Viscosity Standards for High-Pressure, High-Temperature, and High
Transcript of Viscosity Standards for High-Pressure, High-Temperature, and High
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Viscosity Standards for High-Pressure, High-Temperature, and High-Viscosity Conditions Kurt Schmidt Houston, Texas, USA January 22, 2010
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Viscosity in Reservoir Applications
― Ultradeep GOM (Gulf of Mexico) offshore prospects are being found at higher pressures with heavier oils that are characterized by low gas/oil ratios (GORs). ― These prospects typically have low reservoir energy, low compressibilities, and/or no
aquifers.
― Extraction frequently requires artificial lift (i.e., waterflooding, gas flooding) and the potential for success is significantly affected by viscosity.
― Higher temperatures are required to deal with the challenges of bitumen reserve extraction from oil sands (which is also viscosity-driven).
― Importance of viscosity is twofold: ― Determining productivity using Darcy’s law (describing flow through a porous medium).
― Determine displacement (i.e. ,mobility ratios) in waterflooding (recovery).
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Production Rate
Key factors • fluid viscosity (µ) • formation volume factor (β) • rock permeability (k)
Reservoir-Fluid Sampling and Characterization — Key to Efficient Reservoir Management ; N.R. Nagarajan, M.M. Honarpour, K. Sampath, SPE 103501, (2007)
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Fractional Flow
Viscosity uncertainties have significant impact.
Reservoir-Fluid Sampling and Characterization — Key to Efficient Reservoir Management ; N.R. Nagarajan, M.M. Honarpour, K. Sampath, SPE 103501, (2007)
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Viscosity Measurement
Viscosity of reservoir fluids is routinely measured in commercial laboratories with electromagnetic (oscillating piston), capillary, and falling-body viscometers. The viscometers
― are typically calibrated at atmospheric conditions at specific temperatures with standard calibration fluids
― Extended to elevated pressure and temperature conditions with empirical correlations.
― can also be calibrated at limited temperature and pressure conditions with available reference fluids.
― Quality of viscosity data (reference model) and purity of solvent can be issues.
― The accuracy of viscosity measurements, however, cannot be verified by the equipment operators under the desired HTHP test conditions.
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Case Study
― Study looked at viscosity up to 200 cP at 240 degC at low enough pressure to keep volatiles from coming out of solution (e.g., pressures < 2,000 psi).
― The viscometer was calibrated under ambient conditions and could only be validated for accuracy at ambient pressure and temperatures up to 150 degC using traceable fluids.
― It was found that, at best, expected readings of Cannon calibration fluids at other pressures and temperatures could only be extrapolated from the test certificate values.
― The uncertainty of data at these conditions, especially when they deviated from predicted values based on past models, hindered engineering decisions.
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Pressure Corrections
Accurate information is necessary to adjust readings for higher pressures.
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Viscosity Results
Measurements with the oscillating piston viscometer match literature values at four different temperatures.
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Viscosity Calibration
With capillary viscometers, the K factor can vary 20% or more with pressure.
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HTHP Viscosity Standards
― With greater frequency, we are asked to supply high-temperature, high-pressure, and high-viscosity viscometers and experimental viscosity data at these conditions.
― There is interest in establishing a viscosity standard for the petroleum industry; at this time the group consists of Cambridge Viscosity and Schlumberger.
― We will be expanding this to major petroleum companies in the future.
― Our goal is the development of a reference fluid with viscosities close to that required in practical HTHP situations.
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Viscosity Standard Requirements
― Presently the acceptable (petroleum industry) accuracy of live oil measurements is ~10%.
― An uncertainty of 2% in the viscosity standard would allow laboratories to experimentally determine the viscosity to within 5%.
― The long term target specifications on which we have been focusing are aggressive: 300 degC, 200 cP at 300 degC, 35,000 psi with an 1% accuracy rating.
― Near term, we believe a reasonable solution would be 200 degC, 200 cP at 200 degC, 25,000 psi with a 2% accuracy rating.
― This will yield significantly better information for oilfield decisions and performance.
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Viscosity Standard Key Issues
― Fluid selection: ― Thermally stable
― Nonreactive, not sensitive to UV exposure, etc..
― Easily available at specified purities
― Existing dataset
― Available throughout the world
― Quality, health, safety, and environment (QHSE) friendly
― One fluid, certain temperature and pressure ranges, initially (e.g., Squalane)
― Measurement: ― Round-robin effort with variety of methods and different systematic errors
― Molecular dynamics simulations to supplement experimental data set
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Viscosity Standard Key Issues
― Timing and measurement regions: ― Expand to other temperature and pressure ranges with same fluid or second fluids
― Wells are rarely found with both high temperature and high pressures: staged experiments
― Timing: What is the timing to arrive at the needed standards?
― We may need to develop an interim solution while working toward the longer term solution.
― Dissemination: ― Provide a correlation of the measurements with an expanded uncertainty of <5%
― This fluid and correlation would then be used to calibrate viscometers used in the oil and gas business.
― Industrial group ― Industry consortium funding
― Industry perceives this to be important and funding should be available at some level.
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Initial Thoughts About Fluid Selection
― Our specifications with regard to the fluid may not be achievable with one pure substance, e.g., Squalane.
― Base fluids (alpha or iso-olefin mixtures) that go into making drilling muds as candidates for viscosity standards?
― Their thermal degradability is well known and so are their rheological properties from the work done by the drilling fluids industry.
― The other side benefit is a better handle for clients on using the viscosity data for the equation-of-state and viscosity studies for contaminated fluids.
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Next Steps
― Affirm National Institute of Standards and Technology and International Association for Transport Properties (IATP) interest.
― Determine pressure, temperature, and viscosity ranges of interest to industry (and academia).
― HTHP viscosity standard work similar to IATP’s diisodecyl phthalate (DIDP) efforts.
― Obtain funding from: ― industry
― government
― other?
― Anticipate results will be of wide interest in industry/academic journals.