ABSTRACT This paper reviews some key issues regarding the cyclic loading response of offshore piled foundations. Starting with axial loading it considers: the cyclic loading that can be expected; the fundamental responses of piles driven in clays and sands; frameworks for understanding axial cyclic response and specifying cyclic soil testing; and approaches for practical application in design. The review then moves to consider pile responses to moment and lateral loading, distinguishing between flexible and relatively rigid piles and anchors. A range of possible design approaches is considered and it is argued that current routine practice needs to be reconsidered. Practical methods now exist to address the potentially highly significant effects on axial capacity of piles that experience high ratios of cyclic to average loads. New research and calculation procedures are emerging that offer significant improvements in a broad spread of topics. 1. Introduction Interest in the behaviour of piles under cyclic loading grew in the 1980s to meet challenges posed by inherently fail-unsafe Tension Leg Platforms (with the first TLP being installed at Hutton in 1984) and heavily loaded deeper water fixed platforms, such as the Cognac jacket set in 320m water. Briaud and Felio (1986) assembled for API a database intended to resemble fine marine sediments covering the cyclic behaviour of clays in: laboratory tests, cyclic model experiments and axially cyclic field pile tests. They considered 16 studies on piles with diameters greater than 150mm, most of which were strain-gauged to measure axial load distributions. Local shaft friction, pore pressure and radial stress measurements were attempted in some cases, although these parameters are notoriously hard to sense reliably. The response of piles driven in sands was not addressed. The piles were submitted to significant numbers of load cycles (typically 100 to 1,000) with frequencies generally around 0.1 Hz.

1. Introduction With recent developments and application of geographical information system (GIS) capabilities, geohazard assessments can benefit from detailed data integration. This facilitates the merging of different datasets, such as 3D exploration seismic; high-resolution seismic (e.g. HR2D, sub-bottom profiler); geotechnical (e.g. boreholes, cone penetration tests (CPT)); or environmental (e.g. sampling, visual inspection) data. The result of this integration is a conceptual geological model to be used as a support for the geohazard assessment, and which is provided to the engineering team in charge of a facility design. The engineering team, however, expects predictions (time, place, magnitude and probability of an event), while most geoscientists can only offer an improved forecast (general statement of future possibilities). To reduce this subjectivity, the interpreter should conduct an evaluation of the reliability of the model, taking into account the uncertainties related to each dataset (e.g. accuracy, resolution). The quantification of uncertainties may be carried out for each dataset, but that of the conceptual geological model as a whole is not easy to determine. This paper reviews best practice in terms of data integration by means of a GIS and details uncertainties that should be taken into account. It also addresses considerations related to geostatistics and probabilities, in order to provide a reliable conceptual geological model for geohazard assessment. 2. Geographical Information System: A Powerful Tool for Data Integration At that time, geotechnical engineering was still regarded as part of civil engineering, relying upon the principles of mechanics and hydraulics. Today, geotechnical engineering is recognised as an obvious bridge between geology and civil engineering, and in many areas it requires an integrated and multidisciplinary approach. Such an approach linking geosciences and geotechnical engineering should be considered in terms of common concerns and requirements, such as obtaining, organising, validating, displaying and interpreting surface and subsurface data.

ABSTRACT A relatively new technology outside of military applications is low logistics autonomous underwater vehicles (AUV). These vehicles can be programmed with a mission, deployed from a vessel or directly from shore, execute their mission and return with a variety of different data. Using a suite of sensors these vehicles provide a quiet and stable platform for the acquisition of high-resolution data. This paper covers the capabilities of the systems and presents some applications and advantages to the user, as well as some data from projects performed to date. This includes rig site surveys, some of which are in restrictive locations, route surveys and general offshore subsea surveys. 1. Introduction Autonomous underwater vehicles (AUV) have been operating in the upstream oil and gas sector for well over 10 years. In 1995 Kongsberg started the HUGIN project with the first commercial survey being performed in 1997 for Statoil's Aasgaard pipeline route. Since then, the HUGINs have built an impressive track record of performing large area survey very effectively, often in deep water and generally operated from dedicated, specialised vessels. There is no doubting the benefits of these vehicles for large surveys, especially in the deep waters of oil and gas exploration, however, there is a developing need for smaller surveys in relatively shallow water. The manufacturers of some smaller vehicles have realised the benefits of their vehicles, which have primarily serviced military applications (e.g. mine counter measures (MCM)). Similarly, the end clients, the oil and gas operators, have seen the benefits of using these smaller vehicles for some of their survey requirements. These smaller vehicles - often referred to now as low logistics, lightweight, compact or mini AUVs - are now being used more often especially by a few key end clients who have realised their benefits.

