WO2016146989A1

WO2016146989A1 - Assessment of core samples

Info

Publication number: WO2016146989A1
Application number: PCT/GB2016/050698
Authority: WO
Inventors: David Smith
Original assignee: Natural Environment Research Council
Priority date: 2015-03-18
Filing date: 2016-03-15
Publication date: 2016-09-22
Also published as: GB201504580D0

Abstract

An apparatus for use with a core sampling device, comprising a core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a core sample collected by the core sampling device, wherein at least one side wall comprises a transparent portion through which, in use, at least a portion of the core sample can be seen; and an imaging device, the imaging device being operable to image the core sample through one or more transparent portions of the side wall(s) of the core barrel. The apparatus may be adapted for use underwater, e.g. subsea.

Description

ASSESSMENT OF CORE SAMPLES

The present invention relates to apparatus for and methods of assessing core samples, in particular, but not exclusively, core samples which may comprise gas hydrates.

In exploratory seafloor surveys, it is known to collect one or more core samples from a particular location or locations of interest on the seafloor. The properties and/or characteristics of these collected core samples, such as the structure or quantities of certain materials, may have significant implications in a variety of fields. For example, in the oil and gas industry, possible drilling locations may be identified by the presence of specific structural defects (e.g. gas pockmarks) or by the layering of certain rock types in core samples, which may be indicative of a hydrocarbon reservoir. The study of gas hydrates, more specifically methane hydrates, has become increasingly important, for improving surveying techniques to allow hydrate reservoirs to be avoided in hydrocarbon production and/or for developing hydrates as a potential new commercial energy resource. Gas hydrates are found in reservoirs in subterranean formations, typically in deepwater locations, e.g. under the seabed. At the very low temperatures and very high pressures within these reservoirs, gas hydrates exist in a stable crystalline form. When the temperature increases and/or the pressure decreases, the gas hydrate changes state to a gas, which is accompanied by a massive volume expansion.

This volume expansion can be a significant safety hazard in hydrocarbon production, particularly offshore deepwater hydrocarbon production. Generally, in such operations it may be desired to avoid drilling through any reservoirs containing gas hydrates. However, reservoirs containing gas hydrates are typically located less far below the seabed than traditional oil and gas reservoirs. Accordingly, in order that any reservoirs containing gas hydrates can be avoided, reliable surveying and measuring techniques are required.

Vast amounts of gas, typically methane, are stored as hydrates, particularly in marine sediments and cold regions such as the Arctic. Furthermore, the phase-change behaviour of gas hydrates is becoming better understood. Hence, gas hydrates are now attracting interest as an energy resource . Accordingly, when prospecting or surveying for possible gas hydrate resources, reliable, safe and cost-effective survey techniques are required.

Thus, it may be desirable to economically develop hydrate resources. Such resources are often located in deepwater and/or Arctic areas. However, it can be challenging to find and evaluate shallow gas hydrate deposits, e .g. methane hydrate deposits. For instance, indirect geophysical methods such as electromagnetic (EM) methods or seismic methods typically are unreliable, due to the nature of gas hydrates.

Estimating hydrate content based on water freshening may be unreliable, due to uncertainty over baseline porewater salinity.

Measuring the actual hydrate content of cores recovered during drilling offshore has been especially challenging, as known techniques can be unreliable and/or expensive.

It is known to recover core samples and to bring the samples to the surface in pressurised core barrels. A pressurised core barrel is intended to store a core sample at an in-situ pressure and temperature, in order to maintain the structure of the sample and inhibit decomposition of hydrate crystals due to pressure decrease and/or temperature increase when the core sample is lifted to the surface. The sample can then be analysed at the surface .

However, pressurised core barrels are expensive and can be unreliable. For instance, there is a frequent failure to recover the core sample at a lower than in-situ pressure and/or at a higher than in-situ temperature, which may cause a systematic bias in the reported hydrate content from successful core samples. Accordingly, direct measurement of core data from such core samples may be unreliable. In addition, undesired dissociation of the gas hydrate may even result in failure of the pressurised core barrel as it is being brought up to the surface .

Furthermore, significant health and safety issues arise when handling pressurised containers on the surface. Moreover, space may be limited on an offshore drilling platform or vessel for storing and/or handling a pressurised core barrel, thereby increasing the potential risks.

An alternative method is disclosed in WO 201 1/082870. In this method, a methane content of a bottom sample comprising methane hydrate crystals is determined by: taking a core sample from a bottom sediment in a deepwater area; storing the core sample in a storage chamber; lifting the storage chamber to a predetermined water depth at which any methane hydrate crystals in the core dissociate into water and methane; and measuring an amount of methane released by the lifted core sample .

Another alternative method is disclosed in WO 2014/1 1 1701 , in which the gas content of a core sample is determined by measuring directly the amount of gas released from a collected core sample when the collected core sample is lifted from the seabed. An inner core barrel and a core barrel assembly specifically adapted for carrying out the method are also disclosed.

However, there are drawbacks associated with methods such as those disclosed in WO 201 1/082870 and WO 2014/1 1 170, which involve lifting a core sample through the water column without maintaining the in-situ pressure and temperature of the core sample. In particular, the ability to analyse the in-situ properties of the core sample may be severely limited. For example, although the amount of gas present prior to lifting can be inferred by such methods, gases from substances other than hydrates could also be evolved, which may not be identified and/or may not be accounted for. Also, the entire structure of the core sample may have changed by the time it can be analysed at the surface. Thus, limited (if any) accurate information about, for example, the structure or layering of sediments in the core sample, the quality of gas hydrate crystals (or other crystalline materials) or the in-situ condition of the core sample in general can be provided. Obtaining such data would be desirable if the surveying and evaluation of marine sediments, in particular to identify gas hydrate reservoirs, is to be improved.

