Case Study: Fines Generation Controlled To Extract Low-Contamination Fluid Samples

Quicksilver Probe focused fluid extraction minimizes both drawdown and pumping time in high-weight oil-base mud

Challenge: Obtain high-purity fluid samples from a low-mobility, potentially unconsolidated reservoir drilled with heavy oil-base mud.

Solution: Use Quicksilver Probe focused fluid extraction to minimize both drawdown and pumping time while reducing fines production, with real-time optical confirmation of fluid purity.

Result: Controlled fines production to collect low-contamination samples after pumping only 10% of the fluid that would be required with conventional sampling techniques.

Sampling in high-fines environment

BG Group needed to obtain multiple low-contamination fluid samples from a compositionally graded oil column. Deploying a wireline formation tester faced the following challenges:

  • 1.88-g/cm3 oil-base mud with a high solids content
  • potentially unconsolidated formation
  • 725-psi [345-kPa] overbalance, expected to result in significant invasion
  • mobility range of 5 to 75 mD/cP.

In this difficult environment for pumping, fines produced from the formation or suspended in the mud system can plug the pump and probe. To minimize fines production from the formation, the drawdown created during sampling cleanup must be kept as low as possible. However, low drawdown is typically achieved by using low flow rates, resulting in long cleanup times and increased rig time costs and the possibility of sticking.

Minimizing drawdown and pumping time

To control drawdown and minimize pumping time, Quicksilver Probe focused fluid extraction was employed with an extrahigh-pressure displacement unit on the fluid-collection flowline and a high-pressure displacement unit on the guard flowline. With these displacement units the combined minimum flow rate when running both flowline pumps is 5.3 cm3/s.

Maximum Quicksilver Probe Focused Fluid Extraction Flow Rate
at 50-b Overbalance

Displacement Unit Minimum Flow Rate at 300 rev/min
Extra high pressure 2.2 cm3/s
High pressure 3.1 cm3/s

An LFA live fluid analyzer and CFA composition fluid analyzer were used with the MDT modular formation dynamics tester for contamination estimation and compositional analysis, which were monitored in real time onshore.

Collecting low-contamination samples

Multiple samples were obtained at three oil stations and one water station. Although minor probe plugging indicated that formation fines were mobilized with the formation oil, the amount of fines produced was controlled by optimizing the flow rates.

Calculations from the LFA analyzer’s contamination prediction show that using conventional probe technology to obtain samples with 10% contamination would have required an average cleanup volume in excess of 500 L per station. With Quicksilver Probe focused fluid extraction, the cleanup volume per station was 50 L.

Subsequent laboratory analysis measured contamination at 1%, 5%, and 6% by weight percent of reservoir fluid in the oil samples. Managing fines production through the flow rate optimization that is possible with Quicksilver Probe focused extraction reduced sample contamination to trace levels without compromising rig time.

Download: Control Fines Generation to Extract Low-Contamination Fluid (0.10 MB PDF)

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Optical Monitoring Verifies Fluid Acquisition

contaminated fluid diverted to the guard flowline and the formation fluid drawn to the sampling flowline.
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