The question of what to do with the piles of drill cuttings which have accumulated on the seabed is one in which Rogaland Research (RF) in Norway has been closely involved for several years. In work carried out for the Norwegian Oil Industry Association (OLF), RF has investigated possible methods of disposing of the piles.
More than a dozen possibilities exist, the main choice being between leaving them in place and moving them. Piles left in place may be left undisturbed, treated or covered. Piles moved may be relocated on the seabed, injected beneath the seabed, or brought back to land. Further sub-options have been identified within these options.
According to Simon Cripps, Chief Scientist for Aquatic Environmental Technology, the main problem for moving a cuttings pile with present technology is that, in the process, contaminants such as heavy metals and hydrocarbons may be released, causing secondary pollution.
Leaving them in place avoids this problem, and would cost less. If contaminants were leaching out, or if layers were being exposed by surface erosion, a pile could be covered or capped.
Hierarchy of drill cuttings disposal options.
Although this work has produced some interesting pointers as to how piles may be dealt with, Cripps points out that much basic knowledge about them is still lacking.
For example, the volume of cuttings has yet to be satisfactorily established. In 1998, a study by Cordah and RF for the UK Offshore Operators Association (UKOOA) of both the UK and Norwegian sectors estimated a total volume of 1,308,127 cu meters in 102 piles involving 2,631 wells.
Piles vary considerably
The study established that the dimensions of the individual piles vary considerably. Areas covered by the piles were found to range between 1,468 sq m and 22,246 sq m, volumes from 214 cu m to 45,000 cu m, and heights from 0.8 meters to 26 m.
Another question yet to receive a definitive answer is the degree and distribution of contamination within the piles. Yet another is their ecotoxicological repercussions -whether they are harmful to marine fauna and flora. There is evidence of changes in populations of benthic fauna as a result of contamination. If the piles are found to have ecotoxicological effects, this would have implications for the choice of disposal method.
More work is now taking place on both sides of the North Sea which should provide more reliable information on some of these basic parameters.
18 research projects
"Now that we know the right people and what kind of information they have, we can ask more specific questions, and get them to fill in the missing gaps," says Cripps. The deadline for the study is the end of the year. Meanwhile UKOOA is preparing to contract out 18 research projects on a broad range of cuttings-related topics.
Having already carried out a certain amount of field-work, RF has been able to develop relatively simple methods for mapping piles, which is essential if the degree and distribution of contamination is to be established. The dimensions and locations of cuttings piles can be established through sonar surveys, both downward-looking from a boat or upward-looking from an ROV. But it is difficult for such surveys to locate accurately the bottom of a pile and even its edges. For this purpose the most reliable method is to take core samples through the entire height of a pile.
The quality of the data will determine the level of interpretation, Cripps says. If samples have been taken over a grid of locations, it should be possible to map the horizontal distribution of the chemical or physical components analyzed. The definition of vertical profiles will depend on the interval of sub-sampling.
More contamination deeper
It is reasonable to suppose that there will normally be more contamination deeper down in a cuttings pile, says Cripps, because over time, cleaner drilling fluids have been used and the cuttings subjected to better treatment before discharge. It could also be that the worst contamination is sealed in by the upper layers, which may provide another argument for leaving them in place. One drawback about the leave-in-place option, however, is that regular inspections would have to take place.
Together with the Dames & Moore consultancy, RF is now involved in a study of operators' drilling records to try to identify exactly what has been discharged along with the cuttings. "This helps us to identify, for an operator, the piles most likely to be contaminated," say Cripps and Dames & Moore's Managing Principal Jens Petter Aabel.
Establishing the best solution for cuttings piles is still some time away, but Cripps is optimistic about the way things are going. "There's a very balanced dialogue between the authorities and the operators in Norway," he says, "And the future on the information gathering side definitely lies in the kind of collaboration which has already become common.";
First newbuild platform removal unit set
The Offshore Shuttle is one of the first specially designed platform removal vessels set to move from concept to reality. Marine Shuttle Operations, which has the concept, was due to invite bids for a main contractor in July.
The winner, due to be chosen in the fourth quarter, will take on EPC responsibility for the hull, lifting systems, and control systems, according to Project Director Doug Smith. Prices for construction of the hull have already been received from 10 yards, in the UK, Norway, Germany, Spain, Italy, the US, and South Korea. From these, a shortlist of three will be selected, with one of which the main contractor will be expected to place the fabrication contract.
