Schlumberger

Case Study: Performing Two Well Tests
with High-Integrity Isolation System Saves USD 12M

CERTIS system overcomes reservoir testing challenges of a high-pressure well in a high-cost environment

Challenge: Perform two reservoir tests on a high-pressure deepwater rig while minimizing rig time.

Solution: Use the CERTIS high-integrity reservoir test isolation system, an advanced, single-trip retrievable system that performs like a permanent packer.

Result: Achieved all test objectives and saved more than USD 12 million.

Testing a high-pressure well in a high-cost environment

For a high-pressure well in the Caspian Sea, an operator wanted to conduct two reservoir tests, install a temporary completion to monitor the well’s interaction with other producing areas of the reservoir, and then retain the well for production once handling facilities were in place. High rig costs made it imperative that these operations be conducted flawlessly and efficiently.

A key requirement for successful testing was high-integrity annulus isolation from the formation, where maximum bottomhole tubing and annulus pressures could reach 19,000 psi [131 MPa] and 18,000 psi [124 MPa], respectively, and the maximum bottomhole temperature could reach 208 degF [98 degC].

Delivering the right features combination with the CERTIS system

The reservoir test was to be performed on a deepwater, high-pressure, semisubmersible rig with spread costs more than USD 600,000 per day during testing. Schlumberger worked closely with the operator to design a fit-for-purpose string that reduced the time required for any activity during execution phases.

A reservoir test isolation system was needed that provided the operational performance of a permanent packer and would allow the test tools to be run and retrieved in a single trip, eliminating the risky and costly milling operation needed when using a permanent packer. The solution was the CERTIS reservoir test isolation system.

The CERTIS system combines many features of a conventional retrievable packer with those of a hydraulic-set permanent packer, including a built-in floating seal assembly that eliminates the need for drill collars and slip joints. When run as part of the Quartet high-performance downhole reservoir testing system, the CERTIS system can significantly reduce the number of downhole tools in the test string.

During testing, the CERTIS system eliminated the need for the string rotation to set by using its hydraulic setting mechanisms, eliminated the movement of downhole gauges hung below the packer, reduced risks, and improved efficiency in the installing and testing of an isolation packer between tests. It also allowed the same fluid (CaBr) to be used for testing and completion in the well.

To ensure successful retrieval, close attention was paid to the measurement and selection of the liner hanger sections in which the packer was to be set, as well as the verification of all dimensions and tolerances for liner hangers, casing joints, and packer elements.

Each zone was isolated with a combination of gauges and bridge plugs to allow independent monitoring of interactions with other producing areas of the reservoir during the long planned suspension.

Meeting all objectives and saving more than USD 12 million

Use of the CERTIS system enabled all the operator’s objectives to be met in two reservoir tests over a period of 3 months. Pressure-activated setting provided accurate depth control for the tubing-conveyed perforating charges, and the prespaced floating seal assembly eliminated the risk of string movement and ensured that below-packer gauges remained stationary during the test. The operator noted that the pressure data acquired for interpretation were of high quality.

On both tests, the CERTIS system operated and was retrieved without issue. Retrieval of the system with the test string allowed suspension and isolation of the tested zones without having to pull or mill a permanent packer.

With a rig day rate of USD 600,000 and each trip requiring over 24 h, a cost savings of more than USD 12 million was achieved by eliminating multiple milling and cleanout runs per zone. Eliminating milling operations also minimized future well integrity risks.


Download: Performing Two Well Tests with High-Integrity Isolation System Saves USD 12 M (1.56 MB PDF)

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Isolate, Control, Measure, and Sample—All in a Single Run

The Quartet High performance downhole reservoir testing system
Available with wireless telemetry or rated for high-temperature conditions, the Quartet downhole reservoir testing system combines 4 leading downhole tools into one advanced string to deliver altogether better reservoir testing.
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Single-Trip Isolation Solution

CERTIS high-integrity reservoir test isolation system.Sequence of steps for a two-zone reservoir test and completion; the permanent packer solution requires multiple milling and clean-out runs.Sequence of steps for an optimized twozone reservoir test and completion; the CERTIS system eliminates multiple milling and clean-out runs.
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“The CERTIS system permitted two tests to be performed without the need for packer milling or fishing operations and reduced operational time by between 2 and 3 weeks.”
Operator representative