Northwest Coast Of Australia Research Articles

Innovative structural engineering and execution approach to delivering modular facilities for the Gorgon Project

The Gorgon Project on Barrow Island, located about 60 km from the northwest coast of Australia, was given the green light in September 2009. Construction and commissioning of the Gorgon LNG trains is limited to a 300 hectare development on a Class A reserve. Our commitment to the environment has driven our use of extensive modularisation to build the LNG trains. All of the major components have been pre-fabricated and assembled offsite into transportable parts,“ significantly reducing our footprint on the island. Subsequently the structural modules (including pre-assembled Piperacks) have undertaken a journey on a scale and complexity unmatched in the global LNG industry. The modules have been designed and built at diversely located engineering, fabrication and construction sites. These are then loaded out and sea transported from different international shipyards in more than 6. sea-transportation voyages, carrying more than 300 modules weighing more than 280,000 tonnes under constantly varying and hostile sea-faring conditions. The modules reach their final destination at Barrow Island to be installed without impacting the island’s uniquely treasured flora and fauna. These modules are designed to operate for its entire service life on cyclone-rated Barrow Island, which in the past has registered the highest ever wind gust of 408 kmph. Design and execution of the modules to sustain severe environmental conditions during its service lifecycle has been made possible by employing an innovative engineering mindset supported by robust structural methodologies to develop suitable facilities that can operate in a highly complex environment. This extended abstract showcases the structural engineering and execution methodologies that successfully overcame the challenging journey of the modules, thereby delivering a world class development co-existing with conservation in a pristine nature reserve on a very limited footprint.

Abundance indices for long-lived tropical snappers: estimating standardized catch rates from spatially and temporally coarse logbook data

Abstract The Northern Demersal Scalefish Fishery has historically comprised a small fleet (≤10 vessels year−1) operating over a relatively large area off the northwest coast of Australia. This multispecies fishery primarily harvests two species of snapper: goldband snapper, Pristipomoides multidens and red emperor, Lutjanus sebae. A key input to age-structured assessments of these stocks has been the annual time-series of the catch rate. We used an approach that combined Generalized Linear Models, spatio-temporal imputation, and computer-intensive methods to standardize the fishery catch rates and report uncertainty in the indices. These analyses, which represent one of the first attempts to standardize fish trap catch rates, were also augmented to gain additional insights into the effects of targeting, historical effort creep, and spatio-temporal resolution of catch and effort data on trap fishery dynamics. Results from monthly reported catches (i.e. 1993 on) were compared with those reported daily from more recently (i.e. 2008 on) enhanced catch and effort logbooks. Model effects of catches of one species on the catch rates of another became more conspicuous when the daily data were analysed and produced estimates with greater precision. The rate of putative effort creep estimated for standardized catch rates was much lower than estimated for nominal catch rates. These results therefore demonstrate how important additional insights into fishery and fish population dynamics can be elucidated from such “pre-assessment” analyses.

Wave‐cloud lines over northwest Australia

AbstractThe frequency of occurrence and formation mechanisms of wave‐cloud lines off the northwest coast of Australia are investigated. Prior to the present study, little was known about these wave‐cloud lines. Apart from being spectacular atmospheric phenomenon in their own right, these wave clouds can have a role in the secondary initiation of convection and can be a hazard to low‐flying aircraft. A climatology of wave clouds, produced from visible satellite imagery, suggests two main types of cloud lines form over northwest Australia. The first are bore‐like waves, similar in structure to the ‘morning glory’ of northeast Australia, and occur at least 2 to 3 times per month throughout the entire year. The second type are convectively generated cloud lines, which are more circular in shape, appear to originate from convective storms and occur at least 0.5 to 1.5 times per month during the wet season. High‐resolution, nested simulations are performed with the Met Office Unified Model for case‐studies of each type of wave. The bore‐like waves occurred in the presence of synoptic‐scale, low‐level southeasterly flow and a heat low along the northwest coast of Australia. At night, the offshore southeasterlies accelerate into the heat low and collide with the onshore sea breeze. The southeasterlies override the sea breeze and the wave‐cloud lines form at the leading edge of this front. The convectively generated waves radiate outwards from the convective storms producing compensating subsidence and adiabatic warming. These waves take the form of n=2 mode wave fronts, which span the entire depth of the troposphere and are similar in structure to waves produced by deep convection which are described in previous studies.

