Technical Field

[001] The present invention generally relates to a device, tool assembly and/or method for in situ measurement of various soil parameters, for example soil parameters characterising the geotechnical interaction of pipelines on or in a seabed.

Background

[002] The infrastructure for offshore production of hydrocarbons in deepwater locations commonly relies on subsea pipelines. These may comprise flowlines linking wells to a seafloor termination manifold, or may take the form of steel catenary risers linking to a floating production facility or offloading point. In deep water, the pipelines are generally laid directly on the seabed surface under their own weight without specific actions directed at embedding the pipeline and without additional overlying protection. As such, the embedment of the pipeline into the seabed during installation is not only a function of the self-weight of the pipeline relative to the strength of the seabed, but also the additional forces and pipe-soil interactions caused by the laying process, dynamic motion of the lay vessel and natural hydrodynamic forces. Good prediction of this pipeline embedment during installation is important for better estimation of pipe-soil interactions during production.

[003] During production, the pipelines are susceptible to lateral and upheaval buckling movement and axial walking on the seabed through the expansion effects of temperature and pressure variations. In addition, steel catenary risers may also be subjected to cyclic movements due to vessel motion and hydrodynamic loading. Such movements can give rise to critically high stresses and failure zones in the pipeline. In addition, seabed structures, such as pipeline end terminations, pipeline end manifolds and riser support structures may be subjected to additional loading due to pipeline movement, thereby affecting their foundation stability. As such, accurate prediction of pipeline behaviour during production, in which pipe-soil interaction in the upper seabed layers plays a critical role, is thus a subject of considerable importance. Improved accuracy in estimating the pipe-soil interaction will enhance the viability of offshore hydrocarbon developments in deep water. [004] Presently, in practice, the load-deformation response of pipe-soil interaction is estimated empirically using site-specific soil parameters. The soil parameters are conventionally obtained by the use of various in situ geotechnical tools, such as piezocone and piezoball penetrometers, T-bar and vane shear testing, in combination with physical soil samples collected for subsequent onshore laboratory testing (such as measuring a pipe- soil friction factor using a laboratory ring shear test). Samples may be obtained using piston coring methods, or more recently the use of box corers has been adopted to obtain better quality samples of the top 40 to 50 cm of seabed (see for example, H. Dendani & C. Jaeck: Pipe-Soil Interaction in Highly Plastic Clays - Proc. 6th Int. Offshore Site Investigation & Geotechnics Conf. London, 2007).

[005] To assess the complex pipe-soil interaction, various pipe model tests are also performed, in which the axial and lateral resistances to cyclic movements of a pipe section that is partially embedded in the soil are measured. These model tests can be carried out in a laboratory using a laboratory test rig (such as that developed by the Norwegian Geotechnical Institute) or in geotechnical centrifuge facilities. Experimental research performed at the University of Western Australia, Centre for Offshore Foundation Systems, is leading to a theoretical understanding of geometric tool parameters with respect to assessment of pipe-soil interaction parameters. Alternatively, in situ model testing can be carried out on the seabed using an in situ rig such as the Fugro SMARTPIPE®, a complementary tool to the standard geotechnical investigation tools. The in situ rig system consists of a heavy frame in which an instrumented pipe section is suspended and hydraulically actuated while measuring pipe forces and displacements under axial, lateral and vertical movement.

[006] While there is a well-recognised need for accurately measuring or estimating soil parameters to assess and understand pipe-soil interaction, the currently available methods present a number of disadvantages. In deepwater situations, the seabed may be very soft and unconsolidated, making it difficult to accurately measure soil properties in the upper 1 m soil layer, where initial pipe-soil interaction occurs. Traditional in situ measurement methods such as the piezocone do not offer the required sensitivity of measurement in this upper zone. Resolution of the mudline interface and maintaining a datum reference can be difficult with remotely operated systems that have uncontrolled landing and embedment into the seabed. In many instances, the acquired data set lacks adequate information for the uppermost layer that is critical to the analysis of pipe-soil interaction.

