that oil and gas have been generated in the basin. During drilling there have been good gas readings, oil is proven in drill cores, and we have a number of field observations where oil emerges from the rocks, says Christiansen. In a wider regional perspective gas occurrences in Paleocene sandstones on the Canadian shelf are worthy of mention. GEUS has documented onshore seeps in the Disko-Nuussuaq area (for location, compare lower map on page 16). Seepage offshore the Disko-Nuussuaq area is also strongly indicated by a satellite seep detection study carried out for Nunaoil. The possibility of offshore seepage is furthermore indicated by several amplitude anomalies and shallow gas related features observed in the seismic data from the area with satellite slick observations. - Our extensive scientific investigations have now opened up the possibility that we have both Jurassic and Cretaceous (Cenomanian) source rocks and analyses indicate that the latter are the more promising. They can be correlated with similar rocks across much of North America and it is most likely that a marine connection between Greenland and Canada existed at that time. - The seismic data also show many signs of an active petroleum system in the basin. There are many examples of possible hydrocarbon leakages in the form of gas pipes, pock marks, flat spots, bright spots and "smeared seismic" which indicates shallow gas. We hope to get samples of oil and gas from the sea floor in the years to come for analysis in order to establish their composition, according to Christiansen. Rumors concerning the presence of oil on Nuussuaq are very old and in 1992 small amounts of oil were found in volcanic rocks. A drill-hole put down to a depth of 448 m the following year established it to be a genuine show. This was enough to encourage commercial investigation and a small Canadian company was awarded a license. They carried out core drilling down to 900 m, geophysical surveys and a 3 km deep well. The license expired before commercial quantities of hydrocarbons could be proved. Subsequent analyses, however, indicate that thick sandstones should have been tested. According to GEUS, Nuussuaq is still an area in need of further investigation. Later mapping has registered 100 oil shows along the Disko coast. The picture shows drillhole GRO#3 from 1996 on Nuussuaq. Disko island lies on the opposite side of Vaigatsundet.

7 EXPLORATION There is, however, no doubt that reservoir rocks exist. There are many good analogues on land, and in Cretaceous and Paleocene time huge quantities of sand were poured into the basins. Reservoir is not a problem. There are many possibilities throughout the Upper Cretaceous sequence and upwards, says Christiansen. But Jurassic reservoir rocks are also a possibility even though they have not yet been found in drill cores. The seismic data indicate the possible presence of Jurassic rocks in the basins. A programme of shallow seismic, sampling and later drilling is planned to demonstrate this in the coming years. It is not yet proved that these rocks occur in the basin but we have good indications, all geological, which point in this direction, according to Christiansen. Applied Science Flemming Christiansen emphasizes in particular the increased knowledge which GEUS believes firmly that there can be a source rock in the Lower Cretaceous. Both local and regional observations support this. The map shows where it can be mature (dark green colour). All four new areas included in the next licensing round lie where the source rock is thought to be mature. Flemming G. Christiansen in GEUS has many field seasons on Greenland. the seismic investigations have revealed regarding sedimentary thicknesses, regional tectonics and sea floor spreading together with improved understanding of the source rock problem. These breakthroughs have led to new licensing awards being made, the first since the middle 70 s. There is no doubt that improved knowledge concerning possible source rocks has been an important factor for the oil industry and explains their renewed interest, he says. Prospecting for oil and gas offshore West-Greenland was for a long time research-based, says Christiansen. He bases this on the two big breakthroughs GEUS achieved in understanding the hydrocarbon potential latent in the sediment basins (thick sedimentary packages and source rocks).this is due to well focused and good research carried out over many years. This, in turn, convinced the authorities, and in the next instance the oil industry, to invest in areas with considerable risk, but also with large potential. After the two first licensing rounds it was nevertheless necessary to change tactics. We now say that oil search is strategically determined.the reason for this is that before the next round of licensing in 2004 we have improved the working atmosphere by emphasizing close cooperation and a better dialogue with the oil industry. This time we believe it will give results since interest seems to have been aroused. Flemming G Christiansen envisages many exciting years ahead with scientific research closely tied to the intensive search for oil and gas. As a scientist with a focus on applied aspects of knowledge he cannot ask for more. Licensing history The continental shelf offshore West-Greenland is divided into three areas for licensing purposes. In the north and south oil companies can apply for large areas throughout most of the year. These are designated "open door areas". In the middle, between 63ºN and 68ºN, licences are awarded for specific areas, each with its own round of licensing. There have been two licensing rounds so far in the course of the last 10 years. Three licences have been awarded. The third round is now under way. Phillips Petroleum (now ConocoPhillips) and Statoil were operators with one licence each following the first round. Only Statoil drilled and despite the fact that the well was dry it supplied a lot of valuable geological information. It proved the existence of sandstones of Cretaceous age which up to then were unknown from the continental shelf. The second licensing round closed in July 2002 and following negotiations the independent oil company EnCana was awarded a license with Nunaoil (carried partner) in the exploration phase. The Cretaceous sandstone found in Statoil s well was to a large extent decisive for generating interest in this block, but it also gives support to the belief that source rocks can exist in the Cretaceous (Cenomanian-Turonian). The third licensing was officially opened April 1st and will be closed October 1st. 71 N rde Bo Sisimiut-West licence Fylla licence r w it h C a n a d a 63 N Greenland 68 N GRO#3 Hellefisk-1 Ikermiut-1 Sisimiut Kangâmiut-1 Nukik-1 Nukik-2 Nuussuaq Disko Qulleq km IlIulisat Nuuk 60 N 20 GEO ExPro June 2004