Fluid sampling, subsea processing help maximize deepwater development

Growth trends in deep and ultra-deepwater development demonstrate a need to increase hydrocarbon output while improving the asset's net present value. The new application of subsea fluid sampling systems, subsea separators, compressors, multi-phase pumps, and the qualification of critical components would enable remote long-distance assets (even with low reservoir pressure) to be developed economically. Furthermore, the synergy of subsea fluid sampling and subsea processing has evolved into a solution for transforming potential oil and gas reserves into economic return on investment.

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Abili N.
Citi G.
Gassert M.
Eni E&P

Energy demands for oil and gas have driven offshore operators to explore for viable solutions to maximize the recoverable volume of deep offshore assets with innovative technologies. Forecasts from a subsea processing game changer report shows that expenditure on subsea processing systems is expected to exceed $3.4 billion, with deepwater expenditures expected to increase by 130% to $260 billion by 2018. A contributing factor driving this is the demand to deploy over 1,000 additional subsea multi-phase flowmeters, (SMPFM) which provides well diagnostics to measure individual phases (oil, gas, water) without the need for complex conventional testing operations.

Responding to the increase in subsea tree orders for greenfield developments, manufacturers are now developing more SMPFM products to meet well diagnostic demands. In addition, the industry is optimistic on marginal field development prospects (on average 200 to 300 MMbbl each) and growth in viable brownfields. More than 70% of the world's oil and gas production comes from older brownfields, marking a trend for application of enhanced oil recovery (EOR) technologies to meet global demands, such as subsea processing. Due to current development trends, there is pressure on operators to manage capex and opex, increase efficiencies, guarantee flow assurance, and increase production.

Thedeepwater market requires higher capex which is expected to rise from 38% in 2012 to 53% by 2017. This implies that deepwater operators must increase production by maximizing their operating wells in order to future-proof return on investment (ROI). Therefore, SMPFM plays an important role in the financial ROI over the life of the field, and must be configured to determine the optimal recoverable reserves of each production well.

Growth trends in deep and ultra-deepwater development demonstrate a need to increase hydrocarbon output while improving the asset's net present value. The new application of subsea fluid sampling systems, subsea separators, compressors, multi-phase pumps, and the qualification of critical components would enable remote long-distance assets (even with low reservoir pressure) to be developed economically. Offering improved flow assurance and energy efficient processes to topside facilities, these subsea processing technologies are being proven and qualified for deepwater operations, with extensive qualifications under way for ultra-deepwater developments.

Furthermore, the synergy of subsea fluid sampling and subsea processing has evolved into a solution for transforming potential oil and gas reserves into economic ROI. Thus, by adding accurate fluid samples, the potential value of subsea processing can be realized on increased production volume.

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Design life cycle value curve of a typical project.

Field life cycle

The life cycle design for subsea engineering development requires six distinct project phases: explore, appraise/select, FEED, execute, operate, and abandon. The ability to influence the value of the design as it progresses from the appraisal/selection phase to abandonment, follows a logarithmic curve.

The curve shows that the front-end-loading (FEL) region of the engineering design (appraisal/select through FEED) determines the value of the design factor (time, availability and life circle cost). The FEL influences the value for subsea system development, as 80% of the project life cycle is realized at this phase of early engineering development, which accounts for about 20% of the entire project schedule. Therefore, time and effort must be invested during early engineering to get the right design at the conceptual phase.

Development scenarios

Several large oil and gas fields are being developed with multi-phase meters and wet-gas meters. These instruments provide essential data for optimizing production, measuring oil, gas, water fractions, and flowrates.

Recent research and development championed by major operators and original equipment manufacturers is focusing on improving the performance of the metering systems; such as the use of an SMPFM with the developed subsea fluid sampling system implemented at mid-life of the field to check and calibrate the data.

This has created opportunities to improve understanding of the well flow stream for reservoir monitoring, using available transient multi-phase flow model and redundant metering sensors. Obtaining accurate fluid samples for PVT and compositional analysis is vital to understanding the reservoir characteristics, enabling the design optimization and the advancement ofsubsea facilities.

ROV sampling systems

Oceaneering International, Inc., and others have developed ROV capabilities for deployment on deepwater development, providing a reasonable alternative for fluid sampling from subsea facilities. The ability to acquire subsea fluid samples from well production systems without the need for a static platform is key.

The new generation of subsea fluid sampling technologies uses an ROV, a sample collection device, known as a sampling skid, and a storage facility for the collected fluid. The collecting device recovers samples of the fluid from the subsea tree, which is then taken to the vehicle's storage facility. Samples are carried to a second location with temperature and pressure intact, ensuring safe delivery for laboratory analysis.

Subsea fluid sampling provides insight into process conditions at the time of a sample collection. The objective is to collect a representative sample which can be defined as having its physical or chemical characteristics identical to the fluid properties being sampled. This enables the adjustment of SMPFM calibration, bringing many benefits to operators.

Accurate data and detailed knowledge of the reservoir enables efficient production on brownfield and greenfield developments. For fields that have been in production for more than 10 years with life extension capacity, the need for accurate data is vital. This fact, connected to the uncertainty of accuracy in the data currently available or simply the lack of detailed knowledge, reflects the need to acquire reliable data to support EOR programs.

Subsea sampling module

The subsea sampling module (SSM) is ROV operated, providing connections to the subsea sampling interface (SSI). It operates the SSI pressure barriers and captures the required fluid samples by pumping the fluids from the production flow loop or sample point into the sample bottles. It is designed to capture representative samples of the three phases (oil, water, and gas) in isobaric and isothermal conditions. It can meet different requirements in quantity in one subsea deployment, and for use in a wider range of applications.

The SSM is compatible with ROV interface for flexibility of differing sampling applications such as flow rates, water cuts, gas volume fraction (GVF), and viscosities.

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