A first aspect of the invention provides an apparatus for use with a core sampling device, comprising a core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a core sample collected by the core sampling device, wherein at least one side wall comprises a transparent portion through which, in use, at least a portion of the core sample can be seen; and an imaging device, the imaging device being operable to image the core sample through one or more transparent portions of the side wall(s) of the core barrel. The apparatus may be adapted for use underwater, e.g. subsea.

It should be understood that the transparent portion is transparent to the waves and/or particles detected by the imaging device . In other words, the transparent portion is transparent in the sense that the imaging device can "see" through it. The material selection and design choices made in providing the transparent portion will be governed at least partially by the choice of the imaging device(s) . for example, the transparent portion may be transparent to electromagnetic radiation, e.g. gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves and/or radio waves, and/or acoustic waves. In some embodiments, the transparent portion may only be transparent to electromagnetic radiation or acoustic waves of certain frequencies through. Optionally, the transparent portion may be transparent to one or more of visible light (i.e. visibly see-through), and/or ultra violet light, and/or infrared light, and/or radio waves, and/or x-rays etc. Optionally, the apparatus may comprise a core barrel holder. The core barrel holder may be configured to hold the core barrel such that the imaging device may be operable to image the core sample when the core barrel is held by the core barrel holder. In an embodiment, a substantial part of the side wall(s) may be transparent. The side wall(s) may comprise a plurality of transparent portions. In an embodiment, a transparent portion may extend along substantially the entire length of the core barrel. In an embodiment, a transparent portion may extend around the perimeter of the core barrel. In an embodiment, substantially the entire side wall(s) may be transparent. The greater the proportion of the side wall(s) that is transparent, the greater the portion of the collected core sample that can be imaged.

In an embodiment, the apparatus may be configured such that the collected core sample can be imaged from several directions, e .g. from all sides. For instance, if the core barrel is substantially entirely transparent, then the imaging device and the core barrel may be movable relative to each other such that the collected core sample can be imaged along substantially its entire length and/or around substantially its whole perimeter. In an embodiment, the apparatus may comprise a plurality of imaging devices. The plurality of imaging devices may be operable to image, either individually or together, a substantial portion of the collected core sample .

The imaging device(s) may be operable to image the core sample within a core sampling device . Optionally, the imaging device(s) may be arranged to image to core sample when the core barrel is held by a core barrel holder at a spaced location from the core sampling device after extraction.

In an embodiment, the core barrel may comprise a tubular body.

The transparent portion(s) of the core barrel, or substantially the entire core barrel, may be made from any transparent material suitable for use with the imaging device(s) and at the pressures and temperatures to which the core barrel could be subjected in use (e.g. subsea). In some embodiments, a plastic such as polycarbonate may be a suitable transparent material. For a given material, the side wall(s) may be configured to be sufficiently thick to withstand the elevated pressures to which the core barrel may be subjected in use (e.g. subsea).

Many known apparatus for receiving or storing a core sample comprise a triple wall core barrel system, having a dual walled inner core barrel for receiving a core sample and an outer core barrel. Advantageously, the present invention may require only a single-walled inner core barrel per core sample extracted (i.e. a dual walled barrel system). Accordingly, the apparatus of the present invention may be much easier and/or cost effective to both manufacture and transport in comparison to a triple walled barrel assembly or a conventional barrel made from metal (e .g. steel) . In addition, use of the core barrel may save valuable space on an offshore drilling platform or a vessel such as a boat. A core barrel (i.e. inner core barrel) according to an embodiment of the invention, which is made from a plastic such as polycarbonate may be relatively light. Furthermore, the ease and/or relatively low cost of manufacture of such an embodiment may make the core barrel suitable for use as a disposable item. The core barrel may be intended to be used once or may be re-usable, i.e. in the collection and/or assessment of a plurality of core samples at intervals over a period of time .

Preferably, the imaging device(s) may be operable to image the core sample using one or more imaging modalities to assess one or more properties of the core sample in- situ, e.g. underwater at or close to the seabed. For example, imaging using visible and/or UV light may provide information on the visual appearance and structure of the core sample allowing the identification of substances in the core sample, such as gas hydrates, the amount and/or ratio of each substance, the layering of sediments and/or the quality of crystals, including gas hydrate crystals. Additionally or alternatively, infrared (IR) imaging may be used to produce thermal images of the core sample. Additionally or alternatively, x-rays may be used to produce an image or Computerised Tomography (CT) scan of the internal structure of the sample . Additionally or alternatively, fluorescent light imaging may be utilised, which may be particularly useful for imaging any bacteria which may be present in the core sample. Additionally or alternatively, acoustic imaging, including sonograms, may be used to image the internal structure of the sample to evaluate the characteristics and/or properties of the collected core sample.

In one embodiment, the imaging device(s) may be attached, in use, to a structure, typically comprising a frame member, arranged to support the imaging device. The imaging device may be removably or fixedly attached to the structure.

The core barrel holder may be operable to move the core barrel longitudinally, laterally and/or rotatably relative to the imaging device(s).

Additionally or alternatively, the imaging device(s) may be movable relative to the core barrel when the core barrel is contained in the core sampling device, and/or when the core barrel is held in the core barrel holder. In an embodiment, the apparatus may further comprise at least one drive mechanism operable to move the imaging device(s) relative to the core barrel. The movement of the imaging device may include tilting, rotating, displacing and/or otherwise adjusting the position of the imaging device(s) in any direction relative to the core barrel.

Advantageously, the provision of the at least one drive mechanism may allow the imaging device(s) to image a larger portion of the core sample, e.g. from different angles and positions. In an embodiment, at least one imaging device may be mounted on a separate structure or vehicle, e.g. a remote controlled unmanned submarine vehicle or a remote controlled vehicle configured to move on the seafloor.

