ÇAĞRILI KONUŞMALAR / KEYNOTES Invited Speeches ... - TPJD

MWD&LWD and Stethoscope Applications for Subsea Wells
Fadıl Duman
Turkish Petroleum Corporation, Drilling Department, Ankara
Pore pressure modeling and understanding has great importance while drilling a wild cat well in
deep offshore. Not only given fracture and leak off margin is so small, but also keeping well in
optimum overbalance condition are vital for the safety. After BP’s Moconda incident in the Gulf
of Mexico, now understanding of pore pressure regime as well as nature of the high pressure
fluid while drilling becoming more and more critical especially in deep water where the riser and
well control devices are apart few hundred meters. In addition deep water environment play its
critical role being young deposits and buried not deep from the sea bed, and leak off margins
are most of the time in “wellbore breathing” range. Phenomenon variously called “Breathing
wellbore” or “Ballooning effect” is a result of slow mud returns while drilling ahead followed by
mud returns after the pumps have been turned off, such as during a connection or flow check.
Usullay any flows during these periods are cause for a concern as they may be due to influx
of formation water, liquid hydrocarbon or gas. Any influx from the formation can result in a
well control problem, the magnitude of which is dependent on its volume and composition.
On the other hand lithologies under deepwater conditions usually show relatively reduced
effective stress, due to reduced lithological column. This translates into narrow mud weight
windows, driven mainly by shear failure or pore pressure in over pressured conditions, and by
minimum horizontal stress gradients. Drilling operations should consider wellbore collapse,
kick and losses as the primary hazards. These should be investigated and predicted during well
planning, and should also be appropriately monitored during drilling. The workflow know as
“Real-Time Geomechanics” takes into consideration mud weight window planning, identification
of geomechanics related hazards and possible mitigation actions, and while drilling, operations
monitoring by real-time data acquisition and interpretation, drilling occurrences detection,
drilling practices revision, and the real-time update of mud weight window for further drilling.
This paper discussed the deep water cased study from planning and execution stage. Planning
stage discussion based on BHA design and critical components for BHA was MWD and LWD tools.
Measurement While Drilling (MWD) could be defined as the evolution of physical properties
including pressure, temperature, and wellbore trajectory in 3D space while extending a wellbore.
MWD is now standard practice in most wells, where the tool cost is offset by rig time saving and
wellbore stability improvements. The measurements are made downhole, transmitted to the
surface, and also stored in solid state memory for retrieval once the tool has returned to surface.
Real-Time data transmission methods vary from company to company but usually involve
digitally encoding data and transmitting it to the surface as pressure pulses in the mud system.
The pressure pulses can be positive, negative or continuous sine waves. MWD tools that measure
formation parameters (resistivity, porosity, sonic velocity and GR) are referred as logging-whiledrilling
(LWD) tools. LWD tools use similar data storage and transmission systems, and some have
more solid-state memory to provide higher resolution logs for retrieval after the tool is tripped
out that is possible with the relatively low-bandwidth, mud pulse data transmission system.
Keywords: Subsea Wells, MWD LWD Stethoscope
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