Abstract First-order, second-moment (FOSM) approximations provide an efficient way to assess submarine slope stability across large areas for which digital bathymetric data are available. This is demonstrated using 20m bin 3D seismic seafloor data for a deepwater area with typical geotechnical soil properties. Results are obtained in terms of a factor of safety mean and standard deviation for an infinite slope with pseudo-static seismic loading. From this the probability of sliding is calculated for each bin without the computational burden of Monte Carlo or other iterative methods. Because these types of probabilistic model incorporate parameter uncertainty into their input and output, they can be used to support decisions about the value of additional data collection, or justify more sophisticated analyses that may help to reduce output uncertainties. In addition to providing detailed maps of the probability of sliding, the analysis produces global statistics that allow insight into the broader response of the system to seismic shaking. 1. Introduction Evaluation of deepwater geohazards commonly entails assessment of slope stability either to understand the geologic history of a project area, or to anticipate the risk associated with future events, such as major earthquakes. This can be done qualitatively based on the presence or absence of past landslide deposits; semi-quantitatively using simple measures such as slope angle or gradient; or quantitatively using limit equilibrium slope stability analysis (e.g. Mackenzie et al., 2010). Limit equilibrium methods are widely known and attractive because they integrate the essential physics of sliding and allow evaluation of rare or unprecedented conditions (for example the effects of a large future earthquake). However, they also require specification of geotechnical variables, such as sediment shear strength, thickness and unit weight, in addition to some description of slope geometry (minimally the slope angle).

Abstract A study of the break-out factor ( Nc ) for plate anchors is presented in this paper. Comparisons among finite element method (FEM) analysis and laboratory results were performed. A soil corresponding to a soft normally consolidated clay was considered. Numerical FEM analyses were performed with the Plaxis® code, using an elasto-plastic model with a Mohr-Coulomb criterion. Undrained soil parameters and an adhesion factor α = 1 were used. Values of Nc factor for axisymmetric and 2D FEM were obtained. Two geometries considering a perpendicular load applied in the anchor area and horizontal anchor position to different depths were studied. In the same way, anchor plates to a reduced scale were tested in a tank containing a soft soil. It was verified that the factors Nc reach constant values beyond a determined depth of the soil. Finally, the experimental and numerical values were compared with suggested methods reported in the literature. 1. Introduction Plate anchors are frequently used as foundation solutions for offshore structures to transmit forces to surrounding soils at various depths. The capacity estimation of the anchor is nevertheless uncertain insofar as there are factors that have a large influence in its behaviour. Examples of such factors include the installation process, soil characteristics, geometry of plates and large numbers of methods used to calculate the holding capacity of the anchors. In this context, this paper presents a study of Nc values, obtained from axisymmetric and plane strain finite element model (FEM) simulations done in Plaxis® code. In addition, it outlines the results of scaled-down plate anchors tested in the laboratory. In both cases, the soil considered was soft clay with deepwater sediment characteristics. The description of specific FEM analyses and laboratory test characteristics taken into account are described. Comparisons with expressions found in literature were made.

