FORCE Biostratigraphy Seminar Day – 26TH May, 2005
ORAL PRESENTATION ABSTRACTS
Statistical Modeling of Ecological Signals (SMES): New Applications for Biostratigraphy
Barrie Dale1, Amy L. Dale2, Iain Prince3 & Craig Harvey4
1Dept. of Geosciences, University of Oslo, P.O. Box 1047 Blindern, NO-0316 Oslo, Norway.
2GeoResearch Consulting, N. Bakli, 2100 Skarnes, Norway.
3Statoil, A-423 ST-FH, Forushagen, 4035 Stavanger, Norway.
4A/S Norske Shell, P.O. Box 40, N4098, Tananger, Norway
SMES is a new method for identifying ecological signals from assemblage counts of microfossils. The method was first developed by Dale & Dale (2000) to identify ecological signals from recent dinocysts, using a global database of cyst distributions that allowed testing of the signals against known environmental factors. SMES utilizes statistical methods based on correspondence analysis that were found to most accurately reflect and quantify the ecological signals expressed by the recent cysts. Here we report on latest efforts to test and develop this method for applications in industrial biostratigraphy.
The first application of SMES to industrial biostratigraphy used a palynology dataset from Paleocene sequences in four wells along an onshore-offshore transect from the Norwegian North Sea provided by Statoil. The method allowed identification of the statistically most important species, and the relative position of these along the main axes suggested ecological trends (the coastal/oceanic being most dominant). Tracking these trends down-hole showed major shifts in each well that could be correlated between all wells; the shifts corresponded to flooding surfaces, and suggested orientation of the well sites relative to a paleo-shoreline. This first test strongly suggested this method to offer a quicker, more robust application for paleoenvironmental interpretations from the dinocysts than previously achieved by traditional methods.
Within the past two years we have extended the biostratigraphic applications using data sets covering Late Cretaceous to Eocene in six wells from the deep water Norway/Greenland basins provided by Statoil and Shell. The SMES method proved equally applicable to these greatly extended geological intervals, even in older sequences lacking the ecologically significant cyst groups linked to the recent cyst distribution models. This was particularly important for identifying the paleo-shelf/slope break. As important known oceanic indicator species of Impagidinium and Nematosphaeropsis diminished stratigraphically downhole (Campanian), the method still allowed us to identify indicator species for relatively shallower and deeper water depths in these older sequences. Current applications include Early Cretaceous to Pliocene sequences from the Møre Basin using datasets provided by Statoil and Shell. The main objective is to identify relative water depth indicators as input to basin modeling. For the first time this includes both palynology and micropaleontology data. Results so far suggest the method probably could be applied to virtually any industrial dataset of microfossil assemblage counts, covering any geological time period.
The Stratigraphic Framework and Geological Interpretation of the Upper Cretaceous - Lower Cenozoic sequence in the Møre Basin and margin.
Mike Charnock, Norsk Hydro Research Centre, Bergen.
The basis of this presentation is to demonstrate the application of biostratigraphy and applied interpretation techniques by reference to a practical example i.e. the establishment of a stratigraphic framework and the geological interpretation of the Møre Basin and margin.
The talk will emphasise the role of biostratigraphy at a variety of different scales from regional i.e. long distance intra-regional well correlations, field scale studies, with examples from the Ormen Lange field, and on the reservoir scale below seismic resolution. At all these levels the interaction and integration with other disciplines is emphasised.
In addition to the conventional usage of biostratigraphy for dating, correlating rocks, the interpretation of stratigraphic breaks and the timing of tectonic activity, more applied techniques will be shown using microfossils (foraminifera, radiolarian, diatoms and palynomorphs) to characterise potential intra reservoir permeability shale barriers and their use as indicators of palaeoenvironment and sediment source.
A high resolution palynostratigraphic framework for the Forties Sandstone Member, UK CNS. Applications to reservoir modelling, nearfield exploration and well engineering decisions.