Preferably, the apparatus may further comprise one or more data storage devices connectable, in use, to the imaging device(s). The data storage device(s) may be connectable to or integral to the imaging device(s). Typically, the data storage device(s) may be operable to store data and/or images collected by the imaging device(s). Multiple data storage devices may be provided. The data storage device or devices may allow a user to access and analyse the collected data and/or images at his/her convenience. The format in which the images or data are stored may be selected by the user.

The data storage device may be connected or connectable, in use, to a remotely located visual display device (e.g. located offshore on a drilling platform or a vessel, or at an onshore facility) to enable a user to view the images and/or data collected by the imaging device. In an embodiment, the images and/or data collected may be viewable either in real-time or after a delay. In addition to, or as an alternative to, the imaging device(s), the apparatus may comprise at least one sensor or instrument, wherein the at least one sensor or instrument may be operable to measure at least one physical, electrical, material or chemical property of the collected core sample and/or a sub-sample taken therefrom, which optionally may include at least one of: composition; density; temperature; electrical resistivity; magnetic susceptibility; gamma absorbance or emission spectrum; acoustic properties; and elastic properties (e.g. stress, strain or Young's modulus). Optionally, the apparatus may further comprise a micro-gravity sensor operable to detect changes in the background gravitational field caused by the core sample. The sensor or instrument may comprise a mass spectrometer, a gas chromatography machine, a high performance liquid chromatography machine, an x- ray diffraction machine, a nuclear magnetic resonance machine or a microscope, e .g . a polarised light microscope or an electron microscope such as a scanning electron microscope. Consequently, by using the at least one sensor or instrument to log propertie s of the collected core sample, the apparatus may be capable of conducting in- situ (e . g . underwater) one or more of the tests employed under laboratory conditions for core sample s retrieved in pressurised core barrels . Accordingly, the re sults of such te sts may be acquired relatively quickly and/or may be considered more reliable, since the tests may be carried out soon after the core sample or sub-sample taken therefrom is collected and in-situ, e.g. on or close to the seabed under the prevailing subsea temperature and pressure conditions.

The at least one sensor may be connectable to the data storage device or data storage devices. The at least one sensor may comprise an integral data storage device .

Advantageously, by combining data, e .g. images, captured by the one or more imaging means with data captured by the at least one sensor or instrument, a thorough, detailed assessment of the collected core sample may be carried out.

In an embodiment, the side wall(s) may comprise a pressure release means configured to allow fluid to escape from the internal volume when a pressure differential across the side wall(s) exceeds a predetermined amount. The pressure release means may comprise one or more apertures passing through the side wall(s) and one or more plugs adapted to be received within the or each aperture and to seal the or each aperture when received therein. The or each plug may be ejected outwards from the aperture in which it is received when, in use, the pressure differential across the side wall(s) exceeds a predetermined amount. The or each plug may be tethered to the core barrel.

The one or more apertures may be narrower at an inner end than at an outer end. In an embodiment, the pressure release means may comprise one or more frangible portions of the core barrel. For instance, each frangible portion(s) may be defined at least in part by a line of weakness. The or each frangible portion may be configured to break when the pressure differential across the side wall(s) exceeds a predetermined amount, thereby providing an aperture through which fluid can escape from the internal volume of the core barrel.

In an embodiment, the or each pressure release means may be provided with an outer cover layer adapted to break, in use, when the pressure release means. The outer cover layer may be substantially impermeable . The outer cover layer may be disposed over the or each pressure release means on the outside of the core barrel.

In an embodiment, the apparatus may comprise a cap attachable to the core barrel. The cap may have a fluid flow path therethrough. The cap may comprise a flowmeter configured to measure the flow of fluid out of the internal volume of the core barrel through the fluid flow path through the cap. A valve may be provided in the fluid flow path, the valve being operable to open or close the fluid flow path.

In an embodiment, the core barrel and the cap may be provided with complementary threaded portions to facilitate attachment of the cap to the core barrel.

The cap may be configured to fail should the pressure differential across the cap exceed, in use, a predetermined value, e.g. as a result of the dissociation of gas hydrate crystals. In an embodiment, the apparatus may comprise a plurality of core barrels, each core barrel being configured to receive a core sample.

The apparatus may comprise a core barrel storage means capable of storing one or more core barrels. The core barrel storage means may comprise a carousel. The apparatus may comprise a core barrel transport means operable to transport a given core barrel to the core barrel holder for imaging of a sample within the given core barrel. The core barrel transport means may be operable to transport a given core barrel from the or a core barrel storage means to the core barrel holder.

Due to the cost of seafloor drilling and the unpredictable nature of the sea it may be desirable to use only a brief window of time to retrieve as much data as possible . The present invention may facilitate rapid accumulation of useful data by providing the facility to collect and/or assess multiple core samples during only one visit to the seafloor.

The apparatus may further comprise means for lifting the apparatus and/or the core barrel(s) from the seafloor, to recover the apparatus and/or the core barrel(s) and to allow the core sample(s) to be further assessed at the surface. However, unlike the known methods for evaluating a core sample, it is not essential to retrieve the core sample from the seafloor following collection, as the core sample may have been sufficiently assessed in-situ.

The core barrel may be adapted for use with any core sampling device which extracts a core sample that is then stored within the core barrel. Consequently, no additional expensive drilling equipment or parts may be required or any complex retrofitting in order to practise the invention.

The apparatus may further comprise a sub-sampling device operable to extract one or more sub-samples from the core sample. At least one imaging device may be configured to image, in use, the sub-sample(s). Optionally, the sub-samples may be at least or up to 1 cm and/or at least or up to 10 cm across, e .g. in diameter.

Optionally, the sub-sampling device may be configured to cut or drill through the side wall(s) of the core barrel to extract the sub-sample(s).

In some embodiments, the sub-sampling device may further comprise at least one pressurized container configured to store the one or more sub-samples at the in-situ pressure on the seafloor. A second aspect of the invention provides a core sampling device comprising at least one apparatus according to the first aspect of the invention.