Marine Shuttle is organizing funding for the project, which it aims to have in place by year-end. This is intended to take the form of debt financing with part equity.
Ready for 2001
Total development cost for the project is around $200 million, including some contingency funds, Smith says. The first Offshore Shuttle - OS1 - will be ready for operations in autumn 2001, and the company expects to start bidding for work around the end of this year.
Marine Shuttle considers the Offshore Shuttle an effective means of reducing the cost of offshore platform removal due to the ability to remove complete units, thus avoiding the need for extensive offshore preparation work, cutting and dismantling structures and back-loading them onto flat barges, Smith says.
The decision to build the first vessel on spec was helped by the positive feedback coming from operators with upcoming platform removal projects. Marine Shuttle is now performing a series of feasibility studies for, among others, Phillips' redundant Ekofisk platforms, BP Amoco's North-West Hutton and Thistle, and Shell's Brent, as well as more general technical studies.
The Offshore Shuttle is a structure consisting of tubular steel sections 10 meters in diameter. For OS1 the two sides are each about 146 meters in length and 60 meters high. They are joined at the base by a number of transverse tubulars which give the vessel a width of 82 meters. The transverse tubulars, however, run only half the length of the sides, so that in the remaining half a moonpool is formed, with a length of 70 meters and width of 62 meters. The dimensions of OS1 were fixed following last year's Ospar decision to allow only the footings of 10,000-ton plus jackets to be considered for abandonment in situ.
This vessel will be capable of supporting topsides structures up to 22,000 tons and jackets or jacket sections of up to 10,000 tons. The lower limit for both types of structure is 3,000 tons, but for topsides of this size, Smith does not expect the vessel to be competitive with existing alternatives.
Within the Shuttle's tubulars are ballast tanks and pumps. When ballasted down, the vessel can be positioned with a redundant platform within its moonpool, and then undergo deballasting until it is supporting the topsides. If the topsides are wide enough, the platform can rest directly on the vessel's two sides, otherwise it will sit on lifting beams placed on the top of the vessel.
To remove a large jacket, the Offshore Shuttle is rotated into a vertical position, again using the ballasting system, and docked alongside the jacket. Once secured to the vessel, the jacket is cut free at the seabed, and the vessel is returned to a horizontal position, with the jacket supported on its base.
Patents are pending in Norway and elsewhere covering the main functions of the Shuttle's operation, the fendering, and load transfer systems. But Smith is keen to stress that the design is essentially simple. Any abandonment vessel is likely to suffer a lot of deadtime, he says, so the less capital tied up in it, the better.
For this reason, neither controls nor propulsion will be installed on the Shuttle. However, power will be installed on the Shuttle in order to increase the pumping speed of the deballasting operation. The vessel will be maneuvered into position by a spread of four tugs, one of which will control the vessel's operations by telemetry and data link through an umbilical. The vessel will normally be unmanned, except in a topsides lifting operation, when a small crew will be required for adjusting the lifting systems and associated tasks.
For jacket transport, the vessel would have a maximum draft of only 7 meters, enabling it to approach a quay and skid the jacket directly onto shore. But for topsides structures, the draft ranges from 20 meters up to 40 meters, which means the load would have to be transferred to a barge inshore, or to a purpose-built finger pier at a deepwater site.
The Shuttle's potential market is considerably extended by the fact that it is also capable of installing offshore platforms, using what is essentially the reverse of the removal procedure. In the long term, Smith says, the company envisages building at least three units - in addition to OS1, which is intended primarily to work in the North Sea, it hopes eventually to have one located in the Far East and one in the Gulf of Mexico. In the interim it will be possible to transport OS1 by dry tow if it is required for work in theaters outside the North Sea.;
Oil removal technique close to zero discharge
A cost-efficient method has been developed by Rogalands Research (RF) which is claimed to dramatically improve the removal of hydrocarbon components from produced water. Known as CTour, the method dramatically improves the efficiency of dispersed hydrocarbons removal using existing technology and offers a means of removing dissolved hydrocarbons, according to Inge Brun Henriksen, Chief Scientist for process development at RF.
Application of the CTour process.
Development of CTour has been funded by Statoil, BP (now BP Amoco), Elf, Phillips, and Kværner Process Systems, along with the Norwegian State Pollution Agency (STF) and the Research Council of Norway. Patent rights on the process have been secured in Norway and applied for elsewhere, and KPS is licensed to market it worldwide.