ABSTRACT BP has been developing an integrated and systematic approach for the early assessment of deepwater geohazards to support planning and design of several major gas field development in the West Nile Delta (WND). The approach has involved the assembly of a team of experienced geoscientists from the disciplines of geology, geophysics, geomorphology and geotechnics. The paper will demonstrate the value of early engagement of multidisciplinary team approach for the evaluation of 3D exploration-quality seismic data in frontier deepwater areas where the issue of geohazards could be a potential major constraint to the siting of tophole locations and facilities. Early screening of the geohazard challenges to development can be used to guide the appropriate level of investment, resources and data acquisition programme to support subsequent stages of the project. Early acquisition and calibration of field-wide autonomous underwater vehicle (AUV) engineering-quality data is providing opportunities to ensure that development plans are not exposed to unnecessary, avoidable geohazard risks. A key element of the multidisciplinary team approach is the application of integrated geophysical, geotechnical and engineering geomorphological methods that make best use of the high-resolution data these state-of-the-art technologies provide. The integrated approach is providing valuable in guiding BP's offshore development plans towards properly identifying the geohazard risks and accounting for decision-making at all stages of the project programme (see companion paper by Evans et al. 1 ). The product of the geohazard assessment work underpin strategies for the optimization of field architecture (avoidance of geohazards) and the evaluation of cost effective options for geohazard-tolerant equipment design and protection (geohazard-resistant design). West Nile Delta Gas Developments The Nile Delta is one of the world's largest deltas, with a submarine fan of about 100 000km 2 extending northwards into the Mediterranean Sea (Figure 1), and is a major area of hydrocarbon exploration. The delta extends 20–40km offshore to a shelf break where the water depth is about 100m; the maximum water depth beyond the delta slope is about 1500m. BP Egypt, together with partners RWE-Dea and Egyptian Natural Gas Holding Company (EGAS), intend to develop several offshore fields within the West Nile Delta (WND). The modern Nile Valley is thought to have formed during the late Miocene at the same time as a major desiccation of the Mediterranean Basin. The salt deposits formed at this time were progressively covered by deep sea fan sediments discharged from the River Nile throughout the Pliocene and particularly during the Quaternary 2 . The WND has been subject to cycles of rapid sediment deposition, erosion and episodic submarine landslide activity for at least the last 250 000 years 2 . The resulting present-day seafloor is an irregular patchwork of geomorphological forms and geohazard features including incised canyons, plateaux and escarpments, fault scarps, pockmarks and landslide scars (Figure 2). The shallow soils across the WND are predominately soft marine clays of terrigenous origins and hemipelagic clays. The mechanical properties of these soils are strongly influenced by their depositional histories and most significantly by post-sedimentation events and processes such as landslides, debris flows, turbidity currents and fluid expulsion.

ABSTRACT Pockmarks are a ubiquitous feature on the seafloor of the Norwegian Channel, including the Troll area where they exist despite the absence of evidence of free gas or gas migration. Gas concentrations in the pore water do, however, increase in sediments older than those deposited from the last glaciation. Detailed mapping by remotely operated vehicle (ROV) based multibeam echo sounding and sub-bottom profiler of some selected pockmarks has provided the basis for a sampling and analysis programme. ROV video inspections revealed a lag deposit of gravel and the presence of methane-derived authigenic carbonates within some of them. The radiometric analyses indicate formation about 11 Cal kyrs ago, whereas geotechnical data indicate formation by erosion of the overburden. From reconstructions of the pressure and temperature history based on both sedimentation history and sea level, this paper proposes that gas hydrates accumulated in the varied lithology of the morainic sediments from the penultimate glaciation during the last glaciation. At the end of the last ice age, about 11 Cal kyr ago, the hydrates decomposed releasing gas that fractured the overlying sediments and escaped to form pockmarks and the authigenic carbonates found within them. Pockmarks asymmetry indicates that they may have been kept open by current activity after the gas was depleted. INTRODUCTION The Norwegian Channel (Figure 1) was one of the first areas in which pockmarks were discovered 1, 2, 3, 4 , and their formation was interpreted as the result of the expulsion of fluids through the seafloor 5, 6 . Although gas escape has been documented in some North Sea pockmarks 7 , no such activity has been discovered in the Norwegian Channel? an area extensively surveyed in connection with the hydrocarbon industry? despite their ubiquitous occurrence there. Interest in these pockmarks dwindled due to their lack of activity, but was renewed in connection with the studies of the pressure development at the Troll A platform 8 and its possible relationship to natural fluid flow in the area. Several questions concerning pockmarks were posed, the most important being the question of timing: When were they formed, and are they still being formed? Could they be associated with bad weather when no surveys are performed? Another key question is how were they generated. Are they a result of pore water or gas expulsion, or perhaps even due to phenomena on the seafloor? This paper presents background information, the investigations performed and interpretations pertaining to these questions. Geological setting The Troll area lies on the western zone of the area influenced by the Tertiary uplift 9 of the Norwegian mainland. The sub-horizontal Pleistocene sediments are separated from the un-derlying western-dipping strata, tilted during the uplift, by an unconformity. While most of the uplifted sedimentary rocks have been removed by erosion on the mainland to expose the crystalline basement, their dip decreases towards the west from the Troll area, and the unconformity gives way to a more conformable sedimentary package under the central North Sea 10, 11 . During the Pleistocene, glaciers repeatedly expanded across Northern Europe, Scandinavia and North America in response to natural variations

