Offshore Canada Research Articles

Xyloplax princealberti (Asteroidea, Echinodermata): A New Species That Is Not Always Associated with Wood Falls

Xyloplax is a genus of three species of sea stars previously found only on sunken wood in the deep ocean. Their circular and petaloid bodies, which lend them their common name “sea daisy”, and their presumed exclusive diet of wood make them an unusual and rare element of deep-sea ecosystems. We describe here the fourth species of Xyloplax from the eastern Pacific Ocean, Xyloplax princealberti n. sp., which ranges from offshore Canada to the Gulf of California (Mexico) and Costa Rica. Though sampled geographically close to another described species of Xyloplax from the northeastern Pacific, X. janetae, this new species is unique morphologically and according to available DNA data. The short abactinal spines are the most obvious feature that distinguishes X. princealberti n. sp. from other Xyloplax. The minimum distance for mitochondrial cytochrome c oxidase subunit I from Xyloplax princealberti n. sp. to the only other available Xyloplax, X. janetae, was 13.5%. We also describe Ridgeia vestimentiferan tubeworm bushes from active hydrothermal vents as a new Xyloplax habitat, the first record of a non-wood substrate, and a new reproductive strategy, simultaneous hermaphroditism, for this genus. We generated the first mitochondrial genome for a member of Xyloplax and analyzed it with other available asteroid data using nucleotide-coding or amino acid (for protein-coding genes) plus nucleotide coding (for rRNA genes). The nucleotide-coding results place Xylopax as part of the clade Velatida, consistent with a previous phylogenomic analysis that included Xyloplax princealberti n. sp. (as Xyloplax sp.), though the placement of Velatida within Asteroidea differed. The amino acid plus nucleotide coding recovered Velatida to be a grade with X. princealberti n. sp. as sister group to all other Asteroidea.

The role of calcite mineral elastic moduli in carbonate rock physics

Rock-physics models for carbonate reservoirs assume that the mineral elastic moduli are known variables. A review of publications reveals a range of values for calcite that are out of date and misleading. We present a robust compilation for future investigations. We subsequently discuss the application of calcite elastic moduli for rock-physics modeling and interpretation of wireline data through a case study data set from an offshore Canada carbonate reservoir. The data set exhibits an offset between the zero-porosity intercept and the calcite elastic moduli values. Our experience indicates that this phenomenon is present in many wireline data sets from carbonate reservoirs around the world. We demonstrate that the data can be reconciled to the mineral elastic moduli through the interpretation of microcracks in the formation (defined by a crack density of 0.06). Understanding the microcrack effect in relatively low-porosity formations is important for the correct calibration of pore microstructure parameters and for fluid-substitution calculations. Results in the case study data set show a relatively high sensitivity to changes in fluid saturation. The sensitivity can be reduced through the use of effective mineral elastic moduli that are derived from the data. We justify the effective mineral elastic moduli as a representation of the mineral moduli plus microcracks. The effective mineral elastic moduli are proposed as a relatively simple method to constrain the fluid substitution calculations in low-porosity formations where microcracks are present.

Salt geometry in the Central Basin of the Nova Scotia passive margin, offshore Canada based on new seismic data

This study describes the structural architecture of the central portion of the Scotian Basin and focusses on Mesozoic salt deposition and deformation linked to magma-rich rifting. BP acquired a high-quality 3D seismic survey called the Tangier survey and built a detailed velocity model with RFWI (Reflection Full Waveform Inversion) and tomography. This has allowed for high resolution seismic imaging of target sedimentary reservoirs but also for the first time, imaging of the complex crustal architecture along the central part of the Nova Scotia margin. We evaluated the regional basin architecture and salt tectonic evolution in context of Late Triassic and Early Jurassic rifting followed by passive margin gravity spreading. An exploration well (Aspy D-11) was drilled based on the 3D seismic interpretation and penetrated halite, carnallite and anhydrite salt in an allochthonous salt sheet. Basement is thought to have rifted during deposition of interlayered halite, shale, carnallite and anhydrite. Carnallite may have precipitated from enriched brines that formed at the more distal (southern) end of an elongated seaway of rifted basins which began opening first in the North in the Late Triassic and propagated southward towards Florida (e.g., Jansa, 1980; Jansa and Tucholke, 1986; Roberts and Bally, 2012). Water flowed southwards from Tethys along a chain of complexly interconnected areas of rifted basins. Flow of seawater along Nova Scotia is interpreted to have been southward along a widening and progressively subsiding region of rifts possibly as dynamic elevation associated with the CAMP (Central Atlantic Magmatic Province) dissipated southward much like what occurred in the Central South Atlantic and Gulf of Mexico (GoM) (e.g., Quirk et al., 2013; Morgan et al., 2020; Pindell et al., 2020; Pindell and Heyn, 2022). Brine was enriched along the seaway by evaporation, causing deposition of the most-soluble salt components furthest south along the sequence of basins. The presence of weathered basalt in salt and SDRs on the seismic supports magma-rich Mesozoic rifting and suggests that heating of brine pools may not have been exclusively caused by the sun, but that hydrothermal systems probably contributed to heating and the precipitation of Carnallite.

