Drill Cuttings Index

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Drilling, Muds and Cuttings - Frequently Asked Questions What are drill cuttings? Where do they come from? What is the Oil & Gas UK Drill Cuttings Initiative and what does it hope to achieve? Where do cuttings accumulations occur? What are drilling muds? What is the history of using drilling muds in the North Sea? What are synthetic muds and what's in them? How is the Industry currently handling drill cuttings? What do we currently know about the effects of cuttings accumulations on the marine environment? What are the possible solutions for dealing with cuttings accumulations? What is the cost of the Oil & Gas UK Drill Cuttings Initiative and how long will it run? What are the results of R&D phase one? What are drill cuttings? Where do they come from? In the same way that sawdust is produced when a hole is drilled in wood by a domestic drill, small pieces of rock - called cuttings - are created when a well is drilled in rock to reach oil and gas trapped below. These cuttings can vary in size and texture, from fine silt to gravel. The cuttings are carried back to the surface by the drilling "mud", a special fluid used to lubricate and cool the drill bit, and to "plug" the well to prevent blow-outs of oil and gas. At the rig the cuttings are separated from the mud; the mud is recycled to be used again and the small rock cuttings are discharged to the seabed, taken ashore for treatment or re-injected into wells. What is the Oil & Gas UK Drill Cuttings Initiative and what does it hope to achieve? The Oil & Gas UK Drill Cuttings Initiative was launched in June 1998 to tackle the historical legacy of drill cuttings which have accumulated beneath offshore installations in the North Sea. Its goal is to identify the best environmental practice and the best techniques available for dealing with these accumulations in accordance with the principles set out by the OSPAR Convention. Where do cuttings accumulations occur? Cuttings have not accumulated around installations in the southern North Sea, where the higher water currents and wave action have rapidly dispersed them, enhancing natural degradation (the breakdown of any trace hydrocarbons). The rapid dispersal exposes more surface area on the chips of rock, making the breakdown of any traces more effective. But cuttings have accumulated beneath drilling installations in the central and northern areas of the North Sea, in the British and Norwegian sectors, because in these much deeper waters seabed currents are far weaker. The cuttings accumulate on top of each other, so that top layers prevent oxygen and other seawater constituents from penetrating to those below. The lack of oxygen within these accumulations means that bio-degradation is much slower and as a result, any trace hydrocarbons take much longer to break down. What are drilling muds? Drilling muds are liquids used in the drilling process to: control the pressure within a well to prevent oil and gas from forcing its way up and creating a blowout wash the cuttings up out of the well away from the drill bit prevent the well from collapsing during drilling lubricate, cool and provide additional power to the drill bit provide a medium for transferring readings from "downhole" tools Muds have been water-based, oil based or synthetic. They are essentially made of a fluid (water and/or oil), ground rock and clays and have a consistency rather like smooth sauce or custard. They are expensive products and it is clearly in the Industry's best commercial interests to separate as much of the mud as possible from the drill cuttings for re-use before the cuttings are disposed of.

What is the history of using drilling muds in the North Sea? In the 1960s, the first muds to be used were water based. Later, in the 1970s and early 1980s, muds based on diesel, the only lubricant available at the time, were introduced. In 1984, diesel was replaced by low toxicity oil and from 1992 until 1996, in line with regulations, these oil-based muds were in turn phased out to be replaced by synthetic muds. The early water based muds gave poor drilling performance, especially in shale formations. Adding oil lubricant reduced friction and enabled the development of advanced drilling techniques to extend the range and precision of wells, enhancing the recovery of hydrocarbon reserves. Water-based muds have now been improved for more effective drilling of shales, but they still fall short of synthetic mud on performance in the more challenging wells which have increasingly needed to be drilled. The content of drilling muds and their use have long been controlled by strict regulation, as has the discharge of cuttings. What are synthetic muds and what's in them? Synthetic muds get their name from the lubricators which are organic substances (comprising principally carbon, hydrogen and oxygen), selected for their low toxicity and ability to biodegrade. However, research has shown that synthetic muds are not breaking down naturally in seawater as quickly as expected. In a further move to minimise impacts, operators in the UK are in the middle of a significant phased reduction of the discharge of oily cuttings contaminated with synthetic muds. How is the Industry currently handling drill cuttings? Water based muds -a drilling fluid where the main component is water rather than oil - are now used wherever possible and the cuttings disposed of on the seabed after cleaning. (By their very nature, water based muds are easily separated from the cuttings in the cleaning process.) If for technical reasons water based muds cannot be used (when drilling through certain rock formations, for example), synthetic and mineral oil based muds may be employed after consultation with UK Government departments. Where mineral oil-based muds are used, the amount of residue oil which is permitted on cuttings that are discharged overboard after cleaning is limited to 1 per cent. This limit was introduced following a decision by OSPAR in 1992. The technology does not exist to meet this requirement and, as a result, cuttings containing traces of mineral based oil-based muds are not discharged to the seabed. Instead, they are cleaned and taken ashore for treatment or re-injected into wells. Cuttings containing traces of synthetic muds will be dealt with in the same way from the end of 2000. Treated drill cuttings are now being used onshore in the construction of roads and cycle paths, with other possible uses currently being explored. The Industry has invested heavily in new technology to realise this change of approach, involving a commitment by UK operators of some £50 million a year in additional costs. It should also be noted that new drilling techniques such as slimhole, coiled tubing and horizontal drilling (drilling long distances "sideways" through the reservoir and even round corners) are reducing the quantity of cuttings produced.