ABSTRACT The mechanical properties of soils can never be established with complete certainty. The uncertainty is due to natural variability of soils, imperfect interpretation models, measurement errors, insufficient data, etc. The selection of soil properties for geotechnical design is often based on subjective judgment and experience, and the uncertainties in soil properties are only indirectly accounted for when the characteristic design values are selected. Although statistical methods can quantify uncertainties and account for them in a rational manner, they are rarely used in establishing the design soil parameters. The profession also uses imprecise definitions of ‘characteristic’, ‘best estimate’, ‘upper bound’ and ‘lower bound’ values for design. The profession needs to make a recommendation of which values to use in design. The paper demonstrates how characteristic values of soil parameters can be extracted from available data with statistical methods. Examples of characteristic (design) soil parameters over the past 25 years were re-analysed using statistical methods. Recommendations for choosing characteristic values and expressing variability are given. INTRODUCTION Soils are naturally variable because of the way they are formed and the continuous processes of the environment that alter them. The uncertainty in the mechanical properties of offshore soils is due to the natural variability from point to point within a soil volume, insufficient data and imperfect interpretation models, measurement errors and other sources. The selection of soil parameters for geotechnical assessment is often based on subjective judgment and accumulated experience. The uncertainties in the soil properties are only indirectly accounted for when the characteristic (design) value(s) are chosen. Statistics and probability are useful tools for the quantification of the mean (most probable, expected) value and the possible range of values of a parameter. Statistical and probabilistic methods can quantify the uncertainties and make it possible to account for them in a rational and consistent manner. They are, however, rarely used in practice to establish the design soil parameters. The reason for this is unclear. Perhaps it has become a habit that no one questions, or the restricted use of statistical methods maybe a reflection of the fact that often not enough data are available to actually implement statistical methods with confidence. Det Norske Veritas (DNV) and Norsk Hydro 1 prepared a guidance note on the statistical representation of soil data. When describing the design soil profile, expressions such as ‘characteristic’, ‘best estimate’, ‘upper bound’ and ‘lower bound’ values are used in practice. A common understanding or a standard criterion does not exist for the selection of ‘best estimate’, ‘upper bound’ and ‘lower bound’ values, and there is an uncertainty on what is covered by these expressions. The profession now needs to make a recommendation of which values to use in design. The paper attempts to quantify some of these concepts through the reanalysis of case studies in the North Sea and elsewhere, where characteristic (design) values have been selected by experienced engineers. Examples of design soil parameters recommended by the Norwegian Geotechnical Institute (NGI) for offshore sites over the past two decades were re-evaluated using statistical methods

ABSTRACT Modelling algorithms are described for mechanical rock-cutting wheels for subsea rock trenching. The models are used in design and for optimising system operation. Performance prediction algorithms are based on current theoretical, experimental and field data on standard conical picks. Inputs include maximum wheel torque, wheel speed and trencher advance rate. Also considered are the effects of pick spacing and estimated rock unconfined compressive strength (UCS). Benefits of such modelling include new wheel design parameters, improved trenching system designs and more effective operation. INTRODUCTION The growing field of offshore exploration and production necessitates an in depth review of the tools and equipment used. Moreover, the cost of offshore time requires optimisation of processes done from ships, especially at depths. Subsea trenching is an example of such an area for study - in this case, optimisation of the design and operation of a rock-cutting wheel. The prediction of the performance is based on previous studies and on field performance data. This combined with the mechanical constraints of the trencher wheel can dictate optimal rotational and translational speeds along with predicted performance output. This paper presents the basic physics required to predict the performance of a mechanical rock cutter in a subsea application. The objective is to predict the forces, torques and production rate given a rock type and the mechanical design of the machine, including a cutter geometry, pick layout, power supply and drive system. This paper focuses on mechanical trenching, but the principles can be extended to rock excavation (e.g. subsea mining) as well. Overall Cutting Model A basic power flow/causality diagram for the mechanical cutting and drive system is shown in Figure 1. The figure represents an electric motor driving a variable swash-plate hydraulic pump, which drives a hydraulic motor that in turn drives the rock wheel through a gearbox. The diagram assumes that the electric motor runs at a nominal rpm which, through the swash plate setting (fluid displacement per revolution), determines the fluid flow through the hydraulic motor, the resulting motor rotational speed, the speed of the output shaft of the gearbox and the pick speed. The forces on the picks result from two effects: the penetration of the picks into the rock(which dominates), and the drag force of the picks through the slurry. The depth of penetration of the picks into the rock is determined by the ratio of the advance rate of the cutter to the rotational speed of the cutter and the number of sets of picks on the wheel: penetration =(trencher advance rate)/((pick-sets/rev) *(rev/sec)) The net pick force then translates back into torques, pump pressure, and electric motor torque through the same set of relationships that were used on the rotational speed/flow path in Figure 1. Note that, without careful design, the drive system will be prone to stalling. From Figure 1, it can be seen that, as the cutting forces rise, the hydraulic pressure increases, which will result in decreased pump output flow, which causes lower cutter speeds.