[007] Methods such as the T-bar test and the Fugro SMARTPIPE® that employ a cylindrical tool may incur asymmetrical loading if the seabed is uneven in the test area, leading to inaccurate data interpretation. In addition, for accurate soil parameter measurements, it is important to ensure there is no or insignificant applied loading from seabed structures, such as the footings of the seabed rig that can disturb the soil at the testing location. Preferably, though not necessarily, the rig lands on the seabed with footings at least about 2 m distant from an undisturbed soil test zone. The heavy A-frame structure of the Fugro SMARTPIPE®, for example, does not fully meet this criterion.

[008] In the case of sampling techniques, it is often difficult to preserve the in situ properties of the soil for subsequent laboratory testing. Seabed soil sample disturbance can occur due to sampling tools insertion, temperature and pressure changes, transport-induced disturbances, sample mishandling and loss of biogenic activity that can affect the measured soil properties. In addition, due to the low strength nature of the near seabed surface soils, accurate measurement of soil properties from laboratory tests may not be feasible with existing laboratory equipment. For laboratory model testing, the soil samples are reconstituted, with no assurance that they accurately represent true in situ conditions.

[009] There is a need for a device, tool assembly and/or method for more accurately measuring or simulating geotechnical pipe-soil interaction on or in the seabed which addresses or at least ameliorates one or more problems inherent in the prior art.

[010] The reference in this specification to any prior publication (or information derived from the prior publication), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from the prior publication) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. Brief Summary

[Oi l] In a broad form, the present invention provides a device, tool assembly and/or method for more accurately measuring or simulating geotechnical pipe-soil interaction on or in the seabed.

[012] According to another aspect, the present invention comprises an in situ pipeline simulation device and/or tool assembly to simulate pipe-soil interaction on or in the near- seabed layer, i.e. a measurement device or tool assembly. The pipeline simulation device or tool assembly can be deployed in association with a seabed rig, such as a remotely operated seabed drilling rig or ROV (Remotely Operated Vehicle). Typical examples of such known devices include the Seafloor Geoservices ROV Drill M80, the Williamson & Associates DWACS (Deepsea Wireline Automated Coring System), the University of Bremen MeBo Sea Floor Drill Rig and the Benthic Geotech PROD (Portable Remotely Operated Drill).

[013] According to a first example form, there is provided a pipeline simulation device, including: a tool able to be at least partially inserted into a seabed; and, a shaft attached to the tool and able to effect movement of the tool relative to the seabed. [014] Preferably, the shaft is able to be held by a seabed rig and the seabed rig is able to effect movement of the tool relative to the seabed, simulating in situ geotechnical pipe-soil interaction on or in undisturbed seabed.

[015] According to a second example form, there is provided a tool for use as part of a pipeline simulation tool assembly, including: a spherical body; and, one or more piezometer ports.

[016] According to a third example form, there is provided a pipeline simulation device, including: a cylindrical body; and, an offset shaft attached to the cylindrical body and able to effect a rotational sweeping movement of the cylindrical body relative to the seabed. Brief Description of Figures

[017] Example embodiments should become apparent from the following description, which is given by way of example only, of at least one preferred but non-limiting embodiment, described in connection with the accompanying figures.

[018] Fig. 1 illustrates an example pipeline simulation device (i.e. tool assembly) with an example seabed rig.

[019] Fig. 2 illustrates an example pipeline simulation device in the form of a toroidal body with an example seabed rig.

[020] Fig. 3 illustrates an example pipeline simulation device in the form of a flat plate with an example seabed rig. [021] Fig. 4 illustrates an example pipeline simulation device in the form of a cylindrical body attached to an offset shaft with an example seabed rig.

Preferred Embodiments

[022] The following modes, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments.