Paul Cornick, Petrostrat Ltd
Abstract: High-resolution biostratigraphical (palynological) analyses of cored well sections from twelve fields in the UK Central Graben area have enabled a detailed palynostratigraphic framework to be established within the Forties Sandstone Member. This comprises thirteen subzones, based upon the frequency distributions of dinocyst and miospore taxa. High quality sample preparation and data analysis is key to the success of this scheme. The framework facilitates subdivision of the Forties Sandstone Member in to a number of sedimentary packages and promotes recognition of offset stacking patterns, both locally (intra-field) and on a regional scale. This stacked system of sands can be broadly subdivided in to three main cycles or ‘parasequences’. The application of this robust stratigraphic framework has enabled asset teams to refine their reservoir models, promoting more accurate prediction of sand fairways, sedimentary facies and reservoir properties. This has assisted with the planning of development wells and, through the ‘real time’ application of the palynostratigraphic framework at the wellsite, has had significant impact on drilling operations. Palynology is now widely employed to help pick casing points, coring points, well TDs and, not least, to ‘biosteer’ long reach deviated well paths within targeted ‘sweet zones’
Applications of ‘near real time’ chemostratigraphy at wellsite
Neil W. Craigie, Ichron Ltd
Chemostratigraphy is a reservoir correlation tool involving the use of inorganic geochemical data. In the past, it has been used as a conventional laboratory based technique to correlate reservoir intervals that have already been drilled. In more recent years, however, it has become a first choice stratigraphic aid when applied in ‘near real time’ at wellsite. Wellsite chemostratigraphy is used for stratigraphic control while drilling and to aid the placement of coring points, casing points and total depth (TD) picks. Arguably, the most common application of the technique, however, is during geosteering operations/well trajectory monitoring.
The Spectro Xepos portable XRF machine is an ideal analytical instrument for this purpose as it is robust, easy to use, easily transported to wellsite, weighs only 50kg and is capable of generating data for up to 45 elements. Once the cuttings are received, they are washed in liquid detergent to remove drilling additives and dried in an oven. The dried cuttings are then sieved to remove the largest ‘caved’ fragments and ‘picked’ under a microscope to select only the fragments that are considered to be of a representative lithology at a representative depth. The samples are then ground to a fine powder and placed in a sample cup in the XRF machine for geochemical analysis. Full XRF analysis for c.45 elements, including all of the samples preparation, takes around 20 minutes per sample.
Prior to using chemostratigraphy at wellsite, it is necessary to produce a chemostratigraphic framework. This is best achieved by analysing equivalent stratigraphic intervals in two or three wells drilled close to the proposed drilling location. Although more than 40 elements are analysed, typically only 8-12 ‘key’ or ‘index’ elements and ratios are used for chemostratigraphic characterisation/correlation. The distribution of some elements are influenced by variations in source/provenance (e.g. Zr, Hf, Th, Ti), while others may be controlled by changes in depositional environment (e.g. Cu, Co, U, Zn) or weathering/diagenesis (e.g. Al, Rb, Cs).
Ichron Ltd recently used chemostratigraphy to correlate Upper Jurassic sediments in the UK sector of the North Sea. The chemostratigraphic scheme, relating to the analyses of samples from 3 wells, is based on variations in K, Zr and U, which reflect the proportions of K feldspar, zircon and U-bearing heavy minerals respectively. After completion of the pilot study, the technique was used at wellsite to aid the placement of a casing point immediately above the reservoir interval and for geosteering purposes within the reservoir itself. In addition to this study, Ichron Ltd have also used the technique as a stratigraphic aid during drilling of the Lower Jurassic Statfjord Formation in the northern North Sea (UKCS) and in Permian and Carboniferous reservoirs of the southern North Sea (Dutch Sector).
HPHT Wells on Haltenbank: The Role of Micropalaeontology in Planning and Drilling Wells on the Kristin Field
Alex Cullum, Statoil & Pete Mears RPS Energy
Biostratigraphy is making a significant contribution to value creation when planning and drilling wells. The biosteering of production wells provides the support to enable operators to drill more ambitious and technically challenging wells with increased levels of confidence. Precise stratigraphic control whilst drilling increases safety, saves money and greatly increases the long term potential of production wells at relatively small cost.
The Kristin Field, operated by Statoil, straddles NOCS Blocks 6406/2 and 6506/11 in the Haltenbank area of the Norwegian Sea. The primary reservoir unit is the Middle Jurassic Garn Formation, which lies between 4500m and 5000m TVD subsea. It is pressured at +/- 910 bar and has temperatures of around 170°C. The reservoir is therefore classified as High Pressure/High Temperature (HPHT).
The field is currently under development utilising 12 highly deviated and horizontal production wells that are technically challenging and expensive to drill. Biostratigraphy, and in particular micropalaeontology, is helping with both of these issues by providing detailed realtime wellsite stratigraphic support, increasing confidence in the placement of casing shoes, ensuring wells are landed at the correct stratigraphic level/hole angle, and by negating the necessity for costly lookahead VSP’s.