ABSTRACT In March 2007, Nautilus Minerals Inc announced that it has commenced its 2007 exploration and development programme with the mobilisation of the research vessel Wave Mercury and the survey vessel Aquila onsite Papua New Guinea (PNG). The vessels are returning to the territorial waters of PNG after completing similar exploration work during 2005/2006, to commence a three phase seabed massive sulphide deposit exploration programme on the 100% Nautilus owned Solwara 1 Project. The first two phases of this campaign will concentrate on completion of environmental studies, seabed deposit mapping, sampling and geophysical studies - altogether a scheduled 60 day endeavour. Phase 3 is scheduled to be a further 120 day activity in the Solwara 1 location, involving drilling and sampling at pre-determined targets. These drilling activities, scheduled to commence in early June 2007, will be executed using two off specialist ROV mounted drilling/coring rigs performing coring and drilling activities at water depths in the +2000m range. These ROV mounted rigs, Rovdrill® will be provided by Perry Slingsby Systems Inc of Jupiter, Florida, USA, and will be operated by Canyon Offshore Inc, a Helix Energy Solutions Company based in Houston - a world renowned remotely operated vehicle (ROV) operating entity. This paper will describe the conception of Rovdrill®and its subsequent design, development and field testing. The pros and cons of this new technology and the potential further applications of the equipment in the Geotechnical survey and subsea construction market are also discussed. Conception of Rovdrill®and Pre-Existing Equipment One of the primary drivers for the development of a remotely operated vehicle (ROV) mounted drill/coring rig was to provide a system which would be based around proven drilling technology and readily available equipment, but at the same time would not need to rely on expensive and limited supporting resources, such as drill ships, for its deployment and operation. A system that could be readily mounted to, and interfaced with, a variety of ‘equipment of opportunity’ such as work-class ROV systems and their associated existing support vessels, with the minimum amount of subsequent reconfiguration of these host resources, clearly presented a very practical and economical proposition to those enterprises engaged in the business of deepwater seabed surveying and sampling. While the Rovdrill®is the world's first true ROV mounted and operated drilling and coring rig to be commercially developed and supplied to a live project, there are currently a number of other remotely operated seafloor coring systems operating in the field, such as the Benthic Multicoring Systems - BMS-1 and BMS-2, built by Williamson and Associates of Seattle, and currently owned and operated by the Metal Mining Agency of Japan (MMAJ). These systems are ‘stand-alone’ and are highly capable, featuring a suite of instrumentation, cameras, lights, heading, altimeters, depth thrusters; they can operate at depths of 6000m and handle coring samples to 20m length. Other systems have also been successfully developed and trialled, including the British Geological Survey (BGS) range of equipment - Rock Drill 1 and 2, the BGS Oriented Rock drill, and the Geomar/Schilling developed MEBO.