The method consists of injecting condensate into the produced water stream before it is treated in a hydrocyclone to remove oil particles. The process whereby the condensate is mixed with the oily water is part of the secret of the method, says Henriksen.
In one series of tests, the oil content was reduced from an initial 139 ppm to 7.2 ppm following CTour treatment in a hydrocyclone. This is well within the regulatory limit in Norway, which is currently 40 ppm. However, serial treatment in a second hydrocyclone led to a significant further improvement, reducing the oil content to less than 0.3 ppm.
The method also provides an efficient means of mopping up dissolved components - there are at present no regulatory requirements for the concentrations of dissolved components in produced water discharges, as there have previously been no methods for removing them, Henriksen says. These dissolved components are benzene, toluene, xylene, and polyaromatic hydrocarbons (PAHs), all of which are much more toxic than oil particles.
In the same series of tests involving two hydrocyclones, benzene content was reduced from an initial 467.7 ppb (parts per billion) to 24.1 ppb, and naphthalenes from 3,178 ppb to 12.3 PPB. PAH concentration was reduced from 296 to 1.1.
In a white paper, the government has proposed a target of zero discharges for Norway's offshore oil industry by 2005. The CTour method offers this prospect for produced water, Henriksen says - in the above tests, the concentrations of dissolved components were in almost all cases reduced to below the "predicted no-effect concentration" (PNEC) level, which in practice is equivalent to zero discharge.
In the case of the dispersed components, instruments were not available to make a precise measurement. However, there is substantial scope for optimizing the process and every reason to believe that the CTour process can be further developed to achieve "zero" discharge of both dispersed and dissolved components, according to Henriksen.
Feasibility studies have indicated that CTour technology can be introduced onto a platform with only marginal increases in investment and operating costs. But, in addition to its ability to provide compliance with regulatory requirements, it also offers economic benefits such as enhancing the window of primary separation so that maximum oil production can be maintained even while the water-cut is increasing to high levels, Henriksen says.
Shuttle tanker fueled by captured VOC emissions
In early June, the Navion Viking, a 130,000 dwt shuttle tanker, set sail from Moss in southern Norway for the Statfjord Field with some novel equipment installed - a plant for capturing emissions of volatile organic compounds (VOCs) and converting them into fuel to propel the tanker.
The prototype plant represents part of an ambitious project backed by 18 oil companies to solve the problems posed by environmentally damaging VOC emissions during crude loading operations offshore, which are responsible for 55-60% of Norway's total VOC emissions.
Under the same project, technology has also been developed for absorbing VOC emissions and returning them to the crude. An absorption plant installed on the Anna Knutsen shuttle tanker has been undergoing testing and commissioning since last summer. This system has now been debugged and is capable of recovering its target of some 70% of emissions, according to Øyvind Lund, Statoil's manager for the VOC project.
It is the intention of the sponsoring oil companies to implement the new technology widely on offshore loading operations on the Norwegian continental shelf. To this end, through the offices of the Norwegian Oil Industry Association (OLF), they are well advanced in negotiating with the government a voluntary agreement which, if all goes according to plan, will be signed this autumn.
If all goes well, the agreement, which will initially be in force for a five-year period, will lead to some two dozen shuttle tankers being equipped with the new technology. This will represent a major contribution to achieving the government's international commitment to a substantial reduction in the Norway's VOC emissions.
The 70% recovery target represents the average proportion which is susceptible to recovery by condensation. The lighter compounds - methane, ethane, and inert gases - are not condensed and continue to be vented. In fact, the proportion of these compounds varies from crude to crude - Statfjord crude has a much lower proportion of lighter gases than Gullfaks, for example.
In the VOC fuel process, VOC emissions in the ship's storage tanks are collected by a manifold system, then passed through a demister, compressed, cooled and put into a three-phase separator. From here the condensed VOCs are pumped to a coalescer filter and thence to the VOC fuel storage tank.
Meanwhile, the lighter gases are recycled through an absorption drier and into a plate cooler in which the remaining liquids are extracted and returned to the storage tank, while the lighter gases are vented. The third phase, which is separated out, is water.
The VOC fuel is stored at normal temperatures but under pressure of 8-18 bar. Before being injected into the ship's engine, they are passed through a high-pressure membrane pump with an output of 400 bar, and then injected into the cylinder top through a solenoid controlled valve. Because they are much lighter than fuel oil, they do not combust easily, so a pilot fuel oil flame is required to allow controlled combustion of the VOC fuel.