Crustal structure and tectonic evolution of the Newfoundland Ridge, Fogo Basin, and southern Newfoundland transform margin

The southern Newfoundland transform margin is a crustal-scale transfer zone that juxtaposes continental crust of the Grand Banks with the oceanic domain of the Fogo Basin, offshore SE Newfoundland. This crustal feature is generally accepted as a left-lateral transfer zone between the much-studied Scotian and Newfoundland margins, but relatively little is known about either its crustal-scale architecture or tectonic evolution. Interpretation of newly available regional seismic data from the Newfoundland Ridge and Fogo Basin, offshore Canada provides evidence for approximately 500 km of left-lateral displacement and associated segmented extension between the Late Triassic (210 Ma) and latest Jurassic (145 Ma) as a result of differential extension rates between the conjugate margins of Nova Scotia–Morocco and Newfoundland (Grand Banks)–Iberia. We show that the southern Newfoundland transform margin represents a 100–150 km wide zone of distributed left-lateral displacement across extended continental crust at the SW edge of the Grand Banks, and that crust beneath the Newfoundland Ridge and Fogo Basin is unlikely to be oceanic in origin. Kinematic restorations of regional cross sections and crustal area balancing provide the basis for map-based reconstructions of the area. Our results, which integrate existing plate reconstructions, crustal thickness data, and established age relationships, help to constrain the early structural evolution of the North Atlantic as the African and North American plates separated during Triassic to Jurassic rifting.

An Insight of Salt Deposition and Evolution in the Central Basin of the Nova Scotia Passive Margin, Offshore Canada

An Insight of Salt Deposition and Evolution in the Central Basin of the Nova Scotia Passive Margin, Offshore Canada

E&P Notes (December 2020)

E&P Notes (December 2020)

Definition of the Churchill River Delta and its petroleum potential, offshore Labrador, Canada

Starting in 2011, a multiyear modern 2D long offset broadband seismic survey was acquired offshore Labrador, Canada, by TGS and PGS in partnership with Nalcor Energy. This regional survey covers the slope and deepwater portions of the margin. Three Mesozoic and Cenozoic-aged basins were informally defined from these data, the Chidley, Henley, and Holton; also, the poorly constrained Hawke Basin was remapped. The 2D data set imaged for the first time a very large Cenozoic-aged delta adjacent to the mouth of Lake Melville. We have mapped this delta on a [Formula: see text] 2D seismic grid. The delta is 5–8 km thick, and its aerial extent is [Formula: see text]. The age of this delta has been interpreted to be Eocene to Miocene. Adjacent to this Cenozoic delta on the Labrador shelf, there is a working petroleum system within the proximal Hopedale and Saglek Basins where there are five gas discoveries and one oil discovery. The modern long-offset 2D data set appears to indicate a working petroleum system within the newly mapped Cenozoic delta, and two phases of hydrocarbons may be present.

Pore Network Changes Due to Polymer Flooding: Hebron Field Case

A preliminary enhanced oil recovery (EOR) screening was completed for the Ben Nevis Formation, Hebron Field, offshore Canada. Polymer flooding was determined to be the most viable methodology based...

