Complete complex ERD gas well, offshore China
China National Offshore Oil Corporation (CNOOC) wanted to complete an
offshore ERD well that tapped into four different reservoirs in a gas field.
The well plan called for the main well—an 8 1/2-in borehole with a 7-in
liner—to drill into the deepest reservoir first, then commingle production
from the other three reservoirs. Targeting four reservoirs, this well posed
more challenges for the cementing and completion processes than usual.
Use real-time LWD and cement evaluation service
To reduce the overall cost and operation complexity, CNOOC selected an
LWD tool as the cement evaluation service in this ERD well. After discussing
its objective with Schlumberger, CNOOC decided to use the SonicScope service to
provide a cement bond index evaluation. The cement evaluation component of the
SonicScope service enables operators to receive an accurate measurement of the
position and bond quality of the cement behind the casing—without the
additional rig time required for conventional bond log tools. In this well, the
SonicScope service was used purely for cement evaluation.
In addition to the SonicScope service, CNOOC used the arcVISION array
resistivity compensated service to log the borehole while drilling the 8 1/2-in
section.
Identified and remedied poor cement bond above the mud loss
interval
CNOOC successfully used the cement evaluation component of the
SonicScope service to acquire acoustic data inside the liner throughout the ERD
well, confirming good bonding (greater than 80%) in the bottom intervals across
the target sands. There was, however, poor cementing (50%) on the top section
above 5,950 m [19,521 ft] where drillers encountered mud losses while drilling.
This result was very close to CNOOC’s expectation; poor cementing was
expected above the mud loss interval. CNOOC performed squeeze cementing to
reseal the top section, which entailed injecting cement through the opening
between the casing and liner to fill gaps in the existing cement and make a
better seal.
This was the first time the cement evaluation component of the
SonicScope service was run in China, and also the first commercial use
worldwide. CNOOC provided positive feedback about the service, and it is
currently being evaluated in another project.
