Energy efficiency in offshore oil and gas production

The ultimate goal of EFFORT was to develop Energy Efficient technologies and solutions for offshore oil and gas production, and to promote implementation of these technologies. This will result in more efficient power production, reduced energy use and thereby reduced emissions. EFFORT was funded by The Research Council of Norway?s PETROMAKS program and the industrial partners Statoil, PETROBRAS, Shell Technology and TOTAL. SINTEF was project owner and NTNU research partner. Vendor members were Halvorsen Tech, Norway, Alfa Laval Nordic, Sweden, Wartsila, Norway and Dresser Rand, USA. Today 78% of the CO2 emissions from offshore activities are derived from the gas turbines (GT)s used to generate electricity on the installations. However, large amounts of useful energy are lost as heat in the gas turbine exhaust which exits at a temperature of 532°C. The main scope of EFFORT was to investigate utilization of offshore waste heat for power production with focus on offshore specific requirements, the most salient of which are low weight and compact size. The research approach was to characterize the platform heat and power demands, and then develop very sophisticated in-house software models for optimizing the performance of the key heat recovery and power production equipment, such as the WHRU and expanders, as well as evaluating different working fluids, i.e. CO2 and hydrocarbons, for bottoming cycles and other potential power cycles utilizing surplus heat sources such as the gas turbine exhaust, heat from the export compressor and well stream. These models were then used to optimize power production for three real life case studies based on platforms operating offshore on the NCS and in Brazil. The three cases were: 1. An operating semi-submersible platform on the NCS producing mainly gas and some oil operating at 15 MW constant heat demand. 2. An operating brown field on the NCS with marginal heat demand and large power demand, a large reinjection pump installed to maintain reservoir pressure. 3. A green field under construction in Brazil is an FPSO producing mainly oil. Has a high heat demand of up to 65 MW in the initial years of operation, which makes it very different from Case 1. EFFORT showed that there is room to reduce fuel consumption and directly reduce the power production process's CO2 emissions by 22 % for 2 of the 3 cases studied. In both cases engines operate at part load as installed today. For the third case study the room for improvement is 6% reduction in fuel consumption and CO2 emissions. The most effective scenarios for utilizing waste heat were: Scenario 1: Add a Bottoming Cycle Applying a steam bottoming cycle to the gas turbine increases the efficiency of the power production process from 0.38 to 0.51, which is a 34% increase in energy efficiency. For Case 1 which operates at part load, this corresponds to a 22% reduction in fuel consumption and CO2 release which is 60 000 tons CO2/yr. If the engine was operating at a higher load and running more efficiently the reductions would be as high as 25 %. The 22 % reduction in fuel consumption results in an annual savings in operational costs of US$ 17 M due to lower fuel costs and CO2 tax. This gives an equipment payback time of 4 years. The increase in equipment weight on installation of the bottoming cycle is 349 tons. The large weight increase is due to the fact that the now surplus gas turbine cannot be removed as it is installed as part of a crate. The installed weight including framework would be 700 tons. The increase in footprint is 142 m2. Implementation f such a bottoming cycle would be possible if installed during platform construction. A retrofit was not possible in this case as it is not feasible to remove the GT which becomes redundant when installing the bottoming cycle. This is because the GT was installed as part of a crate. A second detrimental cost factor is the very long platform shutdown time required during installation. The bottoming cycle can also be implemented in the FPSO Case 3 also resulting in a 22% reduction in CO2 emissions. The optimum scenario was extraction of low pressure steam to provide process heating. On the FPSO which has a large heat demand the fuel reduction is improved from 12.3% to 21.8% compared to a standard layout by applying a combined heat and power concept. Implementation would result in US$ 13 M Annual Savings in CO2 tax (NCS) and Fuel cost (Brazil). The increase in weight is 198 tons. This weight difference is lower as there was already WHRUs installed on this ship. There are small changes in footprint of 70 m2. Smaller Turbine Size: Replacing a turbine with a smaller turbine running at a higher load and efficiency results in a 2-5% reduction in CO2 emissions. Annual cost savings are approximately US$ 4 M, and pay-back time is less than 1 year. This scenario can be implemented in Cases 1 and 2. It can be performed during routine exchange of the turbine at a minor

SP1 System analysis Concepts meeting the requirements stated in the objectives will be developed in industry partner workshops. Concepts in this context are the compact bottoming power cycles and surplus heat recovery systems in combination with more of t he process equipment on the offshore installation. The potential of i.a. bottoming cycles using transcritical CO2 and compact heat recovery steam generators (HRSG) with once-through (OT) technology will be evaluated with respect to energy efficiency and C O¬2 footprint. Promising concepts will be further subject to techno- economical analyses and Life Cycle Assessment (LCA). SP2 Compact power cycles and utilisation This sub-project will focus on compact bottoming cycles for gas turbines and heat recovery and utilization accommodated for offshore operation, including extending the upper temperature limit for the transcritical CO2 Rankine cycle to beyond 500 °C. Hence, cycles and equipment recognised by low weight and volume, high energy efficiency and work ing fluids that are safe and has a minimum environ. impact are sought. Integration within the existing process with a minimum of modifications and shut-down time is also a topic of research. SP3 Enabling technologies The objective of SP3 is to innovate a nd bring forward compact heat exchanger and expander technologies enabling exploitation of surplus heat for production of electricity and other purposes on offshore installations. The equipment will have to handle novel working fluids and varying stream c onditions. Laboratory and pilot scale experiments will be performed and component pilots will be constructed to support the develop. of the systems, heat exchangers and turbines. Application potential Having 189 gas turbines on the NCS, of which only thr ee are equip. with steam-based bottoming cycles, the applica. potential is large if EFFORT results, dissemin. and spin-offs influence future decisions regarding energy efficiency measures applied offshore.