Investigating the Goban Spur rifted continental margin, offshore Ireland, through integration of new seismic reflection and potential field data

The Goban Spur, offshore Ireland, is a magma-poor rifted continental margin conjugate to the well-studied Newfoundland margin, offshore Canada. Published studies demonstrated that a 70-km-wide zone of exhumed serpentinized mantle lies between oceanic crust and stretched continental crust at the seaward limit of Goban Spur. However, the along-strike extent of this serpentinized zone has, until now, been unknown due to insufficient data coverage. The crustal architecture of the margin is complicated due to its multi-staged tectonic history. Here, six newly acquired multi-channel seismic reflection lines are processed and interpreted, along with vintage seismic profiles, to characterize its structure and evolution. These seismic profiles reveal significant along-strike structural variations along the Goban Spur margin, and allow us to delimit five distinct crustal zones related to different rifting stages and their regional extents. The geometries of each crustal domain are variable along the margin strike, probably suggestive of different extension rates during the evolution of the margin or inherited variations in crustal composition and rheology. The transitional zone between oceanic crust and stretched continental crust consists of both shallow peridotite ridges and deeper exhumed serpentinized mantle, much like the conjugate Iberian and Newfoundland margins. Above the top basement in the exhumed domain, the syn-exhumed sediments show strikingly weak reflectivity, rarely seen at other magma-poor margins. Magmatic events occur coincident with each rifting stage, and the volume of magmatic accretions increases from NW to SE, more than previously interpreted. Plate reconstruction of the Goban Spur and its possible conjugate – the Flemish Cap, shows asymmetry in the crustal architectures, likely due to rift evolution involving more 3-D complexity than can be explained by simple 2-D extensional kinematics.

Submarine canyon-fill reconstruction from integrated seismic-stratigraphic analysis – application to Banquereau formation, Scotian basin – offshore Canada.

Building geological models (integrating stratigraphic, structural and paleo-environmental 3D models) that allow the interpretation of sand bodies deposited by turbidity currents along submarine canyons or channels, is one of the most useful tools used by geoscientists for the definition of new drilling opportunities in both exploration and development phases. In this context, the integration of methodologies such as sequence stratigraphyand seismic attributes, together with well-log and core information, outline the basis for the interpretation of sand-body lithostratigraphy and chronostratigraphy. Similarly, these models allow the interpreter to reconstruct the depositional environment and deformation history of a sedimentary basin [1]. Based on a series of chronostratigraphic stages, this paper proposes a 3D model for the sedimentation history of the Banquereau Formation.This model is based on the integration of seismic stratigraphy, seismic attribute interpretation and well-log analysis. Also, a set of system tracts and corresponding transgression and regression phases were identified for the sedimentary interval of interest. The available dataset provided the information to identify the geometry and changes in the sedimentation patterns of the stratigraphic sequences from the Tertiary to the present, thus defining a 3D model of the sedimentological and structural architecture of this interval. Last but not least, theresulting 3D stratigraphic model made possible the identification and description of an amalgamated channel complex filling a submarine canyon associated with a fluvio-deltaic setting. This sort of analysis might be used as an analog for similar reservoirs, providing key insights and vital information for decision making.

Numerical modelling and evacuation strategies for tsunami awareness: lessons from the 2012 Haida Gwaii Tsunami

On October 28, 2012, an earthquake occurred offshore Canada, with a magnitude Mw of 7.8, triggering a tsunami that propagated through the Pacific Ocean. The tsunami numerical model results show it would not be expected to generate widespread inundation on Hawaii. Yet, two hours after the earthquake, the Pacific Tsunami Warning Centre (PTWC) issued a tsunami warning to the state of Hawaii. Since the state was hit by several tsunamis in the past, regular siren exercises, tsunami hazard maps and other prevention measures are available for public use, revealing that residents are well prepared regarding tsunami evacuation procedures. Nevertheless, residents and tourists evacuated mostly by car, and because of that, heavy traffic was reported, showing that it was a non-viable option for evacuation. The tsunami caused minor damages on the coastline, and several car accidents were reported, with one fatality. In recent years, there has been a remarkable interest in tsunami impacts. However, if risk planners seem to be very knowledgeable about how to avoid or mitigate their potential harmful effects, they seem to disregard its integration with other sectors of human activity and other social factors.

