Comprehensive Flow Assurance Surveillance


An offshore operator requested GATE to develop a virtual meter to allow them to quickly assess the flow assurance risks real-time to support their operations after some of the gauges were reported to be malfunctioning. The tool was designed to require minimum input data but ultimately provide a comprehensive screening of the flow assurance issues which may disrupt the production.

Location: Offshore Ghana, West Africa

Challenges

  • Some of the production flow loops suffered from malfunctioning pressure and temperature gauges. Fluid temperature could not be compared against Wax Appearance Temperature (WAT) as the temperature gauges were located downstream of the comingling point in the manifolds.

  • Dual flowline production through crossover valves (XOVs) could result in flow instability (e.g. slugging or stagnant header).

  • Large flowline size (12” NB) could promote water accumulation and hydrate formation risks. Water inventory calculation was needed to determine how much methanol was required to prevent hydrate formation.

  • Actual cooldown time in certain locations may have been shorter than designed.

  • No means to measure the distribution of production fluids through XOVs.

  • No active monitoring of potential flow restriction in the flowline.

Solution

GATE developed a standalone, comprehensive flow assurance surveillance tool utilizing GATE’s proprietary simulator GATE Prho™ building blocks that, with one simulation run, allows the operator to:

  • Create PT Profiles: determine the current pressure and temperature profiles through water-oil-gas multiphase hydrodynamic calculation.

  • Perform a High-level Wax Risk Assessment: evaluate the temperature profile along the flowlines to determine where paraffin may potentially deposit.

  • Understand Flow Distribution: Calculate the production flow split / distribution through XOVs and evaluate the potential instability.

  • Confirm Water Sweep Velocity: Analyze the oil in-situ velocity along the flowlines and determine where it is not sufficient to sweep the water and causing water accumulation.

  • Determine Water Content: Calculate how much water is in the system and determine how much methanol required to inhibit the water from forming hydrates during shut in condition.

  • Calculate Cool-down Time: Calculate the time where fluid pressure and temperature are favorable for hydrate formation through transient cooldown simulation.

It is important to note, prior to delivering the surveillance tool, GATE conducted an extensive benchmarking study between the tool and the available field data to ensure it is representative of the actual field conditions.

Technical Achievements & Benefits

  • Turnkey, standalone flow assurance surveillance tool which allows the operator to closely monitor potential flow assurance risks.

  • Simple to operate and takes less than approximately one man-hour to input minimal requirements and a current ‘snap-shot’ of any pressing flow assurance risks will be flagged.

  • In future, easy to share with GATE engineers to further support with more thorough analysis, mitigation and remediation efforts.