[023] According to a particular example, a pipeline simulation device (i.e. tool assembly) is provided that preferably, though not necessarily, includes an at least partially spherical, or toroidal shaped tool, with a diameter (or in a range of diameters) chosen to suit the scale factor for the pipe to be modelled. Surface roughness of the spherical or toroidal shaped tool is matched to that of the pipe to be modelled. In particular applications the spherical or toroidal geometry has inherent advantages over cylindrical devices (such as a pipe section), in ensuring a more uniform loading and reducing the uncertainty in measuring embedment of the pipeline simulation device into the seabed (especially for test on the uneven seabed). These advantages reduce the uncertainties in the interpreted test result.

[024] A pipeline simulation device or tool assembly includes a tool mounted on a shaft such that the tool can be rotated in a range of speeds about its axis of symmetry, thrust downwards, or moved in a cyclic downward and upward motion on its vertical axis while in contact with or breakaway from the soil formation. This motion may be provided by gripping the shaft in the chuck of a seabed drilling rig rotation unit and engaging the drive for rotary motion or the elevator control for vertical movement. Alternatively, a self- powered tool assembly may be used, or a separate rotary drive mechanism may be adapted for lateral as well as vertical movement of the tool. As an alternative to the spherical or toroidal shaped tool, a flat plate, circular plate or planar tool may be used in contact with the soil formation for acquisition of load bearing data and friction factor estimation. Preferably, movement of the tool is relative to a known datum of a mudline of the seabed.

[025] The pipeline simulation device is preferably equipped with transducers to measure movement parameters such as rotation speed, torque, linear displacement and force, either as part of the tool itself or integral with a drilling unit and in communication with data logging equipment that provides real-time display of measured parameters to a remote operator. The tool may additionally be equipped to measure soil temperature (with one or more temperature sensors) and pore pressure (with one or more pore pressure sensors) at one or more locations on the spherical or toroidal tool. In addition, the temperature of the tool may be changed (e.g. using a heating element) to simulate the effect of temperature changes on pipe-soil interaction during the pipeline operation. By this means, geotechnical pipe-soil interaction and pipe-soil friction factors may be quantified for analysis of pipeline stability, expansion and lateral buckling.

[026] For accurate soil parameter measurements, it is important to ensure that there are no soil disturbances at the test location caused by loading from nearby structures such as the footings of the seabed rig. In addition, depth control of the measuring tool in relation to the mudline is also important. Therefore, the seabed rig is preferably self-level adjusting on widely spaced footings, and equipped with a measuring gauge and video camera and video link for visual resolution and monitoring of the mudline during in situ testing procedures. The video link also provides visual monitoring of the embedment heave profile as the tool contacts and enters the uppermost layer of the seabed. The soil heave profile around the tool may also be visually monitored using a video camera and/or measured, for example using a laser surface profiler, which can assist in interpreting the test results. [027] Referring to Fig. 1, there is illustrated an example pipeline simulation device, i.e. pipeline simulation tool assembly, including a spherical body 1 (i.e. tool) rigidly attached to a shaft 2, such that the spherical body 1 can be rotated about its axis of symmetry 3 and moved vertically on the axis of symmetry 3. Spherical body 1 is preferably equipped with one or more piezometer ports 4 and, in optional embodiments, may contain one or more temperature sensors and/or tri-axial load cells. Shaft 2 is gripped in chuck 5 of rotation unit 6 in seabed rig 7, which provides controlled vertical movement 8 and rotational movement 9 of spherical body 1. Transducers on seabed rig 7 provide real-time measurement of the motion parameters of spherical body 1 , which include rotational speed and torque, displacement relative to mudline 10 and axial load. At least one remotely operated underwater video camera 13 provides visual monitoring and recording of the heave profile 12 of soil displaced during tool deployment. Optionally, laser surface profiler 14 may be provided to scan and measure soil heave profile 12. [028] According to other optional embodiments, tool 1 may be substantially, or at least partially, toroidal or plate (i.e. planar) shaped. Referring to Fig. 2, there is illustrated an alternate embodiment of the tool in the form of a toroidal body Ia. The substantially toroidal shaped tool Ia is rigidly attached to shaft 2 by struts 15 such that toroidal body Ia can be rotated about its vertical axis of symmetry 3 and moved vertically 8 on axis of symmetry 3.