Pacific‐North America plate boundary reorganization in response to a change in relative plate motion: Offshore Canada

The transition from subduction in Cascadia to the transform Queen Charlotte fault along western Canada is often drawn as a subduction zone, yet recent studies of GPS and earthquake data from northern Vancouver Island are not consistent with that model. In this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of (1) microplate subduction and (2) reorganization of the preexisting strike‐slip plate boundary. We focus on the critical region of outer Queen Charlotte Sound and the adjacent offshore. On much of the continental shelf, several million years of subsidence above thin crust are a counterindicator for subduction. An undated episode of compression uplifted the southernmost shelf, but subsidence patterns offshore show that recent subduction is unlikely to be responsible. Previously unremarked near‐vertical faults and a mix of extensional and compressional faults offshore indicate that strike‐slip faulting has been a significant mode of deformation. Seismicity in the last 18 years is dominantly strike‐slip and shows large amounts of moment release on the Revere‐Dellwood fault and its overlap with the Queen Charlotte fault. The relative plate motion between the Pacific and North American plates rotated clockwise ∼6 Ma and appears to have triggered formation of an evolving array of structures. We suggest that the paleo‐Queen Charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed Revere Dellwood fault propagated to the northwest.

Basalt sills of the U reflector, Newfoundland Basin: A serendipitous dating technique

Research Article| December 01, 2005 Basalt sills of the U reflector, Newfoundland Basin: A serendipitous dating technique Garry D. Karner; Garry D. Karner 1Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar Donna J. Shillington Donna J. Shillington 2National Oceanography Centre, Southampton, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Garry D. Karner 1Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA Donna J. Shillington 2National Oceanography Centre, Southampton, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK Publisher: Geological Society of America Received: 16 Jun 2005 Revision Received: 11 Aug 2005 Accepted: 12 Aug 2005 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2005) 33 (12): 985–988. https://doi.org/10.1130/G21971.1 Article history Received: 16 Jun 2005 Revision Received: 11 Aug 2005 Accepted: 12 Aug 2005 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Garry D. Karner, Donna J. Shillington; Basalt sills of the U reflector, Newfoundland Basin: A serendipitous dating technique. Geology 2005;; 33 (12): 985–988. doi: https://doi.org/10.1130/G21971.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract High core recovery at Ocean Drilling Program (ODP) Leg 210, Site 1276, provided a high-resolution porosity-depth relationship and an equally impressive age-depth model based on first and last occurrences of microfossils. Site 1276 was drilled over transitional crust in the Newfoundland nonvolcanic margin, offshore Canada, between known continental crust on the west and apparent oceanic crust on the east as identified by seafloor-spreading magnetic anomalies M3 to M0 (Barremian–Aptian, 129.8–124.8 Ma). At Site 1276, two diabase sills were drilled at depths equivalent to the U reflection, a bright reflection that overlies transitional crust interpreted from seismic reflection profiles throughout the Newfoundland Basin. The sills were emplaced within uppermost Aptian fine- to coarse-grained sediments, 100–200 m above basement as estimated from seismic reflection data. Magma emplacement occurred at shallow levels within the sediment column, as evidenced by: (1) the occurrence of vesicles in the sill, and (2) compaction-induced folding of calcite veins that were emplaced near vertically in the sediments and are assumed to be coeval with the intrusion. By calculating the degree of shortening of the calcite veins and determining the reconstructed porosity of the sediments during vein emplacement, the age of magma emplacement can be deduced. From the porosity-age curve, the age of sill emplacement is estimated to be 82.5–109.1 Ma, consistent with recent 40Ar/39Ar radiometric dating of the upper sill that gave ages of 105.95 ± 1.78 Ma and 104.7 ± 1.7 Ma. The source of magmatism responsible for the diabase sills is necessarily postrift, and the sills are temporally equivalent to alkali basalts dredged from the Newfoundland Seamounts. The simplest explanation for the Site 1276 diabases and the widespread distribution of the U reflection relates to the migration of the Azores, Madeira, and Canary plumes across the Newfoundland Basin between 80 and 120 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

