CRITICAL ISOLATION IN A DEEP WATER MARGINAL NIGERIAN FIELD

Background

The well was initially drilled in 2015. The 9 5/8” production casing was going through two oil zones. The 9 5/8” casing was cemented and both zones were perforated. The well produced immediately 60% BS&W and the well had to be shut-in after 6 months of production.

When contacted, Welltec advised that the cement only could not provide annular sealing in this well because of the thin shales (7-10 ft) separating the oil zones from gas/water zones. For the sidetrack, Welltec recommended augmenting the cement with a Welltec® Annular barrier (WAB®) above and below each oil zone.

OPERATION

After sidetrack well was drilled, the 7” liner was installed with 2 x 812WAB integrated in the string. The liner hanger was set and the cement operation proceeded as planned up to the point where the cement plug was bumped. Hydraulic pressure was then increased to allow simultaneous expansion of both of the WAB®  in green cement. Thereafter, the liner top packer was set and the completion operations continued.

The top WAB® is installed in a 10ft shaly sand which separates the oil zone from a gas cap. The bottom WAB® is installed in a 7 ft shale separating the oil zone from a water zone.

ACHIEVEMENTS

Two WAB® were installed and expanded successfully in a single trip fully integrated with the liner hanger and cement operation.  After the well was put back on production, it has been producing water and gas-free since May 2017 (BS&W = 0.2%) compared to the initial 60% BS&W produced with the initial completion.

The cement evaluation log also confirms that the sealing in the shaly sand is provided by the WAB® rather than cement.

COMPLETE ZONAL ISOLATION PROVEN FROM THE WELLTEC® ANNULAR BARRIER (WAB®)
LOWER WAB® SUCCESSFULLY PREVENTING WATER PRODUCTION THROUGH A 7FT SHALE
UPPER WAB® SUCCESSFULLY PREVENTING GAS PRODUCTION THROUGH A 10 FT SHALY SAND
PROVEN REDUCTION IN BASIC SEDIMENT AND WATER FROM 60% TO 0.2%

 

Read more completion case stories