What do we currently know about the effects of cuttings accumulations on the marine environment? Knowledge about the accumulations and their impact on the environment is limited, although a picture is beginning to emerge through the work of the drill cuttings initiative. The research is adding to our understanding of the physical and chemical characteristics of the accumulations as well as the feasibility of various options for dealing with the piles and their impact on the environment. The overarching principle driving the initiative is what would be best for the environment, using the best technology available. Would it be better overall to leave the accumulations undisturbed on the sea bed or to remove them? To answer this, the Industry has to consider the possible long-term effects of leaving the piles undisturbed as well as the risks involved in lifting them. Scientists are not only studying the environmental impacts on marine habitats, but also those associated with landfill, discharges and atmospheric emissions. The initial stage of research and development is now complete (click here for the results) and the initiative is now moving on to its second and final phase. The issue is highly complex and further research is required to sharpen our understanding of the technical and environmental issues which need to be considered before any final conclusions can be made. What are the possible solutions for dealing with cuttings accumulations? The options include: Leaving the piles undisturbed. Complete removal either by pumping, dredging or the use of specially designed underwater vehicles, with subsequent treatment onshore. In-situ treatment on the seabed, either involving capping the cuttings with impermeable material to close them off, or bio-remediation in which microbes are introduced to accelerate natural breakdown of hydrocarbons. Other in situ treatment includes covering deposits with gravel, spreading, re-injection into a disused or purpose-built well and sub-sea entombment in a specially dug pit. However, at present there are no proven techniques for dealing effectively with cuttings accumulations. Although the technique of bio-remediation is proving successful in some applications on land, its possibilities in the North Sea are as yet unknown. A key study for the Norwegian oil association OLF by the independent Norwegian research institute RF-Rogaland Research ("Disposal of Oil-Based Cuttings") investigates seven broad options including removal technology and land-based treatment techniques. The study examines how tonnages could be handled and assesses each potential solution in terms of technical feasibility, energy use, emissions and discharges, safety risks, environmental impact and cost. The study concludes that some options do not appear feasible and others have advantages and disadvantages, and that as well as further development of each technique, a case-by-case assessment of each accumulation is needed. One element of the research in 2000 will be a pilot lifting operation with trials planned both onshore and off at BP Amoco's North West Hutton platform. It is hoped that valuable information will be gathered about the effectiveness of the lifting technology currently available as well as the likely impacts on the environment. One element of the research in 2000 will be a pilot lifting operation with trials planned both onshore and off at BP Amoco's North West Hutton platform. It is hoped that valuable information will be gathered about the effectiveness of the lifting technology currently available as well as the likely impacts on the environment. What is the cost of the Oil & Gas UK Drill Cuttings Initiative and how long will it run? A group of North Sea operators are funding the initiative through a "joint industry project" (JIP), committing £5.5 million to date. The initiative was launched in June 1998 and the work is being carried out in two phases: the first was completed at the end of 1999; the second is due to finish by the end of 2001. What are the results of R&D phase one? The key findings of R&D phase one can be summarised under the following headings: Accumulation content Environmental impact Potential management options Please click on this link for full reports on each of the seven phase one study areas. Accumulation content What we know about the physical characteristics of cuttings accumulations has been improved but there is still a shortage of reliable data. UKCS cuttings volumes at production sites are estimated at 700,000 m3 in the central North Sea and 500,000 m3 in the northern North Sea. The characteristics of each accumulation varies greatly, according to the types of muds used while drilling, the volumes drilled, cuttings discharge methods, water depth and currents. Further surveying and sampling of accumulations will be required, using a representative "base" range of cuttings piles with different characteristics. Environmental impact of accumulations Environmental impact depends on the nature of the source material, the "pathways" between the source and its immediate environment, and the "receptors", the marine organisms that could potentially be affected. Source - Total hydrocarbon concentrations within accumulations exceed the "no effect concentration" for typical marker species, such as for mud shrimps. - Further research is required to establish whether pathways exist from the accumulations to marine life in the vicinity, which would be necessary for any further ecotoxicological effect. Pathways - heavy metals do not seem to be leaching from the accumulations, nor indeed do they appear to affect marine life, as long as the pile remains undisturbed. - Hydrocarbons within the surface layers (the top 5mm) are decomposing rapidly and re-colonisation is being observed. Further work is required to quantify the rates of these processes. Receptors - Bio-diversity is greatly reduced within the vicinity of the accumulations. - Opportunistic re-colonisation by bristle worms occurs within one year of cuttings discharges ceasing. Management Options There is no proven remediation method Enhanced bio-remediation is too theoretical as yet, but merits further investigation Covering the drill cuttings accumulations is still a potential solution If lifting to the surface is attempted, there are issues related to the secondary contamination of seawater as a result of the accumulations being disturbed and to the significant volumes of water which would be pumped up along with the solid materials. Re-injection to the reservoir is technically feasible but not possible for all North Sea fields. Its legal status is also uncertain Natural degradation also merits further consideration