The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
- Data Science & Engineering Analytics
The SPE has split the former "Management & Information" technical discipline into two new technical discplines:
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Abstract Exploratory drilling in the Faroe-Shetland Basin of the northeast Atlantic Ocean has been ongoing for several years. One of the greatest challenges of such drilling programs is cost-effectively drilling through the thick layers of Paleogene volcanic rock, which has thicknesses and depths that vary depending on the location of the regional tectonic geography. With the high expense inherent to remote offshore operations, total drilling costs will increase when expected penetration rates and interval lengths are limited due to drillbit inefficiency. An operator planned to drill a second well in the Brugdan prospect, which lies in License 006, Block 6104/21 off the Faroe Islands. The challenge of drilling through a hard, long section of basalt/volcanic sequence presented a great opportunity for investigating and implementing new drillbit materials and design changes to diamond-impregnated bits. A study for materials testing was focused on diamond grit/matrix combinations for wear, durability, and ROP on two representative basalt outcrop columns provided by the customer. The analysis of the physical characteristics of the rock provided an insight of the matrix and diamond combinations for blade material and grit hot-pressed inserts (GHIs) that would offer a reliable product to meet the challenge and drill the long section. Materials testing followed at the drillbit manufacturing facility to find the appropriate diamond-impregnated recipe. A competitive diamond-impregnated bit was developed for the 12¼-in section, resulting in an internal world record and an unprecedented drilling performance in the extremely hard and long volcanic sequence.
Summary We report on a 2D and 3D analysis of multiple types of geophysical data in order to map sub-basalt sediments in License 6 area offshore the Faroe Islands. Integrating multiple types of data is crucial for improving sub-basalt imaging, since seismic data alone can only poorly resolve the low velocity sediment layer under the fast velocity basalt layer due to scattering at inhomogeneities within the basalt. Our analysis is based on low structural resolution types of data acquired in the same target area: magnetotelluric, full tensor gravity and first arrival tomographic seismic data. As they carry complementary information content about the geological structure, this can be efficiently harvested using a joint-inversion algorithm, which inverts the data to a common Earth model by assuming a borehole derived relationship between the physical rock parameters of electrical resistivity, seismic velocity and density. This relatively strong coupling type results in an increase of resolution for the joint Earth Model in comparison with Earth models derived from single methods data. We present two final joint Earth models derived by two different joint inversion codes with different coupling schemes: A 2D model across the Brugdan borehole and a 3D larger regional type of model. The derived Earth models show varying thickness of the basalt layer and the presence of sub-basalt sediments in most part of the regions. The Earth models compare well with the actual physical parameters measured as a function of depth in the Brugdan borehole and seismic reflection data for the 2D model and regional studies for the 3D model and 3D seismic reflection data for the 2D model and information from regional studies for the 3D model.
Summary High-resolution marine seismic data have been interpreted in an attempt to gain detailed understanding of the shallow section in a basalt-covered area, where a subsea tunnel is planned for construction. Problems encountered are analogous to exploration problems in areas with high acoustic-impedance contrasts. The testing of a previously postulated strike-slip fault has been one of the main issues of this study. It will be demonstrated that at least two coherent intra-basaltic reflectors, beneath the water bottom, appear to represent significant unconformities, and that these, because of their extent, tend to refute the hypothesis of faulting in the study area. We interpret relatively thick sedimentary layers to be associated with these unconformities – or intervolcanic hiatuses – and since sediments usually have higher porosities (and permeabilities) than volcanic rocks, these reflectors might well represent zones of streaming fluid. The dip of the basalt flows is small – about 2 or 3 degrees – and therefore fluid could migrate several hundred meters to kilometers until it reaches an excavated tunnel. Incoherent portions of some of the interpreted seismic reflectors, as well as lowvelocity zones detected in previous studies in the uppermost few tens to about 120 m, indicate rock deterioration in this zone. Introduction Creating seismic images of horizons and other geological features within and beneath basalt layers can be a great challenge for geoscientists in both industry and academe. Massive basalt is a high-impedance rock, which normally implies that a large proportion of the seismic energy is reflected back upon incidence at a boundary between a low-impedance medium (such as water or sediment) and the basalt itself. This study relates to the planning of a subsea road tunnel (Figure 1) in the Faroe Islands to be drilled through flow basalts and deals with aspects that are analogous to exploration problems in areas with high-acousticimpedance layers. High-resolution 2D marine reflectionseismic data have been interpreted and visualized for the purpose of obtaining an optimal understanding of the uppermost 100-150 m of rock below the water bottom. Certain intra-basaltic features beneath the water bottom have been recognized, which has served to answer crucial questions related to the study area. The testing of a previously postulated strike-slip fault, which is inferred to have a vertical displacement of 200-300 m, and a lateral displacement of 4-6 km, is an important issue of this work. Methodology Sheriff and Geldart (1995, pp. 150-152) state that most reflections mark unconformities and/or time boundaries that most commonly correspond to distinctive lithologic changes. However, since the geology in the study area is almost entirely made up of flow basalts with mostly thin strata of intercalated volcaniclastic sediments, as well some organic and reworked sediments (Passey et al., 2007; Passey, 2009), significant lithologic changes are uncommon. However, unconformities have been established onshore (e.g. Rasmussen and Noe-Nygaard, 1970; Passey, 2009) and one of them corresponds to the ‘C horizon’, which is also a key feature in the interpretation of the data in question. Migrated seismic data have been used in the interpretation of all the features.