Marine CSEM of the Scarborough gas field, Part 1: Experimental design and data uncertainty

We describe the planning, processing, and uncertainty analysis for a marine CSEM survey of the Scarborough gas field off the northwest coast of Australia, consisting of 20 transmitter tow lines and 144 deployments positioned along a dense 2D profile and a complex 3D grid. The purpose of this survey was to collect a high-quality data set over a known hydrocarbon prospect and use it to further the development of CSEM as a hydrocarbon mapping tool. Recent improvements in navigation and processing techniques yielded high-quality frequency domain data. Data pseudosections exhibit a significant anomaly that is laterally confined within the known reservoir location. Perturbation analysis of the uncertainties in the transmitter parameters yielded predicted uncertainties in amplitude and phase of just a few percent at close ranges. These uncertainties may, however, be underestimated. We introduce a method for more accurately deriving uncertainties using a line of receivers towed twice in opposite directions. Comparing the residuals for each line yields a Gaussian distribution directly related to the aggregate uncertainty of the transmitter parameters. Constraints on systematic error in the transmitter antenna dip and inline range can be calculated by perturbation analysis. Uncertainties are not equal in amplitude and phase, suggesting that inversion of these data would be better suited in these components rather than in real and imaginary components. One-dimensional inversion showed that the reservoir and a confounding resistive layer above it cannot be separately resolved even when the roughness constraint is modified to allow for jumps in resistivity and prejudices are provided, indicating that this level of detail is beyond the single-site CSEM data. Further, when range-dependent error bars are used, the resolution decreases at a shallower depth than when a fixed-error level is used.

Operator competence and capacity – Lessons from the Montara blowout

The blowout of the Montara H1 well in the Timor Sea off the northwest coast of Australia in August 2009 was the first such incident in Australian offshore waters for 25 years. This article seeks to draw lessons for management of complex hazardous activities from these events by analysing critical decisions regarding well control barriers. Concepts such as trial and error learning, sensemaking and the need for multiple barriers are used to demonstrate why the organisation was blind to the developing problems and hence why lack of technical competence alone is not sufficient to explain the events that occurred. Three organisational improvements are proposed – providing active supervision, improved technical integrity assurance and better use of risk assessment. The article concludes with an appeal for changes in regulatory policy regarding safety to include organisational issues in addition to the traditional technical focus.

Multiscale Interactions in the Life Cycle of a Tropical Cyclone Simulated in a Global Cloud-System-Resolving Model. Part I: Large-Scale and Storm-Scale Evolutions*

Abstract The Nonhydrostatic Icosahedral Atmospheric Model (NICAM), a global cloud-system-resolving model, successfully simulated the life cycle of Tropical Storm Isobel that formed over the Timor Sea in the austral summer of 2006. The multiscale interactions in the life cycle of the simulated storm were analyzed in this study. The large-scale aspects that affected Isobel’s life cycle are documented in this paper and the corresponding mesoscale processes are documented in a companion paper. The life cycle of Isobel was largely controlled by a Madden–Julian oscillation (MJO) event and the associated westerly wind burst (WWB). The MJO was found to have both positive and negative effects on the tropical cyclone intensity depending on the location of the storm relative to the WWB center associated with the MJO. The large-scale low-level convergence and high convective available potential energy (CAPE) downwind of the WWB center provided a favorable region to the cyclogenesis and intensification, whereas the strong large-scale stretching deformation field upwind of the WWB center may weaken the storm by exciting wavenumber-2 asymmetries in the eyewall and leading to the eyewall breakdown. Five stages are identified for the life cycle of the simulated Isobel: the initial eddy, intensifying, temporary weakening, reintensifying, and decaying stages. The initial eddy stage was featured by small-scale/mesoscale convective cyclonic vortices developed in the zonally elongated rainband organized in the preconditioned environment characterized by the WWB over the Java Sea associated with the onset of an MJO event over the East Indian Ocean. As the MJO propagated eastward and the cyclonic eddies moved southward into an environment with weak vertical shear and strong low-level cyclonic vorticity, a typical tropical cyclone structure developed over the Java Sea, namely the genesis of Isobel. Isobel experienced an eyewall breakdown and a temporary weakening when it was located upwind of the WWB center as the MJO propagated southeastward and reintensified as its eyewall reformed as a result of the axisymmetrization of an inward spiraling outer rainband that originally formed downwind of the WWB center. Finally Isobel decayed as it approached the northwest coast of Australia.

