TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn field operations from a semi-submersible rig offshore northern Norway, ilmenite has been used as weight material in the drilling fluid. From environmental considerations, it has been desirable to exchange barite with ilmenite to minimise the discharges of heavy metals while drilling with water based drilling fluids. Field trials during the eighties and early nineties have shown that use of ilmenite as weight material can cause severe erosion problems. By adjusting the particle size distribution of the ilmenite to a narrow cut with the particle mean size around 10 micron, the erosion was brought down to a level generally underneath the erosion level experienced when drilling with barite.The paper describes in detail the effect of ilmenite and barite onto erosion of surface lines and manifolds connected to the bulk system, mud mix-, transfer-and supercharge pumps, and mud pump. The erosion of these pipes was reduced when using ilmenite in water based drilling fluids. In oil based drilling fluid there were not observed any significant erosion when using either weight materials. The change in wear on the mud pump pistons and liners will be outlined. Furthermore, the impact the different weight materials have on the erosion of Measurement While Drilling equipment (MWD) will also be outlined. It is also shown that a reduction in rig air pressure for transporting ilmenite in the bulk handling system has reduced the erosion in the exposed bulk pipelines. Finally, the consequences for running the drilling fluid operation are presented.
Barite has to date been the most common weighting material for drillingfluids. Several heavy metal components are associated with the barite. During discharge of drilled cuttings from the use of water based drilling fluid some parts of these heavy metals can be dissolved into the sea. If oil based drilling fluid is used no discharge of drilled cuttings is allowed into the seaon the Norwegian Continental shelf. This cuttings can be re-injected into the formation or can be brought onshore for treatment. If barite is heated to more than 850°C during this treatment, the toxic component barium oxide may be released. The negative impacts from the use of barite in drilling fluids can be avoided if an alternative weight material is used. On the Norne field in Norway a field trial was performed using ilmenite as the weighting material. The paper describes the improved heavy metal content of the ilmenite compared to the barite. Furthermore, it is shown that the heavymetals present are not as biologically available in ilmenite as in barite. The paper describe how the ilmenite improved the ability for the fluid to be recycled and reused. Ilmenite is more resistant to grinding during the drillingprocess, resulting in more stable particle size distribution. This implies a reduced need for dilution of the drilling fluid. This leads to reduced discharges to the sea if water based drilling fluid is used, and less volume tohandle and treat in the case of oil based drilling. The dark color of the ilmenite made it easier to detect and repair any leaks in the transport and bulk handling systems offshore. This will lead to reduced dust problems and an improved occupational hygiene. No significant dust problems were observed during the test at Norne. Introduction Current drilling practice is to use water based drilling fluids whenever feasible, since permanent depositions on the sea bed of cuttings produced when drilled with these water based drilling fluids are allowed. Still, there is a major emphasis onto minimizing the negative impacts from drilling operations on the environment. This emphasis covers the change to less and less harmful chemicals in the drilling operations. Even some of the minerals added to the drilling fluid may contribute to the environmental impact. The leaching of heavy metals from weighting agents to the sea may give a negative impact. The heavy metal content of ilmenite is lower on most components than that of barite. In addition is the bio-availability of the heavy metals lower. Therefore, it is believed to be more desirable to use materials like ilmenitethan barite as weighting agents in drilling fluids. History Ilmenite has been applied earlier in drilling operations in the North Sea. Two tests have been conducted. In the first test two wells were drilled in 1979and 1980 with ilmenite weighted drilling fluids. The ilmenite was a fairly coarse ground material compared to the presently used ilmenite. According to Blomberg et al (1), the drilling fluid properties were easier to control compared to drilling with barite. This is because ilmenite has a lower tendency of being ground down to finer materials. Consequently there is a lesser need offluid dilution. During the drilling operations excessive wear on different types of equipment was observed. This abrasion was anticipated to be a result of usage of a rather coarse ilmenite material. Although the abrasion was anticipated to be merely a result of the particle size distribution than the material itself, no further field evaluations were conducted until the earlynineties.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Barents Sea is an environmentally important ecosystem defined as part of the Arctic. The Norwegian environmental regulation is particular strict for this area, a zero discharge regime prevails. This paper describes the challenges of entering the area for exploration drilling. With reference to a recent operation (2005) a presentation of how the challenges were resolved is given. New procedures and new techniques were implemented to achieve compliance with performance expectations. The succeeding experience lead to important learning that has implications for future exploration drilling in such areas.
