Schlumberger

Case Study: Downhole Fluid Analysis Reveals Compositional Grading

Real-time measurements by the InSitu Density sensor in a near-critical reservoir identify retrograde condensate to manage risk

Challenge: Determine whether the reservoir fluid in a well drilled with oil-base mud is a volatile oil or retrograde condensate.

Solution: Conduct real-time downhole fluid analysis by obtaining fluid density measurements at true reservoir conditions with the InSitu Density reservoir fluid density sensor.

Result: Positively identified the fluid as a retrograde condensate from the corresponding InSitu Density sensor and GOR data to optimize the sampling process and more accurately model facilities sizing.

Quantifying a near-critical reservoir

Whether the fluid content of a near-critical reservoir in a well drilled with oil-base mud was a volatile oil or retrograde condensate was not known at the time of logging. Accurate measurement of the fluid properties was needed to identify the fluid for guiding the logging program and completion design.

Measuring fluid density in real time

Downhole fluid analysis was conducted to measure the properties of the fluid flowed from the reservoir with Quicksilver Probe focused extraction, which diverts filtrate-contaminated fluid—even in the presence of oil-base mud—to the perimeter of the probe to collect pure reservoir fluid into the acquisition flowline. Five stations were logged in a column of approximately 500 ft [150 m] with real-time measurements by the InSitu Density reservoir fluid density sensor and the LFA live fluid analyzer and CFA composition fluid analyzer optical sensors for determining the GOR.

Accurately identifying the reservoir fluid

Compositional grading was revealed by the large change in density values measured by the InSitu Density sensor with increasing depth. The GOR measured by the LFA and CFA analyzers correspondingly decreased from approximately 3,300 to 2,300 ft3/bbl [588 to 410 m3/m3]. This real-time information was used to optimize the sampling process.

The measurements from the InSitu Density sensor quantified the variation of fluid properties with depth for input to a reservoir simulator. Facility-sizing calculations were then accurately based on a representative zonal characterization, not an estimate from a single sampling depth, which would have been misleading.

Additional measurements with a fluorescence detector run on the toolstring further identified the fluid as being in a gaseous phase rather than a liquid phase in the reservoir, confirming the fluid as a retrograde condensate and providing further insight for reservoir evaluation.


Download: Downhole Fluid Analysis Reveals Compositional Grading (0.07 MB PDF)

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Real-Time Identification of Compositional Grading

Real-time downhole fluid analysis identified compositional grading through the inverse correspondence of InSitu Density measurements and GOR values.
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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