ABSTRACT This paper describes and illustrates a number of submarine canyons from various deepwater areas. It is based upon swathe bathymetry and geophysical field data acquired for geohazard site surveys together with re-processed short offset 3D data. The morphology of these canyons is discussed, together with their potential for slope instability. These factors represent potential geohazards to the continuing exploration and production activities in some deepwater areas. INTRODUCTION Submarine canyons have long been recognised as distinct channel features cutting into the majority of continental slope areas so far investigated 1,2 As technology advances and mapping techniques improve, these canyons are being resolved in increasingly clearer detail. Particularly useful are deep towed long range sonar for covering large regional extents, whilst methods such as swathe bathymetry and short offset processed 3D seismic data can provide very detailed grids of seabed data. These latter two methods are providing unprecedented images over areas of typically a thousand square kilometres or more, at grid sizes of 25m by 25m and even to 12.5m by 12.5m. The recent advent of autonomous underwater vehicles, (AUVs), means that detail and resolution will be improved still further due to their ability to acquire swathe bathymetry data closer to the seabed. The stability of submarine canyon systems may, in simplistic terms, initially be related to seabed slope angles, particularly of the canyon sides. The potential for instability then depends on the likelihood of processes modifying these slopes and external triggering mechanisms causing them to fail. Modifying processes are typically currents along and downslope, which may cause erosion and sediment input or deposition. Triggering mechanisms include, for example, seismicity, soils strength variations due to pore pressure changes, disturbance due to halokinesis, shallow gas and hydrate sublimation and cyclical loading. The association of deepwater canyon systems with recent or present flow activity, such as turbidity currents, has long been recognised. Much has also been published following indirect evidence concerning episodic events such as the 1929 Grand Banks and the 1971 Nice/Var canyon related submarine cable breakages. As exploration and production continues in deep water upper continental slope areas, these canyons are being encountered with increasing frequency. Thus, concerns are raised as to their intrinsic stability combined with the present levels of bottom current and sediment activity within the canyon systems3. Research work has also been recognising the relatively recent nature of a number of events4. This is particularly important when, for example, sub-sea facilities are constrained by reservoir characteristics to being positioned close to, or within, such canyon systems. The new techniques mentioned above are progressively revealing much finer detail and will in time allow the frequency of minor flows to be better estimated. Improvements in visualisation and presentation of these results also allow a much more "user friendly" display, which should improve interpretation of actual processes involved.

ABSTRACT In response to the demand of the telecommunication cable market, new tools have been recently developed and introduced for burial assessment purposes, which are now available to the pipeline industry. The CPT has become the reference tool for obtaining geotechnical data required for burial engineenng. It is used m combination with electronic profiling techniques capable to provide an accurate stratigraphy of the subsoil over the target burial depth (a few metres). E-bas techiques are based on the seismic refraction method which characterises the sediments by their compressive seismic velocity Vp or on the measurement of the electrical resistivity. E-bas techniques are implemented via bottom-towed system The paper reviews the equipment and techniques in use and outlines their technical capabilities and limitations. In parallel to these developments, major advances have been made in data processing and integration procedures. The paper emphasises: the last improvements in processing techniques used to produce the velocity or resistivity fields, the integration process of the different sources of data: bathymetry, side scan sonar, seismic reflection, seismic refraction/resistivity, geotechnical data (CPT and sampling/coring). The main engineering phase of the burial assessment consists of determining the maximum burial depth attainable by ploughing and the associated towing forces. Cable and pipeline installation data have been back-analysed and correlations have been established between these quantities and CPT data. INTRODUCTION Route selection and burial assessment of a pipeline or cable require specific data which include: water depth and seabed topography, anomalies on and in the seabed (e.g. geohazards, existing pipelines or cables, other obstructions), differentiation of strata with significantly different geotechnical properties affecting burial operations, geotechnical parameters of importance for burial assessment. Standard offshore surveys for pipeline or cable route selection are aimed at providing the first two sets of data. They consist of bathymetric, side scan sonar and seismic reflection surveys covering a wide corridor centred on the theoretical route Shallow seabed sampling (e.g. grab sampling, gravity coring or vibrocoring) is carried out from the geophysical vessel at more or less arbitrarily chosen locations for ground-truthing geophysical data. The information provided by these standard route selection surveys is insufficient and inadequate to assess the burial feasibility of the pipeline or cable. Burial assessment should address a number of aspects, such as: can the pipeline/cable be buried and If so, to what depth? what is the most appropriate burial method (e.g. ploughing, jetting, trenching, others)? what is the anticipated performance of the recommended burial method (e.g advancement speed)? m case of ploughing, which is the most commonly used method, what are the expected pulling forces? How are these forces affected by the ploughing speed? is the stability of the trench safe (in case of an open trench solution)? is the burial tool stable on the seabed? what is the anticipated wear of the burial equipment?

