WELLTEC® ANNULAR BARRIER FACILITATES SHALLOW GAS ISOLATION IN THAILAND

Background

In May 2018, an operator in Thailand had a unique challenge within a multi-well development program: the formation above a shallow, gas-bearing zone was very soft, and previous attempts to establish an open-hole seal via installation of an external casing packer (ECP) resulted in the intermittent loss of integrity due to the ECP bursting. The reason for this issue was the external casing/inflatable packers used previously by the operator required going to maximum setting pressure to isolate the setting port. However, the formation provided little—or no—support upon contact during inflation, resulting in the packers either bursting or providing no isolation for the shallow gas.

The operator was interested in Welltec’s ability to set the Welltec® Annular Barrier (WAB®) within the soft formation and regulate the WAB’s expanded outer diameter (OD). When set with ports in the base pipe, the WAB® regulates the expanded OD via pressure applied. Additionally, the WAB® also has the ability to rotate during deployment during primary cementing. Welltec® provided the operator with advanced modelling showing the WAB® setting in air to simulate the lack of support from the soft formation. The simulation demonstrated that the WAB® would not burst from the maximum setting pressure. With these results in mind, as well as the WAB’s many proven benefits, the operator agreed to a trial well using the 1214WAB6:0.6.

OPERATION

Welltec® designed the operational process around the simulation modelling to ensure there was no risk of bursting the WAB® and the operations team collaborated with the offshore drilling and fluids team to create the procedure. During the drilling of the 12 1/4” section of a well, the operator encountered a shallow gas zone at approximately 1,050 ft. Operationally, the WAB® was set within this 12 1/4” open-hole section, within green cement, by applying pressure against the primary cement plug. Specifically, the WAB® was deployed with the 9 5/8” casing and positioned directly above the gas zone. Primary cementing operations were then conducted and the WAB® was set after these operations.

The client then requested two weeks to monitor the B annulus for gas migration. Two weeks after installation and cement curing, the B annulus on this well continued to read steadily at 0 psi.

ACHIEVEMENTS

The WAB® proved to be an effective solution for the client, setting within the soft formation, preventing gas migration, and maintaining well integrity. The client’s confidence in moving forward with this trial well resulted from the simulation modelling demonstrating the WAB’s performance in this unique environment as well as Welltec’s strong case history and track record in similar applications.

The WAB® eliminates sustainable annulus pressure (SAP) in the B annulus. This solution improves well integrity, enhances environmental safety, and removes the need for costly operations to lubricate and bleed off B annulus pressure. Ultimately, the WAB® prevents the need for the well to be shut in because of SAP, thus ensuring there will be no deferred production revenue.

The setting time for this application was 15 minutes and so there is minimal impact to the total operational time.  Incorporating the WAB® simplifies the installation process when compared to alternative products with far more complex setting procedures.

WELL TYPE: WATER INJECTOR
WELL FLUID: MUD

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