NOAA efforts in monitoring of low-frequency sound in the global ocean

Since August 1991, NOAA/PMEL has collected continuous recordings from the U.S. Navy SOSUS arrays in the North Pacific. In May 1996, this effort was expanded through the use of PMEL-developed autonomous hydrophones deployed in the eastern equatorial Pacific, and later to the central North Atlantic between 15N and 35N (March 1999), the Gulf of Alaska (October 1999), and the North Atlantic between 40N and 50N (June 2002). Natural seismicity in the Pacific produces nearly 10<th>000 events per year with source levels exceeding 200 dB (re: 1 micro-Pa @ 1 m), with about 3500 events per year exceeding this level in the North Atlantic. Significant contributions from manmade sources are present throughout the data but have not been quantified. Recordings from North Atlantic arrays are dominated by noise from seismic airgun profilers working offshore Canada, Brazil, and west Africa. In September 2001, a cabled vertical hydrophone array was installed at Pioneer Seamount, offshore central California, which will provide continuous, unclassified acoustic data (in the range of 1–450 Hz) to the research community in real time. Future plans call for the expansion of the NOAA monitoring effort to other opportunities worldwide and making the raw data available to the community via the Internet.

Physical Properties of Reservoirs Using an Artificial Neural Network Approach: Example from the Jeanne d'Arc Basin, Eastern Offshore Canada: ABSTRACT

Quantitative statements of the evolution of petroleum systems in the Jeanne d`Arc Basin provides a solid basis for future exploration, reservoir modelling, reservoir development and resource management. As a contribution to such statements, we have integrated physical property measurements (porosity and permeability) and well log data from the major reservoir intervals throughout the basin using an efficient backpropagation artificial neural network (BP-ANN) modified with the Marquardt algorithm. The bulk of the data are from the Avalon Formation (13 wells), the Hibernia Formation (7 wells) and the Jeanne d`Arc Formation (12 wells). After data preprocessing and training/supervising example preparation, a model for the relationship of physical property and well log response was established with the BP-ANN technique. Test of the BP-ANN model in other Mesozoic reservoir intervals in the same basin whose data were not used as the training and supervising examples shows good agreement between the measured and predicted values. The BP-ANN model established was used to construct permeability porosity profiles in 40 wells for the Avalon Formation, 36 wells for the Hibernia Formation and 37 wells for the Jeanne d`Arc Formation from well logs. These profiles offer a more complete basis for understanding physical properties of reservoir intervals ofmore » this basin. They allow a detailed review of vertical and horizontal variations of physical properties in key areas of this basin.« less

Mesozoic stratigraphy of the Goban Spur, offshore south-west Ireland

A Mesozoic stratigraphic framework for the Goban Spur, offshore Ireland is proposed based on results of the 62/7-1 well. This study integrates the well, Deep Sea Drilling Project data and 3000 km of seismic profiles into a stratigraphic analysis showing vertical and lateral associations of facies in the Mesozoic evolution of the basin. Basin development is believed to have been initiated during the Triassic. The discussed geological section is restricted to the Sinemurian to Maastrichtian interval. Two major hiatuses are recognized with the Late Jurassic and the Turonian absent. They reflect the ‘Middle Cimmerian’ predominantly tectonic event and a mid-Cretaceous predominantly eustatic event, respectively. Significant Middle Jurassic volcanic activity is associated with the Middle Cimmerian tectonism. The breakup unconformity is present between Late Barremian or Early Aptian and Early Albian deposits. Detailed biostratigraphic analyses and palaeoenvironmental interpretations indicate close affinities with adjacent offshore southern Ireland, southern England and eastern offshore Canada. Implications for hydrocarbon exploration are discussed with particular emphasis on the potential source and reservoir characteristics.

Dipping shear zones and the base of the crust in the Appalachians, offshore Canada

The Seismological character of the Appalachian mobile belt offshore from eastern Canada includes an unusual concentration of northwest-dipping reflectors which appear to dip through sub-horizontal reflectors at the base of the crust. The geometry of these structures has been characterised by ray-trace migration. They are not point diffractors. They appear to dip at between 25 and 45°, but flatten upwards towards a mid-crustal “bright” band and disappear downwards into the mantle. We interpret the reflectors as shear zones which ramp through the lower crust from a mid-crustal detachment to a diffuse and less reflective set of shears in the mantle. It is suggested that the reflectors were caused by the collision of continental blocks at the final closure of the Iapetus Ocean, but may have been subject to later reactivation, especially during late Carboniferous strike-slip.

