In this blog post, we’ll explore everything from the basic oil and gas production processes at offshore plants to why simulation is crucial in offshore plant design, and how to optimize using Aspen HYSYS.
Offshore resources such as oil and natural gas lie buried deep beneath the seabed. Various offshore facilities are used to explore, drill, produce, and process these resources. Offshore facilities include equipment such as drillships and FPSOs, and they come in various forms—such as fixed or floating—depending on their purpose, water depth, and production method. Therefore, before constructing an offshore plant, it is necessary to review various conditions and perform numerous evaluations and calculations to identify the optimal design that balances economic viability, safety, and productivity.
There are several stages involved in the process from oil production to sale. First, the exploration process identifies strata where oil and gas are likely to exist; if the project is deemed economically viable, a well is drilled to begin production. During the production process, oil and gas move from the reservoir to the wellbore depending on the reservoir pressure and the properties of the fluids. Key mechanisms that influence the maintenance of reservoir pressure and hydrocarbon production include solution gas drive, gas cap drive, and water drive. Since the produced fluid consists not only of crude oil but also of a mixture of natural gas and water, it is sent to an offshore production facility where it undergoes separation and processing. Production facilities use equipment such as separators, valves, and compressors to regulate the flow, pressure, and state of the fluid and to separate and process the necessary components. Separators separate phases—such as gas and liquid—based on the pressure and temperature conditions of the produced fluids; valves regulate fluid flow; and compressors compress gas to raise it to the required pressure. Subsequently, necessary treatment processes—such as gas dehydration, acid gas removal, and crude oil stabilization—are performed to improve the quality of the products and prepare them for transportation. Processed crude oil is stored and can then be transported via oil tankers or pipelines, while natural gas can be sent ashore via pipelines or, depending on the on-site facilities and production methods, reinjected, liquefied, or processed and transported in other ways. In particular, FPSOs are used as representative floating production facilities because they can process fluids produced from subsea wells in the processing facilities on the upper deck of the vessel, store crude oil inside the hull, and then offload it.
As mentioned earlier, not all offshore plants can ensure economic viability. Since offshore plant projects require massive capital investment, operators focus on constructing facilities that are both safe and highly economical. For this reason, numerous simulations are conducted before constructing an offshore plant to identify the most appropriate design. The key here is not simply to minimize the number of pieces of equipment, but to appropriately arrange the necessary equipment and facilities to reduce initial capital expenditures (CAPEX) and increase the production volume and processing efficiency of oil and gas during the production process, thereby ensuring the overall profitability of the project. The performance and cost of a facility can vary depending not only on the type and number of pieces of equipment but also on how factors such as equipment location, process connections, temperatures and pressures as fluids pass through each piece of equipment, and fluid flow conditions are configured. Furthermore, the process of determining pipe length, diameter, and piping configuration can also affect initial capital expenditures and operating conditions. Therefore, it is important to compare various design options through simulation before incorporating these variables into the actual design. Modern process simulation has evolved beyond simply calculating production volume to comprehensively evaluating equipment design, economic feasibility, energy consumption, safety, and emissions.
Aspen HYSYS is one of the leading process simulation programs used for these purposes. Although it was generally known as HYSYS in the past, it is now marketed as Aspen HYSYS and is used for process modeling, simulation, and optimization in the energy sector, including the oil and gas industry. Using Aspen HYSYS, users can configure a process flow, input conditions such as feed composition, flow rate, pressure, and temperature, and then calculate how the state of the fluid changes as it passes through each piece of equipment. Furthermore, users can place equipment such as separators, valves, and compressors within the process and compare various design options by adjusting the operating conditions of the equipment. This allows users to determine under which conditions the desired production volume and quality can be achieved, as well as how economic viability varies depending on the size and configuration of the facility. Aspen HYSYS enables the integration of economic analysis, equipment design, and energy and safety reviews during the process design phase; currently, it is used not only for design but also for optimizing the operation of existing facilities and improving processes.
Developing an optimized offshore plant model is by no means an easy task. Since models generated by software such as Aspen HYSYS are simulation results based on given conditions and input values, they cannot fully replicate every situation that arises in an actual field environment. In actual offshore plants, numerous variables—such as the characteristics of the seabed strata, changes in fluid composition and production rates, the marine environment, facility condition, operating conditions, safety standards, and maintenance—all interact simultaneously. Therefore, even if a simulation yields a result that is close to optimal, it does not guarantee that the exact same result will be achieved in the actual field. However, this does not mean that using simulation to identify optimal conditions is meaningless. On the contrary, simulation plays a crucial role in allowing us to compare various design options by adjusting different variables before the actual facility is constructed. In particular, by utilizing not only steady-state simulations but also dynamic simulations, we can examine situations such as startup and shutdown, changes in process conditions, control, and safety, thereby enabling a more comprehensive evaluation of actual design and operating conditions. Ultimately, what matters is not simply finding a single value, but rather the process of performing multiple simulations while considering various variables and constraints, and then comparing and verifying the results against the actual design. By repeatedly running simulations while adjusting variables one by one, it is possible to find the most appropriate balance between production volume, cost, safety, and operational efficiency.
