Schlumberger

Case Study: Effluents Monitored from the First Opening of a High GVF Well

PhaseTester multiphase flowmeter with Vx technology demonstrates advantages over a test separator for OMV in the Sawan field

Challenge: Test an exploratory well and measure flow rates during cleanup; prove cleanup by measuring the volume of produced completion fluids; minimize rig-up time and time required for well testing operations; estimate well deliverability from surface data; and enable safer operations.

Solution: Install a PhaseTester portable multiphase well testing equipment with Vx† technology in series with a conventional test separator to measure multiphase flow rates.

Result: Acquired flow rate data using the PhaseTester equipment when the well test separator was unable to do so, and enabled faster, more efficient cleanup.

OMV needed to measure high gas volume fraction (GVF) production to confirm cleanup

After OMV (Pakistan) Exploration GmbH drilled an exploratory well in the Sawan field and tested the Lower Goru B sand top layer, it planned a workover operation wherein the Lower Goru B sand bottom layer would be tested and the flow from both layers would be commingled for a completion integrity test.

OMV wanted to test its high GVF well from first flow and monitor the production of completion fluids dynamically so that cleanup could be confirmed.

In addition, OMV desired a straightforward installation that would require minimal time for rig-up and well testing operations and would enable safer operations.

The workover would have to provide base data for further evaluation during extended well testing and production.

PhaseTester multiphase flowmeter selected after being compared with a conventional test separator

Testing was conducted using PhaseTester portable multiphase well testing equipment with Vx technology and a conventional test separator in series. The PhaseTester flowmeter could be switched to upstream or downstream of the choke manifold as required.

Continuous flow rates could not be monitored with a conventional separator, which is not designed to accommodate a major change in fluid flow rates during choke changes. The PhaseTester flowmeter, on the other hand, is able to measure flow rates even during choke changes.

A conventional test separator could not calculate cleanup duration because it is not designed to intake fluids other than water and hydrocarbons. The PhaseTester flowmeter was always inline, measuring the flow rate even during cleanup. Therefore, production of all liquids could be calculated through the entire cleanup.

PhaseTester equipment provided real-time data because measurements were available as flow passed through the venturi throat, whereas fluids had to be separated over time, then measured using a separator.

Compared with a traditional test separator, the PhaseTester equipment improved safety by eliminating the need for pressurized vessels on the platform and by reducing the number of field personnel required.

Finally, a Vx Fluids ID fluid properties model based on an equation of state was generated from compositional analysis of the well effluents to ensure the best possible estimation of standard condition flow rates from line conditions.

PhaseTester equipment allowed much higher flow rates for faster, more efficient cleanup

The PhaseTester equipment immediately demonstrated superior suitability. Measurement of low liquid rates, especially at initial flow, is very difficult—and sometimes impossible—with a conventional testing setup because of the time required for effluents to fill the separator to the appropriate levels, separate, and stabilize. Water production from the Lower Goru B sand top layer during the initial flow of six hours was insufficient to fill the separator to the required level, so a water-gas ratio could not be calculated using conventional separator data.

However, because the PhaseTester equipment was rigged up inline with the testing setup and did not require stabilization or minimum fluid levels, and because of the very large turndown ratio of the PhaseTester flowmeter, real-time measurements of all hydrocarbon phases, as well as completion fluid levels, were available from first flow, making it possible to monitor cleanup status in real time.

Because it was the flow rate limit of the test separator, the test had been planned to flow at 60 MMcf/d, following completion of the safety studies and job analysis that would be required. Because it eliminated the need for pressurized vessels, however, PhaseTester equipment could accommodate flow rates to 116 MMcf/d, as well as pressures to 5,000 psi [34 MPa] and temperatures to 302 degF [150 defC]. The higher flow rates enabled faster, more efficient cleanup.

Accurate measurement in high GVF environments can be very challenging, but the PhaseTester equipment with Vx technology proved its accuracy, even when the gas volume fraction exceeded 90%.


Download: Effluents Monitored from the First Opening of a High GVF Well (1.15 MB PDF)

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