Fault reactivation during Mesozoic extension in eastern offshore Canada

New Seismic data are presented that document reactivation of a thrust fault as a normal fault. Four deep Seismic reflection profiles now straddle the Hibernia oil field region of the Grand Banks off eastern Canada. The profiles intersect each other near the western edge of the 22 km deep Jeanne d'Arc Basin, thereby giving a three-dimensional picture of basement structures. The basin-bounding fault which marks the eastern edge of the Bonavista platform appears to follow a pre-existing fault system. More precisely, the fault that bounds the Jeanne d'Arc Basin just north of Hibernia can be traced on the Seismic data along strike to the south, beneath the Bonavista platform, where it has not been reactivated. The Seismic data show that this feature was probably a Palaeozoic thrust fault. A laterally extensive Palaeozoic(?) basin occupies most of the Bonavista platform. The deeper part of the crust is quite reflective and is characterized by numerous, dipping reflective packages.This detailed study of the Hibernia region suggests that the narrow elongated basins of the Grand Banks may have been formed within the reactivated hanging walls of older thrust sheets. Similar observations have been made for the Mesozoic extensional basins of the U.K. continental shelf. The pre-Mesozoic compressional structures documemed on the central Grand Banks lie along the Appalachian Orogen and may be of Variscan age.

Performance Of Oil-Based Drilling Fluids On Offshore Canadian Lands

Abstract In 1985, Esso Resources Canada Limited successfully introduced oil-based drilling fluids to their Beau/ort Sea and East Coast operations. During the past two years, Esso Resources has drilled a total of six offshore wells using these mud systems. The performance of oil-based drilling fluids, on these wells, will be reviewed with respect to the primary objectives of eliminating wellbore instability and increasing wellbore lubricity. The use of this technology has proven to be very successful and it is recommended for future drilling on Offshore Canada Lands. Introduction Esso Resources Canada Limited (ERCL) recently drilled six offshore wells using a variety of low-toxicity, invert emulsion oil-based muds. Two of these wells were drilled off the East Coast of Newfoundland and four were drilled in the Beaufort Sea. Oil-based mud was determined to be a cost-effective method of reducing the problem time associated with historically troublesome formations. Two of the Beaufort Sea locations were drilled to angles in excess of 55 degrees. At these wells, the oil-based mud proved to be very effective at preventingtorque and drag problems. Oil-based mud has been used world-wide to prevent hole problems(1). The goal of this paper is to summarize the operating experience gained by ERCL(2), and to highlight the benefits observed. East Coast Operations Baccalieu 1–78/ Kyle L-11 ERCL, in partnership with fourteen companies, re-entered the East Coast drilling scene in 1985. As operator, ERCL was responsible for the planning and implementation of a two-well program in the Flemish Pass. Baccalieu 1–78 and Kyle L-11 were drilled in 1985 and 1986 respectively (Fig. 1). Oil-based mud was used at these two locations primarily because of serious wellbore instability which had occurred at the nearest control well, Gabriel C-60. At Gabriel, a massive shale interval below 4500 mKB sloughed severely in the presence of a seawater-bentonite drilling fluid. This problem resulted in extensive reaming and eventually stuck pipe. Increased reaming time on successive trips indicated that the sloughing problem was increasing in severity, and the well was finally abandoned before it had stabilized. Geological evaluation of Gabriel was difficult because the sloughing wellbore hampered cuttings correlation and the rugose nature of the hole resulted in extremely poor wireline log information. The troublesome shale encountered at Gabriel posed a more serious threat to the successful drilling and evaluation of Baccalieu and Kyle because a greater portion of each wellbore would be located below the shale. A study to determine the nature of the sloughing was initiated so that a repeat of the problem encountered at Gabriel could be prevented. Shale samples taken from Gabriel were analyzed using x-ray diffraction and were found to be predominantly illitic in composition These hard brittle shales are known to develop extremely high swelling pressure when exposed to water(3). It was concluded that the sloughing at Gabriel was likely caused by shale hydration and subsequent rock failure. Abnormal pore pressure or abnormal tectonic stresses did not appear to be the likely causes of the sloughing problem.

1983 AGS Symposium: The origin, history and potential of sedimentary basins in eastern and offshore Canada

1983 AGS Symposium: The origin, history and potential of sedimentary basins in eastern and offshore Canada