Summary The need for accurate pipeline network charts m the Mahakam Delta (Indonesia) became imperative for safe and efficient operations. Due to the specific environment conventional pipeline survey methods could not be utilised. A novel deployment method needed to be developed to cope with the particular environmental constraints. An innovative two step survey methodology implementing seabed imagery and magnetism was developed and deployed to produce a comprehensive set of high accuracy as-built pipeline charts. Objective The objective of the survey was to obtain accurate x, y, z charts (+/-0.25m vertical & +/-0.5m horizontal) of the Company pipeline network in the Mahakam Delta (Eastern coast of Borneo - Indonesia). Having such charts is clearly essential for the safe operation of any pipeline system. This need is even greater in the Mahakam Delta due to the high number of 3 rd party river users, the sensitive nature of the environment, the complex pipeline operational constraints, the rapid development and resulting construction activities and the massive production potential. In addition to the above, it was also essential to have accurate as-built pipelines charts before embarking on the planned extensive repair programme. The Mahakam Delta context The Mahakam Delta is a giant oil an gas field of around 400 square kilometre where twenty-two major pipelines ranging m diameter from 16″ to 30″ transport fluids from the producing wells to process units and then to export facilities. All together pipeline network is 750 km. Due to a combination of both process and environmental factors, the operation of this pipeline network is a major challenge. From a process side the wet gas contains between some C02 and Organic Acids making the complete network susceptible to Top of Line (TOL) Corrosion This phenomena only occurs however when the pipelines are subject to external cooling. Inspection by intelligent pigging has proven that lines that are adequately buried are not susceptible to TOL Corrosion Environmental factors also pose a major operational challenge with the ever-changing Mahakam Detla The removal of vast areas of mangrove to make way for shrimp farms has destabilised the soil resulting m extensive erosion and pipeline exposure Where pipelines are exposed they are susceptible to mechanical damage and TOL Corrosion.(The Figure is available in full paper) The complex geo-technical environment and the high pipeline operating temperatures have also created another operational challenge - Upheaval Buckles (UHB). A few UHB's occurred. They actually represent a risk as UHB's protruding from the seabed have no mechanical protection and are therefore susceptible to mechanical damage In addition they have no thermal protection which also makes them susceptible to TOL Corrosion.(The Figure is available in full paper) On the major crossings and on the major rivers further down the delta there are numerous areas of exposed pipelines at risk from, and presenting a risk to, the continuous bustle of river traffic. These exposures are caused by both natural erosion of the river bed and problematic burial.

Abstract The common goal for integrating geotechnics and geophysics is to increase the shallow sub-surface understanding for an area, making optimal use of each survey technique Important in this context is that the understanding of soil conditions between geotechnical sampling locations is increased by performing this integration. This paper presents two Statoil developments, Mikkel development and Kvitebjern Pipelines, where geophysics and geotechnics were successfully integrated in 2001. Performed work, results, benefits and experience are presented for both cases. For the Mikkel development the integration confirmed a similar soil stratigraphy as for the Midgard and Asgard fields. Unit thickness and variability were assessed with higher level of confidence because of a better regional understanding New recommended geotechnical design parameters could be established, based on the integration work, for repositioned templates without performing addition geotechnical surveys. The integration thus reduced costs and introduced a larger flexibility. The main benefit for the Kvitebjern Pipelines was that the pipeline designer had a continuous longitudinal soil profile with the appropriate geotechnical design parameters. The sampling locations were on average every 3 km along the pipeline route and the integration was therefore of great help to the pipelme designers. In addition, bedrock exposure could be mapped, important for pipeline design and pipeline laying Introdution Geotechnical and shallow geophysical surveys are performed for all offshore field developments The collected geophysical and geotechnical data can be integrated and examples of performed work vary from: Pipeline and cable burial assessment studies. Export pipeline studies, including bottom roughness assessments. Geohazard studies, including regional understanding. Shore approach studies, including depth to bedrock determination. Numerous other examples can be added to this list The common goal for these different integration studies is to increase the shallow sub-surface understanding for an area, making optimal use of each survey technique. Important in this context is that the understanding of soil conditions between geotechnical sampling locations is increased by performing this integration. Recent drivers in the offshore industry are contributing to the need of performing these integration studies.

