In many countries, there is an energy pricing policy that varies according to the time-of-use. In this context, it is financially advantageous for the industries to plan their production considering this policy. This article introduces a new bi-objective unrelated parallel machine scheduling problem with sequence-dependent setup times, in which the objectives are to minimize the makespan and the total energy cost. We propose a mixed-integer linear programming formulation based on the weighted sum method to obtain the Pareto front. We also developed an NSGA-II method to address large instances of the problem since the formulation cannot solve it in an acceptable computational time for decision-making. The results showed that the proposed NSGA-II is able to find a good approximation for the Pareto front when compared with the weighted sum method in small instances. Besides, in large instances, NSGA-II outperforms, with 95% confidence level, the MOGA and NSGA-I multi-objective techniques concerning the hypervolume and hierarchical cluster counting metrics. Thus, the proposed algorithm finds non-dominated solutions with good convergence, diversity, uniformity, and amplitude.

Although the oil industry seeks to increase the worldwide production of hydrocarbons, various well and reservoir problems can severely reduce oil and gas production from individual wells, leading to the requirement for intervention. For example, in mature fields offshore Brazil, production platforms with minimal open work space and without workover rigs have been a challenge for restoring production in wells with serious scaling problems. The scale build-up reduces production, month by month, until a rig has to be mobilized to replace the production string. Trying to recover production efficiently, service and operating companies have been presenting solutions that circumvent the practical limitations of these locations. In the last three years, an operator's engineering department has worked with service company engineers to develop the means to rig up a 1–3/4-in., 4500-m-long coiled tubing string in a work area of 234 sq. meters and with a crane with a 12-ton maximum capacity. This cooperation allowed intervention in wells on rigless platforms, reducing working time, environmental impacts and costs. These interventions helped to increase oil production from Field A in the Campos Basin and gas production from Field B in the Santos Basin, currently the most important gas field offshore Brazil. Both fields suffer from severe scale deposition -- barium sulfate in Field A and calcium carbonate in field B -- which builds up in the production string and effectively reduces the internal diameter, consequently reducing production. The new successful interventions in these fields using rigless coiled tubing and scale removal techniques enhanced the hydrocarbon production from these fields. In Field A (oil production), interventions were performed in seven (7) wells, providing around a 40% increase in production. In Field B (gas production), interventions were performed in five (5) wells, providing a production increase of around 27% per day. This paper details the planning, logistics and techniques used to successfully meet both challenges. The same solutions would apply in other fields around the world where platform space and scarcity of rigs limit an operator's ability to remediate scale or other wellbore problems that constrain hydrocarbon production. Introduction Market demand has sparked renewed interest in increasing oil and gas production from mature wells in Brazil for the last three years. The result has been an expansion in stimulation techniques using coiled tubing as a thru-tubing tool. Mature production wells, offshore Brazil, are located in both carbonate and sandstone reservoirs. Most of them are naturally depleted and heavy oil / high basic sediment & water (BSW) producers, with a carbonate, sulfate and paraffin scale deposition history. The choice for Coiled Tubing interventions seems to be obvious due to the speed of operation and almost immediate increase in incremental production without production interruption during operations. However, the barriers to project viability included crane lifting capacity, which hindered the ability to place the working reel onboard existing platforms, and the restricted working area available to execute the intervention (Fig.1) in wells ranging from 3500 to 5770 m total depth. Using the correct approach and planning procedures, and involving both service company and operator technical specialists, a new and innovative technique for rigging up and intervention was arrived at to overcome the existing obstacles.

FPSOs (Floating, Production, Storage and Offloading vessels) are ships with capacity to process, store and transfer oil. On the deck of the ship, there is a processing plant which separates and treats fluids from the wells. After separation, the oil is stored inside the vessel cargo tanks and, periodically, it is offloaded into a shuttle tanker through loading hoses.The biggest FPSOs have capacity to process about 200 thousand barrels of oil per day. They are a good solution to develop exploration projects in offshore oil fields, especially in deep water, due to the comparatively low initial investment, short time for installation and great operational flexibility. However, FPSOs can experience problems arising from scale deposition in flexible sub-sea hoses.Recently, in order to explore giant offshore oil fields in Brazil and to avoid the high installation cost of a great number of sub-sea pipelines, VLCCs (Very Large Crude Carriers) have been converted into FPSO's.Over time, some of these converted floating plants have suffered production drops due to the obstruction of both production and gas lift lines by hydrate or scale depositions.In many of these FPSOs, the reduced space and the lack of cranes in the areas close to the flow line access points were a barrier to restoring lost oil production. In some cases, it was necessary to shut-in production from some lines for several months to allow for the installation of a work-over rig. The financial consequences of such shut-in's were extreme.In order to restore production faster and with lower cost, a pioneering method of intervention in FPSO production and gas lift lines was developed based on the use of coiled tubing .This paper presents case histories of successful jobs that cleared two production lines and a gas lift line, including the description of logistics, rig-up process and operation of coiled tubing units in FPSOs. With minor modifications this method can be used in a wide variety of floating production vessels.The FPSO is a floating, production, storage and offloading ship-shaped vessel. Production facilities are mounted on raised supports above the vessel deck. Reservoir fluids pass from subsea production wells, via flowlines and risers, up into the turret and then to the production facilities. Produced oil is stored in the vessel cargo tanks and periodically offloaded onto a shuttle tanker via a loading hose.

This paper addresses a variation on the unrelated parallel machine scheduling problem with sequence dependent setup times. The problem addressed considers the existence of variable electricity tariffs along the planning horizon and the objective is to minimize the weighted sum of the normalized values of makespan and total energy cost. To solve it, a timeindexed mixed integer linear programming formulation was developed. To test it, instances were created with a maximum of 8 jobs and 4 machines and a planning horizon of 144 10-minute intervals totaling one day. The formulation was validated using the CPLEX solver with two different tariff modes. Resumo: Este trabalho trata uma variação do problema de máquinas paralelas não relacionadas com tempos de preparação dependentes da sequência. No problema tratado considera-se a existência de tarifas de energia variáveis ao longo do horizonte de planejamento e o objetivoé minimizar a soma ponderada dos valores normalizados de makespan e do custo total de energia elétrica. Para resolvê-lo, foi desenvolvida uma formulação de programação linear inteira mista indexada no tempo. Para testá-lo, foram criadas instâncias com um máximo de 8 tarefas e 4 máquinas e um horizonte de planejamento de 144 intervalos de 10 minutos, totalizando um dia. A formulação foi validada utilizando-se o resolvedor CPLEX com duas modalidades tarifárias diferentes.