Seasonal prediction of the Leeuwin Current using the POAMA dynamical seasonal forecast model

The potential for predicting interannual variations of the Leeuwin Current along the west coast of Australia is addressed. The Leeuwin Current flows poleward against the prevailing winds and transports warm-fresh tropical water southward along the coast, which has a great impact on local climate and ecosystems. Variations of the current are tightly tied to El Nino/La Nina (weak during El Nino and strong during La Nina). Skilful seasonal prediction of the Leeuwin Current to 9-month lead time is achieved by empirical downscaling of dynamical coupled model forecasts of El Nino and the associated upper ocean heat content anomalies off the north west coast of Australia from the Australian Bureau of Meteorology Predictive Ocean Atmosphere Model for Australia (POAMA) seasonal forecast system. Prediction of the Leeuwin Current is possible because the heat content fluctuations off the north west coast are the primary driver of interannual annual variations of the current and these heat content variations are tightly tied to the occurrence of El Nino/La Nina. POAMA can skilfully predict both the occurrence of El Nino/La Nina and the subsequent transmission of the heat content anomalies from the Pacific onto the north west coast.

Quantifying FES2004 S2 tidal model from multiple space-geodesy techniques, GPS and GRACE, over North West Australia

Unmodeled sub-daily ocean S2 tide signals that alias into lower frequencies have been detected in the analysis of gravity recovery and climate experiment (GRACE) space gravity fields of GRGS. The most significant global S2 aliased signal occurs off the northwest coast of Australia in a shallow continental shelf zone, a region with high tidal amplitudes at a period of 161 days. The GRACE S2 aliased equivalent water height grids are convolved with Green’s functions to produce GRACE aliased tidal loading (GATL) vertical displacements. The analysis of hourly global positioning system (GPS) vertical coordinate estimates at permanent sites in the region confirms the presence of spectral power at the S2 frequency when the same ocean tide model (FES2004) was used. Thus, deficiencies in the FES2004 ocean tide model are detected both directly and indirectly by the two independent space geodetic techniques. Through simulation, the admittance (ratio of amplitude of spurious long-wavelength output signal in the GRACE time-series to amplitude of unmodeled periodic signals) of the GRACE unmodeled S2 tidal signals, aliased to a 161-day period, is found to have a global average close to 100%, although with substantial spatial variation. Comparing GATL with unmodeled S2 tidal sub-daily signals in the vertical GPS time-series in the region of Broome in NW Australia suggests an admittance of 110–130%.

The Operational Impact of QuikSCAT Winds in Perth, Australia: Examples and Limitations

Abstract The preparation of accurate operational weather forecasts and the timely issuance of severe marine weather and ocean warnings and advisories for major oceanic weather systems impacting both coastal areas and the open ocean are major forecasting problems facing the Australian Bureau of Meteorology’s Regional Forecast Centre (RFC) and its collocated Tropical Cyclone Warning Centre (TCWC) in Perth, Western Australia. The region of responsibility for the Perth RFC is vast, covering a large portion of the southeast Indian and Southern Oceans, both of which are extremely data sparse, especially for near-surface marine wind data. Given that these coastline and open-ocean areas are subject to some of the world’s most intense tropical cyclones, rapidly intensifying midlatitude cyclones, and powerful cold fronts, there is now a heavy reliance upon NASA Quick Scatterometer (QuikSCAT) data for both routine and severe weather warning forecasts. The focus of this note is on the role of QuikSCAT data in the Perth RFC for the accurate and early detection of maritime severe weather systems, both tropical and extratropical. First, the role of QuikSCAT data is described, and then three cases are presented in which the QuikSCAT data were pivotal in providing forecast guidance. The cases are a severe tropical cyclone in its development phase off the northwest coast of Australia, a strong southeast Indian Ocean cold front, and an explosively developing midlatitude Southern Ocean cyclone. In each case, the Perth RFC would have been unable to provide early and high-quality operational forecast and warning guidance without the timely availability of the QuikSCAT surface wind data.