Depth of burial/thermal maturity precludes the use of palynology through most of the Kristin Mesozoic well sections. Micropalaeontology has therefore been utilised as a stand-alone tool for stratigraphic calibration of the Late Cretaceous Intra Lange Sands, the Early Cretaceous ‘Albian Shale’ and the Middle Jurassic Melke Formation, all of which are critical in terms of drilling operations on the field.
Don’t tell the boss- Increasing Resolution in Exploration Biostratigraphy
Felix M.Gradstein, Geology Museum, University of Oslo, Norway
A combination of Ranking & Scaling (RASC) and Constrained Optimization (CONOP) can be used to rapidly rank fossil events according to goodness of correlation. Stratigraphic crossplots of the zonal results with the two methods show which events do not deviate much their stratigraphic position from well to well, and which ones do. The latter often also have above normal zonal variance. The new methodology solves the problem that conventional zonations do not rank taxa according to the degree of diachroneity of range endpoints in a correlation scheme. Four examples from offshore Norway and Gulf of Mexico illustrate the potential of the method in rapidly ranking fossils according to their stratigraphic fidelity.
New microfacies methods & applications in mudrock characterization & reservoir modelling from the Early Paleocene of Mid Norway
Craig Harvey, A/S Norske Shell & Nicholas Holmes, Ichron Ltd
The Ormen Lange Field was discovered in 1997 and is the second largest gas discovery offshore Norway. Ormen Lange is situated in the Møre Basin and the hydrocarbons now fill a north south trending Paleogene dome structure. The Early Paleocene Egga reservoir unit is widely thought to have been deposited by turbidites in a structurally controlled sub basin. Key to modelling of the Egga reservoir unit and field development is the nature and distribution of associated claystones.
The depositional model and facies relationships within the turbidite sediments of the Ormen Lange Field has been significantly improved through the application and interpretation of foraminiferal facies analysis. The link between highest foraminiferal diversities and hemipelagic claystones has long been established. But new techniques in micropalaeontological facies analysis, presented here, have built upon the ‘Pelagic Index’ to better quantify the transitional facies between muddy turbidite and hemipelagic claystone end members. Recognition and correlation within chronostratigraphic boundaries of transitional claystone characteristics has been applied to the Ormen Lange Field and this has provided information on sequential depositional trends through Egga reservoir units 1, 2 and 3, and lateral changes in claystone character within each unit. Moreover trends of turbidite locus deposition have been identified. As such, integration of the micro-facies data has provided valuable input to the further evaluation of reservoir model scenarios. Using a de-sanded system, modelling of the background claystones has elucidated hitherto unobserved potential reservoir barrier/baffle levels and impacts on fault seal and compartmentalization issues. Microfacies data will also be utilized operationally and impact future well planning and design.
Provenance and Reworking Data as a Tool in refining the Tectono- Stratigraphic History of a Basin: A Case Study from the Norwegian Sea
P.S. MILNER (1), T.R. OLSEN, (1), E.K. HANSEN (1) A.C. MORTON (2) and A.G. WHITHAM, (3)
1 BP Norge, Godesetdalen 8, P.O.Box 197, N-4065 Stavanger, Norway
2 HM Research Assocs., 100 Main Street, Woodhouse Eaves, Leics LE12 8RZ, U.K
3 CASP, West Building, 181a Huntingdon Road, Cambridge CB3, ODJ, U.K
Provenance studies in the Norwegian Sea (Figure 1) have been integrated alongside other disciplines in order to address key issues of reservoir distribution in the Upper Cretaceous. An understanding of uplift, erosion and the potential for transport of turbiditic sandstones from East Greenland and Norway is fundamental to the prediction of reservoir distribution in the Norwegian Sea. In particular, integration of subcrop with provenance and reworking data has impacted the understanding of the tectono-stratigraphic history of the area, providing more information about the depositional history of both the basin and source areas. The combination of heavy minerals and palynological reworking analysis is considered complementary and provides provenance information from both sandstones and shales. This combination has identified more provenance areas than would have been identified through application of only one of the disciplines. The analyses are also independent of each other and are therefore ideal for testing and checking the results of one against the other. Examples from the East Greenland/Vøring Basin-Nordland Ridge area demonstrate both stratigraphic and geographic variations in provenance during the Campanian-Maastrichtian. This reflects the changing influence of uplift and erosion of the major sediment sources of East Greenland, the Nordland Ridge and the Norwegian margin during the Late Cretaceous. The potential exists for a wider application of these techniques in areas outside of Mid Norway.
Figure 1. Norwegian Sea Location andStructure map (Modified from Blystad et al., 1995)