Abstract A deepwater integrated geotechnical and geophysical site investigation took place m the central region of the Gulf of Mexico The purpose of the site investigation was to evaluate soil properties and shallow geohazards for future foundation design of a floating production facility. Acquiring the necessary data for foundation design in deepwater involves challenges not normally encountered in more shallow water depths To meet these challenges a new non-tethered geophysical tool was developed and a geotechnical tool not normally used in the Gulf of Mexico was adapted to obtain cost effective data These tools were used to identify and characterize subsurface conditions at the site. They proved to be effective in delivering key data m a cost effective manner Integrating results from these tools proved successful in providing crucial information for evaluating seafloor and sub-bottom features and soil conditions that influence foundation design. Integration of the geotechnical and geophysical data as it was collected provided the flexibility to modify the Initial program to ensure that conditions were characterized sufficiently for design Some geophysical data were specifically collected at the foundation locations to enhance the geotechnical program. Results from the targeted geophysical data identified three geohazards that could affect the design of the sucbon caisson foundations intended to moor the host facility. Additional geotechnical data were gathered and integrated with the geophysical data to fully assess these geohazards. The integration of the data collected during this site investigation provided the information required for installation and design of the suction caisson foundations We note, however, that the relatively benign surface and subsurface conditions at this site were conducive to the tools and methodologies chosen to characterize this site. At other more complex deepwater sites the tools and methodologies used at this site may have to be modified. Introduction To site a floating facility m deepwater a number of issues best resolved using geophysics and geotechnics must be addressed. These include (1) understanding soil properties to facilitate the design of the foundations, (2) understanding shallow geohazards that may effect installation and service of the foundations for subsea equipment and the host facility By integrating geophysics and geotechnics an enhanced understanding of both soil properties and shallow geohazards is obtained (e.g Jeanjean et al, 1998) Geotechnical and geophysical information is obtained through a specifically designed site investigation program Careful consideration of the capabilities of available geotechnical and geophysical tools should be made to maximize value while providing acceptable information for design. An example of a successful integrated site investigation that meets these criteria is presented in this paper. Deepwater offers several unique challenges beyond those encountered in shallower waters. To meet these challenges cost effectively new tools must be developed and existing tools adapted to perform in these harsh environments. A recent integrated site investigation in southern Green Canyon, Gulf of Mexico was undertaken using new and recently adapted cost effective tools.

Abstract The installation of jack-up platforms on sites containing old footprints is known to be problematic. One approach is to place granular infill in the old footprints to produce an approximately level seabed. Jardine et al (2001) recognised that this procedure could lead to uncertain results when the new locations are offset from the crater centre, and when the infill and original seabed soils had different properties. They performed numerical analyses to explore the forces and moments developed by a typical structure installed over infilled craters formed at a North Sea location where clay soils dominated the soil profile, considering an offset between the old and new foundation positions of approximately one-quarter of a footing diameter. Jardine et al (2001) showed that the problem could be treated analytically. This paper presents an updated version of the analysis in which the finite element mesh employed was further refined. It is shown that the composite foundation capacity is reduced by prior cratering and infilling. The reduced capacity is associated with significant lateral and rotational footing displacements, with large lateral forces and bending moments developing in the jack-up's leg. Introduction It is known that problems may occur when installing a jack-up at a location where footprints from previous jack-up operations exist, for example North Sea, or Southeast Asia. As a result there has been a tendency for operators to select either jack-ups with the same footing pattern as previously utilised, or to site subsequent units such that overlap of the foot prints is avoided or minimised. When working over a platform, the geometric constraints are often such that when different jack-up designs are deployed there is no alternative other than to accept that the footprints will overlap, as shown in Figure 1. In such instances the footings have a tendency to move into the old footprints. Whilst the degree of movement is, in some way, related to the footing shape, it is generally not practical to modify the footings when a unit is already contracted for the deployment. There are then only two real options for mitigating the problem, ‘stomping’ and infilling. (Fig. 1 and 2 are available in full paper) Infilling has the advantage that the incoming unit is presented with a relatively flat seabed and can then be positioned using normal procedures infilling of old footprints formed in a coarse grained sea-bed with granular materials has been undertaken previously, and it can be intuitively understood that this should not pose particular problems if the material characteristics are similar. However, many North Sea platforms are founded on layered cohesive materials and it is not obvious how these will behave when infilled with granular materials. It is this situation that was investigated in the study described here.