Revealing the reservoir: Integrating seismic survey design, acquisition, processing and inversion to optimize reservoir characterisation.

SummaryThe escalating cost of drilling wells has meant that first class seismic data quality is essential for delineating reservoirs and identifying new well locations in complex geology. This paper describes an integrated workflow which insured that a new 3D seismic dataset acquired off the North West coast of Australia was designed, acquired, processed and simultaneously inverted to produce enhanced sub-surface image quality over a producing field.A desire for enhanced production required the geological understanding of the oil field to be improved. The poor quality of existing seismic data made it impossible to accurately identify the top and base of the prime volume carrying reservoir. A new seismic survey was designed with the specific requirement of improving the interpretability of the reservoir away from the wells. Both legacy seismic data and well data were used to aid in the design of the optimal seismic acquisition parameters. This along with single sensor technology produced excellent field data which were further enhanced by a high-end processing flow and inversion. In particular, advanced noise and multiple attenuation techniques have revealed the top reservoir and other previously unseen geological structures. Simultaneous AVO inversion was used to produce rock property volumes of Acoustic Impedance and Poisson’s Ratio which demonstrated an extremely high correlation with the well logs further proving the quality of the seismic.

The active tropical cyclone season of 2005–2006 over Northwest Australia: Operational model performance and high resolution case studies

There are three main aims of this study. First, the main features of the active 2005–2006 Australian region tropical cyclone (TC) season are summarized, with particular emphasis on the northwest Australian region. Second, an assessment is made of the skill of the available operational global and regional numerical weather prediction (NWP) models for three of the most significant TCs (TCs Clare, Glenda and Hubert), each of which made landfall on the northwest coast of Australia. Third, high-resolution numerical modelling simulations of these same three TCs are described in detail. The numerical weather prediction (NWP) model used here was developed at the University of Oklahoma, and in this study it utilises initial and boundary conditions obtained from archived analyses and forecasts provided by the Australian Bureau of Meteorology, as well as a 4D-Var data assimilation scheme to ingest all available satellite data. The high-resolution numerical model is multiply two-way nested, with the innermost domain having a resolution of 5 km. It was found that unlike the operational models, which were restricted by relatively low resolution and less data, the high resolution model was able to capture most of the major features of all three TC lifecycles including development from initial tropical depressions, intensification, and their tracks, landfall, and associated rainfall and wind fields.

A rare East Indian Ocean autumn season tropical cut-off low: impacts and a high-resolution modelling study

There are two aims of this study. The first is to provide a synoptic description of the lifecycle and impacts of a seasonally rare but intense cut-off low of tropical origin that developed off the northwest coast of Australia, during the Southern Hemisphere autumn months of late April/early May, 2005. The second, and more important, part of this study is an assessment of the capacity of a state-of-the-science numerical model, assimilating all available satellite-derived observational data, to predict the track, intensity, duration, and severe weather that occurred during the life cycle of the cut-off low. The system was unusual in that its initial development occurred over tropical waters and was associated with a strong and highly involuted subtropical jetstream, generating a cloud band that produced record 24 h rainfall totals in northwest Western Australia for this time of the year. The cut-off low then underwent further deepening which produced more unseasonable heavy rainfall. Confirmed tornado reports occurred over the populous southwest corner of Western Australia.