In an embodiment, the core barrel(s) is/are disposed within the core sampling device during collection of the core sample .

In an embodiment, the imaging device(s) is/are disposed within the core sampling device . In an embodiment, the core sampling device may comprise a transportation means for transporting the core barrel(s) and the core sample(s) from the core sampling device and positioning the core barrel(s) in the core barrel holder for imaging.

The transportation means may comprise a conveyor or a carousel or any other mechanism suitable for moving and positioning the core barrel. Optionally, the transportation means may comprise separate means for removing (e.g. lifting) the core barrel and core sample from the sampling device and for positioning the core barrel in the core barrel holder. The core sampling device may comprise a wire line core sampling device .

The core sampling device may comprise a drill.

The core sampling device may be adapted for use on the seabed. The core sampling device may be operable to move across the seabed.

The core sampling device may be configured to allow the collection of multiple cores before retrieval of the core sampling device to the drilling rig/sea surface . The core sampling device may be adapted to collect one or more oriented cores.

The core sampling device may be operable to collect a plurality of cores on a single visit to the seabed. Operation of the core sampling device may be controllable remotely. Operation of the core sampling device may be controlled automatically at least in part, e.g. in accordance with a computer program. Thus, for instance, the core sampling device may collect a plurality of core samples from a predetermined number and/or spatial distribution of locations within a region of seabed.

An example of a suitable core sampling device is disclosed in GB2465829, the entire contents of which are incorporated herein by reference . A third aspect of the invention provides a method of assessing a collected core sample, the method comprising:

providing the collected core sample in a core barrel having one or more side walls bounding at least partially an internal volume for receiving the core sample, wherein at least one side wall comprises a transparent portion through which at least a portion of the core sample can be seen; and

using at least one imaging device to image the collected core sample through one or more transparent portions of the side wall(s) of the core barrel.

In an embodiment, the method may comprise holding the core barrel in a core barrel holder.

In an embodiment, the method may be carried out at a depth within a body of water, e.g. on or close to the seabed. The method may be carried out at a deepwater marine location.

In an embodiment, the collected core sample may comprise gas hydrate crystals, e.g. methane hydrate crystals.

In an embodiment, the step of using the imaging device to image the collected core sample through one or more transparent portions of the side wall(s) of the core barrel may be carried out at or below a predetermined water depth.

The predetermined water depth may be selected such that any gas hydrate crystals in the collected core sample are present in a stable crystalline form. The predetermined water depth may be within the hydrate stability zone . The hydrate stability zone is the depth or range of depths within a body of water, where the conditions (pressure and temperature) are such that any gas hydrates remain in a stable crystalline form.

By carrying out the invention within the hydrate stability zone, e.g. at or close to the seabed, the in-situ properties of the collected core sample(s) may be more reliably assessed. The method may comprise the initial step of collecting the core sample(s) using a core sampling device . In an embodiment, the core sample(s) may be collected from a bottom sediment in a deepwater area.

The method may comprise determining at least one property of the core sample from the image(s), including at least one of:

(i) type(s) of material present in the core sample;

(ii) amount of at least one material present in the core sample, e.g. any gas hydrates such as methane hydrate;

(iii) structure of the core sample, such as layering of materials, relative locations or depths of deposits;

(iv) crystal quality and/or size of any crystalline materials present, e.g. gas hydrates; and/or

(v) amount or type of any bacteria present in the core sample . The method does not necessarily require that the core sample is lifted from the sea- floor as the core sample is typically imaged in-situ, e .g. at or close to the seabed. The collected core sample can then be assessed by analysis of the images.

Advantageously, the present invention may enable much faster and more cost-efficient assessment of collected core samples, particularly in comparison with known methods which fundamentally require retrieval of the core sample to the surface (which is often a very slow and laborious process and is not always successful) before the core sample can be assessed. In addition to, or as an alternative to, imaging the collected core sample through the transparent portion(s) of the side wall(s) of the core barrel, the method may include measuring at least one physical, electrical, material or chemical property of the core sample and/or a sub-sample taken therefrom using at least one sensor or instrument, wherein, optionally, the at least one measured property includes at least one of: composition; density; temperature; electrical resistivity; magnetic susceptibility; gamma absorbance or emission spectrum; acoustic properties; and elastic properties (e.g. stress, strain or Young's Modulus) . The method may include storing the collected images and/or data on a data storage device connectable to the imaging device or plurality of imaging devices. Optionally, multiple data storage devices may be used.

In an embodiment, the method may comprise transmitting the collected images and/or data to a location where they may be displayed on a visual display device.

Optionally, the method may comprise extracting one or more sub-samples from the core sample. The method may comprise imaging the one or more sub-samples using at least one imaging device.

In some embodiments, the method may comprise storing the one or more sub- samples within a pressurized container at the in-situ pressure on the seafloor, and lifting the pressurized container to the surface.

In an embodiment, the method may comprise lifting the collected core sample in the core barrel from the seafloor. The core barrel may be held at one or more depths as it is being lifted through the water column, e.g. to allow gas to evolve and/or escape .

The collected core sample may be imaged as it is being lifted through the water column. The collected core sample may be imaged continuously or at intervals as it is being lifted through the water column. By imaging the sample as it is lifted through the water column changes in the core sample may be observed as they occur, e.g. as a result of changes in temperature and pressure. Advantageously, cataloguing the effect on a collected core sample during retrieval to the surface (lifting through the water column) may lead to advances in recovery techniques and improved interpolation of the in-situ properties of recovered samples.

The method may comprise imaging the collected core sample after it has been retrieved to the surface. Images of the collected core sample taken at the surface may then be compared with images taken at depth within the body of water. Such a comparison may be useful in assessing the properties of the core sample. For instance, such a comparison may enable the proportion of a particular material or materials within the collected core sample to be determined. The particular material or materials may comprise a gas hydrate, e.g. methane hydrate .