Occupational hygiene requirements for operations on the Norwegian shelf when drilling with oil based drilling fluids favours the use of enclosed system for solids control. Personnel working with shale shakers are often exposed to a base oil mist and vapour at an unacceptable level. A principle with the use of rotating separators as an alternative to shale shakers was therefore developed. The paper describes the principle with rotating separators as an alternative to shale shakers in detail. The paper focuses on tests where the separator efficiency from the rotating separator is compared with the efficiency from conventional shakers. The separator principle is to feed the drilling fluid with cuttings from the mud line into a slowly rotating separator that forces the cuttings to move along a very long screen section with selected screen sizes. The drilling fluid is effectively removed from the cuttings since the area outside the screen is slightly vacuumed. This principle result in an apparatus with an effective solids separation being among the better separation results obtained by conventional shale shakers. The paper also describes the improvement on the occupational hygiene and the environmental impacts resulting from the use of the rotating separator compared to the current status from using conventional shakers. Norwegian drilling equipment standards require that the noise level from a device in the drilling area should be less than 83 dB. The paper describes how this requirement is satisfied and that the noise level is far below the requirement level when using the rotating separator. Introduction Use of solids control equipment is essential to maintain drilling fluid within its desired properties and to avoid generation of unnecessary waste streams during drilling1. Since the early 1930's the shale shaker has been the dominating device for primary solids removal2. Additional equipment like desilters, desanders and centrifuges were often used to maintain proper solids control. The optimum solids control design for a particular drilling fluid may not be generally valid for all fluid types3. A combination of shaker and screens applicable for treating a particular water based drilling fluid may for example not be suitable for treating oil based drilling fluids. Furthermore, the suitability of the screen and shaker combination may change during drilling because the drill cuttings morphology changes. Separation of solids with a particle diameter larger than 100 m can be achieved without problems on most shakers today by the application of the correct screen size4. Still, it is necessary to optimise the flow capacity for many shakers. Some improvements have been performed on the shaker design and other improvements have been performed by creating special shaker screens to handle large flow capacity5. The life time of a fine mesh screen used on shale shakers is often limited since in addition to surface wear, entrapped particles within the screen cloth can erode the cloth from the inside because of continuos vibrations. In this respect there is a need for equipment that separates drilling fluids from cuttings more gently. A focus on occupational hygiene aspects when drilling with oil based drilling fluids has forced the drilling industry in Norway to use non-aromatic base oils with good hydrocarbon damp and mist properties6,7. Still, even though ventilation hoods are used on the shakers, it is, in many cases difficult to reach the requirement to keep the hydrocarbon damp and mist content below accepted levels8.
Drilling and completing 4 horizontal and one vertical injection well during the months from October 2000 to May 2001 cost-effectively developed the Glitne subsea field in the Norwegian Continental Shelf. The operation was completed six weeks ahead of budget time and included an extended drilling programme of additional 5000 m compared to the development plan. This paper will focus mainly on the drilling operation and why it succeeded. It will also include a brief description of the whole field development solution. As time is the main cost driver on a subsea operation, beating the time schedule was the primary goal for this operation. The drilling programme focused on a well planned and effective batch drilling operation for all hole sections, and the extended use of cost-effective rotary steerable assemblies. Introduction The planning phase for the development of the field was extremely short. A cost effective development solution and a plan for development was in place in June 2000. Due to the team integration and efficient co-operation between all the service companies and a short decision-making process, the team was able to start drilling in October 2000. The economic viability of this small project was very dependent on good performed drilling and completion operations. It needed to be compared with the very best within the industry, as the drilling and completion budget was 70 % of the total field investment costs. The experience with drilling horizontal wells in the area and in comparable formations was very diverse and could have been a challenge to the drilling operation. Valuable information was gained by experience transfere from the ExxonMobil operated Jotun Field, the Statoil operated Sleipner Field and the Siri Field in the Danish sector. The cost effective drilling and completion operations became very successful, with the rig performing the most effective subsea drilling operation in Statoil. The production wells were batch drilled, with TD of the first 4300 mMD horizontal well being reached after only 17,1 days. The overall performance of the five wells resulted in 203 m/day drilled ref. Rushmore benchmarking1 (Fig. 1 and Fig. 2). The Overall Glitne Field Development Solution Introduction. The Glitne Field is located app. 40 km north of the Sleipner field close to the border between Norwegian and British sectors in block 15/5. The field is the smallest independent field development on the Norwegian Continental Shelf with 4,0 MSm3 of developed oil reserves and a planned production period of only two to three years. The field was first discovered in 1994. The development solution called for four horizontal production wells and one combined water and waste-gas injection well. The wells were drilled from conventional exploration PGB's and completed with re-use of old x-mas trees with production risers to a FPSO, Petrojarl 1. Fig. 3 shows the overall Glitne Field development layout. The License group for the Glitne field is:Statoil (operator)58,9 %Total Elf Fina 21,8 %Pelican 9,3 %Det Norske Oljeselskap 10,0 % The FPSO Petrojarl 1. The Petrojarl 1 underwent major modifications so as to be able to meet the Norwegian regulations and to handle the production from the Glitne wells. The planned and designed maximum oil production rate from the field was 6400 Sm3/day (40.000 bbl/day). The production came early up to the design rate and has produced up to 8000 Sm3/day (50.000 bbl/day). Petrojarl 1 has a storage capacity of 30.000 m3 (190.000 bbl/day). Introduction. The Glitne Field is located app. 40 km north of the Sleipner field close to the border between Norwegian and British sectors in block 15/5. The field is the smallest independent field development on the Norwegian Continental Shelf with 4,0 MSm3 of developed oil reserves and a planned production period of only two to three years. The field was first discovered in 1994. The development solution called for four horizontal production wells and one combined water and waste-gas injection well. The wells were drilled from conventional exploration PGB's and completed with re-use of old x-mas trees with production risers to a FPSO, Petrojarl 1. Fig. 3 shows the overall Glitne Field development layout. The License group for the Glitne field is:Statoil (operator)58,9 %TotalElfFina21,8 %Pelican 9,3 %Det Norske Oljeselskap 10,0 % The FPSO Petrojarl 1. The Petrojarl 1 underwent major modifications so as to be able to meet the Norwegian regulations and to handle the production from the Glitne wells. The planned and designed maximum oil production rate from the field was 6400 Sm3/day (40.000 bbl/day). The production came early up to the design rate and has produced up to 8000 Sm3/day (50.000 bbl/day). Petrojarl 1 has a storage capacity of 30.000 m3 (190.000 bbl/day).
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