Remote origins of interannual variability in the Indonesian Throughflow region from data and a global Parallel Ocean Program simulation

The mean and interannual variability of the thermal structure of the World Ocean Circulation Experiment (WOCE) repeat IX1‐expendable bathythermograph (XBT) transect between Java and Western Australia were compared statistically for the years 1987–1997 with concurrent, co‐located output from a global eddy‐permitting configuration of the Parallel Ocean Program (POP) model forced with realistic surface fluxes. Dominant variability at long timescales for both model and data in the southern IX1 region was associated with Pacific El Niño–Southern Oscillation (ENSO) events; at the northern end it was due to remote equatorial Indian Ocean forcing and Indian Ocean Dipole Mode events. In the Indo‐Pacific domain the model reproduced the structure and magnitude of observed low‐frequency variability. Event analyses following the warm ENSO phase showed low‐frequency off‐equatorial Rossby waves interacting with the North Pacific western maritime boundary to reflect onto the equator and excite a coastally trapped response that propagated through the Indonesian seas and along the northwest coast of Australia. In turn, the signal progressively propagated away from this coast as free baroclinic Rossby waves to 90°E. Cross‐spectral analyses confirmed that on interannual timescales, both off‐equatorial and equatorial signals remotely forced in the Pacific were largely responsible for the strong observed and modeled variability at the southern end of IX1.

A Numerical Study of the Storm Surge Generated by Tropical Cyclone Jane

Abstract In 1983 Tropical Cyclone Jane crossed the North West Coast of Australia generating a storm surge. Currents associated with this storm surge were recorded at two offshore moorings south of the cyclone track. The data from these moorings are suggestive of the propagation of a continental shelf wave between the two stations. This hypothesis is tested by carrying out a numerical simulation of this storm surge based on the depth-integrated shallow-water equations, with wind-wave-enhanced bottom friction. Analysis of the numerical results shows that the storm surge can be interpreted as due to continental shelf waves.

Genetic population structure of southern bluefin tuna ( Thunnus maccoyii )

Samples of southern bluefin tuna, Thunnus maccoyii (Castelnau), taken from off the coasts of South Africa, Western Australia, South Australia and Tasmania from 1992 to 1994 were analysed for six polymorphic allozyme loci (ADA *, GDA *, GPI-A *, MPI *, PGDH * and PGM-1 *, n = 595 to 733 per locus) and for mitochondrial DNA variants revealed by three restriction enzymes (Bam HI, Bcl I and Eco RI) detecting polymorphic cut sites (n = 555). No significant spatial heterogeneity was detected. There were no sex-related differences in allele or mtDNA haplotype frequencies. Juveniles (30 to 35 cm and 46 to 54 cm) from what are thought to be two temporally-separated spawning peaks showed no significant genetic differentiation. There were also no significant differences in allele or haplotype frequencies between fish smaller than 70 cm and those larger than 70 cm. These data are consistent with the null hypothesis of a single unit stock of southern bluefin tuna, with a single spawning area. This is located to the south of Java and off the north-west coast of Australia.

Ocean dynamics in the region between Australia and Indonesia and its influence on the variation of sea surface temperature in a global general circulation model

Variation of sea surface temperature (SST) in the region between Australia and Indonesia is of crucial importance to Australian winter rainfall. To gain insight into how the SST is maintained and changed, the present study provides a comprehensive description of ocean dynamics in the region, using results from a seasonal ocean general circulation model run by Semtner and Chervin [1988,1992]. We also investigate the heat budget of the surface layer (0–50 m). Indonesian topography is heavily simplified in this model, but some simple results which probably do not depend strongly on topographic detail are obtained. The currents in the model are verified by comparison to observed annual mean and seasonal thermal structures and circulations determined from the expendable bathythermograph data collected in the region since 1983. We found a distinctive difference in the model circulations and heat budgets in two regions: one between the coast of Indonesia and 13°S (called the northern region) and the other between the northwest coast of Australia and 13°S (called the southern region). Net surface heat fluxes in the model's northern region are low compared to those in most climatologies, possibly because the model does not allow for strong tidal mixing within the Indonesian archipelago. The annual mean vertical velocity in the upper 500 m shows strong upwelling in the northern region and weak downwelling in the southern region. The annual variation in the vertical motion near the surface (<50 m) is driven by local wind stress in both regions. Within the depth range of the thermocline, vertical motion is dominated by a remotely forced semiannual signal in the northern region and a local response to wind stress in the southern region. The surface heat flux and advection in the annual mean heat budget are very small, at least an order of magnitude smaller than those in the seasonal budget. In the southern region the model may represent the ocean heat budget quite well: here the primary control on the seasonal variation on SST is the surface heat flux. However, about half of the flux is balanced by advection in the southern region. This suggests that ocean circulation could also play a role in the generation of the SST anomalies north of Australia, which are critical for Australian climate variation as documented by Nicholls (1989). In the northern region, cold advection due to upwelling is largely cancelled by warm advection from within the Indonesian archipelago. This may explain the fact that observed sea surface temperature depressions south of Indonesia are quite small compared to those in other eastern‐boundary upwelling regions. However, model heat fluxes in the northern region may be in error owing to the absence of tidal mixing. In the model the largest terms show that heat transport by Indonesian throughflow and Ekman current is the main heating process and this process is largely balanced by cooling due to upwelling near the coast of Indonesia, and by release of heat to the atmosphere near the northwest coast of Australia.