In another embodiment, the method may further comprise measuring an amount of gas released by the collected core sample during lifting through the water column. Consequently, the in-situ gas content of the sediment from which the core sample was collected may be determined on the basis of the amount of gas released by the collected core sample during lifting.

Advantageously, the measurement of the amount of gas released by the core sample during lifting, e.g. using a capping system and a flowmeter on the core barrel, may result in a quantitative value of the amount of material lost in the core sample due to dissociation. When combined with the imaging and, optionally, sensor data of the core sample (e.g. types of material initially present) obtained in-situ (e.g. at or near the seabed), this may provide more accurate and reliable data as to the in-situ properties of the core sample than either method taken alone . The method may be repeated using a plurality of core barrels to collect and assess a plurality of core samples. Each core barrel in turn may be transported into the or a core sampling device to receive a core sample. Optionally, each core barrel may then be removed from the core sampling device and positioned for imaging. Accordingly, multiple core samples may be collected and/or assessed during a single visit to the seabed.

Since the invention may be practised without retrieving the collected core samples to the surface, the number of core samples that can be collected and assessed in a single visit to the seabed is not limited by the number of core barrels that can be carried by the apparatus. A given core barrel may be used to collect and assess more than one core sample on a single visit to the seabed. A collected core sample may be released from a given core barrel after the collected core sample has been assessed in-situ, allowing the given core barrel to be re-used in the collection and assessment of a further core sample.

The method may be repeated at a plurality of locations within an area of the seabed, in order to survey the area of the seabed.

A fourth aspect of the invention provides a method for surveying an area of the seabed comprising performing the method of the third aspect of the invention at a plurality of locations within the area of the seabed. A fifth aspect of the invention provides a core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a collected core sample, wherein at least one side wall comprises a transparent portion through which, in use, at least a portion of the collected core sample can be seen. A sixth aspect of the invention provides a core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a collected core sample, wherein at least one side wall comprises at least one pressure release means configured to allow fluid to escape from the internal volume when the pressure differential across the side wall(s) exceeds a predetermined amount.

A seventh aspect of the invention provides the use of a core barrel according to the fifth or sixth aspects of the invention in the collection and/or assessment of a collected core sample. In order that the invention can be well understood, embodiments of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross-section of an embodiment of an apparatus according to the present invention along line A in Figure 2;

Figure 2 is a schematic plan view of the apparatus of Figure 1 ; Figure 3 shows schematically another embodiment of an apparatus according to the present invention;

Figure 4 shows a portion of a core barrel according to an embodiment of the present invention; and

Figure 5 shows a capping system according to one embodiment of the invention.

Figures 1 and 2 show schematically an apparatus 100 according to an embodiment of the invention.

Figure 1 shows a cross-section along line A in Figure 2 of an apparatus 100 for use with a core sampling device (not shown) according to an embodiment of the invention. The apparatus 100 comprises a tubular core barrel 1 , wherein at least a portion 2 of the core barrel 1 is transparent. A core sample 3, extracted by the core sampling device, is stored within the core barrel 1. The core sample 3 is typically a cylindrical shape.

The apparatus 100 comprises an imaging device 4, which is arranged to image the core sample 3 through the transparent portion 2 of the core barrel 1.

In some embodiments, the apparatus 100 may be contained within a core sampling device according to an embodiment of the invention. For instance, the imaging device 4 may be disposed adjacent to a break-out table (i.e. extraction point of the core sample), such that it may be operable to image the sample contained within the core barrel 1 as it is lifted within a drill mast. Advantageously, this potentially reduces or minimises the delay between the extraction and imaging of the core sample, thereby minimising the time in which the in-situ condition or properties of the sample may change before the sample is recorded.

In some embodiments, the core barrel 1 may be held by a core barrel holder (not shown), wherein the core barrel 1 is transported to the core barrel holder from the core sampling device after extraction of the core sample and positioned for imaging. The apparatus 100 comprises a frame comprising a plurality of substantially vertical support legs 7 and a rail 5, which is supported by the support legs 7 and extends around the transparent portion 2 of the core barrel 1. Along its entire length, the rail 5 is a substantially constant distance from the outer surface of the core barrel 1. The imaging device 4 is attached to the rail 5 by a drive mechanism 6. The drive mechanism 6 is operable to move the imaging device 4 along the rail 5. Accordingly, the imaging device 4 can image the core sample 3 from any point along the rail 5.

In some embodiments, the imaging device 4 may be connected to a wire or rod suspended from a drilling rig, or the core sampling device, and disposed adjacent to the core barrel 1 . The wire or rod may be retractable to allow the imaging device 4 to be lifted along with the core barrel 1 when removed from the core sampling device.

The imaging device 4 is preferably a camera operable to image at least a portion of the core sample 3 using at least one of visible light, UV light, infrared light, x-rays and fluorescent light. The imaging device 4 may be configured such that its field of view corresponds with or is at least as large as the length of the transparent portion 2 in the longitudinal direction of the core barrel 1. The imaging device 4 may comprise an acoustic imaging device to image at least a portion of the core sample 3 using acoustic waves.

The imaging device may comprise an on-board data storage device comprising a memory and an on-board power supply means, e.g. a battery. The data storage device and/or the power supply means may be integral to the imaging device or may be removable and/or replaceable components.

As illustrated in Figures 1 and 2, the rail 5 surrounds the outer circumference of the core barrel 1. However, in some embodiments the rail 5 may only extend around a portion of the core barrel 1. Therefore, the rail 5 is not limited to a circular shape and may be any shape suitable to support the imaging device relative to the core barrel 1 (e.g. a helix) . The frame member may be made of any strong material or combination of materials suitable to withstand subsea conditions (e.g. steel).

