Case Study: Successfully Sampling Viscous Oils in Northwest India

Quicksilver Probe focused fluid extraction collects ultralow-contamination, PVT-quality openhole samples

Challenge: High-quality samples of viscous oil were needed from wells drilled with oil-base mud to optimize well completion and production facilities design.

Solution: Quicksilver Probe focused fluid extraction separates oil-base mud filtrate from high-viscosity formation fluids for collecting ultralow-contamination samples.

Result: Improved field development on the basis of the data from the PVT-quality samples—some with no measurable contamination—obtained with Quicksilver Probe focused extraction.

Unsuccessful conventional methods

Viscous oils can be especially difficult to sample using conventional technology. With its relatively lower viscosity, oil-base mud filtrate flows preferentially to sampling devices, increasing the contamination level and often leaving high-viscosity formation fluids in the formation.

Cairn Energy India Pty Ltd was plagued with this problem in acquiring oil samples at its Bhagyam field in the Barmer basin in northwest India. The reservoir is saturated and exhibits compositional oil grading, with 15 dAPI oil in the north to 52 dAPI oil farther south. The oils have a high viscosity and pour point resulting from their high wax and asphaltene content. Compounding the sampling challenges was the use of oil-base mud to avoid shale collapse in the reservoir section.

Long pumping times using conventional technology did not achieve good-quality representative samples for laboratory PVT analysis. Contamination-free samples could be collected only from cased wells, which meant they were obtained after the well had been completed and were therefore not of much use in optimizing the well completion and production facility design.

Focused-fluid quality

Quicksilver Probe focused extraction deployed in a campaign to improve fluid-acquisition quality for sampling. Of the 18 samples collected in two Bhagyam wells, 15 samples were of PVT quality, and 6 of these showed no contamination at all. Comparison to a sample obtained in a cased well showed overall similarity in composition, unlike an openhole sample obtained by conventional methods.

PVT insight

With the detailed PVT data obtained from the contamination-free samples acquired with Quicksilver Probe focused fluid extraction, Cairn is conducting field development studies to improve reserves estimation, operation and equipment designs, and flow assurance.

Download: Successfully Sampling Viscous Oils in Northwest India (0.22 MB PDF)

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Improving Completions with Data from PVT-Quality Samples

Map of IndiaComparison of samples collected from the same location in Bhagyam field shows that samples of fluid extracted with the Quicksilver Probe focused-flow method in open hole (red) closely resemble the sample obtained using a monophasic wireline (WL) sampler in a cased hole (green). The sample acquired with a conventional wireline formation tester in open hole (blue) is tainted by unremoved contamination of up to 39.5 wt %.
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Quicksilver Probe
The concentric probe design employed by Quicksilver Probe focused extraction acquires virtually contamination-free reservoir fluid for downhole fluid analysis and sample collection. Visit Quicksilver Probe page