A Test of the Vegetation Mosaic Hypothesis: A Hypothesis to Explain the Decline and Extinction of Australian Mammals

The vegetation mosaic hypothesis suggests that medium‐sized mammals occupying arid and semi‐arid areas of Australia require a habitat that is a fine‐grained mosaic of different vegetation types or seral stages. This mosaic is believed to have been created in the spinifex deserts of central Australia by Aboriginal burning practices. Its loss in the period 1940–1960 is postulated to be a primary reason for both major reductions in range and mainland extinctions of many species of medium‐sized mammals at this time. This study measured the responses of three species of medium‐sized mammals to vegetation patterns within spinifex grasslands that ranged from comparatively uniform to highly diverse. The abundance, condition, and reproductive status of golden bandicoots (Isoodon auratus), northern brush‐tailed possums (Trichosurus vulpecula arnhemensis), and burrowing bettongs (Bettongia lesueur) were assessed within vegetation mosaics of various scales on Barrow Island, off the northwest coast of Australia. Scale of mosaic proved to have no significant effect on the numbers, condition, or reproductive status of any of the three species. Similarly, the creation of fine‐grained mosaics of early seral‐stage vegetation mixed within climax vegetation by extensive oil‐field operations over nearly half the island had no significant effect on the number or condition of animals. Hence, scale of mosaic seems unlikely to be related to the mainland decline or extinction of these species. The pattern of decline and extinction on the mainland but continued survival on offshore islands is more consistent with the presence (mainland) or absence (islands) of introduced predators (foxes and cats) and herbivores (rabbits and stock).

Description of a Giant Circumglobal Lamprogrammus Species (Pisces: Ophidiidae)

L AMPROGRAMMUS Alcock, 1891 (in WoodMason and Alcock, 1891) is a genus of oceanic ophidiid fishes found around the world beneath tropical and subtropical seas. Smaller examples are occasionally captured in the mesoto bathypelagic, whereas larger fish are caught most often with bottom trawls fished at bathyal depths. We have studied four distinctive, elongate, specimens, the largest nearly 2 m long. Three are from the Southern Hemisphere: one from off the coast of Chile, another from off the northwest coast of Australia, and a third from off Angola. A fourth example was caught off the northeast coast of South America. These

Late Jurassic‐Early Cretaceous evolution of the eastern Indian Ocean adjacent to northwest Australia

Over 9700 km of new aeromagnetic data were acquired off the northwest coast of Australia and combined with existing magnetic data to map magnetic isochrons in the eastern Indian Ocean. The isochrons were used to constrain a tectonic model of the evolution of the seafloor in the Argo, Cuvier, and Gascoyne abyssal plains. A complete set of anomalies, from M26 through M16, was found in the Argo Abyssal Plain, trending generally N70°E. Spreading commenced in the center of the basin at or prior to M26 and propagated outward until at least M24 time. Anomalies M10–MO, recording the separation of Australia and India, were found in the Cuvier and Gascoyne abyssal plains, with a trend of about N30°E. A significant crustal age discontinuity occurs in the vicinity of the Joey Rise where the two lineation sets converge. Because there appears to be no overlap of isochron ages in the two groups, it is not necessary to postulate that a triple junction existed off northwest Australia as has been previously suggested. At M4–M5 time a 10° clockwise change in spreading direction occurred on the Cuvier‐Gascoyne spreading system. This event triggered ridge jumps that transferred two pieces of the Indian plate to the Australian plate. Overlapping spreading on the forming and dying ridges, curved fracture zones and lineations, as well as fanned lineation trends, suggest that the ridge jumps occurred by ridge propagation and that the transferred lithospheric blocks behaved as microplates for a brief interval of approximately 1–2 m.y.