In an embodiment, the support legs 7 may be adjustable, so that the height of the imaging device 4 can be varied.

Alternatively or additionally, the imaging device 4 may be tiltable to vary its angle and/or field of view.

In some embodiments, the drive mechanism may be remotely controllable to enable a user on the surface to control the position of the imaging device 4 on the rail 5. Alternatively or additionally, the frame may be movable, e.g. rotatable, so as to move the imaging device relative to the collected core sample. If the frame is rotatable, or the core holder is operable to rotate the core barrel, then a drive mechanism for each imaging device may not be required. Figure 3 illustrates schematically another example embodiment of an apparatus 100' according to the invention. A core barrel 3 1 comprises a tubular body 32, the entirety of which is transparent. The tubular body 32 may be made from a plastic material comprising polycarbonate. A core sample 33 is located within the core barrel 3 1. The core barrel 3 1 is held within the apparatus 100' by a core barrel holder (not shown).

A frame surrounds the core barrel 3 1. The frame comprises a plurality of support legs 37, which support a rail 35. The rail 35 extends around the core barrel 3 1. Mounted at regular intervals along the rail 35 are four imaging devices 34 arranged to image at least a portion of the core sample 33 through the transparent body 32 of the core barrel 3 1. Each imaging device 34 is associated with a drive mechanism 36 operable to move the imaging device 34 along the rail 35. Also mounted on the rail 35 , between neighbouring imaging devices 34 are four sensors 39. Each sensor 39 is operable, in use, to measure at least one physical, electrical, material or chemical property of the core sample, including at least one of: density; temperature; gamma absorbance or emission spectrum; acoustic properties; and elastic properties (e.g . strain or Young' s modulus).

In some embodiments, the imaging devices 4 may be configured to image the core sample 3 using x-rays. Optionally, the imaging devices 4 may comprise a Computed Tomography (CT) scanner operable to image the internal structure of the sample 3.

Optionally, at least one of the sensors 39 may also be connected to a drive mechanism (not shown), operable to move the sensor(s) 39 relative to the core barrel 3 1.

The apparatus 100' also includes an instrument block 38. The instrument block 38 contains a data storage device and at least one battery (or other power source(s)) . The data storage device is connected to the imaging devices 34 and the sensors 39 to log images of and/or other data concerning the core sample 33. The battery is operable to supply power to the imaging devices 34, the sensors 39 and, if required, the data storage device . The instrument block 38 may be connected to the imaging devices 34 and the sensors 39 wirelessly or by wires or other physical connections.

Alternatively, the data storage device and the at least one battery may be provided separately from each other. The imaging devices and sensors may comprise on-board data storage devices and/or power supply means.

Alternatively or additionally, power may be supplied to the data storage device(s) and/or imaging devices and/or sensors from the surface . A data link, e.g. a cable or wireless or contactless connection such as an acoustic or high frequency connection, may also be provided from the data storage device to a terminal located on the surface (offshore or onshore). Conveniently, the terminal may comprise a display device, thereby allowing a user to view and/or analyse the collected images or data without first having to bring the apparatus up from the seabed. For example, the user may be able to view and/or analyse the collected images and/or data in real-time or after a short delay.

Figure 4 shows schematically a portion of a core barrel 41 according to an embodiment of the invention. The core barrel 41 may be made from a transparent plastic material such as polycarbonate. The core barrel 41 has a plurality of apertures

42 extending therethrough. The apertures 42 extend from the inside of the core barrel 41 to the outside of the core barrel 41. The apertures 42 are narrower at the inner surface of the core barrel 41 than at the outer surface of the core barrel 41. In use, each aperture 42 is plugged and sealed with a bung 43. Generally, it may be preferred that the bung 43 does not protrude from the aperture 42, in which it is fitted. Preferably, the bung 43 may fit in the aperture 42 such that the upper surface of the bung 43 is substantially flush with the outer surface of the core barrel 41. During the collection of a core sample, the core barrel 41 is located within a drill string of a core sampling device. Drilling fluid is pumped around the outside of the core barrel 41. The plugs 43 prevent drilling fluid from entering the core barrel 42. The shape and configuration of the apertures 42 and the plugs 43 is such that the plugs

43 cannot be forced into the inside of the core barrel 41 (in the direction indicated by arrow B) by the pressure exerted by the drilling fluid being pumped around the outside of the core barrel 41. This effect could also be achieved if the apertures 42 comprised one or more steps rather than, or as well as, having one or more sloping sides.

After a core sample has been collected, the pressure within the core barrel 41 may increase . In particular, if the core sample contains gas hydrates and the core barrel 41 is lifted to a depth outside the hydrate stability zone, then the pressure within the core barrel 41 may increase due to the volume expansion that occurs when gas hydrate crystals dissociate and change state from a crystalline form to a gas. When the pressure differential between the inside and the outside of the core barrel 41 exceeds a certain value, the bungs 43 will be forced out of the apertures 42 (as indicated by arrow C). Fluid can then escape from the core barrel 41 through the apertures 42, thereby reducing the pressure differential between the inside and the outside of the core barrel 41. Accordingly, a potential catastrophic failure of the core barrel 41 may be avoided. Furthermore, by the time the core barrel is lifted to the surface, any internal pressure build-up may have been mitigated and/or reduced, meaning that it may be relatively easy and safe to handle the core barrel 41 (as compared with handling a pressurised core barrel) .

