Subsalt section creates challenges for deepwater GOM floating rig
An operator on a deepwater floating rig in the Gulf of Mexico (GOM)
faced challenges in a subsalt section due to the potential presence of reverse
pressure trends, rubble zones, and l loss zones. Based on the well requirements
to reach the target, the well construction plan included a 14-in casing inside
of a 16-in liner, which created a tight annulus.
Given these job conditions, which included losses, lack of
centralization, and the presence of compressible drilling fluid used for
drilling and cementing this subsalt section, the conventional interpretation of
surface pressure match and volumetric calculations was insufficient to confirm
the barrier placement in the annulus. The operator was required to verify that
a specific length of cement was placed above defined permeable formations
before proceeding with drilling ahead and prior to well abandonment.
Comprehensive well integrity analysis performed using integrated
drilling, cementing, and logging data
Schlumberger recommended the Invizion Evaluation well integrity
evaluation service's robust workflow, which combines specialized experience
from domain experts with data correlation using tools and services from
multiple areas of well construction. The integrated data is used to determine
the wellbore quality, confirm cement design and placement, and provide cement
Acoustic impedance readings from the USI ultrasonic imager showed a
density increase at 15,269-ft MD. The discriminated cement bond log (CBL)
attenuation also showed an abrupt spike in sonic response, correlating with
stronger formation arrivals observed in the Variable Density log at this depth.
These observations confirmed the TOC at 15,269-ft MD with possible traces at
approximately 15,200-ft MD [4,633-m MD].
Sonic wave analysis indicated clear casing arrivals above 15,250-ft MD
[4,648-m MD], which is indicative of no solids present above this depth. A
partial appearance of compressional wave arrivals below 15,200-ft MD suggested
the presence of solids (cement) behind the casing below 15,200-ft MD.
Below-TOC separation between minimum and maximum acoustic impedance
suggested a nonhomogenous distribution of the slurry. This is shown in the
acoustic impedance map that displays the azimuthal coverage of the cement
placement. Cement placement is identified as primarily on one side of the
casing, which correlates with Invizion Evaluation service's cement placement
Invizion Evaluation service verifies barrier to eliminate wireline runs
in two sections
The accurate barrier verification provided to the operator satisfied
both internal and external reporting requirements. The analysis by the Invizion
Evaluation service was used to optimize the planning and abandonment program
for this well in advance. The data was also used to better understand the
optimal depth to sidetrack for both wells. Intelligence obtained by comparing
LWD data interpretation with analysis of the Sonic Scanner platform and USI
imager logging enabled the operator to eliminate wireline runs on the
subsequent two sections, saving two days of rig time.