The Puffin Field ? a geophysical enigma

The Puffin Field is located within the Vulcan Sub-basin of the Timor sea, off the Northwest Coast of Australia. It lies within the offshore exploration permit AC/P2, operated by BHP Petroleum and its co-venturers. It is situated on the Ashmore Platform, an old Triassic horst which is normal faulted against the Swan Graben, a major Mesozoic depocentre and the regional source area. Three wells were drilled in the 1970's. Puffin-1 and Puffin-3 encountered oil in "FIT" tests from within the Maastrichtian 100 ft sand, and Puffin-2 flowed over 4000 barrels of oil per day from a slightly younger 4 m sand. On examination of the results of the Puffin wells, it was evident that there were severe velocity anomalies and differing oil water contacts in the Puffin field. The top of the 100 ft reservoir sand is at 2031.4 m subsea in Puffin-1, 2045 m subsea at Puffin-2 and 2074 m subsea at Puffin-3. The two way times to these events were 1392 ms, 1328 ms and 1398 ms respectively. The interpreted oil water contacts in Puffin-1 and Puffin-3 were 2033 and 2077 ms subsea respectively with no contact seen at Puffin-2. In an attempt to resolve these anomalies the AC/P2 joint venture undertook a detailed seismic reprocessing project of the 1980 data with special emphasis on detailed velocity analysis. This 1987 reprocessing effort involved two passes of velocity filtering and velocity analysis at every 600 m. Velocity analyses were picked on a horizon-consistent basis, such that variations in interval velocity for key horizons could be established for later use in depth conversion. Although sceptical in using stacking functions as the input velocities to depth conversion, they were used, as no viable alternative was feasible. Data quality was reliable to the top of the Palaeocene Calcilutite, and six horizons were picked with their respective velocities to this level. Analysis of the data indicated that the two major units exhibiting interval velocity variation were the Pliocene "low velocity layer" and the Eocene carbonates. Using the smoothed stacking velocity down to the Top Palaeocene Calcilutite the three wells tied the depth conversion with an accuracy of 0.5%. Below this horizon two constant interval velocities were used from well data as the quality of the seismic pick were not as reliable. To verify this model BHPP also undertook a "layer-cake" velocity approach which, although confirming the anomalous zones, could not be used laterally away from the three wells, which unfortunately all lay in a straight line. Two wells, Puffin-4 and Parry-1 were drilled in 1988 to test the resultant interpretation. The wells intersected the Top Palaeocene Calcilutite within 1% of prognosis at Puffin-4 and within 2.2% of prognosis at Parry-1, therefore confirming the stacking velocity model used in depth conversion. However, both wells came in deep to prognosis at the deeper, objective level as a result, in the case of Puffin-4, of being on the downthrown side of a small fault, and at Parry-1 due to a thickening of the Paleocene section and seismic mispicking of the Top Palaeocene Calcilutite. Had the mispick at Parry-1 been avoided then the tie would have been less than 1.0%. Both these mis-interpretations were made in the part of the section where the quality of seismic was poorest. These two results suggest that even though the depth conversion to the Top Paleocene Calcilutite is accurate to within 1%, the magnitude of the velocity variation is larger than the magnitude of the independent depth closure. The Puffin Field requires both better quality seismic below the Base Palaeocene Calcilutite, or the means to resolve the lateral extent and possible thickness of a 4 m sand away from Puffin-2. Until such a method of obtaining either better quality seismic to the objective level, or to be able to define the seismic resolution of the differing sand bodies of a minimum size of 4 m, the Puffin Field will remain a Geophysical enigma.