Abstract Multiple is a long-standing problem in petroleum seismology. Despite significant achievements in developing advanced techniques to attenuate multiples, there is currently no single multiple-attenuation technique that can be applied to attenuate all the various types of multiples. The performance of each technique depends on the particular dataset. Selecting an optimal technique (or an optimal combination of schemes) lies in determining whether the Earth models implicit in a particular technique match the Earth model from which the seismic data were physically acquired. In this paper we present an integrated workflow using seismic modelling and SRME (Surface-Related Multiple Elimination) to attenuate multiples for the GlyVeST (Glyvursnes - Vestmanna Seismic Tie) seismic data, which were acquired in the Faore Islands. First, we carried out the GlyVeST seismic modelling, which has shown, among other things, that surface-related multiples are much stronger and more of a problem than internal multiples. Subbasalt seismic processing is well known to face challenges from severe scattering losses by impedance contrasts and rugose surfaces, geometrical spreading, velocity heterogeneity and strong multiples. As there can be great uncertainty in going from real data to interpretation, we gain insight by starting with an assumed or 'known' geology and generating synthetic data from it. Then, processing these data, knowing the correct result, guides us to an optimal processing strategy. The synthetic data, produced by an elastic finite-difference modelling scheme, offer excellent possibilities for detailed studies of how seismic waves interact with heterogeneous basalt flows, as well as better understanding of the multiple problem. Instead of resorting to trial-and-error, i.e. testing many different multiple-attenuation methods and picking the most pleasing result - wasteful of time and computer resources - the GlyVeST seismic modelling has helped us to determine a multiple-attenuation strategy for the Earth model from which the real GlyVeST seismic data were acquired. Based on the characteristics of our multiples (i.e. surface-related multiples much stronger than internal multiples), we have applied SRME, a technique that attenuates surface-related multiples as much as possible, followed by predictive deconvolution on the GlyVeST data. Finally, having conditioned the data for velocity analysis, we apply a high-resolution Radon demultiple routine in a series of iterative passes (velocity analysis - Radon demultiple - velocity analysis), progressively harsher as confidence in the velocity trend increases. As a result, multiples have been effectively attenuated without harming primary events in the data. Introduction The Faroe Islands are situated in the central section of the volcanic passive margin of NW Europe, and the Islands constitute part of a thick succession of Paleocene flood basalts, an obstacle for imaging the subbasalt geology (Figure 1a). These basalts have been divided into three series. From the older to the younger they are: the Lower Basalt Formation (LBF), the Middle Basalt Formation (MBF) and the Upper Basalt Formation (UBF) (Waagstein, 1988). Previous research indicates that the MBF thins from Vestmanna to Glyvursnes. At least two hypotheses may explain this thinning:the supply of lava during emplacement of the MBF was from the W or NW and insufficient to retain as great a thickness as far south as Glyvursnes as was observed at Vestmanna and on the northern islands; the Glyvursnes area was uplifted relative to the Vestmanna area during a tectonic phase that took place between emplacement of the LBF and the MBF. In order to test these two hypotheses we have recently acquired the GlyVeST seismic survey (Figure 1b). The Glyvursnes-1 and Vestmanna-1 boreholes, about 30 km apart on the island of Streymoy, are two locations where considerable well-log and surface-seismic data have been acquired. A line between them closely follows Streymoy's west coast, giving us the rare opportunity of acquiring a seismic tie between Glyvursnes and Vestmanna with both marine and land profiles. The survey also includes a second profile that was shot in N-S direction to tie with the Lopra-1/1A borehole on the island of Suduroy.
