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Oil-Based Mud Contamination in Gas-Condensate Samples

Oil-Based Mud Contamination in Gas-Condensate Samples. R&D Results to Date March 2008 Work Completed 2005-2006 Norsk Hydro / ConocoPhillips Open Research Results. Curtis H. Whitson Robert Mott Øivind Fevang. r-z- θ Sensor EOS Compositional Model. Main Conclusion.

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Oil-Based Mud Contamination in Gas-Condensate Samples

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  1. Oil-Based Mud Contaminationin Gas-Condensate Samples R&D Results to Date March 2008 Work Completed 2005-2006 Norsk Hydro / ConocoPhillips Open Research Results Curtis H. Whitson Robert Mott Øivind Fevang

  2. r-z-θ Sensor EOS Compositional Model

  3. Main Conclusion Standard GC-based decontamination methods can provide accurate estimates of true in-situ composition. • Even when BHFP drops below the dewpoint. • Independent of relative permeability effects. • For any type of OBM. • For any richness of the condensate. • Even though the measured PVT properties are not representative of in-situ fluids.

  4. Reservoir Fluid Initial pressure OBM type Grid Relative permeability Horizontal permeability kv/kh Production rate Clean-up time OBM volume How to introduce OBM Rate for sampling Tool contact area Lean & Rich Condensates Near-saturated 2-component & Diesel Heterogeneities Rock & Linear Curves 10 & 1 md 1 & 0.1 0.5 – 1 L/min 6 – 24 hr 5 – 13 cm invasion Initialize & Injection Constant & Variable / Shut-in 5 cm x 5 cm & 10 cm x 10 cm Sensitivities Studied

  5. Obervations • Key to degree of OBM contamination: • Initial OBM depth of invasion. • Cumulative production before sampling. • kv/kh ratio. • Less important parameters: • Heterogeneity. • Drawdown. • Flow area into tool. • Relative permeability.

  6. Observations(continued) • Leaner gas condensates have higher OBM contamination, all else being the same. • Dewpoint may either rise or drop because of OBM contamination. • Recommended method for extrapolating OBM contamination uses mol-% vs time on log-log plot. • Avoid large rate changes just prior to sampling. • It is still possible to obtain in-situ representative samples when FBHP drops below dewpoint.

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