The pressure differential between the inside and the outside of the core barrel at which the plugs are ejected from the apertures can be pre-determined by varying the size, dimensions, number and distribution of the apertures, the material from which the plugs and the core barrel are made, and/or the tightness of the plugs within the apertures. Typically, the plugs 43 and apertures 42 may be configured to ensure that the plugs 43 are ejected before the pressure inside the core barrel 41 reaches a dangerous level, thereby preventing the core barrel 41 from failing. The core barrel 41 may then be re-used with one or more replacement plugs 43, as required. The plugs 43 may be tethered to the core barrel 41 , so as to prevent them being lost when they are ejected from the apertures 42. It will be appreciated that the arrangement of apertures 42 and plugs 43 shown in Figure 4 is just one example of a suitable pressure release means configured to allow fluid to escape from the internal volume when the pressure differential across the side wall(s) exceeds a predetermined amount. Figure 5 shows a capping system 5 1 for use with a core barrel according to an embodiment of the invention. The capping system 5 1 comprises a housing 52 for receiving, in use, a core barrel (not shown). In some embodiments, screw threads may be provided on the outer surface of the core barrel and the inner surface of the housing 52, to enable the core barrel to be received securely within the housing 52.. In an embodiment, at least a portion of the housing 52 may be transparent and located to overlap with a transparent portion of the core barrel, in use, thereby allowing a collected core sample to be imaged. Optionally, the entire body of the housing 52 may be transparent. The capping system 5 1 further comprises a top cap 53 having a fluid flow path therethrough, which is attached to a measurement device 54 having an outlet 55.

The measurement device 54 may comprise a flowmeter connected to a data storage device and a power supply for providing power to the flowmeter and, optionally, to the data storage device. The flowmeter may be a coriolis flowmeter or alternatively the flowmeter may be a three-phase flowmeter for measuring the flow of and distinguishing between liquid, gas and mixtures of liquid and gas.

A data link, e.g. a cable or wireless or contactless connection such as an acoustic or high frequency connection, may also be provided from the data storage device to a display device located on the surface, thereby allowing a user to analyse at least a portion of the data collected by the flowmeter, e.g. in real-time .

The use of a capping system comprising a measurement device such as a flowmeter may allow for the measurement of evolved fluid from a core sample within the core barrel, e.g. as a core sample containing gas hydrates is lifted through the water column. This information may be usefully combined with images of the core sample taken using the apparatus according to the invention, to provide a detailed picture of the nature of a collected core sample.

It should also be noted that the apparatus is not intended to be limited to a single core barrel and that more or fewer core barrel assemblies may be provided. Any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and sub-combinations of one or more features described herein.

While the invention has been disclosed with reference to certain exemplary embodiments, many modifications may be apparent to the person skilled in the art without departing from the scope of the invention.

Claims

1. An apparatus for use with a core sampling device, comprising:

a core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a core sample collected by the core sampling device, wherein at least one side wall comprises a transparent portion through which, in use, at least a portion of the core sample can be seen; and an imaging device, the imaging device being operable to image the core sample through one or more transparent portions of the side wall(s) of the core barrel.

2. The apparatus of claim 1 , further comprising a core barrel holder configured to hold the core barrel such that the imaging device is operable to image the core sample when the core barrel is held by the core barrel holder.

3. The apparatus of claim 1 or claim 2, wherein the transparent portion(s) extend along substantially the entire length of the core barrel.

4. The apparatus of any one of the preceding claims further comprising a plurality of imaging devices.

5. The apparatus of any preceding claim, wherein at least the transparent portion(s) of the side wall(s) is/are made of a plastic material, optionally or preferably comprising polycarbonate.

6. The apparatus of any preceding claim, wherein the imaging device(s) is/are operable to image the core sample using one or more of:

(i) visible light;

(ii) ultraviolet light;

(iii) infrared light;

(iv) x-rays;

(v) fluorescent light; and/or

(vi) acoustic waves.

7. The apparatus of any preceding claim, further comprising a frame member arranged to support the imaging device(s), optionally or preferably wherein the imaging device(s) is/are removably or fixedly attached to the frame member.

8. The apparatus of any preceding claim, wherein the core barrel is movable longitudinally, laterally and/or rotatably relative to the imaging device(s) .

9. The apparatus of any preceding claim, wherein the imaging device(s) is/are movable relative to the core barrel.

10. The apparatus of claim 9, further comprising at least one drive mechanism operable to move the imaging device(s) relative to the core barrel, wherein the movement of the imaging device includes one or more of tilting, rotating, displacing and/or otherwise adjusting the position of the imaging device(s) in any direction relative to the core barrel.

1 1. The apparatus of any preceding claim, further comprising one or more data storage devices connectable, in use, to the imaging device(s), where each data storage device is operable to store data and/or images collected by at least one imaging device.

12. The apparatus of claim 1 1 , wherein one or more of the data storage devices is/are connected or connectable, in use, to a remotely located visual display device.

13 . The apparatus of any preceding claim, further comprising at least one sensor or instrument, wherein the at least one sensor or instrument is operable to measure at least one physical, electrical, material or chemical property of the collected core sample or a sub-sample taken therefrom, optionally or preferably including at least one of:

composition;

density;

temperature;

electrical resistivity or magnetic susceptibility;

gamma absorbance or emission spectrum;

acoustic properties; and elastic properties (e.g. stress, strain or Young's modulus) .

14. The apparatus of claim 13 as it depends on claim 1 1 or claim 12, wherein each sensor is connected to a data storage device.

15. The apparatus of any preceding claim, wherein the side wall(s) further comprise a pressure release means configured to allow fluid to escape from the internal volume of the core barrel when a pressure differential across the side wall(s) exceeds a predetermined amount.

16. The apparatus of claim 15, wherein the pressure release means comprises:

one or more apertures passing through the side wall(s); and one or more plugs adapted to be received within the or each aperture and to seal the or each aperture when received therein;

wherein, the pressure release means is configured such that the or each plug is ejected outwards from the aperture in which it is received when, in use, the pressure differential across the side wall(s) exceeds a predetermined amount.

17. The apparatus of claim 15 or claim 16, wherein the pressure release means comprises one or more frangible portions of the core barrel, wherein the or each frangible portion is configured to break when the pressure differential across the side wall(s) exceeds a predetermined amount, thereby providing an aperture through which fluid can escape from the internal volume of the core barrel.