Summary High-resolution 2D marine reflection seismic data were acquired in a narrow sound in shallow water with high acoustic-impedance contrasts. This yielded a volume of raw data with very strong, short-period multiples and weak signal below the seabed, implying extra demands for the processing. In order to avoid the loss of useful signal when attempting to enhance the S/N, a powerful f-k filter was used early in the processing, followed up by post-stack deconvolution and migration. In spite of extraordinary challenges and drawbacks in the processing the final result is promising, with stacked sections that depict intra-basaltic horizons. Some of those horizons can be identified from onshore extrapolation of their recognized positions and attitudes. After preliminary interpretation of the tight grid of seismic lines, a 3D horizon could be derived for better visualization, and this work can be used to test a recently hypothesized strike-slip fault in the study area. Consequently, as many research projects are carried out aiming at sub-basalt imaging – mostly with the application of low-frequency sources and the utilization of the bubble pulse for deeper penetration – this work exhibits the use of a high-frequency seismic source for intra-basalt imaging in the uppermost few hundred meters with quite interesting results. Introduction Depicting intra-basaltic horizons and other geological features within flow basalts is not a simple task, but a great challenge for geoscientists in both industry and academe. Earlier – as well as nowadays – in the NE Atlantic region much focus has been directed towards sedimentary basins predating flow basalts. However – depending on the thickness of the basalts, acquisition methods and parameters – the base basalt may be fairly hard to estimate from seismic data. This issue combined with the fact that intra-basaltic sedimentary strata in some places have been shown to contain significant hydrocarbons make it even more relevant to look for the intra-basaltic features – how and to what extent they can be distinguished in seismic data. This has resulted in a few projects – both academic and industrial as well as a combination of both – focusing on sub-basalt and intra-basalt imaging. One of these is the PUFFINS project at the University of the Faroe Islands. This paper presents some results on intra-basalt imaging using high-resolution 2D marine reflection seismic data acquired between islands close to coasts in the Faroe Islands (Figure 1). The main challenges in the data arise because of the very high impedance contrast and the rugose surface at the water bottom. Furthermore, the data have been acquired in shallow waters – i.e. about 80 to 120 m – which implies short-period seabed multiples and, therefore, masking of useful signal at short intervals. This work demonstrates seismic data sections that have been processed with powerful f-k filtering, post-stack deconvolution and migration. It furthermore demonstrates the recognition and interpretation of intra-basaltic horizons followed up by the derivation of 3D horizons that serve to test a current hypothesis of a strike-slip fault in the study area. Geology The Faroe Islands is a small archipelago centred around 62º north and 7º west in the north-east Atlantic Ocean (Figure 1).
Summary Imaging prospective structures lying beneath thick basalt flows presents a key technical challenge in the Faroe-Shetland region. The FLARE-2 profile, recorded in 1996 southeast of the Faroe Islands by the Amerada Hess Ltd. Partner group, was used to test a new approach toward better resolution of sub-basalt structures. In this study, we demonstrate that appropriate re-scaling of seismic data in the parabolic tau-p domain has the potential to enhance significantly intra- and sub-basalt reflections. Processing the entire FLARE-2 data set twice, once using conventional time processing and a second time including the new tau-p strategy, illustrates the benefits of the proposed scheme.
