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PETROMAKS2-Stort program petroleum

Improving Efficiency of Offshore Drill-cuttings Handling Process

Alternative title: Effektivisering av Offshore borekakshåndtering

Awarded: NOK 12.4 mill.

Project Number:

234162

Project Period:

2014 - 2018

Partner countries:

In offshore oil drilling, two types of drilling fluids are used: water based fluids (WBFs) and non-aqueous drilling fluids (NADFs). In both cases, the drilling process generates waste fluids and drill cuttings, which consist of residual oil and solids. So lids control techniques are used to separate the solids from drilling waste. Thereafter different technologies are used to make drill cuttings into dry particulate solids as end product. The dry particulates are then conveyed into intermediate storage silos and subsequent processing sites for disposal in landfills or re-use as engineering materials. Transfer from site to site and storage of cuttings can be a challenge and is crucial for cost-effective drilling operation and for minimizing environmental impact. Better understanding of transfer and storage processes will make a positive impact on the whole drilling operation and is necessary for keeping the pace of drilling rigs, currently in operation and also in future designs. SINTEF Tel-Tek, Department of POSTEC has long-term experience, scientific expertise and pilot scale test facilities on handling, storage and processing of particulate materials. Teaming up with oil companies, national and international experts in the field, the project was aimed to address the issues related to handling and storage of drill cuttings. In the proposed project, it is aimed to conduct a detailed research study on transport properties and storage criteria of dry and partially-moist drill cuttings. Modelling of transfer process was tried out to understand the influence of different characteristic properties and to define optimum process parameters. The study focusses on the impact of the drilling fluid towards the conveying properties, storage and the flowability of drill cuttings generated in offshore drilling operation. The experiments have been conducted on fluidization properties, conveying characteristics and flow properties using model drill cuttings. Based on fluidization and pilot scale conveying tests, it could be concluded that the particle mixed with drilling fluid exhibit significantly deviated behavior with respect to the dry conditions. Basically, the minimum fluidization velocity is increased and the pneumatic conveying pressure drop is decreased when drilling fluid is introduced to the dry samples. Since the drilling fluid has a lubricating effect, it lubricates the particle surface and the wall of the pipe. The friction between the air-particles and particle-wall reduce. As a result, in fluidization air stream can penetrate through the bed more easily and hence higher air velocity is required to create pressure drop equal to weight of the bed. The similar effect was observed in pneumatic conveying and hence pressure drop reduces with introducing the drilling fluid. However, when the drilling fluid concentration is increased beyond a certain limit, drilling fluid tends to separate from the solids and accumulate in the voids. Based on the observation, the limiting value was around 10%. Beyond this limit, the mixture starts to behave more like a slurry causing higher pressure drop. Through a multivariate data analysis process on experimental data, a strong correlation is found to calculate the total friction factor comparing the fluidization properties of dry drill cuttings. The correlation is validated with different particle size distributions, bulk densities, oil concentrations, etc., and reasonable good agreements could be seen. Based on the flowability test results, it can be clearly seen that the flowability of the considered sand mixture is reduced with respect to its dry state when it is mixed with a liquid. The main reason for this phenomenon is the increase of inter-particle forces within the bulk solid due to the formation of liquid bridges. It is also observed that the level of flowability depends on the type of the fluid concentration and the time period which the bulk solid has been subjected to a consolidation stress. Different CFD techniques were tried out to simulate conveying of model drill cuttings. The predicted pressure drops under the tested operating conditions are in good agreement with experimental results. Different approaches confirm the possibility of using CFD technique for drill cuttings transportation. However, inclusion of "wetness and/or oil content" in CFD type simulation studies seems still a challenge.

In order to improve drilling performance, many major oil-drilling operators have switched from water-based mud to low-toxicity oil-based system. The waste from oil-based drilling operations consists of the three major substances; water, residual oil and s olids. Different solids control techniques are used to separate the solids from drilling waste. In order to remove residual oil and other environment hazardous chemicals, different technologies are used for treatment of drill cuttings and make dry particu late solids as the end product. The dry particulate solids is then conveyed into intermediate storage silos and further down to sites where it is reused for land filling or as an engineering material. Rig site transfer of cuttings can be a challenge both if pneumatic conveyors or screw conveyors are used. Specially, wet powder is a real challenge since the particles becomes too sticky for easy handling or too dry for acting like slurry Transferring and storage of drill-cuttings in between above mentioned processes are crucial for cost effective oil-drilling operation and to minimize its impact on environment. Better understanding on transfer and storage processes of dry and partially-moist drill-cuttings will make a positive impact on whole drilling oper ation. It is required to improve the present transferring methods/techniques of treated drill-cuttings in order to keep the pace of drilling in oil rigs that are currently in operation and also in future designs. Under the proposed project, it is aimed t o conduct a detailed research study on transport properties and storage criterion of dry and partially-moist solids drill cuttings. Modelling of transfer process, both in dry state and wet state, is necessary to understand the influence of different chara cteristic properties of drill cuttings to define optimum process parameters. On-line monitoring process on drill cuttings, coupled with a reliable modelling technique can be used to optimize the transfer process.

Funding scheme:

PETROMAKS2-Stort program petroleum