18. The apparatus of any preceding claim, further comprising:

a cap attachable to the core barrel, wherein the cap comprises a fluid flow path therethrough; and

a flowmeter configured to measure the flow of fluid out of the internal volume of the core barrel through the fluid flow path through the cap;

wherein a valve is provided in the fluid flow path, the valve being operable to open or close the fluid flow path.

19. The apparatus of claim 18, wherein the cap is configured to fail should the pressure differential across the cap exceed, in use, a predetermined value.

20. The apparatus of any preceding claim, further comprising a plurality of core barrels, each core barrel being configured to receive a core sample.

21. The apparatus of any preceding claim, further comprising a core barrel storage means capable of storing one or more core barrels.

22. The apparatus of claim 2, or any one of claims 3 to 21 as it depends on claim 2, further comprising a core barrel transport means operable to transport a given core barrel to the core barrel holder for imaging of a sample within the given core barrel.

23. The apparatus of claim 22 as it depends on claim 21 , wherein the core barrel transport means is operable to transport a given core barrel from the core barrel storage means to the core barrel holder.

24. The apparatus of any preceding claim, further comprising a sub-sampling device operable to extract one or more sub-samples from the core sample, optionally or preferably wherein at least one imaging device is configured to image, in use, the sub-sample(s).

25. The apparatus of claim 24, wherein the sub-sampling device is configured to cut or drill through the side wall(s) of the core barrel to extract the sub-sample(s).

26. The apparatus of claim 24 or claim 25, wherein the sub-sampling device further comprises at least one pressurized container configured to store the one or more sub-samples at the in-situ pressure on the seafloor.

27. A core sampling device comprising at least one apparatus according to any of claims 1 to 26.

28. The core sampling device of claim 27, wherein the imaging device(s) is/are disposed within the core sampling device.

29. The core sampling device of claim 28, further comprising a transportation means for transporting the core barrel(s) and the core sample(s) from the core sampling device and positioning the core barrel(s) in the or a core barrel holder for imaging.

30. The core sampling device of claim 29, wherein the transportation means comprises a conveyor or a carousel.

3 1. The core sampling device of any of claims 27 to 30, further comprising a lifting means for lifting the core barrel and the core sample from the seafloor.

32. The core sampling device of any of claims 27 to 3 1 , further comprising a drill.

33. The core sampling device of any of claims 27 to 32, wherein the device may be operable to do one or more of:

move across the seabed;

allow the collection of multiple cores before retrieval of the core sampling device to a drilling rig/sea surface;

collect one or more oriented core samples; and/or

collect a plurality of core samples on a single visit to the seabed.

34. A method of assessing a collected core sample, the method comprising:

35. The method of claim 34, further comprising holding the core barrel in a core barrel holder.

36. The method of claim 34 or claim 35, further comprising the initial step of collecting the core sample(s) using a core sampling device .

37. The method of any of claims 34 to 36, further comprising determining at least one property of the core sample from the image(s), including at least one of: (i) a type(s) of material present in the core sample;

(ii) an amount of at least one material present in the core sample, e.g. any gas hydrates such as methane hydrate;

(iii) a structure of the core sample, such as layering of materials, relative locations or depths of deposits;

(iv) a crystal quality and/or size of any crystalline materials present, e.g. gas hydrates; and/or

(v) an amount or type of any bacteria present in the core sample .

38. The method of any of claims 34 to 37, further comprising measuring at least one physical, electrical, material or chemical property of the core sample or a sub- sample taken therefrom using at least one sensor or instrument, wherein the at least one measured property includes at least one of:

composition;

density;

temperature;

gamma absorbance or emission spectrum;

acoustic properties; and elastic properties (e .g. stress, strain or Young' s Modulus).

39. The method of any of claims 34 to 38, further comprising storing the collected images and/or data on at least one data storage device connectable to the imaging device or plurality of imaging devices.

40. The method of claim 39, further comprising transmitting the collected images and/or data to a location where they may be displayed on a visual display device .

41. The method of any of claims 34 to 40, further comprising extracting one or more sub-samples from the core sample .

42. The method of claim 41 , further comprising imaging the one or more sub- samples using at least one imaging device .

43. The method of claim 41 or claim 42, further comprising: storing the one or more sub-samples within a pressurized container at the in-situ pressure on the seafloor; and

lifting the pressurized container to the surface.

44. The method of any of claims 34 to 43, further comprising lifting the collected core sample in the core barrel from the seafloor.

45. The method of claim 44, wherein the collected core sample is imaged as it is lifted through the water column, either continuously or at intervals during the lifting.

46. The method of claim 44 or claim 45, further comprising imaging the collected core sample after the collected core sample has been retrieved to the surface .

47. The method of any of claims 44 to 46, further comprising:

measuring an amount of gas released by the collected core sample during lifting through the water column using a flowmeter.

48. A method of assessing a plurality of collected core samples, the method comprising repeating the method of any of claims 34 to 47.

49. The method of claim 48, wherein each core barrel in turn is transported into the or a core sampling device to receive a core sample and is then removed from the core sampling device and positioned for imaging.

50. A method for surveying an area of the seabed comprising performing the method of any of claims 34 to 49 at a plurality of locations within the area of the seabed.

5 1. A core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a collected core sample, wherein at least one side wall comprises a transparent portion through which, in use, at least a portion of the collected core sample can be seen.

52. A core barrel having one or more side walls bounding at least partially an internal volume for receiving, in use, a collected core sample, wherein at least one side wall comprises at least one pressure release means configured to allow fluid to escape from the internal volume when the pressure differential across the side wall(s) exceeds a predetermined amount.

53. Use of a core barrel according to claim 5 1 or claim 52 in the collection and/or assessment of a collected core sample .