Tunnelling experiences obtained from projects in Madeira, Iceland and the Faroe Islands will be presented in this paper. These experiences include such as tunnelling conditions in general, support and grouting philosophy and also various types of problems encountered and the solutions found to deal with them, In particular, tile applicability of the most common rock mass classification systems will be discussed in tile paper. Tunnelling in volcanic rock mass have been experienced elsewhere too, however, as a first step in gathering experiences it was considered sufficient to include projects from the countries mentioned above. If this exercise would provide any systematic findings that lead to believe that tunnelling in volcanic rock masses is different compared to other rock masses, a further approach on an increased database would be suggested. 1. INTRODUCTION With a rather diversified background the authors of this paper found an interesting interface, namely that related to tunnelling in volcanic rocks. Two of the authors have their experience and background from the Madeira Island, whilst one has his experience particularly from the Nordic countries where tunnelling in volcanic rocks have taken place in Iceland and tile Faroe Islands. On this basis this paper will try to draw the common aspects of tunnelling in volcanic rocks from a number of projects in these countries mentioned above. Common for these is also the fact that they are small groups of islands situated in the Atlantic sea hundreds of kilometres out from the nearest mainland or continent. It was found an interesting exercise to try to draw up the tunnelling experiences from a number of selected projects in these countries and identify common problems and how these were solved. The projects that will be discussed in particular include such as tile road tunnels from Funchal city - Cot a 200 (Marmeleiros: Penteada and Quinta da Palmeira twin tunnels): Porto da Cruz (Cruz da Guarda, Serrado single tunnels); and Água de Pena (Queimada single tunnel). Further, tile water supply and hydropower tunnels of Fajã de Ama, tile connection tunnel of Encumeda to Ribeira Grande São Vicente and in the multipurpose tunnels of Socorridos. From the Nordic countries the experience from subsea road tunnels in Iceland (tile Hvalfjördur tunnel) and the Faroe Islands (the Vagatunnilin tunnel) will be presented together with some general experiences from a wider range of projects. Rock mass classification using various classification systems will also be discussed. In the Nordic countries the Q-system developed by Barton and his colleagues has been the dominating whilst in the Madeira Island the Bienawski geomechanic (Bieniawski, 1989, in Hock. 1997) is most commonly applied. Neither of these two systems were established and developed with particular focus on volcanic rock masses, and are they really applicable as reliable tools these geological circumstances? This paper will discuss these classification systems based on the experiences from the projects mentioned above and specifically focus on the parameters used in the application of quantitative rock mass classification systems in volcanic, basaltic rock types.
Peace, David G. (AOA Geophysics) | Schofield, James (AOA Geophysics Inc) | Orange, Arnold (AOA Geophysics Inc) | Servodio, Raffaele (Agip UK Aberdeen) | Lansdell, Ron (Agip UK Aberdeen) | Woodfin, Mark (Agip UK Aberdeen)
Mark Woodfin Agip UK Aberdeen Recent exploration activity over a large part of the Faroes and West of Shetlands has been considerably hampered by the variable thicknesses of basalt that are present in the region. The Faroe Islands are comprised almost entirely of basalt which has a total thickness of around 5-6000 meters, whereas not far to the east in the West of Shetlands region, this thick basalt has either completely disappeared or at worst thinned to no more than a couple of hundred metres or so which presents few problems for modern exploration methods. Much of the recent exploration activity in the Faroes area has been focussed in the Judd Basin region between these two extremes, where the effects of the basalt are enough to reduce seismic data quality considerably and render seismic interpretation very ambiguous in places. Even though there has been considerable experimentation with seismic acquisition techniques over the last 5 years, and in places some small improvements have been made, in general the experimentation has not often resulted in the required level of improvements being made to remove the interpretive ambiguities. Land (MT) and now Marine Magneto-Telluric (MMT) exploration has been available as a commercially viable alternative exploration tool for many years now, and is now well proven in its application to difficult seismic areas such as sub salt, sub carbonate and sub basalt environments.
Abstract The Faroe Islands are planning to open their territorial waters to oil exploration and production in 1998, when they have their first licensing round. The Faroese economy is presently dependent upon fisheries, with fishing, fish farming and processing accounting for almost 95% of all exports. The seas surrounding the Faroes are renowned for their cleanliness, and are of importance for cetaceans and seabirds as well as fish. In a unique collaboration, 23 oil companies have already started to work together in conjunction with the Faroese Petroleum Administration and Institutes in order to gather data on the environment around the islands. The main objective of the joint industry/institute group is to gather sufficient data to enable operators to carry out environmental risk assessments for future exploration drilling offshore the Faroe Islands. This paper describes the work and philosophy of the Faroes GEM, whose workgroups are studying the Geotechnical, Environmental and Metocean aspects of prospective areas of interest on the Faroese Continental Shelf.