At full load it is possible theoretically to replace 92% of fuel oil consumption with VOCs, but in practice, this percentage will be somewhat lower, Lund says. To use VOC fuel, the engines have to be modified for dual fuel usage. Operation of the VOC fuel plant also requires some 2-3 MW of power. Therefore, the investment on each ship will vary according to how much spare power is available and the degree of modification required to the engines. The main contractor for the VOC fuel plant is Hamworthy KSE, and for the engine modifications MAN B&W Diesel A/S.
Meanwhile the absorption process has been developed with Kværner Process Systems as main contractor. It follows the same initial steps as the fuel process, with the VOCs being collected from the storage tanks, passed through a demister and compressed. They are then passed into an absorption column where they are absorbed into a stream of crude and returned to the cargo tanks. Again, the lighter gases are vented. In the absorption process, the VOCs are not used as engine fuel.
The plant installed in a module on the Anna Knutsen weighs about 100 tons. This is not a significant additional weight for a shuttle tanker, and there is scope for optimization to reduce the weight and size, Lund says. Work is also required to make the system easy for the ship's crew to operate.
During a typical loading of a tanker of Navion Viking's or Anna Knutsen's size on the Statfjord Field, approximately 150-200 tons of VOCs are emitted. The recovery of 70% of these emissions provides enough fuel to take the tanker to Rotterdam to deliver its cargo and back to the field. In the case of Gullfaks, enough VOC fuel would be recovered to take the ship to the Mongstad refinery and back.
In rough terms, the conversion of recovered VOCs into fuel would make possible savings of some NKr 3-5 million year in conventional fuel oil. There is an additional environmental benefit from the fuel process in that the content of smoke particles in the engine exhaust is reduced by about 90%, the nitrogen oxide content is reduced by 20-30%, and as VOCs contain no sulfur, these emissions would also be substantially reduced, Lund says.;
Refurbishment, re-sale service cuts decommissioning wastage
As more fields in the North Sea are depleted and close down, specialist contractors are emerging to serve the market in second-hand equipment.
Stavanger-based Valiant Industrier is a relative veteran, having worked in this market since late 1995. The company has teamed with Amec to prequalify for the disposal of Statoil's 2/4-S riser platform topsides, which are due to be removed before the end of next year.
Valiant made its mark refurbishing and reselling drilling derricks and drilling equipment from seven redundant platforms in and around the Ekofisk area - Ekofisk 2/4-B, 2/4-C, 2/4-D, and the two Albuskjell platforms, Cod and Tor. The company also purchased the drilling deck and derrick from Esso's redundant Odin platform, and drilling equipment from Elf's Frigg TCP2 and DP2 platforms.
The equipment was refurbished and most of it has been sold to new users, says Managing Director Sverre Rott. One of the Ekofisk drawworks and electrical equipment from Odin found re-use on R&B Falcon's Seillean production ship.Other equipment was sold to rig builder and repairer Rauma Repola in Finland. Other customers were found in the UK, US, Kazakhstan, and the Far East, often onshore drilling contractors.
At one time, the company came close to what would have been an excellent example of re-use, providing a complete drilling barge for operations on Lake Maracaibo in Venezuela under a turnkey contract with Shell. "We had lined up a barge from Sweden, drilling equipment from Ekofisk, and power equipment and the living quarters from Odin," says Rott. "It would have been a dramatic success." But at the last moment, the customer pulled out.
Rott's enthusiasm for such projects remains undimmed. "We see solutions like this becoming a reality in the future, and the company which can bring them about will have a profitable business," he says.
At the Environmental Northern Seas exhibition in Stavanger in June, Valiant had a choke panel from Ekofisk, a cooling pump from Odin, and a deadline anchor from Frigg on display, representing instrumental, machine, and mechanical equipment. Though 20 years old, the equipment dates from a time when over-design was common, and is probably good for another 20 years.
Paradoxically, however, at a time when oil prices have collapsed and companies are seeking to lower their costs, the re-use market has fallen sharply, Rott reports. A change of attitude is called for if the industry is to overcome its resistance to the idea of re-using second-hand equipment. This resistance is rooted in the days of big spending, he says, but should not be allowed to obscure the potential cost-effectiveness offered by second-hand equipment. It could make a valuable contribution, for example, to providing the low-cost solution required for developing marginal reserves.