[029] Referring to Fig. 3, there is illustrated another alternate embodiment of the tool in the form of a substantially flat plate Ib (i.e. planar shaped) rigidly attached at its vertical axis of symmetry 3 to shaft 2 such that flat plate Ib can be moved vertically 8 on axis of symmetry 3. Flat plate Ib is preferably circular.

[030] Referring to Fig. 4, there is illustrated an alternate example pipeline simulation device, i.e. pipeline simulation tool assembly, including a cylindrical body 16 (i.e. tool) rigidly attached to an offset shaft 17 such that the axis of symmetry of cylindrical body 16 intersects with, or is substantially in radial alignment with, and perpendicular to, the axis of rotation 3 of offset shaft 17. That is, a section of shaft 17 is offset from a vertical axis of tool 16. The length of cylindrical body 16 is substantially less than the radius of rotation 18 (i.e. the distance of point of attachment of body 16 from the centre of rotation 3 of offset shaft 17). Shaft 17 is gripped in chuck 5 of rotation unit 6 in seabed rig 7, which provides controlled vertical movement 8 relative to mudline 10 and sweeping rotational movement 9 of cylindrical body 16.

[031] In an example method of operation, the pipeline simulation device is preloaded into seabed rig 7 and positioned at the seafloor with tool 1 clear of the mudline 10 by a known vertical distance. There is a choice of several types of test that may then be performed individually or in combination at a particular site, including:

(a) A load controlled test, in which the tool is downwardly thrust into the soil under constant load, simulating the action of a pipe initial embedment under its own weight. (b) A pull-out test, in which the tool is upwardly withdrawn under a controlled pull-out force or at a controlled rate from a depth below the mudline greater than the diameter of the tool, simulating resistance to upheaval buckling and facilitating breakout analysis of a fully buried pipeline. A backfilling mechanism is preferably provided to cover the embedded tool with surrounding soil prior to the pull-out test.

(c) A displacement controlled test in which the tool is cycled in downward and upward movement in the soil at a controlled rate, at different amplitude, frequency and depth 1 1 below the mudline. This simulates the effect of different sea states on the rise and fall dynamic embedment of the pipe in localised remoulded soil during the laying process, or the riser oscillation at the touchdown zone.

(d) A rotational test in which the tool is rotated at a range of speeds, vertical loads and depths below mudline, simulating the frictional resistance of the soil to pipeline movement under buckling and axial loads.

(e) Pore pressure measurement, to measure the development and dissipation of excess pore pressure against the pipe (i.e. changes of effective stress acting on the pipe).

[032] In the case of a variant embodiment that provides for lateral movement of the tool, there is the additional choice of:

(f) A horizontal displacement test in which the tool is moved sideways at a range of speeds (under constant or variable vertical load) and depths below mudline, simulating the resistance to lateral sweeping that governs the level of curvature and bending stress in shallowly embedded pipelines.

[033] In the case of a variant embodiment that provides for rotational sweeping movement of the tool, there is the additional choice of: (g) A horizontal displacement test in which the tool is moved rotationally through an arc at a range of speeds (under constant or variable vertical load) and depths below mudline, simulating the resistance to lateral sweeping that governs the level of curvature and bending stress in shallowly embedded pipelines.

[034] During the abovementioned operations, the heave profile 12 of the soil displaced by the tool may be visually monitored or measured, for example using a video camera and/or a laser surface profiler, to provide an additional correlation link between the in situ data acquired from the pipeline simulation device and other data sets.

[035] Optional embodiments of the present invention may also be said to broadly consist in the parts, elements and features referred to or indicated herein, individually or collectively, in any or all combinations of two or more of the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[036] Although a preferred embodiment has been described in detail, it should be understood that various changes, substitutions, and alterations can be made by one of ordinary skill in the art without departing from the scope of the present invention.