Schlumberger

Case Study: Laboratory-Quality PVT Measured On Site

PhaseSampler multiphase sampling equipment measures changing PVT parameters in a gas-breakthrough environment

Challenge: Develop a new reservoir fluid profile after gas breakthrough invalidated the model that was based on the original reservoir fluid composition.

Solution: Use PhaseSampler multiphase sampling equipment to measure fluid properties at the wellsite.

Result: Captured high-quality fluid samples at line conditions for accurate laboratory-quality data on site.

Since first oil was delivered from its field in eastern Algeria in October 2004, Groupement Berkine has had Schlumberger monitor production continuously using PhaseWatcher fixed multiphase well production monitoring equipment with Vx multiphase well testing technology. Two meters are installed on each manifold: one for single well testing and one for monitoring production through the entire manifold. Produced gas is reinjected to provide pressure support.

Update reservoir fluid profile

To predict the behavior of the light oil being produced, an equation-of-state (EOS) model based on the original reservoir fluid composition had been developed using PhaseWatcher data. However, the early model was unable to account for the excess gas in the production stream once reinjected gas began to break through.

Although reinjecting gas from the main field and its satellites had changed the gas composition, the effect of gas composition on multiphase flow measurements was negligible. The most important measurements to the operator were the increase in the quantity of gas dissolved in the oil and the decrease in live oil density.

Measure fluid properties on site

Schlumberger decided to determine whether an updated reservoir fluid profile could be developed using PhaseSampler multiphase sampling equipment to measure fluid properties at the wellsite.

A three-step validation was planned:

  1. PhaseSampler equipment measurements would be compared with predictions from the original fluid properties model.
  2. PhaseSampler equipment measurements and laboratory PVT measurements, including GOR and gas composition, would be compared.
  3. The repeatability of PhaseSampler equipment measurements would be confirmed by performing multiple flashes in identical flowing conditions.

In May 2008, a well was selected that had shown a considerable increase in gas production over recent months. The PhaseTester portable multiphase well testing equipment and PhaseSampler multiphase sampling equipment were rigged up at the wellhead, with the PhaseWatcher monitoring equipment installed on the manifold 200 m away.

Confirm key expectations with validated data

PhaseSampler equipment data were proved valid through comparison with laboratory PVT measurements, and they demonstrated their repeatability in multiple flashes in identical flowing conditions.

The match between PhaseSampler equipment and laboratory measurements of gas dissolved in the oil was excellent.

The measurements of free and dissolved gas compositions were in close agreement and were determined to be unquestionably accurate because two different types of gas chromatograph were used. The PhaseSampler equipment enabled high-quality samples of multiphase fluids to be captured at line conditions, directly from the flowline, providing laboratory-quality information immediately at the wellsite.

PhaseSampler equipment measurements were compared with predictions from the original fluid properties model, as well as from the black oil model. The differences between the three sets of data were insignificant for gas.

The differences for oil were significant and confirmed what had been expected. The model based on original reservoir fluid composition was no longer valid because of gas breakthrough. Depending on that model would cause oil shrinkage to be underestimated and oil density to be overestimated.

Further, the two sets of oil properties measurements confirmed the excellent repeatability of the PhaseSampler equipment data.


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