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The paper presents Statoil experiences and status for drilling waste management and treatment in offshore operations, as well as the main challenges and a look ahead on technologies and possible applications. After 40 years of drilling on the Norwegian Continental Shelf, NCS, operators are now experiencing more challenging operations than ever. The wells are more complicated with long sections with high inclinations, years of production have depleted reservoir pressures making the hole stability limits tighter. High Pressure High Temperature, HTHP, fields are developed and the number of Extended Reach Wells, ERD, wells are increasing. Fields are also developed under more harsh environments such as deep waters and arctic climate, some in remote locations making logistics a challenge. Drilling wastes are unavoidable and often expensive by-products of all drilling operations. As drilling operations becomes more demanding and moves into environmentally sensitive areas attention should be paid to drilling waste management and handling when planning. This paper outlines current available waste management options as well as providing some suggestions for possible improvements based on future operational challenges and the corresponding environmental regulations.
The paper presents Statoil experiences and status for drilling waste management and treatment in offshore operations, as well as the main challenges and a look ahead on technologies and possible applications. After 40 years of drilling on the Norwegian Continental Shelf, NCS, operators are now experiencing more challenging operations than ever. The wells are more complicated with long sections with high inclinations, years of production have depleted reservoir pressures making the hole stability limits tighter. High Pressure High Temperature, HTHP, fields are developed and the number of Extended Reach Wells, ERD, wells are increasing. Fields are also developed under more harsh environments such as deep waters and arctic climate, some in remote locations making logistics a challenge. Drilling wastes are unavoidable and often expensive by-products of all drilling operations. As drilling operations becomes more demanding and moves into environmentally sensitive areas attention should be paid to drilling waste management and handling when planning. This paper outlines current available waste management options as well as providing some suggestions for possible improvements based on future operational challenges and the corresponding environmental regulations.
Re-injection of drilled cuttings into a subsurface formation has become a common practice for handling oil wet cuttings during drilling operations in the North Sea areas. Currently, re-injection is technically a straightforward process both on fixed installations and subsea developments. Furthermore, it is feasible to re-inject cuttings into the same well as being drilled. Environmentally, cuttings re-injection is currently considered as an optimum solution. Emission of CO2 and further unfavourable environmental effects associated with the introduction of heavy and sophisticated equipment on the rigs compromises the priority. The paper outlines the emissions of CO2 from offshore re-injection operations and onshore treatment in the North Sea area. The rationale behind the priorities governing best handling option is critically addressed. It is shown that emissions to air are significantly reduced when cuttings is re-injected as opposed to treatment on land. This is even more expressed when 12 ¼"-sections are drilled since these operations require additional boats to handle increased volumes of drilled cuttings. If seabed deposition of oil wet cuttings was an accepted alternative, it is shown that the CO2 emissions would be significantly reduced. Introduction Residual materials from drilling and completion operations consist mainly of drill cuttings, drilling fluids and completion fluids. All processes involved in disposal or recycling of these residual materials will have an environmental impact. These impacts may in some cases be harmful for the environment and in other cases insignificant. Discharge of chemicals not benign to the in situ environment generate the highest impact. However, even in the enterprise of recycling there are environmental impacts; not necessarily from discharges to the sea or ground, but resulting from the emission of different gases like CO2 to the air. During drilling operations most water based drilling fluid chemicals in use on Norwegian offshore operations are considered as not harmful to the environment. Therefore, discharge of drill cuttings and drilling fluid volumes to the sea are permitted. Discharge of cuttings contaminated with oil based drilling fluids or synthetic based drilling fluids are restricted. Discharge to the sea of cuttings containing less than one percent oil on cuttings can currently be permitted. Likewise, permits to discharge cuttings contaminated with synthetic drilling fluid can be given in some cases. Presently, there are no practical methods to remove a sufficient amount of the oil base fluid to reach the one percent limit. Therefore, cuttings contaminated with oil based fluids has to be treated as drilling waste and has to be handled by re-injection to the formation or land site handling. Re-injection of cuttings into the formation is a widely used technique in Norway. The technique was first used on the Norwegian shelf by BP on the Gyda field in 19911. BP used a slurryfying unit on the platform and pumped the cuttings slurry down into the formation underneath the 13 3/8" shoe, through the annulus between the 13 3/8" and 9 5/8" casings. Since the first cutting re-injection operation was introduced, the technique has been applied on most platform based drilling operations where extensive use of oil based drilling fluid was planned. More recently, the technique was further developed to be applicable also for drilling operations from floating rigs2,3.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSubsea re-injection of drilled cuttings has been applied on the Åsgard field to handle oil wet cuttings. For various reasons, oil based drilling fluids have been used in all 12 ¼" and 8 ½" sections at Åsgard. Discharge of oil wet cuttings is not permitted. Cuttings have to be re-injected to the formation or sent onshore for treatment. Onshore treatment and logistics, are expensive and involve a large emission of CO2. If reinjection can be performed, big bag handling operations are significantly reduced. Furthermore, it is difficult to have reliable logistics to bring cuttings onshore. Therefore, cuttings re-injection is the optimum solution for this operation, where the preferred injection point is below the 20" casing shoe.Re-injection is straightforward if cuttings can be reinjected into a formation underneath a large sand formation where the liquid phase of the slurry can leak off. At Åsgard there are no such large sands. Therefore, cuttings have to be re-injected into shale formations. Since the fluid does not leak off sufficiently fast in shale there is a danger that the annulus may be exposed to a too high pressure for a long time. If too large a fluid volume is injected at a time, there is a danger that the fluid may propagate as a fluid bubble to the surface.Leakage to surface has been observed four times at Åsgard. It has been recognized that the cementing results must be better than normal to hinder leakage to surface if cuttings are re-injected into shale formations without sand layers. This paper describes the leakages in detail. It focuses on the necessary improved drilling and cementing precautions to hinder leakage. The paper also describes a technique with alternating re-injection and static periods to make the liquid phase leak off into minor sands and shale, preventing the formation of too high an annulus pressure and hindering the formation of a fluid bubble propagating to the surface.
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